Extrusion Minimum Runs Measured in Tonnes Rather than Pieces
Extrusion runs are quoted in tonnes because start-up scrap, thermal equilibration, and bulk resin compounding operate as continuous mass processes.
Unplasticized PVC Compounding
Meaning
Process of mixing PVC resin with necessary additives without the addition of plasticizers to create a rigid material. This compounding step transforms the raw, heat-sensitive powder into a processable form suitable for extrusion or injection molding. Unplasticized PVC compounding involves the careful integration of stabilizers, lubricants, fillers and pigments to achieve a specific set of properties.
Dry Blending
High-intensity mixers are used to distribute the additives evenly through the resin particles. During unplasticized PVC compounding, the friction in the mixer raises the temperature, allowing the lubricants to melt and coat the PVC grains. This pre-treatment prevents the material from sticking to the metal surfaces of the processing equipment.
Formulation Design
Balance between internal and external lubricants is the most complex part of the recipe. If the lubrication in the unplasticized PVC compounding stage is incorrect, the material will either melt too early in the extruder or fail to fuse properly at the die. Precise control over the filler content also determines the stiffness and the final cost of the profile.
Pelletizing Process
Finished blend is often extruded into small pellets to improve the ease of handling and feeding. Some manufacturers bypass this step by using the dry blend directly in specialized twin-screw extruders. Whether in powder or pellet form, unplasticized PVC compounding is the foundation for the entire rigid PVC industry.