Gas Catalytic Oven Maintenance

By Shih-Shin Chou

Powder coatings can be cured with different types of ovens including gas catalytic infrared, electric infrared, and convection ovens. While all of these oven types require regular maintenance for peak performance, this article will specifically address the maintenance requirements of the gas catalytic infrared ovens, which, with proper design and maintenance, can offer years of service with minimal maintenance tasks.

Infrared Heaters
Gas catalytic ovens include several primary components: infrared heaters/emitters, fuel gas train, the oven enclosure, and the exhaust system. The heart of the gas catalytic infrared oven is the infrared heaters or emitters. The infrared emitter in gas catalytic ovens has no moving parts and requires minimal servicing to maintain optimal performance.

While Figure 1 portrays a smaller heater emitter normally not used in an industrial oven, the internal components are the same as the larger versions. The typical operating steps of gas catalytic heaters are as follows:

• Electric power is first applied to the preheat elements for a total of about 30 minutes.
• The thermocouple is used to sense that the desired temperature has been reached and is thus safe to introduce fuel gas via the gas train.
• Gas flows into the back of the heater unit and diffuses through the insulation to come in contact with the catalyst pad.
• The gas is converted to infrared heat emitted from the front of the heater.
• Electric power is removed after the preheat cycle.

While the catalysts in the catalyst pad are not consumed during normal operation, taking some simple steps on a regular basis can help to ensure the longevity of the infrared emitters. The emitter surface should be kept clear of any foreign material including liquid, powder overspray, and dirt.

Care should be taken to avoid excess powder from drifting into the catalytic heater oven area. As shown in the photo at the top of this page, excess powder that collects in the catalytic heater oven can negatively impact the performance of the gas catalytic heater. An infrared camera can be a helpful tool to aid in the maintenance process.

Figure 2 shows a catalytic heater that is operating optimally on the left. It shows a uniform yellow color throughout the entire front of the heater. On the right is a gas catalytic heater that is not performing at 100% capacity. The purple areas indicate this emitter is emitting less energy than intended. This can be due to either excess powder or other contaminants.

While Figure 3 is not a powder coat curing oven, it does show an example of an infrared heater that needs to be repaired. Under the correct lighting conditions, it may be possible to see areas of red versus darker or black color. While some dark spots may be expected, large areas as shown would indicate that the emitter needs to be serviced.

The infrared emitters can often be repaired by the manufacturer to like-new condition. This usually requires the emitters to be removed from the oven so key components can be replaced. Having spare emitters will allow the repair work to be performed without extended downtime.

The Gas Train
The infrared emitters can be arranged as individual units for smaller ovens or in groups called zones for larger ovens. Regardless of the configuration of the infrared emitters, the fuel gas supply is controlled by the fuel gas train. The fuel gas train is required by code to have certain components. An example fuel gas train is shown in Figure 4.

The burner in a convection oven will be more forgiving of the fuel gas supply. The gas catalytic infrared heater on the other hand will require clean, dry gas to achieve optimal performance. The inlet fuel gas filter as shown should be cleaned regularly. The frequency will depend on the gas supply but at least annually and more frequently as needed.

Recirculation and Exhaust Systems
An exhaust system will be installed in all ovens while a recirculation system will only be used in some cases. Both systems will have a fan that will require periodic servicing. The motor bearing in the fans should be lubricated as suggested by the manufacturer.

Control Panel and Enclosure
The enclosure of the oven will require the least amount of maintenance, if any. Service is usually only required due to external damage. Under normal operating conditions, the enclosure should last the life of the oven.

In most instances, the infrared oven will be controlled with a PLC based control panel. A qualified electrician may be needed to replace switching components such as relays when their working limits have been reached. Most control panels function with minimal servicing or maintenance.

Summary
With proper care and regular cleaning, a gas infrared infrared oven can provide years of worry-free operation. As in all cases, proper design and installation of the system will be a critical part to extending the life of the oven. The system should be designed to prevent powder overspray from reaching the inlet of the oven. This will help to keep the infrared emitters operating at optimal levels while minimizing the maintenance required. An infrared camera will be helpful in determining the state of the gas catalytic heaters. Regularly cleaning out the fuel gas filter in the gas train will help to extend the life of the infrared emitters.

It is also good practice to have spare parts on hand as recommended by the oven manufacturer. This will help to keep the down time to a minimum should maintenance be required. Spares such as an extra infrared emitter, thermocouples, gas train components, and relays used in the control panel are good items to have on hand for quick change out.

Shih-Shin Chou is vice president sales and marketing at Catalytic Industrial Systems