Plastic Moulding

Plastics Moulding

Vacuum Moulding

This is a process that is used to manufacture a variety of products in thermoplastic materials. A mould,which is usedfor prducing the interior panels of lorry cabs, is attached to a platen (support plate)
The platen and mould are then lowered and rigid thermoplastic sheet material is clamped onto an air tight gasket and usually heated from above.One the thermoplastic sheet is softened enough then the air is blown in to raise the sheet in a slight bubble before the platen is raised bringing the mould into contact with plastic.Any air trapped between the platen and heated plastic sheet is then evacuated by a vacuum pump. Atmopheric pressure acting over the top surface completes the forming process by pressing the plastic sheet on to the mould. Once the plastic sheet has been cooled down below freezing pointthe air flow is reversed to lift the forming off the mould.
Line Bending


Blow Moulding


Compression Moulding



Injection Moulding

This is a process like Extrustion Moulding as the plastice pellets are put into a hopper that go to a heated barrel, while the mould is being clamped the machine.the heated up plastic is then injected in to the mould. Once mould is filled the cooling process begins and once mould is cooled down the mould is ejected and the process starts again.



Extrustion Moulding

This process can be compared to squeezing toothpaste from a tube.It is a continuous process used to produce both solid and hollow products that have a constant cross-section. E.g: Window Frames, Hose Pipe, Curtain Track, Garden Trellis. Thermoplastic granules are fed from a hopper by a rotating screw through a heated cylinder. The tapered shape of the screw compacts the plastic as it becomes plasticized.This part of the process is similar to the heating and compacting stages in the injection moulding process.The difference being that the softened materials material is allowed to flow out through a die in a continuous stream rather than be pumped intermittently in measured amounts into a mould.The die which is fitted to the end of the extruder barrel determines the cross-section of the extrusion.
Rotational Moulding

 
Rotational Moulding is a process used mainly to manufacture hollow shaped products such as footballs, road cones and storage tanks.
The machine has three arms which rotate about a fixed central point. Each arm stops in turn at one of three stations. Moulds are attached to end of each arm and are rotated continuously.The only time the moulds are not being rotated is when they are positioned at station 1 which is where the proess both begins and ends. At station 1 the mould is either being loaded with thermoplastic powder or the finished moulding is removed to start the process again. The cooling chamber is at station 3 and oven chamber is at station 2. The Temperture goes up to 230-400c whilst being rotated and the roational speed is between 2 and 20 r.p.m.

Jigs,Templates: these are imporant because they keep everything the same.

Polymer Theory

Monomers     ->    Polymerisation     ->   POLYMER
Monomers join together to form a long chain of molecules called polymers ( plastic )

Thermo setting plastics;
Has no links
- they soften when heated and can be remoulded so or more recyclable then thermosetting
Types of thermoplastic;
-ABS - Acrylonitrile Butadiene Styrene
-CA - Cellulose Acetate
-Nylon - Polyamide
-PMMA - (acrylic)
-PP -Polypropylene
-HIPS - High Impact Polystyrene
-PS - Polystyrene
-LDPE - Low Density Polyethylene
-HDPE - High Density Polyethylene
-uPVC - Polyvinyl Chloride
-PVC - (unplasticised flexible) Polyvinyl Chloride
-PET - Polyethylene Terephthalate
-PC - Polycarbonate

Thermoplastics;
Has links so less movement
-it can be moulded into a shape but can not be remoulded
Types of thermosetting plastics;
-Expoxy Resins - surface coatings, encapsulation of electronic components adhesive
-Melanie - Tableware,Decorative laminates
-Polyester Resins - Castings, used in GRP
-Urea formaldehyde - Electrical fittings, adhesives

Polymers are;
-Good electrical an thermal insulator
-Good strength to weight ratio
-Generally good resistance to atmosphere and chemical erosion
-Low melting point
-Lightweight
-Available in a wide range of colours and transparency ( due to different a pigments)
 -Two main categories thermoplastic and thermosetting plastics

Improving the properties of plastics;
-Fillers; bulking- reduces cost and you get more of the product eg: sawdust crushed quartz and limestone - in also strengthens it
-Flame retardants; flame resistance less likely to catch fore or slow the flames down
-Anti Static agents; reduce the effects of static charges that can build up on a product - used in synthetic carpets
-Plasticisers; these make the materials less brittle
-Stabilisers; reduce the effect of ultra violet light found in sun light

Assignment 2

Assignment 1

I should never have purchased Skull-candy in-ear headphone!
The other week my earphones stopped working through one of my favourite songs I had had them for years and it was clear to me it was time for some new ones so I decided I wanted a pair of black and pink in-ear headphones made by Skull-candy as my sister said they have a longer life span and are good quality and I had to get in ear ones because they were better than the outer-ear.

I brought my expensive in-ear pink Skull-candy headphones for £15 to me that is a lot of money for a pair of headphones normally I would spend £5 or less for my other pairs in the past,  but these WERE meant to be worth it. But they weren't!

I don't know if it was just the pair i purchased but they stopped playing sound within five days, the sound quality was poor and fuzzy they burse my eardrum within ten minutes of using them, as well as they never fit into my ear properly, I would have to hold them in just so they would stay so I could listen to one of my favourite songs that sounded like an alien trying to make contact with earth for the first time!

Even thought they look aesthetic pleasing they were not ergonomically good enough for me personally and will not be purchasing them again.