Introduction

Cylinders in large forging equipment, such as 80MN and 50MN hydraulic presses, are prone to surface scratches and damage on the piston rods, leading to oil leaks, reduced pressing accuracy, and even debris contamination of the entire hydraulic system.

Due to the large size of the forging equipment, disassembling the cylinders is labor-intensive and time-consuming. Furthermore, problems like cylinder scratches are difficult to repair quickly. To address this frequent problem, equipment maintenance personnel have exhausted all available resources, utilizing their own maintenance resources and resources to repair some of these issues, enabling them to meet operational requirements.

Based on piston size requirements, there are two main methods: resizing and reducing. These methods include machining, welding (surfacing, repair welding, brazing, etc.), electroplating (low-temperature iron plating, chromium plating), and polymer composite spraying.

Resizing Method

1. For small, concentrated, and relatively small areas of localized piston rod rust, repair with stainless steel argon arc welding, followed by localized repair welding, grinding, and polishing can be used. This method is simple, low-cost, and meets service requirements.
2. For piston rods with localized plating loss, shallow rust pits, or large areas, repair by stripping the chrome layer, polishing, and re-chrome plating. Tolerance requirements must be maintained after electroplating. If deep pits are found in individual areas after polishing, brazing can be used for localized welding, followed by manual polishing. After repair, chrome plating can be performed. The surface should then be hard chrome plated (coating thickness 0.03-0.05mm) and polished. For manual repair, it is best to machine a grinding sleeve to the piston rod's outer diameter and grind the repaired area to a surface roughness of 0.1-0.2μm Ra (although this is difficult).
3. If the piston rod is severely corroded and stripping and polishing do not meet electroplating requirements, the piston rod should be straightened, ground, and turned. Once the ground size is 0.5mm smaller than the original size and meets electroplating requirements, copper plating followed by chrome plating can be used to meet service requirements. If this method still fails to meet the requirements, the original size should be reduced by 4-5mm. Thermal spraying or iron plating should be used to restore the original size, followed by grinding and chrome plating. This method is costly and expensive. Furthermore, the chromium layer is easily detached after iron plating, and the spraying quality is difficult to control.
4. Currently, some high-performance polymer composites are used to repair minor piston scratches. High-performance two-component epoxy composites reinforced with nano-inorganic materials adhere well to the piston surface and have excellent high-temperature and chemical corrosion resistance. After spraying, they can be quickly machined. The technology is simple to operate, provides high-quality repairs, saves time, and is cost-effective. However, for high-pressure cylinders and cylinders with rapid and frequent reversing, the spray coating may detach under pressure shocks. The method should be used according to the operating conditions.

Reduction Repair Method

For pistons with severe plating corrosion or scratches, direct reduction can also be used. Generally, the piston rod is recalibrated, turned, and ground to reduce the diameter. Detailed diagram: How to adjust the output pressure of a Rexroth A10VSO hydraulic piston pump? Even if the piston rod is 5mm smaller than the original nominal size, it can meet electroplating requirements, with low repair costs and sufficient performance.

A 5mm reduction in the piston rod is generally within the standard cylinder rod range, and standard seals can be used. If this repair method is used, the piston sleeve must be redesigned and remanufactured, and the appropriate seals must be selected for assembly. (Remember: Be sure to save this data in the equipment archive for future repairs.)

Alt. Double Piston Rod Cylinder

Summary

In summary, for addressing surface scratches and corrosion on Hydraulic Cylinder Piston Rods in large forging equipment, maintenance personnel can flexibly choose between resizing methods or reduction repair methods based on the severity of the damage and operational requirements. Resizing methods primarily include techniques like welding repair, electroplating repair, and high-performance polymer composite spraying. These are suitable for varying degrees and extents of damage, with composite material repair offering advantages such as simple operation and low cost, although its use requires caution under high-pressure or frequent reversing conditions. The reduction repair method achieves repair by directly reducing the piston rod diameter and matching it with replacement pistons and seals. It features lower costs and reliable performance but necessitates redesigning the piston sleeve and maintaining proper data archives.

In practical maintenance, the choice of method should comprehensively consider factors such as the damage condition, equipment operating environment, repair cost, and time. A rational repair strategy can not only quickly restore equipment performance and reduce downtime losses but also effectively extend the service life of key components, providing important guidance for the maintenance and management of large hydraulic equipment.