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Analysis on the reasons of crane nibbling

Aug 08, 2018

Analysis on the reasons of crane nibbling

During the operation of a crane cart or trolley, the wheel rim contacts with the side of the track, generating horizontal lateral thrust, causing the friction and wear between the wheel rim and the track, commonly known as gnaw rail. The ideal operation condition of crane should be that all wheels are running on the track without slippage, and the wheel rim is not in contact with its running track, that is, the wheel rim and the wheel track maintain a certain gap. In fact, for some reason, the crane in the course of the wheel rim and the track forced contact, resulting in gnaw track. The harm caused by this problem, the reason and the treatment measures are put forward, which will be used for reference in the future inspection work.

Judgment of crane nibbling

1. There are obvious friction marks on the side of the track, and the ground iron particles fall on the track.

2. The wheel rim is worn, and there should be a large arc of wear on the wheel rim. After measurement, the wheel rim wear is up to 3-5mm.

3. There is deviation, twist and abnormal noise when the crane is started and braking.

4. When the crane moves to a certain area, there is a twisting and abnormal friction sound. At this time, the gap between the wheel rim and the rail edge changes significantly, and the running resistance increases.

5. The phenomenon of crane climbing the rail during driving.

6. The crane running resistance increases, and the motor even burns out.

Crane gnaw rail hazard

1. Reduce the service life of wheels and tracks. The forced contact between the wheel and the track is caused by gnawing, which aggravates the mutual wear between the two. In serious cases, it can lead to metal spalling of the wheel rim and the side of the track as well as warping and deformation of the wheel rim outward, thus accelerating the damage of the wheel and the track and reducing the service life.

2. Increase the operating resistance and force the motor and the motor to overload the operation for a long time, which may cause the consequences of burning the motor or breaking the transmission shaft.

3. Loud noise and vibration during crane operation.

4. Damage to the structure of roof beams. The crane must produce horizontal lateral force during operation, which makes the structure of the plant suffer different degrees of damage due to additional lateral loads.

5. The crane suddenly climbs the rail during driving, causing a serious accident of equipment and human casualties.

Reasons for crane to gnaw rail

There are various forms of crane rail phenomenon. Sometimes there is only one wheel to gnaw the rail, sometimes several wheels gnaw the rail at the same time, sometimes the same side gnaw the rail when going back and forth, sometimes the two sides of the track are nibbled separately when going back and forth. The reasons for the nibbling are complex, and may be due to the track, wheels, bridge, or other factors.Therefore, specific problems must be analyzed.

1. Nibbling due to track defects

(1) Excessive horizontal bending of track installation or excessive local deformation of track, which will lead to gnawing of track when the span tolerance is exceeded. This nibbling is characterized by nibbling occurring only on a part or a segment of the track.

(2) Track installation "figure eight". Irregular track installation, resulting in large and small one end of the gauge, the so-called "eight". On this section of track, the wheels will separately gnaw the outside and inside of the track as they travel back and forth.

(3) The relative standard of two orbits of the same section is too large. This situation can cause the crane to move sideways during operation, resulting in the upper side of the track being nibbled on the outside and the lower side being nibbled on the inside.

(4) Out-of-tolerance gauge. After processing and assembling according to the technological requirements, the travelling wheel distance of crane is a constant value. When the gauge is out of tolerance due to some reason, the wheels do not run in the middle of the tread, which leads to the phenomenon of nibbling due to the forced contact and friction between the wheel rim and the side of the track.

(5) The deformation of the main beam causes side bends of the trolley's track. When it is beyond a certain range, the trolley wheels will clip the rail and cause gnawing.

(6) During the operation, due to loose bolts on the platen or no rubber pads on the platen, the track position is moved, which will lead to the phenomenon of nibbling when the gauge, parallelism and straightness are out of tolerance.

2. Wheel defects cause nibbling

Wheel manufacturing and installation quality problems can cause gnawing. Crane overload operation or due to residual stress and other reasons caused the main beam, end beam or trolley frame of the crane deformation, will inevitably cause the wheel skew and span changes, resulting in the operation of gnaw rail, especially the most common large vehicles.

(1) The diameters of the two main wheel tread are not equal. When the crane is running, the speed of the left and right side of the crane is different, causing the vehicle body to deviate, which makes the wheel rim force contact with both sides of the track, resulting in the gnaw track.

(2) When the four wheels are not in the same plane due to installation or bridge deformation, and the active wheel pressure is not equal, the phenomenon of nibbling is inevitable.

(3) Horizontal deflection of wheels. Due to the deformation of the bridge, the end beam is bent horizontally, so that the wheels are out of deviation or the wheels are out of deviation when they are installed.

(4) Vertical deflection of wheels. Due to the deformation of the bridge wheel vertical deflection error caused by gnaw rail. That is, the center line of the wheel tread and the plumb line form an Angle tangential. When the vertical deflection value of the end face of the active wheel exceeds the tolerance, it will cause the gnaw rail. Because the two active wheels are vertically tilted in the same direction, it will also cause the contact area between the wheel tread and the top surface of the rail to become smaller, and the pressure per unit area will increase, resulting in uneven wheel wear and even grinding the groove on the tread. This cause of nibbling, crane operation is often accompanied by hiss.

(5) The front and rear wheels do not run in the same straight line. Excessive deviation of the span or diagonal line caused by installation or bridge deformation prevents the front and rear wheels from running in a straight line, resulting in gnawing track.

(6) Improper installation of wheel taper direction inevitably destroys the speed adjustment performance between the two wheels, making the leading wheels more advanced and the lagging wheels more backward, that is, causing serious car body deviation and gnaw phenomenon.

3. Nibbling due to other reasons

(1) When driven separately, the phenomenon of nibbling will occur because the motor is out of sync.

(2) When driving separately, the phenomenon of nibbling will occur due to the unequal braking torque of the brake.

(3) Unsynchronous starting and braking caused by too large or too loose clearance of transmission shaft coupling and large meshing clearance of gear will lead to nibbling phenomenon.

(4) There is dirt on the track or wheel that affects the friction coefficient, resulting in the two active wheels driving at the same time, which is caused by off-tracking of the car body.

(5) After replacing one driving wheel, the diameter difference between the two driving wheels is too large, which causes the two wheels to travel at different speeds and causes the car body to run off the track.

Repair of overhead traveling crane rail: if the crane rail is found, the related dimensions should be checked and measured in detail, and the reasons should be analyzed comprehensively to determine the repair plan.

(1) For nibbling track caused by excessive horizontal bending of track installation or excessive local deformation of track installation or zigzag of track installation, the track shall be readjusted to meet the specified standards.

(2) For the gnaw track caused by the high standard difference between two rails of the same section, the elevation shall be adjusted to reach the standard.

(3) For nibbling or derailment caused by the change of trolley gauge caused by the disturbance under the main beam or the excessive bending error at the horizontal side of the main beam, it can be repaired by moving the trolley wheel and changing the trolley gauge. If you want to solve the problem fundamentally, the main beam should be repaired, and the method of moving trolley track must not be adopted, because the cutting welding of track pressure plate will cause further downward interference and internal bending of the main beam.

(4) For nibbling the rails caused by loose bolts on the platen or no rubber pads on the platen during use, the bolts should be tightened or the rubber pads on the platen should be added, and the rails should be adjusted according to the standards.

(5) For nibbling rail caused by the difference of two driving wheel tread diameters or improper installation of wheel taper direction, the wheels shall be replaced to make the diameter dimensions equal or the taper direction installed correctly.

(6) For bridge deformation makes a big wheel vertical deflection and horizontal deflection ultra poor, or make four wheels is not in the same plane, or the wheel is not in the same line before and after operation or caused by diagonal out-of-tolerance gnaw rail, should first rectification bridge, conform to the technical requirements, such as there are still gnaw rail phenomenon, the wheels can be adjusted again, and try to adjust the passive wheels.

(7) For nibbling caused by the motor being out of sync when driving separately, the motor should be repaired or replaced to make the motor synchronous.

(8) For nibbling rail caused by unequal brake torque when driving separately, the brake shall be adjusted to make the brake torque equal.

(9) For nibbling rail caused by too large clearance of transmission coupling or too large meshing clearance of gear and unsynchronous starting and braking, relevant clearance should be adjusted to make it synchronous starting and braking.

(10) Nibbling due to oil on track or wheel should be removed.