| 摘要 |
<p>An electrical air heater for a calender roll diameter control device is described. The heater comprises a tube (23) for directing a flow of air along the inside of the tube from a plenum (12) toward an object which is to be heated. An electrically resistive heating element (18) is mounted inside the tube to heat the flow of air as it flows from the rear to the front of the tube. Since the air is heated by the heating element inside the tube, the air is coolest when it first enters the tube and hottest where it escapes at the front of the tube. Similarly, the heating element is cooled by the air and is, therefore, hottest near the front of the tube where the heated air escapes. The hotter front end of the heating element tends to burn out faster than the cooler end of the heating element. To prolong the life of the heater, openings (27) are provided in the tube wall to admit a flow of cooling air at the hottest part of the heating element.</p> |
