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Ask the Expert: What Causes Poor Ultimate Vacuum?

Ask the Expert

What is ultimate vacuum?

Ultimate vacuum levels depend on the user’s specific furnace and/or process. Ultimate vacuum ranges of 10-6 to 10-4 Torr in a clean, leak-free furnace are considered ideal.

What causes poor ultimate vacuum?

The most common causes include air or gas leaks and contamination of the hot zone. Another factor to consider is a poorly functioning pumping system, as this will influence how quickly your furnace is able to pump down and its ability to hold vacuum levels against outgassing.

What measures can I take to prevent poor ultimate vacuum?

Performing regular leak checks and running cleanup cycles can help prevent discoloration. It is also important to correct any improper operating or maintenance procedures that may be introducing contaminants into your system. Putting the furnace under vacuum on a weekly basis helps remove dust and debris so it does not erode the hot zone during pumping/cooling cycles. Keeping your hot zone clean will help eliminate water retention issues as well as improve hot and cold leak rates, resulting in a better ultimate vacuum. This will also help reduce cycle times and increase part quality.

What processes may result in poor ultimate vacuum occurring more frequently?

Certain processes—such as brazing, and debinding and sintering—as well as furnaces that operate at over 2,200 °F (1,204 °C), can suffer from poor vacuum levels.

How severe is the issue of poor ultimate vacuum?

The color of your parts can help indicate the severity of the problem. Colors typically range from yellow (least severe) to orange, green, light blue, dark blue and black (most severe).


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