Abstract:
Gap sealing is a simple and widely used sealing ...
Gap sealing is a simple and widely used sealing method. It prevents leakage based on the tiny gap between the mating surfaces of relative moving parts. The pressure oil is filled into the gap, relying on the adhesion between metal and oil and the viscosity of the oil to produce a throttling resistance effect to prevent leakage. A certain amount of small gap can form a liquid friction state between the mandrel and the fixed shell, which greatly reduces the friction coefficient and energy consumption. Rotary joints allow a certain amount of leakage and a certain amount of pressure loss in practical applications.
A certain amount of leakage takes away the heat generated by the spindle bearings at both ends of the rotary joint during rotation through the leakage oil port, which can prevent the rotary joint from flowing oil between ports A and B during work. Because there is a pressure difference P-P0 at both ends of the ring gap e, the blocked oil flow flows from the side of the high-pressure chamber P to the side of the low-pressure chamber, forming a leakage Q0.
If the gap is too large, the leakage will increase and the pressure loss will be large, so that the actual working pressure cannot meet the work needs; The mating surface is heated due to heating. The gap seal uses an annular smooth gap seal with a constant gap value e, and the oil flow is symmetrical to the center of the gap.
Main items of hydraulic joint installation
(1) When the hose is moving or stationary, it should not be too bent, nor can it be bent at the root, at least it should start to bend at 1.5 times its diameter;
(2) When the rubber hose moves to the corresponding position, it should not be pulled too tightly, but should be relatively loose;
(3) Prevent torsional deformation of the hose as much as possible;
(4) The rubber hose should be kept away from heat radiation components as far as possible, and a heat shield should be installed if necessary;
(5) The external damage of the hose should be avoided, such as long-term friction with the surface of the component during use;
(6) If the rubber hose is seriously deformed due to its own weight, there should be supporting parts.
When the axial length of the annular gap of the hydraulic joint is L, if the gap bending is not considered, the flow rate through the gap, that is, the leakage amount, can be obtained from the Hagen-Poseyier formula:
The kinematic viscosity of a liquid is more related to temperature and less to pressure. The higher the temperature, the lower the viscosity. As mentioned above, the size of the sealing gap can directly affect the working pressure and relative speed of the rotary joint, so the selection of the sealing gap is very critical. The ideal gap seal is achieved through the formula
(4) Calculation and practice need to be combined with each other. We calculate the sealing clearance of the designed rotary joint as follows, known conditions: use No. 46 anti-wear hydraulic oil, oil supply pressure P=14MPa; the pressure of the leakage oil port is usually P0=0.5MPa; the allowable leakage Q=80～ 200mL/min; the density of No. 46 hydraulic oil ρ=0.89kg/cm3; the leakage length L=50mm. Under normal circumstances, the operating temperature of the oil is selected at two points of 40°C and 80°C, and the corresponding kinematic viscosities ν are 30cst and 8cst respectively. Substituting the above data into formula (4), the small gap value at two temperatures can be obtained. According to the calculation results and practical experience, the selection of the clearance value during design can be appropriately enlarged to ensure the clearance required for the rotation of the rotary joint.
英语
西班牙语
