US2015416A - Method of making corrugated asbestos sheeting - Google Patents

Description

p 24, 1935 E. A. TQQHEY Er AL 2,015,416

METHOD OF MAKING CORRUGATED ASBESTOS SHEETING Filed Oct. 10, 1951 INVENTORS E dwardfl Toolngy. BY John 6. flew-12am ATTORNEY M; sq. 24,1935

PATENT OFFICE METHOD OF MAKING CORRUGATED ASBESTOS SHEETING Edward A. Toohey, Somerville, and John C. Kershaw, Dunellen, N. J.,

assignors to Johns-Manville Corporation, New York, N. Y., a corporation of NewYork Application October 10, 1931, Serial No. 568,036

6 Claims.

This invention relates to a shaped sheeting of felted fibers and the method of making the same. The invention pertains especially to the method of shaping, as, for example, corrugating heavy asbestos sheeting, such as millboard, by a method comprising the step of pressing the sheeting while in such condition that the surface is sufficiently dry to separate readily from the pressing member and the interior of the sheeting is sufficiently wet to yield readily under pressure.

The making of asbestos millboard in conventional manner includes distributing asbestos fibers, suitably a mixture of long and short fibers with starch in the proportion of 1 to 8% of the weight of the fibers, in a large volume of water, as in a paper beater, forming a felt continuously on a moving belt, transferring the felt continuously to a cylindrical drum, whereby a laminated felt is formed, and continuing the operation of rolling up the felt around the drum, to the desired thickness. During the rolling, the felt is compressed by an overriding steel or iron roller. When the desired thickness, as for example, three-sixteenths inch is reached, the operation is interrupted, the cylinder of felted material around the drum is slitted-longitudinally and removed from the drum. The resulting felt or millboard is then straightened and dried, as by air previously passed over steam pipes. In this manner there is formed a sheet composed of several plies of felt integrally united, each felt comprising interlocked fibers.

When it is attempted to corrugate the product, as by passage in sheet form continuously between heavy steel rolls with surfaces adapted to shape the sheet into corrugations, in accordance with the usual practice in corrugating asbestos paper, it is found that the millboard is very difiicult to shape into corrugations and that,if the millboard is bent to the desired shape, internal cracks or zones of weakness may develop. Moistening the surface, as with steam, does not solve the difficulty; if sufilcient water is added to soften the interior properly, the surface through which the water enters becomes soft enough to cause adherence to the corrugating rolls, particularly when the rolls are slightly warm. Also, moistening with water does not unlock the fibers from the form in which they were set by the previous There have now been discovered means of producing an asbestos millboard with an interior sufliciently wet to be yielding and an exterior sumciently dry to separate readily from the corrugating rolls.

In one embodiment of this invention, asbestos millboard three-thirty-seconds inch thick was made in a conventional manner from a mixture of short-fiber asbestos with 1 to 8, say 4, percent by weight of starch. As delivered from the millboard machine, the product contained 40 to 60, usually about 50, percent water by weight. It was allowed to dry at room temperature until the average water content was reduced to about 20 to 35, suitably 25, percent. This condition of 10 dryness was reached, in one instance, by drying for 12 hours at atmospheric temperature and humidity.

' The millboard partially dried, as in this manner, has a larger percentage of water in the in- 15 terior than on the surface and has (1) a surface that is not sticky or adherent to corrugating rollers and (2) an interior that is relatively wet and capable of yielding, as to corrugated shape. The material so dried is passed between heavy metal rolls, with shapes of surface adapted to produce corrugations or' corrugations and crossindentations. Rolls of the kind described in U. S. Patent No. 1,444,396 to Siegle may be used. After the shaping, the product is then thoroughly dried.-

The product is useful as a thermal insulator.

It has a degree of strength indicative of minimized internal weakness. It has practically no large internal cracks such as would result from corrugating millboard with a hard and dry center. The internal structure of the product is substantially uniformly strong, in distinction from the condition that would prevail if there were present a network of cracks, formed during the corrugating of the millboard when dry in the central portion. Also, the product has a satisfactory surface that is free from such pitting and/or scaling as would be produced by adherence of a wet, sticky surface to the corrugating rolls, with consequent pulling out of patches of material.

A specimen of corrugated cross-indented asbestos millboard is shown in plan view in Fig. 1. In this example, there are three corrugations, that is, three ridges and three depressions, to the inch. The cross-indentations are 1.5 inches apart, from center to center.

Fig. 2 is a cross sectional view along the dotted line 2-2 of Fig. 1, in the direction of the arrows. Fig. 3 is a perspective view of the'article shown in Fig. 1.

In the various figures, ridges are indicated by the numeral I, troughs by 2, and cross-indentations by 3.

Many variations from the details of the illustrative example may be made without departing from the scope of this invention. Thus, there may be substituted for the asbestos millboard other thick sheeting of asbestos or equivalent material, suitably of thickness less than onefourth inch and greater than that which may be corrugated satisfactorily when the interior is relatively dry. Also, binders other than starch may be used in the asbestossheeting, such as a modified starch, glue, or a rosin sine, although starch or a binder that is weak or yielding when wet and stiff when dry has been found to be especially desirable. Fibers other than asbestos may be present in the sheeting, as, for example, a substantial proportion of wood pulp, old newspapers, cotton, hair, and/or wool. While the mineral fiber used is suitably a mixture of asbestos fibers of relatively short length, such as mixed moderately long and short Canadian fibers, other asbestiform or mineral fibers may be used, particularly in compositions that are yielding when wet and stiff or hard when dry. There may also be used, as a base material to be shaped, thick sheets or boards of wood pulp, such as may be made by compositing and integrally uniting felts, as with a millboard machine. Pressing to other shapes than corrugations, with or without cross-indentations, may be made, as, for example, the formation of relatively deep indents.

In general, the sheeting is corrugated or otherwise shaped while the interior is moist. In a preferred practice, the sheets are kept fresh, that is, not hard pressed to other form and not allowed to dry completely before being submitted to the corrugating or other shaping of the surface to the final form.

The invention is not limited to any theory or explanation.

The action of moisture in the interior of the sheet is possibly. an important factor.

The greater susceptibility to shaping of a relatively fresh sheet, as compared to shaping of a sheet that has been set and then wetted, that is, has been pressed, as to fiat form, dried thoroughly, and then wetted, may be due in part also to the following effects: When a wet felt of asbestos fibers is firmly pressed and dried, there follows more or less interlocking and adherence of fibers. Thus, the ends of some fibers may curl partly around other fibers. Or, the fibers may be mashed together, by the firm pressing, sufficiently to give considerable interlocking and surface adherence on drying. This stiffening effect of adherence and/or interlocking of fibers is avoided by shaping a sheet to the final form desired beforecomplete drying of the sheet or setting of it in anotherform.

In pressing the thick sheet of exterior portion containing a lower proportion of water than the interior, there are developed cracks extending into the sheet from the exterior surface thereof,

whereas the inner parts remain substantially free from cracks.

What we claim is:

l. The providing of irregularities of surface of a thick sheet of composited and integrally united 5 felts by a method which includes the step of pressing to, shape a sheet of the type described that has a smaller proportion of moisture on the surface than in the interior of the sheet.

2. In making a thick sheet of irregular surface including integrally united and felted asbestos fibers, the method which comprises forming a thick sheet including asbestos fibers, water, and a binder that is relatively stiif when dry and yielding when wet, partially drying the sheet to provide an outer surface'thereof that contains a smaller proportion of water than the interior of the sheet, subjecting the partially dried sheet to a pressing operation to provide the desired irregularities of surface, and drying the pressed sheet.

3. In making corrugated millboard including asbestos fibers and starch binder, the method which comprises forming the millboard in wet form, subjecting the wet millboard to incomplete as drying to provide outer surfaces thereof containing a lower proportion of water than the interior of the millboard, subjecting the partially dried millboard to compression between corrugating rollers to corrugate it, and then drying the corrugated product.

4. In making corrugated millboard including asbestos fibers and starch hinder, the method which includes forming the millboard in wet form, subjecting the wet millboard to incomplete drying to render the outer surface thereof relatively non-adherent and to leave the interior portion in readily yielding condition, subjecting the partially dried millboard to shaping between corrugating rollers, and then drying the shaped product.

5. In making an asbestos sheet of irregular surface, the method which comprises forming a thick sheet consisting largely of felted asbestos fibers and water in the proportion of approximately 40 5'; to 60 parts by weight of water to 100 parts of the said sheet, drying the wet sheet to reduce the water content to approximately 20 to 35 parts for 100 parts of the sheet, subjecting the incompletely dried sheet to pressure between rollers of irregular surface to impart irregularities of surface to the sheet, and then drying the product.

6. The method of making a sheet of the type described which comprises forming a thick felt comprising fibers of asbestos and a binder therefor that is yielding when wet and rigid when dry, pressing the felt to provide irregularities of surface while the binder in the central portion of the felt is in yielding undried condition, and then drying the thus shaped felt. '0

EDWARD A. TOOHEY.. JOHN C. KERSHAW.

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