One, general overview
Leakage is a common failure phenomenon in injection molding machines. It is mainly due to the pressure difference caused by the liquid flowing in the hydraulic components and pipelines and the gaps between the components and other causes of leakage. In addition, the adverse working conditions will also produce certain seals on the injection molding machine. Impact. Once the hydraulic system leaks, it will cause the system pressure to not build up. The leakage of hydraulic oil will also cause environmental pollution, affect the production and even produce serious consequences that cannot be estimated. The following simple factors affect the leakage of the injection molding machine hydraulic system. Talk about the cause of the leak and how to deal with it.
Second, the classification of leakage
There are mainly two types of leakage in the hydraulic system of the injection molding machine: leakage at the fixed seal and leakage at the movement seal. The leakage at the fixed seal mainly includes the bottom of the cylinder, the connection point of each pipe joint, etc. The movement seal mainly includes the cylinder piston rod. Multiple valve stems and other parts. From the oil leakage can also be divided into external leakage and internal leakage, external leakage is mainly refers to the leakage of hydraulic oil from the system to the environment, internal leakage is due to the pressure difference between the high and low pressure side The presence of the seal and the failure of the seal causes hydraulic oil to flow from the high pressure side to the low pressure side of the system.
Third, the cause of the leak
(a) design factors
(1) Selection of seals
The reliability of the hydraulic system depends to a large extent on the design of the hydraulic system seal and the choice of seals. Due to the unreasonable use of the seal structure in the design, the selection of seals does not conform to the specification, and hydraulic oil is not taken into account in the design. Sealing material type of compatibility, load conditions, ultimate pressure, working speed, changes in ambient temperature, etc. These all directly or indirectly cause leakage of the hydraulic system. In addition, due to dust and impurities in the environment of the injection molding machine. Therefore, in the design, appropriate dust seals should be selected to prevent dust and other dirt from entering the system to destroy the seal, contaminate the oil, and cause leakage.
(2) Other design reasons
The design takes into account that the geometric accuracy and roughness of the moving surface are not comprehensive enough, and the strength check of the joints is not performed in the design, etc. These will cause leakage in the mechanical work.
(b) Manufacturing and Assembly Factors
(1) Manufacturing factors
All hydraulic components and sealing components have strict dimensional tolerances, surface finishes, surface finishes and geometric tolerances. If the manufacturing process is very poor, for example: piston radius of the cylinder, depth or width of the seal groove, seal ring The hole size is out of tolerance or may be out of round due to machining problems. There are burrs or flaws on the hole itself, and the chrome plating is peeled off. The seal will be deformed, scratched, crushed or not pressed to make it lose its sealing function. Will cause the part itself has congenital leakage points, leakage occurs after assembly or during use.
(2) Assembly factors
In the assembly of hydraulic components, brute operations should be avoided. If excessive force is applied, the parts will be deformed, especially by tapping the cylinder with copper rods, sealing the flanges, etc.; the parts should be carefully inspected prior to assembly and the parts should be hydraulically pressed during assembly. Oil, press gently, use diesel oil for cleaning, especially seals, dust rings, O-rings and other rubber components. If you use gasoline, it will easily deteriorate and lose its original elasticity, thus losing the sealing function.
(3) Oil Pollution and Parts Damage
(1) Gas pollution
Under atmospheric pressure, hydraulic oil can dissolve about 10% of air. Under the high pressure of the hydraulic system, more air or gas will be dissolved in the oil. Air forms bubbles in the oil, if the hydraulic support is in operation In a very short period of time, the rapid change of pressure between high and low pressures will cause high pressure on the high pressure side to burst on the low pressure side. If there are pits and damage on the surface of the components of the hydraulic system, the hydraulic oil will rush towards the high speed. Accelerated surface wear on component surfaces causes leakage.
(2) Particle contamination
Hydraulic cylinders are the main actuators of some hydraulic systems of injection molding machines. Since the piston rods are directly exposed to the environment during the working process, they are in contact with the environment. Although the guide sleeves are equipped with dust seals and seals, dust and dirt are inevitable. Into the hydraulic system, accelerating the scratches and wear of the seals and piston rods, which cause leakage, particle contamination is one of the fastest damage to the hydraulic components.
(3) Water pollution
Due to factors such as wet work environment, water may enter the hydraulic system. The water reacts with the hydraulic oil to form acidic substances and sludge. This reduces the lubricating performance of the hydraulic oil and accelerates the wear of the components. The water also causes the valve of the control valve. Sticking occurs in the rod, making it difficult to control the valve to scratch the seal, causing leakage.
(4) Parts damage
Seals are made of materials such as oil-resistant rubber, which can cause system leaks due to aging, cracking, and damage due to prolonged use. If parts are damaged during impact during operation, they will scratch the sealing element and cause leakage.
Fourth, the main leakage prevention measures
The factors that cause the leakage of the injection molding machine's hydraulic system are the result of multiple factors. With the existing technology and materials, it is very difficult to fundamentally eliminate the leakage of the hydraulic system of the injection molding machine. Only the above affects the hydraulic system. Leakage factors, take reasonable measures to minimize leakage of the hydraulic system. In the design and processing aspects, we must fully consider the important factors affecting the leakage seal groove design and processing. In addition, the choice of seal is also very important, if not Full consideration of the influencing factors of leakage will bring immeasurable losses to future production. Select the correct assembly and repair method and learn from past experience. For example, special tools are used in the assembly of the sealing ring, and in the sealing Apply some grease to the ring. In the pollution control of hydraulic oil, start from the source of the pollution, strengthen the control of the pollution source, and take effective filtering measures and regular oil quality inspection. To effectively cut off external factors (water , dust, granules, etc.) Contamination of the hydraulic cylinders can be added with some protective measures. In short, the prevention of leakage should be comprehensive Hand, considering in order to achieve effective.