"Rail gnawing" is a typical failure phenomenon of crawler construction machinery, which is manifested in the service life of guide rails, supporting wheels, driving wheels, supporting wheels and crawlers when the whole machine is traveling. There is a backlash between the crawler and the above-mentioned "four wheels", of which the backlash with the guide wheel is the smallest, and the backlash with the supporting wheel is the largest. Under normal circumstances, normal friction will occur between the track and the "four wheels", but no "rail gnawing" will occur. The root cause of "rail gnawing" is: the track cannot be wound correctly; the center planes of the "four wheels" do not coincide.
Excavator track derailed
1. "Track gnawing" caused by guide wheels
The guide wheel is an important part of the walking system. 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 wheels. Except for a short side shift when turning, the crawler generally does not slip. However, if the guide wheels are skewed, the track will be subjected to a component of force in a non-skewed direction, causing it to move axially, which will cause the phenomenon of "rail gnawing". The direction in which the guide wheels incline is different, and the position that causes the guide wheels to "gnaw the wheel" is also different. If the guide wheels are inclined in the horizontal plane, they will "gnaw the track" in front of the guide wheels; if the guide wheels are inclined in the vertical plane, it is usually The "rail gnawing" occurs on the top and bottom of the guide wheel, which can cause the front roller to fall off in severe cases; when the two tilts exist at the same time, the phenomenon of "eight-shaped gnawing rail" will occur. It can be seen that the correct installation position of the guide wheel has a great influence on whether the crawler "gnaws the track".
The main factors affecting the installation position of the guide wheel are:
(1) The coaxiality between the center of the 8 screw holes on the end surface of the box hole of the spring box and the box hole of the box spring is out of tolerance. After assembly, the longitudinal centerline of the guide wheel does not coincide with the longitudinal centerline of the trolley frame.
(2) The verticality between the end face of the front hole of the spring box and the longitudinal centerline of the trolley frame is out of tolerance. And the installation verticality with the support wheels of the trolley frame is also out of tolerance.
(3) The parallelism between the base of the spring box and the center line of the spring box hole is out of tolerance.
(4) The center lines of the semi-circular holes where the eccentric pins are installed at both ends of the guide wheel shaft are not parallel, which causes the left and right brackets to be asymmetrical after assembly, causing the guide wheel to tilt.
(5) There is an error in the mutual position of the four holes connecting the left and right brackets and the guide wheel bracket.
(6) Improper adjustment of the gap between the guide wheel, the bracket and the wear reducing plate.
In addition, if the guide wheel has processing defects, it will also cause "rail gnawing", such as: axial deviation during the processing of the middle shoulder of the guide wheel; the diameter of the raceway on both sides is different, so that the tension force of the two crawlers is different, and the crawler is easy to migrate. The raceway generatrix is not parallel to the axis of the track pin, so that the track partially slips.
2. "Rail gnawing" caused by supporting wheels
The role of the support roller is to transfer the weight of the machine to the track. When the machine is running, in addition to rolling along the track surface of the crawler, it also clamps the crawler to prevent it from sliding out laterally; when the machine turns, it also makes the crawler slide laterally on the ground. There are two types of support rollers: unilateral and bilateral. Taking the TY220 crawler bulldozer as an example, there are 12 rollers, of which 4 are bilateral and 8 are unilateral. Unilateral and bilateral support wheels together form a raceway, and the track rolls on the track. When the track generatrix does not coincide with the center line of the supporting wheel tooth block and the center line of the guide wheel, it will cause the supporting wheel to "grab the rail".
The main reasons why the supporting wheels "gnaw the rail" are:
(1) The fixing bolts of the supporting wheels are loose, causing the axial position of the supporting wheels to change or skew.
(2) The positioning groove of the supporting roller is severely worn.
(3) The center line of a set of holes of the trolley frame fixed rollers is not perpendicular to the straight line formed by the half-axle mounting holes and the diagonal support mounting holes (the space is not vertical)
(4) The middle flange of the support roller was offset during machining.
(5) The raceway generatrix is not parallel to the axis of the track pin, causing the track to slide sideways.
(6) The diameters of the raceways on both sides of the supporting wheels are different.
(7) When the supporting roller is processed, the axial dimension of the raceway is too small, so that the gap between the track and the track is smaller than the gap between the guide wheel and the track, causing "rail gnawing".
3. "Track gnawing" caused by driving wheels
The backlash between the driving wheel and the crawler belt is the largest, and “rail gnawing” generally does not occur, but if the center line of the tooth block does not coincide with the center line of the guide wheel and the supporting wheel, it will also cause “rail gnawing”.
The main reasons for driving wheels to "gnaw the track" are:
(1) When the supporting roller is press-fitted, the size of the center line of the supporting wheel tooth block to the end surface of the inner shell is not press-fitted or over-positioned.
(2) The coaxiality of the oblique support hole of the trolley frame and the bearing hole on the half shaft support is poor, which causes the center line of the tooth block to be not perpendicular to the longitudinal center line of the trolley frame.
(3) The axial dimension of the half shaft bracket or the half shaft is out of tolerance during machining, causing the drive wheel to be installed improperly.
(4) Due to non-use, the semi-axle is bent and the driving wheel turns flat and deflects.
4. "Rail gnawing" caused by deformation of trolley frame
The trolley frame is a rectangular frame structure connected by a U shape and an L shape. "Four wheels" and buffer devices are installed on it. The deformation of the trolley frame will destroy the positional relationship between the "three wheels" and the driving wheels, causing "rail gnawing".
The main reasons for the "rail gnawing" caused by the deformation of the trolley frame are:
(1) The trolley beam is bent. The bending of the trolley beam includes the bending in the horizontal plane and the vertical plane; from the point of view of the impact on the use of the whole machine, the bending in the non-planar has the greatest influence on the "rail gnawing", and it will also cause the whole machine to deviate.
(2) The front crotch of the trolley frame is deformed. One is to separate outwards, and the other is to open the crotch crookedly.
(3) The diagonal support of the trolley frame is deformed. This will destroy the installation position of the trolley frame.
5. "Rail gnawing" caused by wear and other reasons
The trolley frame has a harsh working environment and withstands large external forces, so it is prone to wear. The main reasons for the "track gnawing" are:
(1) The mounting surface and mating surface of the trolley frame are worn out, which damages the verticality of the trolley beam and the half shaft.
(2) Loose mounting bolts of the trolley frame cause "rail gnawing".
(3) Foreign matter is caught between the guide wheel and the trolley frame during the use of the whole machine, making the guide wheel unable to be adjusted.
In short, the cause of "rail gnawing" is very complicated. Not only should we pay attention to the problems in the processing and assembly process, but also the running parts should be checked and adjusted irregularly during use to prevent the occurrence of "rail gnawing". . Namely: check the gap between the outer cover of the guide wheel and the trolley beam, and adjust accordingly if the requirements are not met; adjust the axial position of the supporting roller; check whether the fixing bolts of the rear frame are tight; check the guide wheel and the platform Whether there are foreign objects between the frame.
