Leakage is a common fault phenomenon in injection molding machines, mainly caused by pressure differences and gaps between hydraulic components and pipelines when the liquid flows through them. In addition, harsh working conditions can also have a certain impact on the sealing of injection molding machines.
Once a hydraulic system leaks, it will cause the system pressure to not be established, hydraulic oil leakage will also cause environmental pollution, affect production, and even have unpredictable serious consequences. Below, we will briefly discuss the causes and countermeasures of hydraulic system leakage in injection molding machines based on some factors that affect it.
Classification of leaks:
There are two main types of leakage in the hydraulic system of injection molding machines: leakage at the fixed seal and leakage at the moving seal. The leakage at the fixed seal mainly includes the cylinder bottom and the connection of various pipe joints, while the leakage at the moving seal mainly includes the piston rod of the oil cylinder and the valve stem of the multi way valve. From the perspective of oil leakage, it can also be divided into external leakage and internal leakage. External leakage mainly refers to the leakage of hydraulic oil from the system to the environment, while internal leakage refers to the flow of hydraulic oil from the high-pressure side to the low-pressure side inside the system due to the existence of pressure difference between high and low pressure sides and seal failure.
Reasons affecting leakage:
（1） Design factors:
(1) Selection of sealing components
The reliability of hydraulic systems largely depends on the design of hydraulic system seals and the selection of seals. Due to the unreasonable selection of sealing structures and non-standard selection of seals in the design, the compatibility type of hydraulic oil and sealing materials, load conditions, ultimate pressure, working speed, and changes in ambient temperature were not considered in the design. These all directly or indirectly cause hydraulic system leaks to varying degrees. In addition, due to the presence of dust and impurities in the operating environment of injection molding machines, appropriate dust seals should be selected in the design to prevent dust and other contaminants from entering the system, damaging the seals, contaminating the oil, and causing leaks.
(2) Other design reasons
In the design, insufficient consideration was given to the geometric accuracy and roughness of the moving surface, as well as the lack of strength verification at the connection points, which can cause leakage during mechanical operation.
（2） Manufacturing and assembly factors
(1) Manufacturing factors:
All hydraulic components and sealing parts have strict requirements for dimensional tolerances, surface treatment, surface smoothness, and form and position tolerances. If the manufacturing process exceeds the tolerance, such as the piston radius of the oil cylinder, the depth or width of the sealing groove, the hole size for installing the sealing ring exceeding the tolerance, or causing out of roundness due to processing problems, burrs or dents, chrome plating detachment, etc., the sealing component will deform, scratch, crush or not press firmly, causing it to lose its sealing function. Will cause inherent leakage points in the parts themselves, resulting in leakage after assembly or during use.
(2) Assembly factors:
Rough operation should be avoided during the assembly of hydraulic components. Excessive force may cause deformation of the parts, especially when using copper rods to strike the cylinder body, sealing flanges, etc; Before assembly, the parts should be carefully inspected. During assembly, the parts should be dipped in a small amount of hydraulic oil and gently pressed in. Diesel fuel should be used for cleaning, especially rubber components such as sealing rings, dust rings, O-rings, etc. If gasoline is used, they are prone to aging and lose their original elasticity, thereby losing their sealing function.
（3） Oil contamination and damage to components
(1) Gas pollution
At atmospheric pressure, hydraulic oil can dissolve about 10% of air, and at high pressure in hydraulic systems, more air or gas will dissolve in the oil. Air forms bubbles in the oil. If the pressure of the hydraulic support rapidly changes between high and low pressure in a very short period of time during operation, the bubbles will generate high temperature on the high pressure side and burst on the low pressure side. If there are concave spots and damage on the surface of the hydraulic system components, the hydraulic oil will rush towards the component surface at high speed, accelerating surface wear and causing leakage.
(2) Particle pollution
As the main executing component of some injection molding machine hydraulic systems, hydraulic cylinders are exposed to the environment during operation due to the piston rod being in direct contact with the environment. Although dust rings and seals are installed on the guide sleeve, dust and dirt are inevitably brought into the hydraulic system, accelerating the scratching and wear of seals and piston rods, leading to leakage. Particle pollution is one of the fastest factors causing damage to hydraulic components.
(3) Water pollution
Due to factors such as humid working environment, water may enter the hydraulic system and react with hydraulic oil to form acidic substances and sludge, reducing the lubrication performance of hydraulic oil and accelerating component wear. Water can also cause the valve stem of the control valve to bond, making it difficult to operate and scratching the seals, resulting in leakage.
(4) Parts damage
Seals are made of materials such as oil resistant rubber, and long-term use can cause system leaks due to aging, cracking, damage, etc. If the parts are damaged by collision during operation, it will scratch the sealing components and cause leakage.
Main prevention and control measures for leakage:
The factors causing leakage in the hydraulic system of injection molding machines are the result of multiple comprehensive influences. With existing technology and materials, it is difficult to fundamentally eliminate leakage in the hydraulic system of injection molding machines. Only by considering the factors that affect hydraulic system leakage mentioned above, can reasonable measures be taken to minimize hydraulic system leakage as much as possible.
In the design and processing stages, important factors that affect leakage should be fully considered in the design and processing of sealing grooves. In addition, the selection of sealing components is also very important. If the influencing factors of leakage are not fully considered in the initial stage, it will bring incalculable losses to future production.
Choose the correct assembly and repair methods, and draw on past experience. For example, in the assembly of the sealing ring, try to use specialized tools and apply some lubricating grease on the sealing ring. In the pollution control of hydraulic oil, we should start from the source of pollution, strengthen the control of pollution sources, and take effective filtration measures and regular oil quality inspections. To effectively cut off the pollution of external factors (water, dust, particles, etc.) on hydraulic cylinders, some protective measures can be added. In short, the prevention and control of leaks need to be comprehensively addressed and considered in order to be effective.
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