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Pre vacuum tempering furnace
At present, the workpiece deformation of high-pressure gas quenching in China is generally large, the reason is that the typical furnace shape of vacuum high-pressure gas quenching furnace in China is a round furnace, and the quenching cooling nozzles are evenly arranged around the furnace, hoping to obtain a uniform air flow field. In fact, the uniformity of the cooling air flow in the furnace with this structure is very poor, the air flow velocity near the end face of the front and rear furnace is very low, the cooling capacity is poor, and the cooling speed at one end near the furnace door is faster than that at the other end. In the range of effective size, the cooling air velocity is also low, and the gas velocity on the cylinder facing the nozzle is high, while the cooling capacity between two adjacent nozzles is very low, and the jet cooling trace of the workpiece facing the nozzle is obvious. The cooling of workpieces in the same furnace varies greatly in different positions. In this case, the quenching deformation of the workpiece is very large, and the tempering resistance of the workpiece is not consistent.
Pre vacuum tempering furnace is a kind of heat treatment furnace with protective atmosphere. There are two ways to eliminate the oxidizing atmosphere in the vacuum tempering furnace: air charging and air exchange. The charging method is to charge and discharge the furnace continuously to drive out the oxidation impurity gas in the furnace, so that the purity of the atmosphere in the furnace can meet the requirements. The gas exchange method is to use the mechanical pump to extract the oxidation gas in the furnace, and then fill it with protective gas, and then extract the impure gas and fill it with protective gas. This method is repeated several times until the gas purity in the furnace is qualified. The vacuum degree of vacuum tempering of high alloy steel is 133 MPa, and the residual oxygen content in furnace is 0.132%.