Injection Moulding Asia Hot Runners
Optimising high performance polymer moulding These resins are temperature and residence time sensitive meaning that the material will degrade if exposed to heat for extended period of time. The total runner volume in the hot runner system should not exceed a few shots for this reason. The injection moulding machine should be sized in such a way that the total shot-weight of the parts is about 70% of the machine shot capacity, therefore the molten plastic will not remain in the barrel over numerous cycles. Due to a lack of understanding of the above mentioned criteria, cold-runner technology has been primarily used to mould parts from high-temperature polymers (see Figure 1).
When moulding high-temperature polymers,
direct-gating with a hot runner system can save
moulders time and money, says Mohammad Rafi, BASc, Applications Engineer at Husky Injection Molding Systems.
H
ot runner systems Classsification of Plastics amorphous semi-crystalline were introduced in the 1960s to mould PI commodity polymers such as polypropylene High PAI PEKEKK (PP), polyethylene PEEK, PEK temperature LCP, PPS Plastic (PE) and polystyrene PES, PPSU PTFE, PFA (PS). Since that time 300 C PEI, PSU ETFE, PCTFE technology innovations PPP, PC,-HT PVDF have improved the capabilities of hot PA 46 Engineering runner systems. PC PET, PBT Plastic The industry has PA 6-3-T PA 6, PA 11, PA 12 POM evolved from hot 150 C PMP runners direct-gating parts moulded from PPE mod. commodity polymers Standard to hot runner systems PMMA PP Plastic producing parts from PE 100 C engineering polymers, PS, ABS, SAN Long term service such as polycarbonate temperature (PC), polyethylene terephthalate (PET) and polyoxymethylene (POM) - also known as acetal, polyacetal Figure 1: Classification of polymers and polyformaldehyde. (courtesy of Ensigner-Online) Engineering resins are high-strength plastic materials that have superior Producing parts with a cold runner could be mechanical and thermal properties over commodity unnecessary as engineering resins are expensive plastics. They are often resistant to high temperatures, and in many cases the cold runners cannot wear and corrosion. be reground and recycled. Any cold runner applications that are currently using engineering Catering to engineering resins polymers could benefit from a switch to a hot For engineering or high temperature polymer runner system. Converting production from a cold applications, care must be taken to ensure that the hot runner to a hot runner and direct-gating highrunner manifold is thermally stable with : temperature polymer plastic parts can yield a i) no dead spots or areas where the material savings of up to 50%, which includes savings from can sit and degrade resin waste, energy, labour and the mould. ii) without hot or cold spots 1 AU G U ST 2 017
www.injectionmouldingasia.com