What are the common faults in the use of forklift frame structure? How can the frame be repaired?

The frame of a forklift is mainly composed of two structures: the beam frame and the box frame. The frame is a welded structure, and the box frame is made by welding steel plates into a box shape without obvious longitudinal beams, which is very rigid. It connects all the components of the forklift together. The front end of the frame is rigidly installed and fixed to the drive axle, and the rear end is supported by the steering axle through a middle pinion. The drive axle and the steering axle together support the entire vehicle. During operation, the drive axle will bear most of the weight, so the front part of the frame is symmetrically welded with side force plates to strengthen it. The front guard is welded between the side beams to form a solid whole.

1. Common faults of the frame

During the use of the frame, various damages may occur. The most common ones are frame deformation and cracks. The frame has the following situations when it should be replaced:

1) Due to rust, the initial cross-section has lost more than 50%.

2) There are two or more severe fatigue cracks of large length and dangerous positions.

3) Fatigue cracks appear again at the place where welding has been done or nearby.

4) Cracks occur, or a crack is produced due to an accident, and the frame cannot reach the required load-bearing capacity after repair, it should also be replaced.

5) When there are many defects at one node, it should also be replaced.

2. Repair of the frame

1) If there are dents or deformations on the frame body, side plates, or beams, when the deformation is no more than 6mm, it can be corrected by cold correction. However, cold correction can only be carried out when the temperature is above 0℃. The correction can be done using tools such as an arch pliers and a jack.

When the depression and deformation are large, large deformations can be eliminated by quickly heating to 700-1100℃ or at 900-1150℃.

In all cases, when the temperature is below 700℃, the correction work should be stopped immediately. The deformed part should be heated along the outer convex surface using a nozzle at the maximum deformation area. After correction, the component should be cooled at a temperature of 0℃ or above.

2) Inspection and repair of frame cracks

Cracks mostly occur in components with significant changes in cross-section, connection points of components, and nodes with many welds. During inspection, the paint, dust, and dirt can be removed from the possible crack areas to expose the metallic luster. Use a 6-8 times magnifying glass to check, or use the oil hammering method to show the distribution of cracks.

For the detected cracks, holes with a diameter of 8-25mm can be drilled 10-15mm from both ends of the visible crack to control the development of the crack. Before welding, the weld seam should be ground with a bevel, and for carbon structural steel, E4315 or E4316 type welding rods, and for low alloy structural steel, E5015-A1 or E5016-A1 type welding rods should be used for welding.

After welding, check for cracks in the weld. If there are cracks, use a grinding wheel to grind off the weld joint and re-weld. The length of the ground should be more than 50-100mm beyond the obvious tail end of the crack. The new weld seam should be straight, dense, and fully penetrated, and the transition between it and the base metal should be smooth.