How to repair scratches on a precision piston rod?

If a Precision Piston Rod is scratched during operation and not treated promptly, it can affect product use to the point of rendering the hydraulic cylinder inoperable. How do we repair it? Minor scratches are repaired using localized grinding and polishing; more severe scratches are repaired using welding followed by manual grinding.

Scratching Formation: After disassembling the pneumatic-hydraulic booster cylinder, a precision piston rod was found to be severely scratched, with six scratches running side-by-side. The main cause of the scratches was that the dust seal had become brittle and detached in chunks, losing its dustproof function. Furthermore, the expansion joint accumulated a lot of dust and impurities, causing the piston rod to rub directly against these impurities, resulting in scratches. These scratches further damaged the cylinder's rubber seal assembly, causing severe external leakage from the hydraulic cylinder.

Repair Requirements: The filler and base material must have a stable and smooth bond; the filler material must be easy to use and readily machinable by hand; manual machining must ensure that the diameter error of the precision piston rod is less than 0.06mm. After analysis, J422 welding rods were chosen as the filler material. Because acidic welding rods are not sensitive to rust, oil, and moisture, they are less prone to hydrogenation porosity; they have good processability and are easy to operate; the weld formation is aesthetically pleasing; the material hardness is moderate, making it easy to process manually; the arc is stable, the penetration depth is large, and the bond with the base material is stable.

Repair Process:

1. First, clean the area to be welded, then surround the scratch with wet mud.

2. Select a 2.5mm diameter welding rod, adjust the welding machine current to 120A, and weld steadily using a straight-line welding method.

3. After welding, clean off the mud and slag, and use a coarse file to file along the circumference of the precision piston rod, leaving a machining allowance of 0.1-0.2mm.

4. Machine a cylinder with an outer diameter of 185mm, an inner diameter of 125mm, and a length of 150mm to serve as a template (piston rod outer diameter 125mm). Cut it along the axis; one is the rough template, and the other is the precision template.

5. Apply a thin layer of red ink to the inner wall of the rough mold. Then, place the rough mold firmly against the part of the product to be repaired and grind it back and forth along the axis several times. Next, use a fine file to remove any heavy red ink marks. Repeat this filing process, leaving a machining allowance of 0.04-0.07mm.

6. Then, using a 320-grit sanding block dipped in kerosene, grind the product to the specified dimensions using the fine mold.

7. Finally, hand-polish the product using sandpaper dipped in kerosene. Measurements show a maximum error of only 0.03mm.