TREVOR to rotate, this resulting in the cogs

    

    

TREVOR
CHIREMBA    

    

    

 

 

CONTENTS

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TITLE PAGE ……………………………………………………………………..2

TASK 1:  P4 a) ………………………………………………………………….4

                     b)
………………………………………………………………… 4

 

TASK 2: M1 i)
…………………………………………………………………. 5

                     ii)
………………………………………………………………… 8

 

REFERENCES ………..…………………………………………………………9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TASK P4

 

Cold rolling

A lot of energy is required to roll a sheet of metal in cold
rolling than in hot rolling. Whereas heating up a sheet of metal makes it
malleable, therefore when rolled between two rollers a flat sheet can be easily
formed. Yet because a cold sheet that is not heated, when put through the
roller it will consume more energy so as to push it through.

 

Blow moulding

Blow moulding requires a lot of petroleum in order to be
able to produce plastic products. It carries a big risk on the destruction of
the environment.

 

Slip casting

Dimensions of low quality can be achieved as compared to
those of dry pressing or powder
injection molding. The production rate is also lower as compared to that of dry
pressing, extrusion and injection moulding.

 

GRP

 These have poor
stiffness and rigidity.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a)  Piezoelectric crystals in watches

 

Piezoelectric crystals are important factors in a watch, as
these are used to keep time. A clock circuit consists of a battery, quartz
crystal, oscillator, stepping motor, microchip and a cog. The electrons moving
from the battery electrifies the quartz crystal, when the quartz crystal is
electrified it begins to vibrate or swing due to piezoelectric effect (the
ability to produce to produce electricity when mechanical stress is applied).
The microchip responds by counting the number of vibrations in the crystal
therefore it then calculates how many times the crystal should vibrate. After
the microchip has had a fixed number of vibrations it then sends an electrical
pulse to the stepping motor. The polarity of the solenoid changes causing the
magnet to rotate, this resulting in the cogs turning every second or as
programmed.

 

 

b) Shape memory alloys for spectacles   

 

These spectacles were designed in a way that they can reshape
themselves as my factors might make them lose their shape such as temperature. If
one was to fold these spectacles, the stress applied makes the titanium alloy
from which they are made into an entirely different crystalline structure, if
you release them the crystal structure reforms again therefore they go back
into their normal shape. In other word the molecules are just re-arranging
themselves in a reversible way, this is known as a solid-state phase change.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

i) Urea
Formaldehyde when used in the manufacturing of an electric plug

 

Below is an
explain how the properties and structures of Urea Formaldehyde (UF) effects in
their behavior in the manufacturing process, although to a greater extent UF
may still be used to manufacture electric plugs. To prove this, at some point i
might need to compare the properties of UF to those of other materials used to
manufacture plugs such as Acrylonitrile Butadiene Styrene (ABS) 

 

When
choosing a material, first we look for a material which can conduct
electricity. The safe use of a plug depends on the ability of different parts
to conduct electricity. Parts in a plug can be divided like shown in the
diagram below. Note that “not
every part in a plug is made of UF”.

 

Parts of the
plug

 

 

 

 

Electric
plugs are either made by injection moulding or compression moulding.
Compression moulding is used for thermosetting plastics like Urea formaldehyde.
Plugs have pins which might/are likely to suffer impact therefore these pins
have to be secured. Toughness is
an important factor in this case as the plug body has to be strong. The chart
below illustrates the strength against toughness for different materials
therefore it allows us to compare different polymers hereby we may be able to
tell why some polymers are not acceptable.

 

Material
Selection chart

 

 

 

From the
chart above we have seen that there are other materials such as ABS that have more toughness than Urea
formaldehyde(UF), this means ABS a greater impact than UF. Because UF has lower
toughness this means it can only be used for fixed appliances whereby the plug
is less likely to suffer any impact (for example a microwave or television).
Therefore, under physical properties, UF has high toughness and also high hardness
making it more suitable for manufacturing plugs.

 

 

Interpreting
material selection chart

 

 

 

From the
chart, we can easily tell that non-conductive parts in a plug are made from
polymers, this is because they have high resistivity.

 Also from the chart we see that wood is cheaper than polymers, in
this instance our polymer is UF. UF can be shaped by various process whereas
wood can be machined into a shape, which would not be suitable for mass
production.

 

Urea
Formaldehyde is very brittle, this means it is hard but it still can break
easily. This limits the appliances where it can work, these are appliances
where it is less likely to break such as a refrigerator.

 

 

Conclusion 

A plug is a
3D shape, therefore it is of no use to use a perfect material if it can’t form
the desired shape for example wood, is
said to be far much cheaper than UF but it cannot be used for mass production
as it needs to be machined shaped yet Urea formaldehyde can be shaped by
different process making UF the best material to consider over wood. UF is a
very good insulator, plugs made from this polymer are safe to use.

 

 

 

 

 

ii) concrete
when used as a structural beam

 

Flexural
strength – many structures are a subject to flexure and/or bending. When a load
is loaded, the bottom is in tension whilst the upper part is in compression
therefore some steel bars are inserted (reinforced concrete) therefore the
concrete has very good strength both in tension and compression.

 

 

    

 

Durability –
If well designed and laid properly this structure becomes durable and it can
last for more than 500 years.

 

Ductility –
the structure gets ductility from the steel reinforcement.

 

Fire
resistance – reinforced concrete beams are more fire resistant as compared to
other materials such as steel.

 

Seismic
resistance – if the structure is designed properly it can be extremely
resistant to earthquakes.

 

Maintenance
– Maintenance of a reinforced concrete beam is of low cost as compared to that
of steel and pre-stressed concrete.

 

When setting
up this structure it needs a lot of form-work, centering therefore this
requires a lot of site space and skilled labour. Concrete develops cracks even
if it reinforced these are caused by shrinkage resulting in strength loss. When
concrete is in a fluid material it can be economically moulded into nearly any
shape.