Quality of hydraulic system of injection molding machine not only depends on rationality of system design and performance of system components, but also due to pollution prevention and treatment of system, pollution of system directly affects reliability of hydraulic system of injection molding machine and use of components life.

 

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, solid particles enter gap of moving pair, causing cutting or fatigue wear on the surface of part. Impact of solid particles in high-speed liquid flow on the surface of component causes erosion and wear.
Water in oil, oxidation and deterioration products of oil have a corrosive effect on components. In addition, air in oil of system causes cavitation, which leads to erosion and damage to surface of components.

Solid particles block gaps and orifices of hydraulic valve, causing blockage and clamping of valve core, affecting working performance, and even causing serious accidents.

Water and air in oil are main conditions for oil oxidation due to their thermal energy. Metal particles in oil play an important role in oxidation of oil. In addition, water and suspended bubbles in oil significantly reduce strength of oil film between movement pairs and reduce lubrication performance.

Pollutants are substances that are harmful to system in oil of injection molding machine hydraulic 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 include: additives, water condensate, oil decomposition products and polymers, cotton threads and fibers brought in during maintenance.
Liquid contaminants are usually grooving oil, water, paint, chlorine and its halides that do not meet system requirements, which are usually difficult to remove. Therefore, when selecting hydraulic oil, choose hydraulic oil that meets system standards to avoid unnecessary failure.
Gaseous pollutants are mainly air mixed into system:
These particles are often so small that they cannot settle down and are suspended in the oil, are finally squeezed into gaps of various valves. For a reliable injection molding machine hydraulic system, these gaps are extremely important to achieve limited control, importance and accuracy.

Main sources of pollutants in system oil are as follows:
1. Externally invading pollutants: Externally invading pollutants are mainly sand or dust in atmosphere, usually invading system through air holes of fuel tank, sealing shaft of oil cylinder, shaft of pump and motor. Mainly impact of use environment.
2. Internal contaminants: contaminants remaining in components during processing, assembly, commissioning, packaging, storage, transportation and installation. Of course, these processes cannot be avoided, but they can be minimized. Some special components need to be carried out in a clean room or clean bench environment during assembly and debugging.
3. Pollutants generated by hydraulic system of injection molding machine: particles produced by wear of components during operation of system, sand particles falling off from castings, metal particles falling off from pumps, valves and joints, corrosion and spalling in pipeline. Particles and jelly produced by oxidation, decomposition of oil are more serious because system pipeline has not been flushed before formal operation.

A system is generally flushed before it is officially put into use. Purpose of flushing is to remove contaminants, metal shavings, fiber compounds, iron cores remaining in system. In the first two hours of work, even if system is not completely damaged, it will cause a series of failures.
Therefore, system oil circuit should be cleaned according to following steps:
Clean fuel tank with an easy-to-dry cleaning solvent, and then use filtered air to remove solvent residues.
Clean all pipes of system. In some cases, it is necessary to immerse pipes and joints.
Install oil filter in pipeline to protect oil supply pipeline and pressure pipeline of valve.
Install a flushing plate on collector to replace precision valves, such as electro-hydraulic servo valves.
Check whether all pipes are of proper size and connected correctly.
If an electro-hydraulic servo valve is used in system, flushing plate of servo valve should enable oil to flow from oil supply line to collector and return directly to oil tank, so that oil can 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. Do not open bypass at this time. If oil filter starts to be blocked, immediately change oil filter.
Cycle of flushing is determined by structure of system and degree of system pollution. If sample of filter medium has no or few foreign pollutants, install a new oil filter, remove flushing plate, and install valve to work!
Planned maintenance, establish a regular maintenance system, recommend a better maintenance system for hydraulic system of injection molding machine as follows:
Oil filter should be inspected and replaced at most 500 hours or three months.
Flush imported oil filter of oil pump regularly.
Check whether hydraulic oil is contaminated by acidification or other contaminants. Smell of hydraulic oil can roughly identify whether it has deteriorated.
Repair leak in system.
Make sure that no foreign particles enter fuel tank from vent cap of fuel tank, plug seat of oil filter, sealing gasket of oil return line and other openings of fuel tank.