PVC-SeIII

PVC punishes a general-purpose machine. It is corrosive to the screw and barrel, it is highly viscous and slow-moving, and it degrades if it is held too long or sheared too hard. Running it on a standard machine means accepting shorter screw life, burn marks and a narrow processing window.

The PVC-SeIII is rebuilt around those problems. The screw and tip set are chrome-plated, using special screw material and a heat treatment process that gives high wear resistance along with smooth material feeding. Screw geometry — L/D ratio, compression ratio and three-section ratio — is specified for the particular resin and product rather than supplied as a single standard design.

Temperature is where PVC is won or lost. The barrel carries multiple PID-controlled fans with adjustable speed to balance temperature along its length, barrel thickness is optimised for heat retention, and thermocouples are positioned and probed according to resin properties to maximise measurement accuracy. Back pressure is proportional and digitally controlled, which matters because PVC is so sensitive to shearing heat. The plasticising motor is enlarged to supply the high torque that viscous PVC demands, and a further enlarged motor is available as an option for CPVC.

Because most PVC work is pipe fittings, two sets of core pulls are fitted on the moving platen as standard, and the guard door at the clamping unit is widened to accommodate extra-long core pulls. Three or more sets of core pulls are available as an option. The hopper is stainless steel with a powder-collection tray underneath for easy cleaning.

Machines of 380T and above can be equipped with a hopper slider. On large-tonnage machines the screw is driven through a gear box for sufficient plasticising torque, and oil cooling circuits run through the screw centre for better resin temperature control.

Where it fits: PVC and CPVC pipe fittings, electrical conduit fittings and boxes, and any PVC part where screw life and colour consistency have been ongoing problems.

Shot weights in the table are quoted on PVC, as the Welltec sheet does, not on polystyrene — so they are not directly comparable with the general-purpose SeIII table.