Spark Plug Metallic Shell Coating for Corrosion and Chromium Elution

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Solution Overview

Problem

Spark plugs with zinc plating layers face issues with sacrificial corrosion and elution of hexavalent chromium, which is harmful to the environment, despite the use of chromate conversion coatings for corrosion prevention.

Innovation Solution

A metallic shell for spark plugs featuring a zinc plating layer covered with a chromium-containing chemical conversion coating layer that includes a zirconium component of 0.1 mass % or more, with optional cobalt content equal to or less than the zirconium content, to suppress corrosion and hexavalent chromium elution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a zinc plating layer is formed on the metallic shell surface, then corrosion prevention is achieved, but the zinc plating layer is easily consumed due to sacrificial corrosion and tends to whiten due to produced zinc oxide

Engineering Contradiction:

Improvecorrosion preventionVSAvoidservice life of plating layer

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

A chromium-containing chemical conversion coating layer is introduced as an intermediary between the zinc plating layer and the external environment. This conversion coating acts as a mediator that reduces the direct exposure of zinc to corrosive elements, thereby decreasing sacrificial corrosion consumption while maintaining corrosion protection functionality.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates a composite protective system consisting of multiple layers: the zinc plating layer combined with a chromium-containing chemical conversion coating layer. This composite structure leverages the corrosion resistance of zinc while the chromium-based conversion coating reduces zinc consumption and prevents whitening, achieving synergistic protection.

Inventive Principle:

Principle #40Composite materials

2Reliability

If a chromate conversion coating is applied to prevent corrosion, then corrosion of the zinc plating layer is suppressed, but hexavalent chromium is eluted into the environment causing environmental harm

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidhexavalent chromium elution

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent modifies the chemical composition parameters of the conversion coating by incorporating zirconium (0.1-2.0 mass%) alongside chromium. This parameter change transforms the coating's properties to maintain corrosion protection while significantly reducing hexavalent chromium elution. The zirconium content parameter is specifically controlled to achieve this balance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potentially harmful chromium-based conversion coating into a beneficial protective layer by adding zirconium. The zirconium component helps suppress hexavalent chromium formation and elution, transforming a harmful coating system into an environmentally friendly one while maintaining its corrosion protection function.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If the zinc plating layer is covered with chromate conversion coating, then corrosion suppression is achieved, but the appearance of the metallic shell is impaired due to whitening

Engineering Contradiction:

Improvecorrosion protectionVSAvoidappearance quality

Core Design Contradiction:

ReliabilityVSShape

Solution Approach 1:

The patent creates a composite conversion coating system containing both chromium and zirconium elements. This composite coating structure prevents zinc oxide formation and whitening that would otherwise occur with conventional chromate coatings, maintaining the metallic shell's appearance quality while providing corrosion protection.

Inventive Principle:

Principle #40Composite materials

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 solution effectively reduces corrosion of the metallic shell and minimizes the elution of hexavalent chromium, thereby reducing environmental impact while maintaining corrosion protection.

Implementation Method 1

a chromium-containing chemical conversion coating layer which covers the zinc plating layer

Methodology Applied

Scientific EffectChemical conversion coating: Chemical Bonding

Implementation Method 2

the chemical conversion coating layer has a zirconium component content of 0.1 mass % or more... achieving suppressed elution of hexavalent chromium

Methodology Applied

Scientific EffectAdsorption: Adsorption

Data Source

PatentUS11749971B1Metallic shell for spark plug and spark plug using the same

Publication Date: 2023.09.05 NITERRA CO LTD

AI summary

A metallic shell for a spark plug which metallic shell achieves suppressed elution of hexavalent chromium, and a spark plug including the metallic shell. The spark plug has a metallic shell. The metallic shell includes a tubular metallic shell body; a metal plating layer provided on a surface of the metallic shell body; and a chromium-containing chemical conversion coating layer provided to cover the metal plating layer. The chemical conversion coating layer has a zirconium component content of 0.1 mass % or more.