Quality of hydraulic system of injection molding machine depends not only on rationality of system design and performance of system components, but also on 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.
Harm of oil pollution to system is mainly as follows:

 

Various contaminants in oil cause various forms of wear of components, and solid particles enter gap between moving pairs, causing cutting wear or fatigue wear on the surface of parts. Impact of solid particles in high-speed liquid flow on the surface of components causes erosion and wear.    Water in oil and products of oil oxidation and deterioration corrode components. In addition, air in oil of system causes cavitation, resulting in erosion and damage to surface of component.

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

Water and air in oil are main conditions for oil oxidation 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 strength of oil film between moving pairs, which reduces lubrication 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 and can be divided into solid contaminants, liquid contaminants, and gaseous contaminants according to their physical form.
Solid pollutants can be divided into hard pollutants, including: diamonds, cuttings, silica sand, dust, wear metals and metal oxides; soft pollutants include: additives, water condensates, oil decomposition products and polymers, and cotton and fibers brought in during maintenance.
Liquid pollutants are usually grooving oil, water, paint, chlorine and its halides that do not meet system requirements. It is usually difficult for us to remove them. Therefore, when choosing hydraulic oil, we should choose hydraulic oil that meets system standards to avoid some unnecessary failures.
Gaseous pollutants are mainly air mixed in system.
These particles are often so small that they cannot settle down and are suspended in oil. Finally, they are squeezed into gaps of various valves. For a reliable injection molding machine hydraulic system, these gaps are extremely important for achieving limited control, importance and accuracy.

Sources of pollutants in system oil are mainly following aspects:
1) External intrusion pollutants: External intrusion pollutants are mainly sand or dust in atmosphere, which usually invade system through oil tank pores, cylinder seal shaft, pump and motor shaft. It is mainly affected by use environment.
2) Internal pollutants: pollutants left 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 castings, metal particles falling off pumps, valves and joints, particles and colloids generated by oxidation and decomposition of rust and peeling in pipeline and its oil. What is more serious is that system pipeline has a large amount of impurities that have not been flushed before it is officially put into operation.

A system generally needs to be flushed before it is officially put into operation. Purpose of flushing is to remove pollutants, metal chips, fiber compounds, iron cores, etc. remaining in system. In the first two hours of work, even if system is not completely damaged, it will cause a series of faults. Therefore, system oil circuit should be cleaned according to following steps:

 

1) Clean oil tank with an easy-to-dry cleaning solvent, then use filtered air to remove solvent residues.
2) Clean all pipelines in system. In some cases, pipelines and joints need to be soaked.
3) Install an oil filter in pipeline to protect oil supply pipeline and pressure pipeline of valve.
4) Install a flushing plate on collector to replace precision valve, such as electro-hydraulic servo valve.
5) Check whether all pipelines are of appropriate size and connected correctly.
If electro-hydraulic servo valve is used in system, I might as well say a few more words. Flushing plate of servo valve must allow oil to flow from oil supply pipeline to collector and return directly to oil tank. This allows oil to circulate repeatedly to flush system and allow oil filter to filter out solid particles. During flushing process, check oil filter every 1 to 2 hours to prevent oil filter from being blocked by contaminants. At this time, do not open bypass. If oil filter is found to be blocked, change oil filter immediately.
Flushing cycle is determined by structure of system and degree of system contamination. If sample of filter medium has no or very little foreign contaminants, install a new oil filter, remove flushing plate, and install valve to work!
Planned maintenance: Establish a regular maintenance system. Following are recommended maintenance systems for hydraulic system of injection molding machine:
1) Check and replace oil filter at most every 500 hours or three months.
2) Flush inlet oil filter of oil pump regularly.
3) Check whether hydraulic oil is acidified or contaminated by other pollutants. Smell of hydraulic oil can roughly identify whether it has deteriorated.
4) Repair leaks in system.
5) Ensure that no foreign particles enter oil tank from vent cap of oil tank, plug seat of oil filter, sealing gasket of oil return line, and other openings of oil tank.