anti rust M12 Adjustable Feet / Stainless Steel Machine Leveling Feet

Causes of loose connection of threaded fasteners and common anti loose structures
Loose connection of threaded fasteners is one of the common problems. The most commonly used

fasteners are loose due to vibration, high and low load changes and impact during use, resulting in

the reduction of equipment accuracy, safety and reliability, and affecting tire quality and production

efficiency. In order to make better use of threaded fastener connectors, the following standard parts

network will share the causes of loose connection of threaded fasteners and relevant common

structural measures to prevent looseness.

1. Causes of loose connection of threaded fasteners
The essence of threaded fastener connection is to keep the connected parts together through axial

force. When the bolt is tightened, the attenuation of axial force is called loosening of threaded

connection. The main reasons for loosening are as follows.

1.1 design defects
(1) Improper selection of bolts in the process of bolt tightening, the clamping force between

connecting parts increases rapidly with the increase of preload. When reaching the yield point,

plastic deformation begins to occur. At this time, the clamping force increases very little or even

unchanged with the increase of bolt preload. When the preload is increased again, the clamping

force gradually decreases until fracture. Therefore, designers need to accurately analyze and

calculate the tightening torque, and fully consider the weight of parts, bearing load, safety

standards and other factors to select appropriate bolt connection.

(2) Without considering the anti loosening design or poor anti loosening method, the bolt

connection is loose or even the bolt falls off due to vibration, high and low load changes and

impact during use. Therefore, effective anti loosening measures must be implemented in product

design to avoid loosening and falling off of bolts or nuts due to bad working conditions.

1.2 insufficient preload
The pre tightening force of bolt tightening directly determines the clamping force between two

connecting parts. Insufficient pre tightening force will inevitably lead to the loosening of connecting

bolts and the loosening of connecting parts. The bolt preload shall be close to or reach the yield

strength in the bolt material. However, in the actual assembly process, due to the limited arm

strength of the operator or the mismatch of the selected tool model, the output tightening torque

is insufficient, resulting in the bolt unable to meet the required pre tightening force.

The design and process do not put forward specific requirements for the torque of tightening bolts,

and there is no corresponding torque wrench in the assembly station. When tightening, the

operator often judges whether to tighten according to his feeling and experience, resulting in

insufficient bolt preload at some large vibration parts and loosening.

1.3 deformation and looseness of bearing surface
When the bearing surface of the nut or bolt is under great pressure, the bearing surface of the

nut or bolt and the contact surface of the connected parts will be depressed and deformed,

resulting in the reduction or even loss of the preload of the threaded fastener, resulting in loose

connection.

1.4 improper assembly process
For the tightening of multiple bolts with regular distribution, the assembly process did not formulate

reasonable tightening process documents, and the operator carried out tightening operation

completely based on personal experience, resulting in inconsistent tightness and loosening of

some bolts due to incorrect tightening sequence and unbalanced stress. For example, the

installation bolts with four square distribution commonly used in the assembly process, generally

adopt the method of diagonal cross tightening to ensure that the stress of the bolts is balanced

as far as possible, otherwise the bolts will become loose, and even the connecting parts will be

deformed due to uneven stress.

1.5 processing quality defects
When connecting parts, the dimensional accuracy of threaded hole or bolt hole is particularly

important. The size of thread directly affects the preload obtained by the bolt. If the size of the

bolt mounting hole is too small, it is difficult to assemble. If the size is too large, there will be indentation

deformation at the contact between the part surface and the bolt or nut bearing surface, resulting in

the loosening of the bolt or nut.

2. Common structures for connection locking of threaded fasteners
There are three main types according to the working principle. The first is friction locking; The second

is mechanical locking; The third is permanent locking].

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