How to perform vacuum leak detection for VD furnaces?

The requirements and methods of vacuum leak detection for VD furnaces can be elaborated in detail from the following aspects:

1. Requirements for vacuum leak detection

• Detection standards:

Detection standards for ordinary VD furnaces: The leak detection volume should be less than 10^-3 Pa•m3/s.

The detection standards for high-temperature VD furnaces are more stringent, and the leak detection volume should be less than 5×10^-4 Pa•m3/s.

The detection standards for negative pressure VD furnaces are more stringent, and the leak detection volume should be less than 10^-1 Pa•m3/s.

• Preparation before leak detection:

Before vacuum leak detection, the nitrogen or other protective gas in the VD furnace needs to be exhausted to ensure the accuracy of leak detection.

2. Vacuum leak detection method

Mass spectrometry leak detection method is commonly used, This method can ensure that very small leak rates, especially for vacuum chambers below atmospheric pressure can be found. The detection process requires the use of helium to generate a leak in the vacuum chamber, and then the mass spectrometer is used to quickly detect the concentration of helium to calculate the leak rate.

• Specific leak detection steps:

Preliminary leak detection: Press the air bag hard to spray helium from the rough extraction valve toward the furnace body, and conduct a comprehensive leak detection on all welds, flange connections, dynamic seals, thermocouple connections, etc. of the equipment. Slow down the blowing speed and conduct a detailed inspection at irregular welds and uneven flange connection gaps.

Detailed leak detection: Do not press the air bag, and slowly check the suspicious position with a needle. The leak hole will inhale a small amount of helium in the needle. Observe the changes in the leak rate value on the leak detector screen during the blowing process. The point with the largest leak rate and the fastest increase is the leak point.

Special part leak detection: Spray helium into each heating electrode, furnace water jacket and other water-passing cavities to check for leaks. If the pressure increase rate is still unqualified after multiple leak detections, you can use plastic cloth and tape to wrap and seal the suspected weld flange connection, thermocouple, electrode, etc., and then spray helium into the cover to observe the leak rate changes of the leak detector. If it rises slowly, it means that there is leakage at the wrapped position.

3. Leak detection for different situations:

The ultimate pressure is qualified, but the pressure increase rate is unqualified: mainly check the smaller leaks from the roughing valve to the furnace body, usually between 1x10(-9)~9.9x10(-4)pa.m3/s.

The ultimate pressure is unqualified, but the pressure increase rate is qualified: focus on checking the welds and flange connections of each connecting pipeline from the roughing valve to the mechanical pump part or the performance of the vacuum pump itself.

The vacuum degree of the vacuum pipeline and the vacuum chamber is constantly decreasing: check whether the vacuum valve has leaks.

4. Matters needing attention.

• When performing vacuum leak detection, ensure that all equipment is in a safe state to avoid accidents.
• The indication of the leak detector should be carefully observed during the leak detection process to accurately determine the location of the leak.
• After the leak detection, the VD furnace should be thoroughly cleaned and maintained to ensure its long-term stable operation.

In summary, the vacuum leak detection requirements of the VD furnace are strict and the methods are diverse. Through scientific and reasonable leak detection methods and steps, the leakage problem of the VD furnace can be discovered and solved in time to ensure its normal operation and efficient work.