Crane Wheel Gnawing Rail and Measures to Eliminate Rail Gnawing

 

Ⅰ. Analysis of rail gnawing phenomenon

Usually there is a certain gap between the wheel flange and the side of the track, and they will not touch under normal running conditions. However, sometimes the wheels do not run in the center of the track, so that the wheel rim contacts (friction) the rail side.

1.Manifestations of wheel gnawing phenomenon

 

(1) There are spots on the side of the track or the inner side of the wheel rim, and in severe cases, there are burrs or iron filings on the marks.

(2) When the bridge crane is running, the gap between the wheel flange and the track changes significantly within a short distance.

(3) During the operation of the bridge crane, the car body is skewed and the wheels are deflected.

(4) When the cart is running, it will make a louder “hissing” rail gnawing sound.

(5) When the rail gnawing is particularly serious, the cart will make a “squeaky” impact sound when it is running, and even rail climbing will occur.

 

2. Adverse consequences caused by wheel gnawing rails

(1) shorten the life of the wheel. Under normal circumstances, the wheels of intermediate (A4-A5) working-level bridge cranes can be used for more than 15 years; the wheels of heavy-duty (A6-A8) and metallurgical bridge cranes can be used for about 8 years. But for some bridge cranes with severe rail gnawing, the wheels can only be used for 1-2 years or even a few months.

(2) Accelerate track wear. Sideways forces from rail gnawing can displace the rail until it becomes unusable.

(3) Increase running resistance. Increase the power consumption of the motor and the transmission load of the mechanism.

(4) The load condition of the factory building deteriorates.

 

3. Rail gnawing degree of bridge crane

(1) Slight rail gnawing: the controller starts slowly in the first gear, and the inertial running distance is short after parking.

(2) Moderate rail gnawing: the first gear of the controller does not start, and the second gear starts slowly. When parking, sometimes it runs without inertia, and the wheel rim wears quickly and has curling.

(3) Severe rail gnawing: the second gear of the controller does not start, and within 10 meters of reverse running, the car body skew reaches the maximum value and begins to gnaw the rails.

4. Analysis of the cause of rail gnawing

(1) The diameter difference between the two driving wheels is too large. If the diameters of the two driving wheels of the bridge crane are different, the walking distance per revolution is not equal, and the side with the larger diameter will gradually lead, causing the car body to skew and cause rail gnawing.

(2) The installation positions of the four wheels are not the four corners of the rectangle, and the centers of the two wheels on the same side are not on the same straight line. Whether it is a driving wheel or a driven wheel, the deflection of the wheels will cause rail gnawing. The position of the wheels is arranged in four vertices of a parallelogram, the diagonal line D1>D2, and the rail-gnawing wheels are at the diagonal position. The position of the wheels is arranged at the four vertices of a trapezoid, and the positions of the rails are on the same straight line.

(3) The horizontal deviation of the wheel is out of tolerance. The horizontal deflection of the wheel, that is, there is an angle between the centerline of the tread and the centerline of the track in the horizontal direction. At this time, the wheel running speed V can be decomposed into two directions, one is Vx parallel to the wheel track, which makes the car body move forward; the other is Vy perpendicular to the wheel track, which makes the car body slide laterally and causes the wheel to bite the rail. Causes of horizontal wheel deflection:

①Due to the inconsistency of the tightness of the two sets of wheels, different resistances are produced, which makes the drive motors out of sync, causing the car body to skew and causing the wheels to gnaw on the rails.

②If the speed difference between the motors on both sides is too large, the car body will lean and cause rail gnawing.

③If the adjustment of the brakes of the two sets of units is different in tightness, the car body will be inclined during braking and rail gnawing will occur.

④ The gear gaps of the two sets of transmission mechanisms are different, and the keys of the mechanisms are loose, which causes a speed difference between the two sets of transmission mechanisms, causing the car body to lean and gnaw on the rails.

⑤ The influence of unreasonable operation. The trolley often works on one side, which increases the pressure and resistance of the large wheel on this side and causes rail gnawing; excessive starting or stopping will cause the wheels to idling and slip, which may easily cause rail gnawing.

⑥ If the horizontal bending of the track is too large, the left and right movement of the wheels will become smaller; if the track elevation is too high, the car body will be deflected to one side.

⑦The wheels are installed in the wrong direction. In order to prevent the rails from being driven centrally or separately, sometimes the wheels should be made into a taper of 1:10, and the small end should be on the outside during installation, otherwise it will cause rail gnawing.

 

(4)The installation of the cart aisle is not correct and does not meet the technical requirements of the installation, resulting in an out-of-tolerance tolerance and wheel gnawing on the rail.

 

Ⅱ.Measures to eliminate rail gnawing

Generally, it is more objective to judge the severity of rail gnawing by the wear amount of the wheel rim, and the wear amount of the wheel rim is more than 1mm, which is serious rail gnawing and must be repaired.

 

1. Reduce wheel diameter difference

When the diameter of a pair of driving wheels exceeds 0.2% of its diameter, and the diameter of the passive wheels exceeds 0.5%, it should be reprocessed to the same basic size, and the diameter difference between the driving wheels and the passive wheels should not exceed 3mm.

 

2. Adjustment of wheel span, diagonal and alignment difference

The deviation of the wheel span and diagonal of the cart should not be greater than ±7mm; the deviation of the wheel span and diagonal of the trolley should not be greater than ±3mm, and the wheel alignment difference should not exceed 2mm. During adjustment, the method of reducing one side of the spacer ring of the wheel bearing and increasing the other side correspondingly can be used to move the wheel. Or expand the bolt hole where the bearing box is installed on the end beam change plate, and move the positioning key to adjust the span of the wheel and the same position difference of the diagonal.

 

3. Adjustment of the cart transmission

For bridge cranes driven separately, the tightness of the bearings and brakes of the two sets of driving mechanisms should be adjusted to be the same. If the transmission parts of the reducer and coupling are replaced, both sides should be replaced at the same time. The motors of the two carts should be of the same model and parameters.

 

4. The clearance of tapered roller bearings should be the same

 

5. Adjustment of vertical deflection of large and small wheels

The vertical deflection value a of the large and small wheels, that is, the distance from the lower end point of the measured length L to the plumb line, should not exceed L/350. The vertical deflection direction of the wheels on both sides should be in a “V” shape, that is, the upper part of the wheels should be outward, and the wheels will approach vertical when the bridge crane is loaded.

 

In order to correct the vertical deflection value a of the wheel, pads should be added between the corner box and the horizontal positioning key or between the horizontal positioning key and the end beam bending plate. Which side of the wheel to add pads to the bearing box depends on the deflection direction of the wheel. If the wheel is biased to the right, add pads to the left; otherwise, add pads to the right.

When adjusting, if the positioning bolts of the bearing box cannot pass through, the bolt holes on the bent plate can be enlarged. After the adjustment is completed, the positioning key and the adjustment backing plate should be spot-welded on the bent plate of the end beam.

 

6. Adjustment of the horizontal deflection of the large and small wheels

(1) Measurement of wheel horizontal deflection. First find two parallel lines as reference lines to measure the horizontal deflection.

(2) Adjustment of horizontal skew. The horizontal deflection value C of the wheel is specified. In order to correct the horizontal deflection, a cushion can be added behind the vertical positioning key of the angular bearing box, and the position of the cushion depends on the direction of deflection.