Sizing of seamless tube micro-tension reducing machine
Sizing technology of seamless steel tube micro-tension reducer
When the seamless steel pipe is sizing by a micro-tension reducer, the wall of the steel pipe is unevenly thickened due to the transverse deformation of the metal (flowing in the radial direction), so that the inner hole of the cross section is "hexagonal", commonly known as "inner" Six parties". "Inner hexagon" is the result of uneven metal lateral deformation, and it is also a special form of uneven steel pipe wall thickness.
The hot-rolled steel pipe produced by Xining Special Steel Group Co., Ltd. (Xining Special Steel (600117, shares)) has a maximum reduction rate of 3.5% for a single stand of the rolling mill, and an average tension coefficient of less than 0.48. It adopts micro-tension rolling, three-roll type Fourteen two-motor centralized differential transmission micro-tension reducers for sizing can make the diameter and wall thickness of the steel pipe reach the final product size. However, this equipment is prone to "inner hexagonal" defects when rolling thick-walled steel pipes with small diameters, which seriously affects the wall thickness and inner diameter accuracy. This work is mainly formulated by adjusting the reducing rate and modifying the pass parameters of the reducer. The production process can effectively reduce the "inner six party" defects.
1 Production process and process points
The production process is as follows: billet sawing, billet heating, perforating, rolling, micro-tension reducing, cooling, straightening, and cutting tube packaging delivery.
2 Determination of process parameters and pass design
When the factory uses ￠120mm continuous casting billet to produce 114mm×22mm steel pipes, the wall thickness coefficient of the steel pipes is relatively large, which makes the lateral wall thickness of the steel pipes after sizing uneven, resulting in a greater degree of "inner hexagonal" on the inner surface of the steel pipe serious.
In the case of micro-tension reduction, the reduction rate is the most important factor that produces the "inner hexagon", and the total reduction rate and the single frame reduction rate have the same influence mechanism. If the diameter reduction rate is too large, the tension coefficient will increase, which will increase the axial flow when the metal is deformed, while the radial flow will weaken and the radial wall thickness will be uneven. That is to say, the large diameter reduction rate of the single frame means that the unevenness of the height compression at the top and the roll gap and the greater the difference in metal flow will increase the generation of inner polygons.
When the total reduction rate is unchanged, increasing the number of finished racks can reduce the reduction rate of a single frame. Before optimization, 5 sizing machines were used, and 6 sizing machines were used after optimization. The reduction rate of each frame can be calculated from the formula. The reduction rate of the first frame depends on the size of the outer diameter before sizing. In actual production, this number is a range value, so the reduction rate of the first frame is one Uncertain value.
The main parameters of the traditional pass of the micro-tension reducer include: width expansion coefficient, average diameter of the pass, major semi-axis of the pass, minor semi-axis of the pass, and ellipticity coefficient.
3 Actual production effect
After reducing the total reduction rate and the single frame reduction rate and optimizing the pass parameters, the 114mm×22mm finished steel pipe was sampled. The actual measurement data showed that the degree of "inner hexagonal" was significantly reduced and reached the national standard. Fully meet user needs. By comparing the measured data before and after the optimization, it can be known that the "inner hexagonal" measurement value of the steel pipe produced by the optimized 114mm pass is significantly reduced.
4 Conclusion
Production practice has proved that the 114mm unit three-roller fourteen two-motor centralized differential transmission micro-tension reducer can be reduced or eliminated by reducing the total reduction rate and the single frame reduction rate and selecting a reasonable pass design. The "inner hexagonal" defect of micro-tension reducing steel pipe.
