Screw Thread with Varying Pitch for Load Distribution
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Solution Overview
Problem
The uneven distribution of load forces on standard screws and nuts leads to mechanical weakness and fatigue, as the first engaged thread carries the majority of the load, causing it to yield under excessive stress, which is then transferred to subsequent threads, resulting in sequential failure.
Innovation Solution
Implementing a thread with a variable pitch that decreases and increases in a controlled manner, using rolling tools with oblique threads to distribute the load evenly across multiple threads, optimizing the pitch variation within a predefined tolerance interval to enhance mechanical strength and fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard regular thread is used, then the manufacturing process is simple and threads are easy to produce, but the load distribution is very uneven with the first thread carrying the majority of the load
Solution Approach 1:
The patent applies parameter changes by varying the pitch parameter of the thread along its length. The pitch transitions from a first value at the beginning of the thread to a second value at the end, creating a progressive pitch variation. This parameter modification enables more uniform load distribution across multiple threads while maintaining compatibility with standard rolling processes, thus resolving the contradiction between manufacturing simplicity and load distribution uniformity.
2Manufacturing precision
If the pitch tolerance is minimized, then the pitch variation control is improved, but the ability to distribute load across multiple threads is reduced
Solution Approach 1:
The patent utilizes parameter changes by intentionally varying the pitch within a controlled tolerance range. Rather than minimizing pitch variation, the invention exploits the tolerance interval to create a progressive pitch pattern where the pitch systematically transitions from one value to another. This approach transforms what would normally be considered a manufacturing deviation into a functional feature that enables superior load distribution across multiple threads.
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 achieves a more even stress distribution across multiple threads, significantly increasing the resistance and fatigue life of screws and nuts by allowing the entire tolerance interval to be utilized effectively, reducing the likelihood of initial thread failure and distributing axial loads efficiently.
Implementation Method 1
Rolling consists of a deformation of material. Many materials, even non-metallic, can lend themselves to cold rolling.
Data Source
Figure 1~3a
Figure 3b~3c
Figure 4a~4c
AI summary
The distribution of load stresses on the engaged threads of a standard screw or nut is not even. Indeed, the first engaged threads bear a large majority of the load. Consequently, if the load is too great, the threads break and the function is not provided anymore by the screw or nut. The prior art describes threads having a depth or a pitch that vary substantially in order to induce self-tightening. The aim of the invention is to optimise the mechanical resistance and fatigue resistance of the screws via a better distribution of the load on the threads thereof and without inducing said self-tightening. It has been demonstrated that the control of the pitch variation, within a predetermined pitch range, makes it possible to control the distribution of the stresses on the threads. It is possible to determine a different variation corresponding to each load case encountered.