BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Week
1
2
Text(before class, you are required to
study the text of each reference closely)
https://www.myodesie.com/wiki/inde
x/returnEntry/id/3065#BeltDrivePrin
ciples
https://www.myodesie.com/wiki/inde
x/returnEntry/id/3065#BeltDrivePrin
ciples
Content
1. Examples of Belt and
Chain drives,
Belt and
Chain
Drives
2. Applications of Belt and
Chain drives
Explain the principles of belt and chain
drives.
3. Working principles of belt
State 2 advantages and disadvantages
of belt and chain drives.
https://www.myodesie.com/wiki/inde
x/returnEntry/id/3065#BeltDrivePrin
ciples
4.Advantages and
disadvantages belt and chain
drives
State the advantages and
disadvantaged of belt and chain drives,
https://www.myodesie.com/wiki/inde
x/returnEntry/id/3065#BeltDrivePrin
ciples
1. identify different types of
gears;
2. state the uses of the various
types of gears in a mechanical
system;
3. determine gear ratios
4. describe the relationship
between gear ratio and speed
of rotation;
5. State the
functions of
lubricants in
gears;
6. construct and use gears.
1. Examples of
Hydraulic and
Pneumatic Devices
1. identify different types of gears;
See printed notes for details
Belt and
Chain
Drives
3
Gears
4
By the end of this lesson, students
should be able to do the following
Describe belt and chain drives.
Topic
and chain
drives;
2.State the uses of the various types of
gears in a mechanical system
Determine gear ratios
See printed notes for details
1.Describe the relationship between gear
ratio and speed of rotation;
2.State the
functions of lubricants in gears;
1. identify hydraulic
and pneumatic
machines;
2. name the
components of
See printed notes for details
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Hydraulic
and
Pneumatic
Machines
5
Processing
of Materials
(I) Timber
Processing
of Materials
6
(2) Metals
7
each machine;
2. Components of Pneumatic
machines.
3. Operations and uses.
1. Define key terms and
concepts related to timber
processing;
2. Describe the properties of
good timber
3. Explain the
principles behind
the working of
pneumatic
devices;
3. State the uses of the machines.
1. Define key terms and concepts related
to timber processing;
See printed notes for details
See printed notes for details
2. Describe the properties of good
timber
3. Identify common timber
defects;
4. Explain treatments and
preservation methods for
timber;
5. State the importance of
timber treatments.
3. Identify common timber defects. 4.
Explain treatments and preservation
methods for timber; 5. State the
importance of timber treatments.
See printed notes for details
1. Metal processing methods
(smelting, casting, etc.)
2. Advantages and
disadvantages of the
different processing
methods.
1. Describe different ways of processing
metals;
2. Explain the advantages and
disadvantages of the different metal
processing methods;
See printed notes for details
3. Metal alloys: examples,
properties and uses.
1. Methods of
processing:
- clay;
- ceramics and;
- glass materials,
3. Identify metal alloys;
4.
explain the uses of common metal alloys,
1. differentiate between rubber and
plastics;
2. explain the methods of processing
plastics and rubber
See printed notes for details
See printed notes for details
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Processing
of Materials
(3) Clay,
Ceramics,
and Plastics
8
9
10
Isometric
Drawing
Isometric
Drawing
2. Advantages and
disadvantages of the different
processing methods.
3. Production and uses of clay,
ceramics and glass
3. state the advantages and
disadvantages of each methods;
4. describe the uses of plastics and
rubber
See printed notes for details
Examples of Isometric
Drawings
Isometric drawing of
simple shaped blocks without
curves
Isometric drawing of
simple shaped blocks without
curves
Isometric drawing of
simple shaped blocks without
curves
Examples of Oblique drawing
Identify isometric drawings;
See printed notes for details
Use drawing instruments to draw simple
isometric objects.
See printed notes for details
Use drawing instruments to draw simple
isometric objects.
See printed notes for details
draw simple
isometric objects
See printed notes for details
1. describe oblique
drawings;
2. draw simple
oblique objects
draw simple
oblique objects
See printed notes for details
Oblique
Drawing
Simple Oblique Drawings
See printed notes for details
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
BASIC TECHNOLOGY
1ST TERM SUMMARY NOTES FOR WEEKS 1 – 10 FOR JS 2 CLASS
BELT AND CHAIN DRIVE
Belt and chain drive are like gears used to transmit motion and power.
Belt Drives
Belts are made of rubber and materials whose length and nature change with temperature. In a
simple belt, drive devices like the pulley are attached to the rotating shaft of the motor. These
circular pulleys are attached and connected to a belt. Examples of belt drives are motor fan
belts, sewing machines, pepper grinders, corn grinders and beans grinders.
Drive Mechanism
Open belt
Relationship between belts and pulleys
A pulley is the wheel on which a belt runs. The pulley from which power is taken is called the
driving pulley or driver. The pulley to which power is carried is called the driven pulley.
Types (Examples) of belts and pulleys
1.
Open belt
2.
Crossed belt
3.
V-belt
4.
Chain belt.
Chain drives
They consist of an endless series of chain links that mesh with toothed sprockets. Chain
sprockets are locked to the shafts of the driver and driven machinery. Chain drives represent a
1
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
form of flexible gearing. The chain acts like an endless gear rack, while the sprockets are similar
to pinion gears. Friction is greatly needed in belt and chain drives. Belts and chains cannot work
when friction is absent. Belts and chains are used in pulley mechanisms.
V- Belt
Cross Belt
Chain Belt
Chain and Belt drives
Roller chain and sprocket
Uses (Applications) of Belt and Chain Drives
Belt and chain drives are used to:
1. Transmit energy or power (torque) from one shaft to another. From driver: motor,
peddles, engine, windmill, turbine to driven: conveyor belt, back wheels/bike, generator
rock crusher, dryer when both shafts are separated by a distance greater than that
required for gears.
2. Change the speed of a pulley.
3. Change the running direction of a pulley.
4. Carry materials as conveyors from one point to another
5. Used to span large distances or need flexible transmission elements. Gear drives have a
higher torque capability but not flexible or cheap.
Chain Drive Principles
1. Chain drives normally transmit power from one rotating shaft to another.
2. Chain drives maintain a positive speed ratio between driver and driven sprockets.
3. The driver and driven sprockets will rotate in the same direction on typical chain drives.
2
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
4. If the chain has an even number of pitches, the sprockets have an odd number of teeth.
5.
6.
7.
8.
9.
10.
If the sprockets have an even number of teeth, the chain has an uneven number of
pitches. This design feature prevents a single link from contacting the same tooth each
time, causing wear and vibration.
Small diameter sprockets cause the chain to bend sharply; therefore, the chain wears more
quickly.
Short chain links bend less and should be used on small diameter sprockets.
Chains may be installed as single or multiple-strand drives, depending on speed and load.
Chain slack must be adjusted periodically by shifting one of the sprockets or by using a chain
tightener.
Horizontal chain drives should have slack on the bottom (do not allow the chain to rub on the
guard or casing).
Tighteners or idlers should be located on the slack side of the chain.
Chain Types
The six styles of chain used for mechanical transmission are:
1.
2.
3.
4.
5.
6.
Roller chain
Detachable chain
Pintle chain
Silent chain
Leaf chain
Laminated metal chain
Standard Roller Chain
A standard roller chain is made up of alternate roller links, as shown in Figure 1. Roller
links consist of two sidebars, two bushings, and two rollers. Pin links have two sidebars
and two pins, which are normally riveted.
3
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Standard Roller Chain
Belt Drive Principles
Power transmission belting has been used for more than 200 years. The first belts were flat
and ran on flat pulleys. Later, cotton or hemp rope was used with V-groove pulleys to reduce
belt tension. This led to the development of the vulcanized rubber V-belt in 1917. The need
to eliminate speed variations led to the development of synchronous or toothed belts about
1950 and the later development of fabric-reinforced elastomer materials.
4
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Today, flat, V, and synchronous belting is still being used in power transmission. When
compared to other forms of power transmission, belts provide a good combination of
flexibility, low cost, simple installation and maintenance, and minimal space requirements.
Belt-driven equipment uses readily available components. Replacement parts can be easily
obtained from local distributors. This availability reduces downtime and inventory. Sheaves
and pulleys are usually less expensive than chain drive sprockets and have little wear over
long periods of operation.
Belt types
All power transmission belts are either friction drive or positive drive. Friction drive belts rely
on the friction between the belt and pulley to transmit power. They require tension to
maintain the right amount of friction. Flat belts are the purest form of friction drive while Vbelts have a friction multiplying effect because of wedging action on the pulley.
Positive drive or synchronous belts rely on the engagement of teeth on the belt with grooves
on the pulley. There is no slip with this belt except for ratcheting or tooth jumping.
Working principle of Belt and Chain Drives
Figure: showing Roller chain and sprocket
Chain drive is a way of transmitting mechanical power from one place to another. It is often used
to convey power to the wheels of a vehicle, particularly bicycles and motorcycles. It is also used
in a wide variety of machines besides vehicles.
Most often, the power is conveyed by a roller chain, known as the drive chain or transmission
chain,[1] passing over a sprocket gear, with the teeth of the gear meshing with the holes in the
links of the chain. The gear is turned, and this pulls the chain putting mechanical force into the
system. Another type of drive chain is the Morse chain, invented by the Morse Chain Company
of Ithaca, New York, United States. This has inverted teeth.
Sometimes the power is output by simply rotating the chain, which can be used to lift or drag
objects. In other situations, a second gear is placed and the power is recovered by attaching
shafts or hubs to this gear. Though drive chains are often simple oval loops, they can also go
around corners by placing more than two gears along the chain; gears that do not put power into
5
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
the system or transmit it out are generally known as idler wheels. By varying the diameter of the
input and output gears with respect to each other, the gear ratio can be altered. For example,
when the bicycle pedals' gear rotates once, it causes the gear that drives the wheels to rotate
more than one revolution.
Belt Drive Principles
Flat belts and V-belts transmit power by their grip on the pulley or sheave.
Three major factors determine the potential of the grip:
1. Area of contact
2. Belt tension
3. Friction between the belt and pulley or sheave surface (coefficient of friction)
Area of Contact
The area of contact is determined by the width and the arc of contact. The arc of contact with
pulleys of equal diameters is 180 degrees on each pulley, as shown in Figure 1.
Figure 1: Area of Contact
Pulleys of equal size are not always used. With pulleys of unequal diameter, the arc of contact is
less than 180 degrees on the smaller pulley. Under most conditions, this small pulley is the
driver. An example is shown in Figure 2.
Figure 2: Unequal Pulleys
An arc of contact greater than 180 degrees can be obtained in three ways:
1. A crossed belt drive.
6
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
2. Moving the input and output shafts farther apart.
3. Using an idler or snub pulley.
Crossed Belt Drive
A crossed belt drive, as shown in Figure 3, is not usually recommended for V-belts. In the crossed
position, the center-to-center distance between the pulleys must be long enough to limit the
internal stress in a belt. Crossed belt drives make the pulleys rotate in opposite directions to each
other.
Figure 3: Crossed Belt Drive
Pulley Center-to-Center Distance
For maximum power transfer on the belts and pulleys, the pulley ratio should be 3 to 1 or less as
shown in Figure 4 Top. Higher ratios, as in Figure 4 Bottom, lessen the arc of contact, causing
slippage and loss of power.
Figure 4: Pulley Center to Center Distance
The arc of contact on the critical smaller pulley may be increased if the shafts are moved farther
apart as shown in Figure 5. Where a high ratio is required, a two-step drive (counter-shaft) can
be used to avoid excessive single-step ratios or undersize pulleys.
7
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Figure 5: Increase Arc of Contact
Belt Drive is one of the most common and effective devices for transmitting motion from one
shaft to another through a thin inextensible band running over two pulleys. The belt drive is
generally employed whenever rotary motion is to be transmitted between two parallel shafts.
Advantages of belt drive
i.
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.
ix.
They are simple
They are economical.
Parallel shafts are not required.
Overload and jam protection are provided.
Noise and vibration are damped out.
Machinery life is prolonged because load fluctuations are cushioned (shock-absorbed).
They are lubrication-free. They require only low maintenance.
They are highly efficient (90–98%, usually 95%).
Some misalignment is tolerable.
They are very economical when shafts are separated by large distances.
Disadvantages of belt drive
The angular-velocity ratio is not necessarily constant or equal to the ratio of pulley diameters,
because of belt slip and stretch.
i. Heat build-up occurs.
8
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
ii.
iii.
iv.
v.
Speed is limited to usually 7000 feet per minute (35 meters per second).
Power transmission is limited to 370 kilowatts (500 horsepower).
Operating temperatures are usually restricted to –31 to 185°F (–35 to 85°C).
Some adjustment of centre distance or use of an idler pulley is necessary for wear and
stretch compensation.
vi. A means of disassembly must be provided to install endless belts.
CHAIN DRIVE
Chain drives are positive drives with no slip; hence the velocity ratio remains constant.
Chain drives are suitable for small centre distances and can be used generally up to 3
metres but in special cases even up to 8 meters.
ADVANTAGES OF CHAIN DRIVE1. Positive non-slip drives
2. Efficiency is high
3. Employed for small as well as large centre distances up to 8m.
4. Permit high-velocity ratio up to 8:1
5. Transmit more power than belt drives
6. They produce less load on shafts compared to belt drives
7. Maintenance is low
DISADVANTAGES OF CHAIN DRIVE1. The production cost of chains is relatively high.
2. The chain drive needs accurate mounting and careful maintenance, particularly lubrication
and slack adjustment.
3. The chain drive has velocity fluctuations especially when unduly stretched.
4. Driving and driven shafts should be in perfect alignment.
MORE ADVANTAGES AND DISADVANTAGES OF BELT DRIVES
Belt Drive Advantages
a) Wide range of speeds available.
b) Belts permit flexibility ranging from high horsepower drives to slow-speed and high-speed
drives.
c) Belt drives are less expensive than chain drives for low horsepower and low ratio
applications.
9
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
d)
e)
f)
g)
h)
Belts require no lubrication.
Single belt drives will accept more misalignment than chain drives.
Flat belts are best for extremely high-speed drives.
The belt drives cushion shock loads and load fluctuations.
Belts will slip under overload conditions, preventing mechanical damage to shafts, keys,
and other
Belt Drive Disadvantages
a) Belts cannot be used where exact timing or speed is required because slippage does occur
(only timing belts can be used).
b) Belts are easily damaged by oil, grease, abrasives, some chemicals, and heat.
c) Belts can be noisy; also, loose or worn belts can be a major cause of machinery vibration.
GEAR DRIVE→
Gear drives find a very prominent place in mechanical power transmission. Gear drives are
preferred when considerable power has to be transmitted over a short distance positively with
a constant velocity ratio.
ADVANTAGES OF GEAR DRIVE1. They are positive non-slip drives.
2. Most convenient for very small centre distances.
3. By using different types of gears, it will be possible to transmit the power when the axes
of the shafts are not only parallel but even when nonparallel, intersecting, nonintersecting and co-planar or non-coplanar.
4. The velocity ratio will remain constant throughout.
5. They can be employed conveniently for low, medium and high-power transmission.
10
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
6. Any velocity ratio is as high as, even up to 60:1 can be obtained.
7. They have very high transmission efficiency.
8. Gears can be cast in a wide range of both metallic and non-metallic materials.
9. If required gears may be cast integral with the shafts
DISADVANTAGES OF GEAR DRIVE
1. They are not suitable for shafts of very large centre distances.
2. They always require some kind of lubrication.
3. At very high speeds noise and vibrations will be more.
4. They are not economical because of the increased cost of production of precision gears.
5. The use of a large number of gear wheels in gear trains increases the weight of the machine.
APPLICATION OF GEAR DRIVES
Gears are employed for a wide range of applications like watches, precision measuring
instruments, machine tools, gearboxes fitted in automobiles, aero engines, etc.
A GEAR.
A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with
another toothed part to transmit torque. Geared devices can change the speed, torque, and
direction of a power source. Gears almost always produce a change in torque, creating a
mechanical advantage, through their gear ratio, and thus may be considered a simple
machine.
Classification of Gears - External and internal gears
An external gear is one with teeth formed on the outer surface of a cylinder or cone.
Conversely, an internal gear is one with teeth formed on the inner surface of a cylinder or
cone. For bevel gears, an internal gear is one with a pitch angle exceeding 90 degrees. Internal
gears do not cause output shaft direction reversal.
11
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Internal Spur Gear
External spur Gear
Types of Gears
Spur Gears
Spur gears or straight-cut gears are the simplest types of gear. They
consist of a cylinder or disk with teeth projecting radially. Though the
teeth are not straight-sided (but usually of special form to achieve a
constant drive ratio, mainly involute but less commonly cycloidal), the
edge of each tooth is straight and aligned parallel to the axis of rotation.
These gears mesh together correctly only if fitted to parallel shafts. No
axial thrust is created by the tooth loads. Spur gears are excellent at moderate speeds but
tend to be noisy at high speeds
Helical Gears
Helical or "dry fixed" gears offer a refinement over spur gears. The
leading edges of the teeth are not parallel to the axis of rotation but
are set at an angle. Since the gear is curved, this angling makes the
tooth shape a segment of a helix. Helical gears can be meshed in
parallel or crossed orientations. The former refers to when the shafts
are parallel to each other; this is the most common orientation. In
the latter, the shafts are non-parallel, and in this configuration, the gears are sometimes known
as "skew gears".
The angled teeth engage more gradually than spur gear teeth, causing them to run more
smoothly and quietly. With parallel helical gears, each pair of teeth first make contact at a single
point at one side of the gear wheel; a moving curve of contact then grows gradually across the
tooth face to a maximum, then recedes until the teeth break contact at a single point on the
opposite side. In spur gears, teeth suddenly meet at a line contact across their entire width,
causing stress and noise. Spur gears make a characteristic whine at high speeds. For this reason,
spur gears are used in low-speed applications and in situations where noise control is not a
problem, and helical gears are used in high-speed applications, large power transmission, or
where noise abatement is important. The speed is considered high when the pitch line velocity
exceeds 25 m/s.
12
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
A disadvantage of helical gears is a resultant thrust along the axis of the gear, which must be
accommodated by appropriate thrust bearings, and a greater degree of sliding friction between
the meshing teeth, often addressed with additives in the lubricant.
Bevel Gears
A bevel gear is shaped like a right circular cone with most of its tip cut off. When two bevel gears
mesh, their imaginary vertices must occupy the same point. Their shaft axes also intersect at this
point, forming an arbitrary non-straight angle between the shafts. The angle between the shafts
can be anything except zero or 180 degrees. Bevel gears with equal numbers of teeth and shaft
axes at 90 degrees are called mitre gears.
Bevel Gears
The gear teeth of this type of bevel
gear are straight but their sides are
tapered so that they would intersect
the axis at a common point, called
the cone apex if extended inward.
A straight bevel gear is the simplest
type of gear for intersecting shafts. It is
commonly used on shafts that
intersect at right angles.
Rack and Pinion
A typical rack and pinion spur gear arrangement is shown in the Figure below. It is used to convert
rotary motion to linear motion if the pinion is the driver and the rack is driven. If the rack is the
13
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
driver and the pinion is driven, the linear motion is converted to rotary motion. This is a
specialized form of spur gearing where the pinion teeth mesh with gear teeth on a flat rack.
Rack and Pinion
Worm Gears
Worms and worm gears are best suited for applications where a
great ratio reduction is required between the driving and driven
shafts.
Worm gears are used to transmit power between two shafts that
are at right angles to each other and are non-intersecting. As
shown in the Figure Above, the worm is the cylinder upon which
is cut a single or multiple start Acme-type thread. The pressure
angle of this thread ranges from 14.5 to 30 degrees. As the lead
angle of the worm increases, the greater the pressure angle is on the side of the thread.
The worm is the drive gear (input) and the driven gear (output) is referred to as the worm
gear or worm wheel. The teeth on a worm gear are curved to conform with the teeth on the
worm. The worm gear teeth are machined on a peripheral groove which has a radius equal to
half the root diameter of the worm.
Miter Gears
Mitre gears are bevel gears having the same pitch, pressure
angle, and number of teeth. Mitre gears may use the straight
bevel gear tooth form, "Zerol" bevel tooth form, or spiral bevel
tooth form. Mitre gears are usually used on shafts intersecting
at right angles where a one-to-one speed ratio is required. The
Figure shows a mitre gear arrangement.
14
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Herringbone Gears
Herringbone gears, as shown are similar to double helical gears.
The herringbone has no space separating the two opposed sets
of teeth. It is more expensive and difficult to manufacture a
herringbone gear with high accuracy, but both the herringbone
and double helical gears stand up well for long periods under
heavy load conditions.
Hypoid Gears
Hypoid gears are a modification of the spiral bevel gear and the
worm gear, with the axis offset. The distinguishing feature of
hypoid gears is that the shafts of the pinion and ring gear may
continue past each other, never having their axis
intersecting. The figure shows an example of a hypoid gear.
Planetary Gears
The planetary gear is an outer gear that revolves around a central
sun gear. Planetary gears can produce different gear ratios
depending on which gear is used as the input, and which one is
used as the output.
The gears are suitable for the reduction of high RPM electric
motors for use in high-torque low RPM applications. These gears
are used in precision instruments because of their reliability and
accuracy.
USES OF VARIOUS TYPES OF GEARS IN MECHANICAL SYSTEM
Types
Spur Gears
Applications (Uses)
●
Automobiles
●
Textiles
●
Industrial engineering
Bevel Gears
●
●
●
Automotive industry
Textile industry
Industrial engineering products
15
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Helical Gears
These gears are used in areas requiring high speeds, large power
transmission, or where noise prevention is important.
● Automobiles
● Textile
● Aerospace
● Conveyors
Worm Gears
●
●
Rack and Pinion
The gear is commonly used in the steering mechanism of cars. Other
important applications of rack gears include:
●
●
●
●
●
Internal Gear
●
●
●
External Gear
●
●
●
●
Planetary Gears
●
●
●
●
●
Hypoid gears
Electric motors
Automotive components
Construction Equipment
Machine tools
Conveyors
Material Handling
Roller feeds
Light duty applications
Rollers
Indexing
Coal industry
Mining
Steel plants
Paper and pulp industry
Sugar industry
Power industry
Wind turbines
Marine industry
Agriculture industry
For lower speed applications that require extreme smoothness of
motion or quiet operation.
●
In multi-stage gearboxes, hypoid gears are often used for the
output stage, where lower speeds and high torques are required.
●
For hypoid gearboxes is in the automotive industry, where they
are used in rear axles, especially for large trucks.
●
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BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
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Herringbone
Gears
● To transmit torque without axial load. The opposite direction of
teeth on a single gear cancels out the resulting thrust force (radial
and axial).
● Herringbone gears are used in heavy industrial machinery for
transmitting high torque.
GEAR RATIO
The ratio of the Number of turns or Number of teeth of an Output gear (Driven) to the number
of turns or Number of teeth of the Input gear (Drive(r)) is termed the Gear ratio.
In mechanical engineering, a gear ratio is a direct measure of the ratio of the rotational speeds
of two or more interlocking gears. As a general rule, when dealing with two gears, if the drive
gear (the one directly receiving a rotational force from the engine, motor, etc.) is bigger than the
driven gear, the latter will turn more quickly, and vice versa. We can express this basic concept
with the formula Gear ratio = T2/T1, where T1 is the number of teeth on the first gear and T2 is
the number of teeth on the second.
1 Start with a two-gear train. To be able to determine a gear
ratio, you must have at least two gears engaged with each
other — this is called a "gear train." Usually, the first gear is a
"drive gear" attached to the motor shaft and the second is a
"driven gear" attached to the load shaft. There may also be any
number of gears between these two to transmit power from
the drive gear to the driven gear: these are called "idler gears."
● For now, let's look at a gear train with only two gears in it.
To be able to find a gear ratio, these gears have to be interacting with each other — in other
words, their teeth need to mesh and one should be turning the other. For example, purposes,
let's say that you have one small drive gear (gear 1) turning a larger driven gear (gear 2).
2 Count the number of teeth on the drive gear. One simple way to
find the gear ratio between two interlocking gears is to compare the
number of teeth (the little peg-like protrusions at the edge of the
wheel) that they both have. Start by determining how many teeth
are on the drive gear. You can do this by counting manually or,
sometimes, by checking for this information labelled on the gear
itself.
●
For example, purposes, let's say that the smaller drive gear in our system has 20 teeth.
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Name of teacher: Mr. Arowolo Ifedapo
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3 Count the number of teeth on the driven gear. Next, determine
how many teeth are on the driven gear exactly as you did before
for the drive gear.
Let's say that, in our example, the driven gear has 30 teeth.
4 Divide one tooth count by the other. Now that you know how
many teeth are on each gear, you can find the gear ratio relatively
simply. Divide the driven gear teeth by the drive gear teeth.
Depending on your assignment, you may write your answer as a
decimal, a fraction, or in ratio form (i.e., x:y).
In our example, dividing the 30 teeth of the driven gear by
the 20 teeth of the drive gear gets us 30/20 = 1.5. We can also write
●
●
this as 3/2 or 1.5: 1, etc.
What this gear ratio means is that the smaller driver gear must turn one and a half times to get
the larger driven gear to make one complete turn. This makes sense — since the driven gear is
bigger, it will turn more slowly.
Making Ratio/Speed Calculations
1 Find the rotational speed of your drive gear. Using the idea of
gear ratios, it's easy to figure out how quickly a driven gear is
rotating based on the "input" speed of the drive gear. To start,
find the rotational speed of your drive gear. In most gear
calculations, this is given in rotations per minute (rpm), though
other units of velocity will also work.
●
For example, let's say that in the example gear train above
with a seven-toothed driver gear and a 30-toothed driven gear, the drive gear is rotating at 130
rpm. With this information, we'll find the speed of the driven gear in the next few steps.
2 Plug your information into the formula S1 × T1 = S2 × T2. In this
formula, S1 refers to the rotational speed of the drive gear, T1 refers
to the teeth in the drive gear, and S2 and T2 to the speed and teeth
of the driven gear. Fill in the variables until you have only one left
undefined.
Often, in these sorts of problems, you'll be solving for S2,
though it's perfectly possible to solve for any of the variables. In our
example, plugging in the information we have, we get this:
130 rpm × 7 = S2 × 30
●
●
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BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
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3 Solve. Finding your remaining variable is a matter of basic
algebra. Just simplify the rest of the equation and isolate the
variable on one side of the equals sign and you will have your
answer. Don't forget to label it with the correct units — you can
lose points for this in schoolwork.
●
●
●
●
●
●
In our example, we can solve like this:
130 rpms × 7 = S2 × 30
910 = S2 × 30
910/30 = S2
30.33 rpms = S2
In other words, if the drive gear spins at 130 rpm, the driven gear will spin at 30.33 rpm. This
makes sense — since the driven gear is much bigger, it will spin much slower.
FUNCTION OF LUBRICANTS ON GEARS
Lubricant forms an oil film on the surface of metals, converting solid friction into liquid friction to
reduce friction, which is the most common and essential function of lubricants. Especially cooling
is critical to rolling oils, cutting oils, and lubricating oils used in an internal combustion engine.
The following are the functions of lubricants on gears and other parts of machines and engines.
1. Reduced friction
Lubricant forms an oil film on the surface of metals, converting solid friction into liquid
friction to reduce friction, which is the most common and essential function of lubricants.
Reduced friction prevents heating and abrasion on the friction surface.
2. Cooling
Friction certainly causes heating in the area and more heat is produced if metals rub
against each other. Therefore the heat needs to be absorbed or released; otherwise, the
system is destroyed or deformed. To prevent it, lubricants are applied. Especially cooling
is critical to rolling oils, cutting oils, and lubricating oils used in an internal combustion
engine.
3. Load balancing
Components like gear or bearing are limitedly contacted on a certain line or surface, so
load can be increased in a moment, making systems at risk of being destroyed and
attached to each other. Therefore, the application of lubricant protects systems against
increased load by forming an oil film to disperse the load in the film.
4. Cleaning
Long-term use of systems may lead to corrosion or ageing, producing foreign substances.
In the case of using hydraulic oil and gear oil, sediments accumulate such as sludge from
deterioration. Especially an internal combustion engine generates too much soot so that
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it is likely to shorten the life of systems and make them fail to work properly. Therefore,
lubricant itself cleans out foreign substances like soap.
5. Sealing
Sealing is to close the macro-gap between systems. Sealing the space between pistons
and cylinders in the internal combustion engines or air compressors blocks the leakage of
combustion gas and the inflow of external foreign substances to maintain the defined
internal pressure and protect the system. Especially in the hydraulic system, lubricants
themselves serve to prevent leakage by creating a hydraulic film.
6. Rust prevention
Metals produce rust when contacting water and oxygen. However, rust formation can be
controlled and the system lifetime is extended if the surface of metals is coated with
lubricating film.
Hydraulic Machines
Hydraulic machines are machinery and tools that use liquid fluid power to do simple work,
operated by the use of hydraulics, where a liquid is a powering medium.
Pneumatic Machines
Pneumatic machines are machines and tools commonly powered by compressed air or
compressed inert gases. A centrally located and electrically powered compressor powers
cylinders, air motors, and other pneumatic devices.
Components of the Hydraulic Machine
a)
b)
c)
d)
e)
f)
g)
h)
i)
Actuators
A movable piston connected to the output shaft in an enclosed cylinder
Storage tank/Reservoir
Filter
Fluid (or gas)
Electric pump
Pressure regulator
Control valve
Leak-proof closed loop piping/tubes.
a) The output shaft transfers the motion or force, however, all other parts help to control
the system. The storage/fluid tank is a reservoir for the liquid used as a transmission
media.
b) The liquid used is generally high-density incompressible oil. It is filtered to remove dust
or any other unwanted particles and then pumped by the hydraulic pump.
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The capacity of the pump depends on the hydraulic system design. These pumps generally
deliver constant volume in each revolution of the pump shaft. Therefore, the fluid
pressure can increase indefinitely at the dead end of the piston until the system fails.
c) The pressure regulator is used to avoid such circumstances which redirect the excess fluid
back to the storage tank. The movement of the piston is controlled by changing the liquid
flow from port A and port B.
The cylinder movement is controlled by using a control valve which directs the fluid flow. The
fluid pressure line is connected to the port B to raise the piston and it is connected to port A to
lower down the piston. The valve can also stop the fluid flow in any of the ports. The leak-proof
piping is also important due to safety, environmental hazards and economic aspects.
Examples of Pneumatic Devices
Some of the most common pneumatic devices are:
a) Pneumatic bladders: are used to help seal drains and ducts, which greatly reduces
the spreading of chemical gases
b) Pneumatic cylinders: create movement from a compressed air source
c) Pneumatic motors: are sometimes called compressed-air engines. With the help of
rotary/linear motions, compressed air is turned into mechanical motions
Examples of Hydraulic Devices
a)
b)
c)
d)
Lifting equipment - eg hydraulic jacks and wheelchair lifts.
Excavating arms on machinery such as diggers.
Hydraulic Presses - which are used during the forging of metal parts.
Wing flaps and some rudders on aircraft and boats.
Working principle of Hydraulic and Pneumatic machines
The controlled movement of parts or a controlled application of force is a common requirement
in the industries. These operations are performed mainly by using electrical machines or diesel,
petrol and steam engines as a prime movers. These prime movers can provide various
movements to the objects by using some mechanical attachments like screw jacks, levers, racks,
pinions etc. However, these are not the only prime movers. The enclosed fluids (liquids and gases)
can also be used as prime movers to provide controlled motion and force to the objects or
substances. The specially designed enclosed fluid systems can provide both linear as well as
rotary motion. The high magnitude-controlled force can also be applied by using these systems.
These kinds of enclosed fluid-based systems using pressurized incompressible liquids as
transmission media are called hydraulic systems. The hydraulic system works on the principle of
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BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
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Pascal’s law which says that the pressure in an enclosed fluid is uniform in all directions. Pascal’s
law is illustrated in the figure.
The hydraulic systems consist of a number of parts for their proper functioning. The schematic
of a simple hydraulic system is shown.
Components of the Hydraulic Machine
a)
b)
c)
d)
e)
f)
g)
h)
i)
Actuators
A movable piston connected to the output shaft in an enclosed cylinder
Storage tank/Reservoir
Filter
Fluid (or gas)
Electric pump
Pressure regulator
Control valve
Leak-proof closed loop piping/tubes.
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The output shaft transfers the motion or force, however, all other parts help to control
the system.
The storage/fluid tank is a reservoir for the liquid used as a transmission media.
b) The liquid used is generally high-density incompressible oil. It is filtered to remove dust
or any other unwanted particles and then pumped by the hydraulic pump.
The capacity of the pump depends on the hydraulic system design. These pumps
generally deliver constant volume in each revolution of the pump shaft. Therefore, the
fluid pressure can increase indefinitely at the dead end of the piston until the system
fails.
c) The pressure regulator is used to avoid such circumstances which redirect the excess
fluid back to the storage tank. The movement of piston is controlled by changing liquid
flow from port A and port B.
a)
Applications of hydraulic systems:
The hydraulic systems are mainly used for precise control of larger forces. The main
applications of the hydraulic system can be classified into five categories:
1.
2.
3.
4.
5.
Industrial: Plastic processing machinery, steel making and primary metal
extraction applications, automated production lines, machine tool industries,
paper industries, loaders, crushes, textile machinery, R & D equipment and
robotic systems etc.
Mobile hydraulics: Tractors, irrigation system, earthmoving equipment, material
handling equipment, commercial vehicles, tunnel boring equipment, rail
equipment, building, and construction machinery and drilling rigs etc.
Automobiles: It is used in the systems like breaks, shock absorbers, steering
system, windshield, lift, cleaning etc.
Marine applications: It mostly covers ocean-going vessels, fishing boats, and
naval equipment.
Aerospace equipment: There are equipment and systems used for rudder
control, landing gear, breaks, flight control and transmission etc. which are used
in aeroplanes, rockets, and spaceships.
TIMBER PROCESSING
Timber processing is that part of the forest industry involved in transforming logs into new
products. It includes sawmilling, wood, paper and furniture product manufacturing.
Some Methods of Timber Processing/Conversion
Plain Sawn: This is the method of cutting log linearly or flatly in a horizontal manner to produce
planks e.g.
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Plain sawn
Advantages of Plain Sawing
It is quick and the waste generated is quite few.
Disadvantages of Plain Sawing
i.
ii.
Plain-sawn timbers are prone to cupping, twisting and bowing.
Boards from plain sawn do absorb moisture and become distorted with time.
2. Quarter Sawn: This is the method of splitting the log angularly along the grains on the log. It is
usually more technical to split wood using this method. E.g.
Quarter sawn
Advantages of Quarter Sawing
i. In quarter-sawn boards, there is a naturally decorative pattern which is not noticed with plain
sawing.
ii. Boards produced using quarter sawing are more stable than plain-sawn boards since they
release atmospheric moisture naturally.
Disadvantages of Quarter Sawing
i.
This method leaves a lot of wasted timber.
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ii.
Quarter-sawn timbers are more expensive than plain sawn due to the production of much
scrap.
3. Rift Sawing: This is a technique of cutting a log along a radius so that the saw cuts at a right angle
to the log’s growth ring. In this technique, the board has the same original grain pattern. E.g.
Rift sawn
Advantages of Rift Sawing
i. Rift-sawn timbers are the most stable of the three methods used.
Disadvantages of Rift Sawing
i. Rift-sawn boards (planks) are typically the most expensive than the other methods.
ii. This method produces large triangular wastes generated between boards.
PROPERTIES OF GOOD TIMBER
Good timber should have the following qualities:
1. HARDNESS
Good quality timber should be hard enough to resist deterioration.
2. STRENGTH
It should have sufficient strength to resist heavy structural loads.
3. TOUGHNESS
It should have enough toughness to resist shocks due to vibrations. It should not break in bending
and should resist splitting. Timbers having narrow annual rings are generally the strongest.
4. ELASTICITY
It should have the property of elasticity to regain its original shape after the removal of loads.
This is a very important property to be considered if the timber is used in making sports goods.
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5. DURABILITY
It should be able to resist attacks of fungi and worms and also atmospheric effects for a longer
period of time.
6. DEFECTS
Timber should be prepared from the heart of a sound tree and be free from sap, dead knots,
shakes and other similar defects.
7. FIBRES AND STRUCTURE
It should have straight and closed fibres and compact medullary rays. It should give a clear ringing
sound when struck. Dull heavy sound is an indication of internal decay. Its annual rings should be
uniform in shape and colour.
8. APPEARANCE AND COLOUR
The freshly cut surface should give a sweet smell and present a shining surface. It should have a
dark colour, as light-coloured timbers are generally weak in strength.
9. SHAPE AND WEIGHT
It should retain its shape during the process of seasoning. Heavy timbers are always stronger than
lightweight timbers.
10. WORKABILITY
It should be well-seasoned and easily workable. The teeth of the saw should not get clogged
during the process of sawing. It should provide smoothened surface easily.
DEFECTS IN TIMBERS
A defect in Timber Example Image Source: diy.sndimg.com
The followings are the five main types of defects in timber:
1. Defects due to Natural Forces
2. Defects due to Attack by Insects
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3. Defects due to Fungi
4. Defects due to Defective Seasoning
5. Defects due to Defective Conversion
These timber defects are briefly discussed below.
Defects in Timber Due to Natural Forces
a. Knots: Knots are the most common defects caused due to natural forces. During the growth
of a tree, branches close to the ground or lower branches die. Bases of those branches
remain in the tree as the trees grow. These bases may create imperfections known as
knots.
Types of Knots: Knots are of two types.
i.
ii.
Dead knots: The remains of damaged branches after drying out, it become loose
and fall out.
Live knots: They are sound and firm. If small, are not great of a defect.
Live knots are usually not a problem as they remain firmly attached to the timber. But in dead
knots, they are loosely attached and reduce strength. Knots decrease the strength of the wood
and thus lower its value for structural uses. Knots cause serious defects when the load is
perpendicular to the grains.
Dead Knot and Live Knot. Source: woodexportchile.com
b. Twist: Twist in timber rotates the ends of the timber in opposite directions. The main reason
behind this defect is the twisting of the trees by the strong wind.
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Twisting of the trees by the strong wind. Source: commons.wikimedia.org
c. Shakes: Shakes are timber defects that occur around the annual ring or growth ring of timber.
In other words, cracks or splits in the woods are called shakes. It may or may not be a
structural problem depending upon depth and use. The main problem is aesthetics. Where
appearance is important, shakes are undesirable.
Types of shakes: Shakes can be classified into three main categories: i. Star Shakes: This type of shake starts propagating from the bark towards the
sapwood and sometimes even towards the heartwood along the lines of
medullary rays. Cracks are wider on the outer edge of the bark and narrower on
the inside (usually sapwood, sometimes heartwood). The main reasons behind
star shakes are extreme heat or frosting during the growth of the trees and rapid
or uneven seasoning after cutting off the timber. Extreme heat or frost causes
temperature difference, which causes shrinkage leading to the crack.
ii. Cup and/or Ring Shakes: Cup shakes follow the annual growth ring. It is capable
to separate the growth ring partially or completely. When the crack separates the
annual ring completely, it is called ring shake. So, all ring shakes are cup shakes,
but all cup shakes are not a ring shape. Excessive frost action is the main reason
for this type of crack.
iii. Heart Shakes: Unlike star shakes, heart shakes start propagating from the pith to
the sapwood along the lines of medullary rays. Shrinkage of the interior part of
the timber causes this crack.
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d. Rind Galls: The meaning of rind is bark and gall is abnormal growth. So abnormal growth of
the bark of the trees is called rind galls. Improper cutting of branches causes this abnormal
growth. Wood from this portion of the timber lacks strength and is desirable in structure.
e. Upsets: Upsets in various wood indicate that the tree was subjected to crushing or
compression. Improper felling of trees and heavy wind blowing during the young age of the
tree are the main reasons behind this type of defect.
Defects of Timber Due to Attack by Insects
Insects like beetles, termites or marine boars eat wood, make holes and weaken the strength of
the wood.
Beetles are small insects that make holes in almost all the sapwoods. The larvae make tunnels
through the sapwood in all directions and turn wood into powder.
Termites live in a colony. They are very fast in eating wood and making tunnels through it. Only
a few good kinds of wood can withstand the action of termites.
Marine boars are found in salt water. Usually, they make tunnels in wood to take refuge or
shelter. All kinds of wood or timber are vulnerable to this kind of insect.
Defects in Timber Due to Attack by Fungi
a. Stain: When fungi feed only on sapwood, where the food materials are stored, it causes
a stain. Heartwood doesn’t contain these kinds of food materials and is not affected by it.
Stain action causes colour but does not affect the strength of the wood.
b. Decay: wood eating or wood-destroying fungus is responsible for this type of defect in
wood. This type of fungi breaks down the cell structure. Both sapwood and heartwood
are affected by them. Considerable strength reduction occurs.
Defect in Timber due to Defective Seasoning
Faulty methods of seasoning cause serious defects in woods. During the seasoning of timber, the
exterior or surface layer of the timber dries before the interior surface. So, stress is developed
due to the difference in shrinkage. In a perfect seasoning process, stress is kept minimum by
controlling the shrinkage. Some of the defects resulting from defective seasoning are as follows:
a. Bow: Curvature formed in the direction of the length of the timber is called a bow.
b. Cup: Curvature formed in the transverse direction of the timber is called a cup.
c. Check: Check is a kind of crack that separates fibres, but it doesn’t extend from one end
to another.
d. Split: Split is a special type of check that extends from one end to another.
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e. Honey Combing: Stress is developed in the heartwood during the drying process or
seasoning. For these stresses, cracks are created in the form of a honeycomb texture.
Defects of Timber due to Defective Conversion
a. Boxed Heart: This term is applied to the timber, which is sawn in a way that the pith or
the centre heart falls entirely within the surface throughout its length.
b. Machine Burnt: Overheating is the main reason for this defect.
c. Machine Notches: defective holding and pulling cause this defect.
d. Miscut: erroneous cutting or sawing of wood causes this defect. Lack of experience in
sawing and carelessness is the main reason for erroneous cutting.
e. Imperfect Grain: Mismatch in grain alignment
TREATMENT AND PRESERVATION METHOD FOR TIMBER
TYPES OF TIMBER TREATMENT
1. Water-borne preservatives
These preservatives are dissolved in water and then absorbed into the timber when it is
soaked in the solution.
2. LOSP
Instead of being dissolved in water, the chemical components of Light Organic Solvent
Preservative (LOSP) are dissolved in (as the name implies) an organic solvent.
3. Wood Seasoning
This is the process of reducing the moisture or water content of the wood. Since sawn
timber contains some amount of water, it must be seasoned before using them.
(i)
Seasoning makes the wood stronger.
(ii)
It makes the wood lighter in weight.
(iii)
It makes wood to take (absorb) preservatives easily.
(iv)
Seasoning makes the wood more stable when being used for furniture work
(v)
It makes the wood more durable.
(vi)
Seasoning makes the wood take polish easily.
METHODS OF PRESERVATION OF TIMBER.
Preservatives are used by different methods depending upon the extent of preservation
required. Starting from the simplest to the complex, these are:
1. Brush applications,
2. Dipping,
3. Open tank immersion,
4. Pressure application.
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(1) Brush Application;
In this method, timber is given one or two coats of preservatives with the help of a brush. This is
used for painting the ends of beams or the base of poles and posts that go to the ground with
coal tar. The method is quite cheap. At the same time, it is not very effective.
(2) Dipping Application;
The timber part to be treated is made to dip in the preservative and kept immersed in it for
various periods from a few hours to a few days.
It is used when organic preservative solvents are to be applied.
(3) Open Tank Application;
In this method, the timber is kept immersed in a suitable metallic tank of proper size till a proper
saturation is obtained. To ensure deeper penetration of the preservative, the tank is heated while
the timber is immersed in it. The temperature of the preservative is brought to 70°-80°C, and it
is kept at that temperature for several hours.
After this, the timber is allowed to cool within the tank in the presence of a preservative. In this
way, the timber may actually suck a lot of preservatives and ensure complete penetration.
Softwoods (confiners) receive this type of treatment in a remarkable manner because their cells
are more permeable. The treatment has the disadvantage that it increases the weight of the
treated timber considerably.
(4) The Pressure Process;
This is the best and most commonly applied method for the preservation of timber of costly
varieties. It involves the passage of preservatives into the timber under pressure. This is
achieved by either Two Processes.
1. The Full-Cell Process. The timber is placed in a large steel cylinder acting as a
pressure vessel. A vacuum is created and maintained for about one hour or
more.
2. After this, coal tar creosote oil or any other suitable preservative, preheated to a
required temperature, is forced into the cylinder under sufficient pressure.
This is continued till the required quantity of preservative has been introduced into the timber.
Thereafter, the pressure is reduced, and after giving some vacuum, the timber is taken out.
In the empty cell method, no vacuum is created in the beginning.
Instead, timber placed in the pressure vessel is subjected to initial pressure while preservatives
are introduced into the cylinder.
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Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Once the vessel is full of preservatives, full pressure is applied which forces the preservative from
the tank into the timber.
After this, the pressure is released. This causes the air compressed in the cells of timber to come
out along with any excessive preservative.
The main advantage of pressure processes (of one type or another) is that they ensure proper
and deeper penetration of preservatives into the timber in a controlled manner.
Even those timbers which may not absorb preservatives in the open-tank process can be filled
with preservatives by this method.
The main disadvantage is that these are as yet costly processes involving the use of pressure
vessels and require skilled operators for better results.
Charring. It is a common method used for preserving timber poles and posts that are to be dug
into the ground. The outer part of the lower ends is charred (incompletely burnt) before insertion
into the ground. The charcoal layer so formed is an easy safeguard against attacks by fungi or
termites (as these organisms do not find any food in charcoal).
Termite Shields. The base of major timber columns may be preserved against organic attack by
constructing a suitable barrier between the timber and the ground.
These barriers of proper design and shape are called termite shields.
IMPORTANCE OF WOOD PRESERVATION
The term wood preservatives defines preservation as the process of preserving from the
destroying agents like insects or fungus so that the life span of the wood can be extended. It
refers to the treatment of timber with chemicals to impart resistance to degradation and
deterioration by living organisms. The proper application of chemical preservatives can protect
from decay, and stain fungi, insects and marine borers, thus prolonging the service life for many
years. The material contains cellulose, hemicelluloses, starches and other susceptible materials
that attract fungi and insects to be degraded and eaten. After the preservative treatments, the
fungi and insects cannot decompose and feed on these substances, hence the durability of wood
is to be increased. Everybody is well aware that furniture is prone to attacks by insects and
environmental factors such as moisture, mildew decay etc. This is a fact and no need to discuss
more about it.
Everybody is also well aware that the use of the finest quality preservative increases the life and
structural strength of wood greatly. One thing must be remembered that preservatives must
contain spermicides, fungicides, germicides and miticides. Must be environmentally friendly and
safe for humans and cattle and birds. Also, one has to offer many formulations according to
specific species of wood/timber.
There are many enemies of wood. Some of them are listed below. Termites: Queen lives in the
ground up to 20 feet deep. Workers tunnel to the surface under a piece of wood and start eating
it.
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BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
If they can't reach wood from the ground, they build tubes of dirt up to the wood. Some tubes
are self-supporting and reach up to 2 feet. Others are attached to other structures such as block
walls and have been known to go up 8 feet to reach wood.
Termites never work in the open. Always in wood or tubes. There are only two types of homes in
the world those with termites and those that are going to get termites.
Borers: Borers are the great enemy of wood and generate great damage to wood. Wood Borer
adults are 3/4 inch in size, long-horned brown to black in colour. Beetle larvae are whitish and
produce tunnels in wood. The larvae stage is more destructive. Borers feed on both soft and
hardwood. Adult beetles lay eggs in crevices of wood. When larvae hatch tunnels inward, adults
break through the surface leaving tiny round or oval-shaped pin holes.
Adults lay eggs in open pores of wood. Larvae eat causing honeycomb. After pupating and
becoming adults, they bore out of the panels leaving behind small holes and a pile of powder or
"sawdust".
Fungi: A decay fungus is a variety of fungus which can digest wood, causing it to rot. Decay fungi
include those which attack dead wood, such as dry rot, and those which are parasitic on living
trees, such as Armilariahoney fungus. Fungi that not only grow but cause it to decay are called
lignicolous fungi. They do not necessarily need to decay lignin but be termed lignicolous. Dry rot
fungi decay cellulose in wood leaving behind the lignin as the brown crumbly remains.
PROCESSING OF METALS
Definition of Metals
Metal is processed from a natural solid mineral found beneath the earth called iron ore. In its
natural state, iron ore contains a lot of impurities which are removed through a process called
smelting.
What is metal processing?
Iron ore is the first material needed for the processing of metal. The iron ore and other materials
such as coke and limestone are loaded into a device called BLAST FURNACE. The blast furnace
produces a blast of hot air which heat the limestone and iron ore to produce a molten iron. The
molten iron is then transferred to a ladle which will be used to transfer the molten iron to the
mould. Here the molten iron will be allowed to Cool down and form the first metal called PIG
IRON.
33
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
METHODS OF PROCESSING METALS
Blast Furnace: The blast furnace is a smelting (heating or burning) plant used for changing ironore into pig-iron. To smelt iron – ore in the blast furnace, other chemicals like coke (which serves
as fuel and limestone, which removes impurities) are added to the iron – ore so that most of the
impurities may be removed.
Pig-Iron: Pig-iron is derived from iron ore. It is the product derived from the blast furnace.
Further processing or pig iron gives birth to steel. The furnace used for this purpose is called
‘Bessemer Converter”
Bessemer Converter: This is the furnace used for smelting pig iron into steel by further burning
off impurities in the right percentage. Since steel is categorized into three categories, the
Bessemer converter is used for this purpose.
Other Methods: Other Methods of processing metals are: The basic Oxygen furnace, The electric
furnace – for producing cast iron products, and The Open-hearth furnace – which is one of a
number of kinds of furnace where excess carbon and other impurities are burnt out of pig-iron
to produce steel.
Note: These three methods listed make use of oxide at high temperature (16000C) to remove
impurities.
What is casting?
Casting is defined as a manufacturing process in which molten metal is pure into a mould or a
cavity of the desired shape and allow to solidify which forms a predefined shape. This process is
widely used to manufacture complex parts which cannot be made by other processes. All major
parts like a bed of lathe machine, milling machine
There are many types of casting that work differently but all these processes involve
following steps.
A. First metal is melted in a suitable furnace.
B. Now molten metal is poured into a predefine cavity.
C. The molten metal allows it to solidify at the desired cooling rate.
D. Removal of cast part from the mould and cleaning it for further processes like machining,
surface finishing polishing etc.
Advantages:
i. It can create any complex structure economically.
ii. The size of the object doesn’t matter for casting.
iii. The casting objects have high compressive strength.
iv. All structure made by casting has a wide range of properties.
v. This can create an accurate object.
vi. All materials can be cast.
34
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
vii. It creates an isotropic structure.
viii. It is the cheapest among all manufacturing processes.
ix. A composite component can be easily made by casting.
Disadvantages:
i.
It gives a poor surface finish and mostly requires surface finish operation.
ii.
Casting defects involve in this process.
iii.
It gives low fatigue strength compared to forging.
iv.
It is not economical for mass production.
FABRICATION
A fabrication shop tells a lot of stories about the manipulation of various materials to form a
desired product. The process of fabrication involves a collection of methods that will produce a
specific item. The results of this process depend on several factors such as the budget, purpose,
and appearance. It is vital for you to know the advantages and disadvantages of metal fabrication
so that you can determine if this is the right type of fabrication for your new line of products
like commercial garbage cans.
Methods Involved in Fabrication
1. Makes use of machines or tools which remove excess materials from raw materials to
meet the required shape and size. Examples of these tools are cutting torches and band
saws.
2. This involves drilling lathing, honing, and milling. The equipment used in shaping materials
is either manual or automated.
3. This uses equipment and tools for reforming such as hydraulic brakes, which press or bend
materials at a specific angle.
4. This is the process of applying pressure and heat in joining at least two pieces of materials
The Advantages
i.
ii.
iii.
iv.
Extra strong. Metal is harder and stronger than plastic.
Resistant to heat. Metals have higher melting points. Even if the temperature rises a bit,
metal does not easily degrade.
Metal can go through a wider range of processes including chipping, deep drawing,
casting, forging, welding, and soldering.
Metal is more cost-efficient when it comes to long-term, high-volume lines of production.
The Disadvantages
i.
Expensive starter fees. Metal fabrication tools are more expensive than plastic
fabrication.
35
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
ii.
iii.
Post-fabrication process. Metal usually needs processes after its fabrication. Deburring,
finishing, and painting follow and these are considered costlier and time-consuming.
Limited designs. If the metal is molten or viscous, metals are not ideal for creating
advanced shapes and geometries.
PROPERTIES OF ALLOYS
Individual pure metals may possess useful properties such as good electrical conductivity, high
strength, and hardness, or heat and corrosion resistance. Commercial metal alloys attempt to
combine these beneficial properties in order to create metals more useful for particular
applications than any of their component elements.
Steel, for example, requires the right combination of carbon and iron (about 99% iron and 1%
carbon, as it turns out) in order to produce a metal stronger, lighter and more workable metal
than pure iron.
Precise properties of new alloys are difficult to calculate because elements do not just combine
to become a sum of parts; rather, they form through chemical interactions which depend upon
component parts and specific production methods. As a result, much testing is required in the
development of new metal alloys.
Melting temperature is a key factor in alloying metals. Galinstan®, a low-melt alloy
containing gallium, tin, and indium, is liquid at temperatures above 2.2°F (-19°C), meaning that
its melting point is 122°F (50°C) lower than pure gallium and more than 212°F (100°C) below
indium and tin.
Galinstan® and Wood's Metal are examples of eutectic alloys -- alloys having the lowest melting
point of any alloy combination containing the same elements.
PRODUCTION OF MATERIALS – CLAY AND CERAMIC
Ceramics and glass are non-metallic materials used to mould different shapes and items needed for
domestic and commercial applications. The moulds are produced through different processes and
methods.
Section 1: Method of Making Clay
Mud (clay is dug from the earth. This is then pounded with little water until it forms a paste (becomes
malleable). The soft mud is then used to form different shapes before it solidifies.
It can be used to make different objects by putting the mud in moulds representing the object one
intends to make. School children can use it to mould objects like pressing iron, cars, human beings,
reptiles, etc.
36
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
The soft mud can also be used to make bricks by sharpening them with rectangular moulds. These
moulds are removed after one or two minutes. The shape of the object formed is then put in the sun
to dry.
Section 2: Stages in Producing Ceramics
Ceramics are products made from clay and dried to hardness. This follows certain stages which are:
1. Clay preparation
2. Clay moulding
3. The firing of ceramic articles
Clay Preparation
Clay must be prepared before use in pottery. Any trace of sand is removed. The clay is mixed with
water and pounded. This is to remove the air bubbles and also to make the clay more plastic so that it
becomes easier to mould and shape. If sand and air bubbles are not removed, any articles made from
such clay may explode later when heated.
Clay can be used to mould different articles using the pinch pot method or the potter’s wheel. The
pinch pot method is the easiest way to make a pot. A hollow is first formed with the thumb in a small
ball of clay. By carefully pressing between the fingers, the wall is gradually made thinner as the form
develops. The final form, containing some cracks, is then smoothed by using fingers and a small
quantity of water. The pinch pot method does not involve any apparatus. However, most pottery
articles are made by using what is called the potter’s wheel. A potter’s wheel is a device with a rotating
horizontal disc upon which clay is moulded by a potter.
The firing of Ceramic Articles
Any article just moulded from clay is soft. To harden the moulded article, it is baked in fire. One simple
way of baking is by using firewood. A more sophisticated way of heating is called a kiln. A kiln is an
oven or furnace for baking finished articles. Different kilns use different fuels to produce fire for baking.
Such fuels include wood, coal, oil and gas. An example is a kiln using gas. The hot air transfers heat to
the finished piece as it travels through the chamber.
Decoration of Ceramic Articles
An article can be decorated before or after firing. When the clay is partially dry and somewhat
hard, different patterns may be drawn on it.
37
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
METHODS OF PROCESSING PLASTIC
There are a variety of methods used to process plastic. Each method has its advantages and
disadvantages and is better suited for specific applications. These methods include injection
moulding, blow moulding, thermoforming, transfer moulding, reaction injection moulding,
compression moulding, and extrusion.
A. Injection Molding
The main method used for processing plastic is injection moulding. With this process, the plastic
is placed into a hopper. The hopper then feeds the plastic into a heated injection unit, where it
is pushed through a long chamber with a reciprocating screw. Here, it is softened to a fluid state.
A nozzle is located at the end of the chamber. The fluid plastic is forced through the nozzle into
a cold closed mould. The halves of the mould are held shut with a system of clamps. When the
plastic is cooled and solidified, the halves open and the finished products are ejected from the
press.
Thermosetting materials usually are not processed with injection molding because they will
soften, and harden to an infusible state. If they are processed with injection moulding, they need
to be moved through the heating chamber quickly so they do not set.
38
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
B. Blow Molding
Blow moulding is used when the plastic item to be created needs to be hollowed. A molten tube
is created with blow moulding by using compressed air, which blows up the tube and forces it to
conform to the chilled mould.
C. Thermoforming
Thermoforming uses a plastic sheet, which is formed with the mould by applying air or through
mechanical assistance. The air pressure used can be nearly zero psi or several hundred psi. At 14
psi, which is equivalent to atmospheric pressure, the pressure is created by evacuating the space
between the mould and the sheet. This is known as vacuum forming.
D. Transfer Molding
Transfer moulding is generally used only for forming thermosetting plastics. It is similar to
compression moulding because the plastic is cured into an infusible state through pressure and
heat. Unlike compression moulding, however, transfer moulding involves heating the plastic to a
point of plasticity before being placed into the mould. The mould is then forced closed with a
hydraulically operated plunger.
39
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
E. Compression Molding
Compression moulding is the most common process used with thermosetting materials and is
usually not used for thermoplastics. With this process, the material is squeezed into its desired
shape with the help of pressure and heat. Plastic moulding powder and other materials are added
to the mix in order to create special qualities or to strengthen the final product. When the mould
is closed and heated, the material goes through a chemical change that causes it to harden into
its desired shape. The amount of temperature, amount of pressure, and length of time utilized
during the process depends on the desired outcome.
F. Extrusion
The process of extrusion is usually used to make products such as film, continuous sheeting,
tubes, profile shapes, rods, coat wire, filaments, cords, and cables. As with injection moulding,
40
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
dry plastic material is placed into a hopper and fed into a long heating chamber. At the end of
the chamber, however, the material is forced out of a small opening or a die in the shape of the
desired finished product. As the plastic exits the die, it is placed on a conveyor belt where it is
allowed to cool. Blowers are sometimes used to aid in this process, or the product may be
immersed in water to help it cool.
G. Calendaring Method:
Dough-consistent thermoplastic mass is formed into a sheet of uniform thickness by passing it
through and over a series of heated or cooled rolls. Calendars are also utilized to apply plastic
covering to the backs of other materials. Low-cost and sheet materials are virtually free of
molded-in stresses.
METHOD OF PRODUCING RUBBER – NATURAL AND CHEMICAL
There are two types of rubber – natural rubber and synthetic rubber. Natural rubber is made
from the latex obtained from rubber trees, while synthetic rubber is obtained from petroleum
products. In each case, the resulting high-quality rubber is too hard to be processed easily. So,
the first step in processing rubber is to break it down, to make it smoother and more malleable,
in order to get an even mixture, we blend the rubber with certain chemicals and softeners. Carton
black (fine carbon obtained from wood, bones or plants) is added in order to make the rubber
product stronger. After thorough mixing, the rubber is then ready to be formed. Rubber products
are formed by processes similar to those used in making plastics.
ISOMETRIC DRAWING
Isometric drawing is one of the drawings that are used to present views of objects pictorially. A
pictorial drawing presents the views of an object in three dimensions of height, depth and length.
A pictorial object can easily be recognized by anybody even without any technical experience.
Pictorial Drawing has the advantage of enabling Engineers and Architects to communicate their
ideas (both real and imaginary) to anybody, particularly those who are not in technology-related
fields. Pictorial drawing can be in isometric, oblique or perspective views.
41
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
Isometric Drawing is normally drawn in isometric projections. Isometric projection is a method
of producing a pictorial view of an object, which shows three faces of the object simultaneously.
For a good understanding of the Isometric axis, 300 set squares must be used which is important
Oblique Drawing is another method of pictorial drawing. In the oblique drawing, the line of
projection to the horizontal (the receding line) is 450. In practice 450 set squares must be used in
drawing.
Isometric projection is a method for visually representing three-dimensional objects in two
dimensions in technical and engineering drawings. It is an axonometric projection in which
the three coordinate axes appear equally foreshortened and the angle between any two of
them is 120 degrees.
42
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
OBLIQUE DRAWING
OBLIQUE DRAWINGS: A diagram intended to depict a perspective of an item in three dimensions.
It is also a projective drawing in which the frontal lines are given in true proportions and relations
and all others at suitable angles other than 90 degrees without regard to the rules of linear
perspective.
TYPES OF OBLIQUE DRAWING
Cabinet Oblique: It is an oblique projection in mechanical drawing in which dimensions parallel
1
to the third axis of the object are shortened by half (2) to overcome apparent distortion.
Cavalier Projection: is a form of oblique projection in which the projection lines are presumed
to make a 45-degree vertical and a 45-degree horizontal angle with the plane of projection.
43
BASIC 8 BASIC TECHNOLOGY FIRST TERM (2023/2024 session)
Name of teacher: Mr. Arowolo Ifedapo
Office hour: Every school day at break time.
Email: ifedapo.arowolo@jesuitmemorial.org (I always read my messages)
44