Causes of contamination and maintenance recommendations for hydraulic systems of injection molding machines

The good or bad of the hydraulic system of injection molding machine depends not only on the rationality of the system design and the performance of the system components but also on the pollution protection and treatment of the system, which directly affects the reliability of the hydraulic system of injection molding machine and the service life of the components.

According to statistics, about 70% of the hydraulic system failures of injection molding machines at home and abroad are caused by pollution. The main hazards of fluid contamination on the system are as follows.

1. Contamination of components wear

Various pollutants in the fluid cause various forms of component wear, solid particles into the gap of the moving parts, the surface of the parts produce cutting wear or fatigue wear. Solid particles in the high-speed fluid flow cause erosion and wear on the surface of the components by impact.

The water in the fluid and the products of fluid oxidation and degradation produce corrosive effects on the components. In addition, the air in the system fluid causes cavitation, which leads to surface spalling and destruction of components.

2. Component blockage and jamming failure

Solid particles clog the gap and orifice of the hydraulic valve, causing spool blockage and jamming, affecting the performance of the work, and even leading to serious accidents.

3. Accelerated deterioration of fluid performance

Water and air in the fluid with its thermal energy is the main condition of fluid oxidation, and metal particles in the fluid play an important catalytic role in the oxidation of the fluid, in addition, the water and suspended air bubbles in the fluid significantly reduce the strength of the oil film between the moving parts, so that the lubrication performance is reduced.

 

Types of contaminants

Contaminants are substances in the hydraulic fluid of injection molding machines that are harmful to the system, which exists in different forms in the fluid and can be divided into solid contaminants, liquid contaminants, and gaseous contaminants according to their physical forms.

Solid contaminants can be divided into hard contaminants, including diamond, cutting, silica sand, dust, wear metals, and metal oxides; soft contaminants include additives, water condensate, oil decomposition and polymers and cotton filaments and fibers brought in during maintenance.

Liquid contaminants are usually grooving fluid, water, paint and chlorine and its halides that do not meet the requirements of the system, which are usually difficult for us to remove, so we should choose hydraulic fluid that meets the standards of the system when choosing hydraulic fluid to avoid some unnecessary failures.

Gaseous contaminants are mainly air mixed into the system.

These particles are often so fine that they cannot settle and are suspended in the fluid and eventually squeezed into the gaps of various valves, which are extremely important for a reliable injection molding machine hydraulic system to achieve limited control, importance and accuracy.
 

Sources of contaminants

The sources of contaminants in the system fluid are mainly through the following channels.

1. external intrusion of contaminants: the external intrusion of contaminants is mainly atmospheric gravel or dust, usually through the tank air holes, cylinder sealing shaft, pumps and motors and another shaft into the system. Mainly the influence of the use environment.

2. internal pollutants: components in processing, assembly, commissioning, packaging, storage, transportation and installation of residual pollutants, of course, these processes can not be avoided, but can be reduced to a minimum, some special components in the assembly and commissioning need to be carried out in a cleanroom or clean table environment.

3. injection molding machine hydraulic system pollutants: the system in the process of operation due to component wear and tear particles, castings off the sand, pumps, valves and fittings off the metal particles, rust and spalling in the pipeline to its oil oxidation and decomposition of particles and gum, more serious is the system pipeline in the formal operation before the flushing and a large number of impurities.
 

Maintenance of the system

A system is generally flushed before it is officially put into operation, the purpose of flushing is to remove the contaminants, metal chips, fibrous compounds, iron cores, etc. remaining in the system, which can cause a series of failures in the first two hours of work, even if it does not completely damage the system.

Therefore, the following steps should be followed to clean the system oil circuit.

Clean the oil tank with a clean solvent that is easy to dry, and then use filtered air to remove the solvent residue.

Clean all the lines of the system, in some cases, the lines and fittings need to be impregnated.

Install an oil filter in the line to protect the valve supply line and pressure line.

Install a flushing plate on the collector in place of a precision valve, such as an electro-hydraulic servo valve.

Check that all lines are properly sized and connected.

If the electro-hydraulic servo valve is used in the system, the flushing plate of the servo valve should enable the oil to flow from the oil supply line to the collector and return to the tank directly, so that the oil can flow repeatedly to flush the system and let the oil filter out the solid particles, during the flushing process, the oil filter should be checked every 1 to 2 hours to prevent the oil filter from being blocked by pollutants, and the bypass should not be opened at this time.

The flushing cycle is determined by the structure of the system and the degree of system contamination. If there are no or very few foreign contaminants in the specimen of the filter medium, put on a new oil filter, remove the flushing plate and put on the valve to work!

Planned maintenance, the establishment of a system of regular maintenance system, a better maintenance system for injection molding machine hydraulic system is recommended as follows.

At most 500 hours or three months to check and replace the oil filter.

Regularly flush the inlet oil filter of the oil pump.

Check the hydraulic oil is contaminated by acidification or other pollutants, the smell of hydraulic oil can generally identify whether the deterioration.

Repair any leaks in the system.

Make sure no foreign particles enter the tank through the tank vent cap, the plug seat of the oil filter, the sealing gasket of the return line, and other openings in the tank.