US2047136A - Fabrication of leather boards and thinner leather sheets - Google Patents

Description

y 7, 1936- w. T. DOYLE 2,Q47,136y

FABRICATION OF LEATHER BOARDS AND THINNER LEATHER SHEETS Filed Oct. 24, 1935 Patented July 7, 1936 FABRICATION F LEATHER BOARDS AND THINNER LEATHER SHEETS William T. Doyle, Boston, Mass, assignor to Sturtevant Mill Company, Boston, Mass., a corporation of Massachusetts Application October 24, 1935, Serial No. 46,511

4 Claims. (01. 9220) The present invention relates to the fabrication on papermaking machines of leather boards and thinner leather sheets from all sorts of leather scrap. While not restricted thereto, the

5 present invention deals more particularly with the use in the fabrication of leather boards and thinner leather sheets of tanned leather scrap, such as results from the cutting of outsoles, insoles, heels, and other shoe parts from suitably tanned hides or skins.

In making leather board, it is sometimes the practice to beat tanned leather scrap in the presence of water in the usual hollander or beater engine to the stage where the scrap has been resolved into a fibrous suspension or stock capable of being formed on a so-called wet or cylinder machine into a substantially uniformly textured sheet of substantial thickness. It is possible to form a sheet or board of the desired thickness on a cylinder machine by virtue of the fact that the ultimate sheet is composed of a plurality of integrated thin plies, such sheet being produced by picking up a comparatively thin web or ply deposited on the cylinder mold by a transfer felt serving to carry it to a so-called make-up or wind-up roll whereon the web is convoluted into a tube of the desired wall thickness, slitting the tube wall longitudinally into a sheet, and removing and drying the sheet. In other instances, the practice may be to form the sheet on a multi-cylinder machine whose transfer felt serves to pick up a plurality of thin webs or plies in superposed relation from a number of independent cylinder molds and to. carry' the plied webs to a drier which progressively delivers the dried sheet or board. It has, however, heretofore been impractical to produce leather board of the desired quality on a so-called Fourdrinier machine; and this impracticality arises from the fact that one cannot felt the beaten leather fibers into a board of satisfactory strength or texture as a unitary thick layer, as must be done on a Fourdrinier machine. Moreover, all such prior art practices as involve the reduction of leather scrap to a feltable fibrous condition in the presence of water in a beater engine suffer from the drawback that the time of beating is excessive and, accordingly, that the capital investment for beater engines enabling a given leather board output is high.

Attempts have heretofore been'made to dispense to a large extent with beater engines in i the production of leather board by comminuting or shredding the leather scrap in dry condition preparatory to admixing the shredded leather stock or leather fiber with water and delivering the aqueous stock suspension to a board-making machine. However, such practice has been seriously faulty in the respect that the dry-shredding of leather as heretofore performed has been at- 5 tended by excessive reduction of the leather fiber, insomuch that the dry-shredded stock, like beaten leather scrap, could not be formed into a satisfactory board on a Fourdrinier machine unless such shredded stock was admixed with 10 a large proportion of cellulosic or papermaking fibers of the character vof rope, rags, wood pulp, etc. Again, by reason of the high content of extremely fine or short leather fibers in the dryshredded leather stock, as heretofore produced, 15 much of such fiber was lost in the water removed in the sheeting or board-forming operation so that when a particular percentage of cellulosic fiber was admixed with the shredded leather scrap in an effort to realize satisfactory board formation, it was found the resulting board had an even higher percentage of cellulosic fiber than that used in the board-making furnish. Indeed, many commercial leather boards as heretofore made contained as high as three times as much cellulosic fiber as leather fiber, in consequence of which the boards were hardly possessed of those qualities valued in a substantially allleather board. It might be remarked that a substantially all-leather board is frequently desired for shoe-making and other purposes and that such board may be impregnated with various binders to yield an impregnated product not only of high toughness, flexibility, water-resiliency, durability, and other original leather-like quali- 35 ties but closely imitative of the feel and appearance of original leather.

A prime objective of the present invention is to make possible an economical production from tanned leather scrap of substantially all-leather 40 boards of high quality and more especially boards of such porosity or absorptivity as to be capable of being readily andvuniformly impregnated with various binders imparting thereto many of the important original leather-like qualities already 45 mentioned. Another objective of the present invention is to enable the production of such boards on Fourdrinier machines with minimum loss of leather fiber, with little or no beating of the scrap, and with the realization from the scrap 50 of leather fibers of such length as to ensure a finished board of excellent texture or formation and strength.

In accordance with ,the present invention, tanned leather scrap, such as sole scrap, is initially put through a hammer-mill under conditions to comminute the scrap into stock containing a filamentary fibrous portion characterized by its excellent feltability on a paper-making machine and a coarse portion characterized by its unfitness or inutility for board formation. In order to accomplish this objective, the discharge openings in the hammermill casing must be rather sizable, for instance, be in the form of slots about one inch long and one-quarter inch wide extending peripherally of the casing. By using such a hammermill, it is, to be sure, the case that a substantialfraction of the scrap is imperfectly reduced for board-making purposes, but the preponderant proportion of the scrap is resolved into long-fibered or filamentary stock well suited for board formation even on a Fourdrinier machine. attempt is made to reduce the scrap substantially uniformly for board-making purpose in a hammermill by providing the mill with small discharge openings, for instance, round openings of one-eighth inch diameter, the resulting stock as a whole is so short-fibered as to lead to the already-mentioned difiiculties. Because such attempt involves keeping a given input of scrap in the hammermill for a comparatively long period before the sub-division thereof requisite for discharge has been effected, it is attended by danger of scorching and injuring the leather fibers; and as a result of the repeated impacts of the hammers thereon, the fragments tend to acquire such a high density or case-hardened condition that they absorb slowly the aqueous medium with which they are subsequently mixed and hence tend to float, unless beaten and opened up further with attendant further undesirable reduction in fiber length.

Once leather scrap has undergone initial nonuniform reduction in a hammermill in accordance with the present invention, it is subjected to an air-classifying or separatory action that segregates the feltable filamentary fraction from the comparatively coarse, heavier, inutile fraction, which latter fraction may be returned to the hammermill for re-working. The separated useful fraction is then admixed with water to produce an aqueous stock suspension which is delivered to the board-making machine, for instance, a Four-' drinier machine. If desired, such admixture of the satisfactory stock fraction with water may be performed in the usual beater engine, which may be operated essentially as a mixer and hence with virtually no reduction in the fiber length of such stock. It might be noted that the period of mixing in the beater engine need be very short, as such stock contains very little coarse material and it tends to absorb water and to become uniformly suspended therein.

It is thus seen that aside from making possible the realization of substantially all-leather boards of excellent quality, the practice of the present invention is highly economical, since the output of the hammermill used according to such practice is large and the time required for mixing the airseparated satisfactory stock fraction with water in the beater engine is very short.

In the accompanying drawing, I have depicted somewhat schematically instrumentalities that may be employed in the practice of the present invention. Referring now to the drawing, the numeral l0 therein indicates a hammermill of the usual rotary type equipped with swingably mounted hammers 9 adapted to strike repeated blows against, and abrade, leather scrap fed into I have determined that when the mill so as to cause its disintegration or comminution. As already indicated, the hammermill casing 8 may be provided with closely spaced discharge slots 1 extending peripherally of the casing, for instance, over an zone of the casing periphery, and of, say, about one inch length and about one-quarter inch width. The leather scrap may be fed into a hopper l I communicating with the mill interior; and as comminuted leather stock capable of being discharged from the J below the opening 6 whereat substantial tani gential discharge of the air-borne comminuted stock against the internal wall of the drum takes place. Excess air escapes through the top of the tube I6 by way of a relief or vent pipe i! and the rest of the air necessary for satisfying the requirements of the blower l3 and carrying very little dust is discharged substantially tangentially from the tube into a conduit l8 joining with the funnel l2 on its way to the blower I3.

The comminuted leather stock thus collected 0 in the drum I5 is directed by a discharge spout H! at the funnel bottom of the drum into a slow speed air-separator 20, for instance, of the Sturtevant type. As shown, the separator includes a funnel inlet 2! surrounding a rotary vertical shaft 22carrying at its lower end a disc plate 23 above and to which is secured, as by posts 24, an annular plate 25. The comminuted material discharged onto the plate 23 is centrifugally thrown under the high rotational speed of the shaft 22 through the space 5 between the plates 23 and 25 against an inner substantially cylindrical partition 26 defining an inner compartment 5. Arms 4 secured to the plate 25 and projecting above the annular plate 25 and the upper end of the compartment 5 carrya plurality of fan blades or vanes 21 which, as the shaft 22 is being rotated, function to create sufiiciently intense upward air currents in the compartment to cause the desired separatory action therein. The air surging upwardly and continuously in the compartment 25 is of regulated or controlled intensity such that it carries away only the lighter and desirable fraction of comminuted leather stock past an inwardly extending flange 28 at the upper end of the partition 26 and thence against the outer separator wall 29. Of course, the upward air flow induced in the compartment 25 creates suction therein so that air must be supplied thereto for maintaining the desired continuous upward draft. The volume of air necessary for such purpose may be had by returning to the compartmerit the air exhausted therefrom, as by way of louvers 30, located at spaced intervals in the generally funnel-shaped lower wall 3| of the compartment. The louvers 30 preferably return air to the compartment substantially tangentially to the internal surface of the wall 3| so as to create a tangential whirl at the'lower portion of the compartment 5 inhibiting the ingress of dust or selected stockproceeding downwardly through the annular space between the outer wall 29 and the inner partition 26. The louvers 30 may, if desired, be provided with suitable bailles to prevent ingress of any substantial tion into the hammermill 10 for re-working. It

is obvious that by rotating the shaft 22 at the appropriate speed, it is possible to realize an airseparatory action such that the lighter comminuted stock fraction constantly being delivered by the conduit 33 will consist essentially onlyof fibrous fragments or filaments well suited for board formation. In actual practice, under the hammermill conditions already described, it is possible to produce from a given amount of tanned leather scrap, such as oak-tanned sole scrap, fed as raw material into the hammermill, a selected comminuted leather fraction in yield amounting to as high as 85% and yet eminently satisfactory for board formation.

The aqueous stock or fiber suspension prepared in the beater or other mixing machine 34 may be delivered to a. Fourdrinier, or other papermaking machine operating to produce sheets of a thickness of, say, 50 to 100 thousandths of an inch. The resulting board is possessed of sufiiciently high porosity or absorbency so as to be readily and uniformly impregnated with various binders serving to impart to the impregnated product characteristics approaching those of original leather. While the utility of the present invention residesmore especially in the production of all-leather boards or sheets, nevertheless, it may be desirable in some instances to admix with the comminuted leather stock in the beater or other mixing engine some cellulosic fiber, animal hair, or mineral fiber. i

- The utility of the present invention extends to the manufacture of uniformly textured and comparatively strong sheets of a caliper falling into the category of paper, for instance, sheets of a thickness ranging from 50 to as low as 15 thousandths of an inch. Because the present invention enables the realization of long-fibered leather stock of a properly feltable character, such stock yields thin sheets having the capability of withstanding the stresses of continuous papermaking operation even on a Fourdrinier machine, for instance, the stress incident to a bridging of the gap between the Fourdrinier wire and the drier felt. Thin leather sheets made pursuant to the present invention are characterized by the ease and uniformity with which they imbibe various binders to yield impregnated products whose province of use is similar to that of such thin original leathers as calfskin and kidskinl The high absorbency of leather boards or sheets made in accordance with the present invention is attributable to the selected, comparatively longfibered, leather stock used in their fabrication. When scrap leather is beaten inthe presence of water or dry-shredded as heretofore practiced, the stock produced is short fibered; and when the short fibers are sheeted from aqueous suspension on a papermaking machine, they tend to pack closely into a relatively dense texture, whereas, on the other hand, the long fibers constituting the selected stock of the present invention interfelt from aqueous suspension while leaving considerable void or inter-fiber space in the resulting sheet. When the selected stock of the present invention is admixed with water to produce a fibrous suspension for delivery to the papermaking machine, it yields after only little agitation or mixing the substantially uniform aqueous suspension requisite for satisfactory sheeting on the' papermaking machine. Such selected stock is of a fluffy or voluminous character and is made up essentially of leather fragments or units which are sufi'iciently reduced but at the same time sufficiently fibrous or filamentary to be felted into a substantially uniformly textured, absorbent sheet possessed of comparatively high tenacity, as attested by the fact that the sheet can be made without trouble at a thickness as low as about twenty thousandths of an inch on a Fourdrinier machine, which latter result cannot be had from the short-fibered leather stocks heretofore prepared from leather scrap. I

It might be noted that the selected stock fraction used in accordance with the present invention generally requires some manipulative or brushing action in a beater or jordan engine in order to be feltable on a papermaking machine into boards or sheets of the best homogeneity or uniformity of texture. In this connection, it might be observed further that by reason of the particular conditions under which the leather scrap is disintegrated in the hammermill and the careful control of such conditions so as to lead to comminuted stock containing preponderantly sufliciently long-fibered fragments or units feltable into a highly porous, comparatively strong sheet on the papermaking machine, such preponderant stock fraction, when selected from the rest of the stock, may contain more or less long fibers which have been imperfectly cleaved apart from other long fibers or which are so filamentary or long-fibered that they may advantageously be reduced in length or brushed out in the beater engine with a view toward promoting their interfelting on the papermaking machine. Accordingly, the selected stock fraction is preferably admixed with water in the beater engine while the beater roll is kept down in brushing relationship to the bed plate at least during the initial stages of mixing so as to ensure, beyond peradventure, an aqueous suspension of stock lending itself to excellent sheet formation on the paper-making machine. Such beating affect the quality of the resulting sheet, as the fiber units having been isolated or liberated practically entirely during the initial step of drydisintegration or comminution suffer, on the whole, very little reduction in fiber length from the long average fiber length possessed thereby after the dry-disintegrating or comminuting operation in the hammermill.

I claim:--

1. A method of preparing fibrous stock for sheeting from leather scrap, which comprises progressively disintegrating such scrap by combined abrading and 'impact' action in a rotary hammermill whose discharge openings are of such large size as to permit emission therethrough of comminuted leather, a substantial portion of which is'of such coarse fragment size as to be non-feltable but the rest of which is'of sumciently reduced fragment size and at the same duce discharge of said leather through said openings and to carry away said leather, constantly collecting said comminuted leather from said draft, and progressively selecting from the collected mass only said feltable portion by airseparatory action to provide said fibrous stock for sheeting.

2. A method of preparing fibrous stock for sheeting from leather scrap, which comprises progressively feeding such scrap into a rotary hammermill wherein said scrap is progressively disintegrated by combined abrading and impact action and whose discharge openings are of such large size as to permit emission therethrough of comminuted leather a substantial portion of which is of such coarse fragment size as to be non-feltable but the rest of which is of sufllciently reduced fragment size and at the same time sufllciently fibrous to be feltable from aqueous suspension into a substantially uniformly textured sheet, constantly maintaining said discharge openings under air-suctional draft to induce a discharge of said comminuted leather through said openings and to carry away said leather, constantly collecting said comminuted leather from said draft, progressively selecting from the collected mass only said feltable portion by air-separatory action to provide said fibrous stock for sheeting, and progressively returning the coarse portion into said hammermill for further disintegrating action therein. I

3. A method of producing a felted fiber sheet from leather scrap, which comprises comminuting said scrap under combined abrading and impact action in a rotary hammermill into stock inclusive of a preponderant, long-flbered and feltable fraction and a subordinate and substantial, comparatively coarser and heavier nonfeltable fraction, air-separating said stock into said fractions, admixing said separated firstnamed fraction with water to form a substantially uniform suspension, and forming a sheet from said suspension.

4. A method of producing a felted fiber sheet from leather scrap, which comprises conuninuting said scrap by combined abrading and impact action in a rotary hammermill equipped with discharge openings sufficiently large to permit discharge therethrough of comminuted stock inclusive of a substantial but subordinate, coarse and non-feltable fraction as well as a comparatively lighter, preponderant, substantially uniformly feltable fraction, airseparating such stock into such fractions, admixing said separated second-named fraction with water to form a substantially uniform suspension, and forming a substantially uniformly textured sheet from such suspension.

WILLIAM T. DOYLE.

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