PTFE bellows are used, for example, as compensating elements between engineered parts. By specifically using different fold geometries, any combination of properties can be achieved as required—for example, high flexibility or compressive strength.
Teflon PTFE lining high viscosity in the gel state (it does not truly melt) prevents it from being processed conventionally in extruders or injection molding. PTFE tubing is therefore dry molded or extruded in hydraulic extruders with (paste extrusion) or without (ram extrusion) lubricants. Paste extrusion of PTFE yields flexible tubing. However, it occurs in a batch process and thus long continuous lengths are limited to the batch size, unlike the melt-processible fluoropolymers FEP, PFA and ETFE.
A ram extruder is an extruder where, instead of extrusion screw, a ram or plunger is used . The ram extruder was the earliest extruder to be used in the plastics industry. This typical process is applied for producing profiles, sleeves, rod, block, tubing, lining sheet bars, etc. The ram extrusion process is very effective for specific materials like PTFE which are not extruded successfully using screw extruder.