TABLE OF CONTENTS The intimate mixing of polyvinyl chloride (PVC) resin with appropriate additives is necessary prior to converting it into a thermoplastic melt.
Dry blend mixes are powder compounds resulting from the blending together of primarily suspension-PVC (S-PVC) resin together with the other formulation ingredients.
Batch high-speed mixing, followed by a cooling stage, is the most favoured process to produce unplasticised-PVC (PVC-U) and relevant plasticised PVC (PVC-P) dry blends at high outputs. The process is as follows:
Raw material storage and supply of all formulation ingredients to the mixer.
Dosing and spraying of all the ingredients (appropriate for the product form and weight loading), in the correct order if necessary, into the mixer. This can be semi- or fully-automated.
Mixing (a two-speed operation may be used) to the correct temperature by which time mixing has been completed. This is normally automatically controlled.
Discharge from the hot mixer, through a filter mesh if required, into the cooler mixer.
When the dry blend is sufficiently cool, it is discharged via a filter to remove oversize particles. Suction stream or screw conveying is used to transport the dry blend to the feed stations for processing.
Other important criteria also have to be considered for the dry blend mixing stage and subsequent transportation to the processing equipment:
Dry blend homogeneity and consistency.
Free-flow ability.
Bulk density.
Ease of handling and storage stability.
High-intensity mixers are vertically mounted cylindrical bowls, of...
