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Fine maintenance of hydraulic system of injection molding machine


The hydraulic transmission of injection molding machine takes hydraulic oil as the working medium and uses the pressure energy of hydraulic oil in the sealed working volume to transmit energy or power or signal. The quality of hydraulic oil and seals directly affects the stable work of hydraulic system and indirectly affects the product quality. To prevent and reduce the faults of the hydraulic system, reduce wear and prolong service life, we should strictly use and maintain the hydraulic oil.

Generally speaking, 70% of the faults of hydraulic devices are caused by incorrect or improper use and maintenance of hydraulic oil. Maintaining good maintenance habits and preventive maintenance is the most effective way to reduce and prevent hydraulic failure of the machine. Therefore, the fine maintenance of hydraulic oil and hydraulic system is very important. Therefore, it is necessary to introduce the characteristic requirements of hydraulic oil.

The most important properties of hydraulic fluids are viscosity and cleanliness, good oxidation resistance, abrasion resistance, anti foam, rust resistance and good lubricity.

The viscosity of hydraulic oil is expressed by the average value of kinematic viscosity when the temperature is 40 ℃. The commonly used 46 anti-wear hydraulic oil (46cst / 40 ℃) means that the average kinematic viscosity of this hydraulic oil at 40 ℃ is 46m2 / s.

The relationship between hydraulic oil viscosity and pressure and temperature is as follows: when the temperature increases, the viscosity decreases; When the pressure increases, the viscosity increases.

Periodic test of hydraulic oil performance. If the oil is contaminated or deteriorated, the life of the injection molding machine will shrink and failure may occur. Therefore, it is necessary to test the oil regularly to detect the change of oil performance. Based on this, decide whether to change the oil. (it is best to use a professional laboratory to detect the data value if possible) we can use a simple visual method to understand the oil condition:

Appearance test. Put the new oil sample and the old oil sample in use into their respective test tubes, and compare their color, clarity, existing floating objects and water precipitation at the bottom of the test tubes.

Drop test. Drop the old oil on the filter paper (suction sheet) and observe it after 1h. If the oil is dirty or significantly deteriorated, contaminants will be easily observed.

Finger rubbing. Rub the used oil on your fingers. If the viscosity decreases and deteriorates, the feel is very rough and does not feel thick. The oil drops fall smoothly from the fingers without thickening and rebound.

Hydraulic maintenance starts from the following aspects:

1) Replace the old hydraulic oil.

In principle, change the hydraulic oil every 5000 machine operation hours or at most one year. No matter how good the hydraulic oil is, after being used for a certain period of time, the metal and rubber particles of worn pumps and other moving parts will enter the oil, which will cause the generation of oil sludge and dirt. During normal maintenance, pollutants will be stained on the parts and brought into the hydraulic oil.

Even if the hydraulic oil is used correctly, it is generally considered that its service life is 1 year, up to 2-3 years. Once deteriorated, do not hesitate to change the oil. Good oil quality is the cornerstone of maintaining the stability of the oil pressure system.

A special oil filter truck is used to fill hydraulic oil instead of a pumping unit modified by a pumping pump. The author has seen many simple oil pumping vehicles refitted with water pumps. It is used to pump waste water and waste oil, and it is also used to add new oil.

Because there is no filter screen for the water pump that has pumped waste water and oil, the dirtiest impurities are hidden in the water pump and pipeline, and mixed with new oil and added to the oil tank. The author has repeatedly used boxes to observe that the new oil that has just been pumped contains a large amount of pollutants. These pollutants will only pollute the refilled oil and damage the oil pump and valve.

The precision of the filter screen of professional oil filter truck is usually 125um (micron). Generally, there are two filter screens to protect the cleanliness of oil products.

The author once saw Haitian engine with 10 years of service in a company, and the oil pump burned to death. When pumping old oil, the author found that the old oil about 20 cm deep at the bottom was dark yellow cotton wadding, and there was a layer of oil sludge and metal powder at the bottom of the oil tank. I also understand why the pump is broken and there are many injection molding wastes.

2) Clean the inside and surrounding of the oil tank

Hydraulic maintenance is not as simple as pumping old oil and adding new oil, or just adding some new oil. If such a superficial maintenance (laziness) does not need to be paid by a repairman, a part-time general worker can be competent. Not only replace the oil, but also clean the hydraulic equipment.

After the old oil is pumped clean, do not wipe the oil tank with rags to prevent the thread from blocking the filter screen. The use of professional cleaning agents is expensive and residual. An experience taught by a 20-year-old Mechanic: you can use ordinary flour and add an appropriate amount of water to knead it into dry dough, divide it into several, and remove oil, impurities and metal powder in the oil tank. It is clean and economical, and there is no residue.

Clean the magnetic frame and filter screen in the oil tank with kerosene and copper brush, clean with air gun and blow dry.

3) Clean the air filter

The air filter outside the oil tank makes it easy for the air in and out of the oil tank according to the change of the oil level in the oil tank. During each oil change and maintenance, take out the air filter, clean it with kerosene and dry it with an air gun. If not cleaned, it may cause stolen goods to enter the oil tank and affect the oil quality.

4) Clean the inner and outer walls of the oil-water cooler

The scale inside and outside the cooler pipe can be cleaned with weak hydrochloric acid solution, washed with water and dried with air gun.

Clean the dirt on the barrier plate with a copper brush.

5) Cleaning oil valve

First clean the dirt outside the valve with waste cloth and air gun. Unplug the plug and disassemble the oil valve. Clean the oil sludge and sundries on the valve core and valve body with kerosene brush and dry them with air gun. Note that the valve core shall not be installed reversely and the O-ring shall not be omitted.

6) Clean the oil cylinder

Remove the unlocking die, thimble, seat and glue injection cylinder, clean the cylinder block and piston with kerosene, and replace the worn and damaged oil seal, dust seal and 0-ring. Remove the oil cylinder, check the oil seal and replace it. The reasons are as follows:

First, the stability of injection pressure is a major factor determining the quality of finished products. Replace the sealing ring and wear ring every 20000 machine working hours or up to 5 years. Although the oil seal that has been used for 5 years is not greatly damaged, it must also be replaced. It can't be repaired until the oil leakage and carbonization pressure relief strike.

Second, check whether the piston rod is loose.

Third, cleaning and sanitation of equipment components is also a maintenance method.

7) Replace the bypass filter element.

8) Check whether the oil pipe joints are loose and replace the aging and leaking oil pipe.

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