The crawler crane undercarriage comprises various essential parts that form the backbone of these powerful machines. Engineered to provide stability, mobility, and support, each component plays a crucial role in ensuring the smooth operation of the crane. From the robust tracks to the intricate mechanisms, the crawler crane parts of undercarriage work in harmony to enable the crane to conquer challenging terrains and accomplish heavy-duty tasks with precision and efficiency.
the structure of crawler crane undercarriage
In Figure 1, the parts of undercarriage are labeled as follows: 1- Crawler crane track; 2- Sprocket; 3- Tensioning roller; 4- Tensioning device; 5- Buffer spring; 6- Idler; 7- Track roller; 8- Walking mechanism.
1-Track Of Crawler Crane
The track of crawler crane, as main parts of undercarriage, consists of flexible chain links driven by the sprocket and supported by the track roller, idler, and tensioning wheel. The crawler crane track is constructed with track plates and track pins. The track pins connect the track plates, forming a continuous track chain. The ends of the track plates have holes that engage with the drive wheel, while the middle section features idler teeth to guide the track and prevent disengagement during turns or tilting motions. The side of the track plate in contact with the ground is equipped with reinforced anti-slip lugs (treads) to enhance durability and traction.
Operating under harsh conditions, the track must possess sufficient strength, rigidity, and excellent wear resistance. It should be lightweight to minimize metal consumption and reduce the dynamic load during operation. The track needs to maintain strong adhesion with the ground, ensuring optimal traction force while minimizing resistance during travel and steering.
2-crawler crane sprocket
The crawler crane sprocket is typically positioned at the rear of the crawler machinery. This undercarriage parts offers several advantages. Firstly, it shortens the length of the track drive section, reducing friction and wear on the track pins, thus extending the track’s lifespan. Secondly, it helps prevent the formation of a raised portion in the lower part of the track, ensuring that the track remains securely in place during turns and minimizing the risk of track detachment. Lastly, it contributes to improving the efficiency of the walking system.
The height of the sprocket’s center should be conducive to lowering the overall center of gravity (or vehicle body) and increasing the length of track-ground contact, thereby enhancing traction and adhesion. Thus, it is preferable to keep the height of the sprocket as low as possible.
crawler crane undercarriage Tensioning Device
Tensioning device
The tensioning device's main function is to achieve tensioning of the crawler crane track and prevent track disengagement. The buffer spring of the tensioning device must have a certain preload to generate pre-tensioning force in the track. Its purpose is to ensure that the engagement between the track pins and the teeth of the drive wheel is not affected by slight external forces during forward movement, and to generate sufficient traction force during reverse movement to ensure the normal engagement of the track pins and drive wheel teeth. The tensioning spring, due to the recoil effect of the device, pushes against the idler on the right side, keeping it in a certain tensioned state during operation, thereby guiding the track tensioning.
tensioning roller
The tensioning roller's role is to support the track and prevent excessive sagging, reducing track bouncing during movement and preventing lateral slippage. These undercarriage parts are similar to the track rollers but experience lighter loads and operates under better working conditions, resulting in smaller dimensions.
Buffer spring
The main function of the buffer spring is to work in conjunction with the tensioning device to provide elastic tensioning of the crawler crane track. Due to the action of the tensioning device, the buffer spring pushes the idler, achieving the tensioning effect. Therefore, compressive or tensile springs can be used.
6-crawler crane idler
The idler’s front or rear position depends on the placement of the sprocket, usually positioned at the front. This undercarriage parts is used to guide the track in the correct rotation and prevent deviation or derailment. The height of the idler’s center from the ground should be conducive to lowering the center of gravity.
7-Crawler crane track roller
The track roller is the most important parts of undercarriage in the four-wheel track system. Its primary function is to support the weight of crawler crane, enabling the track to move smoothly along with the rollers. The number and arrangement of track rollers should be designed to ensure even distribution of the track’s ground pressure. In construction applications, the walking mechanism often operates in mountainous or hilly areas with dirt roads. The track system requires a relatively small average ground pressure ratio, and the pressure from the track rollers needs to be evenly distributed.
The working principle of crawler crane
The track makes contact with the ground, while the sprocket does not touch the ground. When the motor drives the rotation of the sprocket, the torque from the gearbox causes the sprocket’s teeth to engage with the links of the track chain, continuously rolling the track from the rear. The portion of the track in contact with the ground exerts a backward force on the ground, and in response, the ground provides a forward reaction force to the track. This reaction force propels the machine forward. When the driving force is sufficient to overcome the resistance to movement, the track rollers roll forward on the surface of the track, enabling the machine to move forward. Both the front and rear tracks of the entire track system can be steered independently, allowing for a smaller turning radius.
Precautions when parts of undercarriage operating
- The operating temperature range for rubber tracks is generally between -25°C and +55°C.
- Chemicals, engine oil, and saltwater can accelerate the aging of the tracks. After use in such environments, the tracks should be cleaned.
- Surfaces with sharp protrusions such as rebar or stones can cause external damage to the rubber tracks.
- Road curbs, ruts, or uneven surfaces can cause cracks in the tread pattern at the edge of the tracks. If these cracks do not damage the steel cord reinforcement, the tracks can still be used.
- Gravel or crushed stone surfaces can cause early wear and create small cracks on the rubber surface in contact with the load-bearing wheels. In severe cases, water ingress can lead to core iron detachment and wire breakage.
