When working with heat-treating furnaces, nothing is more important than validating your equipment to ensure uniformity, reliability and—most importantly—repeatability. By utilizing the proper methods of preventive maintenance, you can ensure a longer life for your furnace and get a sense for potential repairs that might come up in the near future.
One of the most important tests you can perform to validate your furnace is a Temperature Uniformity Survey (TUS). For those who need a little more detail, a TUS is a test, or a series of tests, where you measure the temperature variation within the furnace’s effective work zone before and after thermal stabilization. It is also essential to remember that you should perform an initial TUS prior to the first use of the furnace.
Why is this the case? Because, if there are variances in your parts after start up, you do not want the furnace to be one of the variables you have to consider on the list of potential causes. On average, you should perform a TUS no less than twice a year. Of course, how often you perform one depends on the specifications you subscribe to and the overall performance of your furnace.
When a TUS does fail—meaning the temperature is not where it’s supposed to be—it signals that your hot zone is starting to degrade. Which brings up another important maintenance point—generally, you should replace your hot zone every five to seven years.
Other forms of furnace validations include leak detection and System Accuracy Tests (SAT). When it comes to leak detection, you should always know the linear leak rate for your furnace, as well as perform a leak check anywhere from once a week to once a month. Overall, by knowing the leak rate and performing a leak check you are able to verify the integrity of your vacuum. On the other hand, you should typically perform a weekly SAT to validate the accuracy of the control thermocouple. Other forms of preventative maintenance that are important to perform include pump upkeep and cleanup cycles.
In addition to validating your equipment prior to use, having accurate records is also critical to maintaining an efficient and effective maintenance program. After you start up your equipment, it is important to carefully maintain a performance log that records the following:
- Blank-off pressures of the mechanical pumps
- Pumpdown time to a given pressure
- Ultimate vacuum
- Leak-up rate for when the chamber is blanked-off