Vacuum Heat Treatment

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Vacuum Heat Treatment Application

Vacuum furnace, as an advanced heat treatment equipment, has been applied in aerospace, electronic parts and other fields since 1940s because of its characteristics of non-oxidative decarbonization, small deformation, bright surface and long service life. By the 1980s, it was formally batched in the heat treatment fields of modulus tools, automobiles, aerospace, weapons, ships, electronics, railways, military industry, machinery manufacturing, textiles, gears, bearings, standard parts, quartz glass, magnetic materials, etc.
Heat treatment can not only realize the non-oxidation and decarbonization of steel parts, but also realize the production of pollution-free and less distortion of the workpiece. Therefore, it belongs to the category of clean and precise production technology. At present, it has become an irreplaceable advanced technology in the field of heat treatment production. Small distortion of workpiece is a very important advantage of vacuum heat treatment. According to the experience at home and abroad, the distortion variable of vacuum thermology of workpiece is only one third of that of salt bath quenching. It is important to study the vacuum heating mode of various materials, parts with different complexity and the distortion law under various cooling conditions, and to use computer to clamp them, so as to promote the vacuum heat treatment technology. The homogeneity of air flow during vacuum heating and atmospheric or high pressure air-cooled quenching has a great influence on the hardening effect and quality dispersion of parts. It is of great significance to study the law of gas flow circulation in the furnace by means of computer simulation for improving the structure of the furnace. At present, all countries in the world are devoting themselves to the research and development of vacuum furnaces. Many new types of vacuum furnaces have come out, which lay a solid foundation for the vacuum heat treatment of parts.
Modern vacuum heat treatment furnace is a kind of cold wall vacuum furnace which can heat components in vacuum and then quench them in oil or in atmospheric pressure and pressurized gas. Research and development of this type of equipment is a comprehensive, interdisciplinary work involving many scientific and technological fields. Vacuum heat treatment of tool and die materials has great application prospects. Most tool and die steels are heated in vacuum and then quenched in gas. In order to obtain satisfactory mechanical properties both on the surface and inside of the workpiece, vacuum high pressure gas quenching technology must be adopted.

Vacuum Furnace Selection

Vacuum furnace can be divided into vertical and horizontal series according to its structure, and vertical series can be divided into bell jar lifting type and bottom tray lifting type. Horizontal series is divided into single-door structure and front-back double-door structure. Water-cooled sandwich structure is adopted in all the guards. The furnace body can be made of stainless steel, carbon steel or their combination.
The main type selection of vacuum furnace is to select the vacuum furnace and process parameters according to the technical requirements and characteristics of the parts. The vacuum furnace can be used for quenching, tempering, annealing, chemical heat treatment, high temperature brazing, powder metallurgy and sintering, and heat treatment of other special materials.

(1) Vacuum heat treatment furnace type
Vacuum quenching furnace, vacuum chemical heat treatment furnace, vacuum tempering furnace, vacuum annealing furnace, vacuum sintering furnace, special furnace and special vacuum furnace, etc.

(2) Selection of vacuum furnace heating chamber
Graphite reflecting screen: There are two kinds of hard felt and soft felt commonly used in vacuum furnace. They are suitable for quenching, tempering, annealing, high temperature brazing, powder metallurgy and sintering of general steel.
Metal heat shield: usually in stainless steel and molybdenum two kinds. Molybdenum reflective screen is suitable for quenching, annealing, brazing and sintering of high temperature materials (superalloys, titanium alloys, magnetic materials, etc.) which have high requirements for furnace environment.
Stainless steel reflective screen is suitable for tempering, low temperature annealing, aging, vacuum aluminium brazing, etc. Some low temperature furnace types can be selected. In addition, heat-resistant stainless steel, molybdenum screen and carbon felt, mullite fiber or silicate fiber can be used to compound.

(3) Selection of vacuum degree
Medium vacuum furnace (general limit 4X10-1Pa) can be used for quenching heat treatment. Two-stage pumps (front pump and Roots pump) such as bearing steel, die steel and structural steel can be used for vacuum heat treatment. For quenching and heating of most alloy structural steels, alloy tool steels and high speed steels, vacuum degree is 1.33~13.3Pa, tempering vacuum degree of high alloy steels is 1.33X10-3Pa, vacuum degree is controlled in general vacuum heat treatment furnaces. After vacuum extraction of parts reaches the limit vacuum degree, high purity nitrogen (99%) is refilled to reach the set value and kept at a certain level. The required vacuum degree ensures no oxidation, no decarbonization heating and no evaporation of alloy elements. The vacuum degree affects the surface quality of heat treatment. Therefore, the sealing structure is maintained, the furnace is washed regularly and the internal dirt is removed to ensure that the furnace is in good condition and the normal function of the furnace is brought into play.
For some products requiring high vacuum, such as vacuum heat treatment of superalloys, titanium alloys, magnetic materials, or brazing at high temperature, three-stage pumps (front pump) can be selected. Roots pumps, diffusion pumps, etc.) generally require a vacuum limit of 10-4 Pa.

(4) Selection of control system
Standard configuration: With imported temperature controller and programmable controller as the core, temperature programmable, manual and automatic control is realized.
Computer control system: With industrial computer and programmable controller as the core process programming, storage and report forms. It can be operated independently by computer, automatically, manually, process programming, etc.
Computer group control system: a high-tech control system with industrial computer as the core, which integrates monitoring, data acquisition, operation and report management of multi-unit vacuum furnace.

Vacuum Oil Quenching Furnace