Tungsten Carbide Roll Coating With Thin-Layer Adhesion Control

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Solution Overview

Problem

Existing coatings for rolling mill rolls, such as tungsten carbide, face issues with premature layer detachment due to high thickness and internal stresses, and are not economically viable for hot and cold rolling processes, especially 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, followed by optional polishing or blasting to achieve a smooth or rough finish, ensuring 100% coverage and reduced permeability.

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 internal stresses cause premature layer detachment

Engineering Contradiction:

Improvewear resistanceVSAvoidcoating adhesion

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent changes the thickness parameter of the tungsten carbide coating from conventional thick layers to a thin layer of 0.003-0.020 mm. This parameter change reduces internal stresses within the coating while maintaining sufficient wear resistance, thereby preventing premature detachment and improving coating reliability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by creating a specific surface preparation condition through blasting before coating application. This prepares the substrate surface with optimal roughness and cleanliness locally at the coating interface, enhancing adhesion of the thin tungsten carbide layer without requiring thick coating for structural integrity.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

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

Engineering Contradiction:

Improvecoating coverageVSAvoidnumber of coating passes

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies partial action by using a single coating pass instead of multiple passes. The thin coating thickness of 0.003-0.020 mm allows achieving 100% coverage and sufficient protective properties in one application, reducing process complexity and time while maintaining manufacturing precision.

Inventive Principle:

Principle #16Partial or excessive action

3Strength

If conventional chromium coating is used, then wear resistance is achieved, but environmental restrictions will ban the process by 2023

Engineering Contradiction:

Improvewear resistanceVSAvoidenvironmental toxicity

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the toxic chromium coating material with a thin tungsten carbide alloy coating that is environmentally friendly. The thin coating design (0.003-0.020 mm) makes the replacement economically viable despite different material properties, providing an environmentally acceptable alternative that maintains wear resistance without hexavalent chromium toxicity.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Reliability

If the coating thickness is reduced to 0.003-0.020 mm, then internal stresses are reduced, but achieving 100% coverage becomes more difficult

Engineering Contradiction:

Improvecoating stabilityVSAvoidcoverage uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by performing surface blasting before the thin coating application. This pre-treatment creates an optimal surface morphology with increased roughness and cleanliness, ensuring that the thin tungsten carbide coating adheres uniformly and achieves 100% coverage without gaps or defects, thereby maintaining manufacturing precision despite reduced thickness.

Inventive Principle:

Principle #10Preliminary action

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 increases the lifespan of mill rolls by a factor of 2-3 compared to chromium-plated rolls and reduces annual consumption, providing excellent wear resistance and maintaining performance under high compression forces.

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 exhibiting a powder granulometry comprised between 30 μm and 5 μm in a combustion chamber

Methodology Applied

Scientific EffectThermal spraying: Plasma Spray

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 EffectCombustion: Combustion

Implementation Method 3

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

Methodology Applied

Scientific EffectGas flow transport: Convection

Implementation Method 4

is sprayed on the mill roll by means of the gun with a supply flow at values comprised between 1 and 8 kg/h

Methodology Applied

Scientific EffectThermal spraying: Plasma Spray

Data Source

PatentEP4105351A1Method for obtaining rolling mill rolls with a coating of tungsten carbide alloys, and resulting roll

Publication Date: 2022.12.21 FIVES STEEL SPAIN SA

Figure 1A~1B
Figure 1C

AI summary

The object of the method is to obtain rolling mill rolls with a coating of tungsten carbide or of the alloys thereof, wherein the coating is a single layer and is carried out by means of high velocity thermal spraying.