Zn-Ni Coated Stainless Steel Screw for Thread-Forming Anti-Jamming
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Solution Overview
Problem
Stainless steel thread forming screws are prone to jamming due to their soft surface when forming threads, and conventional coatings like Zn-Ni are not suitable for thread forming screws.
Innovation Solution
A zinc-nickel coating with a hardness of 400 to 450 HV is applied to a stainless steel thread forming screw body to enhance hardness and prevent jamming, while maintaining corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stainless steel screw body is used for thread forming, then corrosion resistance is improved, but the surface becomes too soft causing jamming during thread formation
Solution Approach 1:
The invention applies a zinc-nickel coating layer on the stainless steel screw body, creating a composite structure where the stainless steel core provides corrosion resistance and the zinc-nickel coating provides enhanced surface hardness. This composite approach resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The invention changes the surface properties of the stainless steel screw by applying a coating with specific hardness characteristics (400-1500 HV). This parameter change in surface hardness while maintaining the base material's corrosion resistance solves the jamming problem during thread formation.
2Ease of manufacture
If a conventional stainless steel screw without coating is used, then manufacturing simplicity is maintained, but galling occurs during mounting in threaded holes
Solution Approach 1:
The zinc-nickel coating acts as an intermediary layer between the stainless steel screw and the material being fastened. This intermediate coating prevents direct contact and galling between the stainless steel surface and the workpiece, while adding only minimal complexity to the manufacturing process.
3Strength
If a harder coating (500-1500 HV) like chromium is used on self-drilling screws, then surface hardness is improved, but the screw becomes unsuitable for thread forming applications
Solution Approach 1:
The invention optimizes the coating hardness parameter to a specific range (400-1500 HV) that balances two requirements: sufficient hardness to prevent jamming during thread formation, and adequate ductility to allow material displacement. This precise parameter control enables the coating to serve thread forming functions while maintaining enhanced surface properties.
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 zinc-nickel coating provides a hard surface that prevents jamming and galling, enabling effective thread formation in stainless steel screws.
Implementation Method 1
The coating may be formed by electrolytic surface treatment of the (thread forming) screw body, for example electroplating. The present coating may hence be an electroplated coating.
Implementation Method 2
A technical effect of such a screw is that galling, which may occur when a conventional stainless steel screw (without the aforementioned coating) is mounted in a threaded hole, may be prevented due to the coating layer.
Data Source
Figure 1~2
Figure 3a~3b
Figure 4~5
AI summary
The present invention relates to a screw (10), comprising: a screw body (18) made of stainless steel and comprising a head (20), a threaded portion (22), and a tip (24); and a coating (32) applied on at least the threaded portion, wherein the coating is a zinc-nickel coating and has a hardness in the range from 400 to 450 HV.