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ptfe sintering temperature
The lengthy PTFE sintering cycle has been a longstanding constraint on PTFE fabrication productivity. Moreover, the sintering heat treatment also consumes a considerable amount of energy and thus contributes to substantial production costs. Shortening the sintering cycle has been a consistent industrial desire, and improving utilization of sintering oven capacity has become a critical need for industry.
This article demonstrates that by changing the sintering temperature, the deformation of a sinter-molded PTFE component can be substantially reduced during the sintering heat treatment. It is shown that different strain mechanisms cause the sintering deformation: thermal expansion during heating, melting and void closure at high temperatures, and crystallisation and thermal contraction during cooling. It is also shown that the sintering deformation of an isotropic green material can be simulated with an effective plasticity model.
The sintering cycle of the present invention provides for controlled cooling of the sinter-molded PTFE article after the end of the oven segment, so that the specific gravity and physical properties that are primarily determined by the level of crystallinity develop at acceptably uniform values over the entire surface of the article during the final phase of cooling. The control of the cooling rate is achieved by utilizing an insulation system that is sufficiently dense to effectively limit the sintering temperature to a value at which the oven segment of the process ends, without chilling the sinter-molded PTFE. The insulating density should be a minimum of 295 g/m3, but preferably less than this.