Surface Melt Fracture Onset Limits in Polyolefin Profile Extrusion
Surface melt fracture limits in polyolefin profile extrusion are governed by critical wall shear stress thresholds between 0.08 and 0.14 MPa at the die exit.
Regrind Ratio Limit
Meaning
Plastic injection molding and extrusion processes establish a maximum percentage of recycled scrap material that can be blended with virgin resin. This constraint, known as the regrind ratio limit, ensures that the physical properties of the plastic remain within acceptable tolerances after multiple heating cycles. It is a critical specification in high-performance manufacturing.
Processing Restriction
Materials departments calculate the allowable mix of regrind to prevent thermal degradation of the polymer chains. For instance, a regrind ratio limit of twenty percent means that any given batch must contain at least eighty percent virgin material. This balance preserves the mechanical integrity of the final part.
Quality Consequence
Exceeding this limit can cause a severe decline in the impact strength, tensile strength, and color stability of the molded component. When the polymer chains are shortened by repeated processing, the plastic becomes brittle and prone to cracking under load. This degradation can lead to field failures in structural applications, which cost the company in liability and returns, while damaging relations with major clients.
Audit Procedure
Production logs and batch records are audited to verify that the blending ratios are maintained during each run. These audits compare the weight of regrind consumed against the total virgin resin issued to the line. Correct documentation is required to maintain automotive and medical grade certifications.