Wedge Locking Washer Corrosion Resistance via Surface Hardening
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Solution Overview
Problem
Austenitic stainless steel wedge locking washers face challenges in corrosion resistance due to deformation martensite and delta ferrite formation during cold forming, which can lead to localized corrosion and reduction in surface hardness, especially in areas with high deformation, and existing surface hardening methods like plasma nitriding can compromise corrosion resistance.
Innovation Solution
The wedge locking washer is designed with optimized cam geometry featuring smooth transitions and rounded edges to minimize deformation martensite formation, combined with surface hardening through carbon and nitrogen diffusion and electro-polishing or pickling to a controlled depth to maintain the hardened layer and enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If plasma nitriding or salt bath nitriding is used to surface harden austenitic stainless steel wedge locking washers, then surface hardness is improved, but corrosion resistance deteriorates due to chromium nitride formation
Solution Approach 1:
The invention changes the surface hardening parameters by using gaseous thermochemical diffusion processes (carbon and/or nitrogen diffusion) instead of plasma or salt bath nitriding. This parameter change prevents chromium nitride formation while achieving the desired surface hardness through interstitial enrichment of the steel surface.
Solution Approach 2:
The invention extracts the harmful chromium nitride formation mechanism from the surface hardening process. By using gaseous diffusion processes that provide carbon and nitrogen interstitially without creating chromium nitrides, the harmful byproduct is eliminated while the beneficial surface hardening effect is retained.
2Productivity
If cold forming is used to manufacture wedge locking washers, then manufacturing efficiency is improved, but deformation martensite forms during forming which reduces corrosion resistance
Solution Approach 1:
The invention applies preliminary surface hardening through gaseous diffusion before the cold forming process. This preliminary action ensures that the surface is already hardened and resistant to deformation martensite formation during subsequent forming operations, thereby maintaining corrosion resistance while achieving high manufacturing efficiency.
Solution Approach 2:
The invention creates local quality differences by hardening the surface layer through gaseous diffusion while leaving the bulk material properties unchanged. This localized surface hardening prevents deformation martensite formation at the surface during cold forming, maintaining corrosion resistance where it is most needed while allowing efficient bulk forming.
3Strength
If surface hardening is performed after cold forming, then surface hardness is improved, but the hardened layer depth is reduced due to material removal during subsequent electro-polishing
Solution Approach 1:
The invention changes the sequence and parameters of surface treatment processes. By using gaseous diffusion-based surface hardening followed by controlled electro-polishing or pickling to a depth less than the hardened layer depth, the process parameters are optimized to retain a sufficient hardened layer while achieving the desired surface finish and corrosion resistance.
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
This approach increases the corrosion resistance and maintains a deeper surface hardened layer, reducing the risk of localized corrosion and improving the overall performance of wedge locking washers under neutral salt spray testing.
Implementation Method 1
Such a process involves diffusion of carbon and/or nitrogen from a surrounding gas into the surface of the steel resulting in a surface layer enriched in carbon and/or nitrogen
Implementation Method 2
at least the first surface is surface hardened and electro-polished and/or pickled
Data Source
Figure 1~2
Figure 2a~3
Figure 4~4b
AI summary
Wedge locking washer 1a, 1b comprising a central axis, a central through hole concentric with central axis and defining an inner peripheral axial surface, an outer peripheral axial surface, a first side surface adapted to face and engage another wedge locking washer, said first side comprising a pattern of radially extending cams 7, each cam comprising a first surface inclined in relation to a central plane of the washer and a second surface and wherein the first and the second surface of each cam meet in a radially extending cam edge 7a and wherein the second surface of a first cam meet the first surface of an adjacent cam in a radially extending inner corner 7b, each cam having a height h defined between a bottom plane in which the bottom of the inner corner is arranged and a top plane in which the top of the cam edge is arranged, a zone of smooth transition of the inner corner has a horizontal length a, the inner corner has a height H of at least h/4 and at most h/2 defined as the height H in vertical direction from the inner corner bottom to the end of the smooth transition zone, the cam edge having a smooth transition zone, which has a height H' that is equal to or larger than height H of the inner corner of the smooth transition zone, and wherein at least the first surface is surface hardened and electro-polished and/or pickled.