Continuous restrained rolling mill mandrel extraction
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Solution Overview
Problem
Longitudinal rolling mills face issues with productivity, pipe quality, and temperature uniformity due to acceleration-induced compression, non-uniform cooling, and the need for additional processing steps like fossil furnace heating, especially for small and medium pipes.
Innovation Solution
A continuous, restrained-type rolling mill process with a main rolling mill and an extracting rolling mill in line, where the extracting mill is positioned at a distance from the main mill to allow independent speed control and lateral unloading of the mandrel bar, enabling synchronized pipe and mandrel bar movement and reducing cycle time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the mandrel bar is restrained at the favourable rolling speed, then rolling stability and pipe quality are improved, but the cycle time increases and productivity decreases to 2 pieces per minute
Solution Approach 1:
The system is divided into two independent functional units: a main rolling mill for pipe production and a separate extracting rolling mill for mandrel bar removal. This segmentation allows each unit to operate independently at its optimal speed, with the main rolling mill maintaining stable rolling at favourable speeds while the extracting mill handles mandrel removal separately, thus resolving the contradiction between quality and productivity
Solution Approach 2:
The extracting rolling mill acts as an intermediary device between the main rolling mill and the mandrel bar extraction process. It receives the pipe-mandrel assembly from the main rolling mill, performs the extraction operation, and returns the mandrel bar to the inlet, enabling continuous operation without interrupting the main rolling process
2Device complexity
If the extracting rolling mill is placed close to the main rolling mill, then the system compactness is improved, but the mandrel bar cannot be extracted laterally and must pass through the extractor causing alignment issues and longitudinal marking
Solution Approach 1:
The extracting rolling mill is positioned downstream at a distance greater than the maximum length of the hollow body, allowing the mandrel bar to be extracted laterally (in a different spatial dimension) rather than forcing it through the extractor. This dimensional change in the extraction path eliminates alignment issues between roller edges and prevents longitudinal marking on the pipe surface
3Speed
If the mandrel bar is dragged by pressure rollers for unloading, then the unloading speed is improved, but the hot mandrel bar surface is damaged
Solution Approach 1:
The extracting rolling mill serves as an intermediary mechanism that transfers the mandrel bar from the main rolling mill to the unloading position using controlled rolling contact rather than direct dragging. This intermediary approach enables rapid unloading while protecting the hot mandrel bar surface from damage by distributing the contact forces through the rolling mill's roller system
Data Source
Figure 1.1~1.3
Figure 2~3
Figure 4.1
AI summary
A longitudinal, multi-stand rolling mill of the continuous, restrained type for rolling hollow bodies is described, which comprises a main rolling mill (2) and an extracting rolling mill (4) in line and downstream of the main rolling mill, at a distance from the main rolling mill larger than the maximum length of the hollow body and of the spindle, and in which the spindle is extracted at the outlet of the main rolling mill in the gap between said main rolling mill and extracting rolling mill, and is laterally unloaded.