Crawler bulldozers are often constructed in environments with complex terrain and severe working conditions, and various failures may occur in the crawler chassis components. This article describes the common failure types of the chassis components of crawler bulldozers, the factors that cause the failures, and the methods for confirming the causes of some failures.

　　1: Common fault types

　　The chassis components described in this article mainly refer to the drive wheels, guide wheels, rollers, supporting chain wheels and crawlers (that is, "four wheels and one belt") that are prone to failure in the crawler bulldozer walking system, as shown in Figure 1. Because the chassis components of the crawler bulldozer bear the quality of the whole machine, and directly contact with the ground of different soil quality or even run on the muddy ground, the chassis components are more prone to failure than other components. Common failures of crawler bulldozer chassis components can be divided into three categories: wear, leakage, and cracks, as described below.

　　Wear: Chassis component wear includes track shoe tooth wear, chain link tread and side wear, chain link boss wear, pin sleeve outer circle or bore wear, pin shaft outer circle or end wear, wheel train tread wear, drive Tooth wear, wheel shaft wear, etc. Pin and drive wheel wear. The wear of track undercarriage components is inevitable, and the worn parts usually appear in the parts that move with each other or contact with the ground. Wear of one of the chassis components will adversely affect other components. If new parts are mixed with worn parts, it will accelerate the wear of new parts and reduce their service life. Perfect design scheme, strict processing technology and sound quality control system can extend the service life of chassis components and avoid abnormal wear.

　　Leakage: Leakage of track undercarriage components usually occurs in the lubricated parts of the guide wheels, carrier chain wheels, rollers and track pins. The working conditions of rollers are the worst, and their leakage failures are more likely to occur. Leakage of guide wheels, carrier sprockets, and rollers is usually due to the failure of the oil seal, including abnormal wear of the floating seal ring, wear of the O-ring, abnormal wear of the bushing, and abnormal extension of the bushing, etc., which can also cause leakage. The leakage of the lubricating part of the track pin is usually due to the tight sealing of the oil injection plug. This is related to the product quality process control. The manufacturer should take measures to avoid such failures.

　　Cracks: Cracks may occur in various parts of track chassis components, such as track shoe breaks, chain link breaks, track pin breaks, and drive wheel tooth blocks fall off.　 There are many reasons for the fatigue cracks on crawler chassis components, usually because the parts are used for a long time, there are defects in design and selection, manufacturing defects or poor working conditions. The cracks mostly occur at sharp corners or sudden changes in cross-section. The complete failure of parts (such as track shoe breakage) is not directly related to its length of use. The causes of breakage are mostly manufacturing defects, design and type selection defects, and material problems. The causes of cracks in crawler chassis components are mostly manufacturing defects, installation defects and new and old parts matching defects (such as the outer parts of the track pin sleeves). Cracks are also likely to occur after the parts are severely worn. Mass-produced parts have cracks in a short period of time, mostly due to abnormal working conditions, such as corrosive working conditions (phosphorus, sulfur-containing slag or dump).

　　2: Factors of failure

　　Uncontrollable factors: Uncontrollable factors that cause failures of crawler bulldozer chassis components mainly refer to the operating conditions of the bulldozer, including external influence factors such as soil particle size, soil chemicals, air humidity and temperature, terrain, and operation content.

　　Soil: If the soil particles are too small and the soil sand content is too high, a layer of abrasive will be formed on the surface of the wheel body and the crawler, which can accelerate the wear of the chassis components; the soil particles are too large and the crawler walks on the rock, which can make Excessive impact of the crawler chassis will accelerate the wear of the chassis components; when working in the garbage dump, ground debris is easy to be inserted into the moving parts, which affects the meshing and increases wear; the chassis components contact the wet ground, which is prone to chemical corrosion and wear ; The soil contains salt, phosphorus, sulfur, organic chemicals, chemical waste, which will corrode the surface of the chassis components and accelerate cracks.

　　Ambient temperature: Extremely high or low ambient temperature will have an adverse effect on chassis components. When the ambient temperature is extremely high (such as contact with the slag from the steel mill smelting), the metal surface of the chassis components will be annealed and the surface hardness will be reduced, which can reduce its service life; high temperature reduces the viscosity of the lubricating oil inside the wheel body, accelerating the shaft and sleeve Wear. When the ambient temperature is extremely low, the viscosity of the internal lubricating oil becomes high, the fluidity decreases, the lubrication between the relative moving parts becomes poor, and the wheel body tends to generate heat when rotating, which may shorten the service life of the parts. If the ambient temperature is too low, it is easy to cause cracks in the steel parts.

　　Topography: The topographic factors will affect the 5 types of working terrain where the chassis components produce asynchronous wear, and the crawler bulldozer chassis components are easy to wear. Uphill operations will increase the wear on the rear side rollers, drive wheel gears, chain links and pin sleeves of crawler bulldozers. Downhill operations will increase the wear on the guide wheels; side slope operations will increase the side of the rails and rollers And guide wheel edges, pin sleeve end faces, and the lower side of the center of gravity wear on the track shoes; dome terrain operation will accelerate the inner side of the chain link, the wearer and guide wheel treads, drive wheels, and the lower side of the track shoes wear ;Internal arc terrain operation will accelerate the wear of the outer chain link, roller and guide wheel tread, as well as the track shoe, the outer side of the drive wheel and the pin sleeve.

　　Operation content: Different operation content will also cause the chassis parts to wear out synchronously. When the bulldozing operation, the quality of the main machine is higher than the front, which will accelerate the wear of the front roller and guide wheel; when using the ripper operation or bulldozer for traction operation, the quality of the main machine is backward, which will speed up the rear roller and drive wheel Wear of gear teeth and chain rail pin sleeves.

　　3: Some controllable factors

　　The part of the controllable factors that cause the failure of the chassis components of the crawler bulldozer refers to the use conditions and application conditions that can be partially controlled by the operator of the bulldozer. Including driving speed control, turning control, track slip control and reverse operation control. The wear speed of the chassis components increases with the increase of the driving speed. Under high wear or high impact conditions, the driving speed of the crawler bulldozer should be especially controlled. When a crawler bulldozer turns, it will increase the wear of the rims of the rollers and guide wheels, so avoid turning to one side all the time. When the crawler track of the crawler bulldozer slips, it can accelerate the wear of all chassis components, especially the maximum wear of the track shoe teeth. When the crawler bulldozer works in the reverse direction, the wear between the gear teeth of the driving wheel and the pin sleeve is more serious than that in the forward operation. Under the premise of satisfying the use function of crawler bulldozer, the above controllable factors should be controlled as much as possible.

　　4: Controllable factors

　　Controllable factors that cause failure of chassis components of crawler bulldozers refer to factors that the operator can control and have an important relationship with the life of chassis components, including crawler tension, crawler width selection, crawler alignment, parking, and tidyness. Inadequate track tension will cause accelerated wear of chassis components. Especially if the track is too tight, it will accelerate the wear of the pin sleeve and drive teeth. The crawler-type bulldozer crawler track tension f is preferably L/35～L/25. as shown in Figure 4. On the premise of ensuring the traction force and the grounding pressure, a track shoe with an appropriate width should be selected. The width B of the track shoe is preferably 0.17 L to 0.19 L (L refers to the track ground length). If the track shoe is too wide, it can form a lever effect and make the track shoe stressed abnormally. The concentricity of chassis components is the most important attribute to avoid uneven wear and accelerated wear. The concentricity of the chassis components is not good, which can cause many abnormal wear and heat generation of the wheel system and other failures. It should be highly valued during the assembly of the whole machine. Crawler bulldozers should be parked on a flat ground to prevent lubricant leakage. Frequent cleaning of dirt entering the chassis components can reduce their wear.

　　5: Method for confirming some failure causes

　　Wear failure: When the track pin sleeve is abnormally worn, it is necessary to observe whether the tooth block is normal. When the track chain is abnormally worn, it is necessary to observe whether the rollers rotate. When the track pin and bushing are abnormally worn, it is necessary to measure whether the track tension meets the requirements. When the roller rim and the inside or outside of the chain link are abnormally worn, the concentricity of the chassis components should be observed and measured.

　　6: leakage and crack failure

　　If the appearance of the drive wheels, guide wheels, rollers, and support chain wheels is not abnormal, oil leaks, there should be a problem with the quality of the parts. If the chassis components have cracks or breakage failures, after removing the cracks caused by wear, most of them have problems in design, selection or manufacturing.