Extrusion Plastics 001 Profile Extrusion

Extrusion Plastics 001 Introduction – Extrusion is a process that can make long parts with a constant cross-section. Everything from pipes to weather-stripping can be made with this process. For the kinds of parts, no other process can create these parts as cheaply as Extrusion.

Extrusion Plastics 001 To Read – Review Chapter 6.1, 6.1.2, and before beginning the lesson. To Do – Take Quiz 7 after this lesson and before beginning Module 6 Lesson 3.

Extrusion Plastics 001 Topics – Profile Extrusion – Common Materials – Processing Parameters – Film and Sheet Extrusion – Competing Processes – Future Development

Extrusion Plastics 001 Introduction – This process can make long, 2D geometry. – Parts can be made solid or hollow. – Multiple materials can be co-extruded together (rigid material with softer seal). – Process is continuous and fast. Individual parts must be cut from continuous feed. Useful for producing roll-stock.

Extrusion Plastics 001 Product Range – Min: < inches fiber – Max: 30 feet wide sheet 2 inch thick

Extrusion Plastics 001 Areas of Use – Window Profiles – Fibers – Pipe – Packaging Sheet/Film Bags

Extrusion Plastics 001

Extrusion Plastics 001 Basic Process – The material is melted in the extruder. The molten polymer is pushed from the extruder through a die, whose shape it takes on. – The molten polymer exiting the die must be cooled. It is usually pulled through a water bath. – A sizing die or shaping fingers are used to hold the part’s dimensions as it cools.

Extrusion Plastics 001 Sizing dies are used to control the shape of the molten polymer as it enters the cooling bath. If there were no sizing die, the molten polymer will shrink uncontrollably before it solidifies. Sizing dies are usually made of aluminum or brass and take the shape of the part being extruded.

Extrusion Plastics 001 Basic Process – A puller is used to pull the polymer extrudate through the cooling tank after it leaves the die. It usually pulls faster than the velocity of the polymer exiting the die. This causes orientation of the polymer and reduces the part’s size. – Once solidified, the extrudate is usually rolled or cut into individual parts and stacked.

Extrusion Plastics 001 Extruder Sizing Die Water Tank Puller

Extrusion Plastics 001 2D Shape

Extrusion Plastics 001 Sheet – When rolled, the sheet has permanent deformation. It is generally greater than inches in thickness. There is single direction orientation because of the puller. Film – When rolled, the film has no permanent deformation. It is usually less than inches in thickness. It is biaxially orientated from the puller and stretching perpendicular to flow.

Extrusion Plastics 001 Thickness – – 0.50 inches Widths – Up to 36 feet Lengths – Virtually unlimited

Extrusion Plastics 001 A coat-hanger die is attached to the extruder, which is positioned horizontally. The molten polymer is pulled into a frame that grabs the side of the film with hooks and allows it to start cooling. The hooks are set on a track and are allowed to pull the sides of the film to make it wider. At the same time, the film is being pulled faster than the film exits the die.

Extrusion Plastics 001 Coat-Hanger Die & Chill Rolls

Extrusion Plastics 001 Bi-Axially Oriented Film

Extrusion Plastics 001 A tubular die is attached to the extruder, which is positioned vertically. A hollow tube of plastic is extruded and blown upwards, expanding the diameter of the tube as it is pulled upward. A frame at the top of the machine starts to flatten out the tube as it is pulled back down the side of the tower. A set of rollers at the top closes the tube and seals in the air. The film is put on rolls.

Extrusion Plastics 001

Extrusion Plastics 001 Co-extrusion allows different materials to be extruded together. – An elastomer can be extruded over a rigid material creating a self-seal. – Multiple colors can be co-extruded together. – Multiple types of materials can be combined to maximize properties (e.g. a barrier layer, a layer for strength or chemical resistance, and an outer layer for aesthetics).

Extrusion Plastics 001 Materials for extrusion must possess good melt strength so the puller can keep tension on the molten polymer as it exits the die without causing breakage. – Lower barrel temperatures than Injection Molding are used to increase viscosity. – Wide Spec/Higher Molecular Weight grades are used to give the molten polymer more strength.

Extrusion Plastics 001 Common Materials – Polyethylene Tubing

Extrusion Plastics 001 Common Materials – PVC Pipes Grocery Store Signage Siding Tubing Medical Supplies

Extrusion Plastics 001 Common Materials – Polypropylene Tubes

Extrusion Plastics 001 Common Materials – Elastomers Shopping Cart Bumpers

Extrusion Plastics 001 Key Processing Parameters – Melt Temperature – Changes the viscosity of the material. – Extruder Speed – Determines the speed that the part is made. – Cooling Temperature – Determines how quickly the part is cooled. – Puller Speed – It is used to size the part. The puller pulls faster than the extruder.

Extrusion Plastics 001 Die Swell – As the polymer is moved through the screw and pushed through the die, the polymer is compressed. The land, which is the die section with the actual geometry, is usually short. The polymer is squeezed and oriented as it goes through the land. Since it is not in this section very long, the polymer chains do not have enough time to fully realign themselves to this new orientation.

Extrusion Plastics 001 Die Swell – When the polymer exits the die, it tries to recover some of its original orientation and it swells in size. If the land is long enough, the polymer chains have more time to realign to the new orientation and do not swell as much.

Extrusion Plastics 001 Advantages – Because the process is continuous, it is possible to have high production rates. – Compared to injection molding, there is low tooling cost. – The continuous nature of extrusion makes it the lowest cost conversion process for plastics.

Extrusion Plastics 001 Disadvantages – Since the parts are continuously formed, secondary operations are needed to cut parts to size. Any holes or cuts have to be put in after cooling or after the parts are cut to size. – Any changes in viscosity will change the dimensions of the part. It takes constant checking to keep parts in tolerance.

Extrusion Plastics 001 Disadvantages – It takes a long time to debug the die to make parts within tolerance. Once the die is debugged, the output may be limited. Faster speeds would change viscosity and potentially put the parts out of tolerance. – Surface defects can be caused by dirt or scratches on the die. The velocity of the polymer and die temperatures sometimes create surface defects.

Extrusion Plastics 001 Competing Processes – Injection Molding To create some of the complex geometry in injection molding, assembly would be needed and the mold costs would be very expensive.

Extrusion Plastics 001 Future Development – Architectural elements such as decking or fencing are growing stronger. – The use of CAE analysis software to design dies is slowly growing.