Elastic recovery cracks appear in the PTFE preform

After demolding, the blank rebounds along the pressing direction, producing transverse cracks. Cracks may appear on the surface or inside of the product, and in severe cases penetrate the entire wall thickness, mostly exposed during demolding or post-processing.

(1) Raw material characteristic aspect: The elastic recovery force of PTFE powder after pressurization is much greater than the cohesive force of the blank; the physical characteristics of the powder directly affect the preforming and sintering quality. (2) Process speed aspect: Excessively fast demolding speed; the speed parameter affects the synchronization of the material flow state and the reaction process. (3) Material aspect: Insufficient material toughness or excessively high crosslinking density leads to increased brittleness. (4) Process aspect: Excessively fast cooling rate generates thermal stress that exceeds the strength limit of the material. (5) Design aspect: Stress concentration at sharp corners or abrupt wall thickness changes.

(1) Implementation measure: Fully hold pressure after pressurization to relax the elastic recovery stress, formulate specific operation plans in combination with actual production conditions, and verify the implementation effect. (2) Implementation measure: Slowly release the pressure to gradually reduce the stress, formulate specific operation plans in combination with actual production conditions, and verify the implementation effect. (3) Implementation measure: Use a support device after demolding to prevent the blank from freely expanding., formulate specific operation plans in combination with actual production conditions, and verify the implementation effect. (4) Preventive measure: Establish a sound process control standard and quality inspection system, and regularly review process data for continuous optimization.

The essence of cracking is that the internal stress exceeds the strength limit of the material, and it is necessary to proceed from two aspects: reducing stress concentration and improving material toughness.