Tungsten Carbide Mill Roll Coating for Thin-Layer Wear Resistance

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Solution Overview

Problem

Existing tungsten carbide coatings for rolling mill rolls face issues such as premature layer skipping, high thickness requirements, and incompatibility with hot and cold rolling processes, leading to economic and environmental concerns, particularly with the impending ban on hexavalent chromium coatings.

Innovation Solution

A thermal spraying process applying a single layer of tungsten carbide alloy with a thickness between 0.003 mm and 0.020 mm, involving degreasing, preheating, and high-velocity air fuel thermal spraying, along with optional surface activation and polishing steps to ensure adhesion and reduce permeability, allowing for a 100% coverage and improved wear resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a thick tungsten carbide coating is applied to rolling mill rolls, then wear resistance is improved, but the coating thickness becomes excessive (above 0.030 mm) causing detachment under rolling forces

Engineering Contradiction:

Improvewear resistanceVSAvoidcoating thickness

Core Design Contradiction:

StrengthVSLength of moving object

Solution Approach 1:

The invention changes the chemical composition parameters of the tungsten carbide coating by adding boron (0.05-5 wt%) and controlling carbide grain size (0.5-5 μm), which improves wear resistance without requiring excessive thickness. The optimized composition allows achieving high hardness (15-20 HRC) at controlled thickness (0.003-0.020 mm).

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention creates a composite coating material combining tungsten carbide with boron compounds (borides, oxides, or carbides). This composite structure provides enhanced wear resistance and adhesion properties, allowing thin coatings to withstand rolling forces without detachment while maintaining protective function.

Inventive Principle:

Principle #40Composite materials

2Reliability

If multiple passes of coating application are used to achieve sufficient coverage, then coating completeness is improved, but process complexity and time increase

Engineering Contradiction:

Improvecoating coverageVSAvoidcoating process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention performs preliminary surface preparation including shot blasting or grit blasting to create a roughened surface profile, followed by application of a bonding promoter layer before the final tungsten carbide coating. This preliminary action ensures complete adhesion and coverage in a single pass, eliminating the need for multiple coating applications.

Inventive Principle:

Principle #10Preliminary action

3Productivity

If high compression forces are applied during rolling, then productivity is improved, but the coating skips or detaches prematurely

Engineering Contradiction:

Improverolling speedVSAvoidcoating durability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention applies a bonding promoter layer (such as nickel, cobalt, or copper-based alloys) between the substrate and the tungsten carbide coating. This intermediate layer acts as a cushion that absorbs and distributes the high compression forces during rolling, preventing stress concentration that would cause coating detachment while allowing high productivity operation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

4Strength

If electrolytic chromium coating is used for wear resistance, then protective properties are improved, but environmental harm increases due to hexavalent chromium

Engineering Contradiction:

Improvewear resistanceVSAvoidenvironmental toxicity

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The invention replaces the toxic electrolytic chromium coating with a tungsten carbide-based coating that is applied by thermal spray or HVOF methods. While the chromium coating was effective for wear resistance, the tungsten carbide alternative provides comparable or superior wear protection without the environmental and health hazards of hexavalent chromium, enabling safe disposal and environmental compliance.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 process significantly extends the lifespan of mill rolls by a factor of 2-3 compared to chromium-plated rolls and reduces annual consumption, maintaining wear resistance and allowing for continuous rolling campaigns without frequent changes.

Implementation Method 1

coating the mill roll with a tungsten carbide alloy or alloys thereof by means of thermal spraying wherein a powder of a tungsten carbide alloy is melted

Methodology Applied

Scientific EffectThermal spraying:

Implementation Method 2

a powder of a tungsten carbide alloy is melted exhibiting a powder granulometry comprised between 30 μm and 5 μm in a combustion chamber

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 3

heating the surface of the mill roll

Methodology Applied

Scientific EffectHeating: Heating

Implementation Method 4

the molten material is transported to a spraying gun by means of a carrier gas

Methodology Applied

Scientific EffectGas flow transport:

Data Source

PatentUS11702727B2Method for obtaining rolling mill rolls with a coating of tungsten carbide alloy, and resulting roll

Publication Date: 2023.07.18 FIVES STEEL SPAIN SA

AI summary

The method for obtaining rolling mill rolls with a coating of tungsten carbide or the alloy thereof, wherein the coating is a single layer and is carried out by high velocity thermal spraying is disclosed.