Hydraulic seals are commonly used for seal design

1 Overview Hydraulic equipment relies on liquid medium to transmit power. The working pressure, speed and applicable working environment of the equipment are restricted by the medium seal. The sealing device is the main component of the equipment. The reliability of the whole unit depends on the working capacity of the sealing device. The hydraulic support adopts 5% emulsion medium, which has poor lubrication and anti-corrosion performance. It is very difficult to repair in the underground, so it puts higher requirements on the applicability and reliability of the seal.

2 Hydraulic support piston seal The most important seal of the hydraulic support is the piston seal installed on the column, because its role is to maintain the pressure of the cavity supporting the top plate. If the piston seal is damaged, the consequences may be catastrophic. In the double telescopic column, since the area ratio of the inner and outer telescopic cylinders can be as high as 60 MPa or more, the emulsion lubrication performance is poor, and thus the main problem faced by the designer is that the seal is extruded and worn.

1 Extrusion extrusion damage is caused by high pressure and friction acting on the seal, unlike the usual double-acting hydraulic cylinder, where the friction on the seal is opposite to the pressure direction, and the friction in the bracket is The pressure exerted by the top plate is generated, so this pressure acts in the same direction as the friction force, which puts higher requirements on the anti-squeezing design of the seal.

Hydraulic support seals are usually equipped with anti-extrusion rings, generally using polymers (such as polytetrafluoro, polyoxymethylene, etc.). The pressure of the anti-extrusion ring is affected by the thickness of the F ring. The pressure of the sealing elastomer is due to the flowability of the sealing elastomer. The number is usually greater than 0.5, if it is stuck, it may exceed 1) I contact length Generally contact length 1 is greater than the thickness t of the ring, so it can be concluded that F and Fm are close in size, and in many cases the friction force Fm may be greater than the pressing force. F. The effect of extrusion damage caused by friction can be illustrated by experiments. Taking the single hydraulic prop as an example, the static load test and the reciprocating test are carried out according to the national standards. The test results show that the anti-extrusion ring has little extrusion damage when only static pressure is used, but in operation, the friction prevents the seal from being sealed. The ability to squeeze has dropped dramatically.

2.2 Friction, wear The wear of the seal is caused by a series of factors. In order to study the change in sealing performance caused by reciprocating motion to seal wear, the International Organization for Standardization has developed a program that is commissioned by the British Society of Fluid Mechanics to commission seven different laboratories around the world. Tested according to the same test conditions, using extrusion seal and lip seal, the surface of the piston rod is hardened after high-frequency quenching, hardness HV800~1100, surface polishing Ra0.2~0.4. After 150,000 reciprocating tests The conclusion is that the squeeze seal shows that the leakage is inversely proportional to the friction. The lip seal does not find any relationship between the leakage and the friction. The rough piston rod is not more serious than the smooth piston rod. .

The above analysis shows that the sliding wear in the usual sense on a smooth surface has little effect on the sealing performance of the stent. In fact, the friction and wear of the bracket seal are usually caused by the adhesion caused by the seal under a high-pressure static load for a long time and the scratching of the rust point on the inner wall of the hydraulic cylinder.

Commonly used seal design The commonly used seals are as shown. The seals are rubber U-rings on both sides, and the middle is a molded nitrile rubber drum ring. The drum ring is interference-fitted with the cylinder bore to form a low pressure seal. The combination of the high-pressure cloth rubber U-ring and the wear-resistant support ring can prevent the drum ring from being extruded, and the L-shaped support ring is pressed against the cylinder tube to generate a self-tightening action to minimize the extrusion gap formed by the U-shaped ring, and the piston is In this case, the L-shaped support ring also functions as a bearing. This type of sealing is widely used, and the sealing performance is excellent. The disadvantage is that the frictional resistance is large, and it is only suitable for the split piston.

A similar piston design differs in the structure of the anti-extrusion ring and the support ring. As shown, the self-tightening action of the specially shaped anti-extrusion ring can be optimized by the designer to achieve the best anti-squeezing effect and less frictional resistance. The support ring can be split to meet the main requirements of the integral piston.

In a period of time, the bracket is mainly made of a high-elastic material extrusion type seal. The main point is to design a suitable seal belt width, optimize the initial pressure distribution, and skillfully design the anti-squeeze support structure. Under the premise of meeting the anti-extrusion requirements, try to reduce the frictional resistance.

The rusting phenomenon of the cylinder tube with water-based medium brings a new field of thinking to the seal design, namely the scalability of the seal diameter. “Scalability” refers to the removal of the rust layer by mechanical processing after the cylinder is rusted. The matching clearance between the inner diameter of the cylinder and the piston is expanded, and the performance is restored by replacing or adjusting the seal. In this way, maintenance costs can be greatly reduced and the maintenance cycle can be shortened. Although it brings some difficulties to the management of various spare parts, the benefits are enormous.

Piston seals for piston rod seals are key seals for safety. This is in contrast to engineering machinery that uses mineral oil, which typically allows a small amount of leakage from the piston seal, while leakage at the piston rod causes hydraulic pressure. Oil loss and environmental pollution.

Piston rods are also usually extruded, as shown, with anti-extrusion rings, rubber U-rings and grooved seal rings, which have been widely used. Multi-layer V-shaped seals have high frictional resistance. Poor wear resistance has been phased out.

Conclusion The hydraulic support still seems to be based on the extrusion seal of high elastic material. The design points are anti-extrusion and wear reduction. In view of the damage of the sealing material by the rust point of the cylinder, the scratch resistance and wear self-compensation performance of the sealing material are important. Considering the difficulty in repairing the cylinder and piston rod after rusting, the cost is high, and the "extensibility" view of the seal is proposed to maximize the exchange of the original parts and minimize the maintenance cost "scalability" point of view. Whether it is established or not seems to be not a purely technical issue and an economic issue, and needs to be explored in more depth.

He is a mechanical design engineer at the University of Mining Machinery. He is currently the head of the sales department of the Machinery Plant of Xuzhou Mining Group Co., Ltd.