With the development and innovation of industrial technology, the application of electromechanical and hydraulic integration technology in modern construction machinery has been widely developed. The performance of hydraulic system is directly affected, which directly affects the performance of construction machinery. In hydraulic systems, hydraulic fluid is the working medium that transmits power and signals, while also providing cooling, lubrication and rust protection. When the hydraulic oil is seriously polluted, the wear of the hydraulic components will increase and the malfunction will occur, which will deteriorate the working performance of the hydraulic system. According to statistics, more than 70% of hydraulic system failures are caused by oil pollution, and more than 75% of them are solid particles.

1. Causes and hazards of hydraulic oil pollution

1.1 hydraulic oil oxidative deterioration

When the construction machinery is working, the hydraulic system generates a large amount of heat due to various pressure losses, so that the temperature of the system hydraulic oil rises. When the system temperature is too high, the hydraulic oil is easily oxidized, and an organic acid is formed after oxidation, and the organic acid will corrode the metal components. A gel-like precipitate that is insoluble in oil is formed, so that the viscosity of the hydraulic oil is increased, and the abrasion resistance is deteriorated.

1.2 Hydraulic oil mixed with moisture and air

The new hydraulic oil has water absorption and contains a trace amount of water; when the hydraulic system stops working, the system temperature decreases, and the moisture in the air condenses into water molecules mixed into the oil. When the hydraulic oil is mixed with water, the viscosity of the hydraulic oil is lowered, and the hydraulic oil is oxidized and deteriorated, and water bubbles are formed, so that the lubricating performance of the hydraulic oil is deteriorated and cavitation is generated.

Hydraulic oil dissolves some of the air and sometimes sucks in air bubbles. Air mixed into the hydraulic oil can accelerate the oxidation and deterioration of the hydraulic oil, and also cause noise, cavitation, vibration and the like.

1.3 Hydraulic oil mixed with particulate dirt

Hydraulic systems and components are mixed into the system during processing, assembly, storage and transportation; insoluble materials are formed after leaking or leaking during use; wear debris generated after wear of metal parts in use; mixing of dust in the air, etc. Forming particulate contaminants in the hydraulic fluid. The hydraulic oil is mixed with particulate dirt, which easily forms abrasive wear, reduces the lubricating performance of the hydraulic oil, and cools the performance. There are several reasons for solid particle contamination:

(1) The original residual impurities of the hydraulic system itself, such as those produced during the manufacturing process, have not been completely removed;

(2) The new oil contains impurities because the oil pipe through which the oil flows and the oil drum in which the oil is stored contain impurities;

(3) The open air working environment in the field is harsh, and various flying material particles are immersed in the hydraulic system;

(4) Intrusion of pollutants during the process of disassembling components and pipelines during maintenance of the hydraulic system, or the use of unclean filter containers to bring in pollutants when refueling or changing oil;

(5) Contamination from mechanical friction, deformation and chemical reactions.

2. Control of hydraulic oil pollution

In order to ensure the working performance of the construction machinery, it is necessary to ensure the normal and reliable operation of the hydraulic system. To ensure the normal and reliable operation of the hydraulic system, the hydraulic oil pollution must be controlled.

2.1 Control the working temperature of hydraulic oil

Excessive operating temperature of the hydraulic oil is detrimental to the working components of the hydraulic system, and at the same time accelerates the oxidation of the hydraulic oil. Generally, the working temperature of the mechanical hydraulic system is preferably controlled below 65 °C, and the working temperature of the hydraulic system of the construction machinery is controlled below 80 °C. The working temperature of the control hydraulic oil is mainly the control of the performance of the cooler of the hydraulic system, the reasonable control of the hydraulic oil quantity of the whole hydraulic system, the control of the load and the speed of the hydraulic system components.

2.2 Components and systems are cleaned during processing and assembly

In the processing and manufacturing of components, each process must clean and remove the residual pollutants in the process; the components must be cleaned before assembly, and must be strictly cleaned and inspected after assembly; the fuel tank and pipeline are removed from burrs, welding slag, etc. After the contaminants, pickling is required to remove the surface oxides; the initial installed hydraulic system is cycled, and samples are periodically sampled and analyzed, and the system is cleaned until the system is cleaned.

2.3 Preventing the incorporation of pollutants into the hydraulic system

The fuel tank should be properly sealed and equipped with high-efficiency air filter to prevent the entry of dust and moisture; the injection of new oil must be effectively filtered, and the oil return of the system should be effectively filtered; the joints of the pipe joints are tightly sealed. To prevent dust, moisture and air from entering the hydraulic system; moving parts (such as the piston rod end of the hydraulic cylinder) must be equipped with a dust seal.

2.4 Filtration and purification of hydraulic oil

The hydraulic oil filter (oil filter) is an important component in the hydraulic system to control oil pollution. The application of the oil filter must ensure that the filtration accuracy meets the requirements of the system, and the pressure loss caused by the fluid resistance should be as small as possible. Have sufficient grease capacity; check and purify the oil filter at regular intervals. The pollution degree of the hydraulic system oil increases with the increase of the external pollution particle intrusion rate and the number of various wear particles in the system, and decreases with the increase of the filtration ratio. Therefore, the reasonable selection of the filtration ratio can effectively reduce the system. Pollution degree. Solid particles are the main source of pollution in engineering machinery hydraulic systems. The reasonable selection of the filter ratio of the oil filter is the main measure to control system pollution.

2.5 Regular inspection and replacement of hydraulic oil

During the use of hydraulic oil, the intrusion of pollutants will adversely affect the hydraulic system. To effectively control the hydraulic oil pollution, the seals and joints must be inspected regularly to carry out the hydraulic oil of the hydraulic system. Check the analysis and replace the hydraulic oil regularly. When replacing the hydraulic oil, the old hydraulic oil must be drained. The entire hydraulic system must be cleaned before the new hydraulic oil is injected.

2.6 Online monitoring technology using hydraulic oil pollution degree

On-line monitoring of hydraulic oil pollution degree on construction machinery can monitor the quality of hydraulic oil during use at any time, and can display the pollution level and corresponding reason through the display in time and accurately, even if the staff does not observe the display of the display. When the pollution degree reaches the corresponding level, the alarm device will also perform a grading alarm to ensure the performance and quality of the hydraulic oil in the use of the construction machinery.

3. Verification conclusion

The main measure to control the pollution of the hydraulic system of engineering machinery is to rationally select the filtration ratio of the oil filter, and to control the pollution source. Through scientific control and timely replacement and modification, the hydraulic system of the engineering machinery can work normally, and the life and use value of the machine are improved.