Chuck Yung
EASA Technical Support Specialist
We are cleaning a motor that is too large for our bake oven. In the past, we have placed the motor in front of the oven with the doors open, and draped a tarp over the frame to trap the heat. Is there a better way to dry it out?
Most readers in our industry have used variations on that method to dry the windings of a motor that simply won’t fit in the bake oven. There is a better way. Use Energy Shield®, the insulation home builders install between the exterior frame and siding or brick. It is a stock item in most lumber yards and construction-supply superstores.
Energy Shield is basically just a hard foam material with a layer of aluminum foil on both sides. The insulating value (R-29) is phenomenal, so it is ideal for building a temporary oven. Use Energy Shield to box the motor, including the top. Seal the joints with aluminum duct-tape. The motor may be placed in front of the shop oven, or an alternate heat source may be used to force air through the temporary oven.
Open exhaust ports near bottom corners
If using a torpedo blower, situate it so that it blows hot air directly into the center of the bore. Thermometers should be placed to monitor the temperature.
The trick is to keep the heat uniform within the motor. Because heat rises, our natural inclination is to open exhaust ports at the top, to let the heat out. A better way is to open exhaust ports at each corner of both ends. (See figure.) Simply adjust the dampers to regulate the temperature. To increase the temperature at one corner, open that damper further. The increased flow of hot air through that area will increase the temperature.
Insulation reduces heat loss
With a fabricated box-frame motor, place the Energy Shield directly on the frame to minimize the volume of air that must be heated. Drying time is reduced because the insulation minimizes heat loss. The ability to regulate temperature really improves the process, too. Energy Shield can be saved and reused, as long as it is stored where it won’t be damaged. At less than $25 per sheet, this “portable oven” is a good investment.
Sheets are lightweight, can be easily cut
For drying out a customer’s motor on-site, this method works well. It also looks more professional than a tarp. The 4' x 8' sheets are lightweight and easy to handle, allowing a temporary oven to be set up quickly. The foam board can be easily cut with a safety knife, so custom sizes and shapes are a snap. When faced with a deluge of work due to a flood, use Energy Shield to construct several ovens and remove the traditional bottleneck of workflow through the shop.
Tip: Use dial face thermometers to monitor the temperature in various parts of the oven. If the motor is supplied with RTDs, monitor them directly for an accurate record of winding temperature.
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