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Vacuum Heat Treatment Furnace

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Tool and mold vacuum heat treatment process

Vacuum heat treatment has the advantages of high quality, low energy consumption, no pollution (or less pollution), etc. It can effectively prevent tool and mold defects, improve surface roughness, and reduce friction factor. The vacuum heating is carried out in the form of radiation, the heating is slow, the furnace temperature is uniform, the product deformation is small, and it also has a dehydrogenation effect. It is beneficial to improve the cutting life of the mold, and the vacuum quenching of the mold can increase the life of quenching by 3 to 4 times compared with that of the salt furnace.

The tools and molds for vacuum heat treatment are mainly various types of punching dies, drawing dies, cold extrusion dies made of SKD11, SKS3 and SK steel, as well as drill bits and milling cutters made of high-speed steel.

Vacuum heat treatment process:

1.Install card

In order to reduce quenching deformation, clamping is very particular. Due to the different geometric shapes and sizes of the workpieces, it takes more than a year for new workers to master them proficiently. In a nutshell, the following aspects should be paid attention to when loading workpieces:

(1) It is one of the effective methods to ensure uniform heating and cooling of the workpiece by trying to keep the workpiece from directly contacting the fixture when the workpiece is clamped.

(2) The tools and molds should not overlap each other as much as possible when loading the card.

(3) When loading the card, put the small piece into the center of the fixture, and put the large piece around the inside of the fixture.

(4) Very small workpieces can be put into a small box made of barbed wire, and the workpieces are separated by barbed wire, and then put into the fixture.

(5) Extra-thin and extra-large workpieces can be vacuum quenched and tempered after being clamped by a fixture.

2.Clean the workpiece

After the workpiece is clamped, it is hoisted into the cleaning tank, and then the cleaning agent is heated by electricity. When the temperature reaches 74.1°C, the cleaning agent boils to generate steam, and the steam rises to cover the surface of the workpiece, and the surface of the workpiece is cleaned. After cleaning, hang out the workpiece. The cleaning time is generally 20 to 30 minutes. Trichloroethane can be used as cleaning agent for carburizing and nitrocarburizing. During the long-term use of the cleaning agent, due to the increase in oil pollution, rust spots will appear on the surface of the workpiece after cleaning, so the cleaning agent should be replaced. For old cleaning agents regenerated and reused, emission problems can be avoided.

3.Calculate the heating time by weight

Vacuum quenching heating does not calculate the heating time based on the effective thickness of a single piece, but the workpiece regardless of size (the effective thickness difference between the smallest workpiece and the largest workpiece is 30-50mm) is loaded into the same fixture, and the heating time is calculated based on the weight of each card. The workpiece is weighed after being clamped, and the heating time is different for different furnace loads (weight).

4.Vacuum quenching, heating and cooling all adopt program control

According to the requirements of the work instructions, the operator can automatically enter the vacuum furnace, come out of the furnace, heat and cool as long as he presses the button on the touch screen. The temperature control instrument automatically digitally displays the vacuum furnace temperature at that time, and the recording instrument automatically draws the temperature curve and vacuum degree curve, so the operation and process management are greatly simplified. The vacuum heat treatment process of commonly used tool steel is as follows:

(1) Vacuum heat treatment of high speed steel (SKH9)

Cleaning: 20-30 minutes

Loading card: 70kg

Preheating: 900°C (time: 30 minutes)

Heating: 1180～1200℃ (time: 30 minutes)

N2 cooling: 86450～87780Pa (time: 40 minutes)

Vacuum tempering: 550℃×5h×2 times.

(2) Vacuum heat treatment of die steel (SKD11, SKD61)

Cleaning: 20-30 minutes Loading card: 200kg

Preheating: 750°C (time: 60 minutes)

Heating: 1020°C (time: 90 minutes)

N2 cooling: 86450～87780Pa (time: 50 minutes)

Regarding the vacuum tempering of SKD11 steel, because of the different performance requirements of the molds made, the tempering temperature and tempering times are also different. For molds with simple shapes or small specifications, it is generally tempered once at the corresponding temperature. For molds with complex shapes or large specifications, the following vacuum tempering methods are used:

Molds that attach importance to wear resistance (hardness above HRC60): Temper twice in the range of 170-200°C.

Dies that require both wear resistance and toughness (hardness requirements HRC58~62): 170°C×5h×1 tempering, second tempering at 230°C.

Molds that emphasize toughness (hardness requirements HRC53~57): After tempering at 170C to remove stress, temper twice at 510C.

(3) SK, SKS3 steel vacuum heat treatment clamping: 200kg

Cleaning: 20-30 minutes (time: 60 minutes)

Preheating: 750°C

Heating: 820°C (time: 90 minutes)

Cooling: oil cooling (time: 15-20 minutes)

Tempering 170℃×5h (in a dry box)

5.Cold treatment

The cold treatment agent uses dry ice, and the cold treatment temperature is -70°C. For molds with simple shapes, put them directly into the cold treatment tank after vacuum quenching. For those with complex shapes or large specifications, after vacuum quenching, stress relief tempering at 170°C is carried out in advance, and then cold treatment is carried out. The cold treatment time is 3 to 5 hours. After cold treatment, put it directly into a 70°C trichloroethane cleaning tank to raise the temperature for 10 minutes, and then carry out corresponding vacuum tempering. This method is very effective in preventing cracks and can effectively improve the quality of finished products.

Selection of heat treatment equipment: The vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tools and molds. Good temperature control accuracy and temperature control uniformity ensure the effective vacuum heat treatment process. SIMUWU company focuses on the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.