ISO/TS TECHNICAL SPECIFICATION 14521 First edition 2020-04 Gears Calculation of load capacity of worm gears Engrenages - Calcul de la capacité de charge des engrenages a vis Reference number ISO/TS14521:2020(E) Tso @IS02020 IS0/TS 14521:2020(E) COPYRIGHTPROTECTEDDOCUMENT @ ISO 2020 All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either IsO at the address below or Iso's member body in the country of the requester. ISO copyright office CP 401 : Ch. de Blandonnet 8 CH-1214 Vernier, Geneva Phone: +41 22 749 01 11 Fax: +41 22 749 09 47 Email: [email protected] Website: www.iso.org Published in Switzerland ii @ IS0 2020 - All rights reserved IS0/TS 14521:2020(E) Contents Page Foreword ..vi Introduction.. ..vii 1 Scope. 2 Normative references 3 Terms, definitions and symbols 3.1 Terms and definitions .1 3.2 Symbols... 4 General consideration 4.1 Worm gear load capacity rating criteria .7 4.2 Basis of the method. 4.3 Concept of absolute and relative parameters .8 4.4 Applicability .9 4.5 Validity. ..10 4.6 System considerations ..11 4.7 Calculation methods A, B, C. ..11 4.7.1 Generality on methods A, B and C .11 4.7.2 Notes on numerical formulae. .12 4.7.3 Base conditions, interaction. ..12 4.7.4 Othernotes ..13 4.8 Standard reference gear. ..13 5 Required date for calculation. ..13 5.1 Input variable. ..13 5.2 Safetyfactors ..15 6 Forces, speeds and parameters for the calculation of stresses. ..15 6.1 General .15 6.2 Tooth forces .15 6.2.1 Application factor. ..15 6.2.2 Dynamic factor. .. 15 6.2.3 Load distribution factor. .15 6.2.4 Tooth force components .16 6.3 Sliding velocity at reference diameter .17 6.4 Physical parameters. .17 6.4.1 Generality on physical parameters ..17 6.4.2 Parameter for the mean Hertzian stress ..18 6.4.3 Parameter for the mean lubricant film thickness. .19 6.4.4 Parameter for the mean sliding path 20 6.5 Calculation of mean contact stress .21 6.6 Calculation of mean lubricant film thickness .22 6.7 Calculation of the wear path .23 6.8 Calculation of the lubricant kinematic viscosity .23 7 Efficiency and power loss. ..23 7.1 General 23 7.2 Total efficiency 24 7.2.1 Method A. 24 7.2.2 Method B 24 7.3 Total power loss. 24 7.3.1 Methods of calculation. .24 7.3.2 Idle running power loss 25 7.3.3 Bearing load power loss .25 7.3.4 Sealing power loss. 25 7.3.5 Adaptation of the calculation procedure to a specific test. .26 7.4 Gear efficiency 26 @ IS0 2020 - All rights reserved ii IS0/TS 14521:2020(E) 7.4.1 Efficiency calculation .26 7.4.2 Base coefficient of friction, μoT, of the standard reference gear 26 7.4.3 Size factor 28 7.4.4 Geometry factor 29 7.4.5 Material factor. 29 7.4.6 Roughness factor 29 7.4.7 Adaptation of the calculation procedure to a specific test 29 7.5 Meshing power loss. 30 7.5.1 Method A. 30 7.5.2 Method B. .30 7.5.3 Method C. 30 8 Wear load capacity 30 8.1 General. 30 8.2 Wear safety factor. 30 8.3 Expected wear 31 8.3.1 Method A. 31 8.3.2 Methods B, C 31 8.4 Permissible wear 35 8.5 Adaptation of the calculation procedure to a specific test. .36 9 Surface durability (pitting resistance) 36 9.1 General. 36 9.2 Pitting safety factor. 36 9.3 Actual contact stress 37 9.3.1 Method A. 37 9.3.2 Methods B, C 37 9.4 Limitingvalueofcontactstress 37 9.5 Adaptation of the calculation procedure to specific test .38 10 Deflection 38 10.1 General. 38 10.2 Deflection safety factor 39 10.3 Actual deflection. 39 10.3.1 Method A. .39 10.3.2 Method B 39 10.3.3 Method C 39 10.4 Limiting value of deflection 40 11 Tooth root strength 40 11.1 Safety factor for tooth breakage. 40 11.2 Actual tooth root stress 40 11.2.1 Method A. 40 11.2.2 Method B. 40 11.2.3 Method C 40 11.3 Limiting value of shear stress at