Use of Gear Pump in Extrusion of Plastics

A gear pump is a type of positive displacement pump. It displaces a known quantity of liquid -- in this case, molten plastic or melt -- with each revolution, by trapping it between the pumping elements and the stationary casing.

Gears

In the process of plastic extrusion, gear pumps are located between the extruder and a forming device, known as a die. Each pump has two gears, a drive gear and an idler gear, which rotate in opposite directions to convey the molten plastic.

Bearings

The four bearings -- one at each end of each shaft -- are lubricated by molten plastic during the extrusion process. Gear pumps should therefore never be operated without molten plastic inside because this damages the bearings and the pump.

Heat

A gear pump must be heated to prevent plastic polymer material from solidifying inside it at the start of the extrusion process, or if the process is interrupted for any reason. Typically, the majority of the heat is generated by the rotating gears to minimize the amount of external heating required.

References

• "Concise Encyclopedia of Plastics"; Donald V. Rosato, Marlene G. Rosato, Dominick V. Rosato; 2000
• "Extrusion: The Definitive Processing Guide and Handbook"; Harold F. Giles, John R. Wagner, Eldridge M. Mount; 2005