After the powder has been applied to the component it is heated. When heated, the powder film will first melt, flow and bond to the substrate being coated. Continued heating will “cure” the powder – curing involves a chemical reaction called “cross linking” and the resultant “cured” coating will not, like the original powder, melt or dissolve in solvents – it forms the protective coating we seek.
Most powders cure at around 180C Powdercoating and must be at this temperature for around 10 to 12 minutes and this time does not include the heating up or cooling down of the component but is the dwell time: the length of time that the component must be held at the appropriate temperature for curing to take place.
The dwell time and oven temperature will vary according to the size of component, atmospheric conditions and the manufacturer’s recommendations for that particular product.
The most frequently used methods of heating powder coatings are convection and radiation, both involve the component being passed into or through the heated area of an oven in order to melt and cure the powder film. The ovens will usually have an extractor to purge the chamber of the small amount of waste gases produced during the curing process.
This type of curing is by far the most popular method used in the curing of powder coatings. The component will be thoroughly heated to the required temperature where curing will take place. This type of oven usually consists of a large insulated box into which the parts will be placed for curing, or a tunnel through which the parts travel, via heat seals, into the main chamber of the oven.
This type of curing is particularly suited to flat panels with little or no returned edges and is a faster alternative to convection curing. This type of oven is typically a bank of radiant panels either side of a conveyor through which the parts travel and are subsequently cured.
When the powder film is fully cured and cooled it is then ready for its intended use and final assembly.
Chris Shannon has been involved with both the practical and technical coating of metals and plastics throughout his adult life working for trade coating organisations throughout the midlands.