Automatically tuning heating zones to match workload thermal characteristics provides very tight temperature tolerances for high-temperature brazing.
Furnaces used for vacuum aluminum brazing operate at temperatures in the 1200 to 1300 F (650 to 705 C) range and at a vacuum level of 10-5 torr. In addition, because aluminum brazing is very sensitive to temperature uniformity, these furnaces are required to have a very tight temperature uniformity within +/-5 F (+/-3 C) or better. The heat-treating process requires uniform heating to ensure that portions of the workload are not overheated or underheated. In the case of brazing, the term "temperature window" describes the upper and lower allowable temperatures for the process to be accomplished without distortion from overheating and not melting the filler metal because of underheating. The temperature window in certain heat-treating processes can be as narrow as 20 to 30 F (10 to 15 C) throughout the workload. Therefore, controlling the furnace trim zones within a few degrees of the required temperature in that work location ensures performance of the process without rejects. PV/T achieves excellent uniformity control using multiple temperature trim zones (typically 6 to 12 zones), with each zone having its own control system and power transformer.