Pneumatic Can
Crusher
28/05/21
HND Graded Unit
Liam Saunders
West Lothian College
Contents
1.0 Introduction ............................................................................................................... 8
2.0 Project Brief ............................................................................................................... 9
3.0 Project Specifications .............................................................................................. 10
4.0 Project Objectives ................................................................................................... 11
4.0 Literature Review .................................................................................................... 12
4.1 Existing Products ................................................................................................. 12
4.2 Material Selection ................................................................................................ 15
4.2.1 Casing ........................................................................................................... 16
4.2.2 Pneumatic Tubing Material............................................................................ 32
4.2.3 Piston Rod..................................................................................................... 34
4.2.4 Piston Rod Coating ....................................................................................... 36
4.2.5 Piston and Ram............................................................................................. 38
4.2.6 Barrel ............................................................................................................ 40
4.3 Double Action or Spring Return ........................................................................... 42
4.3.1 Spring Return ................................................................................................ 42
4.3.2 Double Acting ................................................................................................ 42
4.3.3 Comparison ................................................................................................... 43
4.4 Safety Feature ..................................................................................................... 45
4.4.1 Two Hand Control Panel ............................................................................... 45
4.4.2 Washing Machine Door Lock ........................................................................ 45
4.4.3 Microwave Door Switch ................................................................................. 46
4.4.4 Coded Magnetic Interlock Switch .................................................................. 47
4.4.5 Comparison ................................................................................................... 48
5.0 Methodology ............................................................................................................ 49
2
5.1 Casing ................................................................................................................. 49
5.2 Piston Rod ........................................................................................................... 50
5.3 Piston................................................................................................................... 51
5.4 Ram ..................................................................................................................... 52
5.5 Barrel ................................................................................................................... 52
5.6 End Caps ............................................................................................................. 53
5.7 Assembly ............................................................................................................. 53
6.0 Testing and Results................................................................................................. 54
6.1 Experimental Findings ......................................................................................... 54
6.1.1 Materials and Equipment .............................................................................. 54
6.1.2 Experimental Procedure ................................................................................ 54
6.1.3 Results .......................................................................................................... 55
6.2 Equations ............................................................................................................. 55
6.2.1 Force Required to Crush a Can .................................................................... 55
6.3 Sizing of the Cylinder ........................................................................................... 58
6.3.1 Theoretical .................................................................................................... 55
6.3.2 Actual ............................................................................................................ 58
6.3.3 Comparison ................................................................................................... 58
7.0 Discussion ............................................................................................................... 59
7.1 Experiment .......................................................................................................... 59
7.2 Fatigue Strength .................................................................................................. 60
8.0 Novel Feature .......................................................................................................... 61
9.0 Conclusion .............................................................................................................. 62
10.0 Appendices ........................................................................................................... 63
10.1 Appendix 1 Gantt Chart 1 .................................................................................. 63
3
10.2 Appendix 2 Gantt Chart 2 .................................................................................. 63
10.3 Appendix 3 Gantt Chart 3 .................................................................................. 63
11.0 Bibliography .......................................................................................................... 64
4
Table of Figures
Figure 1- Frightprops Can Crusher ............................................................................... 12
Figure 2 - DIY Can Crusher Barrel ................................................................................ 13
Figure 3- DIY Can Crusher............................................................................................ 13
Figure 4 - Manual Can Crusher ..................................................................................... 13
Figure 5 - 500ml Can Next to Crusher........................................................................... 14
Figure 6 -330ml Can in Crusher .................................................................................... 14
Figure 7 - Young's Modulus-Density Graph .................................................................. 15
Figure 8 - Relevant Materials ........................................................................................ 16
Figure 9 - Wood Stains.................................................................................................. 19
Figure 10 - Silicon Carbide Products ............................................................................. 23
Figure 11 - Powder Coatings ......................................................................................... 26
Figure 12 - Washing Machine Door Lock ...................................................................... 46
Figure 13 - Microwave Door Switch............................................................................... 46
Figure 14 - Coded Magnetic Interlock Switch ................................................................ 47
Figure 15-Casing ........................................................................................................... 49
Figure 16-Piston Rod .................................................................................................... 50
Figure 17-Piston ............................................................................................................ 51
Figure 18-Ram .............................................................................................................. 52
Figure 19-Barrel ............................................................................................................ 52
Figure 20-Assembled Pneumatic Can Crusher ............................................................. 53
Figure 21-Exploded View .............................................................................................. 53
Figure 22-NASA Equation ............................................................................................. 57
5
Table of Tables
Table 1-Wood Advantages and Disadvantages ............................................................ 19
Table 2-Ceramics Advantages and Disadvantages ...................................................... 22
Table 3-Metal/Alloy Advantages and DisadvantagesОшибка!
Закладка
не
определена.
Table 4-Composite Advantages and Disadvantages .................................................... 28
Table 5-Polymers Advantages and Disadvantages ....................................................... 30
Table 6-Weighted Decision Matrix for Casing ............................................................... 31
Table 7-PU Advantages and Disadvantages................................................................. 32
Table 8-PVC Advantages and Disadvantages .............................................................. 33
Table 9-PE Advantages and Disadvantages ................................................................. 33
Table 10- Piston Rod Material Properties...................................................................... 35
Table 11-Weighted Decision Matrix for Piston Rod ....................................................... 35
Table 12- Weighted Decision Matrix for Piston Rod Coating......................................... 37
Table 13-Piston and Ram Material Properties ............................................................... 39
Table 14-Weighted Decision Matrix for Piston and Ram ............................................... 39
Table 15-Barrel Material Properties............................................................................... 41
Table 16-Weighted Decision Matrix for Barrel ............................................................... 41
Table 17-Spring Return Advantages and Disadvantages.............................................. 43
Table 18-Double Acting Advantages and Disadvantages ............................................. 43
Table 19-Weighted Decision Matrix for Safety Feature ................................................. 48
Table 20-Experiment Results ........................................................................................ 55
6
Table of Equations
Equation 1-Average Radius .......................................................................................... 56
Equation 2-Knockdown Factor ...................................................................................... 56
Equation 3-Classical Buckling Knockdown Factor ........................................................ 56
Equation 4-Axial Stress ................................................................................................. 57
Equation 5-Area ............................................................................................................ 57
Equation 6-Force ........................................................................................................... 57
Equation 7-Area ............................................................................................................ 55
Equation 8-Diameter ..................................................................................................... 55
7
1.0 Introduction
Improper disposal of waste is one of the largest negative impacts on the Earth’s
environment. This problem can be improved by recycling. Recycling reduces the need for
more raw materials and the pollution cause by landfills and litter. It takes 20X the energy
to make one new aluminium can rather than one recycled can. West Lothian College has
requested a machine that can be used in the food environment to assist with the recycling
of the drinks cans used by the customers. Many countries already incentivise the
population to recycle by offering money back for packaging that is recyclable.
First a project brief was made to provide an overview of the project and initiate the
foundation. Afterwards the projects specifications were determined to define the
constraints, expected features and budget. The project objectives convey the expected
order of the actions that will take course in the designing and manufacturing of the project.
Existing products are researched to develop an understanding of what key features are
incorporated in other designs. Materials are selected through a combination of weighted
decision matrices and pros & cons lists. To decide whether it is appropriate to design the
product as a single acting cylinder or a double acting cylinder another advantages &
disadvantages table is made. The comparison between safety features uses a weighted
decision matrix. The methodology describes the processes used to fabricate the project.
The testing and results section outlines the experiment conducted and compared the
actual results to the theoretical results obtained via equations. The discussion covers
improvements to the process of this project. The novel feature is a section to suggest
improvements to the design. The project will be concluded and it will be known if the
project was successful at completing the task. Gantt charts were made to assist the
timekeeping of the project see appendices 1,2&3.
8
2.0 Project Brief
Project name: Pneumatic Can Crusher.
Project Director: Liam Saunders
Project Supervisors: Tomasz Sliwinski and Gavin Culliven.
Customer: West Lothian College
The requirements of this project as requested by the customer, West Lothian College, is
to design and manufacture a product that will crumple a drinks can in order to reduce their
size to 30mm and save space in their recycling bin. This will assist in the Colleges’ goal
of becoming more environmentally friendly. Using this product in the cafeteria offers more
room in the recycling bin as well as separating the aluminium in advance for recycling.
The College will provide an air compressor that supplies air at 2 Bar. Existing products
already exist however the customer has requested additional features including a safety
mechanism to prevent accidental injury as well as a method to dispense the cans
automatically into the bin. An investigation on material properties will be conducted to
determine the best suited materials for each component including the piston, casing,
barrel, tubing, piston rod and coating. With this research an educated decision will be
made on which materials will be used for manufacturing.
Detailed research will be carried out on pneumatic systems and what design features
that could be implemented to improve the efficiency of the product such as the materials
used and proper dimensioning. This information will be utilized to decide suitable
features.
Existing products will also be researched to help pinpoint aspects of other designs that
could be improved upon e.g. aesthetics, ease of use, cost effectiveness and safety.
To assist the management of the project a Gantt chart will be completed see
appendices 1,2&3.
The project is not to exceed the given budget of £100.
The deadline of the project is the 28th of May 2021.
9
3.0 Project Specifications
This project requires specifications to ensure that the end-product is in line with the brief
provided by the customer.

The product must crush a standard sized drink can to 20mm in height.

It must exert 570N of force to be able to crush the can.

The product must remain within the budget of £100.

The product must be aesthetically pleasing.

The crusher must be safe to use in a food environment.

It must be safe to use.

The pneumatic cylinder must be sized in accordance with IS0 15552 (This
document establishes the appropriate dimensions for fluid power cylinders with
interchangeable mountings and accessories up to 10 Bar)

Must conform to ISO 4393 (This standard details the correct series of piston
strokes for pneumatic and hydraulic cylinders)

Must conform to ISO 3320 (This standard establishes ratios of bores to piston rods)

The project must be compatible with a 2 Bar compressor.

Must not require training to use.

BS EN 1088 must be adhered to (This standard demonstrates how to select
interlocks associated with machine guards to ensure equipment safety.)
10
4.0 Project Objectives
To ensure that the project stays on schedule, keeps within the budget stated and is
completed successfully crucial objectives must be accomplished:

Weekly meetings with project supervisors must be held.

Thorough research on the materials, function of the cylinder and the safety feature.

Complete the necessary experiments.

Complete the necessary equations.

Compare both theoretical and experimental findings.

Manufacture the final product.
Following the meeting with the supervisors a Gantt chart can be made. A Gantt chart
allows for keeping track of the progress and how it compares to the schedule. Unexpected
circumstances can throw the project off track which is why the Gantt chart is so important.
It is important that throughout the project the Gantt chart is regularly reviewed and kept
up to date to prevent the project from failing.
11
4.0 Literature Review
4.1 Existing Products
In this section existing designs of similar products to avoid flaws when designing this
project as well as attempt to develop improvements on features.
Figure 1- Frightprops Can Crusher
This design uniquely employs the air being exhausted to propel the crushed can
outwards. The components consist of high-quality steel. The lowest cost is $185.19 with
two optional additional costs, a controller at $49.99 and a bracket at $39.99 meaning that
the total cost would come to $275.17 or £197.81. This model accommodates up to a can
of 16oz or approximately 455ml. This product may allow incidental injury as the face is
uncovered. This product works using a double acting cylinder. Reviews on this product
12
detail that it is very durable, it is good value for money and gives consistent results
throughout continuous use.
Figure 3- DIY Can Crusher
Figure 2 - DIY Can Crusher Barrel
This DIY version uses a single action spring return cylinder. Before the cylinder was
painted the plastic used is prominently marked “NOT FOR PRESSURE”. The product is
Figure 4 - Manual Can Crusher
aesthetically appealing as it is painted in vibrant colours. This design does not contain a
13
feature that automatically dispenses the crushed cans, and it does not have a cover over
the front face. This design has the ability to crush any size of drink can.
This has an extremely simple design. It is lightweight and compact, allowing it to be
portable. The material is a thin flimsy metal making it prone to deformation and buckling
after regular use. The product has an open face which means that sometimes it allows
for cans to propelled away meaning the it cannot crush the can to a satisfactory degree
before the can it pushed out of place, which is shown in the video linked. It is also not
able to crush 500ml size cans as they do not fit inside. Online reviews show that it is not
very durable and after regular use the components began to warp. It is very inexpensive
at £8.50 which includes wall mounting screws. The product being designed will be
pneumatic powered and automatic however this is manual.
Figure 5 - 500ml Can Next to Crusher
Figure 6 -330ml Can in Crusher
14
4.2 Material Selection
Material selection is paramount to the products capability, so in order to ensure the correct
choice of material each of the relating properties will be scored and compared in a
weighted decision matrix. The product must be manufactured from durable materials to
increase longevity. The tensile strength of the materials must be considered because
tensile forces will be acting upon parts of the pneumatic cylinder. Repeated loading will
take place when the product is in use, this can cause localised damage therefore fatigue
resistance of the material will be researched. As the project is intended for crushing a
metal drink can the material used for the cylinder head must be harder than this metal.
The material must have good machinability. The finish of the material will be factored into
the research as they can add to the aesthetic value as well as enhance the materials
durability, abrasion resistance, chemical resistance as well as other properties. The finish
can protect the material from things such as moisture and the mould that comes with it.
The project has a budget of £100 therefore the cost effectiveness will be factored.
Figure 7 - Young's Modulus-Density Graph
15
4.2.1 Casing
The ideal material for the casing will be lightweight whilst also strong. The machinability,
durability, availability and cost will all also be taken into account. The casing has the most
significant impact in terms of aesthetics, for this reason the finish of the materials will also
be taken into consideration. The bottom of the casing will be the part that the can is
crushed on so it will be under cyclic loading and so the material must possess good
fatigue resistance. As shown below, the top left of the chart contains the materials with
the most suitable properties for this part. Various wood and wood products, polymers,
ceramics, composites, metals and alloys will be studied and a conclusion as to the
topmost material and finish of said material will be made. The back will have a gap of
30mm to allow the can to be dispensed automatically as well as a hole on the bottom to
allow for the air to escape.
Figure 8 - Relevant Materials
16
Wood and wood products- It is a common misconception that the difference between
hardwoods and softwoods is the hardness of the wood however this is not the case. The
type of tree that a wood is harvested from determines whether it is a hardwood or a
softwood. Hardwoods come from deciduous trees whereas softwoods come from
coniferous (evergreen) trees. Typically, hardwoods have a higher hardness but not
always. There are also manufactured woods, these are composite woods made by
binding particles, fibres or veneers together using special adhesives. Hardwoods are
typically used for furniture, decking and flooring that are of a higher quality as well as
being used or construction and the manufacturing of boats. Softwoods are popular as
they are lower in price than hardwoods and can be used for lower quality furniture,
decking and flooring as well as paper. Manufactured woods are mostly used for interior
furniture and panelling due to their easy machinability. Wood is anisotropic, meaning it
has different properties in different directions. It can be easy to snap wood in half however
the same piece of wood will perform extremely well in tension and compression. If wood
is properly preserved and cared for it can be very durable. Wood can be sourced very
sustainably as it can be farmed. The different woods that will be considered are MDF,
Scots pine, European oak, Zebrawood, Beech. To determine which wood is superior for
this use a table that lists the advantages and disadvantages is made. (Woodford, 2010)
17
Type of Wood
MDF
Scots Pine
European Oak
Advantages
 MDF is cheap.
 It saves trees as it is
made from recycled
wood.
 Excellent
machinability
 Incredible
dimensional stability
 It takes well to paint.
 It is lightweight.
 Cheaper than
hardwoods.
 Has fair dimensional
stability.
 It is easy to work
with.





Zebrawood




Beech



Disadvantages
 Weaker than natural
woods.
 It has a poor weather
resistance.
 It is heavier.
 Cannot support
much weight.





It is very durable.
It has a great
longevity.
It has good weather
resistance.
It takes well to stain
and polish.
It is also highly
resistant to wear and
tear.
It has an
aesthetically
pleasing grain
It is moderately
stable
It is very durable.
It is a good
hardness.

It is hard.
It is tough.
Strong,








Susceptible to
scratches
and dents.
It has a low stiffness.
It is not impact
resistance.
It needs to be
carefully treated with
high strength
preservatives to
prevent rot.
It is a very heavy
wood.
It is very costly.
It is difficult to work
with.
It splits easily.
It contains tannic
acid which corrodes
certain metals.
It is a very expensive
wood as it is exotic.
It can be difficult to
plane due to the
grain.
It is fairly heavy.
It possesses very
poor weather
resistance which
18


It polishes well.
Resistant to wear.


directly impacts the
durability.
It can be heavy
because it is so
dense.
May be difficult to
work.
Table 1-Wood Advantages and Disadvantages
From this table it can be concluded that the best wood for this product is beech wood as
it has the best ratio of advantages to disadvantages being 5:3. Varnishes and lacquers,
oil, French polish, stains, paint and sanding sealer are all finishes that are applied to
wood. The most appropriate finish for beech is a gel stain followed by polyurethane.
Using a gel stain on beech wood prevents the blotching that will occur from other types
of stain. Polyurethane will enhance the durability. Polyurethane is a very easy finish to
apply however it takes a long time to dry.
Figure 9 - Wood Stains
19
Ceramics and porous ceramics- Ceramic material is an inorganic non-metallic solid
that has been shaped and then hardened by firing in order to heat it to a high temperature.
Typically, ceramics are hard, corrosion-resistant and brittle. The word ‘ceramic' is of
Greek origin and can be traced back to the Greek word for ‘pottery’. Common clay-based
products used at home, sculptures and construction materials are all widely known and
fall under the category of the traditional ceramics- pottery. It is one of the oldest materials
that people have employed. In a southern Chinese cave fragments of clay pottery were
discovered and have been carbon dated to around 16,000 BCE. There are three main
categories of pottery: earthenware, stoneware and porcelain.
To make earthenware, one of the oldest materials to be used in pottery, the clay is heated
to a temperature anywhere from around 1000°C to 1150°C. This is done using a large
fire oven named a ‘kiln’. This makes the product coarse and slightly porous which is
undesirable. This is resolved by covering the pottery with a finely ground glass powder
and suspended in a glaze. Afterwards, to achieve the end product, it is fired again.
To create stoneware first clay put into a kiln at a temperature about 1,200°C until vitrified.
Vitrified means it has been converted to a glasslike substance. Glaze can be applied for
decoration purposes although it is not required as it is non-porous. These processes
make the pottery sturdy, chip-resistant and durable that is suitable for uses especially in
the kitchen.
Porcelain is very hard and translucent white. Originating in 1600BC China, porcelain
became a popular good for Arabian traders. When used for plates, cups, vases and art it
is often known as ‘fine china’ since it is related to China. Porcelain is made by grinding
up small amounts of glass, granite and feldspar minerals with white kaolin clay. In order
for it to be able to be worked and kneaded into shape water must be added. This is fired
in a kiln to between 1,200–1,450°C. Before the second firing it will be decorated with
glaze.
Nowadays ceramics can mean many different things including advanced ceramics, glass
as well as some cement systems. Advanced ceramics have many applications in various
areas such as the automotive industry, aerospace, electronics and medical technology.
In general, advanced ceramics are not clay based however they are based on oxides,
20
non-oxides
or
a
mix
of
the
two:
Typical
oxides
used
are alumina (Al2O3)
and zirconia (ZrO2). At the start of production, the materials will be blended as fine
powders. Once it has been shaped it will be fired at a high temperature between 16001800°C to allow the ceramic composite grains to combine this process, named sintering,
will create a product that is hard, tough, durable and corrosion resistant. (Pūtaiao, 2010)
21
Type of Ceramic
Earthenware
Silicon Carbide
Advantages
 Has a high
hardness.
 Cost effective.




Aluminium Nitride




Porcelain





Stoneware




Low density.
High strength.
Excellent chemical
resistance.
Excellent thermal
shock resistance.
High hardness.
Wear resistant.
Extreme thermal
shock resistance.
Excellent electrical
insulation
properties.
High hardness.
Chemical resistant.
Has an upscale
look.
Non-porous.
Durable when
compared to other
clay based
ceramics.
A little more durable
than earthenware.
Non-porous.
Cheap.
Chip resistant.
Disadvantages
 Very brittle.
 Heavy.
 Hard to control the
dimensional tolerance.
 Weak.
 Porous.
 Prone to chipping.
 Very expensive.
 Carbon footprint and
environmental impact.
 Energy intensive as it
needs to be sintered.










Very expensive.
Carbon footprint and
environmental impact.
Energy intensive as it
needs to be sintered.
Dimensional tolerances
are difficult to control.
Very weak in tension.
Possesses
poor shock resistance.
Easily cracked.
It is sensitive to sudden
changes of
temperature.
Very brittle.
Does not perform well
in tension.
Table 2-Ceramics Advantages and Disadvantages
22
From the table above, it can be ascertained that silicon carbide is the most advantageous
material to use with 6 advantages and 3 disadvantages. This material is produced using
CNC machining, gas pressured sintering and is then finished by grinding or lapping.
Figure 10 - Silicon Carbide Products
23
Metals and Alloys- Metals have a vast range of useful properties. They are
characteristically shiny, and most are malleable, ductile, dense, very good electrical
conductors and have high melting points. It is possible for the crystals of a metal to be
visible on the surface. These indicate the arrangement of positive metal ions in the
underlying structure that is not visible.
The positive ions in a metal are packed closely together and the gaps between them are
minimal. When metal atoms pack together to form crystal, they can be:hexagonal close
packed, face-centred cubic or body-centred cubic. Once a metal that is molten has cooled
down the atoms will form into a crystal lattice. An individual crystal in the body is called
a grain. Imperfections in the grains will distort the crystalline structure and impact the
properties.
Alloys are a homogenous mixture or solution of metallic elements. Alloys are made to
improve the properties of the metal. This could be to increase the strength or even
decrease the cost whilst retaining the key properties. Alloys are more commonly used
than pure metals. Solder is a mixture of tin and lead, these metals are mixed to create an
alloy with a low melting point that is also hard. Steel is a very ubiquitous alloy composed
mostly of iron as well as carbon. The metals that are being looked into are stainless steel,
brass, aluminium, titanium and low carbon steel. (Pūtaiao, 2009)
24
Metal/Alloy
Stainless Steel
Brass
Advantages
 Strength.
 Aesthetics.
 Resistant
corrosion.
 Durable.





Aluminium



Titanium






Low Carbon Steel






Disadvantages
 Expensive.
 Hard to machine.
to
 High cost of finishing
and polishing.
 Can have difficulty
joining.
Easily machined.
 A lot of maintenance
is required.
Excellent
corrosive
resistance.
 Not
weather
resistant.
Finishes very well.
 Can
be
easily
Good
joining
scratched
and
characteristics.
dented.
Aesthetically
pleasing.
Lightweight.
The most abundant
metal on Earth.
Fairly
corrosion
resistant.
Durable.
Highest
strengthweight ratio out of any
metal.
Corrosion resistant.
Stiff.
Weather resistant.
Recyclable.



Is a soft metal.
Weak.
Expensive.

Machined easily.
Greatly affordable.
Lightweight
in
comparison to other
steels.
Outstanding
toughness.
Easily weldable.
Can be heat treated to
improve
the
properties.



Extremely expensive
as it is very rare.
Hard to machine, it is
very unforgiving if
machined in the
wrong way.
Creep resistance is
unstable.
Relatively soft.
Relatively weak.
Corrodes easily if
untreated.


Table 3-Metal/Alloy Advantages and Disadvantages
25
From this table low carbon steel otherwise known as ‘mild steel’ is the favourable metal
with 6 advantages to 3 disadvantages. Before applying a finish to the steel any welds
must be grinded down and then the surface must be made smooth using abrasive paper.
Applying a powder coating will provide an attractive finish that is also very durable and
weather resistant.
Figure 11 - Powder Coatings
26
Composites- These are materials made up of two or more materials. This is done so that
if a material is lacking in a certain property, it can be greatly improved. A good example
of this is reinforced concrete. Concrete is a cheap material that is extremely strong in
compression however it is very weak in tension whereas steel is much more expensive
but possesses a very high tensile strength. Steel rebar is used in concrete to make it
perfect for constructing buildings. There are two main classes of composite materials:
thermoset and thermoplastics. Thermoplastic composites can be reheated and reworked
after they have been formed unlike thermoset composites. Glass fibres, aramid fibres or
carbon fibres can be woven into tape or cloth and combined with thermoset polymer resin
resulting in a structure that is very hard, strong and lightweight composite materials. They
are generally made up of a reinforcement material and a matrix material. The matrix is
usually a viscous material that hardens to gives the component the net shape and defines
the surface quality, the fibres or fragments are embedded in the matrix to be protected
from being damaged. Fibreglass is a composite that was created in the 1930’s. Fibreglass
has fine glass fibres as reinforcement in a plastic or resin matrix. The matrix provides
rigidity and the glass fibres increase the strength. Fibreglass has had many uses such as
surfboards, car exteriors and boats. Advanced ceramics can be employed as matrices for
highly specialised purposes. An example of this is the use of carbon where the composite
has to endure friction and wear such as disc brake pads. The disc brake pads are made
from using silica as a matrix embedded with a framework of carbon fibres for the
reinforcement. This develops a material that is both resistant to heat and has extreme
wear resistance. The different composite materials to chose from will be carbon fibre
reinforced polymer (CFRP), fibreglass, glass fibre reinforced concrete (GFRC), tungsten
carbide and steel reinforced concrete. (Pūtaiao, 2013) (Moose, 2016)
27
Composite
CFRP
Fibreglass
Tungsten Carbide
GRC
Steel reinforced
concrete
Advantages
 Great strength to
weight ratio.
 Exceptional durability.
 Resistant to corrosion.
 Stress resistant.
 Incredibly high rigidity.
 Unique aesthetics.
 It can last a long time.
 It can have a coloured
coating.
 Good strength to
weight ratio.
 Easy to work with.









Extremely hard.
High corrosion
resistance.
Resistant to abrasion.
Low in cost.
Weather proof.
Very durable.
High compressive
strength and fair tensile
strength.
Low in cost.
Easy to maintain.
Disadvantages
 Fragile.
 Costly.
 Hard to repair.











Needs gel coating
reapplied every five
years.
Can cause glass fibres
to become airborne
which can result in
health problems.
Can be costly.
Very heavy due to
tungsten’s’ density.
It is a brittle material.
Can lose strength over
time.
Not aesthetic.
Can be hard to work
with.
Tensile strength is ten
times lower than
compressive.
Cannot be used for thin.
Not environmentally
friendly.
Table 4-Composite Advantages and Disadvantages
28
From this table it is found that carbon fibre has the best advantage to disadvantage ratio
out of the composite materials. Carbon fibre is made by combining individual strands of
pure carbon into a large sheet (either woven or unidirectional) which is then infused with
epoxy resin. This forms a composite material known as prepreg carbon. The sheet can
be cut to size by hand or using a CNC profiler. The individual pieces will be assembled
around pre-formers and bladders. The part is then moulded and debulked to create an
even distribution of resin as well as eliminate creases and air gaps. The component is
heated up in order to cure the resin which removes any moisture left. The pre-formers
and bladders are removed to get ready for surface treatment. The component is then
cleaned, sanded, varnished and then polished. Afterwards it can also be painted if
desired. Carbon fibre is unlike any of the other materials from the other categories in the
sense of fatigue. Carbon fibre is anisotropic meaning that because of its multidirectional
fibres the materials properties are very sensitive to the orientation of the reinforcement.
(Bridgewood, 2020)
Polymers- The majority of polymers are a product of crude oil. Each polymer molecule
is made up of lots of smaller units called monomers. Bonds within the polymers are all
covalent bonds which are really strong, meaning they require very high temperatures to
break. However, to be able to melt the polymer it is the intermolecular forces between
separate polymer molecules that need to be broken. These are much weaker although
they have a high surface which results in the temperature necessary still needing to be
high. This is the reason why polymers are generally solids at room temperature. Polymers
can be found in applications such as parts for vehicles, clothing, 3D printing, sports
equipment, circuit boards and more. Polymers can possess many useful properties such
as high strength to weight ratios, toughness, corrosion resistant, cost effective and the
choice of colours. ABS, acrylic, PVC, polypropylene and HDPE will all be investigated.
29
Type of polymer
ABS
Acrylic
PVC
Polypropylene
Advantages
 Sturdy.
 Low production
costs.
 Lightweight.
 Versatile range of
textures and
colours.
 High tensile
strength.
 Resistant to
scratching.
 Wide range of
colours.
 UV resistant.
 Cost effective.
 Good strength to
weight ratio.
 Abrasion resistant.
 Good strength to
weight ratio.
 Durable.





HDPE



Resistant to
corrosion.
High impact
resistance.
Relatively
inexpensive.
Easily repaired.
Good impact
strength.
Impact resistant.
Excellent chemical
resistance.
Low cost.
Disadvantages
 Poor fatigue
resistance.
 Poor UV resistance.
 Poor wearing
resistance.













Easily scratched.
Subject to cracking
from stress.
Low impact
resistance.
Easily cracked.
Less cost effective
than other polymers.
Not UV resistant.
Negative
environmental
impact.
Affected by UV
degradation.
Does not take well to
paint.
Susceptible to
oxidisation.
Susceptible to stress
cracking.
Has a low stiffness.
High mould
shrinkage and poor
UV resistance.
Table 5-Polymers Advantages and Disadvantages
30
The polymer ‘Acrylonitrile Butadiene Styrene’ shortened to ‘ABS’ has six advantages to
three disadvantages therefore it will be selected and taken forward. It is used for many
purposes such as Lego, computer keyboards, pipes and 3D printing. ABS can be cut to
shape then filed down smooth. It can be heat formed at this stage if required. Afterwards,
the plastic will be polished and bonded using a solvent cement.
Table 6-Weighted Decision Matrix for Casing
The most suitable materials from all 5 groups were scored using a weighted decision
matrix. As shown above the materials were scored in eight different categories. Mild steel
scored the highest out of all the materials therefore it will be taken forward and used to
manufacture the casing of the can crusher. A clear acrylic lid will be attached with hinges.
31
4.2.2 Pneumatic Tubing Material
The material for pneumatic tubing must have the desirable properties of kink resistance
and flexibility. The aesthetics of the tubing are also important therefore it would be
valuable if the tubing is available in an array of colours. The pneumatic tubing should be
compatible with push to connect fittings. It should be easy to work with whilst also being
cost effective. Ideally the tubing will be durable.
Polyurethane (PU)- Dr Otto Bayer discovered the basic polyurethane chemistry in the
year 1937 however this material was not yet used until the early years of WWII as a
cheaper alternative to rubber. Polyurethane has a combination of the best aspects of both
rubber and plastic which is why manufacturers use it for many purposes such as shoe
soles, foam insulation and mattress foam. There are two basic formulations for this
plastic, ester and ether. Water attacks ester- based urethane reducing its physical
properties significantly. Ether based urethane is more resistant to fungus growth.
(Anon, n.d.)
Advantages
High tensile and elongation values.
abrasion and wear resistance.
Disadvantages
Can be tacky which can result in tangling.
Softness of wall is not compatible with
push to connect fittings.
good chemical resistance.
High load bearing capacity meaning they
will not damage easily unless under a
particularly heavy load and will return to
its original shape.
Kink resistant.
Table 7-PU Advantages and Disadvantages
32
Polyvinyl Chloride (PVC)- PVC was prepared by the French chemist Henri Victor
Regnault in 1835 and then by the German chemist Eugen Baumann in 1872, but it was
not patented until 1912, when another German chemist, Friedrich Heinrich August Klatte,
used sunlight to initiate the polymerization of vinyl chloride (Britannica 2020). Its extreme
rigidity restricted it’s commercial uses until 1926 when a more flexible plasticized PVC
was discovered. (Kauffman, 2016)
Advantages
Corrosion resistant.
Abrasion and wear resistant.
Excellent flow characteristics.
Kink resistant.
Disadvantages
It does not have good weather resistance
and can become less pliable if exposed to
weather conditions.
Can be more costly.
Table 8-PVC Advantages and Disadvantages
Polyethylene (PE)- In 1933 while Imperial Chemical Industries Ltd. were high pressure
experiments they accidentally discovered polyethylene because their equipment had a
leak and allowed oxygen into the experiment. Commercial production began in 1939. The
first use of PE was an insulator for airborne radar cables by in WWII. (Encyclopaedia,
2019)
Advantages
Extremely Lightweight.
Relatively low cost.
Good chemical resistance.
Disadvantages
Not the most pliable.
It can kink if bent too far.
It has limitations in temperature and
chemical compatibility.
Flexible and ductile.
Possesses good durability.
Outstanding resistance to fatigue.
Ideal for push to connect fittings.
Table 9-PE Advantages and Disadvantages
It is determined through the advantage and disadvantages tables that PE pneumatic
tubing is the superior choice for this design. The material has more appropriate properties
than the other two options therefore it will be utilised as the tubing for this product.
33
4.2.3 Piston Rod
The majority of failures in pneumatic cylinders are due to buckling or fatigue. This is
caused by the compression and tension stressed applied to this component hence the
material must have properties to guarantee to prevent this. The piston rod ideally must
be very smooth. (Bohman, et al., 2017)
431 Stainless Steel- This material is used as pneumatic piston rods as they retain
qualities that are sought after for this component. It is a martensitic steel meaning it can
be heat treated to improve the resistance to wear. It has excellent corrosion resistance,
torque strength, high toughness and tensile properties. 431 stainless steel is easily
machined unless it is hardened above 30HRC. Other applications include propellor
shafts, nuts and bolts, golf clubs, bearings and more. (Midland Bright Steel, 2018) (AZoM,
2001)
Inconel 625- This “superalloy” is known for possessing exceptional strength, high
resistance to corrosion (especially pitting), high creep resistance and temperature
resistance. Since Inconel 625 has such desirable properties it lends itself to many
applications namely: flare stacks, jet engine exhausts, sea water equipment and hydraulic
piston rods. This can be a more expensive option because of the widely coveted
properties. It can prove to be difficult to machine as it has properties such as rapid work
hardening. (Newman, 2020) (Kotzem, et al., 2019) (Eiselstein & Tillack, 1991)
PVC- This is the more cost effective solution by far. It would also significantly decrease
the weight of the product especially if hollow PVC pipe is used. It also has the advantage
of being easily machined. The drawbacks of this choice would be that the mechanical
properties are inferior. It also is not as smooth and would be less efficient due to the
higher coefficient of friction.
34
Properties
PVC
431 Stainless Steel
Inconel 625
1.38
7.8
8.44
Modulus 3.275
190-210
160-200
Strength 48.25
1230-1510
830
925-1135
427-625
Density(g/𝑐𝑚3 )
Young’s
Materials
(GPa)
Tensile
(MPa)
Compressive
72.5
Strength (MPa)
Table 10- Piston Rod Material Properties
Table 11-Weighted Decision Matrix for Piston Rod
431 Stainless steel was chosen for the high scoring properties of strength, smooth
surface, resists corrosion, machines well. The material is not cheap however the piston
rod is not a component where the cost of the material should outweigh other properties.
35
4.2.4 Piston Rod Coating
The piston rod must be incredibly smooth for the project to function properly an efficiently.
Thusly, the piston rod cannot be painted but instead it must be coated which will provide
the desired qualities. Another main reason of failure is corrosion therefore the coating
needs to be highly resistant to corrosion, wearing, pitting, and abrasion. (Stridick &
Laukaitis, 2010)
Hard chrome plating (HCP)- This is a process where a coating of chromium is applied
to the surface of a metal, via electroplating, to improve corrosion and wear resistance,
reduce the coefficient of friction, and durability without having any negative impact on the
base metal. HCP was developed to be economical yet still perform competitively. The
bond strength is less than 5000. It has a porosity of around 5-10%.Micro-crack
characteristic permits for increased lubrication retention. (RHK, 2020)
Corex- This is a very hard, dense, cohesive piston rod coating. Corex is a thermal spray
that uses a tungsten-chromium-carbide compound. It has an extremely high bond
strength in excess of 10,000 psi. It is capable of excellent wear, impact and corrosion
resistance. The density of this coating ensures that it has a low porosity of less than 1%
and does not crack or peel when impacted unlike HCP. It also takes less time to apply a
corex coating than HCP. (Apex, 2015) (Richter, 2014) (ASM International, 2014)
High velocity oxygen fuel (HVOF)- This coating is a process where the component is
sprayed in order to improve the surface finish, resistance to corrosion, wear resistance
and the longevity of a product. This process is a form of thermal spraying that was
developed in the 1980s. A mixture of fluid fuel and oxygen is ignited and sprayed whilst
simultaneously melting a powder that is added. The melted powder creates a uniform,
dense coating with low permeability. The bond strength of this coating is over 10,000 psi.
The process can be very complex and the properties of the coating are dependant on
many variables. (Papatheodorou, 2012) (Özbek, et al., 2015)
36
Plasma sprayed ceramic- Ceramic coatings are not as common nowadays however it
was invented in 1940 and remain a versatile and broadly used thermal spray process.
Powder particles are injected into a plasma jet which in turn melts the powder and ejects
it at a high speed onto the surface. They are very effective in applications such as
aerospace, automotive engineering and even household appliances. They protect piston
rods against mechanical wear, although other coatings can achieve this more effectively.
The resulting coating is brittle and not very tough. The resistance to corrosion is
dependant on how the rods are used. (Bilal, 2011)
Laser cladding- This coating application method is becoming increasingly popular, The
effectiveness has improved considerably in recent years. The process of laser cladding
is the employment of laser energy to coat a material in a metal alloy powder. It is
becoming more and more popular because the laser power applied is progressively
becoming more affordable. This provides new prospects for laser cladding in various
applications that this sophisticated coating would not have been found in. Some
applications include aerospace, power generation, valve manufacturing, military use and
more. Principally laser claddings’ purpose is to mitigate the corrosion and wear a material
endures. This modern technique of coating materials is thought to eventually result in
piston rods that have a longevity better than ever before and retain the necessary
efficiency.
Table 12- Weighted Decision Matrix for Piston Rod Coating
From this table it is found that the best coating for the piston rod is HCP because it is
affordable yet still has competitive properties. The available diameters for HCP 431
stainless steel 5mm, 6mm, 8mm, 10mm, 12mm, 16mm, 18mm, 20mm, 25mm.
37
4.2.5 Piston and Ram
The piston and ram have separate functions however the required properties are similar
which is why the material used will be the same however the manufacturing process it
undergoes will not be. The piston functions as a part that separates the two pressure
zones present inside the barrel. The difference of pressure on the two sides of the piston
determines whether the cylinder is expanding or retracting. The material of the piston
greatly contributes to the cylinders durability and performance. The ram is the solid
cylinder that is in contact with the can whilst the product is in action.
Grey Cast Iron- the most common cast iron, is a ferrous metal that has excellent casting
qualities. This material can be used as a piston because of the properties it holds. Grey
cast iron performs very well in compression, is hard, is tough, is brittle and is not
malleable. It is also resistant to wear and galling and possesses good machinability.
These properties lend themselves to applications such as: such as engine cylinder blocks,
flywheels, gearbox cases, manifolds, disk brake rotors and cookware. (Reliance Foundry
Co. Ltd., 2020) (Raghul & Gautham, 2017)
4032 Aluminium Alloy- This lightweight material is outstandingly corrosion resistant.
The strength to weight ratio is good and it can be can be forged or casted and can be
machined easily. Aluminium is roughly three times lighter than cast iron. Applications of
this alloy are mainly engine components, pistons and chassis components. (AZoM, 2012)
EN19 Grade Steel – This grade of steel has a combination of desired properties namely;
shock resistance, tensile and compressive strength. Although steel is denser than
aluminium it is roughly three times stronger than aluminium. It is much more robust and
performs better in higher temperatures meaning that it can be used in more challenging
circumstances. This grade of steel is used for compressors, turbines, pistons, and
agricultural machine parts. (Saguenay, 2019) (AZoM, 2012) (AZoM, 2012)
38
Properties
Material
Grey Cast Iron
4032
Aluminium EN19 Steel
Alloy
Young’s Modulus
80-150
70-80
190-210
Density (g/𝑐𝑚3 )
6.9-7.35
2.69
7.85
Tensile Strength
100-450
370
655
(GPa)
(MPa)
Table 13-Piston and Ram Material Properties
Table 14-Weighted Decision Matrix for Piston and Ram
EN19 Steel will be used for both the piston and the ram. For the piston grooves will be
cut into the steel to allow pneumatic seals. Nitrile O-rings will be used as the pneumatic
seals as they are cheap and work well in a range of temperatures. At least 2 piston rings
are required to prevent the piston going at an angle and sticking however more rings
increase friction.
39
4.2.6 Barrel
The barrel is the main body of the cylinder that contains the pressurised air. The cylinder
barrel must have a smooth inner surface, be durable ,have high strength as well as high
corrosion resistance and precisely dimensioned. This particular barrel will be a round tube
than is dimensioned in accordance with ISO 15552 to allow standard made end caps and
tie rods to be fitted.
304 Stainless Steel- Is the most ubiquitous stainless steel. This, very corrosion resistant
metal is, able to withstand extreme temperatures. It can also have a very smooth finish
which is needed for the barrel of a pneumatic cylinder. Stainless steel is a food safe metal
and can therefore be found in the food and beverage industry. Other applications include
cutlery, saucepans, architecture, nuts and bolts. (AZoM, 2001)
Aluminium 2024- Is used for pneumatic barrels because it reduces the air friction even
more than steel. The resistance to corrosion is paramount to the quality of the air as well
as the quality of the surface. The main disadvantage of aluminium is the high cost. It also
performs well in high temperatures and pressures as well as tension and compression.
This aluminium alloy is used for aircraft parts, pneumatic cylinders and truck wheels.
(Gabrian, 2018)
CZ109 Brass- This metal alloy, a combination of copper and zinc, is very popular in the
use of pneumatics because of the unique properties. The malleability allows for the
material to be produced to a precise standard, has low friction, it is able to withstand high
pressure, highly resistant to corrosion and is also very durable. Other applications of
brass include instruments, weapon ammunition and locks. It is also found in furniture
because of the appealing colour. (Anon, n.d.)
Black Amalgon- This composite material, similar to fibreglass, is a lighter alternative to
metal however it still retains all of the required properties. This material is not able to be
dented unlike metals and can withstand high pressures. It owns outstanding corrosion
resistance, toughness and durability. It requires less maintenance as the surface is so
smooth that it does not even require lubrication. It can last over a million uses with no
grease before it requires replacement. The main applications are pneumatic and hydraulic
cylinders, valve actuators and pump housings. (AmalgaComposites, 2008)
40
Properties
Materials
304 Stainless
Aluminium
CZ109 Brass
Black Amalgon
Steel
2024
Density (g/𝑐𝑚3 )
8
2.8
8.39
1.6-2.0
Compressive
170
30-280
165
187-255
515
455-483
360
82-110
Strength (MPa)
Tensile Strength
(MPa)
Table 15-Barrel Material Properties
Table 16-Weighted Decision Matrix for Barrel
Black Amalgon came out on top as it is a lightweight material with a smooth finish which
will decrease the maintenance costs. It has superior corrosion resistance and impact
resistance.
41
4.3 Double Action or Spring Return
4.3.1 Spring Return
A single-acting cylinder’s output force is developed in only one direction. A single port
allows the compressed air both in and out. When the air is allowed in, the piston will move
to the desired position, when the air is allowed out the same port, the piston will return to
the original position. A fitted spring, a weight, gravitational force, mechanical movement,
or an external spring will force the piston to return to the original position. For this project
the cylinder will be lying horizontal, so using a spring return would be best suited. The two
types of single acting cylinder are a push type and a pull type.
4.3.2 Double Acting
A double-acting cylinder’s output force is developed in two directions, both the extending
and the retracting direction. There are ports at both ends of the cylinder. When the
pressurized air enters the cap-end port it forces the piston to the desired position, it is
returned when the air is exhausted through the cap-end port and pressurized air enters
the rod-end port. When air pressure is applied it is applied to opposite ends alternately.
Double-acting cylinders are typically used when the necessary thrust is larger than that
available from a single-acting cylinder.
42
4.3.3 Comparison
Spring Return
Advantages
Disadvantages
Simple Design.
The return spring side of the cylinder is
vented to the atmosphere, this may allow
for dirt or dust to enter, which could lead
to the piston becoming faulty, less
efficient or could reduce the longevity of
the product.
Compact Size.
Over time the force of the spring can
become inconsistent.
It requires less pneumatic piping and valves
therefore reducing the cost and complications.
Bore size and stroke of the cylinder is restricted
due to limitations of the spring size and force.
Best fail Safe.
The spring creates an opposing force which could
reduce efficiency.
Compared with equivalent sized double acting
cylinder the air consumption is halved.
Table 17-Spring Return Advantages and Disadvantages
Double Acting
Advantages
Generally, ISO standards are based on
the design of double-acting cylinders.
A more extensive range of double-acting
cylinders than for single-acting cylinders,
giving many more options of bore and
stroke sizes.
Many variations are available on the
basic double-acting cylinder design.
Faster and stronger.
More Efficient.
Disadvantages
Cannot be simply held in a mid-position.
More costly than single acting.
It is not as compact.
More difficulty maintaining it.
Table 18-Double Acting Advantages and Disadvantages
43
Both options have the same amount of advantages and disadvantages. It can be
ascertained that both options are viable however most ISO standards are based on the
double acting cylinder design. This also allows for a broader range of universal parts that
can be used since the majority of parts are also designed for the double acting cylinder.
44
4.4 Safety Feature
The customer has requested that the product includes a safety feature to reduce the risk
of any accidental injury to the user. This section will cover the various ways that this is
possible and will determine the most suitable method.
4.4.1 Two Hand Control Panel
Safety two hand control switches are used to safeguard the hands of an operator in
industrial situations where machine operation may be hazardous. In order to operate the
machine, both buttons must be pressed simultaneously therefore eliminating the chance
that a hand can be caught in the machine. This means machinery will not start until both
hands are confirmed to be in a safe position which also prevents the machine from being
started accidentally.
4.4.2 Washing Machine Door Lock
A washing machine door lock is a safety interlock switch. These are safety devices used
for checking whether movable guards such as the door is opened or closed. This prevents
the washing machine from operating in the unsafe condition that the door is open. It can
also have a function that prevents the door from opening whilst the product is in use. This
can be an important feature to ensure machine safety, with many standards that pertain
to it. Two of the most typical standards are ISO 14119 and ISO 13849, and safety
performance that meets these standards is essential. Most interlock switches have three
terminals: a live, a neutral and a common. However, they can have a fourth terminal that
goes to an LED to display whether the door is open or shut. When the live and neutral
heat up the PTC heater it will in turn heat up the bimetal strip that moves the mechanical
switch. Inside the interlock, when the common is activated, a locking pin is thrown over
which keeps the door locked. The door cannot be opened for roughly two minutes after
use whilst the bimetal strip cools down.
45
Figure 12 - Washing Machine Door Lock
4.4.3 Microwave Door Switch
The microwave door switch is an interlock microswitch. A microswitch changes the
direction of power when the arm is moved. It utilises a spring-loaded lever to open and
close a set of internal contacts. The switch has three connection points: common,
Figure 13 - Microwave Door Switch
normally open and normally closed. Typically, power is attached to the common terminal,
this energizes the spring that is in contact with the normally closed pin. When nothing is
pushing against the activating arm it is called the resting state. When the door is closed
and the arm is moved, the spring snaps into a different position where the power leads to
the normally open pin.
46
4.4.4 Coded Magnetic Interlock Switch
This type of switch requires power to work and has an LED to show when the switch is
activated. The switch detects several magnets with varying polarities that are verified
before the switch is activated. This feature proves itself useful as the sensor is not able
to be used with any magnet. These are extremely long-lasting devices that require
minimum upkeep. Additionally, they are impervious to shock and vibrations. (Spano,
2019)
Figure 14 - Coded Magnetic Interlock Switch
47
4.4.5 Comparison
Table 19-Weighted Decision Matrix for Safety Feature
This weighted matrix conveys that the best safety feature for the product is the coded
interlock magnetic switch by far. This feature is far more difficult to trick than the other
options. They do not require physical contact this prevents the most common fail mode
for the other interlock options therefore improving the reliability. This is because after
regular use the door and switch can become misaligned, this can damage the interlock
switch when the misaligned door is repetitively striking the switch. They can come in
different package styles and materials. The switch will be connected to a 5/2 solenoid
valve. The wiring used will be across the hinges and therefore strain relief will be required
via feeding the wiring through a corrugated tube.
48
5.0 Methodology
5.1 Casing
1. The 10mm thick mild steel is cut into 5 pieces. (Two 70mm x 70mm squares for
the top and bottom, two 210mm x 70mm rectangles for the sides and one rectangle
30mm shorter)
2. Holes in the shorter rectangle of the casing will be made in the corners to allow for
mounting.
3. A 15mm hole is made in the top to allow the rod through.
4. A 5mm hole is drilled into the bottom to allow air to escape.
5. The mild steel is welded together.
6. The casing is be powder coated.
7. The acrylic door will be cut to 210mm x 90mm.
8. The acrylic door is joined by a hinge.
9. The interlock switch is screwed onto the acrylic door.
Figure 15-Casing
49
5.2 Piston Rod
The piston rod is made from HCP 431 stainless steel with a diameter of 14mm.
1. The rod is cut to 210mm.
2. The rod ends are faced to 200mm.
3. The M14 thread is cut 10mm down from the top.
4. The M14 thread is cut 15mm up from the bottom.
Figure 16-Piston Rod
50
5.3 Piston
1. The lathe is used to reduce the diameter to 63mm.
2. The lathe is used to face off the ends at a length of 30mm.
3. The piston is drilled with a diameter of 14mm and a depth of 15mm.
4. The piston is tapped at M14.
5. Using the lathe, grooves are cut in the side to allow pneumatic seals to be placed.
6. The piston is polished using emery paper.
Figure 17-Piston
51
5.4 Ram
1. The lathe is used to reduce the diameter to 70mm.
2. The lathe is used to face off the ends at a length of 10mm.
3. The top of the ram is drilled at a diameter 14mm with a depth of 10mm.
4. The top of the ram is tapped at M14.
5. The ram is polished using emery paper.
Figure 18-Ram
5.5 Barrel
The barrel can be bought at the necessary diameter and length.
Figure 19-Barrel
52
5.6 End Caps
The standardisation of pneumatic cylinders allows for the end caps to be sourced
externally.
5.7 Assembly
1. The pneumatic seals are placed onto the piston.
2. The piston rod is screwed into the piston.
3. The piston is inserted to the barrel.
4. The end caps are fitted, held together by tie rods.
5. The ram is screwed onto the piston rod whilst the casing is in place.
Figure 21-Assembled Pneumatic Can Crusher
Figure 20-Exploded View
53
6.0 Testing and Results
This section will go over how the experiment was performed, what was the purpose and
compare those results with the theoretical findings. There will also be equations used to
find the dimensions of the product.
6.1 Experimental Findings
An experiment was conducted to find the force required to crush an aluminium drinks can.
6.1.1 Materials and Equipment

5x330ml cans manufactured by Ball.

5x500ml cans manufactured by Ball.

Mass Scale

Camera

5kg weight plate
6.1.2 Experimental Procedure
1. All 10 cans were rinsed and dried to prevent any impact on the results.
2. The camera was set up to record the mass displayed on the scale.
3. The first can was placed in the centre of the weight scale.
4. The scale was zeroed.
5. A 5kg weight plate was placed on top of the can in the centre to provide a stable
surface.
6. Mass was added by standing on top of the weight plate until the can buckled.
7. The process was repeated for the remaining cans.
8. The results were recorded.
54
6.1.3 Results
Can Size
Test 1
Test 2
Test 3
Test 4
Test 5
Largest
Weight
330ml
55.7kg
35.1kg
54.5kg
59.8kg
58.4kg
586.638N
500ml
33.0kg
35.7kg
54.9kg
52.8kg
59.9kg
587.619N
Table 20-Experiment Results
6.3.1 Theoretical
A=
𝐹
𝑃
Equation 1-Area of Cylinder
A=
1108
200,000
A = 5.54x10−3 m2
4𝐴
𝑑2 = √
𝜋
Equation 2-Diameter
4(5.54 ∗ 10−3 )
𝑑1 = √
𝜋
𝑑1 = 0.084𝑚
The diameter has to be rounded up to 100mm to conform to the appropriate standards. If
the diamter were to be rounded down the force would not be great enough.
6.2 Equations
It was found that drink cans from the “Ball” manufacturer are made from aluminium alloy
3004 with a wall thickness of 0.097mm. The standard 330ml can has a diameter of
66.3mm and can be 115mm or 168mm in height. (AZoM, 2012) (Anon, n.d.) (Anon, n.d.)
6.2.1 Force Required to Crush a Can
To calculate the force required to buckle a thin-walled cylinder an equation derived from
Donnell’s shell theory is used.
55
𝑟𝑎 =
𝑟𝑜 − (𝑟0 − 𝑡)
2
Equation 3-Average Radius
𝑟𝑎 =
33.15 + (33.15 − 0.097)
2
𝑟𝑎 = 33.1015
Where:
𝑟𝑎 = Average radius in mm
𝑟𝑜 = Outside radius in mm
𝑡 = Wall thickness in mm
1
𝑟
𝜙 = 16 √ 𝑡𝑎
Equation 4-Knockdown Factor
𝜙=
1 33.1015
√
16 0.097
𝜙 = 1.154563935
Where:
𝜙= Reduction (knockdown factor)
𝑟𝑎 = Average radius in mm
𝑡 = Wall thickness in mm
𝛾 = 1 − 0.901(1 − 𝑒 −𝜙 )
Equation 5-Classical Buckling Knockdown Factor
𝛾 = 1 − 0.901(1 − 𝑒 −1.154563935 )
𝛾 = 0.3829906521
Where:
𝛾= Classical buckling knockdown factor
e= Euler’s number
Φ= Reduction (knockdown factor)
56
𝜎𝑥 =
𝛾𝐸
𝑡
√3(1−𝑣 2 ) 𝑟𝑎
Equation 6-Axial Stress
𝜎𝑥 =
0.3829906521 ∗ (80 ∗ 109 ) 0.097
33.1015
√3(1 − 0.332 )
𝜎𝑥 = 54.91340475 ∗ 106 𝑃𝑎
Where:
𝜎𝑥 = Axial stress in Pa
v= Poisson’s ratio
𝛾= Classical buckling knockdown factor
E= Young’s modulus in Pa
t= Wall thickness in mm
𝑟𝑎 =Average radius in mm
Figure 22-NASA Equation
(Hilburger, 2020)
𝐴 = 𝜋𝑟𝑜2 − 𝜋𝑟𝑖2
Equation 7-Wall Area
𝐴 = 𝜋33.152 − 𝜋33.0532
𝐴 = 20.17433727 𝑚𝑚2
𝐴 = 20.17433727 ∗ 10−5 𝑚2
Where:
A=Area of wall in mm
ro =Outside diameter in mm
ri =Inside diameter in mm
𝐹 = 𝜎𝑥 ∗ 𝐴
Equation 8-Force
𝐹 = (54.91340475 ∗ 106 ) ∗ (2.017433727 ∗ 10−5 )
𝐹 = 1107.841548N
Where:
F= Force in N
A=Area of the wall in m
𝜎𝑥 =Axial stress in Pa
57
6.3 Sizing of the Cylinder
This section conveys the dimensions that are required to exert the forces needed
employing both the theoretical and the actual results. The pressure supplied by the air
compressor is 2 Bar, the diameter of the rod is given in 5.2. From this the bore can be
found nominally using the ISO 15552.
6.3.2 Actual
𝐹
𝑃
588
A=
200,000
A=
A = 2.94x10−3 m2
4𝐴
𝑑2 = √
𝜋
𝑑1 = √
4(2.94 ∗ 10−3
𝜋
𝑑1 = 0.061𝑚
The closest diameter that conforms to the appropriate standards is 63mm
6.3.3 Comparison
The aforementioned equations show that the dimensions derived from the theoretical
results will lead to the product being oversized. Oversized components would increase
unnecessarily increase air consumption and cost more for materials.
58
7.0 Discussion
This section details what processes can be improved upon to ensure the project runs as
smoothly as possible.
7.1 Experiment
The experimental findings and the theoretical findings had a difference of 520N (53kg).
This can be attributed to the damage obtained by the samples before the experiment and
the fact that the cans are not perfect cylinders. During use, when the can is opened, the
internal pressure decreases therefore the cylinder walls flex easily. If the walls sustain
any damage during use this significantly decreases the tensile strength. In order to
improve the experiment to achieve more accurate results the mass could be added in
Figure 22 - Crushed Cans
steady increments. The experiment could have been timed as well as the height of the
crushed can could be measured in order to draw a stress/strain graph. To further improve
the accuracy the experiment could have been repeated more.
As can be shown above 4 out of 5 500ml cans that were used in the experiment were not
crushed but instead they had only buckled near the top or bottom. This is because during
the experiment as soon as they buckled the weight on top of them forced them off the
scales. This experiment could be further improved by containing the can on the weight
scale by using something to prevent it from coming off. This could cause inaccuracies
with the experimental findings as what has been recorded is the force required to buckle
the wall of the can using axial stress rather than the force required to crush the can to a
desired height.
59
7.2 Fatigue Strength
Wood and composite materials are unlike the other materials that were looked into for the
casing of the material. These materials are anisotropic meaning they have different
properties depending on the direction the forces are applied. Therefore the comparison
between the materials’ fatigue resistance was not necessarily fair because it is a very
complicated process to accurately determine the fatigue strength of a material. A software
has to be used to replicate the manufacturing process of composites to understand
roughly the formation the reinforcement would take to in the matrix.
60
8.0 Novel Feature
To further improve this design a reciprocating piston would be incorporated into the
design. This could be done by using two roller levers. Once the case is closed the interlock
switch will actuate the cylinder then the roller will detect when the piston is extended fully
and will return the cylinder to the off position. When the piston is fully retracted the other
roller will detect this and extend the piston again. This cycle will repeat until the door is
opened again. This will allow the product to be loaded with multiple cans at a time which
are crushed consecutively. This feature will make the product more automatic as well as
minimising the downtime.
Figure 23-Reciprocating Piston
61
9.0 Conclusion
The pneumatic can crusher is a suitable solution for the problem posed by West Lothian
college as it can be used for the standard sized cans sold in the canteen. Provided
students return empty cans to the staff this solution successfully assists the college in
moving towards becoming ’greener’. This solution is economically viable due to the simple
construction and the materials researched in detail. The product satisfies the restrictions
stated is 3.0 as well as the objectives stated in 4.0. It is lightweight, durable, inexpensive
and safe to use. The user requires no training or skills. This concept is a feasible solution
to the presented problem.
62
10.0 Appendices
10.1 Appendix 1 Gantt Chart 1
10.2 Appendix 2 Gantt Chart 2
10.3 Appendix 3 Gantt Chart 3
63
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