In the convective drying process the work piece travels through a dryer with circulating hot air. The heat passes from the air to the work piece which in turn heats up. In the case of continuous conveyors, the dryer door cannot be used. In order to reduce the heat loss through ingress and egress openings, the so-called A-dryer has become favoured; it allows for the work pieces to enter the drying area from the bottom upwards.
A special type of convective drying is polymerisation or curing, which is used in the event of powder coating. In such case, the coating is not dried, but instead overheated to the extent that it melts and burns off – polymerises onto the work piece. The polymerization process is usually done at the temperatures around 180°C and lasts for approximately 30 minutes. However, the curing temperature and time depend on the requirements of the powder coating suppliers. Once cured, the conveyor transports the objects into the cooling tunnels where they are cooled to temperature, which is appropriate for their unloading. The similar process takes place during electrophoresis, which requires the coating to be consolidated.
Drying with radiation
During the drying with radiation process, the work pieces are heated with infrared or ultraviolet heaters.
The first advantage of such drying is in its short readiness time and work piece efficient heating up. As a result, the infra-red dryers can be shorter, which is a major advantage if we are limited with space.
The second advantage is that we no longer need to heat up the whole work piece; instead, the heating can be limited to the place where the coating was applied to. This drying method is very useful when the coated surface needs to be fixed only in some places and we do not need to return a work piece with tinny mistakes back to the whole coating procedure.