Analysis of Carbon Steel and Aluminum Materials Used in Vacuum System Technology
In vacuum system technology, stainless steel is an excellent material for constructing chambers or components. Stainless steel has sufficient strength at the flange connection-- It will not affect its hardness even during the baking process. It can be welded to ensure its vacuum seal, and its surface has been completely passivated to provide sufficient protection for many applications.
For carbon steel used in vacuum system technology, as long as the pressure is lower10-5hPa, There is no need to create and maintain pressure, and there is no need for corrosion protection. Compared with stainless steel, it is a building material with relatively low price, good weldability and easy processing. However, when using this type of steel, the continuous outgassing of toxic gases and the tendency to corrode by air must be taken into account. On the atmospheric side, corrosion protection can be provided by painting, while on the vacuum side, it can be provided by nickel plating. When manufacturing containers, the steel grade used must be carefully selected, especially in terms of weldability and airtightness. The manufacturing method of boilers can only be transferred to the manufacture of vacuum vessels to a limited extent. When dimensioning, the stress caused by external air pressure must be considered, and the welding must ensure that the vacuum system is sealed. In addition, the tools used must be strictly separated from the tools used to process stainless steel to avoid contamination of stainless steel. This also applies to the storage and transportation of mild steel and stainless steel. Mild steel is usually used for fasteners for flange connections, and the surface of the fasteners is usually galvanized, nickel-plated or chrome-plated to prevent corrosion.
Aluminum is mainly used in the low and high vacuum range, usually as an alloy, and in special cases, it is also used as pure aluminum. When selecting materials, shrinkage and porosity must be considered. When used for centring rings and mating sealing rings, the parts are made from bar stock. Annealed aluminum-silicon alloys are preferred for gaskets or linear metal seals. The vapor pressure of aluminum is very low.660°CThe melting point of only6.10-9 HPALeft and right.The thermal expansion coefficient is high, the thermal conductivity is high, the alumina layer is stable, and the aluminum welding is difficult. There is a risk of pores and cracks, which are very easy to twist. Uniform heating before welding will reduce these risks. Since aluminum cannot be magnetized, to a certain extent, aluminum flange connections can only be used for metal sealsUHVconnections because their hardness is usually too low. Although special bimetallic flanges have been developed, including aluminum-based and stainless steel plates, or aluminum flanges with tough sealing surfaces, due to the relatively high price, certain risks in processing performance, limited applicability, and unsuccessful applications.
To improve their wear resistance as well as to increase corrosion protection, aluminum surfaces are often anodized. This results in a thickness increase of a few microns and the presence of a porous oxide layer, which has very limited applicability in vacuum system applications. Gas molecules are gradually deposited on these surfaces, resulting in higher desorption rates. In addition, gas molecules in the surface area can form channels under the seal, leading to leaks. There are a variety of anodizing methods to choose from, and when deciding whether to use this method, we must consider the limitations and weigh the benefits.