Corrosion-Resistant Fastener Assembly with Polymeric Sleeve
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Solution Overview
Problem
Corrosion, particularly galvanic corrosion, poses a significant challenge in fastened assemblies exposed to the elements, as different metals in contact with electrolytes can lead to preferential corrosion, compromising the reliability of the assembly.
Innovation Solution
A reduced-corrosion assembly design featuring a steel fastener with a coated threaded portion, an aluminum washer, and a compression limiter, along with a polymeric sleeve, which together minimize corrosion by preventing moisture accumulation and reducing electrical conductivity, while using materials like magnesium for the second component to enhance strength-to-weight ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different metals are used in the fastening assembly (e.g., steel fastener, aluminum washer, magnesium component), then the assembly achieves diverse functional properties and strength-to-weight optimization, but galvanic corrosion occurs when metals contact in the presence of electrolytes
Solution Approach 1:
A polymeric sleeve is introduced as an intermediary component between the steel fastener and aluminum washer/magnesium component. This non-conductive barrier prevents direct electrical contact between dissimilar metals, eliminating the galvanic couple while allowing mechanical fastening to occur. The sleeve acts as a mediator that preserves the benefits of diverse material selection without the harmful electrochemical interactions.
Solution Approach 2:
The polymeric sleeve creates an inert, non-conductive environment between metal components. By surrounding the metal-to-metal contact interface with this chemically and electrically inert material, the sleeve prevents the formation of electrolyte pathways that would enable galvanic corrosion, effectively isolating the metals from each other in an protective atmosphere.
2Reliability
If a coating is applied to the fastener body, then corrosion resistance is improved, but the coating may compromise thread engagement or fastener functionality
Solution Approach 1:
The coating is applied selectively only to specific portions of the fastener body where corrosion protection is needed, while deliberately leaving the threaded portions exposed or lightly coated. This localized application ensures that the coating provides corrosion resistance in critical areas without interfering with thread engagement and fastener functionality where metal-to-metal contact is required.
Solution Approach 2:
The fastener is segmented into different functional zones with different coating requirements. The shank and head portions receive full coating for maximum corrosion protection, while the threaded portion is either left uncoated or receives a thin coating that allows thread engagement. This segmentation allows each portion of the fastener to be optimized for its specific function.
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 assembly effectively limits corrosion by creating a stable environment with a neutral pH, reducing the risk of galvanic corrosion and maintaining structural integrity and reliability in corrosive conditions.
Implementation Method 1
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when in electrical contact with a different type of metal and both metals are immersed in an electrolyte.
Implementation Method 2
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when in electrical contact with a different type of metal
Implementation Method 3
the compression limiter is embedded in a third component and adapted to protect the third component from being damaged when the assembly is tightened
Implementation Method 4
The screw and nut pairing are generally kept together by a combination of friction between the mating threads, a slight stretch of the screw, and compression of the components in the assembly
Implementation Method 5
a slight stretch of the screw, and compression of the components in the assembly
Data Source
AI summary
A reduced-corrosion assembly includes a first and a second component joined by a fastener having a head and a body. A coating covers a section of the body. The assembly also includes a washer, a compression limiter, and a nut arranged on the first component and adapted to engage the fastener body to thereby tighten the assembly. When the assembly is tightened, the compression limiter is arranged on the fastener body between the first and second components, while the second component is arranged on the fastener body between the compression limiter and the washer. Furthermore, the washer is arranged on the fastener body between the fastener head and the second component, while the coating covers the body substantially up to where the nut engages the body such that corrosion of the assembly is limited or reduced. A vehicle employing the reduced-corrosion fastening system is also provided.