Break Nut Web Geometry for Precise Torque Limiting
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Solution Overview
Problem
Existing torque limiting devices for expansion anchors, especially those used in push-through installations, face issues with breaking precision due to axial inertial forces and loads during hammering, leading to premature weakening of webs and scatter in limit torques.
Innovation Solution
The device features a holding element with webs dimensioned such that the minimum wall thickness section forms an acute angle greater than 45° to the longitudinal axis, reducing the influence of hammer blow forces on fracture behavior and ensuring precise torque limitation with minimal manufacturing effort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the web wall thickness is reduced to achieve precise torque limitation, then the torque limitation precision is improved, but the web becomes more susceptible to premature weakening from axial inertial forces during hammering
Solution Approach 1:
The web is designed with an asymmetric thickness distribution, where the wall thickness minimum section is positioned at a specific angle (greater than 45°) to the longitudinal axis. This asymmetric configuration ensures that the weakest point (minimum wall thickness) is oriented to minimize the influence of axial inertial forces during hammering, while still providing precise torque limitation through controlled fracture at the predetermined breaking point.
Solution Approach 2:
The predetermined breaking point is pre-positioned at the wall thickness minimum section during manufacturing. This preliminary action ensures that the web will fracture at the exact location and under the exact torque conditions designed, preventing premature failure from axial forces while ensuring reliable torque limitation when the limit is reached.
2Ease of manufacture
If the web is made thinner to reduce manufacturing effort, then the ease of manufacture is improved, but the scatter in limit torques increases due to premature weakening
Solution Approach 1:
By positioning the minimum wall thickness section at a specific asymmetric angle (>45°) rather than uniformly thinning the web, the design achieves ease of manufacture through localized material removal while maintaining consistent fracture behavior. This asymmetric configuration ensures that all webs fracture at the same torque value regardless of minor manufacturing variations, reducing scatter in limit torques.
3Reliability
If the web thickness is increased to resist axial forces during hammering, then the reliability under axial load is improved, but the torque limitation precision deteriorates due to increased scatter in limit torques
Solution Approach 1:
The asymmetric positioning of the minimum wall thickness section at an angle greater than 45° to the longitudinal axis creates an orientation where the web is strongest in resisting axial inertial forces (by positioning more material in the axial load path) while maintaining a well-defined weak point for precise torque limitation. This geometric asymmetry simultaneously achieves both reliability under axial load and precision in torque limitation.
Data Source
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AI summary
The invention relates to a device for limiting torque by means of a nut, comprising at least one internal thread and a holding element, wherein in a rear area of the holding element, the holding element has a head part having a driving profile for coupling the head part with a setting tool in a rotationally fixed manner. In a front area of the holding element, the holding element has a receiving part having a receptacle, in which the nut is accommodated in a rotationally fixed manner. The head part has a passage, through which a threaded rod that is screwed into the nut can be guided along the longitudinal axis of the device through the head part and out of the holding element. In at least one longitudinal section plane of the device, according to the invention, the smallest wall thickness of the at least one web is given on a wall thickness minimum section, which runs at an angle of greater than 45° to the longitudinal axis of the device. The invention further relates to a fastening arrangement comprising such a device.