Processing Thermoplastics

HideShow resource information

1.1 Blown Film

  • The process involves extrusion of a plastic through a circular die, followed by "bubble-like" expansion.
  • Mainly Polyethylenes (HDPE, LDPE and LLDPE) but a wide variety of other materials can be used as blends with these resins or as single layers in a multi-layer film structure. these include PP, PA and EVOH
  • Industry packaging (e.g. shrink film, stretch film, bag film or container liners), Consumer packaging (e.g. packaging film for frozen products, shrink film for transport packaging, food wrap film, packaging bags, or form, fill and seal packaging film), Laminating film (e.g. laminating of aluminium or paper used for packaging for example milk or coffee), Barrier film, films for the packaging of medical products, Agricultural film (e.g. greenhouse film, crop forcing film, silage film, silage stretch film).
1 of 16

1.2 Extrusion Blow Moulding

The blow moulding machine is based on a standard extruder barrel and screw assembly to plasticise the polymer. The molten polymer is led through a right angle and through a die to emerge as a hollow (usually circular) pipe section called a parison.

click here to view a large image

Typical Materials Used:
Polypropylene (PP), Polyethylene (PE), Polyethylene - Terephthalate (PET) and Polyvinyl chloride (PVC)

Typical Products Produced:
Bottles and containers, Automotive fuel tanks, Venting ducts, Watering cans and Boat fenders etc

2 of 16

1.3 Extrusion Profiles & Sheet

Along with Injection moulding, Pro-file Extrusion of plastics materials is a widely used method of forming plastics materials. The Plastic raw material is both melted and trav-ersed along by the action of heated rotary screws. It is a continuous process and is thus able to manu-facture long lengths of a product. This is ideal for such applications as pipes and gaskets.  However very often the continuous extrusion is cut into application lengths

Typical Materials Used:
HDPE, PVC and and PTFE filled PVC

Typical Products Produced:
Land Drainage Tubing, Animal Feeding Troughs, Cable Harness, Door Seals, Light Diffusers, Electrical Conduit and Cable Protector, Rainwater Pipes and Guttering, Facia & Soffit Sections, Curtain Track, Fridge Seals, Edge Trim, Caravan Window Surrounds, Garden Fence Posts & Decking, Blood Drip Tubes & Catheter Tubes, Dip Tubes, Gas Pipes, Water Pipes, Soil Pipes and Window, Door and Conservatory Sections

3 of 16

1.4 Injection Blow Moulding

1.4 Injection Blow Moulding

Injection blow moulding is used for the Production of hollow objects in large quantities. The main applications are bottles, jars and other containers. The Injection blow moulding process produces bottles of superior visual and dimensional quality compared to extrusion blow moulding. The process is ideal for both narrow and wide-mouthed containers and produces them fully finished with no flash.

click here to view a large image  

Typical Materials Used:
Polyethylene (Low Density) LDPE, (LLDPE), Polypropylene (PP), Polyethylene - Terephthalate (PET), Polyvinyl chloride (PVC), Polyethylene (High Density) HDPE)

Typical Products Produced:
Plastic Bottles

4 of 16

1.6 Injection Moulding (Gas Assisted)

Developments over the past years in Gas Assisted Moulding or (Gas Assisted Molding to use the US spelling or Gas Injection Moulding being a common reference term) have resulted in advances in the way in which injection moulded components are manufactured. Enhanced quality, reduced cycle times and component weight reductions can be achieved by the process.

click here to view a large image

Typical Materials Used:

Typical Products Produced:
Power-tool housing, Telephone

5 of 16

1.7 Injection Stretch Blow Moulding

Injection stretch blow moulding is used for the production of high quality containers.

click here to view a large image

Typical Materials Used:
Polyethylene - Terephthalate (PET)

Typical Products Produced:
Carbonated and soft drink bottles, Cooking oil containers, Agrochemical containers Health and oral hygiene products and Bathroom and toiletry products

6 of 16

1.8 Insert Moulding

Inserts can either be incorporated at the time of the moulding process, or be inserted as a post moulding operation. When incorporated as part of the moulding process, the inserts can either be loaded by robot assistance or by the process operator. If the inserts are applied as a post moulding operation, they can usually be applied any time after the moulding process. In some cases, they are inserted as part of a series of post moulding operations. This helping to minimize the actual cost of insertion. The fundamentals of process speed (and economics), and process repetition must be borne in mind when making the decision when to apply the insert. It is not good practice to allow the cycle time to vary from shot to shot; this can have an adverse effect on the quality

7 of 16

1.9 Machining of Plastics

Where a plastics component is specified and the numbers to be used are not large, then machining the component becomes more economical.

8 of 16

1.10 Moulding Expanded Polypropylene (EPP)

EPP is a highly versatile closed-cell bead foam that provides a unique range of properties, including outstanding energy absorption, multiple impact resistance, thermal insulation, buoyancy, water and chemical resistance, exceptionally high strength to weight ratio and 100% recyclability. EPP can be made in a wide range of densities, from 15 to 200 grams per litre, which are transformed by moulding into densities ranging from 18 to 260 grams per litre. Individual beads are fused into final product form by the steamchest moulding process resulting in a strong and lightweight shape.

9 of 16

1.11 Moulding Expanded Polystyrene (EPS)

Expanded polystyrene (EPS) is used for the production of a number of applications. However its major application is as a protective packaging for consumer electronic products and white goods. Its excellent thermal insulation and mechanical protection properties make it ideal to package fish and other foodstuffs. EPS also has applications in horticulture as seed trays. The outstanding shock absorbency of expanded polystyrene packaging ensures the protection of a broad range of products.

10 of 16

1.12 Process Cooling

The necessity to cool or chill plastics processing machinery is mainly related to thermoplastic materials. At room temperature thermoplastic materials (polypropylene, nylon and PET etc) are solid. In order to shape them they must first be heated to their molten temperature. When molten, they can then be manipulated (injection moulded, extruded etc) to a new shape. When formed to their new shape they must then be cooled to solidify them. Considerable amounts of heat energy have to be extracted from the material, the tooling and the machinery that is doing the forming.

11 of 16

1.13 Rotational Moulding

Rotational moulding (often referred to as Rotamoulding or Rotomoulding) is a process used for producing hollow plastic products. By using additional post-moulding operations, complex components can be produced enabling the process to compete effectively with other moulding and extrusion practices.

click here to view a large image

Rotational moulding differs from other processing methods in that the heating, melting, shaping, and cooling stages all occur after the polymer is placed in the mould, therefore no external pressure is applied during forming.

This provides the following advantages Economically produced large products, Minimum design constraints, Stress-free products, No polymer weld lines and Comparatively low mould costs.

12 of 16

1.14 Structural Foam

Structural Foam is a term commonly used to describe thermoplastic injection moulding components made by the injection moulding process which have a cellular core. A cellular plastic is one in which the outer surface is denser than the inner layers. The core of the moulding is of a honeycomb nature and less dense than the outer surface. The combination results in a moulding of a high stiffness ratio compared with non-structural foam (compact) mouldings.

13 of 16

1.15 Thermoforming

Thermoforming has close similarities with Vacuum Forming except that greater use is made of air pressure and plug assisted forming of the softened sheet. The process is invariably automated and faster cycle times are achieved than in the Vacuum Forming process. Only thermoplastics sheet can be processed by this method.

14 of 16

1.16 Vacuum Forming

Thermoforming is one of the oldest and most common methods of processing plastic materials. Vacuum formed products are all around us and play a major part in our daily lives. The process involves heating a plastic sheet until soft and then draping it over a mould. A vacuum is applied sucking the sheet into the mould. The sheet is then ejected from the mould. In its advanced form, the vacuum forming process utilizes sophisticated pneumatic, hydraulic and heat controls thus enabling higher production speeds and more detailed vacuum formed applications.

15 of 16

1.17 Other Extrusion Processes

Extrusion of Cast Film
Description: From a silt die melt is fed onto a roll or band to produce thin film.
Notable Points: High gloss finish on very thin film.

Calendering of Thin Sheet/Film
Description: Production of precision thin sheet/film by passing through a series of rolls.
Applications: Decorative sheet for flooring. Protective sheet. Stretch wrap film.
Notable Points: Exclusively for long runs.

Description: Production of sheet with layers of different materials.
Applications: Packaging, refrigerator door liners, outdoor applications.
Notable Points: Sheet has improved balance of properties.

16 of 16


No comments have yet been made

Similar Engineering resources:

See all Engineering resources »See all Processing Thermoplastics resources »