Fermion's 100 Questions, Issue 8 | Accessories in a Vacuum

20. Classification and usage environment of copper washers?

Copper washers can be divided into standard copper washers and non-knife-edge copper washers.
Standard copper washers are used the most. In principle, standard copper washers of the same size and material can be mixed. The standard copper washers can be expanded into annealed washers, gold-plated washers, and thickened washers: Annealed copper washers are softer than standard copper washers and are generally used for installation in windows, electrodes, or feedthroughs. In addition, annealed washers are softer and can have a larger deformation, so they can be used where angles need to be adjusted. Gold-plated copper washers are suitable for corrosive situations, such as near-normal pressure or S, Se growth chambers. Gold-plated washers are recommended. Experience shows that copper washers are easily corroded and contaminated, and gold-plated washers are much better. Thickened copper washers are mostly used to correct flange angles. In order to have more deformation, they are generally heat-treated.
In addition to standard copper washers, the most promising is non-knife-edge copper washers. The main advantage is that they can be reused, but they are slightly more expensive than standard copper washers. They can be used for damaged flanges or in special cases:
Flanges that need to be disassembled and assembled many times are best used with a torque wrench
Sensitive flange installation, such as windows, feedthroughs, etc. After research and actual testing, it was found that the screw torque required for non-knife-edge copper washers to seal is 1/3 to 1/2 less than that of ordinary copper washers, and can be used instead of annealed washers.
This type of copper washer is easily stuck on the flange and is suitable for the installation of some difficult and heavy parts.

21. What is the difference between a beveled copper gasket and an ordinary knife-edge copper gasket?

See the figure below for details. Ordinary knife-edge copper gaskets rely on flange knife-edge extrusion for sealing, and there will be indentations after use. The inner diameter of the beveled copper gasket is larger than that of the traditional gasket, which expands the available size of the connection port, and achieves vacuum sealing through close contact between the inner wall of the gasket and the outer bevel of the flange knife-edge. It does not require the flange knife-edge to cut in, and is suitable for the use of damaged flanges.

▲ Beveled sealing copper gasket (left) and ordinary knife-edge copper gasket (right)

22. If the new bevel seal is used in the future, will the old knife-edge seal be completely eliminated?

Generally speaking, the new bevel seal gasket has a higher manufacturing cost, and it is necessary to pay attention to parameters such as torque when it is reused. The hardware cost and labor cost used are higher than traditional copper gaskets. In addition, it is very important that the copper gaskets for bevel sealing have high requirements for the size and shape of the knife edge. In fact, there is no internationally agreed standard for metal sealing flanges (CF). Europe, the United States, Japan, and China all have their own local standards. These local standards differ in some details of size and tolerance control (for example, knife edge angle, etc.), which limits the use of bevel sealing rings. Because the current processing angle of bevel sealing rings can only adapt to a certain angle, if the parameters change, it may cause sealing failure. So please note that the main use environment of bevel sealing rings is: scenes where the knife edge is damaged and cannot be repaired; scenes where it is difficult to disassemble but replace the sealing ring. For most conventional uses, from the perspective of installation difficulty and cost, conventional copper gaskets still have a lot of room for use.