The installation structure and maintenance methods of the outriggers of truck cranes

The outriggers of a truck crane are supporting structures installed on the frame that can be folded or retracted and extended.

Outrigger type

The outriggers of truck cranes can be divided into two types: manual and hydraulically operated. At present, manually operated outriggers are rarely seen, and the vast majority of truck cranes use hydraulic outriggers. Hydraulic outriggers can be further classified into the following types.

(1) Breaststroke outriggers

The movable outriggers of this type are hinged to the fixed outriggers, and their expansion actions are accomplished by hydraulic cylinders. Its features include a simple structure and relatively light weight, but the span of the outriggers is not large, making it only suitable for small-tonnage cranes.

(2) H-shaped outriggers

This type of outrigger has two hydraulic cylinders. When the movable outriggers are extended, the vertical legs support the ground during operation, forming an H shape, hence the name. It features a relatively large outrigger span and good adaptability to the site. Currently, it has been widely adopted.

(3) X-shaped outriggers

When this type of outrigger is in operation, it is in an X shape with a small ground clearance. During the process of the outrigger feet touching the ground, there is a horizontal displacement. When it is a small amplitude, the space for the heavy object to move is larger than that of the H-shaped outrigger. Therefore, it is often used in combination with the H-shaped outrigger to form a front H and rear X pattern.

(4) Radial outriggers

With the rotation center of the turntable as the center, four outriggers extend outward in a radial pattern from the bowl-shaped frame of the frame downward. The feature is good stability. During lifting operations, all the load does not pass through the frame but directly acts on the outriggers. In this way, the self-weight of the frame can be reduced and the height of the center of gravity of the entire machine can be lowered, protecting the chassis from damage. It is mainly applied to some extra-large cranes.

(5) Swing the outriggers

When performing lifting operations, this type of outrigger can swing to a position perpendicular to the longitudinal axis of the frame under the action of the hydraulic cylinder. When not in operation, it can be fixed parallel to both sides of the frame. The feature is its light weight. However, due to the limitation of space size, the outriggers cannot be too long, so the lateral support distance is relatively small.

The function of the outriggers is to provide a larger support span for the crane during operation without increasing its width, thereby enhancing its lifting performance without reducing the maneuverability of the truck crane. The faults of outriggers can be classified into two types: mechanical parts and hydraulic systems.

2. Faults and Handling of mechanical parts of outriggers

(1) Repair of worn frog outriggers

The most easily worn part of the frog outriggers is the guide groove 8 on the movable outriggers. If the wear on its working surface reaches 1.5mm, it should be replaced. Otherwise, when the outriggers are retracted or extended, the movable outriggers and the fixed outriggers will collide, which is likely to cause an accident. At this point, the working surface of the guide groove must be welded and repaired, as shown in Figure 2.

First, remove the movable outriggers, measure the size of the guide groove, and determine the thickness of the repair welding. When performing repair welding, install the rectangular red copper pad 4 with screw 5 and nut 7 as shown. Then, place the red copper tube 3 on screw 5. After completing the repair welding of one section, move and repair the next section until all sections are welded. For convenience, the welding rod can also be moderately bent. However, it should be noted that the welding repair position must be on the lower surface of the guide groove as shown in Figure 1. This approach will not affect the stroke of the hydraulic cylinder piston rod or the relative Angle between the fixed and movable outriggers when the outriggers are under load. After welding, use a standard shaft (with the shaft diameter equal to the outer diameter of the rolling sleeve) as a reference for shaping and

If the outer diameter wear of rolling sleeve 9 exceeds 1mm, it should be replaced. Otherwise, it is prone to being crushed during work, which will change the force condition of the outriggers and pose a hidden danger to safe production.

There is another key point in the maintenance of the frog outriggers, which is the screw 4 shown in Figure 1. There are a total of three screws on one frog outrigger. Due to the large radial force, these three screws are very likely to be cut off (turn over). The cut screws are not easy to turn outward, so many baffles 5 are welded dead. This not only looks bad but also requires gas welding and cutting when disassembling, which is inconvenient. After a long period of observation, we suggest the following: The screws used for axial positioning of the pin shaft in this way should be inspected frequently. It is best to replace it within no more than two years. Here is a simple inspection method. That is, remove the screw and compare it with a new screw of the same pitch. Press the two screws tightly together and observe the gap between the threads. If the gap is large and the two screws cannot fit together, it indicates that the old screw has deformed significantly and is fatigued, and should be replaced. You can also use a tap of the same size for comparison.

(2) Repair of the wear on the upper and lower parts of the H-shaped outrigger horizontal beam

When the crane is fully loaded, the lifted object is located directly behind the vehicle, higher than the outriggers. At this time, the person is looking at the outriggers from the very rear of the vehicle. If the situation as shown in Figure 3 occurs, that is, the horizontal distance between points A and B in the figure is greater than the thickness of the metal plate on the vehicle body 2, or if there is a crawling phenomenon when the outriggers extend and reextend, the outriggers must be removed for inspection. If there are deep grooves or severe damage on the plate surface, new outriggers should be replaced or the worn parts should be welded and repaired. The cost of welding and repairing outriggers is relatively low, making it suitable for adoption.

3. Faults and Maintenance of the outrigger hydraulic system

From the hydraulic principle diagram of the frog-type outriggers, it can be known that the bidirectional hydraulic lock 8 is installed at the upper end of the front outrigger cylinder. Therefore, the tightness of each fixing bolt on it must be consistent; otherwise, it will cause damage to the sealing ring and oil leakage. Its function is to prevent the outriggers from retracting by themselves when the crane is in operation. Prevent the outriggers from automatically lowering during the crane's movement or parking. In the hydraulic system of H-shaped outriggers, there is no diverter valve but a rotary valve. The outriggers can act independently and have good adaptability to the ground. However, the situation of failure is similar to that of frog-type outriggers

Common faults of outrigger hydraulic systems

(1) Oil leakage in the fuel line

The reason is that the joint is loose. The location should be found and tightened. The seal is damaged and should be replaced. There are cracks in the pipeline. It should be replaced or welded.

(2) The outriggers fail to retract and extend properly

The bidirectional hydraulic lock malfunctioned, and the plunger inside the lock was stuck and motionless. It needs to be disassembled, cleaned, reinstalled and adjusted. The plunger is severely worn and a new hydraulic lock should be replaced

(3) The outriggers automatically retract when lifting

There are two reasons: First, the one-way valve in the bidirectional hydraulic lock has poor sealing performance. It should be disassembled for inspection, cleaned, and then reinstalled and adjusted. The second issue is internal leakage of the hydraulic cylinder. It is necessary to remove and inspect the seal on the piston, replace it with a new one, and then reinstall it.