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Plastics extrusion bulk handling complete guide

Bulk Handling for Plastics Extrusion

Extrusion is one of the most widely used plastics processing methods for producing film, pipes, profiles and sheets. Efficient bulk handling of base polymers, colour concentrates and additives is essential for quality and profitability.

Key points

PVC dry blend combines powder (PVC resin) with liquid and powder additives in precise ratios — deviations directly affect extrudate quality
Masterbatch dosing (colour and functional concentrates) typically occurs at 1-5% of the base material and requires gravimetric accuracy
Static charge in plastic granulate can cause caking in silos and transport lines
Moisture content in hygroscopic polymers (PET, PA, PC) must be dried below a critical limit before extrusion to prevent hydrolysis

PVC dry blend production

PVC profile manufacturers produce their own dry blend by mixing PVC powder with stabilisers, lubricants and fillers in high-speed mixers. Cooling mixers cool the warm dry blend after mixing. Storage in silos, transport via pneumatic systems to the extruder hopper.

Additive dosing in extrusion

Colour concentrates, UV stabilisers and processing aids are dosed via gravimetric dosing devices. More info: hecht-technology.nl.

Granulate transport and static charge

Plastic granulate is generally transported pneumatically from silo to extruder hopper. Friction during transport builds up static charge, which can cause caking against pipe walls ("rat-holing") and bridging in the hopper. Grounded, antistatic transport lines and hoppers with proper angle construction limit this risk.

FAQ — Plastics extrusion bulk handling

Why must hygroscopic polymer be dried before extrusion?

Polymers such as PET, PA and PC absorb moisture from the air. When heated during extrusion, this moisture reacts with the polymer chains (hydrolysis), weakening the mechanical properties of the final product. Drying hoppers with dry air or vacuum dryers remove this moisture prior to processing.

How is masterbatch accurately dosed at low dosing percentages?

Gravimetric dosing screws with loss-in-weight control continuously measure the weight loss from the dosing hopper and adjust screw speed, enabling accuracies of up to ±0.5% — even at dosing percentages of just a few percent.