Grouped Three-Roll Stretch-Reducing Mill for Pipe Tolerance Control
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Solution Overview
Problem
Existing stretch-reducing mills for seamless tube production face issues with uneven internal cross-section formation due to speed distribution disparities and temperature differences, leading to internal polygon formation, which is exacerbated by the three-roller design and limited installation space for four-roller alternatives.
Innovation Solution
The stretch-reducing mill is designed with multiple roll stands arranged in groups, each with three rolls at 120° angular spacing, where rolls within groups are offset by a group-internal angle (e.g., 60°) and groups are skewed relative to each other by a smaller group angle (e.g., 30°), with a neutral roll stand between groups to counteract torsional moments and improve temperature equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a three-roll design is used in the stretch-reducing mill, then the installation space for roll bearings is reduced and capacity to absorb forming forces is limited, but the uneven velocity distribution between base and incremental diameter leads to internal polygon formation and non-uniform wall thickness
Solution Approach 1:
The rolling process is segmented into multiple passes with different roll configurations. The mill alternates between rolling at the bottom of the caliber and at the caliber inflection point, dividing the deformation process into distinct stages that collectively achieve more uniform wall thickness than a single configuration could provide.
Solution Approach 2:
The mill employs dynamic adjustment of roll speeds and positions during the rolling process. By varying the velocity distribution between rolls and adjusting the caliber position dynamically, the system compensates for the inherent limitations of the three-roll design and maintains more uniform deformation across the tube wall.
2Temperature
If temperature differences exist from the preceding stretching unit, then the forming conditions between base and incremental diameter become different, but this superimposes internal polygon formation and intensifies the effect
Solution Approach 1:
The mill employs periodic alternation between rolling at the bottom of the caliber and rolling at the caliber inflection point. This periodic change in rolling position creates alternating deformation patterns that, when combined over multiple passes, average out the temperature-induced forming differences and reduce internal polygon formation.
3Ease of operation
If rolls are arranged symmetrically at 120° angular intervals, then three sides of the tube are rolled, but this creates uneven velocity distribution between base and incremental diameter
Solution Approach 1:
While maintaining the symmetrical 120° roll arrangement for operational simplicity, the system dynamically adjusts the rotational speeds of individual rolls and the position of the caliber during the rolling process. This dynamic control compensates for the inherent velocity distribution issues created by the symmetrical geometry.
Solution Approach 2:
The mill changes operating parameters such as roll speeds, caliber positions, and rolling forces during the process. By varying these parameters between passes and adjusting them based on the specific rolling conditions, the system optimizes velocity distribution while maintaining the benefits of symmetrical roll arrangement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the uniformity of rolled wall thicknesses, approximates a circular internal cross-section, and improves temperature equalization, thereby improving rolling quality and reducing deviations in wall thickness.
Implementation Method 1
each with three rolls arranged at an angular distance of 120°... in order to exert a rolling force on the outer circumference of the tube
Implementation Method 2
at least one neutral rolling stand... The shape of the rolls counteracts any torsional moment acting on the pipe
Data Source
Figure 1
Figure 2~3
AI summary
A stretch-reducing mill (1) for producing seamless pipes (R), which comprises a plurality of roll stands (10), which are arranged one after the other in a conveying direction (F) of the pipes (R) and each have three rolls (11) arranged at an angular distance of 120°, wherein the roll stands (10) are divided into at least two groups (A, B) each having at least two roll stands (10); the rolls (11) of adjacent roll stands (10) within a group (A, B) are staggered relative to each other by an intra-group angle αI; and the rolls (11) of the roll stands (10) of adjacent groups (A, B) are staggered relative to each other by a group angle αG that is less than the intra-group angle αI.