ISO/TC 60/SC 1 - Nomenclature and wormgearing

This document provides nomenclature for general modes of gear tooth wear and failure. It classifies, identifies, and describes the most common types of failure and provides information that, in many cases, enables the user to identify failure modes and evaluate the degree or change from original condition. This document is based on experience with steel gears; however, many of the failure modes discussed apply to gears made from other materials. Not all failure modes that can occur on other types of gears, such as plastic, bronze, or powder metal gears, are included. The solution to many gear problems requires detailed investigation and analysis by specialists and is beyond the scope of this document. This document specifies only the terminology intended to help with the identification and reporting of the appearance and conditions of gears after a period of operation. Neither causes nor preventive measures for any condition described are discussed. In this document, gear refers to both gear wheels and pinions, unless the gear is specifically identified. This document does not define “gear failure”.

This document specifies requirements for the accuracy of general-purpose hobs of 0,5 module to 40 module. These hobs are intended for producing gears which conform to ISO 53 and ISO 54. This document applies to hobs for spur and helical gears. It applies to solid (monobloc) and inserted blade hobs. The elemental features of hobs are graded according to accuracy, as follows: — Grade 4A; — Grade 3A; — Grade 2A; — Grade A; — Grade B; — Grade C; — Grade D. Grade 4A is the highest order of precision. In addition to the elemental tests for hobs, this document gives permitted tolerances for composite tests that are taken along the cutting edges on the line of action. The two groups of tests are not equivalent and one can choose between one or the other. If there was no previous agreement, the hob is regarded as belonging to the precision class specified if it satisfies one or the other of the two methods of inspection. NOTE The tolerances in this document were determined for gear hobs whose dimensions conform to ISO 2490, but with certain precautions they can be applied to hobs not specified in this document.

This document specifies formulae for calculating the load capacity of cylindrical worm gears and covers load ratings associated with wear, pitting, worm deflection, tooth breakage and temperature. Scuffing and other failure modes are not covered by this document. The load rating and design procedures are only valid for tooth surface sliding velocities, , less than or equal to 25 m/s and contact ratios greater than 2,1. For wear, load rating and design procedures are only valid for tooth surface sliding velocities which are above 0,1 m/s. The rules and recommendations for the dimensioning, lubricants or materials selected by this document only apply to centre distances of 50 mm and larger. For centre distances below 50 mm, method A applies. The choice of appropriate methods of calculation requires knowledge and experience. This document is intended for use by experienced gear designers who can make informed judgements concerning factors. It is not intended for use by engineers who lack the necessary experience. See 4.7. WARNING — The geometry of worm gears is complex, therefore the user of this document is encouraged to make sure that a valid working geometry has been established.

ISO/TR 10828:2015, thread profiles of the five most common types of worms at the date of publication are described and formulae of their axial profiles are given. The five worm types covered in this technical report are designated by the letters A, C, I, K and N. The formulae to calculate the path of contact, the conjugate profile of the worm wheel, the lines of contact, the radius of curvature and the velocities at points of contact are provided. At the end the application of those formulae to calculate parameters used in load capacity calculations are provided.

Concerns the part of the international vocabulary of gears which is devoted solely to geometrical definitions. It gives, for each of the geometrical terms relative to gears, a standard definitions which will be valid internationally, to corresponding term in each langauge being chosen as far as possible in such a way as to directly reflect the meaning of the definition.

ISO 2490:2007 specifies the nominal dimensions of general-purpose single-start solid (monobloc) gear hobs with axial keyway or tenon drive of 0,5 to 40 module. These hobs are intended for the production of gears which conform to ISO 54:1996 and present a 20° pressure angle in conformity with ISO 53:1998.

ISO 21771:2007 specifies the geometric concepts and parameters for cylindrical gears with involute helicoid tooth flanks. Flank modifications are included. It also covers the concepts and parameters for cylindrical gear pairs with parallel axes and a constant gear ratio, which consist of cylindrical gears according to it. Gear and mating gear in these gear pairs have the same basic rack tooth profile.

This part of ISO 1122 concerns the part of the international vocabulary of gears which is devoted solely to geometrical definitions. It gives, for each of the geometrical terms relative to gears, a standard definition which will be valid internationally, the corresponding term in each language being chosen as far as possible in such a way as to directly reflect the meaning of the definition. NOTE — Since the choice of corresponding terms can only be partially fulfilled in any particular language, due to the necessity of respecting certain established conventions, it is advisable, as far as translation into other languages is concerned, to refer always to the meaning of the definition itself, rather than to a simple transposition of the original term.

Defines terms used to describe the appearance of the visible surfaces of tooth flanks or the damage that can be observed on gears. Causes and preventive measures are not discussed.

ISO/TR 14521:2010 specifies equations for calculating the load capacity of cylindrical worm gears and covers load ratings associated with wear, pitting, worm deflection, tooth breakage and temperature. Scuffing and other failure modes are not covered by ISO/TR 14521:2010. The load rating and design procedures are valid for sliding velocities over tooth surfaces of up to 25 m/s and contact ratios equal to or greater than 2,1. For wear, sliding velocities over tooth surfaces are not below 0,1 m/s. The rules and recommendations for the dimensioning, lubricants or materials selected by ISO/TR 14521:2010 only apply to centre distances of 50 mm and larger. For centre distances below 50 mm, method A applies. The choice of appropriate methods of calculation requires knowledge and experience. ISO/TR 14521:2010 is intended for use by experienced gear designers who are able to make informed judgements concerning factors. It is not intended for use by engineers who lack the necessary experience. The geometry of worm gears is complex, therefore the user of ISO/TR 14521:2010 is encouraged to make sure that a valid working geometry has been established.

ISO 4468:2009 specifies requirements for the accuracy of general-purpose hobs of 0,5 module to 40 module. These hobs are intended for producing gears which conform to ISO 53 and ISO 54. ISO 4468:2009 applies to hobs for spur and helical gears and to solid (monobloc) and inserted blade hobs.