Two-telescopic legs with channels drilled in the cylinder coats

Stoiński K., Madejczyk W.

Summary:

A method for adaptation of two-telescopic legs with channels drilled longitudinally to take up an additional load resulting from the dynamic action of the rock mass on powered roof support units was presented.
The results of simulation analyses and stand tests of the hydraulic two-telescopic legs of the Glinik-08/22-Oz powered roof support unit loaded dynamically by the impact and blasting methods, were given.
The performed tests enabled us to find out the time process of the leg’s internal load, caused by a mass impact or by blasting materials. The full tests cycle included tests with standard legs, with a hollow upper prop of the II degree (change of design form), without relief valves and with the valves of a different flow capacity.
The stand tests were preceded by the following theoretical analysis:
of an impact of the leg’s design form on its ability to take up the loads resulting from the rock mass bump, performed on a base of changeability of leg’s permanent rigidity,
of a condition of cylinder’s coat effort in the area of drilled channel by the classical methods and using the FEM method; basing on the finite element method calculations, the impact of a channel drilled longitudinally on a stress distribution on the cylinder surface, was determined; the results obtained from the finite elements method were compared with the results obtained from stress measurements using an extensometer method,
of expected loads in legs in a result of rock mass bumps, basing on the Bilinski’s model of a disturb rock mass, where a dynamic effect of the rock mass impact on a support is a derivative of the mass load, of a leg’s dynamic loads simulation. On the basis of proposed physical models of a leg and a relief valve, a mathematical model, which consists of the system of four common differential equations of the second order, making a record of balance of forces and a balance of operational fluid capacity, was presented; partial solution of the equation system was presented in a form of time processes of the pressure in a cylinder of the I degree.
On the basis of two-telescopic legs’ (Φ 0.21/16 metres) test results, under a dynamic load realized by the impact and blasting methods, and a theoretical analysis, a possibility of taking up the additional load coming from the rock mass bump by legs with the channels drilled in cylinder coats (by changing a design form) or using a relief valve with specified flow capacity.
There is a possibility of practical use of obtained test results in the mines which would be interested and have the above mentioned legs.