Meaning
Steel cavity structures used for moulding engineering thermoplastics require specific design adjustments to account for the semi-crystalline nature of the resin. Specialized polyamide gear tooling incorporates precise shrinkage allowances to produce gears that meet tight tolerance specifications after they cool. This equipment often includes advanced thermal management systems to ensure even cooling across the tooth profile.
Proper design prevents the formation of voids or internal stresses that weaken the gear teeth.
Thermal Management
Hot oil or pressurized water systems maintain the mould at the high temperatures required for nylon crystallization. High tool temperatures promote a more stable and complete crystal structure. This stability prevents the part from shrinking further after it is removed from the tool.
Venting Strategy
Rapid injection of molten nylon can trap air at the tips of the gear teeth, leading to burn marks or incomplete filling. Deep and wide vents are necessary to allow gas to escape while preventing the thin resin from flashing. Placing these vents at the end of the flow path ensures that the material reaches the furthest edges of the gear geometry.
Failure to vent properly results in weak tooth tips that can fail under torque. Designers often use porous steel inserts to provide extra venting without creating witness marks.
Wear Resistance
Glass-filled nylons are highly abrasive and can erode the sharp edges of a gear cavity over time. Toolmakers select hardened steels or apply specialized coatings to protect the fine details of the tooth profile.
