COMPRESSION & TRANSFER
MOULD DESIGN
CORORATE TRAINING AND PLANNING
TYPES OF THERMOSET PLASTICS
 Phenole formaldehyde (PF)
 Urea formaldehyde (UF)
 Melamine formaldehyde (MF)
 And others
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 Compression molding of the thermosetting materials
has certain advantages as follows :• Waste of material in the form of sprue runners and transfer
culls is avoided and there is no problem of gate erosion.
• .
• A maximum number of cavities can be used in a given mold
base without regard to demands of a sprue and runner system.
• Compression molding is readily adaptable to automatic loading
of material and automatic removal of molded articles. Automatic
molding is widely used for small items such as wiring device
parts and closures.
• In general, compression molds are usually less expensive to
build than transfer or injection types.
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 Limitations of Compression Molding :

In the case of very intricately designed articles
containing undercuts, side draws and small holes, the
compression method may not be practicable. Articles of
0.35 in thickness compression molding would be slower
than transfer slights fins or "flash" are to be expected on
molded articles where the mold sections meet.
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Articles of polyesters require very careful adherence
to all rules for draft; they also require generous ejector
areas to avoid fracture on release from the molds. In
some cases, compression molding of thermosetting
material may be unsatisfactory for production of articles
having extremely close dimensional tolerances,
especially in multiple cavity molds, particularly relation to
non-uniformity of thickness at the parting line of the
molded article.
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Procedure for Compression Molding :
 The sequence of operations constituting the
molding cycles is as follows : Open the mold ;
 Eject the molded articles ;
 Place article in shrink or cooling fixtures when
necessary to maintain close dimensional
tolerances (if necessary) ;
 Remove all foreign matter and flash from the
mold, usually by air blast
 Place inserts or CORPORATE
other loose
mold parts if any ;
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 Load molding compound (powder or performs, cold
or preheated);
 Close the heated mold (breathe if necessary);
 For thermosetting materials, hold under heat and
pressure until cure is completed. Certain materials
require cooling under pressure for best control of the
dimensions ;
 For thermoplastic materials hold under pressure and
cool to harden the articles.

The temperature of the mold and the pressure
applied are extremely important and it is advisable to
follow the recommendations
of the manufacturer for
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each grade of materialPLANNING
used.
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There are five very important variables in the
compression molding of thermosetting materials
which determine the pressure required to
produce the best molding in the shortest length
of time. These are as follows :1. Design of the article to be produced :
projected area and depth
wall thickness
obstruction to vertical flow (such as pins, louvers and
sharp corners)
2. Speed of press in closing ;
use of slow or fast acting self contained press
use of fast acting press served by hydraulic line
accumulator system
capacity of accumulator to maintain constant follow
up of pressure onCORPORATE
material
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3. Plasticity of material ;
degree and type of preheating
density of charge (perform or powder)
position of charge in cavity
mobility of resin under pressure
type of filler (wood flour, cotton flock, macerated fabric,
asbestos, glass or mica).
4. Over all temperature of mold ;
temperature variations within cavity and force of mold
5. Surface condition of mold cavity and force ;
highly polished chrome plated surface
polished steel
poor polish (chromium plating worn ; pits, gouges and nicks)
Molding pressures required for most thermosetting materials
follow the pattern established for phenolic materials.
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Compression Moulds
 Compression moulds are made of High Carbon high
Chromium H11, H 13 Hot die Steels. It consists of a
lower cavity or cavities also known as Bottom force,&
core or Punch also called as an upper force . The
molding portions of the molds are hardened and highly
polished.
 The two halves of the mold are mounted between the
platens of a hydraulic compression press. The weighted
raw material or Charge is placed in the cavity of heated
mould in Powder form or performs. Both the mould
halves are closed by the press, the top force causes the
Plastics material to flow in the mold. The material is
compressed into the shape by the application of heat
and pressure which causes a chemical reaction in the
material .The material is chemically cross linked or set or
cured into the shape
of the required Product.
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Types of Compression Moulds
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Hand Moulds
Semi–automatic moulds
Automatic moulds.
 For most economic production moulds are
made from High grade HDS i.e, H 11,or H 13
steels which are hardened and polished.
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Hand Compression Mould
These moulds are used for smaller production runs or
Prototypes, experimental jobs that require minimum
mold cost & Parts having Open Tolerances. These
moulds are used advantageously for complex Parts
incorporating number of loose pull pins and
wedges. A Hand Mold weights less than 10 Kgs for
easy manual handling. As all the mould operations
are manual, Automation is not possible. Hence
Hand Moulds are slow in operation which requires
longer cycle time and is labour intensive, adding to
Production cost as compared to other type of
moulds Moreover, the molds are more easily
damaged by misalignment and mishandling etc
which may result from Improper mould operation
and closing of the mold.
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1.Top force ret. Plate
2. Bottom force plate
3. Bottom force
4. Top force
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5. GuidePLANNING
pillar
6. Guide bush
7. Bottom force insert
Semi-automatic Compression Mould
 Semi-automatic moulds are fastened in the
press for the duration of the run. The pressoperator automatically releases the mould piece
as the press opens, thus permitting ready
removal, semi-automatic moulds are used for
mass production of jobs.
 While operating semi-automatic moulds the
operator is required for only a brief period during
each molding cycle. Almost all Parts with limited
design complexities can be produced by semiautomatic compression molds.
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Classification of Semi automatic Moulds.
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3.
4.
Semi-automatic Open Flash Mould
Semi-automatic Fully Positive Mould
Semi-automatic Landed Positive Mould
Semi-automatic Semi Position Mould
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HEAT SOURCE
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Automatic Mould
 In principle Automatic Moulds are similar to semiautomatic moulds. They have additional mechanical
features, which serve to perform all operations
automatically in sequence, when used in an automatic
press. The Plastics material is measured & charged in
to the mould from a hopper by a automation device
that are set in a motion by a master timer. The timer
operates the valve or linkage device to close the press
and open it again, when the molding cycle is
completed. Mould opens & subsequently Ejector pins
demoulds the molded piece from the mold cavity or
core so that it may be picked or blown in to a receiving
pile by external device.
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 Automatic moulds are used when automatic presses are available.
These moulds are generally expensive than semi-automatic moulds
but their operational cost is considerably low.Automatic Moulds
eliminates human errors but there may be difficult to keep in
adjustment for certain jobs & from maintenance standpoint.
 Automatic Moulds are best adopted for jobs requiring better accuracy
, stringent Tolerances & for mass Production.
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4.
OPEN FLASH MOULD
LANDED PLUNGER MOULD
POSITIVE MOULD
SEMI POSITIVE MOULD
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CALCULATION OF LOADING CHAMBER DEPTH
D
=
VT – VC
A
Where,
D – Depth of loading space from top of cavity to pinch-off land
VC - Volume of actual cavity space (cm3)
VT - Total volume of loose powder (cm3)
A – Projected area of the loading chamber (cm2)
Where,
V – Total volume of part including flash factor Around 10 to 20%.
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This is the standard Practice
adapted
PLANNING to calculate the depth of
loading chamber .
DESIGN OF THE MOULD CAVITY
Generally Moulds are designed ruggedly to
withstand Thrusts, Pressures, loads, stress
from mechanical standpoint, hence the mould
cavity should have adequate dimensions to
withstand the clamping pressure & also to
prevent distortion within the specified
tolerance limits of deformation. Cavity
Strength Calculation
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For Rectangle Cavity
In the case of larger moulds the distortion
tendency due to Internal pressure should be
considerd & in case small distortion takes
place, the effect is not determinant, where the
moulds are built in sections & fitted into a
bolster, then distortion at the core, of the open
side may be found using the following
formula.
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FLASH THICKNESS ALLOWANCES
 Allowances for flash thickness in compression moulds, using
thermosetting compounds are:Rag-filled high impact compound
0.25mm
Cotton – flock compounds in large molds
0.2mm
Wood – flour compounds in small molds
0.1mm
 All other moulds are for all other compounds allow 0.13mm (except as
previously noted)
 Because of the flash thickness that we are considering in the mould
design the depth of cavity become:
Depth of Cavity
=
Minimum dimension of moulding +
Shrinkage of compound
 The flash thickness adds to the total thickness of the part and this
thickness must be subtracted from the basic cavity depth in order that
the finished Part may have the desired wall thickness.
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Technological Determination of the Number of Cavities OR
Impressions in Compression Mold
 During calculation of the number of cavities or impressions by
technological method for multi-cavity moulds, the following
parameters should be considered. On the machine side we
have to consider – available machine clamping force, and size
of the platen.
 For the moulding materials we have to consider the
compression pressure of the material and for the moulding the
projected area should be taken into account during calculation.
 The calculation as follows:
Claming force (kgf) = Projected area of the moulding (cm2) x
Compression pressure of the plastic
material kgf/cm2
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 The projected area can vary depending on the size of the
component as well as on the design of cavity or loading
chamber and the compression pressure also can vary based
on the type of plastics materials.
 For example, in a vertical flash or positive type of mold, there
is no need of horizontal land. But in the case of horizontal
flash type of mold the flash width should be taken in to
account for the determination of the projected area.
 So the projected area in the case of vertical flash type is same
as the projected area of the component. But, in the case of
horizontal Flash type, 20% of the projected area of the
component should be taken into account for the flash.
Therefore, the actual projected area is 1.2 x Projected Area of the component.
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 The compression pressure must be regulated in order to
produce satisfactory parts economically. Pressure needed to
mold a particular article depends on the flow characteristics of
the material, the cavity depth and the projected are of the piece
part. Generally it is recommended that minimum molding
pressure of 240 kg/cm2 of projected area be used. However, in
practice, about 300 kg/cm2 of projected area is used to
compensate for any variables that may be encountered.
 After finding the clamping force required for one impression, the
number of impressions can be determined from the actual
clamping force available for a particular machine –
i.e. No. of Impression = Clamping force available on the machine
possible
Clamping force required for an impression
Using this Technical formula, the number of impressions can be
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determined.
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Heat Treatment of mould parts
Hardening and Tempering
Dimensional & Shape stability
Surface treatment
Testing of mechanical properties
Stress relieve
Mould polishing
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 ADVANTAGES OF COMPRESSION MOULD OVER TRANSFER
MOULD : Waste of material in the form of sprue runners and
transfer culls is avoided and there is no problem of gate
erosion.
 Internal stress in the molded article is minimized by the
shorter and multi directional flow of the material under
pressure in the mold cavity. In the case of high impact
types with reinforcing fibers, maximum impact strength
is gained. This results because reinforcing fibers are not
broken up as is the case when forced through runners
and gates in injection molding.
 A maximum number of cavities can be used in a given
mold base without regard to demands of a sprue and
runner system.
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• Compression molding is readily adaptable to automatic
loading of material and automatic removal of molded
articles. Automatic molding is widely used for small items
such as wiring device parts and closures.
• This technique is useful for thin wall parts that must not
warp and must retain dimensions. Parts with wall thickness
as thin 0.025 in are molded, however, a minimum wall
thickness of 0.060 in is usually recommended.
• For parts weighing more than 3 lb, compression molding is
recommended since transfer or screw injection equipment
would be very expensive for larger parts.
• For high impact, fluffy materials, compression molding is
normally recommended because of the difficulty in feeding
the molding compound from a hopper to the press or
performer.
 In general, compression molds are usually less expensive
to build than transfer CORPORATE
or injection
types.
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Compression Mould Design Tips
 When designing a mould for the compression molded part,
it is important to keep in mind that the goal is to produce
quality parts in as short a cycle as possible with a
minimum of scrap. To achieve these goals, you will need a
mold that has a uniform mold temperature, and is properly
vented
 MOULD HEATING SYSTEM: A uniform mold temperature means that the temperature of
each half of the mold is the same (within 3° C ) for all
locations when the mold is heated by oil or steam. Molds
that are heated with electric cartridge heaters can vary by
as much as 6°C. A mold with a uniform temperature, will fill
easier and produce parts with less warpage, improved
dimensional stability and a uniform surface appearance.
Achieving a uniform mold
temperature is dependent on
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your method of mold heating.
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 HEAT REQUREMENTS & HEAT CAPACITY: To determine the amount of wattage needed to
heat a mold the use of the following formula might
be helpful: 1 1/4 kilowatts for every 45kg (100
pounds )of mold steel. (Note this formula will
normally allow the mold to be heated to molding
temperature in 1 to 2 hours) This does not include
the ejector housing in the weight for the mold but
it does include the “A” & “B” plates and the
support plates behind the “A” & “B” plates.
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 Locating a heater on the center line on the mold is
not recommended, because the center of the mold
is normally hot enough without any additional
heat. Typically, the cartridge heaters are located in
the support plates at a distance between heaters
of 65mm. There should be a minimum of one
thermocouple to control each half of the mold. In
larger molds, it is recommended to have more
than one thermocouple in each mold half. This will
result in better control and more uniform mold
temperatures. The thermocouples must be located
in the “A” & “B” plates, between two heaters if
possible & at a distance of 32mm to 38mm from
the closest cartridge heater. This distance is to be
measured from the edge of the thermal couple
hole to the edge of the cartridge heater hole.
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 The distance from the thermal couple to the heater
is important because a heater that is too close will
cause the thermocouple hole to the edge of the
cartridge heater hole. The distance from the
thermal couple to the heater is important because
a heater that is too close will cause the
thermocouple to turn off the heat before the mold
is at temperature. A heater that is too far away
from the thermal couple will result in a mold that
over heats and then gets too cool. Likewise, it is
not a good practice to position a thermal couple
so it senses the external surface temperature of
the mold. If possible, it should be located 38mm to
51mm inside the mold, since the temperature
taken there, is less susceptible to outside
influences and therefore
more
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AND stable.
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TRANSFER MOULD DESIGN
 Transfer Molding material is used when the molding
dimensions, shape or configuration, impose conditions which
cannot be met by compression molding. Two of the main
conditions imposed by the molded component which
necessitate the use of the transfer molding method are:
 In case where the wall thickness & dimensions of the molding is
critical and has to be held to a close tolerance.
 Where the shape of the molding necessitates the use of thin, weak
sections of metal or thin small diameter pins, which could be
damaged by the force created by the initial flow of material when
using the compression method.
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TRANSFER POT CALCULATIONS
 The dimensions of the pot, if it is round or square can be
calculated once the area is known:Total area of Pot Ap
= Total projected area of cavities, runners and sprue +
25 – 30% of total projected area.
Volume of Pot Vp
= Total volume of all the piece parts, the runners and the
sprue plus approximate volume of a small amount for a 0.5 to
1mm thick cull multiplied by Bulk factor of the compound.
Depth of Pot
=
Vp
Ap
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CLOSED POSITION
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RECOMMENDED DESIGN OF LOWER PLUNGER
FACTORS THAT INFLUENCE
THERMOSET MOLDING
Three important factors that must be
considered in thermo set molding are:
a) Temperature,
b) Pressure, and
c) Cure Time
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TEMPERATURE
 Thermosetting Plastics materials must be heated to
approximately 170 to 190C for optimum cure.
 Temperature for molding various materials can be
determined by getting the information from the Material
manufacturer.
 Higher temperature may degrade some of the physical
properties , electrical characteristics & mechanical
Properties of the material. Particularly in transfer
molding, may cause the material precure before the
cavity is completely filled.
 High temperatures may also cause blisters and burn
Marks on the finished articles.
 Low Processing Temperatures will not allow the material
to flow properly and result in incompletely cured parts
with poor consistency, thus reducing the productivity of
the cycle.
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 There is Normally an optimum temperature which
produces the best flow characteristics for the
particular material and cavity Design.
 The Optimum mold temperature not only varies with
the material being used, but also varies with the
geometry of the molded articles, and whether loose
powder or pre-heated preforms are used.
 Because plastics are generally good heat insulating
materials, preheating of the charge is often used to
shorten the moulding cycle time .
Pre-heat
temperature are between 70C and 130C, higher
temperature are possible when heat is more rapidly
transferred to the material.
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 Pre-heated material generally flows more rapidly during
the actual molding process and because the material
starts at an elevated temperature, the time of complete
the cure in the mold cavity is shortened, generally
yielding a more economical overall cycle.
 Another source of heat input to the plastic during the
molding process is from frictional or shear heat during
the closing of the mold. In the case of compression
molding, the material is forced in to flow by the closing
action of the mould. This flow may be at fairly high
localized velocities, which impart a certain amount of
frictional heat energy to the plastic.
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 In transfer molding, the frictional heat is even
more pronounced as the material is forced along
feed system and through relatively small gates
leading to the cavities. The amount of frictional
heat added to the material in transfer molding is
dependent on the speed of the plunger advance,
the size and configuration of runners and gates
and the surface finish of the mold. It must be
taken in to consideration when using relatively
heat-sensitive materials.
Mold temperatures
must be maintained with ± 3C for the best
results.
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PRESSURE
 Moulding with thermosetting plastics requires
greater pressure for two basic reasons:
a) To ensure that the plastic fills all of the cavity
and has relatively uniform density throughout.
(Pressure causes the cavity to fill and resists the
tendency of internal gases to form voids or gas
pockets, pressure must of course be sufficient to
overcome resistance of the plastic to flow).
b) To ensure better heat transfer to the material
(Higher pressure produces a higher density,
which
generally
means
faster
thermal
conductivity.
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 In compression Moulding a pressure of 210 kg/cm2 has been
found suitable for phenolic materials. Material manufacturers
recommend that 160 kg/cm2 is sufficient. But normally this
pressure is low and it is sufficient for easy flow materials and
a simple uncomplicated shallow moulded Parts. Moulding
Pressue should be optimised based on material type, type &
level of filler loading, Part Design, mould Design & moulding
conditions.
 For a medium flow material and where there is a number of
average sized cutouts( Openings), cores and pins in the
molding cavity where the material has to flow in to small
intricacies and orifices and to produce a good quality packed
and dense moulding, a pressure of 210 kg/cm2 or above is
necessary.
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 Also the deeper the moulding cavity, the more
Moulding pressure is required and a fairly simple rule
is to add approximately 20 kg/cm2 per cm of depth in
excess of 2.54 cm of cavity depth (maximum up to
30 cm depth) for the material without pre-heat. For
the
material
with
pre-heat,
the
pressure
approximately 70 kg/cm2 or above, is required and
for deeper moulding a pressure of 7 kg/cm2 per cm of
depth in excess of 2.54 cm is added.
 For molding urea and melamine material, pressures
of 2 times that needed for phenolic material are
necessary (i.e.) approximately 320 kg/cm2 per cm of
depth in excess of 2.54 cm is added for material
without pre-heat. CORPORATE TRAINING AND
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 For transfer moulding, generally pressure of 3 times
the magnitude of those required for compression
molding are required.
Depending upon the
configuration of the moulding, the design of mould
(eg. Whether direct sprue type or that employing a
runner system) and the flow properties of the grade
of material used. It is possible some times to mould
with a pressure of between 530 kg/cm2 – 560 kg/cm2
but in general, a pressure 630 kg/cm2 and above is
required for phenolic material, the pressure referred
to here being that applied to the powder material in
the transfer chamber ( for Material without pre-heat)
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CURE TIME
 The time required to harden thermosetting
materials to partial or complete polymerization is
called the cure-time. Many moulders produce
parts that are hard enough, blister free and
apparently cured, yet the polymerization of the
resin system is not complete and a post bake
cycle may be required to optimize properties.
 The curing time variables are as follows:
Material Temperature
Mold Temperature
Material Type
 Part Cross-Sectional Area
Moulding Pressure
Material Preheat & use of Preform
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MATERIAL TEMPERATURE
To obtain minimum cure time, the material
must be at the maximum Preheated
temperature when it is loaded into the
moulds.
Material may be pre-heated by using infrared lamps, radio frequency pre-heaters
and extrudates formed from screw feed
material in a heated barrel.
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MOULD TEMPERATURE
The designer must have good knowledge
of the recommended mould temperature
for each type of the Plastics material and
he must arrive at the maximum mould
temperature and cycle, that will produce
quality parts at the shortest overall cycle.
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CROSS-SECTIONAL AREA
The Cross-sectional Area or wall thickness will
determine the cure time required to produce
the part. A cross section upto 2 – 3 mm thick
will cure in few seconds, where as enhanced
wall sections may require few minutes. Parts
having thickness or cross-sectional areas in
excess of 9 – 13 mm are difficult to mould by
compression moulding. In order to establish
minimum cure cycles; transfer or injection
methods of moulding will be better.
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DEGREE OF CURE
Determining the degree of cure, regardless of
the moulding process used, are vitally important
in establishing the following important factors:
Maximum moulded density
Proper moulded part rigidity
The optimum point for moulded part ejection
Dimensional stability of the moulded parts.
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MOULD HEATING TECHNIQUES
Electrical Heating
Steam Heating
Oil Heating
Hot water
 GAS etc
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ELECTRICAL ENERGY REQUIREMENT TO HEAT
THE MOLD
 Empirical = 30-40 W/kg of mould
 By calculation – The heat required to raise the mold to operating
temperature is given by, QR = Q1 + Q2 + Q3 + Q4
 While the heat required to maintain the mold at operating temperature and to
provide heat for curing plastic material is given by , Q0 = Q1 + Q2 + Q3 + Q5
Where,
Q1= Conduction losses through asbestos insulation from mold to
platens (Btu/h or cal/h – (a)
Q2 = radiation losses from mold faces (Btu/h or cal/h – (b)
Q3 = convection losses from mold faces (Btu/h or cal/h) – (c)
Q4 = heat required to raise temperature of metal to operating
temperature (Btu or cal) – (d)
Q5 = heat required for heating plastic material (Btu/h or cal/h) – (e)
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Q1 = kA1T1
L
Where k = thermal conductivity of
asbestos/ hylem insulation (tps or cgs units)
A1= total area of mold top and bottom
faces in contact insulation (ft2 or cm2)
L = total thickness of top and bottom
asbestos insulation (ft2 or cm2)
T1 = temperature difference between
mould and press (deg F or deg C)
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Q2 = 1.38 X 10-9 (T2 + 460)4 X A2
Where 1.38 x 10-9 (T2 + 460)4 is the modified
Stefan’s constant for a rough finished tool
surface
= temperature of mould (deg F or deg C)
= area of exposed tool faces (ft2 or cm2)
 During initial heating up, the tool is normally
closed and hence normally the radiation losses
are from the vertical faces. In operation,
however, the horizontal faces are exposed for a
long time and hence an additional allowance
must be made when determining the heat
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requirements duringCORPORATE
moulding.
PLANNING
 The heat lost by convention from the vertical
faces is
Q3 = (0.7 + T3) T3 A2
375
_
Where T3 = temperature difference between
tool and surrounding air (deg F or deg C)
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 The heat lost by convention from horizontal faces lying
upwards is
Q3’ = (0.7 + T3) T3 x 1.1 x A3
375
 The heat lost by convention from horizontal faces lying
downwards is
Q3” = (0.7 + T3) T3 x A4
375 x 2
Where A3 = area of mould face lying upwards
(ft2 or cm2); and
A4 = Area of mould face lying downwards
(ft2 or cm2)
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The initial heat required to raise the tool from
room temperature to operating temperature,
considering the heat losses listed, is
Q4 = m1 X Cp1 x T4
Where m1 = weight of mould (lb or kg)
Cp1 = specific heat capacity of mould steel
T4 = temperature rise from room
temperature to operating temperature
(deg F or deg C)
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Heat required to cure the moulding material is
given by
Q5 = m2 X Cp2 x T5
Where m2 = weight of mould (lb/h or kg/h)
Cp2 = specific heat capacity of moulding
material
T5 = temperature rise required from
room (or pre-heat temperature) to
moulding temperature
(deg F or deg C)
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Dimensions of Steam and Hot Water Heating
The determination of the heat balance of
steam and hot water heating, i.e., the
exact determination of the length and dia
of the pipe required for supplying the given
heat & heat losses, involves as extremely
complex calculation process.
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 The clearance between the force and cavity mold halves on
the vertical wall as is shown in the sketch should be 0.001”
to 0.002” per side except for mold for BMC which should
be 0.002” to 0.003”. With this tight of a mold, it will be
necessary to add vents to this wall in order for the mold to
close. These vents should be located near the last places
to fill and should start out being 0.005” deep and extending
up the entire length of the wall. When molding PLENCO
BMC materials, it is very important to maintain this
clearance between the mold halves. If this clearance
becomes to large, it will not be possible to hold the internal
cavity pressures causing scrap rates to increase and part
appearance to suffer.
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
General Mold Design Check list
 All mold components contacted by the molding
compound-runners, gates, cavities, land areasshould be made of through-hardened tool steels,
hardened to 65 to 68 on the Rock-well C scale,
highly polished, and hard chrome plated.
 Because most thermoset compounds are slightly
soft at the time of ejection from cavities, ejector
pins should have an adequate correctional area to
minimize the possibility of distorting or puncturing
the molded plastic at this point in the cycle.
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 In automatic molds, it is vital to ensure, with part design,
undercuts, or hold-down pins, that the molded parts,
during mold opening, consistently remain in the desired
half of the mold, so that when the parts and the runner
system are ejected, the comb or extractor will always
"find" them and effect positive removal.
 Flash removal from the mold, each cycle is critical for
successful automatic moulding (the “flash-free molds”
are myths). Every effort must be made to have the flash
ejected with the molded part. An air blast, directed
appropriately to cavities and land areas each molding
cycle when the mold or press to further ensure the
absence of flash each cycle.
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 Should flash being to accumulate in or on
the mold, the mold should be cleaned,
polished, and/or repaired.
 Molds should be of uniform temperature in
the cavities, and should have adequate
heating capacity to ensure maintenance of
the desired temperature despite continual
heat extraction by the relatively cooler
molding compound each cycle.
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 Temperature sensors and heating cartridges
must be judiciously placed to provide this
uniformity of temperature. Insulating blankets
may prove helpful to minimize mold heat losses
and variations due to local air currents around
molds and presses.
 to minimize local temperature variations in large
molds, heating cartridges often are grouped in
zones, with each zone having is own
temperature controller and sensor. Sensors
should be positioned with ¼ inch of heating
cartridge to prevent significant temperature over
swings.
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
It also is prudent to provide for a “mold over temp”
sensor, which will cut off power to the heating
cartridges whenever it senses a mold temperature more
than a few degree over the desired mold temperature.

Excessive mold temperature not only will results in
reject parts, but also may anneal the mold steels and
warp critical mold components.

An adequate moulding press should be used
considering the required tonnage capacity of mould.
Over tonnage application may damage the mould.

For a transfer mould, the pot dimension must be
adequate to the required
volume of loose power for
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THANK YOU
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