1. UNIT 16: Extrusion and Injection moulding Manufacturing Engineering Unit 16 Copyright © 2012 MDIS. All rights reserved. 1

2. 6-2Unit 16 Copyright © 2012 MDIS. All rights reserved. Extrusion of Polymers A polymer stock is fed to a hopper. This feeds the main extruder of the machine. Here a rotating screw with transports the material beads thru' the heated barrel. The barrel is externally heated using band heaters in controlled temperature profiles so that the polymer softens. The screw of the extruder is a variable depth, variable pitch screw. It pushes the materials along the axis of the barrel in a way similar to the Archimedes screw,

3. 6-3Unit 16 Copyright © 2012 MDIS. All rights reserved. it causes a compression of the plastic. This compression also makes the by the time it reaches the extruder die. The melt is pushed through the die which is designed to provide the correct shape of the extruded The die is created from special tool steels, and is also heated. It contains special flow control zones and paths that lead to a uniform wall thickness in the final profile. Downstream of the extruder is the cooling tank, and the pulling apparatus, to draw the continuously extruded profiles through the cooling tank to the winding or cutting section. The cutter is a timed device that travels along with the extruded material to cut to precise lengths as desired by the manufacture.

4. Injection moulding The hopper feeds the injection screw, which is similar to the extruder screw in design. The barrel of the injection moulding machine is divided into several heating zones with a temperature profile that causes the melting. 30 percent of the heat for the melting is provided by the shearing forces from the screw rotation. Once the melt reaches the end of the barrel, it enters the metering zone where a controlled volume of the melt reaches the injection zone. The screw is pushed towards the nozzle of the barrel, shooting the melt at tremendous pressure into the die attached to the mold platten. 6-4Unit 16 Copyright © 2012 MDIS. All rights reserved.

5. The molding on this side now involves a sequence of operations like mold closing, injection, cooling, mold opening and part ejection. Mold open and close are achieved by the moving platten which is hydraulically operated on the other side of the machine. Ejected parts are collected in a chute below the plattens and can be moved to a conveyor for further manufacturing processes. 6-5Unit 16 Copyright © 2012 MDIS. All rights reserved.