Mill Shell Stress Distribution Element for Flange Hard Spots

Solution Overview

Problem

Large-scale grinding mills face stress concentration issues at flange connections, leading to potential cracking and long-term failure due to 'hard spots' caused by sudden changes in stiffness, which existing solutions either increase mass or ignore stress raisers, both with drawbacks.

Innovation Solution

A stress distribution element with a varying dimension, such as height or width, is introduced to distribute stress from the joint of mill shell sections, using a dummy flange that connects to the mill shell joint, reducing stress concentrations by gradually transitioning from a stiffer to a less stiff area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the mass of the shell section is increased to reduce stress concentrations from hard spots, then the reliability and strength are improved, but the manufacturing cost and weight increase

Engineering Contradiction:

Improvejoint integrityVSAvoidmill shell mass

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

A stress distribution element is introduced as an intermediary component between the longitudinal flange and the circumferential flange at the hard spot location. This element has a varying cross-sectional area that gradually transitions from a larger area at the longitudinal flange connection to a smaller area at the circumferential flange connection, serving as a stress transition zone that distributes concentrated stresses along its length rather than allowing them to concentrate at the joint

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The stress distribution element utilizes gradual geometric parameter changes, specifically a varying cross-sectional area along its length, to create a progressive stiffness transition. This allows the element to distribute stresses by gradually changing from a stiffer region (larger cross-section) to a less stiff region (smaller cross-section), eliminating sudden stiffness changes that cause stress concentrations

Inventive Principle:

Principle #35Parameter changes

2Strength

If the mass of the shell section is increased to reduce stress concentrations from hard spots, then the strength is improved, but the manufacturing cost increases

Engineering Contradiction:

Improveresistance to crackingVSAvoidmanufacturing cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

A stress distribution element is introduced as an intermediary component between the longitudinal flange and the circumferential flange at the hard spot location. This element has a varying cross-sectional area that gradually transitions from a larger area at the longitudinal flange connection to a smaller area at the circumferential flange connection, serving as a stress transition zone that distributes concentrated stresses along its length rather than allowing them to concentrate at the joint

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The stress distribution element utilizes gradual geometric parameter changes, specifically a varying cross-sectional area along its length, to create a progressive stiffness transition. This allows the element to distribute stresses by gradually changing from a stiffer region (larger cross-section) to a less stiff region (smaller cross-section), eliminating sudden stiffness changes that cause stress concentrations

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If the mill shell is divided into modular shell sections with split flanges to facilitate assembly and transportation, then the ease of manufacture and transportation is improved, but stress concentrations and reliability deteriorate

Engineering Contradiction:

Improveassembly and transportationVSAvoidjoint integrity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

A stress distribution element is introduced as an intermediary component between the longitudinal flange and the circumferential flange at the hard spot location. This element has a varying cross-sectional area that gradually transitions from a larger area at the longitudinal flange connection to a smaller area at the circumferential flange connection, serving as a stress transition zone that distributes concentrated stresses along its length rather than allowing them to concentrate at the joint

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The stress distribution element utilizes gradual geometric parameter changes, specifically a varying cross-sectional area along its length, to create a progressive stiffness transition. This allows the element to distribute stresses by gradually changing from a stiffer region (larger cross-section) to a less stiff region (smaller cross-section), eliminating sudden stiffness changes that cause stress concentrations

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3019277B1Stress distribution element for a grinding mill shell

Publication Date: 2022.02.09 METSO OUTOTEC FINLAND OY

Figure 1
Figure 2A~2C
Figure 3A~3C

AI summary

The invention provides a stress distribution element (20) for a mill shell joint, comprising an elongated body (21) having a proximal end (22) and a distal end (23). The elongated body (21) varies in one dimension (24, 45) from the proximal end (22) to the distal end (23) to distribute stress forces from the proximal end to the distal end. The invention also provides a stress distribution system, a stress distribution assembly, a mill shell section, a mill shell and a method of distributing stress incorporating the stress distribution element (20).