Solid Height - Spring Manufacturers Institute

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A clamshell furnace opened to reveal the heat shield, which prevents heat loss and reflects heat back onto parts. a regular maintenance program and replace them approximately once a year. Heat Shield The next item that warrants attention is the heat shield. A cheap furnace may not have one, but most of the major oven makers have them in one form or another. The heat shield does pretty much what its namesake indicates. Its purpose is to keep as much 24 SPRINGS July 2006 heat in the heat chamber as possible and not let it leak into other areas. Heat can bounce off a heat shield and reflect back onto your parts, assisting in the heat-treatment process. A good heat shield that can reflect heat will reduce the need for the elements to stay on, thus improving the useful life of an element. As with thermocouples, the heat shield should be checked for any buildup of materials on its surface. The more “gunk” that lodges up in the heat shield, the less heat that will reflect back down. Further, too much buildup of oil can potentially cause a fire. Standard cleansers that work on stainless steel can be used to restore a heat shield, but make sure the chamber is cool before applying them, and follow the directions on the cleanser’s label for further safety. Fan Motor and Fan Blades These items can vary dramatically among oven makers and even from model to model from the same maker. All inline ovens need circulating air to even out the temperature inside the heat chamber. Without such air circulation, you will only have radiant heat coming from the heating elements, and very little heat transfer (heat treatment) will take place. The most common method to circulate air is with a fan blade unit attached to a motor. Smaller ovens can be connected directly to a good-quality motor.
Average-quality motors will consistently burn out quickly, so if you try to save money by using a cheap replacement motor, you will end up spending more through more frequent replacements. Large ovens absolutely require an indirect connection between the fan and the motor. In large ovens, the heat in the chamber would travel up the fan shaft and burn out the motor if the two were directly connected. The fan blade unit rotates quite fast, so it must be balanced and properly secured to the fan motor. If even one blade got knocked off, the whole unit could become unbalanced enough that it could disintegrate. A jam-up in the chamber could cause parts to pile up high enough to touch the fan blades. The unit needs to rotate freely in the space between the heating elements and the heat shield. Furthermore, care must be given not to place the fan blades too close to the elements, as the elements can bend upward slightly when they get hot and could possibly get nicked by a rotating blade. Another factor for allowing the fan blade unit to rotate freely is the condition of the fan bearings. The bearings must be able to withstand BOTH high speeds and high temperatures. This goes for the bearing grease, too. There are some bearing greases that may be good for high temperatures but not necessarily for high rpm activity. Don’t skimp on the grease. Most oven makers recommend specific grease for their ovens in their user manuals. In conclusion, there are several items that wear out over time in the heat system of an oven: heating elements, thermocouples and fan bearings. Each of these items can have extended useful life through care and A fan evens out the oven tem- proper maintenance, perature and promotes heat but eventually they do transfer to parts. need replacing. Many old, beat-up ovens can be brought back to life in your maintenance department with a thorough cleaning of the heat chamber, and a quick check of the parts mentioned in this article. Daniel Pierre III is president of JN Machinery Corp. in Bensenville, IL. Readers may contact him by e-mail at daniel@jnmachinery.com or phone at (630) 860-2646 v SPRINGS July 2006 25
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