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What are the causes of bolt breakage in the tube mill?

Date:2019-10-12 10:27     writer:cement editor     Views:

Tube mill in the cement industry is widely used, the use of grinding body, end cover bolt fracture often bring trouble to production, tube mill bolt fracture reasons are what?

1. Cause of fracture of the worn lining bolt

There are many reasons for fracture of grinding bolt in tube mill, which can be summed up in several aspects.

tube mill

(1) quality problems

When the bolt is machined, there are some defects, such as too deep thread processing, the screw has knife pattern, the head is not perpendicular to the screw, etc., the section stress increases when the thread is too deep.Knife mark will cause stress concentration;When the screw rod is not perpendicular to the end face, it will cause unilateral stress on the bolt and increase local stress, etc. These defects will virtually make the bolt local overload, and when it exceeds its strength limit, the bolt will produce crack and fracture.

(2) improper installation

Improper installation will also produce bolt fracture, such as bad contact between the bolt head and the lining plate pit, not fitting, will make the bolt unilateral or local stress, local stress increase, easy to make the bolt fracture;The contact of nut and tube mill grinding body is bad, also can make bolt unilateral force, cause fracture, of course, the uneven thickness of the irregular pad is also so.

(3) excessive pre-tightening force

Excessive preload will also promote the fracture of the bolt, especially when the bolt is under local stress.The concentricity of the hole between the lining plate and the bolt hole of the grinding body of the tube mill is not good, and it is seriously deviated. If the bolt is hard hit during the installation, the cylinder or the lining plate will cause damage to the screw, such as scratch, wear, etc., making the bolt easy to break.

2. Causes of bolt fracture at the end of the barrel

The bolt at the end of the barrel of the tube mill consists of the bolt at the end of the liner and the bolt connecting the hollow shaft and the end cover

tube mill

(1) connection bolts for hollow shaft and end cover

The connection bolt between the hollow shaft and the end cover of the tube mill is generally of higher strength and higher machining accuracy. Part of it has positioning function and needs holes with hinge holes, so the requirements are higher.There are several reasons for its fracture.First of all, the material selection is improper, insufficient strength.

(2) quality problems

The machining precision is insufficient, and there are defects, such as rough machining, insufficient size, screw and bolt head are not vertical, etc., which often produce stress concentration and cause fracture in operation.

(3) installation reasons

During installation, the bolt head or nut is not fitted with the end cover or hollow shaft, and the bolt is unilateral, causing local stress to be too large and causing cracks.

(4) end face of hollow shaft

The end face of the hollow shaft stop or end cover stop is not perpendicular to the bolt hole, which causes the end face of the nut and the bolt head not to fit, resulting in excessive local stress on the bolt.

(5) pre-tightening force

The pre-tightening force is too large during installation, and when the bolt is under tension during operation, the over-large pre-tightening force coincides with the tension, exceeding the strength limit of the bolt, it will also break, and so on.The above bad conditions will make the bolt local stress is too large, easy to produce cracks and fracture.

In addition, the new bolt of the tube mill must be checked and tightened every day until it is not loosened. It must prevent the bolt from breaking due to the damage caused by loosening.The pre-tightening force of bolts can be carried out according to the instruction or manual.

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