Since the late 1980s, the analysis technology has widely used the finite element method (FEM). Recently, with the development of computer output, the analysis technology has developed from two-dimensional to three-dimensional advanced deformation analysis. As a result, the dimensional accuracy and quality of products have been improved, and representative analysis techniques are introduced below.
1. Analytical technology of elongation rolling
The mandrel rolling mill adopts the mandrel and the grooved roll for rolling, so it is different from the plate rolling, there is a free deformation zone where the car roll and the mandrel are not in contact with each other in the circumferential direction of the roll. Since the free deformation zone is rolled on the next stand, it is important to predict the deformation including the free deformation zone in order to correctly understand the comprehensive characteristics of the mandrel mill.
Such complex deformation prediction cannot obtain high precision by using the conventional cache implementation algorithm, so high-precision analysis is required. Considering the shear deformation in the rolling direction, an approximate three-dimensional analysis is carried out by using ordinary expansion plane deformation analysis. The results show that the calculated and experimental values are in good agreement.
Recently, with the development of computer technology, the development of a complete three-dimensional finite element method analysis technology has been accelerated, and it can also be used for the analysis of the influence of tension between stands and the analysis of the speed difference between the roll and the billet.
2. Analytical technology of sizing rolling
When sizing rolling is used, since there is no tool on the inner surface, the shape of the inner surface of the rolled material is irregular when rolling thick-walled pipes. When using a three-roll rolling mill, the inner surface of the rolled material is hexagonal in shape. Through the analysis of the three-dimensional finite element method, the mechanism and countermeasures of this inner surface edge phenomenon are clarified. A substantially uniform wall thickness can be obtained when a hole pattern with an ellipticity close to a perfect circle = 0.986 is used, but when a pass pattern with an ellipticity close to a perfect circle = 0.960 is used, clear inner hexagonal corners appear. This analysis can predict the change of wall thickness when rolling with tension reducer, and clarifies the influence of roll pass characteristics and tension between stands on the hexagonal angle of inner surface.
3. The reasons for the surface defects of seamless pipes:
① Due to the surface defects or internal defects of the tube blank.
② Produced during the production process, such as incorrect rolling process parameter design, rough mold surface, poor lubrication conditions, unreasonable pass design and adjustment.
③ During the heat rolling, heat treatment and straightening process of the tube blank (seamless steel pipe), if the heating temperature is not properly controlled, the deformation is uneven, the heating and cooling rate is unreasonable, or the straightening deformation is too large, resulting in excessive residual stress , Then it may also cause surface cracks in seamless steel pipes.
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