What are the common faults in the use of forklift frame structures? How to repair a frame?

Forklift frames mainly adopt two structures: side beam type and box type. The frame is a welded structure. The box-type frame is made by welding steel plates into a box shape, without obvious longitudinal beams, and has high rigidity. It connects all the components of the forklift together. The front end of the frame is rigidly installed and fixed to the drive axle, while the rear end is supported on the steering axle through an intermediate hinge. The drive axle and the steering axle together support the entire vehicle. During operation, the drive axle will bear the majority of its weight. Therefore, side force plate reinforcing ribs are symmetrically welded to the front of the frame, and the front fenders are welded between the side beam bodies, making the frame form a solid whole.

1. Common faults of the frame

During the use of the frame, various damages may occur to the frame, the most common of which are frame deformation and cracking. When the frame has the following conditions, it should be dismantled and replaced with a new one

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

2) Two or more severe fatigue cracks of large length and dangerous location appear.

3) Fatigue cracks reappear at or near the area that has already been rewelded.

4) Frames that develop cracks or have notches due to accidents and fail to meet the required load-bearing capacity after repair should also be replaced.

5) When there are a large number of various defects on a node, it should also be replaced.

2. Repair of the frame

When there are dents or deformations on the frame, side panels or side beams and the deformation does not exceed 6mm, the cold correction method can be used for correction. However, cold calibration can only be carried out at temperatures above 0℃. When making corrections, tools such as bow-shaped calipers and jacks can be used for the correction.

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

In all cases, when the temperature drops below 700℃, the correction work should be immediately stopped, and the deformed part should be heated along the outer convex surface with a nozzle at the place where the deformation is the greatest. After correction, the component should be cooled when the ambient temperature is above 0℃.

2) Inspection and repair of frame cracks

Cracks mostly occur in components with drastic changes in cross-section, at the connection points of components, and at nodes with excessive welds. When inspecting, paint, dust and soil can be removed from the areas where cracks may occur to expose the metallic luster. Then, a 6-8 times magnifying glass can be used for inspection. The oil-immersed hammering method can also be employed to reveal the distribution of the cracks.

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

After welding, check if there are any cracks in the weld. If there are cracks, use a grinding wheel to grind off the weld joint and then reweld. The length worn off should exceed the obvious tail of the crack by 50 to 100mm. The new weld seam should be straight, dense, truly penetrated, and have a smooth transition with the base metal.