Infrared heating has enabled the paintshop to keep up with the demands of increased production meaning that these days you can watch paint dry in next to no time

Since its introduction in the 1950s, the application of infrared heating has increased in the automotive industry. It has been instrumental in eliminating production bottlenecks, speeding up production and saving costs. A good example of how a company can benefit from its application is found in the UK’s Federal Mogul, which has quadrupled throughput in the curing of powder coating on brake pads.

Federal Mogul brake pads have an anti-corrosion coating, which protects the brake pad against spray water damage in operation. After this black epoxy coating is applied on the production line, it must then be cured and this was originally carried out using conventional medium wave infrared emitters. However, increasing sales demands meant that this kind of drying could not keep pace with production requirements and the company had to eliminate the bottleneck to remain competitive.

Medium-wave means minutes

There are various restrictions on the heating/curing process. For one, any heat applied should be effective only at the product surface and not within the material of the whole brake pad.

Medium-wave infrared radiation is ideal for melting and curing the epoxy coating and consequently an infrared system with fast-response medium wave emitters form Heraus Noblelight was chosen for the task. Fast-response, medium-wave emitters emit the effective medium-wave radiation, while at the same time delivering the power necessary to speed up the process. But more than this, fast medium-wave emitters have a response time of seconds, compared with the minutes required by conventional medium wave emitters to heat up and cool down. The reaction speed of modern fast-response emitters also means that they are easy to control. This means that it is possible to achieve temperature profiles inside the drying oven to suit a range of brake pads.

The new 162kW infrared oven is fitted with 30 fast-response emitters. It first brings the powder to melting point and then holds the coated products at the correct temperature to ensure curing. The installation of the modern infrared system has quadrupled the powder coating curing of a range of brake pads.

Wide application

Today, every well-known carmaker has an infrared system installed somewhere. They are still used for bodywork. They are also used in pre-drying, drying of finishing lacquer, as well as in repair drying. Moreover, more and more components are processed with infrared. Petrol tanks, pumps, gears, oil sumps or the brake pads discussed earlier, everywhere there are coatings or protective lacquers that have to be cured or dried.

There are also the heating processes for the plastics used in motor vehicles. For example, injection moulded plastic parts can be deburred by heating, a step which improves quality if the plastic part is to be coated or lacquered later.

If necessary, power densities of up to 1000 kW/m² can be transferred. Such high power is needed for applications such as coil coating. For most applications, powers of around 100 kW/m² are sufficient. Usually, 20 to 30 kW/m² is sufficient to achieve a fast, economical drying of most coatings.

Fitting the bill

Modern infrared modules are so compact that they can easily be retrofitted into or complement existing ovens. An example is the infrared booster which can be located in front of a hot air oven for coated plastic bumpers. Pre-drying with infrared speeds up the process.

For complicated components, hot air heating and infrared can be combined to advantage. The infrared emitters provide the direct heat while the heat from the hot air oven seeks out all hidden nooks and angles.

Modern infrared emitters can be perfectly matched to product and process in terms of wavelength, power and emitter shape. In every case it is worthwhile to match the heating source exactly to the process and material, as this ensures that not only is the production speed increased but quality is also improved, reject rates are cut and costs are saved.

The history of infrared heating

The first applications of infrared heating technology in car manufacture stretch right back to the 1950s. At that time, infrared heat was considered innovative in the drying of car bodywork. The infrared emitters were medium wave and slow, and mostly made from metal tube, ceramics or quartz glass. The first infrared emitters of quartz glass consisted of an opaque tube and were fitted with an external reflector plate. Very slow in response and not particularly powerful but, because of their contact-free mode of operation offering significant advantages over the previously-used hot air tunnel ovens.

As the automobile developed, plastic components and electronics became more and prevalent. This meant that heating processes had to be carried out much more precisely, as electronics and plastics do not tolerate hot air for very long. There were few heating processes that could manage long oven dwell times at 80ºC, the trend being to targeted heat only where required. The production machines, the local environment and the rest of the vehicle, for example the passenger compartment, could then remain relatively cool.

The pressure to ever-higher production speeds and ever lower costs have further driven the development of more efficient heating sources.

Quartz glass infrared emitters, such as those produced by German company Heraus Noblelight, are now used as twin tubes, as that design is more stable and also transfers more power to the surface to be heated. Modern reflectors are no longer external but are now integrated in the emitter itself. A gold coating also reflects particularly well, as around 95 per cent of the infrared radiation reaches the product. This means that the coating is warm more quickly and associated machinery is not heated. An integrated reflector is much less liable to getting dirty.