THERMAL DRILLING OPTIMIZATION IN MULTI HOLE PLATES

The article presents the results of simulation of thermal deformations by the finite element method for round multi-hole plates used in heat exchangers. The heat generated when drilling holes causes thermal deformation of these objects, which contributes to errors in the location of the holes. Obtained results of simulation were compared for different drilling strategies (the studies considered 24 different strategies). It was found that the maximum drilling temperatures according to different strategies may differ by up to 100%. Similar conclusions can be drawn for thermal deformations. The general conclusion that results from the conducted research indicates the need to choose a strategy that ensures the symmetry of the drilled holes in relation to the axis of symmetry of the object. Then, both thermal deformation and maximum temperature are the smallest. The thus identified thermal deformations can form the basis for the correction of the coordinates of the holes on a CNC multi-spindle drilling machine.

New Method for Reducing Coal Mine Gas Disasters via Directional Drilling and Hydraulic Jet

Gas extraction is an important topic because of poor permeability and high gas seam in coal mines. A new method for reducing stress and improving permeability of coal seam was proposed to reduce the cost of gas extraction and danger of coal and gas outbursts. In this method, the roadway in coal floor was replaced with directional main borehole, directional branch boreholes were used to replace crossing holes, and soft coal was mined along soft sub layers using a directional drilling machine and a directional hydraulic jet. The numerical simulation showed that the porosity and permeability of coal seam significantly improve after soft sub layers being removed by the directional hydraulic jet. The application of the proposed method and its supporting equipment was carried out under the special gas conditions of Hudi Coal Mine. Results show that the soft coal is mined efficiently along the soft sub layer using the main borehole, branch boreholes, and directional hydraulic jet. Compared the hydraulic punching in the borehole with the ordinary drilling machine, the average speed of mining soft sub layers increased from 0.5 t/h to 3.6 t/h, the equivalent diameter of mining soft sub layers increased from 1.2 m to 7.6m, and the average flow of gas extraction increased from 0.41 m3/d to 6.25 m3/d. The conclusions obtained in this study can provide a reference to the similar coal mining methods.

Process Transferability of Friction Riveting of AA2024-T351/Polyetherimide (PEI) Joints Using Hand-Driven, Low-Cost Drilling Equipment

The present work deals with the transferability of Friction Riveting joining technology from laboratory equipment to adapted in-house, low-cost machinery. A G13 drilling machine was modified for the requirements of the selected joining technique, and joints were performed using polyethermide plates and AA2024 aluminum alloy rivets of 6 mm diameter. This diameter was not previously reported for Friction Riveting. The produced joints were mechanically tested under tensile loading (pullout tests) with ultimate tensile forces of 9500 ± 900 N. All tested specimens failed through full-rivet pullout, which is the weakest reported joint in Friction Riveting. In order to understand this behavior, FE models were created and analyzed. The models produced were in agreement with the experimental results, with failure initiated within the polymer under stress concentrations in the polymeric material above the deformed metallic anchor at an ultimate value of the stress of 878 MPa at the surface of the joint. Stresses decreased to less than half of the maximum value around the anchoring zone while the rivet was removed and towards the surface. The paper thus demonstrates the potential ease of applying and reproducing Friction Riveting with simple machinery, while contributing to an understanding of the mechanical behavior (initialization of failure) of joints.

Study of the dependence of efficiency on the load of a drilling machine

The question of research of dependence of efficiency on loading of the drilling machine is considered. To achieve this goal in the work were set and solved the following tasks: - to analyze the design and technological features of the drilling machine part; - to develop a new design of a drilling machine with a network analyzer; - to investigate the new design of a drilling machine with a network analyzer. About 80 % of drilling machines at Ukrainian enterprises are operated in excess of the established shelf life, which leads to their low quality of operation, high accident rate and failure of electromechanical equipment. The average shelf life of the electric drive in the industry does not exceed 6 years. Up to 10–18 % of electric motors and up to 30 % of auxiliary equipment fail and are repaired annually. The vast majority of engines can be repaired 4-5 times and after repair often do not work even for one year. The operation of drilling machines with an induction motor (short-circuited rotor), which are in poor technical condition, leads to an increase in financial costs due to increased power consumption. The cost of electricity consumed by the electric drive of drilling machines during the service life is significantly higher than the cost of equipment and maintenance costs and more than 4 times higher than its own. The electricity bill includes a system of surcharges for additional reactive power consumption. Reactive power charges at enterprises account for up to 10% of total electricity costs, and these costs tend to increase. Today, there is a need to apply the latest technical solutions and scientific approaches to solving the problem of improving the quality of operation of asynchronous electric drives of drilling machines. A research stand has been developed to determine the asynchronous motor of a drilling machine, which allows to identify the dependence of efficiency on the magnitude of the load, calculate the parameters of the substitution scheme and energy characteristics for the nominal mode of operation of the electric drive. Key words: drilling machine, network analyzer, research stand