Crawler Crane Structural Analysis

A crawler crane is a kind of crane that travels on crawler tracks and is used for lifting. It is the most commonly used crane for lifting single-story industrial plants. Crawler cranes are flexible, easy to use, can rotate 360°, can travel with loads, and have low requirements on roads. However, it has low stability and should not be used overloaded. It travels slowly and has a certain degree of damage to the road surface. It is not suitable for long-distance travel. Flatbed trailers are generally used for long-distance transportation.

The crawler crane consists of a power unit (engine), a transmission device (main clutch, reducer, reversing mechanism, etc.), a slewing mechanism, a traveling mechanism (crawlers, traveling brackets), a hoisting mechanism (hook and boom lifting mechanism), and an operating mechanism. It is composed of system, working devices (boom, lifting pulley block, etc.) and electrical equipment.

In order to reduce costs and reduce the mass of structural parts, high-strength materials have become the first choice for host structures, with a yield strength of more than 500 MPa. Its structural size has been significantly reduced. Taking the product as an example, except for the special plates (the connection between the track and the frame) of the turntable, frame, and crawler frame structures, the thickness of the main load-bearing plates is within 35 mm (while the previous structure required 40 mm Above, commonly used boards are 50 to 70 mm).

The wide-limb thin-wall structure is adopted, which greatly improves the overall stability and load-bearing capacity of the structure. The proportion of the host structure's self-weight to the total machine's self-weight has also been reduced from the usual 60% to 40%. There are two main types of turntable structures, one is the closed turntable structure represented by Europe and the United States, and the other is represented by Japan. small box turntable structure. The closed structure consists of two I-shaped or box-shaped sections with larger height, which has good rigidity and is widely used in large products. The small box structure is equipped with a support connection mechanism on the small box section, and a shed is set up on both sides to place the engine, fuel tank, slewing mechanism and other components. For the convenience of maintenance, Japan has newly introduced a semi-open turntable structure. Parts are placed on one side and a walking platform is set on the other side. It is completely open. It is easy for maintenance personnel to access the mechanism and power components, replace wearing parts or check the operating status.

There are two ways to combine the turntable. One is that the turntable, slewing bearing and part of the frame are connected into one. The other parts of the turntable can be transported independently or disassembled for transportation, such as Manitowoc's M21000 product. The other is to transport the upper and lower vehicles separately, and use a quick connection method between the separated part and the slewing bearing, such as the quick pin connection method of Terex-Demag's CC5800 product.

Considering increasing the walking traction capacity and increasing the working speed, the four-wheel drive type can be used for the traveling mechanism. The structure of the crawler frame was subsequently improved, and its tensioning was achieved by being sleeved into the crawler frame structure through a tensioning beam. In order to reduce the driving torque, the driving wheel uses a sprocket type to reduce the diameter. Terex-Demag's CC2500 product adopts this type. The number of crawler assemblies is not just the traditional left and right crawler assemblies, but multiple assemblies. For example, Manitowoc's 21000 product has 8 crawler tracks, and each two crawler tracks are one Group. Each track carries a more even load, requires less foundation, and can be formed into wide and narrow patterns to adapt to the requirements of different workplaces. The frame structure has also been significantly improved. Considering the convenience of transportation, the frame of super large cranes is generally composed of 3 parts or even more parts.

The crawler crane is composed of a power unit, a working mechanism, a boom, a turntable, a undercarriage, etc.

Boom

It is a multi-section assembled truss structure. The length can be changed by adjusting the number of sections. Its lower end is hinged on the front of the turntable, and its top end is suspended and supported by a luffing wire rope pulley block to change its inclination angle.

There are also those that install a jib on the top of the boom, and the jib and the boom form a certain angle. The hoisting mechanism has a main and auxiliary winch system. The main winch system is used for boom lifting, and the auxiliary winch system is used for jib lifting.

Turntable

By installing the slewing bearing on the undercarriage, all the weight on the turntable can be transferred to the crawler undercarriage, which is equipped with power unit, transmission system, winch, control mechanism, counterweight and machine shed, etc. The power unit can make the turntable rotate 360° through the slewing mechanism. The slewing bearing is composed of upper and lower rollers and rolling parts (balls, rollers) between them. It can transfer all the weight on the turntable to the track undercarriage and ensure the free rotation of the turntable.

Undercarriage

It includes a traveling mechanism and a traveling device: the former enables the crane to travel forward and backward and turn left and right; the latter consists of a crawler frame, sprocket, idler, bottom roller, top roller and track shoe. The power device rotates the speocket through the vertical axis, horizontal axis and chain transmission, thereby driving the idler and track roller, so that the whole machine rolls along the crawler track.

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