BS-3406-1-1986.pdf

BRITISH STANDARD BS 3406-1: 1986 Methods for Determination of particle size distribution Part 1: Guide to powder sampling UDC 620.168.36:620.113-492.2 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 This British Standard, having been prepared under the direction of the General Mechanical Engineering Standards Committee, was published under the authority of the Board of BSI and comes into effect on 31 October 1986 © BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference GME/29 Draft for comment 83/79599 DC ISBN 0 580 15305 3 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the General Mechanical Engineering Standards Committee (GME/-) to Technical Committee GME/29 upon which the following bodies were represented: BCIRA British Aggregate Construction Materials Industries British Ceramic Society British Laboratory Ware Association Cement and Concrete Association Cement Makers Federation Coated Abrasives Manufacturers Association Department of Trade and Industry (Warren Spring Laboratory) Department of Transport (Highways) Guild of Metal Perforators Incorporated National Association of British and Irish Millers Institution of Chemical Engineers Institution of Mining and Metallurgy Mechanical Handling Engineers Association Ministry of Defence National Coal Board Society of Chemical Industry Society of Cosmetic Scientists Woven Wire Association The following bodies were also represented in the drafting of the standard, through subcommittees and panels: AERE Harwell Aluminium Federation British Steel Industry (Wire Section) China Clay Association Department of Trade and Industry (National Physical Laboratory) Pharmaceutical Society of Great Britain Royal Society of Chemistry Sunderland Polytechnic (Magnet Centre) University of Bradford University of Technology, Loughborough Wellcome Federation Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 © BSI 09-1999i Contents Page Committees responsibleInside front cover Forewordiii Section 1. General 0Introduction1 1Scope1 2Definitions1 Section 2. Collection of gross and laboratory samples 3Guidelines3 4Sampling strategy3 Section 3. Selection of a sampling method for subdivision of the laboratory sample 5General5 6Homogeneity5 7Flow characteristics5 8Preliminary examination and precautions6 9Quantity of material to be sampled7 10Sampling efficiency8 Section 4. Methods for subdivision of the laboratory sample 11Scoop sampling9 12Coning and quartering9 13Chute riffling10 14Rotary sampling12 Section 5. Methods for the preparation of very small test portions 15General16 16Suspension sampling16 17Paste sampling16 18Sampling for microscopic analysis17 Appendix A Comparative sampling efficiencies19 Appendix B Relationship between minimum sample mass and mass fraction of coarsest size24 Appendix C Bibliography25 Figure 1 Sampling strategies4 Figure 2 Coning and quartering process10 Figure 3 Chute riffler11 Figure 4 Whole stream sampling12 Figure 5 Whole stream rotary sample divider type 113 Figure 6 Whole stream rotary sample divider type 214 Figure 7 Divided stream sampling14 Figure 8 Divided stream rotary sample divider14 Figure 9 Suspension sampler18 Figure 10 Minimum sample mass as function of mass-fraction of largest-size class in a well-mixed bulk material and required precision24 Table 1 Relative efficiencies of sampling methods for free flowing powders21 Table 2 Powder sampling methods: variation of subsample masses21 Table 3 Relative efficiencies of powder sampling methods: subsample composition22 Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 ii © BSI 09-1999 Page Table 4 Relative efficiencies of powder sampling methods: subsample mass23 Table 5 Comparison of sampling methods to obtain small test portions23 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 © BSI 09-1999iii Foreword This Part of BS 3406, prepared under the direction of the General Mechanical Engineering Standards Committee, supersedes BS 3406-1:1961 which is withdrawn. This revision is Part 1 of a series in which the other Parts describe recommended methods for determining particle size distribution. This Part of BS 3406 is based on sampling methods which have come into more widespread use since BS 3406-1 was published in 1961. Current and proposed Parts of BS 3406 are as follows: Part 1: Guide to powder sampling; Part 2: Recommendations for gravitational liquid sedimentation methods for powders and suspensions; Part 3: Air elutriation methods; Part 4: Optical microscope method; Part 5: Recommendations for electrical sensing zone method (the Coulter principle); Part 6: Recommendations for centrifugal liquid sedimentation methods for powders and suspensions; Part 7: Recommendations for single particle light interaction methods1). Differences between this revision and the original BS 3406-1:1961 include: a) the introduction of: 1) the scoop sampling method; 2) the chute riffling method; 3) further rotary sampling methods; 4) methods for preparing small (0.5 mL) test portions; 5) more comprehensive guidelines on collection of the gross sample; 6) additional comments on precautions; 7) clauses on preliminary examination and selection of methods; 8) sampling efficiency data; b) the deletion of: 1) the halving method; 2) the turntable type method; 3) the oscillating hopper type method; 4) the grid type method. Representative sampling of particulate material is an essential prerequisite for the determination of size distribution. The procedures described in this Part of BS 3406 have been selected to provide a test portion as representative of the laboratory sample as is possible. Guidelines on procedures for obtaining the gross and laboratory samples are also included. This Part of BS 3406 is intended to be a practical guide to the representative subdivision of the laboratory sample. Other related British Standards, some of which include more theoretical detail, are BS 1017, BS 5309, BS 5660, BS 5661, BS 5662, BS 6000, BS 6001 and BS 6002. NOTE OF CAUTIONSome of these standards include a particle size reduction step in the sampling process, e.g. in the preparation of the sample for general analysis and for total moisture determination in BS 1017 and in BS 5309. This step should obviously be omitted when preparing samples for particle size distribution analysis. BS 3406-1 is also of relevance to BS 1796 and to BS 4359. 1) In preparation Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 iv © BSI 09-1999 A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 26, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 © BSI 09-19991 Section 1. General 0 Introduction There are a number of stages in the application of sampling techniques to powders. A gross sample is taken from a defined quantity of material. This sample is either one in a series of spot samples required to measure, for example, variability of the material through its bulk or is meant to be fully representative of the bulk material sampled. In some cases the gross sample is inconveniently large to send to the laboratory for testing and has to be reduced in quantity. This sample reduction should produce a laboratory sample which is fully representative of the gross sample. When this reduction is unnecessary, the gross sample is the laboratory sample. The laboratory sample is often required for a number of different tests of which particle size distribution analysis is only one, and it is therefore sometimes necessary to reduce the quantity of the laboratory sample to provide a test sample which is fully representative of the laboratory sample. Finally, the quantity of sample which is used in its entirety for the appropriate test or observation, the test portion, has to be obtained by reduction of the test sample and should be fully representative of the test sample and thus of the original gross sample. In some cases the test portion is obtained directly from the laboratory sample. In many cases the analyst making the particle size distribution measurement is presented with a laboratory sample from which the test portion(s) will eventually be obtained, and has no control over the taking of the gross or laboratory samples. Whilst this Part of BS 3406 is primarily written to recommend methods for the reduction of laboratory samples to a quantity suitable for a particle size distribution analysis, the analyst should be aware of the possible errors caused by inadequate gross and laboratory samples. Some guidelines and strategy for the collection of gross and laboratory samples are given in section 2 and they should be considered when assessing the adequacy of such samples. Methods of sample subdivision described in this Part of BS 3406 range from the relatively simple and inexpensive scoop sampling through coning and quartering, and chute riffling, to divided stream and whole stream rotary sampling. 1 Scope This Part of BS 3406 provides guidance on powder sampling. It recommends methods for the subdivision of gross or laboratory powder samples into test portions suitable for analysis by methods for the determination of the particle size distribution described in other Parts of BS 3406 and for particle characterization analyses described in other British Standards. Ways of obtaining very small test portions are described. This Part of BS 3406 indicates points to look for in a preliminary examination of the sample to assist in the selection of the most appropriate method to subdivide the powder in question. Factors affecting this selection are considered and recommendations made to ensure that the integrity of the sample is maintained throughout the subdivision process. Appendix A gives the results of investigations by several workers into the relative efficiencies of the sample dividing methods. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purpose of this Part of BS 3406, the definitions given in BS 2955 apply together with the following. 2.1 gross sample the sample obtained or prepared from the bulk material under the sampling plan from which subdivision for testing, reference or storage can be made 2.2 laboratory sample the sample delivered to the laboratory 2.3 spot sample a sample of specified quantity taken from a specified place in the bulk material, gross sample or laboratory sample, or at a specified place and time in a stream and representative of its own local environment 2.4 test sample the sample prepared from the laboratory sample from which the test portions are withdrawn Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 2 © BSI 09-1999 2.5 test portion the portion withdrawn from the test sample and entirely used in the test or observation 2.6 heterogeneous material material in which a spot sample will have a significantly different value of the characteristic under consideration from the mean value of the characteristic for the whole material 2.7 homogeneous material material in which a spot sample will not have a significantly different value of the characteristic under consideration from the mean value of the characteristic for the whole material Licensed Copy: sheffieldun sheffieldun, na, Wed Nov 29 03:46:58 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 3406-1:1986 © BSI 09-19993 Section 2. Collection of gross and laboratory samples 3 Guidelines The purpose of sampling is to obtain a sample or samples of the bulk material which is representative of that material in some particular property. To ensure accuracy, the sampling operation has to be free of systematic errors; for precision, the random errors should have small variation about the mean. A suitable theoretical model for the sampling operation is that in which the particles forming the sample have been chosen one by one and at random from a homogeneously distributed bulk. A well-designed sampling procedure is one in which both theoretical and practical errors arising from differences between the sampling operation and the model have been minimized. Generally the size of sample to be taken will be given in a specification or determined by the requirements of any subsequent analysis. However, there is a minimum size of sample which needs to be taken, due to the discrete nature of the material, even if all other errors are zero. This arises because even in a well-mixed material the various particle sizes will not be uniformly distributed throughout the bulk. The coarsest size class will, generally, contain the fewest particles and consequently will have the greatest coefficient of variation. A sample mass which gives the required precision for the coarsest size class will then satisfy the requirements of the other classes. See Appendix B for a graphical relationship between the minimum sample mass and the mass fraction of the coarsest size class and the required precision. For example, for powders with a largest size class of about 1 mm and material density of 2.5 g/cm3, a minimum sample of 4.4 g would be required if the largest size class formed 3 % (m/m)2) of the bulk and was to be determined with a coefficient of variation of 0.1. The corresponding figure for a largest size class of 100 4m would be 4.4 mg. For finer powders any practical sample mass would be adequate. Since the bulk material will rarely be homogeneous in the characteristics to be tested, it is often required that a measurement of this variability be made. It is then necessary to take several spot samples, the number and size of which will depend on the quantity and particle characteristics of the material. The variability can be assessed by the variance or by the range of the characteristic, derived from these spot samples. The mean value of the characteristic is an estimate of the mean value