ISO/TC 60/SC 1/WG 7 - Worm gears

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.

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.