Vacuum system of the welding problems which | vacuum unit - to the requirement of weld

by:J&T     2020-05-26

in the case of vacuum unit configured to determine that the equipment can achieve ultimate pressure depends on the total system external to internal leakage rate Qo with total 'leakage rate' which is formed by the virtual leak ∑ Q1 the sum of the size and the effective pumping speed of extraction system.

in the vacuum technology of leak hole refers to the inside and outside of the container when closed gas pressure or concentration at the same time, can make the gas from the wall on one side of the leak to the other side of the hole, defects, or gap and osmosis components or leak device. Leak due to the complexity of tiny size, shape, size cannot be expressed in geometry size, so generally use equivalent conductance or leak rate ( 'Leakage rate' for short) To show its size, the unit for Pa L/s.

weld vacuum in the manufacturing process is one of the most prone to leak hole area

common appearance of welding defects and other defects, such as incomplete fusion, incomplete fusion, slag inclusion, porosity, crack, and internal stress are all in the ultra high vacuum system leakage hole or virtual source leakage hidden trouble. In order to minimize weld defect to facilitate testing, ultra high vacuum for welding parts make weld as far as possible in the vacuum side, atmospheric side only as a continuous strengthening of weld seam, at the same time can make the largest number of weld in manufacturing phase test respectively, to give correct before final assembly. Due to some parts is small, the section size of the lining of welds is restricted, certain parts can only use atmospheric side weld, the weld should be a good welding, to avoid harmful space twice during welding, and so must ensure that the single side welding forming effect is good.

in addition, it should be pointed out that, due to reasons such as differential pressure, vibration and thermal cycling within the joint creation of stress and strain, may make the weld crack containing defects so that the weld is damaged, or in the process of using a weld corrosion, which may form funnelled.

so the welding methods must be adopted under these conditions can make weld leakage rate to meet the technical requirements.

at present, the widespread adoption of stainless steel ultra high vacuum container. Should speak, the weldability and welding technology of stainless steel is good, why want to ask for ultra high vacuum container to weld? The reason for this is ultra high vacuum container leakage rate is very low, also brings to the demanding requirement of the welding seam sealing, small leakage difficult, difficult, difficult to eliminate. Practice has proved that the ultra-high vacuum container usually adopts pressure leak detection method can not meet the requirements of ultra-high vacuum container leak rate, that is, in the pressure leak check out funnelled, under the condition of using helium mass spectrometer leak detection, can still be found leak hole, can not meet the requirements. For ultra high vacuum container, therefore, must use high sensitivity of the helium mass spectrometer leak detection.

in order to ensure the weld meet the requirements of ultra-high vacuum container leak rate, for stainless steel, the welding process on the main attention to two questions:

it is to prevent the generation of hot crack, its mechanism is a crystallization of the weld of low-melting-point eutectic content accumulation in the weld centerline, formed under the action of thermal stress. Should prevent carbide formed at the same time, due to rigid organization crack.

2 it is to minimize the weld defects.

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