First, general overview

Leakage is a common fault phenomenon of injection molding machine, mainly due to the liquid flow in hydraulic components and pipeline pressure difference and the components of the gap caused by leakage. In addition, bad working conditions will also have a certain impact on the sealing of injection molding machine. Once the hydraulic system leaks, it will cause the system pressure cannot be established, and the leakage of hydraulic oil will cause environmental pollution, affect production and even produce serious consequences that cannot be estimated. The following for some of the influence of the hydraulic system of injection molding machine leakage factors to briefly talk about its leakage causes and countermeasures.

Two, the classification of leakage

The leakage of the hydraulic system of injection molding machine is mainly divided into two types: fixed seal leakage and motion seal leakage. The leakage parts of the fixed seal mainly include the bottom of the cylinder and the connection of the pipe joints. The motion seal mainly includes the piston rod parts of the cylinder and the multi-way valve stem and so on. The leakage of oil can also be divided into external leakage and internal leakage. The external leakage mainly refers to the leakage of hydraulic oil from the system to the environment, and the internal leakage refers to the existence of the pressure difference on the high and low pressure side and the failure of seals, so that the hydraulic oil flows from the high pressure side to the low pressure side in the system.

3. Causes of leakage

(1) Design factors

(1) The selection of seals

The reliability of hydraulic system largely depends on the design of hydraulic system seal and the selection of seals, because the design of the seal structure is not reasonable, the selection of seals is not in line with the specification, in the design did not take into account the compatibility type of hydraulic oil and sealing materials, load, limit pressure, working speed size, environmental temperature changes. All of these directly or indirectly cause hydraulic system leakage to varying degrees. In addition, due to the use of the injection molding machine with dust and impurities in the environment, so in the design to choose the appropriate dust seal, to avoid dust and other dirt into the system to destroy the seal, pollution of oil, resulting in leakage.

(2) Other design reasons

The design takes into account the geometric accuracy and roughness of the moving surface is not comprehensive enough and the strength check of the connecting part is not carried out in the design, which will cause leakage in the mechanical work.

(2) Manufacturing and assembly factors

(1) Manufacturing factors

All hydraulic components and sealing components have strict dimensional tolerances, surface treatment, surface finish and form tolerances. If in the manufacturing process, 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 order or due to processing problems caused by the loss of circle, itself has burrs or pits, chrome plating off, the sealing will have deformation, scratch, crushing or compaction phenomenon occur to make it lose the sealing function. The parts themselves will have congenital leakage points, after assembly or during the use of leakage.

(2) Assembly factors

Hydraulic components in the assembly should eliminate savage operation, if excessive force will make parts deformation, especially with copper rod beating cylinder block, sealing flange, etc.; Before assembly, parts should be carefully checked, assembly should be dipped in a little hydraulic oil, gently pressed into, when cleaning the application of diesel, especially sealing ring, dust ring, O-ring and other rubber components, if the use of gasoline makes it easy to aging lose the original elasticity, thus losing the sealing function.

(3) oil pollution and damage to parts and components

(1) Gas pollution

At atmospheric pressure, the hydraulic oil can dissolve about 10% of the air, in the hydraulic system of high pressure, in the oil will dissolve more air or gas. Air bubbles form in the oil, if the hydraulic support in the process of working in a very short time, the pressure between high and low pressure rapid transformation will make the bubbles in the high pressure side high temperature in the low pressure side burst, if the surface of the hydraulic system components have concave points and damage, the hydraulic oil will rush to the surface of the components accelerated surface wear, causing leakage.

(2) Particle pollution

Hydraulic cylinder as some injection molding machine hydraulic system of the main executive components, due to the piston rod exposed in the process of work and direct contact with the environment, although the guide sleeve is equipped with dust ring and seals, but it is inevitable to dust, dirt into the hydraulic system, accelerate the seals and piston rod scratches and wear, thereby causing leakage, Particle pollution is one of the fastest damage factors of hydraulic components.

(3) Water pollution

Due to the influence of wet working environment and other factors, may make water into the hydraulic system, water will react with hydraulic oil, forming acidic substances and sludge, reduce the lubrication performance of hydraulic oil, accelerate the wear of parts, water will also cause the control valve stem bonding, control valve operation difficulties scratch seals, resulting in leakage.

(4) parts damage

Seals are made of oil-resistant rubber and other materials. Aging, cracking, damage and so on will cause system leakage due to long-term use. If the part is damaged by collision in the process of working, it will scratch the sealing element and cause leakage.

Four, the main prevention and control countermeasures of leakage

The factors that cause the leakage of hydraulic system of injection molding machine are the result of the comprehensive influence of many aspects. With the existing technology and materials, it is difficult to eliminate the leakage of hydraulic system of injection molding machine fundamentally. Only from the above factors affecting the leakage of hydraulic system, take reasonable measures to reduce the leakage of hydraulic system. In the design and processing link to fully consider the important factors affecting the leakage of sealing groove design and processing. In addition, the selection of seals is also very important, if not the initial comprehensive consideration of leakage factors, will bring immeasurable losses to the future production. Choose the correct assembly and repair method, learn from the past experience. For example, in the assembly of the sealing ring, special tools are used as far as possible, and some grease is coated on the sealing ring. On the pollution control of hydraulic oil, we should start from the source of pollution, strengthen the control of pollution source, but also 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 comprehensive consideration can be effective.