The term "twist-off caps" is used to denote special lug caps for glas jars or bottles of printed or lacquered tinplate. Compared to conventional screw caps, these lug caps, which are clamped under spring tension, bring about a particularly tight closure of the glas containers. A sealing compound made of plastic (epoxidized soybean oil) is injected in the cover area opposite the mouth edge of the glass to ensure a tight seal.
Manufacturing of Twist-Off Caps
Twist-off caps / lug caps made of tinplate for glass closures are manufactured on a fully automatic production line comprising the following individual machines:
portal press with sheet feeder (KAPPA IV)
for punching raw caps with a multi-die tool directly from the tinplate sheet
The safety button is molded directly in the press for large-diameter caps.
cap forming machine (GAMMA III)
for the final processing of the drawn cups to twist-off closures in the following operations:
- pre-hemming the upper end of the cap (optional)
- hemming the upper end of the cap
- curling and lug forming
- embossing of the safety button (optional, for small caps)
for injecting sealing compound into the cap for a tight seal on the glass
for drying the sealing compound (reduction of residual moisture)
for automatic or semi-automatic packaging of the caps in cartons