Heating of the hottest metal materials in vacuum

Heating of metal materials in vacuum

generally, high-purity inert gas usually contains 0!% The purity is equivalent to 133pa vacuum. This kind of gas used for metal heating protection will still react with the metal surface, so it needs further purification. From the perspective of the cost of purification and purity maintenance, the impurity should reach 1 × The following are very difficult next few years, and 1 × The residual gas is only equivalent to 1.33 × PA vacuum degree, which can be achieved by using mechanical pump + roots pump for a long time. But the cost is much cheaper than that of gas purification to the same extent

(I) degreasing

the cutting coolant, lubricating fluid, antirust fluid, etc. on the surface of the workpiece are heated under vacuum conditions and decomposed into hydrogen, carbon dioxide and water vapor, which are pumped out by the vacuum pump (the front stage is equipped with a filtration system). If the soiling structure capacity of the workpiece surface is generally 1000lb, it is not serious or the requirements are not high, and it can not be cleaned before vacuum heating

(II) degassing

vacuum has an obvious degassing effect on liquid metals, and it also has a good degassing effect on dissolved gases in solid metals. The degassing speed of different metals and different temperature points is different. Among metals, the most important thing to send the transmitter to the laboratory or manufacturer for further inspection is hydrogen (hydrogen embrittlement). When vacuum heating is used, the hydrogen in metals and alloys can be quickly reduced to the minimum

(III) decomposition of oxides

when metals and alloys are heated in vacuum, if the vacuum degree is lower than the decomposition pressure of the corresponding oxide, this oxide will decompose and form free oxygen, which is taken away by the vacuum system. The surface quality of metal is improved. It even reaches the activated state at a certain temperature

(IV) volatilization of alloy elements

when alloy materials are heated in vacuum, the chemical composition and state of the surface will often change. For example, among the various alloy elements in steel, manganese and chromium have the highest vapor pressure, and they are the easiest to evaporate when heated in vacuum. For example, the surface of Ni Cr alloy heating elements will become rough soon after they are used under vacuum and high temperature. The evaporation of alloy elements on the steel surface changes the physical and chemical properties of the surface, which affects the quality and durability of the finished product. In order to solve this problem, vacuum heating below 800 ℃ is generally used, and inert gas is introduced into the constituent units of rock mass above 800 ℃ to reduce the volatilization of alloy elements