Advanced Thermoforming, 2nd Edition

Chapter 8Production of Refrigerator Liners

Written in cooperation with Rudi Salmang, Terneuzen, The Netherlands, and Kurt Brunner, Kiefel GmbH, Freilassing, Germany

Thermoforming offers significant advantages for the manufacture of large formed parts. Just based on the costs of forming tools, thermoforming is superior to injection molding. While most large‐size formed parts are vacuum formed, there is also the possibility to use compressed air or a combination of vacuum and compressed air. In this chapter the manufacturing of plastic refrigerator inner liners is discussed.

The refrigerator body consists of an inner liner (Figure 8.1), polyurethane foam, and a metal outer case. Approximately 15 years ago inner liners consisting of steel sheets were still being used; worldwide these products are nowadays almost exclusively manufactured in plastic. For the manufacturing of refrigerator inner liners mainly PS‐HI and ABS are used.

8.1 HIGH‐IMPACT POLYSTYRENE (PS‐HI)

Polystyrene and styrene copolymers are noted for their high tensile strength and optical clarity, but these polymers are brittle under many normal use conditions. Some general‐purpose polystyrene grades (PS‐GP) cannot be unwound from the reel after being extruded to film. The material is also so brittle that it cracks after being penetrated with the chain pins of the thermoformer’s transport system. A high‐speed blow at temperatures below glass‐transition temperature causes catastrophic failure without significant ...