Apparatus for thermoforming of containers, plugs with integrated valve

摘要

Each cavity in the upper part of the tool has a film clamp inside which there is a stretch assisting plug(32) operated by a tube(16). The tube acts as a supply line for forming air. A valve(27) located at the connection point between the tube and plug controls air supply to the tool from inside the tube to outlets in the plug. A rod(23) or tube moves axially inside the tube(16) to open or close off the air supply via the valve(27). Air is supplied via a bore(28) in a supporting plate(17) for the tube and an annular space(30) between the tube and rod. The rod end acts with an axial bore(34) in the stretching plug holder(31) to form the air supply valve. In an alternative design the rod end has an axial bore(36) into which one or more openings(37) enter. The openings are positioned so that rod movement releases or shuts off the air supply from the annular space. In the latter design the lower end of the axial bore is sealed off by a seal(38) in the prestretching plug(32) when in the closed position or alternatively the openings are located so that in the closure position they lie inside the axial bore(34) and in the open position connect with the annular space. When a movable tube is used instead of a rod inside the outer tube the air is supplied via a bore in the carrier plate into the interior of the tube and the lower end of the tube either: a) acts with a seal in the prestretching plug to form the valve or b) slides in a bore inside the plug and has openings which in the valve open position align with outlets in the plug and in the closed position sit inside the bore. The air valve may alternatively be pressure operated and in this case the valve comprises a shut-off piston pressed against a bore supplying air by a compression spring. Piston diameter is greater than the diameter of the air supply bore in the plug supporting plate. Spring force and the air supply bore diameter are matched to each other so that the valve opens under 6 bar and closes with a residual pressure of 2-5 bar.