Both extruder and injection molding machine plastify plastics and process them into certain shapes. Althogh, they have similar functions, their differences still exists.
For structure, screw and barrel is used in both machines to plastify and convey plastics. However, for extruder, the screw has bigger diameter and L/D ratio.
For procedure, extruder continuously extrude plastics through die head to form products, for example, plastic pipes, sheet/profiles and bars. Injection molding machine is not continuously working. Plastics will be injected into closed mold cavity. When the cavity is filled, machine will stop working and plastics in mold will be cooled and shaped. The machine will work again after shaped plastic taken out from opening mold. The products produced by injection molding machine have relatively complex structure, for example, plastic cup, pot and shell.
Both machines can process most of plastics. The difference between materials used is that material used by extruder can have higher viscosity. The reason is injection molding machine requires plastics flowing inside mold and the flow channel inside mold is usually curved and narrow.
When starting both machines, current will be 3 to 4 times or maximum 6 to 7 times as current when machines operate normally.
These are general differences and similarities between extruder and mold injection machine.