Heated plastic film movement and stretching method while feeding film thermoforming machine involves gripped movement through slower first and faster third zone and non-gripped movement in middle zone

摘要

A film strip(1) is gripped at the edges and moved through a first zone at a speed (v1). In a second zone, 50-500mm in length, it continues to move forward with no gripping of the edges. On reaching a third zone the film edges are gripped again and speed of movement is increased to a speed(v2), 0.5-5% higher than v1, which slightly stretches film in the second zone. Speed(v2) in the third zone is 1-2% higher than in the first zone. The middle zone is 100-200mm long. Gripped strip edges are further apart in the third zone than in the first zone and produce lateral stretching. An independent claim is included for the process plant which includes a first pair of chains(2,3) with film edge grippers and a second pair of chains(10,11), also with grippers. Chains in the first zone lie 50-500mm behind those in the second zone. Chain wheels(5,7) at the trailing end of the first pair of chains are coupled with the corresponding leading chain wheels(12,13) of the second pair of chains by a gear arrangement(17,18) with a ratio of 1.005-1.05.