Spring Head Screw Assembly With Washer for Preload Retention
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Solution Overview
Problem
Existing spring head screw designs experience reduced preload force retention and increased risk of screwing issues due to creep deformation under high temperatures, particularly in materials with significant surface pressure, leading to unfavorable screwing cases where the washer gets caught, resulting in decreased preload force below the permissible minimum value.
Innovation Solution
Incorporating a washer between the thread-bearing part of the shaft and the skirt of the spring head screw, which reduces surface pressure on the clamping part, and designing the screw with a cylindrical area between the support plane and the shaft transition to prevent premature contact with the washer, allowing for a larger screw-in angle and improved preload force retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a washer is added between the shaft and the apron to reduce surface pressure, then creep deformation is reduced and preload retention is improved, but device complexity increases
Solution Approach 1:
A washer is introduced as an intermediary element between the shaft and the apron (clamping part). The washer distributes the contact pressure over a larger area, reducing the surface pressure on the clamping part and thereby minimizing creep deformation. This mediator component directly addresses the reliability issue without fundamentally changing the spring-head screw mechanism.
2Ease of operation
If the shaft transition radius is reduced to allow larger screw-in angle, then elastic spring travel is utilized more reliably, but stress concentration increases
Solution Approach 1:
The shaft transition from the cylindrical shaft to the conical apron is designed with a radius (curved transition) rather than a sharp corner. This curved geometry allows the shaft to achieve a larger screw-in angle and utilize the elastic spring travel of the skirt more effectively, while the radius distributes stress more evenly compared to a sharp transition.
3Ease of manufacture
If the washer inner diameter is made slightly larger than shaft diameter for captive mounting, then ease of assembly is improved, but probability of shaft transition contact with washer increases
Solution Approach 1:
The shaft is designed with different diameters in different regions: a smaller diameter in the transition area and a larger diameter in the unthreaded portion. This local variation in geometry allows the washer (with inner diameter slightly larger than the shaft's unthreaded portion) to be easily mounted captively while preventing the washer from contacting the shaft transition during screwing, as the smaller transition diameter creates clearance.
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 effectively reduces creep deformation and maintains preload force under elevated temperatures, enhancing assembly security and dynamic safety by ensuring reliable elastic spring travel and homogeneous stress distribution.
Implementation Method 1
creep deformation occurs particularly in the area of high surface pressure of the clamping part
Implementation Method 2
the elastic spring travel of the skirt can be utilized more reliably
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a spring head screw assembly (8) comprising a spring head screw (10) having a head (12) with a conical skirt (14) that widens towards the free end of a threaded shank which adjoins the head (12), wherein the spring head screw assembly (8) has a washer (30) which is located between the skirt and the threaded part (20) of the shank (16) in a threadless part (18) of the shank that has a bolt diameter (d0), wherein the inner surface (22) of the skirt transitions into the shank at a radius (Ru), wherein the inner surface (22) forms a contact angle (α) with a support plane (EA), and wherein the support plane is defined by the end of the skirt facing the free end of the screw and is orthogonal to the screw axis. The invention is characterised in that the shank has, between the support plane and the radius in the transition to the skirt, a cylindrical region having the bolt diameter.