Hydraulic drive of injection molding machine uses hydraulic oil as working medium, uses pressure energy of hydraulic oil in sealed working volume to transmit energy or power or signals. Quality of hydraulic oil and seals directly affects stable operation of hydraulic system and indirectly affects product quality. To prevent and reduce failure of hydraulic system, reduce wear and extend life, we should strictly use and maintain hydraulic oil.

 

Generally speaking, 70% of failures of hydraulic devices are caused by incorrect or improper use and maintenance of hydraulic oil. Maintaining good maintenance habits and preventive maintenance are the most effective ways to reduce and prevent hydraulic failure of machine. Therefore, meticulous maintenance of hydraulic oil and hydraulic system is very important. Therefore, it is necessary to introduce characteristics of hydraulic oil.
The most important properties of hydraulic oil are viscosity and cleanliness, as well as good anti-oxidation, anti-wear, anti-foam, anti-rust properties and good lubrication properties.
Viscosity of hydraulic oil is expressed as average value of kinematic viscosity at a temperature of 40℃. Our commonly used No. 46 anti-wear hydraulic oil (46csT/40℃) means that average kinematic viscosity of this hydraulic oil at a temperature of 40℃ is 46m2/S.
Relationship between viscosity of hydraulic oil and pressure, temperature is as follows: temperature increases, viscosity decreases; pressure increases, viscosity increases.
Periodic testing of hydraulic oil performance. If oil is contaminated or deteriorated, life of injection molding machine will be shortened and failures may occur. Therefore, it is necessary to regularly test oil to detect changes in oil performance. Based on this, decide whether to change oil. (It is best to use a professional laboratory to detect data value if possible.) We can use a simple visual method to understand oil condition:
Appearance test. Put new oil sample and old oil sample in use into their respective test tubes, compare their color, clarity, existing floats and water precipitation at the bottom of test tube.
Drop test. Drop old oil on filter paper (suck dry sheet) and wait for 1 hour to observe. If oil is dirty or significantly deteriorated, contaminants will be easily observed.
Rub your fingers. Dip old oil in use on your fingers and rub it. If viscosity decreases and deteriorates, hand feels very rough and does not feel thick. Oil droplets fall from fingers very smoothly, and there is no phenomenon of thick rebound.
Hydraulic maintenance starts from following aspects:

In principle, hydraulic oil should be changed every 5000 machine operating hours or at most one year. No matter how good hydraulic oil is, after being used for a certain period of time, metal and rubber particles of worn pump and other moving parts will enter oil, which will cause generation of sludge and dirt. In normal maintenance, there will be some contaminants stained on parts and carried into hydraulic oil.
Even if hydraulic oil is used correctly, it is generally considered that its working life is 1 year, up to 2-3 years. Once it deteriorates, do not hesitate to change to new oil. Good oil quality is cornerstone of maintaining stability of hydraulic system.

 

A special oil filter truck is used to fill hydraulic oil instead of a pumping unit modified from a water pump. Author has seen many simple pumping trucks modified with water pumps. It is used for pumping waste water and waste oil, and it is also used for adding new oil.
Because pump that has pumped waste water and oil has no filter screen, the dirtiest impurities are lurking in pump and pipeline, mixed with new oil and added to tank. Author has used boxes to observe on many occasions that new oil that has just been pumped contains a lot of contaminants. These pollutants will only add to pollution of refueling, damage oil pumps and valves.
Precision of filter screen of professional oil filter car is usually 125um (micron), and there are generally two filters, double protection filter, and protect cleanliness of oil.
Author once saw a 10-year-old Haitian machine in a company, and oil pump burned to death. When author was pumping old oil, I found that old oil about 20 cm deep at the bottom was all dark yellow cotton wool, there was a layer of sludge and metal powder at the bottom of oil tank. I also understand why pump is broken and there are many injection molding wastes.

Hydraulic maintenance is not as simple as pumping old oil, adding new oil, or just adding some new oil. If such superficial maintenance (lazy) does not need to be paid by a maintenance technician, a general worker can do it part-time. Not only is oil changed, but it is also important to clean hydraulic equipment.
After draining old oil, do not use a rag to wipe oil tank to prevent end of thread from blocking filter. Use of professional cleaning agents is expensive and has residues. An experience taught by a twenty-year-old mechanic repairer: You can use ordinary flour, add an appropriate amount of water to knead a dry dough, divide it into several pieces, remove oil, impurities, and metal powder in oil tank. It is clean and economical, there is no residue.
Use kerosene and copper brushes to clean magnetic frame and filter in fuel tank, use an air gun to clean and blow dry.

Air filter outside fuel tank makes air in and out of fuel tank easy to enter and exit according to change of oil level in fuel tank. Every time oil is changed for maintenance, air filter should be taken out, cleaned with kerosene, and dried with an air gun. Failure to clean may cause stolen goods to enter fuel tank and affect oil quality.

To clean scale inside and outside of cooler tube, use a weak hydrochloric acid solution, rinse with water, and blow dry with an air gun.
Use a copper brush to clean dirt on barrier.

First use a waste cloth and air gun to clean dirt outside valve. Unplug plug and disassemble oil valve. Use a kerosene brush to clean valve core, sludge and debris on valve body, and blow dry with an air gun. Note that spool should not be installed in reverse, and O-ring should not be missed.

Disassemble clamping mold, thimble, seat table, rubber injection cylinder, clean cylinder body and piston with kerosene, replace worn and damaged oil seals, dust seals, and 0-rings. Reason for dismantling oil cylinder, checking oil seal and replacing it. Reasons are as follows:
First, stability of injection pressure is a major factor in determining quality of finished product. Every 20,000 machine working hours or at most 5 years, sealing ring and wear ring should be replaced. Although oil seal that has been used for 5 years is not badly damaged, it must be replaced. It cannot be repaired until oil leaks and carbonization pressure relief has completely stopped.
Second is to check whether piston rod is loose.
Third is that cleaning and sanitation of equipment parts is also a maintenance method.