MACHINING TIPS: Grinding of Plastics with Refrigeration Assistance

Grinding plastics can pose a problem due to the generation of heat and the subsequent softening of the plastic, particularly if the material is thin-walled or overly flexible. As the plastic softens from the heat, the grinding wheel will clog and load up generating more friction and then melting at the part surface, resulting in very poor surface finish and a grinding wheel that will require significant dressing to clear the clogged material. Freezing the plastic prior to grinding can alleviate the overheating by making the material harder and more brittle as well as cool. Parts may be kept in a chest freezer near the grinding machine and then fixtured and ground. Engineered parts may be limited in size and shape to fit inside commercial chest freezers. Repeated freezing may be necessary where the stock removal is high. In some very specialized situations cryogenic fluids may be applied to the grinding zone to provide a more consistent cooling of the interface between the grinding wheel and the plastic surface. The proper use of a cryogenic grinding fluid, however, can be very expensive to implement and control. Having parts kept in a chest freezer is a far less expensive option.

*Some plastics can experience a significant change in size due to the temperature gradient from the freezer to ambient temperature; thinner parts may become brittle and crack so it is important to be aware of these effects prior to grinding with this method.

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JIM HEBEL
Application Development and Technical Service Manager

 

MACHINING TIPS: Critical Aspects to Grinding - Surface Finishes
MACHINING TIPS: Machine Set-Up for Grinding
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