Mfg. hollow shapes from thermoplastics - involves continuous extrusion into heat insulated chamber for uniform temp., reduced heat loss and parison sag, before transferring to blowing mould

摘要

Hollow shapes in thermoplastics are mfd. by extrusion blow moulding. During continuous extrusion of the parison, this is held in a thermally-insulated chamber, before transferring to the blowing mould. Several parisons may be extruded simultaneously into a common insulated chamber, with separate blowing moulds. Alternatively, two or more blowing moulds may operate with a single extrusion head and common insulated chamber. When the parison has extruded to the required length and the chamber and mould open, either the mould may move into position to close round and remove the parison, or it may be separately transported, e.g. by a gripper to the stationary mould, which may be alongside or beneath the insulated chamber. The blowing mould and chamber may be moved and/or opened/closed synchronously or independently. USE/ADVANTAGE - For continuously extruded blow mouldings, esp. those which because of weight or size would otherwise be intermittently extruded. Permits continuous extrusion for improved extruder operation and reduced complexity and cost of arrangement, esp. for greater product range. Reduces or avoids heat loss, giving more uniform parison temp. for improved product uniformity. Parison temp. at start of blowing is independent of time between start of extrusion and mould closing. Reduced heat loss permits lower extrusion temp., at or near blowing temp., reducing parison sag, and undesirable variations to product thicknes