Zhuojin Pipe Fitting Co., LtdOblique Continuous Rolling Process Parameters Effect on Rolling Force and Blank Tube Dimensional Accuracy
Literature Overview
This paper by Mao Feilong, Shuang Yuanhua, Wang Qinghua, and Wang Fujie (2018) investigates the influence of oblique continuous rolling process parameters on rolling force and blank tube dimensional accuracy for seamless steel tubes. Published in the Journal of Plasticity Engineering (Vol. 25, No. 3, pp. 108–114), the study was supported by the Shanxi Province Overseas Research Fund (2017-084). The research is highly relevant to seamless tube manufacturing, where the oblique continuous rolling (OCS) process is employed to produce small-diameter tubes with high dimensional accuracy.
Core Technical Content
Oblique continuous rolling is a continuous production process that combines piercing and tube rolling in a single pass through sequentially arranged rolls at an oblique angle. The process eliminates the need for a separate tube rolling mill, making it economically advantageous for small-diameter seamless tubes. However, the process parameters are interrelated in complex ways, and optimizing them is essential for achieving acceptable rolling forces, product quality, and equipment loading.
Experimental Design and Parameter Ranges
The study employed a single-variable multi-group experimental approach on an oblique continuous rolling experimental mill, using Φ40 mm and Φ42 mm billets. The parameter ranges investigated are summarized below:
| Parameter | Range | Unit | Description |
|---|---|---|---|
| Mandrel projection (顶头前伸量) | 15–28 | mm | Distance the mandrel extends beyond the roll gap |
| Piercing section feed angle (送进角) | 7–9 | degrees | Angle of the piercing roll axis relative to the horizontal |
| Piercing section roll throat (孔喉) | 34–35 | mm | Throat diameter of the piercing rolls |
| Tube rolling section roll speed (轧辊转速) | 182–190 | r/min | Rotational speed of the rolling rolls |
Rolling Force Analysis
Mandrel Projection Effect
As the mandrel projection increases from 15 mm to 28 mm:
- The piercing section rolling force decreases progressively.
- The mandrel axial force first decreases and then increases, exhibiting a minimum at an intermediate projection value.
This non-monotonic behavior of the mandrel axial force suggests that there exists an optimal mandrel projection that balances the reduction in rolling force against the axial load on the mandrel. A projection that is too small results in excessive rolling force due to insufficient deformation distribution, while a projection that is too large causes the deformation to shift toward the mandrel tip, increasing axial resistance.
Feed Angle Effect
Increasing the feed angle from 7° to 9° results in:
- A decrease in piercing section rolling force.
- A slight increase in mandrel axial force.
The reduction in rolling force with increasing feed angle can be attributed to the increased inclination promoting a more axial deformation component, which reduces the radial compressive stress on the roll contact area. However, the slight increase in axial force indicates that the mandrel bears a marginally higher load as the deformation becomes more axially oriented.
Roll Throat Effect
The roll throat diameter has a direct and significant influence on rolling force:
- For a given billet diameter, decreasing the roll throat increases the rolling force (greater deformation intensity per pass).
- For a given roll throat, increasing the billet diameter increases the rolling force (larger volume of material to deform).
This is consistent with classical metal forming theory, where the deformation intensity is proportional to the reduction ratio (1 - d_throat / D_billet).
Tension vs. Push Rolling
A particularly important finding concerns the effect of rolling mode (tension vs. push) on rolling forces:
| Rolling Mode | Piercing Section Rolling Force | Tube Rolling Section Rolling Force | Mechanism |
|---|---|---|---|
| Tension rolling (张力轧制) | Decreased | Decreased | Tensile stress in the tube reduces the required compressive force |
| Push rolling (推力轧制) | Increased | Increased | Compressive stress adds to the required rolling force |
The tension rolling mode effectively pre-stresses the tube in tension, which reduces the effective yield stress required for further deformation. This is analogous to the beneficial effect of back-tension in sheet rolling. The push mode, conversely, adds a compressive component that must be overcome by the rolls, increasing energy consumption and equipment load.
Dimensional Accuracy Results
The study reports that micro-tension rolling achieves the following dimensional accuracy for the blank tube:
| Dimensional Parameter | Tolerance |
|---|---|
| Wall thickness accuracy (壁厚精度) | ±0.2 mm |
| Outer diameter accuracy (外径精度) | ±0.35 mm |
These tolerances are competitive with conventional tube rolling mills for small-diameter tubes and demonstrate the potential of the oblique continuous rolling process as a viable production technology.
Process Optimization Recommendations
Based on the experimental findings, the following process optimization strategies are recommended for industrial application:
- Mandrel projection: Select an intermediate value (approximately 20–22 mm for the tested parameters) to balance rolling force reduction against mandrel axial force. This can be further refined through FEA simulation of the specific roll geometry and material properties.
- Feed angle: Use the upper end of the investigated range (8.5–9°) to minimize rolling force while accepting a marginal increase in mandrel axial force.
- Roll throat: Optimize the roll throat to achieve the desired wall thickness in the fewest number of passes, considering both rolling force constraints and the need for adequate dimensional accuracy.
- Tension control: Implement micro-tension rolling as the default operating mode. The tension level should be carefully controlled to avoid excessive thinning or ovality. A tension-to-rolling-force ratio of approximately 5–15% is typical for achieving the reported dimensional accuracy.
Study Insights and Reflections
From a manufacturing engineering perspective, this study provides valuable quantitative data for the process design and optimization of oblique continuous rolling mills. The single-variable experimental approach, while computationally intensive in terms of the number of tests required, provides clear cause-and-effect relationships that are essential for developing empirical process models.
The finding that tension rolling reduces both piercing and tube rolling section forces is particularly significant from an energy efficiency standpoint. In industrial operations, rolling force directly correlates with motor power consumption, roll wear, and equipment fatigue life. By implementing controlled tension, manufacturers can extend equipment service intervals and reduce energy costs.
The dimensional accuracy achieved (±0.2 mm wall thickness, ±0.35 mm outer diameter) is sufficient for many downstream applications but may require additional sizing passes for precision tube applications. Engineers should evaluate whether the oblique continuous rolling output meets the specific tolerance requirements of their target market before committing to production investment.