Plastic Screw Plug Spiral Shoulder Railway Fastening
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Solution Overview
Problem
Existing plastic screw-anchors for railway tracks on concrete sleepers face issues with uniform force application, assembly complexity, interchangeability, and risk of cracking due to thin walls, which lead to damage and weakening under stress peaks and incorrect screw positioning.
Innovation Solution
A plastic screw-anchor with a spiral shoulder reducing inner diameter over a partial length and a sawtooth-shaped external thread, combined with optimized thread geometry and increased thickness, prevents thread cutting and ensures secure assembly and interchangeability for both round and pointed thread screws.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the wall thickness of the plastic dowel is reduced to accommodate thin-walled design, then the assembly becomes simpler and interchangeability improves, but the force transmission directly into concrete causes extreme stress peaks and cracking
Solution Approach 1:
Instead of having the screw transmit force directly through thin walls to concrete, the invention inverts the force path by using a thick-walled dowel body that distributes forces over a larger area, with the thread geometry optimized to transmit forces through the substantial wall thickness rather than through thin walls
Solution Approach 2:
The invention changes the wall thickness parameter from thin to substantial thickness (ratio of core diameter to outside diameter ≤ 0.67), fundamentally altering how forces are transmitted and distributed, thereby reducing stress peaks in the concrete while maintaining assembly simplicity
2Manufacturing precision
If the lower area of the anchor body is adapted to a rounded external thread, then the risk of cutting into the thin wall is avoided, but the thin walls still transmit force directly into concrete causing extreme stress peaks
Solution Approach 1:
The invention changes the wall thickness parameter from thin to substantial thickness, so that even with rounded thread adaptation, the walls are thick enough to prevent direct force transmission to concrete, thereby eliminating stress peaks while maintaining precise thread engagement
3Strength
If the plastic dowel is made thicker to prevent stress peaks, then fatigue strength improves, but screwing in the sleeper screw requires special care to avoid cutting a new thread
Solution Approach 1:
The spiral shoulder performs a preliminary centering action that guides the sleeper screw into correct alignment before thread engagement, preventing incorrect positioning that would lead to cutting new threads, thereby simplifying assembly while maintaining thick wall design
Solution Approach 2:
The spiral shoulder acts as an intermediary element between the screw and the threaded hole, providing preliminary guidance and centering that ensures proper alignment during assembly, eliminating the need for special care while maintaining thick wall construction
4Force
If a V-thread screw is used with a plastic dowel, then clamping force is improved, but incorrect positioning causes the screw to cut a new thread leading to considerable weakening
Solution Approach 1:
The spiral shoulder performs preliminary centering and alignment of the V-thread screw before thread engagement, ensuring correct positioning that prevents cutting new threads, thereby maintaining both high clamping force and assembly reliability
Solution Approach 2:
The spiral shoulder serves as an intermediary guidance mechanism that aligns the V-thread screw correctly before engagement, preventing positioning errors that would compromise reliability while maintaining the high clamping force benefits of V-threads
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
The invention relates to a plastic screw plug (6) for attaching a rail to a sleeper, in particular concrete sleeper, having an essentially cylindrical plug body which has at the head end a stem region (7) which preferably adjoins a plug crown (8) toward the bottom, and in the continuation of which stem region (7) has an outer thread (9) with which it can be turned out of or into the sleeper, and is provided with an inner thread (10) underneath the stem region (7) in order to receive a sleeper screw. The intention is to improve such a plastic screw plug, in particular, with regard to its operating properties such as uniform application of force into the sleeper, simpler mounting and replaceability, reduction of the risk of fracturing, and additionally to permit it to be used in a variable way. For this purpose, the stem region (7) has on the inside, in the junction with the inner thread (10), a shoulder (13) which reduces the internal diameter over part of the length of the stem region (7) and extends in a spiral shape over at least part of the circumference.