Selecting Polypropylene Block Copolymers for Cold Temperature Automotive Applications
Selecting polypropylene block copolymers for cold automotive parts depends on balancing ethylene-propylene rubber phase dispersion with matrix melt flow rate.
Cold Drop Failure
Meaning
Moulding defects occur during the initial stages of injection when unheated polymer slugs from the nozzle enter the mold cavity. A cold drop failure describes the fracture or cosmetic blemish caused by un-melted resin particles embedded within a molded component. It governs process validation during cold runner tool startup and stops at thermal defect identification, leaving mechanical tool fixes and nozzle heater controls to mold maintenance procedures.
Thermal Process
Nozzle tip solidification creates cold slugs when temperature controls fail to maintain melt uniformity between cycles. Proper sprue bushing contact prevents heat loss into cooled mold plates.
Defect Geometry
Unmelted resin inclusions create localized stress risers under dynamic loading conditions. Solidified boundaries do not fuse with the surrounding melt stream, forming weak mechanical zones inside the part structure. Impact forces cause immediate crack initiation along the un-fused interface created by cold drop failure.
Part wall thickness amplifies stress concentrations when large cold slugs sink below surface layers. Molders clear sprue wells to capture stagnant material before it reaches critical wall sections.
Scrap Consequence
Uncontrolled nozzle droop increases scrap rates during automated production runs. Defective parts fail quality inspections due to surface visual flaws and premature mechanical fractures. Unresolved cold drop failure causes costly press downtime during high volume molding operations.