1、C677.1/.5 : 677.022 : 620.1 : 531.71 : 001.4 DEUTSCHE NORM October 1980 Testing of textiles Determination of the length of staple fibres Terminology and general principles DIN 53 805 - Prfung von Textilien; Lngenbestimmung an Spinnfasern; Begriffe und allgemeine Grundlagen In keeping with current pr
2、actice in standards published by the International Organization for Standardization (ISO), a comma has been used throughout as the decimal marker. Introduction As a rule, the conditions applicable to the determination of fibre length vary according to the type of fibre concerned. It is thus appropri
3、ate that the methods of measuring the fibre length of, say, cotton, wool or other fibres, be individuall specified in separate standards. By contrast, the terminology relating to fibre length determination, and the sampling and evaluation procedures involved, are common to all types of fibre. It is
4、particularly necessary to provide a general introduction to the terminology, so that later clear distinctions may be drawn between the different mean lengths and frequencies obtained according to which method of determination is applied. It is thus both necessary and expedient to combine in the pres
5、ent standard a treatment of the terminology and general principles of fibre length determination, independently of the standards which deal specifically with different types of fibre. 1 Scope and field of application Apart from fineness, staple length is the most important property of a fibre that c
6、an be determined by measurable quantities in order to characterize its quality. The terminology relating to the measurement of fibre length, together with some other aspects, is common to all types of fibre, but the individual application of the various methods of measurement is often restricted to
7、particular types of fibre. Those aspects that are common to all measurements of fibre length, irrespective of the type of fibre, are dealt with in this standard, which is also appli- cable to all stages of processing of a fibre product. 2 Other standards to be observed DIN 53803 Part 1 Testing of te
8、xtiles; sampling; statistical principles of sampling by simple splitting Testing of textiles; sampling, practical procedure Statistical interpretation; measurable (continuous) characteristics DIN 53803 Part 2 DIN 53804 Part 1 3 Terminology 3.1 Length of the crimped fibre During processing the fibres
9、 of a fibre product are rendered parallel on the machines, the individual fibres being straightened lengthways. This kind of straightening of the individual fibres may also be produced by the length measuring method itself. In both cases, the straightened fibre position is the result of the individu
10、al fibres being subjected to a very light tension. The length of a straight line joining the two end points of a fibre straightened by a very light tension of this kind, produced either by the method or by the equipment, .e. the ex- tension of the fibre measured in the direction of the applied tensi
11、on (see DIN 53803 Part 2, March 1979 edition, subclause 5.2.1). is known as the length of the crimped fibre. This length is generally dependent on the particular state of processing of the fibre product and on the measurement method used. 3.2 Length of the decrimped fibre (actual length) The length
12、of the de-crimped fibre (actual length) is the length measured when a crimped fibre is drawn with a suitable tensile force, so that the crimp is removed without the fibre being stretched. 3.3 Nominal length The nominal length is a term commonly used in con- nection with man-made staple fibres, which
13、 are generally cut to the same length. The nominal length is the length specified in delivery documents. It is the rounded, theo- retical length of cut, .e. it is identical neither with the crimped length nor with the de-crimped length. Note. In the case of man-made fibres, the de-crimped length of
14、individual fibres may considerably ex- ceed the nominal length. Such fibres are designated “over-length“. The length above which fibres are considered “over-length“ depends on a variety of factors and circumstances but it is not the purpose of this standard to specify them. The proportion of over-le
15、ngth fibres is normally less than 0.01 %. 3.4 Length class In order to simplify fibre length measurements, it is customary to employ a system of classification (see also DIN 53804 Part 1). Each length class represents a determined length range. The width of such a range is the class width, the arith
16、metic mean of the two class boundaries is the class mid-point. With certain excep- Continued on pages 2 to 5 See page 6 for Explanatory notes Eeuth Verlag GmbH. Berlin 30. has exclusive sale rights for German Standards (DIN-Normen) 08.85 D f N 53 805 .Eng/. Price group Sales No. 0105 Page 2 DIN 5380
17、5 Class Designation used associated mean length frequency of the Fibre Mean length by number number frequency length of fibres or unbiased mean tions, all classes shall, for measurement purposes, be of the same width, .e. the class boundaries shall be set at equal intervals. All fibres whose length
18、is such that they fall into a particular length class shall be included in that class and treated as though their lengths are equal to the class mid-point value. The choice of class width depends on the length of the longest fibres and shall be selected so that at least ten populated classes are obt
19、ained during the measurement. 3.5 Frequency 3.5.1 Class frequency The main task involved in measuring fibre lengths is determining the distribution of the lengths of either the crimped fibres or the de-crimped fibres in the different length classes. The relative frequency with which each length clas
20、s is represented shall also be established. This class frequency, or simply frequency, indicates the ratio within the population of the fibre product under investi- gation of the fibres belonging to a particular class to the fibres of the whole population, in respect of a particular property. Accord
21、ing to the chosen terms of reference, this ratio can be determined in one of several ways which must, however, be strictly distinguished one from the other. The most important are described in subclauses 3.5.2 to 3.5.5. 3.5.2 Fibre number frequency This is based on the number of fibres. The ratio of
22、 the number of fibres in a particular length class to the total number of fibres is the fibre number frequency of this class (frequency by number of fibres); it is also known as the unbiased frequency. 3.5.3 Fibre length frequency This is based on the fibre lengtht). The ratio of the total length of
23、 the fibres of a length class to the total length of all fibres is the fibre length frequency of this class (frequency by fibre length). The more numerous and the longer the fibres of a length class are, the greater is their influence on the overall fibre length frequency. The fibre length frequency
24、 is thus also known as the length-biased frequency. Note. Instead of “biased“, it would also be correct to use “related“, which would in fact be a more accurate expression. “Biased“ has, however, become so entrenched in practice and in the literature that it was considered inexpedient to change the
25、term. See also literature references 3 and 41. (frequency by fibre cross section) (frequency by fibre number) (frequency by fibre length) 3.5.4 Fibre crow saction frequency This is based on the cross-sectional area of the fibre. The ratio of the total cross-sectional area of the fibres of a length c
26、lass to the total cross-sectional area of all fibres is the fibrecrosssection frequency of thisclass (frequency by fibre cross section); it is also known as the cross section-biased frequency. Assuming, for the sake of simplicity, that the average fibre cross section is the same for all length class
27、es, then the fibre cross section frequency can be taken as equal to the fibre number frequency. Symbol La 3.5.5 Fibre mass frequency This is based on the fibre mass. The ratio of the total mass of the fibres of a particular length class to the total mass of all fibres is the fibre mass frequency of
28、this class (frequency by fibre mass); it is also known as the mass-biased frequency. The more numerous and the longer they are, the greater their average cross section and the higher their density, the greater is the influence of the fibres of a particular length class on the overall fibre mass freq
29、uency. On the generally valid assumption that all fibres are of the same density, the fibre mass frequency may also be designated the cross section-and- length-biased frequency. Further assuming, for the sake of simplicity, that the average fibre cross section is also the same for all length classes
30、, the fibre mass frequency may be equated with the length-biased, .e. the fibre length frequency. 3.6 Mean length by fibre number, by fibre length, by fibre cross section and by fibre mass The mean length L is generally the quotient given by the sum of the products of class frequency and associated
31、mid-point value being divided by the sum of the frequen- cies. Thus the mean length will differ according to which frequency is used and shall be distinguished as shown in table 1. Table 1. (frequency by fibre maw) Fibre length frequency Mean length by fibre length or length-biased mean length Li Fi
32、brecrocs section frequency Mean length by fibre cross biased mean length section or cross section- L, Fibre mass frequency 1) Strictly, a distinction should be made as to whether the extension of the fibre, .e. the length of the crimped fibre, or the length of the de-crimped fibre is to be the defin
33、itive measurand. Thus, for example, sampling might be carried out on the basis of the extension of the fibre, .e. the length of the crimped fibre, whilst the length measurement itself is made on the de-crimped fibre. Since, in general, the ratio of the length of the crimped fibres to the length of t
34、he de-crimped fibres is virtually the same in all length classes, it is not essential to take account of this fine distinction. It would only have to be considered in cases where very little parallelization of the fibre material has taken place and the sample is not being measured on a fibre number
35、basis. Mean length by fibre mass or mass-biased mean length Lg DIN 53805 Page 3 An approximate agreement between mean length by fibre length and mean length by fibre mass may only be assumed on the basis of the same simplifying premises as were made in subclauses 3.5.4 and 3.5.5. 3.7 Mean length of
36、crimped and de-crimped fibres Just as distinctions have to be made in the case of frequencies, so the mean fibre lengths have to be distin- guished not only according to the basis used for the frequency (fibre number, fibre length etc.), but also as to whether the measurement taken is that of the cr
37、imped or of the de-crimped fibre, the former giving the mean length of the crimped fibre, the latter giving the mean length of the de-crimped fibre. An apostrophe, placed after the appropriate symbol, is used as a distinguishing mark. Thus, for example, L is the mean length of the crimped fibres by
38、fibre number; L, is the mean length of the de-crimped fibres by fibre number; and the same principle applies to Li and LI, L, and L, Li and L,. There are thus, in all, eight different mean lengths to be distinguished. Depending on the measurement method used, one of these lengths will be obtained. A
39、lthough measurement methods are generally designed to suit particular types of fibre, the particular mean langth obtained shall be stated in each case. The same applies to the frequencies and, where required, to the calculation of the coefficients of variation and the representation in the form of g
40、raphs, both as specified in DIN 53 804 Part 1. 3.8 Staple length diagram The staple length diagram is the cumulative curve ob- tained by cumulative summing of the frequencies. It is used for displaying the fibre length distribution. Starting from the class with the longest mid-point value, the lower
41、 boundary of each class is plotted as ordinate against the corresponding cumulative frequency as abscissa, and the points thus obtained are joined together to form a smooth curve. If the staple length diagram is to be drawn in step form, the class mid-point values shall be plotted as ordinates. As i
42、n the case of the mean lengths, staple length dia- grams shall be distinguished according to their reference basis (fibre number, fibre mass) and also according to whether the fibre under consideration is crimped or not, these distinctions being comprised in the designation, e.g. fibre mass staple d
43、iagram for the length of the de- crimped fibres. 3.9 Frequency diagram Instead of a staple length diagram, a frequency diagram may be used in order to show the distribution of fibre lengths more clearly. Such a diagram is obtained by plotting the class frequencies as ordinates against the class mid-
44、point values as abscissae, and then joining the points thus obtained to produce a step curve. Frequency diagrams shall also be distinguished according to the method specified above for staple length diagrams, thus a correct designation might read: fibre number fre- quency diagram for the length of t
45、he crimped fibres. 4 Sampling 4.1 General The principles of sampling are specified in DIN 53803 Part 2; the specification of conditions that are peculiar to a particular type of fibre has been left to the relevant standards dealing with the fibre length determination of that type of fibre. When samp
46、ling, particular importance shall be attached to ensuring that either a true number sample or a true length-biased sample is obtained (see DIN 53803 Part2). Note. Supplementary to the provisions of DIN 53 803 Part 2, reference may be made here to the pre- paration of fibre number samples by the stai
47、ning method, which is designed for the inspection of carded web and which takes account of the comparatively random orientation of the fibres. A detailed description of this method is given in: Wool Research, vol. 3 (see Bibliography). For example, the method often used in manual testing, of drawing
48、 tufts from a sliver by gripping the tuft be- tween thumb and index finger, gives a sample that is accurately representative neither as a number sample nor as a length-biased sample, representing instead an uncertain compromise between the two, and is thus unacceptable. If a sliver of fibres (top, o
49、r other such twistless slivers) is split by pulling the fibres apart by hand, the fibre com- position of the ends thus obtained is no longer an accurate representation of the complete sliver, and this unrepre- sentative state extends over a length equal to the length of the longest fibres in the sliver. Manual splitting of slivers is therefore not permitted. The sampling pro- cedure shall in all cases be based on the cut square method, using either a velvet board and glass plate or a needle field; the cut shall be made at a point separated from the end of the sliver by more th
