Because high-precision cold-drawn tubes have good mechanical properties and excellent economic and technical value, more than 80% of the cylinders in economically developed countries in the world are made of high-precision cold-drawn tubes, and high-precision cold-drawn tubes are used to make cylinders and rollers. It is the only way for my country's hydraulic and pneumatic industries to connect with international standards. Pay attention to the following points about rolling:
1. Whether the selection of rolling pressure is correct will affect the surface roughness, size and accuracy after rolling. In general, as the rolling pressure increases, the surface roughness increases. However, when the rolling pressure is increased to a certain degree, the surface roughness no longer increases. If it continues to increase, the rolled surface begins to deteriorate and even cracks appear.
2. To improve the surface roughness of the workpiece, the effect of rolling is the best. When the pre-processing roughness reaches Ra1.6, as long as the interference is appropriate, the roughness can reach Ra0.2 or more. But when the pre-processed roughness is only Ra6.4～Ra3.2, and the machined surface has vibration and chaotic knife marks, then the deeper knife marks cannot be rolled, which only increases the interference and rolls again. If the ovality and taper of the hole are too large, the above-mentioned defects still exist after rolling, and the roughness is large. Therefore, the pre-processed surface is better to be less than Ra3.2, and the geometric accuracy is one or two or more, which can obtain small roughness and ideal accuracy.
3. The material is soft and has large plasticity and is easy to be rolled out. As the plasticity decreases and the hardness increases, the amount of permanent deformation decreases. Generally speaking, the rolling effect of steel and copper is better, and the effect of cast iron is poor. Malleable iron and ductile iron have a better rolling effect than gray cast iron. When rolling iron castings, when the material hardness of the casting is uneven, defects on the rolled surface (pores, blisters, etc.) will be immediately revealed. Therefore, the rolling process should not be used when the casting surface has many defects and poor quality.
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