Extrusion

What is extrusion

the process which metal or other material is forced through series of dies.

what materials are used for extrusion

PE, PP, PS, PVC, Fluropolymers, polyamide, Polyester polyurethane.

what is the difference between injection molded plastics

it has a higher melt viscosity

what is extrusion compounding

process used to blend plastics with additives or plastics

what is profile extrusion

softened plastics are forced through a die directly into cool water where the product solidifies

pipe extrusion

plastic is forced through a die with a mandrel in the middle to produced open section

profile and pipe extrusion tolerance

is looser than other molding operations

advantages of profile and pipe extrusion

short lead times, relatively small cooling cost, inexpensive process, product combinations possible

Disadvantages of profile and pipe extrusion

design possabilites due to the linear nature of the process

Filament Extrusion process

similar to profile extrusion, dies usually contains multiple orifices, the orifices are called spinnerets

how many types of filament extrusion process are there

3

melt spinning

melted and forced through a spinneret

what material is used for melt spinning

PP, PE, PA, Polyester

solvent spinning

dissolved in solvent then force through a spinneret, it passes through stream of hot air which dissolves solvent and leaves fibers

what material is used for solvent spinning

acetates and acrylics

wet spinning

dissolved in chemicals and forced through a spinneret, material goes through a coagulating bath with gels plastic

what material is used for wet spinning

some acrylics

sheet/film extrusion definitions

sheet thickness > 0.25mm

film thickness <= 0.25mm

process for sheet/film extrusion

it is extruded through a die either shaped as a coat hanger or a T- shaped. then goes through a series of rollers to get proper shaped.

Calendering

thermoplastic material formed with heated rollers

disadvantages of Calendering

the rollers are very expensive

blown film extrusion process

1. Plastic melt is extruded through a annular die slit, usually vertically
2. Air is introduced through the die to blow it up (like a balloon)
3. high speed air ring on top and blows air to cool it.
4. The tube of film contiunes upwards continually cooling until it passes through the nip rolls where the tube is flattened this is known as lay flat tube of film
5. it is taken down the extrusion tower via rollers
6. the lay flat is either kept as is or is the edges are slit off make film sheets
7. if kept as is they are made into bags by sealing across the width

what are the advantages of blown film extrusion

Can produce tubing in a single operation, can regulate of film width and thickness by controlling the air bubble, eliminate end effects (has uniform temperature unlike flat die film extrusion, capability of biaxial orientation, very high productivity

what materials can be used for blown film extrusion

PE (HDPE, LDPE, LLDPE) most commonly used, PP, PA, EVOH (Ethyl Vinyl Alcohol)

Extrusion Blow Molding Process

1. melted polymer flows through a die to emerge as a hollow usually circular pipe section
2. when the parison reached a sufficient length a hollow mold is closed around it the mold, the bottom end is seal the top is cut off with a knife.
3. the mold is moved sideways to a second position where air inflates the parison to the mold shape
4. after cooling the mold is opened and the final article is ejected

Extrusion Coating

extrusion coating is the application of a thin film of molten plastic to a substrate

types of substrates

paper, fabric, metal foil, and wire