Itasca, Ill. — Plastic closure makers are more familiar with strip-thread and unscrewing molds, but they should consider molds that have collapsible cores, Carlos Saboga said at the Plastics Caps & Closures Conference.
Saboga is technical sales manager at Roehr Tool Corp. in Hudson, Mass., which makes collapsible-core molds. Roehr is owned by Progressive Components International Corp.
Closures, with molded-in thread, must be removed from the tool with special molds. Saboga said the strip-thread method can make rejected caps, since it forces the part out. Unscrewing molds are complex and large, to house the moving parts inside, and that means you may need a larger injection press than necessary.
“Once you start moving the collapsible core, there's no stress on the part,” Saboga said. The mold system gives closures with very sharply defined threads, he said. The process also allows for part designs, such as a groove for an O-ring, retention features, snap-fits, slots and solid shutoffs.
It also can reduce wall-thickness, Saboga said.