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The phenomenon of gnawing rail on the walking device of crawler type engineering machinery

Jul 18, 2018

"Gnawing rail" is a typical failure phenomenon of caterpillar type engineering machinery, which is manifested in the service life of guide rail, supporting wheel, driving wheel, supporting heavy wheel and caterpillar belt when the whole machine is walking. There is a side gap between the crawler belt and the above "four wheels", among which, the side gap between the crawler belt and the guide wheel is the smallest and the side gap between the supporting wheel is the largest. Under normal circumstances, there would be normal friction between the crawler and the "four wheels", but there would be no "rail gnawing". The fundamental reason for the "gnawing" is that the caterpillar can't be wound properly. The center of the four wheels does not coincide.


The excavator tracks off

1. "gnaw track" caused by guide wheel

The guide wheel is an important part of the walking system, and the correct installation position has a great influence on the life of the walking system. Under normal circumstances, the crawler should be wound in the middle of the guide wheel. Except for a short lateral shift during a turn, the crawler generally does not slip sideways. However, if the steering wheel is tilted, the track will be subjected to a component force in the direction of the non-slanting direction, causing it to move in an axial direction, resulting in the phenomenon of "rail gnawing". If the guide wheel tilts in the horizontal plane, there will be a "gnaw track" in the front of the guide wheel. If the tilt occurs in the vertical plane, it usually occurs on the upper and lower part of the guide wheel "gnaw rail". In serious cases, it can cause the front heavy wheel to lose the edge. When two kinds of tilt exist at the same time, "figure eight gnaw rail" phenomenon will occur. It can be seen that the correct installation position of the guide wheel has a great influence on whether the track is gnawed.


The main factors influencing the installation position of guide wheel are:

(1) the circle formed by the 8 screw hole centers on the end face of the box hole of the spring box is out of sync with the coaxial degree of the box hole of the spring box. After assembly, the longitudinal center line of the guide wheel does not coincide with the longitudinal center line of the frame.

(2) the vertical deviation between the orifice end face of the front hole of the spring box and the longitudinal center line of the platform frame is too poor. And with the platform frame heavy wheel installation vertical degree is also too poor.

(3) the parallelism between the base of the spring box and the center line of the spring box hole is too poor.

(4) the center line of the semicircle hole with eccentric pin installed at both ends of the steering wheel shaft is not parallel, resulting in the asymmetry of the left and right bracket after assembly, causing the steering wheel to tilt.

(5) there is an error in the interposition of the four holes connected to the left and right bracket and the guide wheel bracket.

(6) improper clearance adjustment between guide wheel, bracket and anti-wear plate.

In addition, if the guide wheel has machining defects, it will also cause "gnaw rail". The diameter of both sides of the track is different, so the tension force of both tracks is different, the track is easy to migrate, and the track bus is not parallel to the track pin axis, thus making the track partially slip.


2. "gnawing track" caused by supporting heavy wheel

The action of the supporting wheel is to transfer the weight of the machine to the track. In the process of running the machine, it should not only roll along the track surface of the track belt, but also hold the track belt to prevent it from sliding out horizontally. When the machine turns, it makes the caterpillar slide across the ground. The supporting wheel is divided into two kinds, one side and the other side. Taking the TY220 crawler bulldozer as an example, there are 12 supporting wheels in total, 4 of which are bilateral and 8 are unilateral. The single side and the double side supporting heavy wheel form a raceway and the track roll on the track. When the track bus does not coincide with the center line of the trunnion gear block and the center line of the guide wheel, it will cause the supporting wheel to "gnaw the track".

The main reason why the supporting wheel "gnaw rail" is:

(1) the retaining bolt of the supporting heavy wheel is loose, causing the axial position of the supporting heavy wheel to change or skew.

(2) the positioning groove of the supporting heavy wheel is seriously worn.

(3) the center line of a set of holes fixed by the platform frame supporting heavy wheels is not vertical (the space is not vertical) with the straight line formed by the half shaft mounting hole and inclined supporting mounting hole.

(4) the center flange of the supporting heavy wheel is offset during processing.

(5) the roller track bus and track pin axis are not balanced and the track track slip sideways.

(6) the diameter of the raceway on both sides of the supporting heavy wheel is different.

(7) when the supporting heavy wheel is processed, the axial dimension of the raceway is too small, so that the clearance between it and the track belt is smaller than that between the guide wheel and the track belt, causing the "gnawing track".


3. "gnaw rail" caused by driving wheel

The side gap between the drive wheel and the track belt is the largest, and generally there will be no "gnaw rail". However, if the center line of the gear block does not coincide with the center line of the guide wheel and the supporting wheel, the "gnaw rail" will also be caused.

The driving wheel "gnaw rail" is mainly caused by:

(1) when mounting the supporting wheel under pressure, the size of the Central Line of the supporting wheel gear block against the end face of the inner shell body is not pressed in place or over position.

(2) the difference in coaxial degree between the inclined support hole of the platform frame and the bearing hole on the semi-axle support seat, resulting in that the center line of the tooth block is not vertical to the longitudinal center line of the platform frame.

(3) the oversize of the semi-axle bracket or semi-axle is too poor in processing, which results in insufficient installation of the driving wheel.

(4) due to the non-use, the semi-axis bending is caused, which drives the cyclic leveling to produce deflection.


4. "rail gnawing" caused by the deformation of the frame

The frame is a rectangular frame structure connected by U shape and L shape. It has four wheels and a buffer. The deformation of the frame will damage the position relationship between the "three wheels" and the driving wheel, thus causing the "rail gnawing".

The main reason for the "rail gnawing" caused by the deformation of platform frame is:

(1) bending of trolley beam. The bending of trolley beam includes the bending in its horizontal plane and vertical plane. From the perspective of the influence on the whole machine, the bending in the plane has the biggest influence on the "gnawing rail", and will cause the whole machine to run off.

(2) deformation of the front crotch of the frame. One is to separate outwards, the other is to crotch crooked.

(3) deformation of platform frame oblique support. This will damage the mounting position of the frame.


5. Wear and other causes

The working environment of platform frame is bad and it can bear large external force, so it is easy to wear out. The main causes of "rail gnawing" are:

(1) the mounting surface of the platform frame and the mating surface have large wear and tear, which damages the perpendicularity of the platform beam and half shaft.

(2) loose mounting bolts of platform frame cause "rail gnawing".

(3) during the use of the whole machine, foreign matter is sandwiched between the guide wheel and the platform frame, so that the guide wheel cannot be adjusted.


In short, the causes of "gnawing rail" is very complex, not only should pay more attention to the problem of processing and assembly process, should be more in use is often not periodically check, adjust parts to walk, to prevent the happening of the "gnawing rail". Namely: check the gap between the outside cover of guide wheel and the beam of platform car, and make corresponding adjustment if it fails to meet the requirements; Adjust the axial position of the supporting wheel; Check the rear frame fastening bolts; Check whether there is any foreign matter between guide wheel and platform frame.