{"id":1676,"date":"2022-06-06T14:18:22","date_gmt":"2022-06-06T06:18:22","guid":{"rendered":"http:\/\/yj.bbswaimao.com\/?p=1676"},"modified":"2025-05-20T01:29:19","modified_gmt":"2025-05-20T01:29:19","slug":"bolt-loose-cause-analysis-and-solution","status":"publish","type":"post","link":"https:\/\/yijin.seo2.au\/de\/news-blog\/bolt-loose-cause-analysis-and-solution\/","title":{"rendered":"Lose Schraube - Ursachenanalyse und L\u00f6sung"},"content":{"rendered":"

Thread connection is widely used in the connection and fixation of product parts because of its low cost, simple structure, convenient disassembly and assembly, reliable connection, and other characteristics.<\/span><\/p>\n

A loose bolt may cause parts to loosen abnormal sounds, fall-off damage, and other situations, even endanger personal safety, and may even put the whole production plant at a standstill, and make the company suffer heavy losses.<\/span><\/p>\n

So, what is the main cause of bolt loosening?<\/span><\/b><\/p>\n

Today, Yijin Solution will carry out the cause investigation and verification analysis, and summarize the corresponding anti-loosening measures.<\/span><\/p>\n

Cause Analysis<\/span><\/h2>\n

1. Bolts<\/span><\/h3>\n

If the bolt material strength is lower than the standard, in the tightening process, with the increase of bolt pre-tightening force, the clamping force between the joint components also increases, and bolt elastic deformation occurs in this process. <\/span><\/p>\n

When the yield point is reached, the bolt begins to plastic deformation, and with the increase of pre-tightening force, the increment of clamping force becomes smaller or even unchanged, and then gradually becomes smaller, resulting in bolts loosening.<\/span><\/p>\n

If the bolt pitch is not reasonable, although it can meet the requirements of self-locking and anti-loosening, due to the pre-tightening force required by the joint assembly being too large, the bolt selected under the action of the pre-tightening force beyond the limit, the screw tooth damage (or screw hole damage), to bolt loose.<\/span><\/p>\n

If the bolt type is too small or the bolt grade is too low, the bolt cannot offset the action of the axial tensile force and radial shear force between the joint components under the working state, and the repeated cycle of the force eventually makes the bolt fatigue, plastic deformation, the pre-tightening force is reduced, and the bolts loosening occurs.<\/span><\/p>\n

Thread size also affects the size of the bolt preload obtained, too large thread with a threaded hole fits too tight, and the same torque in the case of a small preload, the tightening effect is low; <\/span><\/p>\n

When the thread is too small and the threaded hole is too large, the contact area of the screw tooth in the thread pair is too small, and the screw tooth under the same pre-tightening force is too large, which may lead to the screw tooth collapse and release after the force of the joint assembly.<\/span><\/p>\n

2.\u00a0Design<\/span><\/h3>\n

The pre-tightening force that the bolt can achieve in the tightening process directly determines the clamping force between two connecting parts. <\/span><\/p>\n

The mating mechanical analysis shows that under the condition of static load, the general thread meets the self-locking condition and will not cause bolts to loosen. <\/span><\/p>\n

But, variable load, vibration, and impact are the main factors causing bolt loosening; <\/span><\/p>\n

Designers do not fully consider the actual working conditions of this element, and easy to appear design requirements can not meet the requirements of the situation, resulting in the bolt loosening.<\/span><\/p>\n

Serious compression will make the bolt preload reduce or lose the preload, resulting in the loosening of the nut or bolt. The thread contact interface is usually uneven. <\/span><\/p>\n

After preloading, the inner and outer threads can’t complete contact, and the micro-convex body on the inner (outer) threads may be embedded into the concave area of the outer (inner) threads. <\/span><\/p>\n

Under the action of periodic external force, the reciprocating micro-sliding motion of internal and external threads will occur, resulting in adhesive shedding and loss of pre-tightening force, which is called fretting wear loss. <\/span><\/p>\n

After tightening, the bolt pre-tightening force will produce convex point collapse and permanent plastic deformation, so that the clamping length of the bolt will be reduced, and finally lead to the reduction of the bolt pre-tightening force.<\/span><\/p>\n

3. Tools<\/span><\/h3>\n

Tool failure is one of the main causes of bolt loosening. A Pneumatic wrench is a common tool for pre-tightening bolts equipped by the company. <\/span><\/p>\n

After investigation, the main reasons for the failure of the pneumatic wrench are as follows: <\/span><\/p>\n

First, the employee does not normally use the tool, resulting in abnormal wear, such as the continuous impact of the pneumatic wrench after the bolt is tightened in place; <\/span><\/p>\n

The second is that the supporting equipment is not used correctly or has failed, and the tool has been in a non-maintenance environment for a long time, such as directly connecting the pneumatic wrench to the compressed air pipeline without the pneumatic triplet. <\/span><\/p>\n

Improper tool configuration is also one of the reasons for bolt loosening. The company uses a large-range torque wrench to assemble low-torque bolts. <\/span><\/p>\n

Because the torque value corresponding to each scale is too large, the precise torque cannot be grasped, and the bolt tightening torque may be insufficient, resulting in bolt loosening.<\/span><\/p>\n

\u00a04. Operator<\/span><\/h3>\n

The bad working habits of the operator are one of the direct causes of bolt loosening. After investigation, the operator\u2019s bad working habits are in many aspects. <\/span><\/p>\n

One is that the continuous impact of the pneumatic wrench is still maintained after the bolt is tightened in place, destroying the supporting surface of the joint assembly (it may also be the deformation of the flat pad and the failure of the spring pad); <\/span><\/p>\n

The second is that the operator is cutting corners, not using torque wrenches, or not pressing the thread to tighten the glue or to tighten the bolts in an order that is not required. <\/span><\/p>\n

Third, the operator diagram assembly is convenient to switch to other kinds of bolts.<\/span><\/p>\n

\u00a05. Processing defects and other problems<\/span><\/h3>\n

The chamfering of bolt mounting holes is too large, which may occur when the size of mounting holes is too large. <\/span><\/p>\n

In addition, the surface of the joint assembly is uneven, so that the bolt and the joint assembly are not completely fit, and can not play enough friction; <\/span><\/p>\n

When there is a relative slip between the bolt and the joint assembly, the joint surface will wear, eventually leading to a decrease in preload, resulting in bolt loosening.<\/span><\/p>\n

Bolts Anti-Loosing Measures<\/span><\/h2>\n

Design Process<\/span><\/h3>\n

Fully consider the bolt installation position of the operating requirements, considering the weight of the joint component, load, safety standards, and other factors, select the appropriate specifications of the bolt, accurately analyze and calculate the size of the preload, reserve enough working space to ensure the bolt connection safe and reliable.<\/span><\/p>\n

Adopt an anti-loosen bolt design. Combined with the company’s actual situation, the following anti-loose design can be selected: <\/span><\/p>\n