Screen Scale for Testing Sieves

Screen Scale for Testing Sieves

Since the adoption by the U. S. Bureau of Standards several years ago of specifications for standard 100- and 200-mesh sieves, frequent requests have been received that this Bureau test and certify sieves of other sizes than these. With a view to the adoption of a series of standard testing sieves which might be of use to all industries making fineness tests, this Bureau for two years has been studying the question of such a standard screen scale. Various scales that have been proposed were considered, and information was sought of representative firms in the various industries interested as to their requirements. Manufacturers of sieves have also been consulted as to the desirability of different screen scales and the practicability of their manufacture. As a result of this study of the question, a conference was called at the Bureau of Standards, Apr. 20, 1916, of representatives of various committees of the American Society for Testing Materials, American Society of Civil Engineers, American Institute of Mining Engineers, American Foundrymen’s Association, Mining and Metallurgical Society of America, American Water Works Association, American Institute of Metals and the American Spice Trade Association; also representatives of the Committee of Revision of the U. S. Pharmacopoeia, the U. S. Geological Survey, the U. S. Bureau of Mines, the U. S. Office of Public Roads and Rural Engineering, the U. S. Office of Grain Standardization and the U. S. Bureau of Standards; also representatives of a number of private firms engaged in industries in which sieves are used, such as the glass, the drug milling, the abrasive, the asphalt, the mining, the spice, the chemical, and the graphite industries; also representatives of the firms in this country manufacturing wire cloth and sieves.

This Conference, after considering the various screen scales either proposed or now in use, adopted as a Standard Screen Scale that given in Table 1, and recommends that it be adopted generally by scientific,

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technical, and engineering societies and committees, and by branches of National, State, and Municipal Governments as a part of their specifications for materials and methods of test; also that it be used by private firms who have need of standard sieves.

This screen scale is essentially metric. The sieve having an opening of 1 mm. is the basic one, and the sieves above and below this in the series are related to it by using in general the square root of 2, or 1.4142, or the fourth root of 2, or 1.1892, as the ratio of the width of one opening to the next smaller opening. The first ratio is used for openings between 1 mm. and 8 mm. while the fourth root of 2 is used as the ratio for openings below 1 mm. to give more sieves in that part of the scale. The series has been made large enough, it is hoped, to meet the needs of all industries. Some industries may have occasion to use all the sieves in a certain section of the series and none of the others, while in other industries it may be desirable to use only certain sieves selected from the whole range of the series. In making such selections it is recommended that this be done on some systematic plan as, for example, the selection of every other sieve or of every fourth one in the series below 1 mm. opening and every other sieve above 1 mm., in which case the ratio of each opening to the next smaller one would be as 2 to 1.

Because of the wide range of openings in sieves now manufactured which are possible with a given number of meshes of wire per unit length by the use of wires of different diameters, and the consequent confusion and uncertainty which arises in designating sieves by the number of meshes per unit length, the sieves of this series have been designated by the width of the opening in millimeters as, for example, a 1.41-mm. sieve, or a 0.36-mm. sieving equipment. It is urgently recommended that all users of sieves in the future designate these standards sieves in this way and that the manufacturers mark and list the sieves in this manner rather than by the meshes per inch.

In the designation and certification of the sieves the metric units will be used by the Bureau of Standards. In Table 1, however, are also given the equivalents of these metric quantities in inches in order that the series may be more readily related to work previously done. It is, of course, immaterial whether units of the metric system, or of the customary system, or of any other system, are used in the manufacture of the sieves, provided they are within the tolerances.

To meet the need for sieves of this series at the present time, a temporary provision has been made in the specifications for the acceptance of sieves of slightly different mesh and wire diameter than that called for in the screen scale, provided the resultant opening is the same as the nominal opening within a small range. This will make possible the use of a number of sieves now on the market in which the ratio of wire diameter to opening is only slightly different from that of the screen scale. This provision will be withdrawn when conditions are such that the manufacturers of sieves can furnish sieves made more exactly in accordance with the specifications.

The Bureau of Standards hereby announces that it will test sieves of this series to determine whether they conform to specifications given below. This test will consist of the examination of the mesh of both the warp and shoot wires of the cloth to ascertain whether it comes within the tolerances allowed; also measurements of the diameter of wires in each direction to determine the average diameter, and a measurement of any large openings to ascertain whether they exceed the limits given in these specifications; also an examination of the sieve to discover any imperfections of the sieve which may seriously affect its sieving value. Sieves which pass the specifications will be stamped with the seal of this Bureau and will be given an identification number. A certificate will be furnished for each sieve that passes the requirements.

For sieves which fail to meet the specifications, reports will be rendered showing wherein the sieve was not up to the standard.

A fee of $2 per sieve will be charged for the test of the sieves when submitted singly. For from 2 to 9 sieves submitted at one time the fee will be $1.50 per sieve. For lots of 10 or more the fee will be $1 per-sieve. Only half of the above fees will be charged for such sieves as may be rejected for exceeding the tolerances of mesh, in which case the wire diameter will not be measured.

In Table 1, in the first column headed “Openings,” is given the width of the opening (on the first line in millimeters, on the second line in inches), for each sieve. In the second column, headed “Mesh,” on the first line is given the number of meshes per linear centimeter, and on the second line the equivalent number of meshes per linear inch. In the third column, headed “Wire Diam,” is given on the first line the diameter of wire in millimeters, and on the second line its equivalent in inches. In the fourth column, headed “Ratio Wire Diam. to Opening,” is given the ratio of the wire diameter to the width of the opening between wires. In the fifth and sixth columns, headed “Tolerances,” are given the tolerances for these sieves mentioned in the specifications below. These tolerances will, for testing purposes, be used essentially in the metric dimension, but on the second line in each case is given the equivalent in inches in order that the tolerances may be compared readily with those in previous use. The tolerance in the fifth column is that for the meshes per centimeter and per inch, respectively, and in the sixth column the tolerances for wire diameter in millimeters and inches, on the first and second lines respectively.

In Table 2 is given a list showing the dimensions of sieves now on the market which would most nearly meet the specifications and tolerances of the Standard Screen Scale. The headings of the columns of this table are self-explanatory. Where the dimensions of more than one sieve are shown for a given sieve of the screen scale, one set of dimensions is that of one manufacturer, and the other that of another. In some cases the third set, if one is given, is made by two or more manufacturers.

In Table 3 is given a list of sieves between 1-mm. opening and 8-mm. opening which would be interpolated in the series of the Standard Screen Scale if the fourth root of 2 or 1.1892, were used as the ratio of successive

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sieves throughout the series. Suitable meshes and wire diameters to give these openings are also given, together with the tolerances under which such sieves would be tested if used. These sieves have not been included in the Standard Screen Scale, as it is believed to be unnecessary to have so many sieves in this part of the scale. This list is given separately, however, in case any organization in selecting sieves systematically from the Standard Screen Scale in the series of openings less than 1 mm. finds it desirable to use any of these interpolated sieves above 1 mm. in carrying out a systematic plan of selection of sieves. In case any organization or firm should adopt any of these six sieves under such circumstances, the Bureau of Standards will test and certify them in accordance with the dimensions given herewith.

standard screen scale additional sieves

In Table 4 is given an extension of the metric series beyond the 8-mm. opening using the square root of 2, or 1.4142, as the ratio of successive openings. A suggested diameter of wire for use in making such sieves is also given. No tolerances for these sieves are given, however, as it is not proposed to test such sieves at the Bureau of Standards, since the user of the sieves could ordinarily make such tests of them as are necessary with sufficient accuracy. Such sieves would generally be made up into sieves of larger diameter than those of the Standard Screen Scale and would usually be made of iron or steel wire.

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In the specifications given below the diameter or other dimensions of the sieve frames are not given, with the idea that any organization or firm in adopting these specifications will decide upon the size of sieve frame that best meets its needs. For purposes of uniformity and interchangeability of sieves, pans, and covers, it is recommended that sieves be purchased in diameters of either 20 cm., 15 cm., or 10 cm. (7.87 in., 5.91 in., or 3.94 in.). These are the outside diameters of the bottom of the sieve or the inside diameter of the top of the sieve.

Specifications for Sieves of the Standard Screen Scale

Wire cloth for standard sieves shall be woven (not twilled, except that the cloth of 0.062-mm., the 0.052-mm., and the 0.044-mm. sieve, may be twilled until further notice), from brass, bronze, or other suitable wire and mounted on the frames without distortion. To prevent the material being sieved from catching in the joint between the cloth and the frame, the joint shall be smoothly filled with solder, or so made that the material will not catch.

The number of wires per centimeter of the cloth of any given sieve of the Standard Screen Scale shall be that shown in the accompanying Table 1 in the second column, headed “Mesh,” and the number of wires in any whole centimeter shall not differ from this amount by more than the tolerance given in the 5th column, that headed “Mesh” under the heading “Tolerances.” No opening between adjacent parallel wires shall be greater than the nominal width of opening for that sieve by more than the following amounts:

10 per cent, of the nominal width of opening for the 8-mm. to 1-mm. sieve, inclusive.
25 per cent, of the nominal width of opening for the 0.85-mm. to the 0.29-mm. sieve, inclusive.
40 per cent, of the nominal width of opening for the 0.25-mm. to the 0.125-mm. sieve, inclusive.
60 per cent, of the nominal width of opening for the 0.105-mm. to the 0.044-mm. sieve, inclusive.

The diameters of the wires of the cloth of any given sieve shall be that shown in the third column of Table 1 headed “ Wire Diam.” and the average diameter of the wires in either direction shall not differ from the specified diameter by more than the tolerance given in the last column of Table 1, that under “Tolerances” headed “Diam.”

The Bureau of Standards also reserves the right to reject sieves for obvious imperfections in the sieve cloth or its mounting, as, for example, punctured, loose or wavy cloth, imperfections in soldering, etc.

Until, further notice, to permit the use of sieves now on the market which have slightly different mesh and wire diameters from that specified above, sieves will be certified as satisfactory if the measurements of mesh and wire diameters show the resulting average width of opening to be within 4 per cent, of the nominal opening of a given sieve, and the ratio of wire diameter to opening of the sieve in question is within 0.03 of that given in Table 1 in the column headed “Ratio Wire Diam. to Opening” for the 8-mm. to the 2-mm. sieves, inclusive, and within 0.06 of the ratio given for sieves of smaller openings than 2 mm.