The state of the art technology used for producing industrial powder coatings consists of several distinct stages, namely:
- Weighing, premixing and size reduction of raw materials
- Extrusion of pre-mix, cooling and crushing of the extrudate into chips
- Micronising the chips into the final powder
- Post mixing, packaging and storage
At each stage of the production process the quality must be checked because once the powder coating material has been produced, it cannot be changed or adjusted in any significant way. The formulation and the manufacturing conditions are therefore critical. Reworking of an ‘out of specification’ product is difficult and costly.
Raw materials typically consist of resin, curing agents, pigments, extenders and additives such as flow and degassing aids. Each raw material must pass their individually pre-set quality controls.
Each component is then weighed with the necessary degree of accuracy (which may be to the nearest ten-thousands of a gram). All pre-weighed components are placed in a mixing container according to the formulation. The container is then attached to the mixing drive and the raw materials are thoroughly mixed by the specially designed premixer cutting blades for a pre-set period of time. The raw materials can also be reduced in size to improve the melt mixing later in the process.
A final sample of the raw material pre-mix is checked for conformity and processed through a small laboratory extruder and grinder. The resulting powder is then applied onto a test panel, cured in the oven and subjected to various tests:
- Color, surface flow and gloss
- Mechanical performance (including curing)
- Gel time
If adjustments are required both the mixing process and quality control procedures are repeated until the powder achieves the specification.
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