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1. Repair of hydraulic cylinder with strain by brush plating combined with brazing
(1) Cleaning oil stains Fix the piston rod, remove the surface oil stains with metal cleaning agent, and scrape the dirt in the strain groove; scrub the inner surface with acetone, electrochemically clean with electrocleaner (connect the workpiece to the negative pole, 12-15V, 60-90s), and rinse with water.
(2) Activation Electrochemical decontamination with No. 2 activation liquid (remove oxides, connect the workpiece to the positive pole, 10-12V, 40-60s), until the surface is black/gray-black, rinse with water; then electrochemically clean with activation liquid (remove impurities, connect the workpiece to the positive pole, 16-20V, 50-90s), until the surface is silvery white, rinse with water.
(3) Flash plating of fast nickel Flash plating of fast nickel on the surface of the treated workpiece (the workpiece is connected to the negative pole, 18V, and the plating pen swings). After 3 to 5 seconds, when the surface turns light yellow, the voltage drops to 12V (brush plating speed 9 to 11m/min). The plating thickness is 1 to 3μm and then rinsed with clean water.
(4) Brush plating of alkali copper layer After the fast nickel layer is plated, brush plate the alkali copper layer. When brush plating the alkali copper layer, the voltage is 6 to 8V, the workpiece is connected to the negative pole, and the brush plating speed is 9 to 14m/min. After the thickness of the alkali copper layer increases to 20 to 50μm, rinse with clean water.
(5) Brazing alloy: Wipe the brush-plated workpiece with a clean silk cloth, apply zinc oxide flux to the position where repair welding is required, and use a 300 to 500W electric soldering iron to repair the brazing alloy to the stretched part to the required size, scraper trim, and then polish with an oilstone to make it smooth.
(6) Use electro-cleaning liquid to clean the surface of the brazing layer and remove oil and impurities; use No. 2 activation liquid to remove surface oxides (control the time of electrochemical cleaning to prevent blackening); use No. 3 activation liquid to remove impurities; and perform rapid hot brush plating of the alkaline copper layer on the brazing surface.
(7) Brush plating again to enhance the strength of the brazing surface: brush plating alkaline copper (the workpiece is connected to the negative electrode, 6-8V, the brush plating speed is 9-14m/min, and the thickness is 30-50μm), and then wash with clean water; brush plating fast nickel (the workpiece is connected to the negative electrode, 12V, the brush plating speed is 9m/min, and the thickness is 60μm), rinse the machine parts with clean water, wipe them dry with a clean silk cloth, and then assemble.
2. Repair of the plunger cylinder
(1) Repair of the plunger Process flow: disassembly → straightening → grinding the outer circle → degreasing and rust removal → iron plating → chrome plating → grinding the outer circle to size (surface roughness is Ra1.6μm) → quality inspection → assembly.
(2) Repair of the cylinder body Since the length of the piston cylinder body hole and the plunger is not long, it can be repaired by inserting the bushing. The bushing is made of wear-resistant materials, such as tin bronze, wear-resistant cast iron, stainless steel, etc. Process flow: disassembly → flatten the inner and outer corners at both ends → rough boring the cylinder body hole (to ensure a light press fit with the bushing) → insert the bushing → bore the inner hole of the bushing and roll it to size (slip fit with the plunger, surface roughness is Ra0.8μm) → quality inspection → assembly.
3. FJY brush plating repair of piston rod
For the repair of local damage (millimeter level) with large depth (millimeter level) and small area (Figure 1) such as pit damage, electric shock damage, and bump damage that occur at the work site, it is not suitable to use electroplating method to repair. FJY series fast ultra-thick brush plating repair technology is the best choice to solve this kind of problem. Process flow: mechanical shaping → electrocleaning → water washing → removal of oxide film (activation treatment) → chromium surface activation → chromium surface bottom nickel → water washing → high-speed thick copper pit filling → mechanical grinding → electrocleaning → water washing → chromium surface activation → chromium surface bottom nickel → water washing → brush plating of wear-resistant surface layer → water washing → mechanical grinding → surface polishing.Figure 1Figure 1Figure 1
(1)Mechanical shaping: Use an electric grinding head to grind the area to be repaired until it has a smooth arc transition, ensuring that the plating pen can contact the bottom of the pit (Figure 2).
(2) Electrocleaning: Its function is to remove oil stains on the surface of the workpiece. In order to prevent oil stains from contaminating the plating solution, electrocleaning should be performed on all places where the plating solution may flow. The electrocleaning area can be larger, and the electrocleaning operation can be performed more than twice to ensure that the oil stains on the workpiece are completely removed after this step.
(3) Chromium surface activation: The material of the piston rod is mostly carbon structural steel that has been quenched and tempered. Generally, No. 2 activation liquid and No. 3 activation liquid are used to remove the oxide film, cementite and free carbon (supersaturated carbon) on its surface. FJY all-purpose chrome surface activation liquid is used to remove the oxide film on the surface of the chrome plating layer. If the chrome surface activation liquid is not used to treat the chrome plating surface, the plating layer on the chrome surface will not be firmly bonded to the chrome plating layer, and it is difficult to achieve a smooth transition during post-plating grinding. The rough boundary will scratch the oil seal during use.
(4) Chrome surface bottom nickel: Its function is to brush-plate a firmly bonded bottom layer at the repaired part. The time for chrome surface bottom nickel should not be too long, and it is best to make the plated surface appear uniform and bright white. If the bottom layer is gray (or dark gray), the bottom layer should be ground off and the pre-plating treatment and chrome-bottom nickel process should be repeated.
(5)High-speed thick copper filling The local damage depth of the piston rod is generally between 0.5 and 3 mm. Use FJY series fast ultra-thick high-deposit thick copper to fill the pit, and the brush plating time is 0.5 to 1 hour (under normal circumstances, a depth of 1 mm can be filled within 15 to 20 minutes). (Figure 3) shows a photo of high-speed thick copper filling.
Figure 3(6) Mechanical grinding Use a contoured grinding tool to grind the brush-plated surface in the order from coarse to fine until it is smooth and meets the tolerance requirements.
(7) Brush-plated wear-resistant surface layer The purpose is to improve the surface hardness and corrosion resistance. Generally, nickel and its alloys are used as the surface layer. Because the surface layer is covered on the copper layer and the chromium layer, the chromium surface activation and chromium surface nickel bottom process are still required before the brush-plated surface layer.
(8)Surface polishing Its function is to fine-tune the brush-plated surface. Use fine sandpaper dipped in polishing paste to polish the brush-plated surface to make the surface present a mirror-like gloss. Surface polishing has a dual function. One is to improve the sealing performance, and the other is to prevent the oil seal from being worn.
(Figure 4) shows the repaired piston rod.
The FJY series brush plating repair process is used to repair the local damage of the chrome-plated piston rod on site, which can overcome the difficulties of other repair methods. The service life of the repaired workpiece is equivalent to that of a new part. This is a new maintenance method with low repair cost, simple operation and high production efficiency. This technology is particularly suitable for repairing local defects of chrome-plated parts.
4. Honing repair of cylinder bore
Honing is used to repair cylinder bores, and a honing head is used. The structure of the honing head is divided into two categories: mechanical expansion type and hydraulic expansion type. Figure 5 shows the mechanical expansion type, and Figure 6 shows the hydraulic expansion type. In Figure 5, the body 1 is connected to the machine tool spindle through a floating coupling, and the grinding bar 5 is fixed together with the grinding bar seat 4 with an adhesive and installed in the groove of the body 1. The two ends of the grinding bar seat are clamped by spring hoops 6. The adjustment of the working size of the honing head depends on the adjustment cone 2. When the rotating nut 7 is turned downward, the adjustment cone is pushed downward, and the grinding bar is radially opened through the top block 3. When the grinding bar contacts the hole surface, the nut 7 is continued to rotate to obtain the working pressure; on the contrary, when the nut 7 is turned upward, the pressure spring 8 moves the adjustment cone upward, and the grinding bar shrinks due to the spring hoop 6. In Figure 6, the expansion and contraction of the oilstone is determined by the size of the adjusted hydraulic pressure, and the rest is the same as the mechanical expansion honing head.
Figure 5 Mechanical expansion honing head: 1-body; 2-adjustment track; 3-top block; 4-ink bar seat; 5-grinding bar; 6-spring hoop; 7-rotating nut; 8-pressure spring
Figure 6 Hydraulic expansion honing head: 1-spring holder; 2-oil stone; 3-oil stone seat; 4-body; 5-oil separator; 6-oil guide plate; 7-connecting plate; 8-pipe joint; 9-oil hole; 10-overflow valve; 11-pump; 12-pressure reducing valve; 13-reversing valve; 14-cooling pump safety valve; 15-cooling pump