In the painting of new car bodies and many other products, long-term durability and consumer appeal depend on the quality of the coating application processes. This quality, determined by adhesion, hardness, corrosion resistance, finish and color, is highly dependent on curing temperature cycles. Calex non-contact infrared temperature sensors are able to provide the user or OEM with precise control over this cycle, where none existed before.
The automotive painting process generally consists of the application and curing of one or two coats of primer and one or two coats of paint. Radiation and convection heated ovens are used to “build up” the temperature at a controlled rate and “maintain” (hold) the temperature for a predetermined time as optimum for proper curing of all parts of the coating.
Before the installation of infrared temperature sensors, indirect measurement methods were used. One method was to monitor the air temperature in the oven to deduce the temperature of the car, which was inaccurate, especially in the radiant heat sections. Another method consisted of a time-consuming offline spot check by periodically passing a special car body equipped with thermocouples through the furnaces.
Calex sensors enabled direct, accurate, in-line measurement. The infrared sensor also made it possible to introduce separate controls for roof and sidewall heating. This was very useful due to the different thermal masses and thus heating rates of the roof and sides of the car.
Two important facts emerged during the work:
- The emissivities of different paint colors did not vary by more than 1%. A setting of 0.95 was used.
- Peak and valley hold functions could be used to eliminate the effects of looking at heaters or oven walls between car bodies.
Some automotive manufacturers quickly realized the value of IR sensors, in the form of reduced rework, improved adhesion, more uniform color and greater overall process and quality control, which would provide a quick return on investment. There has been an improvement in their competitiveness in the automotive market. The precise, non-contact temperature measurement capability of these sensors is equally applicable to all other coating and paint applications.
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