Plastics and Plastic Manufacturing

Many polymer-forming processes are essentially two stage; the first stage with polymers being the production of the polymer in a powder, granule or sheet form and the second stage being the shaping of this material into the required shape. The first stage can involve the mixing with the polymer of suitable additives and other polymers in order that the finished material should have the required properties. Second-stage processes for thermoplastics forming generally involve heating the powder, granule or sheet material until it softens, shaping the softened material to the required shape and then cooling it. For thermosets the second-stage processes involve forming the thermosetting materials to the required shape and then heating them so that they undergo a chemical change to cross-link polymer chains into a highly linked polymer. The main second-stage processes used for forming polymers are:

Plastics Moulding

This includes injection moulding, reaction compression moulding and transfer moulding.

Plastics Forming

This includes such processes as extrusion, plastic vacuum forming, plastic blow moulding and calendering.

Plastics Cutting

Injection moulding,

In addition, products may be formed by polymer joining. The processes are:

Adhesives, Plastic Welding,Fastening systems such as riveting, press and snap fits and screws.

The choice of process will depend on a number of factors, such as:

The quantity of items required The size of the items

The rate at which the items are to be produced, i.e. cycle time The requirements for holes, inserts, enclosed volumes, threads Whether the material is thermoplastic or thermoset

Plastic Injection moulding

Moulding uses a hollow mould to form the product. The main processes are injection moulding, reaction injection moulding, compression moulding and transfer moulding.

A widely used process for thermoplastics, though it can also used for rubbers, thermosets and composites, is injection moulding. With this process, the polymer raw material is pushed into a cylinder by a screw or plunger, heated and then pushed, i.e. injected, into the cold metal mould. The pressure on the material in the mould is maintained while it cools and sets. The mould is then opened and the component extracted, and then the entire process repeats itself. High production rates can be achieved and complex shapes with inserts, threads, holes, etc. produced; sizes range from about 10 g to 25 kg in weight. Typical products are beer or milk bottle crates, toys,

control knobs for electronic equipment, tool handles, pipe fittings.

Reaction injection moulding

Reaction injection moulding involves the reactants being combined in the mould to react and produce the polymer. The choice of materials that are processed in this way is determined by the reaction time, this must be short, e.g. 30 seconds, so that cycle times are short. It is mainly used with polyurethanes, polyamides and polypropylene oxide and composites incorporating glass fibres. The preheated reactants are injected at high speed into a closed mould where they fill the mould and

combine to produce the finished product. This method is used for large automotive parts such as spoilers, bumpers and front and rear fascia.

Compression moulding

Compression moulding is widely used for thermosets. The powdered polymer is compressed between the two parts of the mould and heated under pressure to initiate the polymerisation reaction. The process is limited to relatively simple shapes from a 2-3 g to 15 kg in weight. Typical products are dishes, handles and electrical fittings.

Transfer moulding

Transfer moulding differs from compression moulding in that the powdered polymer is heated in a chamber before being transferred by a plunger into the heated mould.

Plastic Forming processes

Forming processes involve the flow of a polymer through a die to form the required shape.

Plastic Extrusion forming

A very wide variety of plastic products are made from extruded sections, e.g. curtain rails, household guttering, window frames, polythene bags and film. Extrusion involves the forcing of the molten thermoplastic polymer through a die. The polymer is fed into a screw mechanism which takes the polymer through the heated zone and forces it out through the die. In the case of an extruded product such as curtain rail, the extruded material is just cooled.

If thin film or sheet is required, a die may be used which gives an extruded cylinder of material. This cylindrical extruded material is inflated by compressed air while still hot to give a tubular sleeve of thin film . The expansion of the material is accompanied by a reduction in thickness. Such film can readily be converted into bags.

Polyethylene is readily processed to give tubular sleeves by this method but polypropylene presents a problem in that the rate of cooling is inadequate to prevent crystallisation and so the film is opaque and rather brittle. Flat film extrusion can be produced using a slit-die. The rate of cooling, by the use of rollers, can be made fast enough to prevent crystallisation occurring with polypropylene. The extrusion process can be used with most thermoplastics and yields continuous lengths of product. Intricate shapes can be produced and a high output rate is possible.

Plastic Blow moulding

Blow moulding is a process used widely for the production of hollow articles such as plastic bottles from thermoplastics. Containers of a wide range of sizes can be produced. With extrusions blow moulding the process involves the extrusion of a hollow thick-walled tube which is then clamped in a mould. Pressure is applied to the inside of the tube to inflate it so that it fills the mould. Blow moulding can also be used with injection moulding.

Plastic vacuum forming

Vacuum forming is a common method of thermoforming. It uses a vacuum on one side of a sheet of heat-softened thermoplastic to force it against a cooled mould and hence produce the required shape. Sheets, such as 6 mm thick acrylic, are likely to be preheated in ovens before being clamped, but thinner sheets are likely to be heated by radiant heaters positioned over the mould. Vacuum forming can have a high output rate, but dimensional accuracy is not too good and such items as holes, threads and enclosed shapes cannot be produced.

Calendering

Calendering is a process used to form thermoplastic films, sheets and coated fabrics. The most common use has been for plasticised PVC. Calendering consists of feeding a heated paste-like mass of the plastic into the gap between two rolls, termed nip rolls. It is squeezed into a film which then passes over cooling rolls before being wound round a wind-up roll. This process can also be used to coat a fabric with a polymer.

Plastic machining

The processes used to shape a polymer generally produce the finished article with no further, or little, need for machining or any other process. With injection moulding, compression moulding and blow moulding there is a need to cut off gates and flashing; with extrusion, lengths have to be cut off. As with metals, single-point and multi-point cutting tools can be used with polymers. Where discontinuous, rather than continuous, chips are produced and the machined surface becomes excessively rough as a result of chips being sheared off. It is thus desirable to select cutting conditions which result in the formation of continuous chips.

Polymers tend to have low melting points and thus machining conditions which do not result in high temperatures being produced are vital if material is not to soften and deform.

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Making Plastic - Plastic Moulding

Ever wondered how plastic is moulded into the exceptionally useful things that we employ in our daily life? Is it as simple as melting plastic and lathering the sides of a mould with it and cooling it, much like chocolate? The answer, actually, is no. Moulding plastic is a little more complex than that. Plastic is made using a process often called plastic injection moulding.

What is this type of moulding

Plastic injection moulding is the method of manufacturing parts made of thermoplastic and thermosetting plastic by melting and forcing into moulds where they cool to form the desired object.
How does plastic injection moulding work?

The process of plastic injection moulding usually begins with an industrial designer or engineer who designs a product. This is followed up by the work of a toolmaker or mould maker who makes the mould to fit the design created. These moulds are metallic and usually made using either steel or aluminum.

Using machines, they are made to acquire the exact shape desired by the design. Once this is done, the process of actually making the plastic follows. This involves thermoplastic and thermosetting plastic being fed into a heated barrel and mixed. This melted material is then forced into the cavity of a mould and there it cools and hardens to form the desired part.

Some characteristics of the process:

1. I uses melted and mixed thermoplastic or thermoset plastic as the base
2. It uses a plunger which acts like a screw or a ram to force the melted material in the mould
3. It makes a shape that is open-ended and has taken the shape of the cavity of the mould
4. It shows a parting line and gate marks on the finished products and the ejector pin marks can also usually be made out.

Some history

Alexander Parkes invented plastic in 1851 in Britain. This was worked on and bettered by John Hyatt, an American inventor in 1868. He also patented, in 1872, the first injection moulding machine. In the 1940s, the need for mass production of plastic products increased and saw the invention of the first screw injection machine by inventor James Hendry of America. This increased not only the speed of production but also the amount of precise control that could be exercised on the finish of the product.

Since then, this type of moulding has been used widely in the production of everything right from milk cartons to entire car panels and automotive parts. Since it is not a very costly material, it is best suited for mass produced goods.

Advantages of this type of moulding:

1. The rate of production are very high and therefore mass production is much benefitted
2. Since tolerance levels are high, they can be repeated
3. The labour cost is very low
4. The losses in scrap are very minimal
5. The products require very minimal finishing
6. A wide range of materials can be used

Disadvantages using this type of moulding:

1. Although labor expense and scrap loses are minimal, the cost of equipment and therefore investment is high
2. The running costs have the potential to be high
3. There is also need to design the correct parts

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The Complete Part Design Handbook: 'For Injection Molding of Thermoplastics

Book Description

Publication Date: March 1, 2006 | ISBN-10: 1569903751 | ISBN-13: 978-1569903759

This indispensable, all-inclusive reference guide to plastic part design was compiled with the product designer in mind, who is looking for more detailed information on plastic resins, the rules and geometries underlying their use in product design, and the advantages and limitations of their use in industrial applications. The designer will also find valuable advice on resin and tool selection and processing parameters that allow fast and successful product development and manufacture. Thousands of hours of research and cross referencing have gone into the completion of this work. In addition, the hands-on knowledge of a plastics expert with more than 35 years experience is incorporated.

Product Details

• Hardcover: 870 pages
• Publisher: Hanser Publications (March 1, 2006)
• Language: English
• ISBN-10: 1569903751
• ISBN-13: 978-1569903759
• Product Dimensions: 10.8 x 8.3 x 2 inches
• Shipping Weight: 6.4 pounds

Amazing Polymorph Plastic Easy to Mould Thermoplastic Endless Uses

Amazing Polymorph Plastic Easy to Mould Thermoplastic Endless Uses

Handbook of Engineering and Specialty Thermoplastics, Polyolefins and Styrenics (Wiley-Scrivener) (Volume 1) [Hardcover]

Book Description
Publication Date: June 8, 2010 | ISBN-10: 047062583X | ISBN-13: 978-0470625835 | Edition: Volume 1
Utilizes an encyclopedic approach to cover the developments in polyolefins and styrenics during the last decade

This book focuses on common types of polymers belonging to the class of polyolefins and styrenics. The text is arranged according to the chemical constitution of polymers and reviews the developments that have taken place in the last decade. A brief introduction to the polymer type is given and previous monographs and reviews dealing with the topic are listed for quick reference. The text continues with monomers, polymerization, fabrication techniques, properties, application, as well as safety issues.

Providing a rather encyclopedic approach to polyolefins and styrenics, The Handbook of Engineering and Specialty Thermoplastics:
* Presents a listing of suppliers and commercial grades
* Reviews current patent literature, essential for the engineer developing new products
* Contains as extensive tradenames index with information that is fairly unique
* Concludes with an index of acronyms
The Handbook of Engineering and Specialty Thermoplastics: Polyolefins and Styrenics provides a comprehensive reference for chemical engineers and offers advanced students with a textbook for use in courses on chemically biased plastics technology and polymer science.

Editorial Reviews
About the Author
Johannes Karl Fink, PhD is Professor of Macromolecular Chemistry at Montanuniversitãt, Loeben, Austria. His industry and academic career spans more than 30 years in the fields of polymers, and his research interests include characterization, flame retardancy, thermodynamics and degradation of polymers, pyrolysis, and adhesives. Professor Fink has published several books on physical chemistry and polymer science including A Concise Introduction to Additives for Thermoplastic Polymers (Wiley/Scrivener-2010).

Product Details
* Hardcover: 383 pages
* Publisher: Wiley-Scrivener; Volume 1 edition (June 8, 2010)
* Language: English
* ISBN-10: 047062583X
* ISBN-13: 978-0470625835
* Product Dimensions: 6.5 x 1 x 9.5 inches
* Shipping Weight: 1.6 pounds (View shipping rates and policies)

Do it Yourself Thermoplastic Molding

Thermoplastic molding is a method of creating objects using a mold and heated plastic. When the plastic is heated, it becomes soft and is capable of being formed into a wide variety of shapes. It can be used as an inexpensive way to create replacement parts for plastic components or durable and attractive art projects. You can build a thermoplastic molding rig at home designed around your kitchen stove and shop vac. This design allows you to tightly mold heated sheets of thermoplastic material to a premade form, allowing you to create multiple precise copies of thin plastic.

hings You'll Need

    *
      2-inch by 4-inch timber
    *
      Saw
    *
      3-inch wood screws
    *
      Drill
    *
      Plywood sheet
    *
      2-inch by 2-inch wood cube
    *
      2-foot by 2-foot pegboard sheet
    *
      Angled shop vac attachment
    *
      Small screws
    *
      Duct tape
    *
      Form
    *
      Coins
    *
      Shop vacuum cleaner
    *
      Thermoplastic sheets
    *
      Hobby knife
    *
      Stapler
    *
      Oven
    *
      Oven mitts
    *
      Pencil eraser
    *
      Sandpaper

Instructions

   1.
      Building the Molding Frame
          * 1

            Measure the inside of your oven. Cut four lengths of 2-inch by 4-inch timber long enough to make a rectangular frame that will fit inside your oven with a few inches of clearance on each side. Fasten these boards together using a pair of 3-inch wood screws in each corner.
          * 2

            Cut a square of plywood slightly larger than the bottom of your timber frame. Cut four lengths of plywood long enough to form the sides of a shallow box with the square of plywood as the bottom. The side pieces of the plywood box should be slightly taller than the nozzle of the angled attachment on your shop vac. The angled attachment needs to be fastened to the outside of the plywood box and maintain a good seal against the wood.


    * 3

      Drill a large hole in one of the plywood side pieces. Screw the plywood boards together into a shallow box using the wood screws. Attach a 2-inch by 2-inch cube of wood to the inside of the plywood box at the center. This will help to support the top of your box during vacuum forming. Cut a square of pegboard large enough to overlap the frame of the box on all sides. Attach it to the top of the box using wood screws.
    * 4

      Use small screws to fasten the angled attachment of the vacuum cleaner over the hole drilled in the side of the plywood box . Drive the screws through the lip of the angled attachment on all four sides to ensure a good seal. Seal all the seams of the plywood box and the seam between the angled attachment and the side of the box using duct tape.

Molding the Plastic

    * 5

      Place your form in the center of the pegboard on top of the plywood box. Put some coins under the edges of the form to allow the air to flow freely between the form and the pegboard. Attach your vacuum cleaner hose to the attachment on the side of the plywood box.
    * 6

      Cut a sheet of thermoplastic material to the size of your timber frame using a sharp hobby knife. Place the sheet over your timber frame and attach it to all sides of the frame using a stapler, placing the staples no more than an inch apart.
    * 7

      Place the timber frame in the oven with the plastic side up. Set the racks in the oven so that the plastic is about five inches away from the broiler. Set the broiler on high without closing the oven door. As soon as the plastic begins to sag in the center, press down on one corner with a pencil eraser. If the plastic is soft, remove it using a pair of oven mitts.
    * 8

      Place the frame on top of your form, plastic side down. Press gently until the sides of the frame are flush with the top of the box. Turn on the vacuum. Continue pressing down for 20 seconds until the plastic has hardened. Turn off the vacuum and lift the frame.
    * 9

      Remove the form by tapping one edge of the frame against the side of a counter until it falls out. Remove the plastic from the frame and trim away the edges using a sharp hobby knife. Sand the cut edges smooth using high-grit sandpaper.


Tips & Warnings

    *

      You can use almost any three-dimensional object as a form, as long as it cannot be damaged by contact with the hot plastic. You can also make your own object out of plaster, wood or urethane foam.
    *

      When the plastic comes out of the oven, it is hot, soft and sticky. Keep it away from your skin and clothes or you could be badly burned.
    *

      Have plenty of ventilation in your work area. The buildup of fumes from thermoplastic can be harmful in a confined area.
    *

      Don't leave the plastic under the broiler for too long. If it is overheated, the plastic melts completely and then burns.


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Thermoplastic Moulding Brion Experimental "Bollo"