Repair forklift methods

1. Repair size method for machining

Using mechanical processing methods, the worn surface of a matching part, which is usually more complicated and more expensive, is machined to the repair size; the other matching part is generally relatively simple, according to the first part. The corresponding repair size is prepared so that there is a standard gap or interference between the two mating parts. However, the size of the piece is different from the normal one. This size is called the repair size.

Repair size can be standard and free. When the standard repair size is adopted, one of the parts is processed to a given standard size, and the matching part (such as the bearing sleeve) is prepared in advance according to this standard size. This eliminates the need for spare parts. However, this method requires more metal to be cut than the method that only repairs the journal to the correct geometry (free-size method).

When processing according to the free repair size, there is less metal cut from the parts, as long as the parts are restored to the standard geometric shape, but the matching parts must be prepared at the time, so the service life of the parts is extended.

The standard repair size method is adopted, and the parts are interchangeable, which can shorten the repair period and reduce the repair cost. Therefore, it is best to use the standard repair size method.

Standard repair dimensions are used to repair crankshafts, camshafts, cylinders and other parts. When preparing standard size parts, the parts factory can prepare bearing bushes, bushings, pistons, and piston rings in advance according to the specified repair size.

2. Additional parts method

When the parts with complex shapes are partially worn or damaged beyond the allowable level, these local worn or damaged parts of the parts are cut off, the size is trimmed, and an additional part (compensation part) is installed. After adding additional parts, the original parts return to their standard shape and size.

This method can be used to repair vehicles that have been repaired by forklifts many times and repair parts such as cylinder blocks, cylinder heads, valve seats, rolling bearing holes, journals, ring gears, etc., which are large to the limit.

Additional parts are usually made of the same material as the repaired part. The sleeve can be made of 20 steel with a minimum thickness of 2.5-3mm for cast iron parts. The surface roughness and hardness should meet the requirements of technical conditions, and heat treatment should be carried out if necessary. Additional parts should be connected to the essential parts before machining, so a certain amount of machining allowance should be left during manufacturing.

3. pressure processing repair

Pressure processing repair uses the plastic deformation of the part to restore the size and shape of the part’s damaged part.
Pressure processing repair is characterized by high repair quality, labour-saving and material-saving, and high productivity. Commonly used pressure processing repair methods include: swelling (reduction), thick emblem, lengthening, straightening (rectification) and so on.

(1) The rough method. Reduce the length of hollow and partially solid parts to enlarge their cross-sectional area. This method is used to repair the working surface and journal of the microvalve.
(2) The drawing method uses the extension method to shrink the partial cross-sectional area of ​​the part to restore the length of the tie rod, shaft and other parts.
(3) Pressure straightening uses the plastic deformation method to remove the residual deformation (bending, twisting and warping) on ​​the parts to repair the damaged parts. When using a press to straighten the shaft, you can mount the shaft on the V-shaped block, let the arch upward, load in the middle, give a certain amount of reverse bending, the amount of reverse bending should be 2 to 5 times the amount of bending and make the load Stay for 1.5 to 2 minutes.

The parts after pressure straightening often undergo bending deformation again. Heat treatment for stable deformation should be carried out to stabilize the deformation after pressure straightening. For parts quenched and tempered or normalized, it can be heated to a temperature slightly higher than the recrystallization temperature (450-5000C) for 0.5-2h; for surface-hardened parts (camshafts, crankshafts), it can be heated to 200-2500C, Keep warm for 5 -6h.

When the accuracy of the parts is very high, or the deformation of the crankshaft is less than 0.05% of the shaft length, the local surface cold work deformation method can be used to repair it.