Created on:2022-02-18 13:03

On site comprehensive repair method of large hydraulic cylinder

On site comprehensive repair method of large hydraulic cylinder

1. Introduction

35MN extruder has huge volume, difficult disassembly, long maintenance cycle of conventional machining, difficult repair and high cost, and it is difficult to ensure the surface roughness after machining. When using 35MN extruder, the guide belt and sealing ring between the hydraulic cylinder plunger head and the cylinder block of the extruder were damaged, resulting in direct contact between the plunger head and the inner surface of the hydraulic cylinder, resulting in serious strain between the plunger head and the surface of the hydraulic cylinder and forced shutdown. In order to ensure the repair quality of cylinder block and plunger head, shorten the maintenance cycle and reduce the maintenance cost, after careful research, formulate a feasible scheme and decide to carry out on-site repair.

2. Damage

(1) Damage of plunger rod. Figure t is the schematic diagram of plunger rod. The diameter of plunger is 1050mm and the weight of plunger is 17T. The total area of plunger rod strain is 20000mm2, the average strain depth is 2mm, and the deepest strain depth is 7mm.

(2) Damage of hydraulic cylinder block. Figure u shows the schematic diagram of the hydraulic cylinder block. The weight of the hydraulic cylinder is 30t, the inner diameter of the cylinder block is 1120mm, the length of the cylinder block is 3550mm, and the inner surface roughness is 0.8. The total area of the hydraulic cylinder body is 350000mm2, the average tensile depth is 3mm, and the deepest tensile depth is 10mm.

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3. Site repair scheme

Brush plating, pulse cold welding and viscose are comprehensively used for on-site repair.

(1) Brush plating. The plane with uniform surface wear and less wear shall be repaired by brush plating. Under the action of electric field, brush plating makes metal ions move directionally and deposit on the brush plated surface through electrochemical redox reaction, so as to repair the worn surface. In the process of brush plating, with the cylinder body as the cathode and the brazing solution as the anode, brush plating is carried out on the repaired surface with a plating pen. The plating pen is wrapped with wrapping cloth to keep contact with the workpiece and make relative movement under a certain pressure, and the deposition process is carried out intermittently.

Before repairing by brush plating, the substrate surface needs to be treated. The treatment process is as follows:

1) Mechanical treatment. Use angle grinder, file, scraper and other tools to manually remove sharp angles, burrs, rust, scale, etc. on the surface of the substrate;

2) Electric purification and activation treatment. Remove oil stain, rust, oxide scale, fatigue layer and other dirt on the surface by electric purification method and activation method. The electrocleaning method uses alkaline electrocleaning solution to remove oil stain, and the activation method uses hydrochloric acid solution to remove the oxide film and fatigue layer on the surface, so as to expose the metal crystal on the surface, so as to improve the strength of the coating.

Brush plating has the advantages of good performance, high bonding strength, fast deposition speed, no thermal deformation of workpiece, convenient construction, easy to master, less environmental pollution, low cost, good economic benefit and technical effect.

(2) Pulse cold welding. The slight scratch part shall be repaired by pulse cold welding.

This method is to release the electric energy stored in the capacitor at the connection between the workpiece with high resistivity and the filler material in an instant, and the contact resistance makes the welding wire and the substrate heat rapidly and weld together, so as to achieve the purpose of repairing the tool and die.

Before pulse cold welding, the substrate shall be purified by mechanical treatment to remove the burr and oxide scale on the surface.

During pulse cold welding, the heating range is small (< 3mm) and the heating time is short (MS level), and the workpiece will not be deformed, annealed and discolored.

(3) Viscose. The parts with large area and deep damage shall be repaired by viscose. In this method, the adhesive added with special fillers such as molybdenum disulfide, metal powder, ceramic powder and fiber is directly coated on the surface of materials or parts to make it have the functions of wear resistance and corrosion resistance.

The adhesive method has the advantages of simple process, convenience, flexibility, safety and reliability. It does not need special equipment. It only needs to apply the prepared adhesive to the cleaned part surface and repair it after curing. It is often operated at room temperature and will not affect and deform the part. The gluing process is;

1) Cleaning. The grease, water, rust and dust on the surface of parts shall be cleaned with gasoline, diesel or kerosene, and then cleaned with acetone after volatilization, so as to ensure the thorough cleaning of the repaired surface.

2) Treat the substrate. The surface of the substrate shall be treated with sandpaper to make the substrate completely exposed.

3) Secondary cleaning and activation treatment. Clean with acetone or special cleaning agent. Then it is treated by sand blasting, flame or chemical method to improve the surface activity.

4) Prepare repair agent. The agent (a) and curing agent (b) shall be fully mixed in strict accordance with the specified proportion and used up within the specified time.

5) Coating. Apply a thin layer of the prepared repair agent on the bonding surface, scrape it repeatedly to fully soak it with the parts, and then evenly apply the prepared repair agent to the specified size, and leave finishing allowance. When coating, move in one direction as far as possible to discharge the bubbles inside the repair agent.

6) Curing. It takes 10h in summer and longer in winter, generally more than 24h. It takes 2 ~ 3H for heating and curing (about 80 ℃).

7) Trim. The repaired surface shall be polished manually. According to the curved surface of the inner wall surface of the cylinder block, a pre made profiling grinder shall be used, wrapped with fine sandpaper, and polished along the curve of the cylinder block. When the size is close to the requirements, the surface treatment shall be combined with tools such as oilstone, and the grinding amount and surface roughness shall be strictly controlled until the repair meets the use requirements. See Figure V for the surface of the cylinder block after comprehensive repair by the above three methods.

4. Repair effect

After adopting the above three methods to repair the preloading cylinder of 35MN extruder of our company, after 8 months of operation, except for one part of the rubber surface with an area of about 40 mm2, it was found that the rubber surface fell off during the inspection one month after repair, the others were intact. After repairing the falling surface, it was found that the inner wall of the cylinder was intact and the surface was free of wear and fall off after repeated inspection during use, All parameters of the pressure of the preloading cylinder shall be kept in good condition.

5. Comparison between conventional mechanical repair methods and on-site repair methods

Using the conventional mechanical repair method, the component needs to be disassembled first, the damaged part needs to be welded and repaired, and then transported to the machining manufacturer for machining. The maintenance cycle takes about 7 months. The on-site surface repair does not require disassembly and thermal stress during welding repair, and the spare parts are free from deformation. The maintenance cycle is about 80 days. The maintenance cost is low and the cycle is short, and the damage to the equipment caused by the disassembly of spare parts can be avoided.

Using the on-site comprehensive repair method to repair the large hydraulic cylinder not only has high repair quality, short maintenance cycle, low maintenance cost, safety and reliability, but also will not cause damage to the cylinder.

 

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