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What are the Design Requirements and Methods of the Fastener Assembly Space and Boundary?

Sep. 15, 2020

As a Railway Fastening System Supplier, share with you.

Fastener assembly space requirements

Fastener assembly is driven by a special sleeve or gun head to achieve the designed torque value. In the process of fastener product design, it is necessary to take into account that a certain distance should be left from the surrounding parts during the assembly process, and it should not interfere with other parts of the parts, and it is easy to operate by the assembly workers on the production site.

Railway Fastening System

Railway Fastening System

Fastener assembly boundary design requirements

When designing fasteners, the tool installation space should be considered, and the following situations should not occur:

1. The location of the fastening point is in a confined space and cannot be seen by the operator. In this case, it is difficult to locate tools and fasteners, and it is not easy to remove the fasteners after they are dropped.

2. There are other parts covering the top of the fastening point (interference in the axial direction), there may be a small space in the final installation position, but the length of the fastener should be considered, and the tool in the initial state interferes with other parts above.

3. The surrounding space of the fastener is too small (interference in the radial direction), and the tool head or sleeve interferes with the surrounding parts. It needs to be tightened by abnormal methods, such as not tightened vertically.

4. The installation path of fasteners is not straight, and special sleeves such as universal joint sleeves are needed to meet the installation requirements. The structure of the special head sleeves will affect the accuracy of the tools.

5. Fasteners require a structure with bolts and nuts to twist. Try to design anti-following structures, such as internal rotation and external rotation. Two-handed operation reduces personnel efficiency and increases working hours. If the torque is greater than 60 Nm, it does not meet the ergonomic requirements.

The assembly method of the fastener connection

There are four methods for assembling fasteners: torque control method, torque-angle control method, yield point control method and elongation method.

Torque method

Torque method is the most widely used control method. According to the basic relationship between the bolt axial pre-tightening force and the tightening torque, the tightening torque is adjusted to realize the control of the pre-tightening force, which is generally used in the elastic zone.

Torque method

The relationship between the tightening torque T and the axial preload F is:

Where, T: tightening torque, F: axial preload, P: pitch, α: flank angle, d2: thread pitch diameter, dW: equivalent friction diameter of the supporting surface, μS: thread friction coefficient, μW: support Coefficient of surface friction.

During the torque method assembly, due to the influence of the friction coefficient, the axial preload force fluctuates greatly, and the material potential is not fully utilized, the bolt strength utilization rate is low, but because of its simple operation, low cost, and for most threaded connections Effective, it is still the most commonly used assembly method.

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