Oil quenching vacuum furnace instead of salt furnace

Necessity of replacing salt furnace with oil quenching vacuum furnace

Oxidative corrosion is one of the fatal defects in products. In the past, the heat treatment of many products in our company used salt furnace quenching. When the rainy season comes every year, the parts must be surface treated within a week, otherwise the retention of residual salt will lead to corrosion of the workpiece, resulting in mass scrap quality problems. In this season, the products are usually treated immediately after heat treatment to solve this problem. However, due to the large output and variety of products, this practice in the rainy season aggravates the workload of the surface treatment workshop and causes pressure on the production schedule. In order to relieve the pressure and achieve balanced production, the enterprise introduced the oil quenching vacuum furnace.

1. Part processing technology analysis and new equipment support capability

My company produces a variety of products for thin wall and complex shape, a flange, blind holes, such as design of parts, and require heat treatment after surface does not allow oxidation decarburization, USES is salt furnace heating, the original process can effectively prevent the decarburization, but often have residual salt retention surface, due to the difficult to clean up, so the waste caused by oxidation corrosion.

The workpiece can be heated in vacuum to remove the surface grease, decompose the oxide, and achieve the activation state of the surface to improve the surface quality. The two-chamber quenching tempering furnace can guarantee the vacuum condition with high vacuum degree < 10Pa. Firstly, it can completely meet the requirements of heating and quenching without oxidation and decarburization of the workpiece. Secondly, the equipment is controlled by the program to automatically execute the set process parameters, excluding the influence of human factors; Thirdly, the temperature control system adopts PID mediation to automatically control the temperature, the furnace temperature uniformity can be controlled within the range of ±2℃, so as to ensure that the workpiece quenching can be evenly heated, the surface after processing smooth, no oxidation, can save the shot peening treatment after heat treatment, because of reducing the process and reduce the workload of the surface treatment workshop. In addition, the simple operation of the equipment not only reduces the number of operators, but also improves the work efficiency. At the same time, get rid of the salt furnace treatment caused by environmental pollution, improve the operating environment.

2. Test results and improvement process

Taking the spring of the left and right switch of the spring of the spring silo with the material of 65Mn as an example, the process was tested. The equipment is a high vacuum double chamber quenching furnace.

(1) design auxiliary equipment according to the reasonable design of furnace volume, the purpose is to ensure that the workpiece can be vertically heated, to minimize deformation. The single hanging device of salt furnace is changed into multiple hanging device for vacuum furnace, including 1 stainless steel tray, 1 set of support and 6 hanger.

(2) quenching medium KR328 vacuum quenching oil, using temperature of 20 ~ 70℃.

(3) loading method: 500 pieces/each piece, a total of 3000 pieces for 6 pieces of each piece.

(4) vacuum heating mainly depends on thermal radiation, when the parts are placed, to ensure that there is a proper gap between the parts, according to the shape of the parts, should be hung on the hanger to make it evenly heated.

(5) process adjustment according to the characteristics of slow vacuum heat transfer, in order to ensure that the parts are heated evenly and the obtained organization is good, the process parameters are adjusted. The quenching heating temperature is changed from (830±10) ℃ in the salt furnace to (850±10) ℃, and the holding time is set as 55min. After the vacuum oil temperature rises to (30±10) ℃, select the automatic button, and the equipment can automatically take the material and feed the oil to quench according to the program requirements.

(6) the tempering and tempering equipment adopts rjj-35 well-type furnace, and the loading quantity is 3000 pieces/each furnace; The tempering temperature was (360±10) ℃. The holding time is 1 ~ 1.5h.

The high vacuum furnace is used to replace the salt furnace for the heat treatment of the left and right switch spring. Through the mass production verification, the hardness test of the workpiece is all 47 ~ 52HRC, 100% meeting the product design requirements. After the heat treatment, the surface is smooth and clean without oxidation.

3. The conclusion

Double chamber vacuum furnace to replace salt furnace is applied to a variety of parts heat treated in the past two years, a new device with the advantages of automatic program control, not only significantly increase the gun parts heat treatment hardness uniformity, more has obviously improved the appearance of the surface quality, truly achieve the quenching heat treatment without oxidation, fundamentally solves the residual stranded oxidation corrosion caused by salt waste problem. Moreover, the efficiency of heat treatment is significantly improved, the working environment of workers is greatly improved, and the labor intensity of workers is reduced.

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