Vacuum quenching of slender shaft

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Using double chamber high vacuum furnace, the vacuum quenching of slender shaft is realized successfully

Vacuum furnace quenching equipment replaces converter for workpiece heating and quenching, so that the hardness of workpiece heat treatment is more uniform, the surface is bright and clean without oxidation, the problem of large deformation of heat treatment is solved, and the working environment is improved.

1. Process principle
(1) the slender shaft has a long and thin shape. In the past, it was heated and quenched by converter. In the process of rotary heating and quenching in furnace, the thin rod has warping deformation in different degrees, which makes it difficult to straighten and discard.
(2) the box of double chamber high vacuum furnace is heated in bulk, which realizes the high vacuum heating and quenching of slender shaft. The surface of workpiece is smooth without oxidation, the hardness is more uniform, and the heat treatment has no obvious deformation. The qualified rate of workpiece straightening is 100%.

2. New process of high vacuum heating and quenching
The shape of the slender shaft is slender rod. The heat treatment is carried out after forming. Oxidation and decarburization are not allowed on the surface. Converter propane atmosphere is used to protect heating. Although quenching and heating are prevented from oxidation and decarburization, the deformation of the thin rod part of the workpiece exists in different degrees. The straightening workload after heat treatment is large, and the straightening scrap rate of the workpiece with large deformation after heat treatment is up to 1.5%. By using double chamber high vacuum furnace instead of converter, the high vacuum heating quenching of the workpiece is realized, the internal and external quality is improved significantly, which can effectively solve the problem of heat treatment deformation scrap.

3. Feasibility analysis of new high vacuum heating quenching process
Under the vacuum degree of < 10Pa, the double chamber high vacuum furnace can completely meet the requirements of non oxidation and decarburization heating and quenching of workpieces; in addition, the process parameters of the new equipment are set to program automatic control, which can eliminate the influence of human uncertainties; the temperature control system adopts PID to adjust the automatic temperature control, and the furnace temperature uniformity is guaranteed to be ± 3 ℃, the workpieces are uniformly heated at the quenching temperature by program control, and the hardness dispersion of heat treatment is small, table The surface is smooth without oxidation. For the slender shaft with the shape of slender rod, the material box tooling is used for heating and quenching to effectively ensure that the workpiece without surface cooling, uneven quenching hardness and small heat treatment deformation.

4. New process plan of high vacuum heating and quenching for slender shaft
Through the test and trial production of heat treatment process, a new process of vacuum heating and quenching for slender shaft is improved and introduced.
(1) equipment selection: high vacuum double chamber quenching furnace.
(2) design and process the vacuum heating tooling, change the converter bulk heating and quenching to the heating and quenching on the auxiliary equipment of the vacuum furnace charging box, including 1 set of support, 20 stainless steel charging plates, and the structure is shown in the figure.

(3) quenching and cooling medium: kr328 vacuum quenching oil, service temperature 20-70 ℃.
(4) charging mode: 240-260 pieces / box, 10-20 boxes in total, 1000-3000 pieces / furnace.
(5) the workpiece shall be placed horizontally in layers, and the workpiece head and the thin rod shall be placed in the material box alternately to ensure that there is no warping out of the workpiece.
(6) for the slow heat transfer of vacuum heating, in order to ensure that the workpiece is evenly heated and well organized, the quenching and heating time is changed from 15 minutes of converter to 60-80 minutes, and the holding time is changed from 30 minutes to 60 minutes. After the vacuum oil temperature rises to 20 ℃, select the automatic button to automatically take out materials and oil for quenching.
(7) the tempering equipment is rj-35-6 strong convection well type tempering furnace, with a furnace capacity of 1000-3000 pieces, tempering temperature of 200 ℃± 10 ℃, and holding time of 1.5-2h.

5. Batch process verification
Tooling capacity: 240-260 / box, 2453 / furnace.
Quenching process: 850-870 ℃× 60min;
Tempering process: 190-210 ℃× 90-120min.
The hardness is 46 ~ 50HRC, the surface is bright, no warping, and the metallographic examination is tempered troostite.
It is verified that the hardness of heat treatment is in the range of 44-50 HRC, and the metallographic structure is qualified, indicating that the heat treatment process is correct and feasible.
Since the high vacuum furnace was successfully used in the batch production of heating and quenching of slender shaft, the quality of heat treatment inside and outside has been improved significantly, the working environment of workers has been greatly improved, and the labor intensity of workers has been reduced.

Dual chamber Vacuum Gas Quenching Furnace