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BSI PD ISO/TS 14521:2020

$215.11

Gears. Calculation of load capacity of worm gears

Published By Publication Date Number of Pages
BSI 2020 100
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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.

PDF Catalog

PDF Pages PDF Title
2 undefined
8 Foreword
9 Introduction
11 1 Scope
2 Normative references
3 Terms, definitions and symbols
3.1 Terms and definitions
12 3.2 Symbols
17 4 General consideration
4.1 Worm gear load capacity rating criteria
18 4.2 Basis of the method
4.3 Concept of absolute and relative parameters
19 4.4 Applicability
20 4.5 Validity
21 4.6 System considerations
4.7 Calculation methods A, B, C
4.7.1 Generality on methods A, B and C
22 4.7.2 Notes on numerical formulae
4.7.3 Base conditions, interaction
23 4.7.4 Other notes
4.8 Standard reference gear
5 Required date for calculation
5.1 Input variable
25 5.2 Safety factors
6 Forces, speeds and parameters for the calculation of stresses
6.1 General
6.2 Tooth forces
6.2.1 Application factor
6.2.2 Dynamic factor
6.2.3 Load distribution factor
26 6.2.4 Tooth force components
27 6.3 Sliding velocity at reference diameter
6.4 Physical parameters
6.4.1 Generality on physical parameters
28 6.4.2 Parameter for the mean Hertzian stress
29 6.4.3 Parameter for the mean lubricant film thickness
30 6.4.4 Parameter for the mean sliding path
31 6.5 Calculation of mean contact stress
32 6.6 Calculation of mean lubricant film thickness
33 6.7 Calculation of the wear path
6.8 Calculation of the lubricant kinematic viscosity
7 Efficiency and power loss
7.1 General
34 7.2 Total efficiency
7.2.1 Method A
7.2.2 Method B
7.3 Total power loss
7.3.1 Methods of calculation
35 7.3.2 Idle running power loss
7.3.3 Bearing load power loss
7.3.4 Sealing power loss
36 7.3.5 Adaptation of the calculation procedure to a specific test
7.4 Gear efficiency
7.4.1 Efficiency calculation
7.4.2 Base coefficient of friction, µOT, of the standard reference gear
38 7.4.3 Size factor
39 7.4.4 Geometry factor
7.4.5 Material factor
7.4.6 Roughness factor
7.4.7 Adaptation of the calculation procedure to a specific test
40 7.5 Meshing power loss
7.5.1 Method A
7.5.2 Method B
7.5.3 Method C
8 Wear load capacity
8.1 General
8.2 Wear safety factor
41 8.3 Expected wear
8.3.1 Method A
8.3.2 Methods B, C
45 8.4 Permissible wear
46 8.5 Adaptation of the calculation procedure to a specific test
9 Surface durability (pitting resistance)
9.1 General
9.2 Pitting safety factor
47 9.3 Actual contact stress
9.3.1 Method A
9.3.2 Methods B, C
9.4 Limiting value of contact stress
48 9.5 Adaptation of the calculation procedure to specific test
10 Deflection
10.1 General
49 10.2 Deflection safety factor
10.3 Actual deflection
10.3.1 Method A
10.3.2 Method B
10.3.3 Method C
50 10.4 Limiting value of deflection
11 Tooth root strength
11.1 Safety factor for tooth breakage
11.2 Actual tooth root stress
11.2.1 Method A
11.2.2 Method B
11.2.3 Method C
52 11.3 Limiting value of shear stress at tooth root
11.3.1 General
11.3.2 Shear endurance limit, τF lim T
11.3.3 Life factor, YNL
54 11.4 Adaptation of the calculation procedure to a specific test
12 Temperature safety factor
12.1 Temperature safety factor for splash lubrication
12.1.1 General
55 12.1.2 Determination of oil sump temperature
56 12.1.3 Limiting values
12.2 Temperature safety factor for oil spray lubrication
12.2.1 General
12.2.2 Cooling capacity PK
57 13 Determination of the wheel bulk temperature
13.1 Wheel bulk temperature with splash lubrication
13.1.1 General
58 13.1.2 Method A
13.1.3 Method B
13.1.4 Method C
13.2 Wheel bulk temperature with spray lubrication
13.2.1 General
13.2.2 Method A
13.2.3 Method B
59 13.2.4 Method C
60 Annex A (informative) Notes on physical parameters
61 Annex B (normative) Methods for the determination of the parameters
66 Annex C (normative) Lubricant film thickness according to the Elasto Hydrodynamic Lubrication (EHL) theory
68 Annex D (normative) Wear path definition
71 Annex E (informative) Notes on calculation wear
72 Annex F (informative) Notes on tooth root strength
73 Annex G (informative) Adaptation of formulae for the reference gear with results from testing
76 Annex H (informative) Life time estimation for worm gears with a high risk of pitting damage
78 Annex I (informative) Examples
94 Annex J (informative) Examples of limit load capacity in a range of working conditions
97 Bibliography
BSI PD ISO/TS 14521:2020
$215.11