BS 4231:1992 pdf download.Viscosity grades of industrial liquid lubricants.
1 Scope This International Standard establishes a system of viscosity classification for industrial liquid lubricants and related fluids. This includes mineral oils used as lubricants, hydraulic fluids, electrical oils and for other applications. The usual method for kinematic-viscosity determination is that specified in ISO 3104, but this may give anomalous results when used with non-Newtonian fluids (i.e. those whose coefficient of viscosity varies significantly with rate of shear). For such fluids, it is therefore important to state the particular method by which viscosity has been determined. It is also recognized that there may be some pure chemicals and naturally occurring products, used as lubricants, which will not fall within this classification.
2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 3104:1976, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and calculation of dynamic viscosity.
3.2 Each viscosity grade is designated by the nearest whole number to its mid-point kinematic viscosity in square millimetres per second (mm 2 /s) at 40 °C, and a kinematic-viscosity range of ± 10 % of this value is permitted. The 20 viscosity grades with the limits appropriate to each are given in Table 1.
3.3 The classification is based on the principle that the mid-point kinematic viscosity of each grade should be approximately 50 % greater than that of the preceding one. The division of each decade into six equal logarithmic steps provides such a system and permits a uniform progression from decade to decade, but in order to provide simple numbers the logarithmic series has been rounded off. The maximum deviation of the mid-point viscosities from the logarithmic series is 2,2 %.
3.4 The classification implies no quality evaluation, and provides information only on the kinematic viscosity at the defining temperature of 40 °C. The kinematic viscosities at other temperatures will depend on the viscosity/temperature characteristics of the lubricants, which are usually reported as viscosity/temperature curves or stated in terms of a viscosity index (VI).
3.5 The kinematic viscosities of the same lubricants defined by this International Standard, but identified at other temperatures customarily used in some countries, are shown in Annex A. Three values of the viscosity index have been used. These data are given only for the purpose of general guidance in understanding or adoption of this International Standard.
BS 4231 pdf download.