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Hydraulic cylinder seal selection introduction

2018-08-22

Hydraulic Cylinder is the 500t Rally machine part of the implementation of power to meet the test requirements, its bore diameter of 320mm or more, and must be 25MPa, V

1, the hydraulic cylinder seal requirements

(1) In the pressure of 28MPa and 100 ℃ temperature range, should have good sealing performance, and with the pressure increase can automatically improve the sealing performance.

(2) the friction between the seal and the moving parts should be small, the coefficient of friction should be stable, and there is no creeping phenomenon at low speed.

(3) anti-corrosion ability, not easy to aging, long working life, good wear resistance, wear to a certain extent, can automatically compensate.

(4) Simple structure, use, easy maintenance, low price.

2, the cylinder seal structure

Cylinder mainly by the cylinder, piston, piston rod, guide sleeve, front and rear end caps and seals plus seal composition.

2.1 Piston seal structure

Piston seal structure by the wear ring, the combination of seals. Wear ring on the piston from the support, guide role to prevent scratching or eccentric, and improve the durability of the seal. Wear ring made of PTFE bronze PTFE wear ring. It has low friction, no crawling and bite, can inhibit the mechanical vibration, has excellent bearing capacity and wear resistance characteristics, fully suitable for low speed Rally case without crawling requirements. Wear ring width calculation formula:

T = (F · f) / (d · Pr) (1)

Where: T - wear ring width, mm;

F - maximum radial load, N;

f - safety factor

d - piston or piston rod diameter, mm;

Pr - the maximum allowable radial load, MPa. If the calculated minimum width is small, choose a slightly larger possible guide width.

According to the requirements of the cylinder seal, from the economic choice of combination ring Glei ring as a piston seal. This combination seal consists of two components, a Tecom ring and an O-ring. It has a low frictional resistance, no creeping phenomenon, no sticking phenomenon, the maximum working pressure up to 70MPa characteristics, and in low frictional resistance conditions, the leakage at 28MPa is 0.18mg, only with the O-ring with 2 Back ring leakage of 1/4.

Piston and cylinder clearance directly affects the size of the seal life and processing costs. Large gap easily lead to seal root tear edge tear, static root tear and roots are rooted, leading to seal failure, affecting the sealing performance. The size of the gap with the dynamic side diameter, the choice of seal material and cross-sectional thickness, system pressure, ambient temperature by a direct relationship, take the gap S = 0.4mm.

2.2 Piston rod seal

Piston rod seal by the ring, guide ring, dust ring and other components. The guide ring mainly plays a supporting and guiding role on the piston rod to prevent scratching or eccentricity and improve the durability of the seal. The width of the guide ring is calculated according to formula (1).

Piston rod seal reference to foreign application experience, the use of a Stewart seal and a Y-ring to seal the piston rod. Steele seal is a single-acting sealing ring, it has a similar seal with the Glei ring features.

Dust ring to prevent dust from entering, protecting equipment and maintain the sealing performance. Its incidental function is anti-scratch oil. The movement of the piston rod in the guide sleeve requires a certain amount of oil film to lubricate. These oil films will accumulate as a result of the action of the outer lip of the dust ring causing leakage. Therefore, the inner lip of the dust ring should have oil scraping function, Prevent between the dust seal and the main seal, so that the oil film both play a role in lubrication without leakage. Dust ring on request A-type dust ring. Its material is nitrile rubber, with a comb-shaped sealing surface on the outside to ensure its reliable positioning in the groove.

2.3 static seal

Cylinder static seal with O-ring seal, material selection of nitrile rubber, Shore hardness of 75 to 90. Due to the high system pressure, O-ring must be added stop ring to prevent the O-ring is squeezed into the gap with the damage. Therefore, the piston and piston rod seal O-ring seal, the front cover and cylinder with O-ring plus one-sided seal ring form.

2.4 cylinder assembly and testing

Cylinder design, assembly quality, test methods and inspection rules to implement JB / T (hydraulic cylinder technical conditions), and with the use of GB / T (General technical conditions of hydraulic components), GB / T (hydraulic cylinder test methods) and other standards.

500t Rally machine to meet the requirements of the cylinder sealing system conditions, the 500t Rally cylinder sealing system was designed. The design of the cylinder sealing system at 28MPa, low-speed operation without creeping phenomenon, stable work, and the leakage is small, fully meet the requirements of the cylinder seal system.

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