Hydraulic system

The first condition for the normal operation of the hydraulic system is that the inside of the system must be clean. Hydraulic system in the manufacturing and assembly and use of the process is inevitable to be polluted, even new oil, sometimes contain some unexpected pollutants, therefore, measures must be taken as soon as possible to filter out the pollutants, otherwise it is possible to malfunction after the equipment is put into operation, and early failures are often very serious. Some components such as pumps, valves, and motors can be fatally damaged.

The purpose of system cleaning is to eliminate or minimize the early failure of equipment. The goal of cleaning is to improve the cleanliness of the oil, so that the cleanliness of the system oil is kept within the pollution tolerance of the key Hydraulic Components in the system, in order to ensure the working reliability of the hydraulic system and the service life of the components.

1, the common cleaning method of hydraulic system

1.1 Solvent heating immersion

The cleaned parts are immersed in the cleaning tank with heating equipment (heating temperature is generally 35~ 85℃), and compressed air or steam is injected into the cleaning solution, so that the cleaning solution is in a dynamic state, impregnating time 0.5~2h, in order to improve the cleaning effect, the common additives shown in Table 1 can be added to the cleaning solution to improve the anti-rust decontamination and cleaning capacity.

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1.2 Spray Cleaning

Using pressure, force jet cleaning, suitable for large and medium-sized factory workshop continuous operation. Through the corrosion resistant pump, the prepared heated aqueous solution is sprayed with a pressure of 0.3MPa. Generally speaking, the cleaned parts go through the three continuous spraying process of pre-washing room, cleaning room and hot water cleaning room.

In addition, the air flow generated by compressed air can also be used to blow away the pollutants, of which the best effect is pulsating air flow.

1.3 Power scrubbing

Dirt can be removed with soft wool to maintain component accuracy and low roughness. For example, a mesh oil filter is always used with a hard wire brush, which sometimes damages the filter element or changes the filtration accuracy. Also such as high precision, low roughness of the hydraulic valve body, the use of abrasive ball nylon brush, brush grinding valve hole end, hole junction and sink groove. The brush head of the nylon needling brush is made of black nylon wire with a diameter of 0.3~0.6mm and green silicon carbide abrasive with a size of M20.

1.4 Ultrasonic Cleaning

The use of appropriate power of ultrasonic injection into the cleaning fluid, the formation of a point-like small cavity, when the cavity expanded to a certain extent, suddenly collapsed, the formation of a local vacuum, turnover fluid at a high speed to fill the vacuum, producing thousands of atmospheric pressure orders of magnitude of strong sound pressure and mechanical impact force (that is, cavitation), Remove contaminants from the surface of parts placed in the cleaning solution. This method has short cleaning time, good cleaning quality, and can also clean parts with complex shapes that cannot be cleaned manually. Compared with manual, the efficiency is increased by more than 10 times, and the cost is reduced. However, the porous material of the oil filter may affect the cleaning effect because of its effect of absorbing sound waves.

1.5 Heating volatilization method

Some dirt can be removed by heating it to volatilize, but this method cannot remove the remaining carbon, ash and solid attachments inside the hydraulic components.

1.6 Acid treatment

When this method is used, different pickling fluids are used for different metal materials. After the surface contaminants are removed, the surface is impregnated with a solution of CrO3, H2SO4 and H2O to produce a corrosion-resistant film.

2. Cleaning of hydraulic components

Hydraulic components are an important part of hydraulic system, and their cleanliness has a direct impact on the reliability of the system after assembly. Therefore, before assembling the hydraulic system, it is necessary to check whether the cleanliness of the components meets the requirements, and the cleanliness level of the ISO standard for typical hydraulic components is shown in Table 2.

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In the process of machining and manufacturing of mechanical parts, it will bring a variety of pollution impurities, therefore, purification measures must be taken before assembly to remove the residual pollutants in the processing. In the cleaning, according to the structure, size and the type, nature and cleanliness of the pollutants on the surface to be cleaned, the appropriate process method can be adopted for cleaning. The oxidized skin, sand, burr and rust on the workpiece can be removed by pressure jet or pickling process. If you want to clean the lubricating oil, stearic acid, paraffin, soil forest and mechanical impurities on the workpiece, you can use cleaning agent to clean. Metal cleaning agents can be used to remove rust and oxides, and to increase the anti-rust ability of the workpiece. There are many types of metal cleaning agents, which should be selected according to the dissolution ability of the surface attachment to be cleaned, whether the workpiece has an erosion effect and whether the action with pollutants produces harmful gases. In order to improve the decontamination effect of metal cleaning agent and enhance the anti-rust ability, appropriate washing aid additives can also be added. For burrs on the workpiece, vibration deburring machine, nylon deburring brush with abrasive can also be used to clean up. For parts with complex geometric shapes, ultrasonic cleaning can be used. After cleaning, a thorough inspection should be carried out to ensure that all dirt has been cleaned off during assembly.

When all parts are cleaned, put into a clean place that is closed and easy to clean and keep clean. The air in the site should be filtered, and the air pressure in the site should be higher than the external air pressure to prevent the intrusion of external air dust. If necessary, the parts can also be wrapped in polyethylene plastic for easy handling and short-term storage. The humidity in the site should be maintained at 35%~45%, and the temperature is generally 20% ° C to ensure that the parts do not rust.

Assembly should be carried out on a clean workbench, and the workers themselves should be kept clean. After assembly, it is also necessary to plug all the openings in the assembled hydraulic components and wrap them with polyethylene plastic for easy delivery. The hydraulic cylinder can be installed in a separate pre-cleaned tank system for cyclic shock cleaning with pre-cleaned oil. The amount of oil required is at least 5 times more than the capacity of the hydraulic cylinder, usually after 5 times of repeated washing, can be cleaned.

The oil tank should be cleaned manually with silk or vinyl sponge, and can not be scrubbed with cotton yarn or cotton cloth. The welding slag and iron filings in the dead Angle of the Fuel Tank can be glued with mastic or flour. In addition, grain blowing, vacuum vacuuming and steam cleaning are also available. After the cleaning is completed, it is pickled to completely remove the surface oxide, and then treated with anti-rust agent on the inner surface of the tank. Pickling can be done by soaking in the tank and washing.

3. Cleaning of hydraulic system in assembly

(1) Select cleaning oil

When the system pipeline and fuel tank are clean, the cleaning oil with the same viscosity as the working oil can be selected; If the system is not clean, you can choose a slightly lower viscosity cleaning oil. The cleaning oil should be compatible with the working medium of the system and the material of all seals. The amount of cleaning oil is usually 60% to 70% of the standard oil amount of the tank, and the tank should be cleaned before the injection of cleaning oil.

(2) Heat cleaning oil

Hot oil can make the attachment in the system easy to free off, generally need to be heated to 50~60℃, the cleaning pressure is 0.1~0.2MPa, the cleaning oil flow should be as large as possible, in order to facilitate the removal of dirt.

(3) Install the oil filter

In the cleaning circuit, the crude oil filter of 50~100 m is installed at the oil inlet, and the fine oil filter of 10~50m is installed at the oil return port. Coarse filter at the beginning, when rinsed for a period of time, gradually use a fine mesh filter for fractional filtration. At the beginning, disassemble the oil filter every half an hour to clean it, and then gradually change to a fine-mesh oil filter and extend the cleaning interval according to the situation. The cleaning time of the general vehicle hydraulic system is 8h.

(4) Intermittent operation of hydraulic pump

In order to make the cleaning effect good, the hydraulic pump should be turned around and stopped. During the cleaning process, the wooden hammer is used to gently tap the tubing several times to promote the dirt to fall off as soon as possible, and the bending and welding parts of the pipeline should be hammered more, but not too hard to prevent damage to the tubing, and the hammering time accounts for about 15% of the cleaning time.

(5) Ensure that the cleaning fluid flow is turbulent

In order to effectively clean, the flow of the cleaning fluid must become turbulent, that is, to ensure that the Reynolds number is above 4000 to ensure the cleaning effect is good; Otherwise, the cleaning solution should increase the flow rate, increase the temperature, and reduce the viscosity. Small flow at room temperature cleaning, the general effect is poor.

(6) Drain clean oil

At the end of cleaning, the cleaning oil should be removed, including the pump, valve, pipeline and oil cooler memory oil, you can loosen the pipeline after discharging oil and purge with compressed air, or add the working oil to take away the cleaning oil.

(7) Add hydraulic oil

When the cleaning oil is drained, the hydraulic oil should be added as soon as possible and a short time test run to prevent corrosion of the pipeline.

4, cleaning precautions

(1) In the general hydraulic system cleaning, the use of working hydraulic oil or test oil, can not use kerosene, gasoline, alcohol, vapor or other liquids, to prevent the corrosion of hydraulic components, pipelines, fuel tanks and seals.

(2) In the cleaning process, the operation of the hydraulic pump and the heating of the cleaning medium are carried out simultaneously. When the temperature of the cleaning oil is 50~80 ° C, the rubber slag in the system is easy to remove.

(3) In the cleaning process, the non-metallic hammer can be used to knock the tubing, which can be continuously knocked or not continuously knocked to facilitate the removal of attachments in the pipeline.

(4) The intermittent operation of the hydraulic pump is conducive to improving the cleaning effect, and the intermittent time is generally 10 to 30 minutes.

(5) On the circuit of cleaning the oil circuit, a filter or filter screen should be installed. At the beginning of cleaning, due to more impurities, 80 mesh filter can be used, and more than 150 mesh filter can be used in the later period of cleaning.

(6) The cleaning time is generally 48~60h, depending on the complexity of the system, filtration accuracy requirements and pollution degree and other factors.

(7) In order to prevent rust caused by external moisture, at the end of cleaning, the hydraulic pump should continue to operate until the temperature returns to normal.

(8) After cleaning, the cleaning oil in the loop should be removed.

Hydraulic system cleaning is absolutely necessary for the hydraulic system in assembly or newly put into use, and any chance to give up cleaning will bring fatal damage to the equipment. After strict cleaning, it can reduce and avoid the failure in system debugging and early operation, shorten the debugging cycle of the system and reduce unnecessary losses. However, the pollution control of the system is an ongoing process, which cannot be once and for all. During the operation of the system, the oil status should be regularly detected, and the pollutants should be controlled to ensure that they are within the cleanliness allowed by the system.