Low-Friction Washer Assembly for Thermal Expansion in Bolted Joints
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Solution Overview
Problem
Conventional bolted joints in vehicles experience reduced thermo-mechanical fatigue life due to friction forces that restrict thermal expansion and contraction, leading to potential damage and deformation of components like the exhaust manifold.
Innovation Solution
A bolted joint configuration utilizing high temperature resistant, low friction washers with a multi-layer coating, such as diamond-like carbon tungsten, to reduce friction between the bolt and components, allowing for sliding during thermal expansion and contraction while maintaining clamping force, thereby preventing bolt bending or shearing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional bolted joints are used to couple components, then the joint provides structural stability and clamping force, but the friction force from the bolted joint restricts thermal expansion and contraction of the exhaust manifold, potentially causing damage or deformation
Solution Approach 1:
A washer with a thermal resistant, low friction coating is introduced as an intermediary element between the bolt head and the exhaust manifold. This mediator allows the manifold to expand and contract freely during thermal cycles while the bolt maintains clamping force, preventing damage to the manifold or deformation of the bolt.
Solution Approach 2:
The friction coefficient parameter is changed by applying a thermal resistant, low friction coating to the washer. This coating reduces the coefficient of friction between the bolt assembly and the exhaust manifold, enabling free thermal expansion and contraction while maintaining the necessary clamping force for structural stability.
2Force
If the exhaust manifold is constrained by friction force from the bolted joint, then the joint maintains clamping force, but the manifold cannot expand and contract freely during thermal cycles, leading to potential damage or bolt deformation
Solution Approach 1:
The low friction coating washer acts as a mediator that decouples the clamping force function from the thermal expansion constraint. It allows the manifold to move freely during thermal cycles while the bolt maintains clamping force through the washer, preventing stress concentration and improving fatigue life.
Solution Approach 2:
The friction parameter is modified by applying a thermal resistant, low friction coating to the washer. This parameter change reduces the restraining force on thermal expansion while maintaining sufficient clamping force, thereby improving the thermo-mechanical fatigue life of both the bolt and the exhaust manifold.
3Ease of operation
If a low friction coating is applied to the washer, then the coefficient of friction is reduced to enable free sliding during thermal expansion, but the coating must maintain thermal resistance up to approximately 600° C.
Solution Approach 1:
A multi-layer coating system is applied to the washer, combining materials with complementary properties. The coating includes a diamond-like carbon tungsten (DLC-W) outer layer providing low friction, with underlying layers (chromium, chromium-nickel, primer) providing adhesion and thermal stability. This composite structure achieves both low friction for free sliding and thermal resistance up to 600° C.
Solution Approach 2:
The physical and chemical parameters of the washer surface are modified through the application of a multi-layer thermal resistant coating. The coating system maintains thermal stability at elevated temperatures while providing a low friction surface that enables free sliding during thermal expansion and contraction cycles.
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 significantly enhances the thermo-mechanical fatigue life of both the bolt and coupled components by reducing friction forces, allowing free expansion and contraction without causing deformation, and preventing bolt loosening under thermal loads.
Implementation Method 1
A first washer having a thermal resistant, low friction coating is configured to be disposed between one of the two components and the bolt head
Implementation Method 2
wherein the thermal resistant, low friction coating is resistant to temperatures up to approximately 600° C.
Data Source
AI summary
A bolted joint for coupling two components that undergo thermal expansion and contraction includes a bolt having a head and a stem, the bolt configured to provide a clamping force between the two components. A first washer having a thermal resistant, low friction coating is configured to be disposed between one of the two components and the bolt head to enable the one component to slide relative to the bolt during the thermal expansion and contraction, while maintaining the clamping force, to facilitate preventing bending or shearing of the bolt.