The roll is the main component of the rolling mill. In actual use, due to a certain impact force, the surface will be rubbed by the rapid and hot red steel. The surface must have good wear resistance and at the same time have sufficient toughness to prevent damage caused by impact.
Considering the special purpose of the roller, determine the material requirements:
- 1. High-speed wear-resistant;
- 2. Sufficient redness and hardness.
- 3. Sufficient strength and toughness.
In actual use, white cast iron is suitable. However, since this material is usually used in the as-cast state, casting defects are inevitable, and the hardness can reach 50-60 HRC. In addition, the drum (as shown in the picture) places high demands on the coaxial cable, which makes turning very difficult.
1. Reasonable selection of tool grade
The strength and hardness of the roller material has reached the strength and hardness of ordinary carbide tools (YT), so normal cutting cannot be performed with ordinary tools. Quenching and tempering can appropriately reduce the hardness and facilitate cutting, but the cost is too high and the cycle is long, so direct processing in the as-cast state is selected.
Repeated comparisons with various high-hardness cutting tools such as ceramic cutting tools and imported cutting tools.
Finally, a YS8 turning tool with relatively low hardness and wear resistance that meets the cutting requirements is selected for turning.
Of course, when repairing the roller after use, the hardness is very high, comparable to the cold curing and quenching in the process. If the YS8 tool cannot cut, please use a ceramic blade for repair.
2. Reasonable choice of tool shape and cutting amount
Because the blank contains quite a lot of elements such as Cr and Mo, it has good plasticity, high strength and hardness, high deformation resistance, and the cutting force is 2 to 3 times that of ordinary steel. The cutting heat also increases, the thermal conductivity is low, the heat dissipation is difficult, the temperature in the cutting zone becomes very high, and the tool is easily damaged. In addition, the blank is a casting, and the surface has defects such as crust, pores, blisters, uneven machining allowance, uneven material hardness, etc., which inevitably lead to increased processing instability. Shorten tool life, increase production costs, and reduce production efficiency. In view of these factors, the cutting process is improved through reasonable selection of cutting parameters.
For rough machining, the surface of the machined surface is uneven, and the surface of the blank has a hard skin. Therefore, the maximum cutting depth must be selected. The greater the cutting depth, the greater the cutting heat generated, and the greater the cutting force that the tool can withstand. Use negative rake angle and negative rake angle (0° to -5°) to increase the rigidity of the tool so that the tool can withstand sufficient compressive stress. The back angle is generally 6°-8°, the lead angle is 10°-30°, and the secondary declination angle is 10°-15°. Due to the high hardness of the blank and poor heat dissipation, low speed (80r/min) is used for roughing. Small feed rate (0.15mm/r) appropriately reduces cutting resistance. Choose the cutting depth from 2 to 3 mm.
Due to the small cutting depth, the cutting force is small, and the cutting heat is small. In order to improve the surface quality, a large rake angle is adopted, and the rear angle is a larger value of 10°. Minimize the friction and extrusion between the tool and the workpiece, and improve the quality of the work surface. The lead angle is 10° to 30°, and the second deflection angle is 5° to 10°. Use a positive blade tilt angle between 0° and 5° to prevent chips from overflowing and damaging the machined surface. Use a higher spindle speed (120r/min). Small gap (0.2-0.3 mm) and a small feed rate of 0.1 mm/revolution.
Round surface processing
When turning the outer circle, inner hole, and full length, it is more economical to use an ordinary lathe to process. However, it is not easy to ensure the round surface with an ordinary lathe, so the arc surface of the roller is finished by a CNC lathe. If the margins are not uniform, the material is hard, and the number of passes should be increased during programming to set a low spindle speed and small feed. If sand and air holes are easy to sharpen, the starting point of the program must be set before each programming. By avoiding the process of “starting from scratch” for each cutter, a lot of time can be saved, “useless work” can be reduced, and production efficiency can be improved.
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