Plastics Processing and Safety Issues. Foam Processing.

Plastics Processingand Safety Issues

Foam Processing

Nerf balls, invented by Reynolds Guyer and developed by Parker Brothers, are made from synthetic foam. Polyurethane material has CO₂ released into it during processing, creating the air pockets within the ball that make it lightweight, soft and pliable.

Foam Processing

To create the spongy foam material, NERF begins with a reaction between polyester and a diisocyanate.

Foam Processing

The air pockets in the foam come from the release of carbon dioxide during another reaction.

Foam Processing

Silicone Molds & Plastic Resins

Mold Casting

• Open mold

• Closed Mold

Mold Casting

• Low pressure– You can use flexible molds– It is easy to get undercuts and intricate details

that are more difficult in some of the other process

http://www.b9robotresource.com/molding1.htm

Silicone Molds & Plastic Resins

1. The process involves heating a plastic sheet made of a thermoplastic until soft.

2. The softened sheet is draped over a mold.

3. A vacuum sucks the sheet into/onto the mold.

4. The newly shaped sheet is taken off the mold.

Vacuum Thermoforming

Vacuum Thermoforming

Sheet of plastic Heated (soft) Molded using a shaped die

Vacuum Thermoforming

Advantages:• Vacuum forming uses low pressures so only

relatively low cost equipment/components are required.

• Low pressures mean that moulds can be made of inexpensive materials and in a short time.. 

Vacuum Thermoforming

Disadvantages:• More complicated machines and moulds are

needed for automatic or continuous production of ‘high volume’ items, eg. disposable cups and sandwich packs.

• The vacuum forming process starts with a flat plastic sheet and there may be a need for a second process to trim the moulded end product. This means more expense to obtain additional equipment.

Vacuum Thermoforming

These processes use composite materials – plastics made up of polymers and added material such as fiber glass or graphite fiber

Lay up processes

Graphite Fiber

Fiber Glass

Uses of Composites

Graphite Snowboard

Composite Bicycle

Laminated Fiberglass Bow

Dodge Viper

Front grill of an Automobile Different parts of an airplane

Uses of Composites

Hand Lay-up

Resins are impregnated by hand into fibres which are in the form of woven, knitted, stitched or bonded fabrics. Laminates are left to cure under standard atmospheric conditions.

Laminated Composites

Laminated composites can be thought of as sheets of continuous fiber composites laminated such that each layer has the fiber oriented in a given direction.

Wet lay up

Spray lay up

Other Types of Processes

• Injection molding• Blow molding

– Injection blow molding

• Extrusion• Rotational molding• And many others!

Injection Molding - Probably the most common, most important, most economical process

Injection Molding

Blow Molding

• Air pressure is used to inflate soft plastic into a mold

cavity

• Material limited to: thermoplastics

• Accomplished in two steps:

1. Fabrication of a starting tube, called a: parison

2. Inflation of the tube to desired final shape

• Two methods:

1. Extrusion blow molding

2. Injection blow molding

Injection Blow Molding

• Preform is injection molded• Preform is placed in the blow

molding machine• Preform is heated• Preform is pressurized• Part is removed

PET Preform

Injection Blow Molding

Preforms Placed in Mold

Formed Bottles

Safety Issues

• Mechanical and pressure dangers• Thermal dangers• Eye protection (plastics are brittle)• Proper tools• Workable safety rules• Compliance with legal rules and guidelines• Gloves• Loose clothing• Emergency procedures• Proper training• Cleanliness

Safety First

Preventable Accidents

Preventable Accidents

Preventable Accidents