The general high purity inert gases usually contain 0! Active gas impurities%, the purity of vacuum is equivalent to 133Pa. This gas is used for heating the metal, and metal surface will react, so also need further purification, purification and purity from the cost point of view, to make the impurities to achieve the following 1 × 10-6 is very difficult, but the residual gas of 1 x 10-6 is equivalent to 1.33 × 10-1Pa vacuum, the vacuum the mechanical pump, roots pump can achieve longer. And the costs are compared to the same degree of gas purification is much cheaper.
The surface of the workpiece cutting coolant, lubricant, antirust liquid is decomposed into hydrogen, carbon dioxide and water vapor in vacuum heating, and the vacuum pump (before install filtering system) out, if stained surface not serious or request is not high, the vacuum heating Teng ago may not be clean.
The liquid metal vacuum degassing effect obvious, also have very good removal effect on gas dissolved in solid metals, degassing speed metal, different temperature are different. The most harmful metal in hydrogen (Qing Cui), the vacuum heating, the metal and alloy hydrogen quickly fell to the lowest degree.
3. oxide decomposition
Metal and alloy heated in a vacuum, if the vacuum degree below the decomposition pressure of the oxide, the oxide will be decomposed, the formation of free oxygen, free oxygen is vacuum system. Surface quality of the metal is improved. Even to the activation state at a certain temperature.
4. the evaporation of alloy element
Alloy material is heated in a vacuum, chemical composition and state of the surface will change frequently, such as all kinds of alloy elements in steel, manganese, chromium to the vapor pressure of the highest, heated in a vacuum which is the most easy to evaporation. As the heating element of Ni Cr alloy in vacuum and high temperature conditions will soon found the surface become rough. Alloy elements in the steel surface evaporation, the physical and chemical properties of the surface changes due to the effect of product quality and durability. In order to solve this problem, usually used in the vacuum heating below 800 ℃, 800 ℃ inert gas, to reduce the evaporation of alloy element.