BS 4231:1992 download free.CI assoication for Viscosity grades ofbindustrial liquid lubricants.
Introduction
BS 4231 has been prepared to meet the immediate needs of those ISO Technical Committees that promulgate International
1 Standards for equipment and need to refer to lubricants, i.e. TC 39, Machines tools;TC 123, Plain bearings; TC 131, Fluid power systems; and others, by providing a classification of liquid lubricants according to viscosity grades. The purpose of this classification system is to establish a series of definite kinematic-viscosity levels so that lubricant suppliers, lubricant users and equipment designers will have a uniform and common basis for designating or selecting industrial liquid lubricants according to the kinematic viscosity required in a particular application.
When the first edition of BS 4231 was being prepared, systems for classifying the viscosity characteristics of industrial liquid lubricants were simultaneously under study by the American Society for Testing and Materials (ASTM) in collaboration with the Society of Tribologists and Lubrication Engineers (STLE) (ASTM D 2422—68), by the British Standards Institution (BSI) (BS 4231) and by the Deutsches Institut für Normung (DIN). The cooperative effort first resulted in this ISO classification in 1975. It is desirable that any such classification system should cover the entire range of kinematic viscosities of liquid lubricants normally used: at the same time, the number of kinematic-viscosity grades within the classification should be limited. A continuous system, in which any lubricant within the viscosity range could be given a grade number, was first considered, but it was recognized that this would involve either an unduly large number of grades or an unduly wide range of permitted kinematic viscosities for each grade.
For the classification to be of direct use in engineering design calculations, in which the kinematic viscosity of the lubricant is only one of the parameters, it is desirable that the viscosity grade width be not more than 10% on either side of the nominal value. This would reflect an order of uncertainty in calculation similar to that imposed by dimensional manufacturing tolerances. This limitation, coupled with the requirement that the number of viscosity grades should not be too large, has led to the adoption of a discontinuous system with gaps between the viscosity grades.
The reference temperature for the classification should be selected to be reasonably close to average service experience. It should also closely relate to other selected temperatures used to define properties such as viscosity index which can aid in defining a lubricant. A study of a series of possible temperatures indicates that 40 °C is particularly suitable for the purposes of industrial-lubricant classification as well as for the lubricant-definition properties mentioned above. This viscosity classification is consequently based on kinematic viscosity at 40 °C.
The viscosity designations are identical to those in the well-known ASTM/STLE and BSI classifications previously mentioned.
Although this ISO classification is bound to lead to a number of existing lubricants (possibly including some at present widely used) not being accommodated within the classification, there is nothing to prevent the continued use of such products by agreement between supplier and consumer. The kinematic viscosities of such out-of-classification oils should, however, be determined at 40 °C. It is expected, however, that lubricant producers will move towards the adjustment of their products so that each product will fall within one of the viscosity grade designations; that users will, in the interests of rationalization and the reduction of the number of oils which they use, call increasingly for lubricants covered by the classification; and that machine and equipment manufacturers and their component suppliers will take due note of the classification in the design stages and in their lubricant viscosity recommendations.
It is not expected that liquid lubricants of every quality, or those designed for very specific purposes, will be, or will need to be, available within every viscosity grade of BS 4231.
NOTE 1 The Society of Automative Engineers USA) established many years ago standards for identifying and/or classifying the viscosity characteristics of lubricants used in automotive engines or gears. Their systems, which are widely known and used in most countries of the world. are based on the measurement of kinematic viscosity at temperatures that are considered to represent the normal operating range: the nomenclature used is for example SAE lOW, 20W and 20, 30. etc.. for engine oils (SAE .J 300) and SAE 75W, 80W, 90. 140, etc., for gear oils (SAE J 306). It should be noted that this ISO classification for industrial liquid lubricants is not intended to replace either of the SAE systems; on the other hand, the latter systems, while they have desirable features for automotive lubricants are not suitable for extension to industrial lubricants in general.
1 Scope
BS 4231 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 BS 4231. 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 3 104:1976, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and calculation of dynamic viscosity.
3 Classification
3.1 The classification defines 20 viscosity grades in the range 2 mm2/s to 3 200 mm2/s at 40 °C. This covers, as far as petroleum-based liquids are concerned, approximately the range from kerosine to cylinder oils.
3.2 Each viscosity grade is designated by the nearest whole number to its mid-point kinematic viscosity in square millimetres per second (mm2ls) 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.
4 Designation
The following wording shall be used to designate a particular viscosity grade:
ISO viscosity grade … (ISO 3448)
which may be abbreviated to:
ISOVG…