In the paper working conditions and requirements for cylinders of hydraulic actuators, used in mining roof supports to protect the roof of workings in underground coal mines are discussed. Significant functional effects that can be obtained by using the surface strain hardening of internal surfaces of cylinders of hydraulic actuators are indicated. A device designed for a dynamic method of percussive burnishing of internal cylinder surfaces with the use of a special hydraulic system is presented. The device enables an implementation of high-efficiency surface strain hardening. This treatment makes it possible to improve the resistance of cylinders to fatigue cracks and to harmful tribological phenomena resulting in a leakage of the working medium, affecting the environment negatively. An application of a strengthening device for cylinders enables a more favourable adjustment of hydraulic cylinders for use in extreme working conditions, in particular in the workings threatened by bumping hazards. Besides, the surface plastic deformation also serves to improve usage conditions of high-pressure sealing nodes and it reduces the leakage of water-in-oil emulsion.Keywords: Hydraulic leg, percussive burnishing
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