Mandrel Mill with 4-Roll and 2-Roll Stands for Pipe Elongation

Solution Overview

Problem

Current mandrel mills, particularly 2-roll mills, face challenges in achieving high working ratios and dimensional accuracy when rolling difficult-to-roll materials like stainless steel or thin-walled pipes due to uneven stress distribution and complexity in equipment design and adjustment.

Innovation Solution

Incorporating at least one 4-roll stand for wall thickness reduction upstream and a 2-roll stand or a hydraulically-loaded 2-roll stand as the final stand downstream in the mandrel mill, with driven rolls in the 4-roll stand to maintain uniform deformation and facilitate easier zero-point adjustment, enhancing the working ratio and dimensional accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a 2-roll mandrel mill is used for elongation rolling, then the equipment structure is simple and zero point adjustment is easy, but the working ratio is low and dimensional accuracy is poor due to uneven stress distribution

Engineering Contradiction:

Improveequipment structureVSAvoidworking ratio

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The mandrel mill is divided into multiple roll stands (typically 5-8 stands) with each stand containing rolls that apply localized deformation. This segmentation allows the hollow shell to undergo progressive elongation with controlled stress distribution at each stage, improving the working ratio while maintaining manageable equipment complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each roll stand applies localized reduction at specific positions around the hollow shell circumference. The rolls are positioned to create controlled local deformation zones that progressively elongate the shell while maintaining overall stress balance, thereby achieving higher working ratios and dimensional accuracy

Inventive Principle:

Principle #3Local quality

2Device complexity

If a 2-roll mandrel mill is used for elongation rolling, then the equipment structure is simple, but the dimensional accuracy is poor due to difficulty in guaranteeing zero point adjustment

Engineering Contradiction:

Improveequipment structureVSAvoiddimensional accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The elongation process is divided into multiple stages across several roll stands, with each stand contributing a controlled portion of the total reduction. This segmentation allows for cumulative precision control, where each stand's contribution to the final dimensions can be optimized and maintained within tight tolerances

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each roll stand applies localized reduction at specific positions around the hollow shell circumference. The rolls are positioned to create controlled local deformation zones that progressively elongate the shell while maintaining overall stress balance, thereby achieving higher working ratios and dimensional accuracy

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If roll stands with different numbers of rolls are installed in the same mandrel mill to suppress thickness deviations, then thickness deviation is reduced, but the equipment becomes complicated and design improvement becomes difficult

Engineering Contradiction:

Improvethickness uniformityVSAvoidequipment complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The mandrel mill employs multiple roll stands (typically 5-8 stands) where each stand performs a specific function in the elongation sequence. This segmentation allows the system to achieve uniform thickness control through progressive localized reduction while maintaining a standardized modular structure that facilitates design and improvement

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each roll stand applies localized reduction at specific positions around the hollow shell circumference. The rolls are positioned to create controlled local deformation zones that progressively elongate the shell while maintaining overall stress balance, thereby achieving higher working ratios and dimensional accuracy

Inventive Principle:

Principle #3Local quality

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 allows for significantly higher working ratios and dimensional accuracy in elongation rolling, reducing operational issues and ensuring consistent pipe quality, even with challenging materials.

Implementation Method 1

the shell undergoes elongation rolling using a mandrel mill, which typically comprises 5 to 8 roll stands, to decrease the wall thickness to a predetermined value and form a mother tube

Methodology Applied

Scientific EffectPlastic deformation: Plasticity

Data Source

PatentUS8122749B2Mandrel mill and process for manufacturing a seamless pipe

Publication Date: 2012.02.28 NIPPON STEEL CORPORATION

AI summary

A mandrel mill is provided which can perform elongation rolling with a markedly increased working ratio and dimensional accuracy on a material which is inherently difficult to roll such as a hollow shell made of stainless steel or a thin-walled material. A mandrel mill for manufacturing a mother tube by performing elongation rolling of a hollow shell comprises a plurality of roll stands, having at least one 4-roll stand for wall thickness reduction of a hollow shell and at least one 2-roll stand including the final stand downstream of the 4-roll stand.