Grinding of Natural Stone Balls with Planetary Movement of the Tool

The article presents a diagram of a modernized machine with planetary movement of the tool for grinding balls of colored stone and test results when processing serpentinite. There are various methods and devices for processing metal balls using abrasive methods used in the production of bearings. These devices simulate the operation of a thrust bearing. One of the tools contains a V-shaped groove, in which the workpieces being processed receive predominantly biaxial rotation. Quantitative criteria for evaluating the ball processing process are productivity, dimensional accuracy, spherical shape and surface roughness. Currently, balls made of non-metallic materials are also used: ceramics, glass, glass ceramics and stones, which differ from steel ones in their physical and mechanical properties, primarily such as fragility and lower strength. This is especially noticeable when processing minerals used in the jewelry industry, which differ in structure, the presence of layering,   internal defects, etc. All this makes it necessary to process such materials under conditions different from the conditions for processing steel balls (lower pressure forces, speeds). However, insufficient attention has been paid to issues devoted to methods of processing balls made of fragile materials, including jewelry stones. In many cases, the necessary methods and conditions for processing such materials are determined throughout practice by trial and error. The increasing volume of production of beads for making jewelry from natural stone necessitates comprehensive research and generalization of the results of these studies in order to develop recommendations for their practical use. In this work, we propose a method for processing balls in a device that ensures planetary motion of the balls due to the fact that the disk-shaped tool receives periodic rotation from the friction force that occurs when its side surface touches a table performing planetary motion. As a result, the balls located in the conical sockets of the disk receive accelerated motion and roll along a cycloid trajectory. The additional path that the balls travel in the same time, as well as the change in the ratio of the angles of rotation of the balls around their three axes, create conditions for increasing the productivity and accuracy of processing.  The experiments were carried out on a pilot plant when processing workpieces made of serpentinite, which belongs to the group of soft stones. The results of the work showed that the batch processing time for each part grinding ope-ration until dimensional stabilization is achieved does not exceed 30 minutes. The amount of allowance removal and the degree to which the required ball dimensional accuracy and roughness are achieved are determined by the size of the abrasive grain.

1. Olender L. A. (1974) Technology and Equipment for Ball Production. Minsk, Vysheyshaya Shkola Publ. 336 (in Russian).

2. Sokhan’S. V., Maistrenko A. L., Borimskii A. I., Sorochenko V. G., Voznyi V. V., Gamanyuk M. P., Zubanev E. N. (2018) Diamond Finishing of Ceramic Balls Made of Boron Carbide. Oborudovanie i Instrument [Equipment and Tools], (3), 54–57. Available at: https://www.inform dom.com/uploads/metal/18_3/54_Almaznaya_dovodka_ 2018_3.pdf (in Russian).

3. Sobchak N., Sobchak T. (2002) Encyclopedia of Minerals and Gems. St. Petersburg, Neva Publ. Moscow, OLMA-PRESS Publ. 479 (in Russian).

4. Sinkankas J. (1984) Gem Cuttung. A Lapidary`s Manual. Van Nostrand Reinhold Company.

5. Yashcheritsyn P. I., Zaitsev A. G., Barbotko A. I. (1976) Fine Finishing Processes for Processing Machine Parts and Devices. Minsk, Nauka i Tekhnika Publ. 328 (in Russian).

6. Shchetnikovich K. G. (1996) Method of Processing Balls. Patent No 1444 Republic of Belarus (in Russian).

7. Shchetnikovich K. G., Kiselev M. G. (2009) Ball Kinematics in Fine Polishing between Misaligned Disks in Conical Openings. Vestnik Belorusskogo Natsional'nogo Tekhnicheskogo Universiteta [Bulletin of the Belarusian National Technical University], (3), 39–45 (in Russian).

8. Mikhnev R. L., Shtandel S. K. (1991) Equipment for Optical Workshops. Moscow, Mashinostroenie Publ. 367 (in Russian).

9. Vasin, L. N., Korobchenko I. A. (1995) Method of Grinding Balls. Patent of Russian Federation No 1510250 (in Russian).

10. Nikolaev N. N., Orobinsky S. P., Akramovskaya T. M. (1990) Method for Processing Balls Made of Optical Materials. USSR Author’s Certificate No 31572794 (in Russian).

11. Shchetnikovich K. G., Stalmoshonok B. B (1993) Method of Processing Balls. USSR Author’s Certificate No 1787747 (in Russian).

12. Lobankin A. S. (1992) Device for Processing Balls. USSR Author’s Certificate No 1713819 (in Russian).