A rig for modeling pneumatic percussive machines

Abstract

A promising development in countering vibration hazards of percussive machines is the creation of machines with "limiting operating cycles" [1] which enables us to eliminate the main source of vibrations and simultaneously to reduce the thrust required for normal operation.Proposals [2] have been made which, in principle, would realize such an operating cycle. However, their practical realization is difficult, owing to the lack of theoretical and experimental research results on this topic.Machines with limiting operating cycles are fairly complex dynamic systems comprising two or more strikers, or a striker with one or more inertia pistons. In operation, the strikers and pistons reciprocate under the influence of the energy-carrying medium, and interact with each other and with tile handle of the instrument. The forces acting on the strikers and pistons can be regulated in accordance with the relative positions of the inertial elements (strikers and pistons) or according to tile position of one of these elements relative to the casing.The large number of independent parameters determining the behavior of the system creates many possibilities for making machines with the required properties, but also greatly complicates the work of investigation. The main requirements which limit the choice of parameters are: 1) stable operation over a reasonably wide range of characteristics of the medium being worked; 2) reliable starting for any initial position of the system; 3)reduction of the size and weight of the machine for a given power and a given energy per impact.The simplifying assumptions are unavoidable in a theoretical discussion of the optimization of the operating process of a limiting-cycle machine, and they distort the true picture. Theoretical conclusions therefore reflect only the qualitative aspect of the phenomena, and cannot serve as a reliable basis for choice of parameters,The most reliable data can be found by comparing a large number of experimental sample machines with various combinations of the main parameters. However, this method is very laborious, and also extremely expensive. It is sufficient to point out that several hundred experimental specimens are necessary to study only one of the simplest schemes.At the Institute of Mining, Siberian Branch, Academy of Sciences of the USSP~ we have built a test rig [3] for modeling percussive pneumatic machines with limiting operating cycles.The rig is simple in construction and easy to maintain, and enables one to make models of various schemes, thus reducing the labor required and speeding up the investigations.The percussion mechanism of the rig comprises the instrument and a perforated cylinder with inertia elements (strikers and pistons). The cylinder is placed in an elastic casing and is fixed in the dismountable ring. The elastic casing enclosing the cylinder is made of a strip of sheet rubber with holes and grooves via which the working chamber of the percussion mechanism communicates with the compressed-air main and the atmosphere. The casing...