MM SCIENCE JOURNAL I 2020 I MARCH 3764 LONG SPINDLE DESIGN FOR GRINDING LUKAS RUDOLF, JIRI FRIES, OLDRICH UCEN VSB-Technical University of Ostrava, Department of Production Machines and Design, Czech Republic DOI: 10.17973/MMSJ.2020_03_2019120 E-mail: lukas.rudolf@vsb.cz This article is focused on design issues concerning the long spindle used to grind the internal pipe diameters. In the article an example of spindle design for an internal pipe diameter grinder can be found to process 11 m long pipes with external diameters ranging from 270 to 610 mm. Furthermore, this article offers a theoretical proposal for the spindle stroke in connection with its engagement, taking into consideration the internal diameter of the ground pipe and the outside diameter of the grinding wheels. The pipes used in this example are designed for transport in the mining industry, requiring a high quality of inner pipes surface for their long service life. KEYWORDS: long spindle, grinding machine, pipe, internal diameter, spindle length 1 INTRODUCTION To minimize the contamination of the conveyed medium it is necessary to remove iron scales from the inner surface of the pipe together with any superficial defects. The elimination of iron scales and superficial defects also has a positive effect on the overall pipe life, as it reduces the frequency of micro-break occurrence in the pipe walls during their lifetime [Hapla 2017] [Fries 2018]. To remove these defects the most appropriate technology used is the grinding method. When grinding the internal diameter of the pipes it is necessary to ensure that the removal of chips from the place of processing is sufficient enough, as well as the cooling. It should be noted that during grinding roughly 90% of output turns into the heat [Marek 2014]. For this reason it is advisable to leave one side of the pipe completely free to allow connection of a device removing the chips. A device supplying the refrigerant to the place of grinding is also a part of the spindle. With regard to the length of the pipe workpieces and the size of the workpiece surface, the optimal principle appears to be the use of axial grinding for internal rotating surfaces. For the design of the grinder it is therefore appropriate to use the cursory fixed grinding wheels, located on the spindle. The spindle is in its length supported by a pair of supports, and it is attached to a moving carriage which ensures feed during the grinding. The layout of the grinding machine is shown in Fig. 1. 2 INSTALATION REQUIREMENTS FOR SPINDLE With regard to the total length of 11 m pipe workpieces and the associated lining with a limited internal diameter of the pipe workpiece, the selected design layout does not allow us to create a sufficiently rigid spindle. This fact is typical for the axial grinding of the internal rotating surfaces. When removing any surface defects from the internal diameter of the pipes high demands are not placed on the geometrical tolerances for the machined surfaces. Thanks to this fact the spindle does not have to be designed with any requirement to the minimum position changes in the area, caused by external forces and moments, as is the case for the regular construction of the spindles for grinders. 2.1 Minimization of the spindle length Since there are no geometrical tolerances for the inner diameter of the spindle determined, it is possible to process pipes gradually from both sides by turning them around their vertical axes. This method of processing allows us to reduce the length of the required spindle. By minimizing the length of the spindle we can also reduce the necessary dimensions of the foundations to anchor these machines. The foundations for grinders must be suitably constructed to minimise vibration transfer to the machine surroundings [Rudolf 2017]. Figure 1. The grinder of an internal pipe diameter