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DIN Standards Committee Tools and Clamping Devices

Overview

The International Standard ISO 666:2012 "Machine tools - Mounting of grinding wheels by means of hub flanges" has been prepared by Technical Committee ISO/TC 29 "Small tools", Subcommittee SC 5 "Grinding wheels and abrasives" with the participation of German experts of Working Committee NA 121-04-05 AA "Flansche" ("Mounting of plain grinding wheels by means of hub flanges"). The standard specifies the essential requirements, especially the dimensions, for hub flanges for plain grinding wheels according to ISO 603-1, ISO 603-2, ISO 603-4, ISO 603-6, ISO 603-7 and ISO 603-8, with a ratio of the bore diameter to the outside diameter H/D 0,2. It is also applicable to super abrasives with diamond or cubic boron nitride having the same diameters as the grinding wheels in accordance with ISO 603, independently from the material of the core. It applies to grinding wheels with peripheral speeds up to 50 m/s and driving powers of the wheel spindle up to 30 kW. DIN ISO 666 does not specify in detail a fixed arrangement of the interface of the fixed flange with the wheel spindle. This depends on the conditions of the grinding machine spindle. Therefore, this standard provides five different types of flange sockets with the dimensions corresponding to defined nominal sizes. Annex A (informative) contains a guideline for the calculation of the clamping force and tightening torque for the mounting of abrasive products by means of flanges. It allows for an approximate calculation. The content of this annex corresponds to Annex C of DIN EN 13218 "Machine tools - Safety - Stationary grinding machines". When revising DIN EN 13218 to DIN EN ISO 16089, the annex will not be taken over. The standard is not applicable to mounting devices for cutting-off wheels. Due to a known safety problem that had occurred in the previous edition of DIN ISO 666, arising from the reduction of the flange's shaft tolerance class from f7 to g6, a new version of the standard was necessary. For example, for a bore of the grinding wheel with a nominal diameter of 203,2 millimetres, the specification of this tolerance reduced the minimum permitted clearance between the shaft and the mounted grinding wheel from 50 micrometers to 15 micrometers. In this most unfavourable case, due to the differing thermal expansion coefficients of steel (shaft) and ceramic (grinding wheel), a temperature rise in the entire system could lead to an interference fit with considerable radial compressive stress which could cause tangential tensile stress within the grinding wheel. This could, however, have resulted in a breakage of the grinding wheel and, thus, in serious events of damage, in particular, for ceramic grinding wheels or, more generally, for bonded abrasive products. In the event of failure, the temperature of the wheel spindle can practically rise up to 70 °C under extreme circumstances. Also under normal circumstances the temperature in the entire system frequently rises to temperatures around 35 °C. In the present new edition, these issues relating to the temperature rise of the entire system, the differing thermal expansion coefficients of the components involved and the risk of an occurring interference fit resulting in dangerous breakage of the grinding wheel have been solved by changing the tolerance classes to increased clearances.

Document: references other documents

Responsible national committee

NA 121-04-05 AA - Mounting of plain grinding wheels by means of hub flanges  

Responsible international committee

ISO/TC 39/SC 10 - Safety