To heat thermoplastic sheet material for vacuum forming, heating must be rapid, uniform and controllable. Heating equipment must be quickly available, easy to assemble, reliable in operation, mobile and low in cost.
Previous Heating Methods:
1. Forced convection hot air ovens were discarded as being too slow, cumbersome, costly, massive and hard to control. Heating
time was 2 to 3 minutes.
2. Infrared lamps were tried and abandoned. Heating was spotty, sensitive to change in color and difficult to control.
3. Heaters of the glass blanket, black-heat type were eliminated as being too costly and slow.
4. Travelling heat bank containing tubular or strip heaters reduced heating time to 30 seconds.
The desire for even faster preheating combined with construction savings, led this prominent manufacturer of refrigerator parts to search for a more rapid heating medium for use in his vacuum forming machines to be built in the future. Fig. 2 shows a bank of two RADD-7604 Chromalox Electric Radiant Panels, each 10.8 kW, and 12" x 48" with provision for a third panel to be added later. These completely prefabricated panels come complete with insulation, steel frame, reflectors, end connection channels and heating elements factory connected to 100-ampere enclosed bus bars. The far-infrared radiation produced by these panels heats the thermoplastic sheet material in 12 seconds at a work spacing of 12 inches. Heating is uniform and under the complete control of a percentage timer and contactor. There is no variation in time due to color.
- Fast heating-a reduction of 60% in time requirement over fastest previous method.
- Increase in capacity of 66% due to faster heating.
- Accurate, low-cost control.
- Uniform heating-fewer rejects.
- Prefabricated panels available from stock. Built-in features and light weight permit fast, low cost connection and building on the job.
- Enclosed bus bars energized through a single feeder.