The rack is a type of gear transmission component and is a special form in which the outer diameter of the gear tends to ∞. Under normal circumstances, the fan-shaped rack is forged into a whole ring before the milling process, and the whole heat treatment is performed. After the heat treatment is used to eliminate the stress, the forging ring blank is reserved, and the processing flow is reserved according to each process of the ring gear, on the vertical vehicle. In order to prevent deformation, after the turning is completed, the natural aging treatment for stress relief is required, and then the actual size is cut according to the pattern to become a single rack, and then the milling is performed.
The shape of the rack is mostly linear, and the hardness of the tooth surface is required to be 240 to 280 HBW. The rack produced this time is the transmission component used on the floating crane of the ship crane. The rack is made of forging 42CrMo, the tooth surface hardness is 290-320HBW, the rack shape is 110° sector tooth surface, and the order quantity is 4 pieces.
This new structure, hard toothed rack processing is the first production in our company. If the conventional forging ring blank is used, the three racks are forged into a circular blank, and the three racks are 330°. The entire forging circle is 360°. When one by one is cut, one rack will be scaled. If two racks are used to forge a circular blank, the two racks have a shape of 220°, and four racks are forged into two full-circle blanks, which will cause 50% of material and processing waste. At the same time, since the outer diameter of the entire sector rack is 5343 mm (m=26, z=207, the outer diameter of the rack D=mz+2m), large heat treatment equipment (6.0m×5.5m) is required for quenching and tempering.
At present, the company's equipment can not meet the overall roughing requirements of the entire ring gear, in order to reduce the material and processing costs, improve the company's existing equipment utilization rate, how to choose the premise of the rack hardness in the heat treatment process of the rack The proper form of heat treatment prevents deformation, so that the stress release of the rack is uniform during heat treatment and the deformation of the rack is small, which is one of the difficulties in the processing of the rack. To this end, we decided to use a process for forging, machining and heat treatment of a single rack to ensure the quality of the rack processing.
In order to prevent the uncorrected deformation of the rack during the heat treatment process, the rack processing method and the heat treatment process are combined to ensure that the single rack has high strength, hardness, good ductility and toughness after quenching and tempering. And high processing accuracy.
Firstly, the deformation caused by the stress release after the rough opening of the rack and before the heat treatment is detected, and the appropriate machining allowance is selected according to the deformation. The choice of the balance is: the rack is tempered after rough opening, the left side of the tooth side is left with 8mm margin, the bottom of the tooth is left with 25mm margin, the outer circle is 16mm on each side, and the upper and lower end faces of the web are left 40mm, 15mm respectively. The remaining amount ensures that once the deformation occurs, there is enough machining allowance to compensate the deformation amount, which provides guarantee for the subsequent processing. Figure 1 shows the machining allowance of the rack.
