Leakage causes and treatment methods of hydraulic system of injection molding machine
Leakage causes and treatment methods of hydraulic system of injection molding machine
Leakage is a common fault phenomenon of injection molding machine, which is mainly caused by the pressure difference when the liquid flows in the hydraulic components and pipelines and the gap between each component. In addition, bad working conditions will also have a certain impact on the sealing of the injection molding machine.
Once the hydraulic system leaks, the system pressure will not be established. The hydraulic oil leakage will also cause environmental pollution, affect production and even produce incalculable serious consequences. Here are some factors affecting the leakage of the hydraulic system of the injection molding machine to briefly talk about the causes and Countermeasures of the leakage.
Classification of leakage:
There are two kinds of leakage in the hydraulic system of the injection molding machine: the leakage at the fixed seal and the leakage at the moving seal. The leakage at the fixed seal mainly includes the cylinder bottom and the connection of each pipe joint, and the moving seal mainly includes the oil cylinder piston rod, multi-way valve stem and so on.
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. 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 on the high-pressure side and seal failure.
Causes affecting leakage:
1. Design factors:
Selection of seals
The reliability of the hydraulic system largely depends on the design of the hydraulic system seal and the selection of the seal. Due to the unreasonable selection of the seal structure in the design, the selection of the seal is not in line with the specifications, and the compatible type, load condition, limit pressure, working speed and ambient temperature of the hydraulic oil and sealing materials are not considered in the design.
These all directly or indirectly cause hydraulic system leakage to varying degrees. In addition, due to the dust and impurities in the operating environment of the injection molding machine, appropriate dust seals should be selected in the design to avoid dust and other dirt entering the system, damaging the seal and polluting the oil, resulting in leakage.
Other design reasons
In the design, the geometric accuracy and roughness of the moving surface are not comprehensive enough, and the strength check of the connecting parts is not carried out in the design, which will cause leakage in the mechanical work.
2. Manufacturing and assembly factors
Manufacturing factors:
All hydraulic components and sealing components have strict requirements for dimensional tolerance, surface treatment, surface finish and geometric tolerance.
If the manufacturing process is out of tolerance, such as the piston radius of the oil cylinder, the depth or width of the sealing groove, the size of the hole with the sealing ring is out of tolerance, or out of roundness due to processing problems, burr or depression, chromium plating falling off, etc., the seal will be deformed, scratched, crushed or incompletely pressed, making it lose its sealing function. It will make the parts have congenital leakage points, and leakage will occur after assembly or during use.
Assembly factors:
Rough operation of hydraulic components shall be avoided during assembly. Excessive force will deform the parts, especially knocking the cylinder block and sealing flange with copper bar.
Before assembly, the parts shall be carefully inspected. During assembly, the parts shall be dipped in a little hydraulic oil and gently pressed in. During cleaning, diesel oil shall be used, especially rubber components such as sealing ring, dust ring and O-ring. If gasoline is used, it will be easy to age and lose its original elasticity, so as to lose the sealing function.
3. Oil pollution and damage of parts
Gas pollution
At atmospheric pressure, about 10% air can be dissolved in the hydraulic oil. Under the high pressure of the hydraulic system, more air or gas will be dissolved in the oil.
The air forms bubbles in the oil. If the pressure changes rapidly between high and low pressure during the working process of the hydraulic support in a very short time, the bubbles will produce high temperature on the high-pressure side and burst on the low-pressure side. If there are pits and damages on the component surface of the hydraulic system, the hydraulic oil will rush to the component surface at high speed, accelerate the wear of the surface and cause leakage.
Particle contamination
As the main executive element of the hydraulic system of some injection molding machines, the piston rod is exposed to the outside and in direct contact with the environment during the working process. Although the guide sleeve is equipped with dust rings and seals, it is inevitable to bring dust and dirt into the hydraulic system to accelerate the scratch and wear of seals and piston rods, resulting in leakage, Particle contamination is one of the fastest damage factors of hydraulic components.
Water pollution
Due to the influence of wet working environment and other factors, water may enter the hydraulic system. Water will react with hydraulic oil to form acidic substances and oil sludge, reduce the lubrication performance of hydraulic oil and accelerate the wear of components. Water will also cause the valve stem of control valve to bond, make it difficult to operate the control valve, scratch the seals and cause leakage.
4. Part damage
The seal is made of oil resistant rubber and other materials. Aging, cracking and damage will cause system leakage due to long-term use. If the parts are damaged by collision during operation, the sealing elements will be scratched, resulting in leakage.
Main prevention and control measures for leakage:
The factors causing the leakage of the hydraulic system of the injection molding machine are the result of various comprehensive effects. With the existing technology and materials, it is difficult to fundamentally eliminate the leakage of the hydraulic system of the injection molding machine. Only from the above factors affecting the leakage of the hydraulic system, take reasonable measures to minimize the leakage of the hydraulic system.
In the design and processing link, the important factors affecting leakage shall be fully considered, and the design and processing of sealing groove shall be fully considered. In addition, the selection of seals is also very important. If the influencing factors of leakage are not fully considered at the beginning, it will bring immeasurable losses to future production.
Select the correct assembly and repair methods and learn from previous experience. For example, try to use special tools in the assembly of the sealing ring, and apply some 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 source, and take effective filtration measures and regular oil quality inspection. In order to effectively cut off the pollution of external factors (water, dust, particles, etc.) to the hydraulic cylinder, some protective measures can be added. In short, the prevention and control of leakage should be started comprehensively and considered comprehensively in order to be effective.
