Cooling cracks generated inside the product

Cracks are generated inside the product during the cooling process. 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) Temperature parameter aspect: Excessively fast cooling rate causes a large temperature gradient between the core and the surface of the product, generating thermal stress; temperature deviations directly affect the physical and chemical state of the material and the reaction process. (2) Crystallization behavior aspect: Stress caused by volume change of material crystallization phase transition; crystallinity changes affect the mechanical properties and dimensional stability of the product. (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) Parameter adjustment: Reduce the cooling rate to decrease the temperature gradient; note that after cooling, it is still necessary to ensure that the material is fully reacted or melted, adjust step by step and observe the effect. (2) Implementation measure: Set a holding platform in the phase transition temperature range of the material (PTFE 310-327℃) to release stress., formulate specific operation plans in combination with actual production conditions, and verify the implementation effect. (3) Design improvement: Avoid sharp corners and abrupt wall thickness changes, and increase the fillet radius to reduce stress concentration. (4) Material modification: Add toughening agents or adopt flexible segment resin systems to improve material toughness. (5) 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.