Calculation of Unit Rolling Pressure in Oblique Rolling of Seamless Steel Tubes

Literature Overview

This technical paper by Luo Tao from Chengdu Chengwu Steel Pipe Technology Co., Ltd. and Deng Jigang from Sichuan Metallurgical Design and Research Institute presents an analytical method for calculating the unit rolling pressure in oblique rolling of seamless steel tubes. Published in Steel Pipe, Volume 49, Issue 1, 2020, the study addresses a critical aspect of seamless tube manufacturing process design.

Core Technical Findings

The authors developed an analytical calculation method for oblique rolling unit pressure based on engineering plasticity mechanics, considering the deformation characteristics and spatial relationships of the oblique rolling process. The method involves establishing the geometric relationships of deformation characteristic cross-sections, analyzing the stress state of deformation unit slices, and solving the stress differential equations to derive the unit rolling pressure formula.

The analytical method was validated through practical examples, demonstrating its applicability for general oblique rolling force energy parameter calculations and stress-strain analysis of oblique rolling deformation.

Technical Interpretation

Oblique rolling is a continuous forming process used to produce seamless steel tubes, particularly for large-diameter pipes. Unlike conventional cross rolling, oblique rolling involves the rotation of the workpiece around an axis that is inclined relative to the roll axis, creating a more complex deformation pattern. The unit rolling pressure calculation is fundamental for determining the required rolling force, roll design, and drive power requirements.

The engineering plasticity approach used in this study simplifies the complex three-dimensional deformation into a series of two-dimensional analyses on characteristic cross-sections. This approach is practical for engineering applications because it balances accuracy with computational tractability. The stress differential equations derived for each unit slice account for the non-uniform deformation across the rolling zone, providing a more accurate pressure distribution than simplified uniform deformation models.

The geometric relationships of the deformation characteristic cross-sections are critical because they determine how the material flows during the rolling process. In oblique rolling, the cross-sections are not perpendicular to the roll axis, which introduces additional complexity in the deformation analysis. The authors' approach of analyzing individual unit slices allows for detailed examination of the local deformation behavior while maintaining the overall process framework.

Process Parameters and Design Considerations

The unit rolling pressure is influenced by several process parameters, including the roll diameter, roll groove geometry, workpiece material properties, reduction ratio, and rolling speed. Each of these parameters affects the stress state within the deformation zone and must be carefully considered in the calculation.

For practical rolling mill design, the calculated unit pressure is used to determine the total rolling force, which in turn governs the roll bearing loads, roll housing design, and motor power requirements. Accurate pressure calculation is therefore essential for ensuring the mechanical integrity and operational efficiency of the rolling mill.

Engineering Practice Implications

This analytical method provides rolling mill designers and process engineers with a tool for evaluating different process configurations without relying solely on empirical data or numerical simulations. During the design phase of a new rolling mill or when optimizing an existing mill for a new product, the ability to quickly calculate unit rolling pressure for various parameter combinations is invaluable.

The method can also be used for troubleshooting production issues. When unexpected rolling forces or roll wear patterns are observed, the analytical approach can help identify whether the problem stems from process parameter deviations, material property variations, or equipment condition issues.

Reflection and Key Questions

While the analytical method provides valuable insights, several limitations must be acknowledged. The engineering plasticity approach assumes plane strain conditions on each characteristic cross-section, which may not fully capture the three-dimensional deformation characteristics of oblique rolling. Additionally, the method does not explicitly account for temperature effects during hot rolling, where material flow stress decreases significantly with increasing temperature.

The validation through practical examples is encouraging, but more extensive validation across a wider range of products, materials, and process parameters would strengthen the method's credibility. Future work should consider incorporating temperature-dependent material properties and friction conditions to improve prediction accuracy for hot rolling applications.

Concluding Remarks

This study presents a rigorous analytical framework for calculating unit rolling pressure in oblique rolling of seamless steel tubes. The approach combines engineering plasticity theory with practical process considerations to provide a method that is both theoretically sound and practically applicable. The validation through practical examples demonstrates the method's utility for rolling force energy parameter calculations and deformation analysis. Further refinement to account for temperature effects and three-dimensional deformation characteristics would enhance the method's accuracy and broaden its applicability across different rolling conditions and product specifications.