SIST-TP ISO/TR 18792:2009

TECHNICAL ISO/TR
REPORT 18792
First edition
2008-12-15
Lubrication of industrial gear drives
Lubrification des entraînements par engrenages industriels

Reference number
©
ISO 2008
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ii © ISO 2008 – All rights reserved

Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Terms and definitions. 1
3 Basics of gear lubrication and failure modes.3
3.1 Tribo-technical parameters of gears. 3
3.2 Gear lubricants. 5
3.3 Base fluid components . 6
3.4 Thickeners . 8
3.5 Chemical properties of additives . 9
3.6 Solid lubricants . 10
3.7 Friction and temperature . 10
3.8 Lubricating regime. 11
3.9 Lubricant influence on gear failure. 11
4 Test methods for lubricants . 15
4.1 Gear tests . 15
4.2 Other functional tests. 16
5 Lubricant viscosity selection . 19
5.1 Guideline for lubricant selection for parallel and bevel gears (not hypoid). 19
5.2 Guideline for lubricant selection for worm gears. 24
5.3 Guideline for lubricant selection for open girth gears. 24
6 Lubrication principles for gear units . 26
6.1 Enclosed gear units. 27
6.2 Open gearing. 34
7 Gearbox service information . 39
7.1 Initial lubricant fill and initial lubricant change period . 39
7.2 Subsequent lubricant change interval. 39
7.3 Recommendations for best practice for lubricant changes. 40
7.4 Used gear lubricant sample analysis. 41
Bibliography . 52
Figures
Figure 1 — Load and speed distribution along the path of contact. 4
Figure 2 — Scraping edge at the ingoing mesh . 5
Figure 3 — Schematic diagram of shear effects on thickeners. 9
Figure 4 — Mechanisms of surface protection for oils with additives. 11
Figure 5 — Examples of gear oil wear test results. 15
Figure 6 — Immersion of gear wheels . 27
Figure 7 — Immersion depth for different inclinations of the gearbox. 29
Figure 8 — Immersion of gear wheels in a multistage gearbox . 30
Figure 9 — Examples of circuit design, combination of filtration and cooling systems . 34
Figure 10 — Immersion lubrication. 37
Figure 11 — Transfer lubrication. 37
Figure 12 — Circulation lubrication . 38
Figure 13 — Automatic spraying lubrication . 38
Tables
Table 1 — Symbols, indices and units. 1
Table 1 (continued) . 2
Table 2 — General characteristics of base fluids. 6
Table 3 — Example of influence factors on wear . 12
Table 4 — Example of influence factors on scuffing load (transmittable torque). 13
Table 5 — Example of influence factors on micropitting (transmittable torque) . 14
Table 6 — Example of influence factors on pitting (transmittable torque) . 14
1)
Table 7 — ISO Viscosity grade at bulk oil operating temperature for oils having a viscosity
2)
index of 90 . 20
1)
Table 8 — ISO Viscosity grade at bulk oil operating temperature for oils having a viscosity
2)
index of 120 . 21
1)
Table 9 — ISO Viscosity grade at bulk oil operating temperature for oils having a viscosity
2)
index of 160 . 22
1)
Table 10 — ISO Viscosity grade at bulk oil operating temperature for oils having a viscosity
2)
index of 240 . 23
Table 11 — ISO viscosity grade guidelines for enclosed cylindrical worm gear drives . 24
Table 12 — Advantages and disadvantages of various open girth gears lubricants . 25
Table 13 — Minimum Viscosity recommendation for continuous lubrication [mm /s at 40 °C]. 26
Table 14 — Minimum base oil viscosity recommendation for intermittent lubrication [mm /s at
40 °C] . 26
Table 15 — Typical maximum oil flow velocities. 33
Table 16 — Advantages and disadvantages of greases .35
Table 17 — Advantages and disadvantages of oils. 35
Table 18 — Advantages and disadvantages of lubricating compounds. 36
Table 19 — Lubrication system selection based on pitch line velocity . 39
Table 20 — Lubrication system selection based on the type of lubricant. 39
Table 21 — Typical recommended lubricant service . 40
Table 22 — Examples for an on-line oil condition-monitoring system . 40
Table 23 — Sources of metallic elements . 47
Table 24 — What the ISO codes mean. 49
Table 25 — Example of particle size and counts. 49
Table 26 — Characteristics of particles. 51

iv © ISO 2008 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 18792 was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 2, Gear capacity
calculation.
Introduction
Gear lubrication is important in all types of gear applications. Through adequate lubrication, gear design and
selection of gear lubricant, the gear life can be extended and the gearbox efficiency improved. In order to
focus on the available knowledge of gear lubrication, ISO/TC 60 decided to produce this Technical Report
combining primary information about the design and use of lubricants for gearboxes.

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