Double-chamber Vacuum Oil Quenching Gas Cooling Furnace Operation
The safety operation of double chamber vacuum oil quenching gas cooler should pay attention to the following matters:
In the process of cooling the workpiece into oil, nitrogen with pressure of (0.4-0.67)*105Pa (300-500 torres) should be filled into the oil cooling chamber. Nitrogen filling in the cooling chamber can not only improve the cooling capacity of vacuum quenching oil and make the workpiece achieve quenching hardness under normal pressure, but also, more importantly, the nitrogen filling can inhibit the volatilization of vacuum quenching oil, reduce the concentration of oil mist (flammable gas) in the air-cooled chamber and protect the safety of oil-cooled quenching. At the same time, it also reduces the loss of vacuum oil and pollution of furnace, which is beneficial to product quality and safety.
After entering oil, the workpiece should be fully cooled (oil cooling time should be determined by test). After the oil is discharged, it should stay in the air-cooled chamber, drain the oil brought by the workpiece (especially for the workpiece with holes), and vacuum the oil-cooled chamber to remove the oil mist in the air-cooled chamber space, then close the vacuum valve, open the air-discharging valve of the cooling chamber, and unload the furnace door after the average pressure (to prevent explosion first and second). Conditions occur at the same time.
Special care should be taken in the safe operation of vacuum oil quenching of high alloy die steels (such as 4Cr5MoSiV, Cr12MoV, etc.). In order to reduce the deformation and cracking of the die, the temperature of the workpiece will often reach the flash point or near the ignition point of the vacuum oil when the oil is discharged. If the air is rushed out of the furnace to the cold chamber at this time, the heat from the center of the workpiece will ignite the oil and gas attached to the surface of the workpiece and cause open fire (the third part of the explosion). In the instant of opening the door of the furnace, explosion accidents are easy to occur!
The correct way is:
1. The oil cooling time stipulated by strict technology shall not be arbitrarily shortened or prematurely discharged.
2. After the oil is discharged from the workpiece, it is necessary to stay in the air-cooled chamber for a sufficient time, such as 15-30 minutes (determined by the load), which can not only drain the oil from the workpiece, but also condensate a large amount of oil mist into oil droplets through the wall of the oil tank and return to the oil tank, so that the combustible oil mist can be reduced to the lowest concentration, which is both fuel-saving and safe.
3. Vacuum the air-cooled chamber to further reduce the concentration of oil mist;
4. Before preparing for discharging, the residual oil mist in the oil-cooled chamber should be checked from the observation hole of the furnace door to confirm that there is no oil mist (the workpiece and the basket can be clearly seen) before discharging gas into the cold chamber.
5. Open the vent valve of the cold chamber, open the furnace door and unload the material. If the above operation procedures are followed, the probability of simultaneous occurrence of three explosions can be eliminated, thus effectively preventing the occurrence of explosion accidents. The explosion accidents of vacuum oil quenching furnace mostly occur in large-scale equipment. The bigger the furnace specifications, the more the furnace loading, the higher the heating temperature of workpiece materials, the greater the probability of accidents. It is suggested that when dealing with high alloy steel dies, the furnace loading should be reduced appropriately, and overloading should be avoided. In addition to carrying out the above safety operation procedures, the following points should be noted in production:
Strictly according to the instructions of the equipment, add enough oil in the quenching tank (usually the weight of vacuum quenching oil should be 10-15 times of the maximum furnace loading), and the volatilization loss of quenching oil is large (some parts are taken away by the workpiece). Therefore, the oil level should be checked frequently, and the oil level should be added in time when it is not in the prescribed position, so as to ensure that the quenched workpiece is submerged in sufficient depth below the oil surface.
The workpiece should not be overloaded, and the weight of the basket should be included in the weight of the furnace; the workpiece should be evenly placed in the basket to prevent local dense loading; and the height of the charging should be controlled to prevent the quenched workpiece from being too close to the oil surface.
It is very important for the safe operation of the vacuum furnace to do well the daily maintenance work of the vacuum furnace and eliminate the potential safety hazards caused by the equipment failure, such as checking whether the oil mixer and the workpiece quenching oil elevator are running normally and whether the ground insulation resistance meets the requirements. Oil mixer mixing and non-mixing, oil cooling intensity difference of 3-4 times, mixer failure, will cause local oil temperature is too high, not only oil volatilization, but also will make the work piece oil temperature is too high. If the hoist suddenly breaks down when the workpiece enters (or discharges) oil, and the hot workpiece stops on the oil surface partially, the air-cooled chamber will be filled with flammable oil mist. At this time, we must calm down and not rush to open the furnace door, which will inevitably cause an explosion (domestic accidents have occurred accordingly). The correct solution is to fill the air-cooled chamber with nitrogen (negative pressure) to extract the true gas, alternately, until the workpiece gradually cooled, when there is no oil mist on the oil surface, then close the valve to release gas, or keep the cold chamber vacuum, and then open the furnace door to troubleshoot.
Operating places should eliminate open fires and ignition. Before unloading the furnace door, smokers should be checked. Different types and specifications of vacuum equipment, different materials and processes for processing workpieces, the situation will be different, but the principles of safety operation specifications should be common.