Zhuojin Pipe Fitting Co., LtdCold Oblique Rolling Process for Steel Pipes and Bimetallic Tubes
Literature Overview
The paper by Zhou Cunlong, Liu Xueyun, and Qin Jianping, published in Steel Pipe (2004, Vol. 33, No. 4), presents a novel cold oblique rolling process for steel pipes, developed at Taiyuan Heavy Industry Institute. This process addresses limitations of traditional cold rolling and cold drawing methods, offering a viable alternative for pipe deep processing and bimetallic tube composite manufacturing.
Core Technical Approach and Process Principles
The cold oblique rolling process exploits the motion and deformation characteristics of the workpiece during oblique rolling. In this process, the steel pipe blank is fed into a pair of rotating rolls at an oblique angle, causing the pipe to undergo simultaneous axial shortening and radial thinning. The key innovation is the design of roll profiles that accommodate the specific deformation pattern of tubular workpieces.
The authors employed rigid-plastic finite element analysis to simulate the deformation process, calculating the velocity field, strain distribution, and stress state during rolling. This analysis provided the basis for designing roll profiles that achieve uniform deformation and minimize defects.
Process Parameters and Roll Design
The cold oblique rolling process involves several critical parameters that must be optimized for different pipe geometries and materials:
| Parameter | Typical Range | Effect on Process |
|---|---|---|
| Reduction per pass | 5–15% | Higher reduction increases stress and risk of cracking |
| Oblique angle | 5–15° | Affects feed force and deformation uniformity |
| Roll surface speed | 500–2000 m/min | Must be matched to material strain rate |
| Lubrication | Synthetic oil or emulsion | Reduces friction and surface damage |
| Roll profile | Custom-designed | Determines deformation pattern and quality |
| Temperature | Room temperature to 200°C | Higher temperature reduces flow stress |
Comparison with Traditional Processes
The cold oblique rolling process offers several advantages over traditional cold rolling and cold drawing:
| Feature | Cold Drawing | Cold Rolling | Cold Oblique Rolling |
|---|---|---|---|
| Applicable pipe diameter | Small (<100 mm) | Medium | Wide range |
| Reduction per pass | High | Low | Moderate |
| Production speed | Low | High | High |
| Surface quality | Excellent | Good | Good |
| Equipment cost | High | Moderate | Moderate |
| Bimetallic composite capability | Limited | Limited | Excellent |
Engineering Practice and Quality Control
The industrial trial described in the paper demonstrates the feasibility and practicality of the cold oblique rolling process. The process can partially replace traditional cold rolling and cold drawing, particularly for medium to large diameter pipes where drawing is impractical. More importantly, the process enables the production of bimetallic tubes with excellent bonding between the inner and outer layers.
Quality control for cold oblique rolled pipes includes:
- Dimensional inspection of outer diameter, wall thickness, and straightness
- Surface inspection for scratches, cracks, and roll marks
- Mechanical property testing (tensile strength, hardness, elongation)
- Hydrostatic testing for leak detection
- Metallographic examination of the cross-section for internal defects
Study Insights and Reflections
This paper represents a significant contribution to the field of pipe manufacturing technology. The cold oblique rolling process offers a flexible and efficient method for pipe deep processing, with the added advantage of enabling bimetallic composite production. The use of rigid-plastic finite element analysis for roll design demonstrates the value of computational methods in process development.
From a welding perspective, cold worked pipes may require stress relief before welding to prevent cracking. The cold working introduces residual stresses and strain hardening that can affect the weldability of the pipe. For bimetallic tubes, the welding procedure must account for the different thermal expansion coefficients and corrosion resistance of the inner and outer layers. The welding electrode or filler metal must be selected to be compatible with both layers, and the heat input must be controlled to avoid excessive dilution or cracking.
The cold oblique rolling process also has implications for pipe fitting fabrication. Elbows, tees, and reducers formed from cold rolled pipes may exhibit improved mechanical properties and surface finish compared to hot formed fittings. However, the increased hardness and reduced ductility in the cold worked regions must be considered in the design of the forming process to avoid cracking or excessive springback.
In conclusion, the cold oblique rolling process represents a promising technology for steel pipe deep processing and bimetallic tube manufacturing, with potential applications in the oil and gas, chemical, and power industries where high-performance pipe materials are required.