How to Avoid Hot Runner Shear Overheating of Melt

In hot runner injection molding, melt shear overheating is an undetectable quality issue. Due to violent shear friction during high-speed flow, the plastic melt produces an instantaneous high temperature that is significantly higher than the set process temperature. This causes local material decomposition, discoloration, and a decline in performance, which must be managed by combining temperature control and process optimization.

Optimize the smoothness of the hot runner's internal flow channel first. Polish the inner wall of the flow channel on a regular basis to keep it smooth and free of burrs and carbon deposition, lower the degree of friction and flow resistance as melt goes through, and significantly lessen the production of shear heat. Design the flow channel transition radian sensibly to prevent right-angle dead corners, which can easily result in violent extrusion and melt shearing.

Second, match the basic temperature of the hot runner in a reasonable manner. Reduce the initial temperature foundation of the melt, set aside temperature buffer space for shear instantaneous temperature rise, and appropriately lower the manifold base temperature within the safe range of raw materials. Assist with multi-point thermocouple real-time monitoring to guaranty that the total basic temperature won't be too high.

Third, maximize the distribution of flow rate and injection speed. Avoid prolonged use of ultrahigh uniform injection speeds. Reduce strong shear friction, regulate instantaneous shear temperature rise within the safe range of materials, use segmented speed adjustment, and slow down the flow rate at narrow flow channels and gate places.

Fourth, regulate the residence time of hot runner materials. The melt's thermal stability will be diminished by an extended retention period, increasing its susceptibility to shear heat and facilitating deterioration. To ensure that fresh melt is constantly circulating during intermittent manufacturing, create a set material discharge cycle.

Additionally, avoid heat concentration and temperature surges by choosing hot runner special alloy flow channel materials with strong thermal conductivity and promptly conducting away local shear collected heat. Melt shear overheating may be successfully prevented and the forming quality and physical characteristics of plastic parts can be completely guarantyd by integrating structure optimization, temperature exact control, and process matching.