Use of pressures as high as 1.8-2.0 MPa in pneumatic drills helps increase drilling speed. By efficiently using the energy of compressed air it is possible to increase substantially the power of the pneumatic striker. This is achieved by optimizing the design parameters and air distribution system of a pneumatic drill.The filling volume of the working chamber and the design parameters determining the duration of air inflow are crucial characteristics of'an airhammer's performance.The filling volume of a working chamber is defined as the volume of the chamber at the time of opening or shutting of the inlet channels.In a valve-free pneumatic drill air is distributed by the moving piston; the air inflow into the chamber occurs on a portion of the piston travel path (the inlet path). The inlet path is determined by the relative position of air duct channels and openings of the "cylinder-piston" system.Depending on the drill type and size, the filling volume of the working chambers and the air inlet path may vary, mainly depending on piston diameter Dp and its travel length Sp. For comparing various drill types and sizes, design parameters can be represented in relative units.The filling volume of the piston working stroke chamber can be expressed as Kv= = Vr/Vp; the filling volume of the idle stroke chamber is Kvx -Vx/Vp; the inlet path of the working stroke chamber is K~r -~=/Sp; and the air inlet path of the idle stroke chamber is K~x -~x/Sp, where Vz, Vx, ~r, and ~x are the filling volumes of the working chambers and the air inlet paths in absolute values, respectively; Vp is the working volume of the chamber; and Sp is the full piston stroke.Generally, the working volume of a working or idle stroke chamber is expressed as .n % = r - %,where Dp is the maximum piston diameter; 71 is the ratio of the piston diameter that determines its effective area on the side of the respective chamber to the maximum piston diameter; and ~2 is the ratio of axial channel diameter in the piston to the maximum piston diameter.In a pneumatic drill using a piston with a single setting surface and no axial channel, 71 " 1 and 72 " 0.Drills have diverse filling chamber volumes and air inlet paths.In order to understand the relationship between these design parameters and the performance characteristic of pneumatic drills and to find optimal values, we studied an experimental valve-free pneumatic drill with variable working chamber capacities and air inflow parameters.In the experimental drill (Fig. I) the filling volumes could be modified by means of additional, smoothly adjustable working chamber capacities attached to the outside of the cylinder." The air inlet path was varied with the use of interchangeable pistons with different positions of air ~ F. Ponomarchuk, I. N. Maksimenko, L. A. Shablii, and N. A. Yurchenko, Inventor's Certificate 358504, "A pneumatic impact mechanism," Byull. Otkr'tlya Izobret., Promyslennye Obraztsy, Tov. Znaki, No. 34 (1972).
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