Quality of hydraulic system of injection molding machine not only depends on rationality of system design and performance of system components, but also because of pollution protection and treatment of system. Pollution of system directly affects reliability of hydraulic system of injection molding machine and service life of components.
According to statistics, about 70% of hydraulic system failures of injection molding machines at home and abroad are caused by pollution. Main hazards of oil pollution to system are as follows:

 

Various pollutants in oil cause various forms of wear of components, and solid particles enter gap of moving pair, causing cutting wear or fatigue wear on the surface of parts. Erosive wear is caused by impact of solid particles in high-velocity liquid flow on the surface of element. Water in oil and products of oxidative deterioration of oil have a corrosive effect on components. In addition, air in oil in system causes cavitation, causing erosion and damage to component surfaces.

Solid particles block clearance and orifice of hydraulic valve, causing valve core to be blocked and jammed, affecting working performance and even causing serious accidents.

Water and air in oil are main conditions for oxidation of oil with their thermal energy, and metal particles in oil play an important catalytic role in oxidation of oil. In addition, water and suspended bubbles in oil significantly reduce motion pair. Strength of oil film between them reduces lubricating performance.

Pollutants are substances in oil of hydraulic system of injection molding machine that are harmful to system. They exist in different forms in oil. According to their physical forms, they can be divided into: solid pollutants, liquid pollutants, and gaseous pollutants.
Solid pollutants can be divided into hard pollutants, including: diamond, cutting, silica sand, dust, wear metals and metal oxides; soft pollutants are: additives, water agglomerates, oil decomposition products and polymers, cotton silk and fibers brought in during maintenance.
Liquid pollutants are usually grooving oil, water, paint, chlorine and its halides that do not meet system requirements. Usually, it is difficult for us to remove them. Therefore, when selecting hydraulic oil, we should choose hydraulic oil that meets system standards to avoid some unnecessary failure.
Gaseous pollutants are mainly air mixed into system.
These particles are often so small that they cannot settle down and become suspended in oil, and are eventually squeezed into various valve gaps. For a reliable injection molding machine hydraulic system, these clearances are extremely important to achieve limited control, importance and accuracy.

Sources of pollutants in system oil mainly include following aspects:
1. Externally invaded pollutants: Externally invaded pollutants are mainly grit or dust in atmosphere, usually through air hole of fuel tank, sealing shaft of oil cylinder, shaft of pump and motor. Mainly due to use of environment.
2. Internal pollutants: pollutants remaining in components during processing, assembly, debugging, packaging, storage, transportation and installation. Of course, these processes are unavoidable, but they can be minimized. Some special components need to be assembled and debugged in a clean room or clean bench environment.
3. Pollutants generated by hydraulic system of injection molding machine: particles generated by wear of components during operation of system, sand particles falling off from castings, metal particles falling off from pumps, valves and joints, particles and gelatinous particles produced by oxidation and decomposition of rust and exfoliation in pipeline with its oil, more serious is large amount of impurities that system pipeline has not been flushed before it is officially put into operation.

A system is generally flushed before it is officially put into operation. Purpose of flushing is to remove contaminants, metal chips, fibrous compounds, iron cores, etc. remaining in system. During the first two hours of work, even if system is not completely damaged, it will cause a series of failures. Therefore, following steps should be followed to clean oil circuit of system:
Clean tank with an easy-drying cleaning solvent, then use filtered air to remove solvent residue.
Clean all pipes of system, in some cases, it is necessary to immerse pipes and joints.
Install an oil filter in pipeline to protect oil supply line and pressure line of valve.
Install a flush plate on collector to replace precision valves, such as electro-hydraulic servo valves.
Check that all piping is properly sized and connected correctly.
If an electro-hydraulic servo valve is used in system, servo valve must be flushed so that oil can flow from oil supply line to collector and return directly to oil tank, so that oil can be circulated repeatedly to flush system and let oil filter out solid particles. During flushing process, check oil filter every 1-2 hours to prevent oil filter from being blocked by pollutants. Do not open bypass at this time. If oil filter starts to be blocked, change oil filter immediately.
Cycle of flushing is determined by structure of system and degree of contamination of system. If sample of filter medium has no or little foreign contamination, install a new oil filter, remove flushing plate, and install valve to work!
Planned maintenance: Establish a regular maintenance system for system. Recommendations for a better maintenance system for hydraulic system of injection molding machine are as follows:
Check and replace oil filter every 500 hours or every three months.
Regularly flush inlet oil filter of oil pump.
Check hydraulic oil for acidification or other contaminants. Smell of hydraulic oil can roughly identify whether it has deteriorated.
Repair leaks in system.
Make sure that no foreign particles enter tank from breather cap of tank, plug seat of oil filter, gasket of return line, and other openings in tank.