Screw Head Bearing Surface Lubricant Pockets for Galling Prevention
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Solution Overview
Problem
Existing screws with head bearing surfaces and coatings experience unwanted seizure when tightened multiple times due to coating wear, leading to uncontrollable friction and unreliable screw connections, especially with coatings having poor adhesion to the base metal.
Innovation Solution
The introduction of lubricant pockets on the head bearing surface of screws and washers, which release lubricant during tightening, reducing frictional forces and preventing galling by providing fresh lubrication throughout the screwing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating is applied to the head bearing surface to achieve defined friction and corrosion protection, then the initial screw connection quality is improved, but the coating is rubbed off during multiple tightening cycles causing metallic contact and uncontrollable friction
Solution Approach 1:
The patent applies lubricant to the head bearing surface before the coating is applied, so that the lubricant becomes embedded in the coating structure. This preliminary action ensures that the lubricant is already in position to reduce friction when the screw connection is made, preventing the coating from rubbing off completely during multiple tightening cycles.
Solution Approach 2:
The patent creates a composite structure by combining the coating material with lubricant, forming a multi-layered head bearing surface. This composite structure allows the coating to provide corrosion protection while the embedded lubricant provides sustained friction reduction, resolving the contradiction between coating durability and friction control during repeated tightening.
2Ease of operation
If the head bearing surface is made smooth to reduce initial friction, then the first tightening is improved, but there is no lubricant reservoir to prevent galling during the second half or third of the tightening process
Solution Approach 1:
The patent prepares the head bearing surface by applying lubricant before the coating process, creating a pre-lubricated surface. This preliminary action ensures that lubricant is available from the beginning of the tightening process, allowing smooth initial tightening while also having sufficient lubricant reservoir to prevent galling in the later stages of tightening.
Solution Approach 2:
The patent creates different zones on the head bearing surface with varying lubricant concentration and coating properties. The local quality variation allows certain areas to provide low friction for ease of tightening while other areas with higher lubricant content prevent galling during the critical second half or third of the tightening process.
3Ease of operation
If organic coatings based on waxes or polymers are used to reduce friction, then the initial friction is reduced, but the adhesion between coating and base metal is poor leading to seizure during multiple tightening
Solution Approach 1:
The patent applies the organic coating with embedded lubricant to the head bearing surface before the screw connection is made. This preliminary application allows the coating to adhere to the base metal while the lubricant is already positioned to reduce friction. The pre-application process ensures proper adhesion development before the coating undergoes the stress of multiple tightening cycles.
Solution Approach 2:
The patent creates a composite coating structure where the organic material (wax or polymer) is combined with lubricant and applied in a specific sequence. This composite approach allows the organic coating to provide friction reduction while the embedding process enhances adhesion to the base metal, preventing seizure during multiple tightening operations.
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
Enables reliable multiple tightening of screw connections without seizure, particularly beneficial for aluminum components and high-strength screws, by maintaining consistent lubrication and minimizing wear-related issues.
Implementation Method 1
lubricant is introduced into these lubricant pockets, which is then gradually released when the screw connection is tightened and the head contact surface of the screw is deformed as a result. This causes a reduction and equalization of the frictional forces between the head support surface and the surface that comes into contact with it.
Data Source
Figure 1
Figure 2
Figure 3~7
AI summary
A screw (2) has a head (5) with a head bearing surface (12). Lubricant pockets (13) are arranged in at least part of the head bearing surface (12) to receive lubricant and release it again during the tightening of a screw connection (1) to prevent galling during multiple tightening operations.