This incredibly detailed description of how to separate and measure asbestos fibers shows just how seriously the production was taken by manufactures years ago.

The book “Asbestos from Rock to Fabric” gives us an amazing insight into the now condemned world of asbestos manufacturing.

Read all about it below

The chemical and physical properties of asbestos fibres vary considerably from mine to mine, and even within the same mine, according to the geological formation of the deposits, methods of extraction, and the extent of the fiberisation.

            In the commercial production of asbestos yarns and fabrics it is often necessary to blend together asbestos fibres from different sources, and a knowledge of their properties is essential in the preparation of different types of fibres to be used in a given blend, in arranging the sequence of the operation and machines through which the fibres must ber passed, and for the development of special blends to meet specific requirements.


The length of the asbestos fibre is its most caluable property and in the case of chrysotile it varies from a fraction of an inch up to 2 or more inches. Asbestos fibres reaching manufacturers, either in crude or milled form, are composed of pure fibres, fibre bundles, dust (fibrous or granular) and particles of serpentine rock.

It is extremely difficult to grade or evaluate asbestos fibre, as, with the exception of crude fibre, it is practically impossible to measure its length. In order, however, that there may be some specification or standard applicable to the many grades of mill fibre, the various asbestos mines in Canada have adopted a standard screen test by which milled fibre is classified into its various grades.

The Quebec standard asbestos grading machine

This machine consists of 4 boxes superimposed one above the other, resting on a table which is driven by an eccentric at 327 r.p.m. (total test 600 revolutions). Shaking motion causes screening of the fibres. The bottoms of the boxes are made of brass screen with the following measurements:-

Box No. $ is a receptacle for the dust the which falls through the other boxes.

A standard weight of sample (16 oz.) is placed on tray No. 1.

The shaking motion separates the fibres according to their length.

The longest remain on the screen with the largest openings, whilst the shorter will drop down and remain on Box No. 2 or 3, and the very small will be collected by Box No. 4, the better would be the quality of the asbestos.

            Such test not only check the mine’s fibre specification, but also give useful information about the general fibre length, blending possibilities and estimation fof yield, as a greater proportion of fines collected by Box No. 4 means more drops in willeying and carding processes. Further, it will help to solve the problem of carrier fibres addition, settings of rollers, speeds, twist, etc. The usefulness of the tests could be compared with the fibre draw in worsted spinning.

Retesting of fibres after they have passed the opening stages, and comparing the results with those previously obtained will give an indication of the physical properties such as strength, flexibility, etc. It is obvious that the stronger fibres will be less reduced in length by opening processes than will the weak and brittle ones.


            Results obtained by the screen test show considerable variation.

It is a roughly accurate method of grading asbestos, and in order to get more detailed information about the length of the fibres, the Array test may be used.

It is a well known fact that the long fibres have a tendency to carry a high percentage of short fibres. Higher saturation of these small fibres causes greater carding losses. The Array Test offers th4e opportunity to determine in advance of processing the relative value of this shirt fibre saturation, whilst the Quebec method may fail to disclose them and may produce a somewhat erroneous indication of the spinning qualities. One disadvantage of the Array method is that numerous and laborious tests are necessary to obtain the approximate average lengths of the fibres.

The test is carried out by means of such devices as Suter-Webb* Duplex fibre sorter, or “Uster” type originally developed for cotton fibres, but modified for asbestos (comb, dimensions and spacing).

Table 8

Array Test

Canadian Fibre 3K. Average Length = 0.229 in.



            Among all the varieties of asbestos, only crociodolite, chrysotile** and amosite fibres possess enough strength and flexibility for processing as textile products. Regardless of the kind of raw material whether it is natural or man-made, the principle of processing remains preserve the natural virgin fibre conditions as far as possible. The separation of the fibres from the wall rock. If this process is gentle and does not produce fractures, the best result is obtained.


Living under a Cloud: Fire-Resistive Communities in the Cold War In 1950, Mill and Factory published a lavishly illustrated article called “What Is Asbestos Good For?” which listed scores of industrial applications for the mineral. The editors asserted, “Asbestos helps man and industry defy these public enemies: fire—weather—heat—acids.” The article was typical of postwar engineering literature about asbestos, for which new uses continued to be found, including valves, ductwork, and pipes of all kinds but especially those that were subject to corrosion from acids or sewage. Asbestos manufacturing flourished, more than tripling its work force between 1930 and 1970. The Occupational Outlook Handbook, published by the U.S. Bureau of Labor Statistics, asserted in 1951, “The outlook for asbestos workers [in insulation and construction] is good. This trade is employed extensively in some kinds of defense construction and is important in peacetime.” Wages, which were “in accordance with collective bargaining agreements,” ranged from $2.05 per hour in the south to $2.75 in New York City, about the same as for roofers. No unusual occupational hazards were mentioned in this or the subsequent (1957) edition of the handbook, in which government analysts predicted substantial growth in employment through the1960s “as a result of the anticipated sharp rise in the volume of construction of commercial and industrial buildings” and the increased use of industrial pipe and ductwork in the petroleum and chemical industries, refrigeration equipment, and air conditioning. At this period, asbestos was thought to be good for practically everything from dentistry to rockets. Workbasket magazine and the Spool Cotton Company, makers of J.&P. Coats yarn and thread, published patterns for colorful crocheted-lace “Hot Plate Mat Covers” to liven up the appearance of the 8½- inch round gray asbestos pads that had been available for kitchen and stove use since the end of the nineteenth century. Typically, these covers were crocheted to match the ornate potholders popular in the 1950s. According to the Science News Letter, it was possible in 1948 to buy dishtowels of an asbestos-cotton blend that would double as extinguishing blankets for kitchen fires. Schools used asbestos-containing materials for papier-mâché and modeling clay, a practice that experienced its fifteen minutes of infamy in 1983. Mining, of course, benefited from the great expansion of markets for asbestos after 1945 and the apparently insatiable worldwide demand for the mineral. In the 1930s, a nine-tiered system of grading asbestos had been developed by the Quebec Asbestos Producers’ Association, in which group  was crude asbestos with a staple (fiber) length of ¾ inch or longer and group 9 was asbestos-bearing gravel and stone. Before the 1920s, there had been few uses for any but the top two grades, then called “Crude No. 1 and 2,” and thus no need to classify the remaining products of mining with staple lengths under ⅜ inch; but as new uses, primarily in thermal and electrical insulation, began to be


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