Nitrided Inner Diameter Surface in Aluminum Caster Roll Shells

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Solution Overview

Problem

Current methods for reducing galling and corrosion on the inner diameter surface of aluminum caster roll shells in strip casting processes are inadequate, leading to debris accumulation, heat transfer issues, and potential catastrophic failures due to interference shrink fits, increased brittleness, and galvanic corrosion from chromium plating.

Innovation Solution

The inner diameter surface of the steel roll shell is nitrided using ion nitriding to create a hard, dense, crack-free surface layer, enhancing galling and corrosion resistance without the limitations of chromium plating, such as heat extraction barriers and galvanic corrosion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If interference shrink fit is increased to reduce galling and debris generation, then galling resistance is improved, but outer diameter surface heat checking or cracking occurs due to excessive circumferential tension stresses

Engineering Contradiction:

Improvegalling resistanceVSAvoidresistance to heat checking and cracking

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent applies ion nitriding treatment specifically to the inner diameter surface of the roll shell where it contacts the core, creating a localized hard nitrided layer (0.002-0.006 inches deep) with hardness of 58-62 HRC. This local hardening provides galling resistance at the contact interface without requiring increased overall interference fit that would cause circumferential stress and cracking in the roll shell body.

Inventive Principle:

Principle #3Local quality

2Reliability

If chromium plating is applied to improve galling resistance, then surface hardness is increased, but galvanic corrosion occurs and heat extraction is hindered

Engineering Contradiction:

Improvegalling resistanceVSAvoidgalvanic corrosion and heat transfer barrier

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces expensive chromium plating with ion nitriding, which creates a nitrogen-enriched layer within the steel substrate itself rather than a separate metal coating. This eliminates galvanic corrosion between dissimilar metals (chromium and steel) and maintains thermal conductivity since the nitrided layer is chemically bonded to the base material. The nitrided surface provides equivalent or superior galling resistance without the harmful side effects of chromium plating.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If higher carbon steel alloys are used to increase hardness and galling resistance, then surface hardness is improved, but brittleness increases leading to reduced shrink fit and increased movement at the interface

Engineering Contradiction:

Improvegalling resistanceVSAvoidshrink fit stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent creates a localized hard nitrided surface layer (0.002-0.006 inches deep) on the inner diameter surface through ion nitriding, while the bulk roll shell material remains ductile with appropriate hardness (45-55 HRC). This gradient structure provides galling resistance at the contact interface while maintaining overall shrink fit stability and reducing brittleness compared to using high carbon steel throughout the entire roll shell.

Inventive Principle:

Principle #3Local quality

4Reliability

If ion nitriding is applied to create a hard surface layer, then galling resistance is improved, but the process complexity and treatment time increase

Engineering Contradiction:

Improvegalling and corrosion resistanceVSAvoidnitriding process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs ion nitriding, which uses plasma (ionized gas) to deliver nitrogen atoms to the steel surface, replacing traditional thermal nitriding methods. This plasma-based approach allows for more precise control of nitrogen diffusion depth and surface hardness, enabling optimization of the nitrided layer thickness (0.002-0.006 inches) to achieve adequate galling resistance with shorter treatment times and reduced overall process complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

The nitrided surface layer provides improved galling resistance and reduced corrosion, maintaining heat conductivity and preventing debris buildup, thus extending the service life and productivity of the roll set.

Implementation Method 1

The inner diameter surface of the steel roll shell is nitrided using ion nitriding to create a hard, dense, crack-free surface layer

Methodology Applied

Scientific EffectIon nitriding: Nitriding

Data Source

PatentUS9896757B2Galling and corrosion resistant inner diameter surface in aluminum caster roll shell steels

Publication Date: 2018.02.20 SHULTZ STEEL

AI summary

A strip casting apparatus having a roll shell with a nitrided inner diameter surface mounted on a steel core and method of manufacturing the same. The inner diameter of a steel roll shell may be nitrided by ion or plasma nitriding. The nitriding process can form tight, crack free nitride layer that provides a corrosion resistant barrier and exhibits a surface hardness that is greater than the surface hardness of the steel core and that improves galling resistance while maintaining efficient heat transfer of the roll shell. After nitriding, the roll shell can be shrink fit over a steel core.