Analysis of Cold Material Issues in Hot Runner Processing of TPE Elastomers

Hot runner molds are molds that use external heating devices to keep the melt in the runner from solidifying. Compared to traditional molds, they have advantages such as shorter molding cycles, material savings, and improved surface quality and mechanical properties of products, and are thus rapidly developing in the plastic processing industry. Hot runner molds have been successfully used to process various plastic materials, such as TPE, PP, PE, PS, ABS, PBT, PA, PSU, PC, POM, LCP, PVC, PET, PMMA, PEI, ABS/PC, etc. Any plastic material that can be processed with cold runner molds can be processed with hot runner molds.

Thermoplastic elastomers (TPE/TPR) possess the reprocessability of thermoplastics and the high elasticity of rubber, along with advantages such as soft texture, flexible hardness range, multiple processing techniques, non-toxicity, and environmental friendliness. They are now widely used in automotive, medical products, electronic products, daily necessities, household appliances, and polymer material modification, among many other fields. When producing large TPE products, some manufacturers often choose hot runner production methods. Sometimes, inconsistencies arise in the molding of each runner, which is mostly caused by cold material.

How to prevent cold material in hot runner molds:

Causes: Insufficient melt temperature, too small gate, excessive cooling at the gate, too large direct contact area between the hot nozzle and the fixed mold, incorrect gate profile or type.

Remedies: Increase the hot nozzle temperature, increase the mold temperature in the gate area, check the hot nozzle recess to ensure minimal direct contact area, check the gate profile machining, and trim the gate profile if necessary.