Abstract
The paper gives a description of the technical solution for the design of a hydraulic leg piston for mechanized roof supports. This technical solution allows the sealing gap to remain almost constant in a wide range of pressures of the working fluid, while significantly improving the working conditions of the lip seal on the piston. This technical solution consists in the fact that, on the side of the piston cavity of the hydraulic leg, the piston contains a sleeve with a seal located on it, which under the action of the pressure of the working fluid deforms in the radial direction, compensating for an increase in the diameter of the working cylinder. In this case, the described technical solution is not subject to inertia and is able to work with static and with dynamic external loads on a hydraulic leg. The results of a comparative finite-element simulation of the stress-strain state of a hydraulic leg at the junction of the piston and the working cylinder are given for the 360 mm dia hydraulic leg of Glinik support with serial and proposed pistons. It is shown that with the proposed piston, when the pressure of the working fluid in the piston cavity is 62 MPa, the change in the radial sealing gap is less than 20 times compared with the serial design.
Highlights
Hydraulic legs are the main unit of powered roof supports, which take up pressure from rock pressure, and ensure the functioning of the other coal mining machines of the system and safe working conditions for miners [1,2,3]
Hydraulic legs of powered supports are highly loaded with internal pressure of the working fluid, which varies from 32 MPa to 42–56 MPa
During the collapse of the main roof there are dynamic loads on the support and on the hydraulic system of the hydraulic legs, caused by the destruction of rock into the blocks, the size of which is determined by the physical and mechanical properties and thickness of the layers [7,8,9]. These blocks of the main roof move at a speed of up to 3.5 m/s to the value of 0.1 to 50 mm. At such high speeds of the piston of the hydraulic leg, the safety valve protecting its hydraulic system from critical pressures does not have time to work due to its inertia [7]
Summary
Hydraulic legs are the main unit of powered roof supports, which take up pressure from rock pressure, and ensure the functioning of the other coal mining machines of the system and safe working conditions for miners [1,2,3]. Hydraulic legs of powered supports are highly loaded with internal pressure of the working fluid, which varies from 32 MPa (nominal working pressure in the hydraulic system of pumping stations) to 42–56 MPa (nominal working pressure in the hydraulic system of hydraulic legs of modern powered supports corresponding to the pressure setting of the safety valve). Under the action of such a high pressure, the diameter of the inner surface of the working cylinder increases with an increase in the gap between the piston and the cylinder, which complicates the operation of piston lip seals. The size of the sealed gap is proportional to the pressure of the working fluid and depends on the design dimensions of the working cylinder, leg extension [4,5,6] and the properties of the material from which the parts are made
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