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Safety Precautions of Double-chamber Vacuum Oil Quenching and Gas Quenching Furnace

In order to ensure the safe operation of the vacuum oil quenching furnace and prevent the currence of accidents, the operation must be standardized, the existing hidden dangers should be controlled and prevented, and the three conditions of explosion should be prevented from occurring at the same time. The safe operation of the double-chamber vacuum oil quenching and gas quenching furnace should pay attention to the following matters:

1.When the workpiece is cooled in the oil, the oil cooling chamber should be filled with nitrogen with a pressure of (0.4-0.67)×105Pa (300-500 Torr). Nitrogen in the cold chamber can not only improve the cooling capacity of the vacuum quenching oil, also make the workpiece reach the quenching hardness under normal pressure. More importantly, the filled nitrogen can inhibit the large volatilization of the vacuum quenching oil and reduce the oil mist in the air-cooled chamber . The concentration of (combustible gas) protects the safety of oil quenching. At the same time, it also reduces the loss of vacuum oil and pollution to the furnace, which is beneficial to product quality and safety.

2.After the workpiece enters the oil, it needs to be fully and thoroughly cooled (the oil cooling time should be determined by experiments), and should stay in the air-cooled chamber after the oil is discharged to drain the oil from the workpiece (especially important for the workpiece with holes), and Vacuum the oil-cooled chamber to remove the oil mist in the air-cooled chamber , then close the vacuum valve, open the cold chamber deflation valve, and open the furnace door to discharge the material after the pressure is averaged (to prevent the explosion of the first and second conditions at the same time) .

3. Special care should be taken for the safe operation of vacuum oil quenching of high alloy die steel materials (such as 4Cr5MoSiV, Cr12MoV, etc.). The heating temperature of this kind of workpiece usually reaches 1030°C. The oil mist of the quenching oil is volatile and high in concentration. In order to reduce the deformation and cracking of the mold, the temperature of the workpiece will often reach the flash point or ignition point of the vacuum oil when the oil is discharged. If let air into the cold chamber after the furnace is released, and the heat feedback from the core of the workpiece will ignite the oil and gas attached to the surface of the workpiece to cause an open flame (the third condition of explosion), and an explosion is likely to occur the moment the furnace door is opened! The correct way is:

① The oil cooling time stipulated by strict process shall not be shortened or discharged in advance;
②After the workpiece is out of oil, it should stay in the air-cooled chamber for enough time, for example, 15-30 minutes (depending on the load). This stay is very necessary, not only can drain the oil from the workpiece, but also a large amount of oil mist It can be condensed into oil droplets by the oil tank wall and returned to the oil tank to reduce the combustible oil mist to the lowest concentration, which is fuel-efficient and safe;
③ Keep a vacuum in the air-cooled chamber to further reduce the oil mist concentration;
④Before the furnace is ready to be discharged, check the remaining oil mist in the oil cooling chamber from the observation hole of the furnace door, and confirm that there is no oil mist (the workpiece and the material basket can be clearly) before venting to the cold chamber;
⑤ Open the air deflation valve of the cold chamber, open the furnace door, and discharge the material.

According to the above operating procedures, the probability of the three explosion conditions occurring at the same time can be eliminated, thereby effectively preventing the occurrence of explosion accidents. Explosion accidents of vacuum oil quenching furnaces mostly occur in large-scale equipment. The larger the furnace specification, the more furnace capacity, the higher the heating temperature of the workpiece material, and the greater the probability of accidents. It is recommended to handle high-alloy steel molds. The amount of furnace installed should be appropriately reduced, avoid overloading!

In addition to the implementation of the above safety operation procedures, the following matters should also be noted during production:

4.In strict accordance with the equipment manual, add enough oil to the quenching oil tank (usually the weight of the vacuum quenching oil should reach 10-15 times of the maximum furnace installed), and the evaporation loss of the quenching oil is large (some parts are taken away by the workpiece) ), so the oil level should be checked frequently, and the oil level should be added in time if it does not reach the specified position to ensure that the quenched workpiece is immersed in a sufficient depth below the oil level.

5.The workpiece should not be overloaded, and the weight of the material basket should be included in the weight of the furnace; the workpiece should be evenly placed in the basket to prevent local intensive loading; the height of the charging should be controlled to prevent the quenched workpiece from being too close to the oil surface.

6. Do the daily maintenance of the vacuum furnace to prevent potential safety hazards caused by equipment failure. For example, check whether the oil agitator and the workpiece quenching lift are operating normally, and whether the insulation resistance to the ground meets the requirements, etc., which are safe for the furnace Operation is very important. When the oil agitator is agitated or not, the oil cooling intensity is different by 3 to 4 times. The failure of the agitator will cause the local oil temperature to be too high, which not only causes a large amount of oil volatility, but also makes the workpiece oil temperature too high. In the event of a sudden failure of the elevator when the workpiece enters (or exits) oil, the hot workpiece partially stops on the oil surface, which will fill the air-cooled room with combustible oil mist. At this time, please calm down and do not vent in a hurry Open the furnace door, this will inevitably cause an explosion (there have been accidents in China). The correct response is to fill the air-cooled room with nitrogen (negative pressure) and pump vacuum alternately until the workpiece is gradually cooled and there is no oil mist on the oil surface, then close the valve and release the air, or keep the cold room evacuated, and then wait for another shift. Open the oven door to troubleshoot.

7. Open flames and fires should be eliminated in the operating place, and before opening the furnace door to unload, check whether there are smokers at present.