1. General remarks
Leakage is a common fault phenomenon in injection molding machines, mainly due to the pressure difference caused by the pressure difference and the gap between the components when the liquid flows in the hydraulic components and pipelines. In addition, harsh working conditions can also have a certain impact on the sealing of the injection molding machine. Once the hydraulic system leaks, it will cause the system pressure to not be established, and the hydraulic oil leakage will also cause environmental pollution, affect production and even produce incalculable serious consequences. The following is a brief discussion of the causes and countermeasures of some factors affecting the leakage of the hydraulic system of the injection molding machine.
Second, the classification of leakage
There are two main kinds of leakage of hydraulic system of injection molding machine, leakage at fixed seal and leakage at motion seal, leakage at fixed seal mainly includes cylinder bottom, connection of each pipe joint, etc., and motion seal mainly includes cylinder piston rod part, multi-way valve stem and other parts. From the leakage of oil 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 existence of pressure difference between high and low pressure side and seal failure, so that hydraulic oil flows from the high pressure side to the low pressure side inside the system.
Third, the reasons affecting the leakage
(1) Design factors
(1) Selection of seals
The reliability of the hydraulic system, to a large extent depends on the design of the hydraulic system seal and the choice of seals, due to the unreasonable selection of the sealing structure in the design, the selection of seals is not in line with the specifications, and the compatibility type, load situation, ultimate pressure, working speed, ambient temperature change and so on 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 use environment of the injection molding machine, a suitable dust-proof seal should be selected in the design to avoid dust and other dirt entering the system to destroy the seal and contaminate the oil, resulting in 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 connection parts is not carried out in the design, which will cause leakage in the work of the machine.
(2) Manufacturing and assembly factors
(1) Manufacturing factors
All hydraulic components and sealing components have strict dimensional tolerances, surface treatment, surface finish and shape and position tolerances. If the manufacturing process is out of tolerance, such as: the piston radius of the cylinder, the depth or width of the sealing groove, the hole size of the sealing ring is out of tolerance, or the roundness caused by processing problems, the burr or depression itself, the chrome plating is off, etc., the seal will be deformed, scratched, crushed or uncompacted, etc., so that it loses its sealing function. It will make the part itself have a congenital leakage point, which will occur after assembly or during use.
(2) Assembly factors
Hydraulic components should be put to an end to brutal operation in the assembly, if excessive force will cause the parts to be deformed, especially with copper rods and other knocking cylinder blocks, sealing flanges, etc.; Before assembly, the parts should be carefully inspected, the assembly should be dipped in a little hydraulic oil, gently pressed in, cleaning the use of diesel, especially sealing rings, dust rings, O-rings and other rubber components, if gasoline is used, it is easy to age and lose the original elasticity, thereby losing the sealing function.
(3) Oil contamination and damage to parts
(1) Gas pollution
At atmospheric pressure, about 10% of the air can be dissolved in the hydraulic oil, and under the high pressure of the hydraulic system, more air or gas will be dissolved in the oil. Air in the oil to form bubbles, if the hydraulic support in the working process in a very short time, the pressure between high and low pressure rapid change will make the bubbles in the high pressure side to produce high temperature in the low pressure side burst, if the hydraulic system component surface has pits and damage, hydraulic oil will rush to the component surface at high speed to accelerate the wear of the surface, causing leakage.
(2) Particle pollution
Hydraulic cylinder as the main executive component of the hydraulic system of some injection molding machines, due to the piston rod exposed in direct contact with the environment during the working process, although the guide sleeve is equipped with a wiper and seals, etc., but it is inevitable to bring dust, dirt into the hydraulic system, accelerate the scratch and wear of seals and piston rods, etc., thereby causing leakage, particle pollution is one of the fastest damage factors of hydraulic components.
(3) Water pollution
Due to the influence of factors such as humid working environment, water may enter the hydraulic system, water will react with hydraulic oil, forming acidic substances and sludge, reducing the lubrication performance of hydraulic oil, accelerating the wear of components, water will also cause the stem of the control valve to bond, making it difficult for the control valve to operate and scratch the seal, causing leakage.
(4) Damage to parts
The seal is made of materials such as oil-resistant rubber, which can cause system leakage due to aging, cracking, damage, etc. due to long-term use. If a part is damaged by a collision during operation, it will scratch the sealing element, causing leakage.
Fourth, the main prevention and control measures of leakage
The factors that cause the leakage of the hydraulic system of the injection molding machine are the result of the comprehensive influence of many aspects, and it is difficult to fundamentally eliminate the leakage of the hydraulic system of the injection molding machine with the existing technology and materials. 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 process, the important factors affecting leakage should be fully considered, and the design and processing of sealing grooves should be fully considered. In addition, the selection of seals is also very important, if the impact of leakage is not fully considered at the beginning, it will bring immeasurable losses to subsequent production. Choose the right assembly and repair method, drawing on past experience. For example, use special tools as much as possible in the assembly of the sealing ring, and apply some grease to the sealing ring. In the pollution control of hydraulic oil, it is necessary to start from the source of pollution, strengthen the control of pollution sources, and take effective filtration measures and regular oil quality inspection. In order to effectively cut off the pollution of the hydraulic cylinder by external factors (water, dust, particles, etc.), some protective measures can be added. In short, the prevention and control of leakage should be comprehensively started, and comprehensive consideration can be effective.
