US2635298A - Apparatus for defibering fibrous material - Google Patents

Description

April 21, 1953 T. w. LEPKOWSKI APPARATUS FOR DEFIBERING FIBROUS MATERIAL Filed Oct. 10, 1947 2 SHEETS-SHEET 1 IN V EN TOR.

Patented Apr. 21, 1953 APPARATUS FOR DEFIBERING FIBROUS MATERIAL Thomas W. Lepkowski, New York, N. Y. Application October 10, 1947, Serial No. 779,005

11 Claims.

1 This invention relates to apparatus and methods for defibering fibrous materials. Examples of such materials are leather, cotton linters, sugar cane bagasse, palm leaves, asbestos, etc.

Such apparatus may be in the form of a the hammer mill screen. The draft through this screen may be used to carry the fibers to a collecting station.

The operation of such apparatus involves the problem of getting the fibers through the screen and away from the hammers, the instant the fibers are separated. As long as the fibers are inside the screen they are being worked on by the hammers, which may break them into shorter fiber lengths or grind them to powder.

Prior art hammer mill screens have customarily been of two types, one being the bar-cage screen comprising parallel arcuate bars which are laterally spaced to provide the screen openings, the other being a metal plate having a plurality of perforations which are usually round. The first type has the disadvantage that it cannot eificiently screen fibrous material being worked in the mill. If the bars are spaced closely to prevent the passage of incompletely defibered material, this type has the disadvantage that the separated fibers cannot exit before they are broken into shorter pieces or ground to powder. The secondly named type has the same disadvantage. If the holes are made small enough to prevent the passage of incompletely defibered pieces, then the separated fibers cannot get out before they are struck again and again by the hammers. As a result of all this, the prior art has heretofore been unable to defiber fibrous material so as to obtain fibers having lengths comparable to those they naturally possessed in the original material.

It has been proposed to defiber leather by using a hammer mill having a special hammer arrangement and using a screen of the perforated plate type with the perforations in the form of slots which are all longitudinally aligned circumferentially respecting the screen, with the screen also having one section including the usual round holes. The object was to defiber leather so as to obtain fibers having their original lengths, but this expedient has not worked out in practice, the screen failing to pass the separated fibers before they are disintegrated by the hammers.

Oneobject of the present invention is to defiber fibrous materials so as to obtain fibers having their original lengths and strength, or at least as to represent its practical realization.

such a close approach to this perfectionist aim The manufacture of artificial leather from scrap leather, has heretofore sufiered from the prior arts inability to ,defiber scrap leather so as to obtain long fibers of good strength. Defibering attempts have resulted in a material much in the nature of a powder, and when this material is used as a base for the manufacture of artificial leather, it can function only as a filler, as contrasted to a fibrous material that might be processed to a produce having good tensile strength and wearing properties.

It follows that successful attainment of the stated object will advance the artificial leather making art very greatly, and it is equally obvious that it will provide a start in many other arts that have languished because of the inability to obtain long and strong fibers from fibrous material by prior art defibering attempts.

The present invention attains the above object by providing an improved hammer mill screen having perforations so shaped and oriented as to decrease the chances for the escape of fibrous material prior to its being defibered while increasing the chances for the separated fibers to get through the screen quickly. That is to say, a much smaller percentage of the material escapes prior to defibering and a much greater percentage of the separated fibers escape from the hammers before being seriously fragmented, than was ever before possible. The invention involves a method in that it is necessary to correlate the dimensions and shapes of the screen perforations, to the character of the fibrous material being defibered, this correlation obtaining optimum results. Since the screen has maximum value when used in a hammer mill, the invention embraces an improved hammer mill and a method of operating the same.

Another object of the invention is to provide a hammer mill screen having the advantages noted yet which is not unduly weakened. Other objects may be inferred from the following disclosure of a specific example.

This specific example is illustrated by the accompanying drawings in which:

Fig. 1 shows an opened hammer mill to illustrate its general features;

Fig. 2 is a cross section of the mill;

Fig. 3 shows the hammer mill screen developed, that is to say as it is prior to being arcuately shaped; and

Fig. 4 is like Fig. 3 but shows a modification.

nals the hammer shaft 6 and encloses the hammer screen and hopper. A chute 1 leads through the top of the casing so the fibrous material may be fed to the hammers and screen. The top of the casing 5 is hinged to swing open, this swinging part being numeraled 5a.

A motor 6a powers the shaft 6, and the blower 3, outside of the casing 5, is powered by the hammer shaft.

In operation, the fibrous material is fed in the form of small pieces through the chute l and the hammers 2, which revolve with their ends very close to the inner surface of the screen I, shred the material and separate its fibers. The screen should not permit the piece of material to escape prior to defibering, ,yet the instant the fibers are separated they are subject to disintegration by the hammers unless they can immediately get through the screen. I IIheefiiciency of the machine depends upon how many of the pieces are prevented from escaping prior to defibering and how many separated fibers get through the screen before, they are materially disintegrated by the hammers. I

According to the present invention the screen I, shown developed in Fig. 3, has screen perforations 8 in the form of longitudinally curved slots. These slots should be curved about in the manner of the immediatelyseparated, previously intermatted fibers. These curved slots .8 extend circumferentially around the screen .I .in succession with progressively rotated orientations and preferably with the slots adjacent the .circumferential center of the screen, at least approximately, and preferably as accurately as is possible, aligned .circum-ferentially respecting the screen.

Preferably the curved slots are arranged in groups 9 .and [.0 wherein, respectively, the orientations of the slots are rotatively reversed, the groups being in mutual alignment. That is to say, the .slots extend .circumferen-tially around the screen in circumferential rows and are arranged in each row with progressively rotating orientations .rotatively reversing .at least once.

Preferably this reversal occurs near the center of the screen and the slots are there, at the center, oriented .circumferentially respecting the I screen, as previously described. As illustrated,

the slots in both groups -9 and I .0 at the screens ends are in axial alignment with the screen, or are circumferentially transverse the screen, and the slots in each group are oriented so that successive slots in the respective groups are rotated in opposite directions gradually until, near the center of the screen, the slots in both groups are in mutual alignment and are in alignment ciroumferentially respecting the screen.

Generally speaking, the dimensions and curvatures of the slots should be proportioned to the lengths and curvatures of the fibrous material being defibered. The entire screen may be practically filled with these circumferentially extending, parallel rows of perforations.

As the hammer mill operates the hammers try to push the pieces of material through the slots while the rotary motion causes the application of centrifugal force to the pieces which :also tends to drive them through the slots. However, prior to defibering the :material is efiectively in the form of rigid straight pieces which'cannot be forced through the slots because of their curvatures, so little if any of the material can escape prior to separation of its fibers. Also the hammers are proceeding-to pull the fibers of the 'oriented in the same direction it is. When this occurs the fiber is immediately drawn through the screen by way of this oriented slot because the separated fibers are flexible enough to conform to the curvatures of the slots by flexing. The fibers are thus gotten away from the hammers immediately. 'Immediateremoval is practically positive as compared .to the chances for its removal when the plate contains the prior art round holes, or straight slots all oriented in the same direction, in which cases there is an extremely small chance for the fiber to pass through the screen. In .such'instances the fiber'must either hit thescreen head on, or it must ride along the screen in circumferential alignment with the screen and with the plane ofits .curve normal to, the plane of the screens inside, it being almost impossible for many of the fibers to meet these conditions. If the holes Or slots are large the undefibered pieces are driven through by the forces acting on them. The contrast between the new and the old is very apparent.

When defibering fibrous material having fibers comparable to those .of leather, cotton, asbestos, etc, the slots may have widths ranging from A to of an inch, inner or shorter side lengths ranging from to 2 .inchesand an inner or shorter curvature radius ranging from to 2 inches. The curved sides .of the slots may be parallel. Preferably the screen contains as many of these perforations as it can safely carry, and they are arranged as previously described, although other arrangements are possible. The exact dimensions and curvatures of the perforations dependon the particular fibrous material being defibered.

. The proportions suggested above are applicable to .defibering work. However, either the curved slots or their particular arrangement may prove of value in-other operations exemplified by scalping. In such instances wider and longer slots, with a larger curvature radius, may be used While incorporating to advantage the general teachings of the invention.

As a general aid in practicing the present invention so as to obtain optimum results with various fibrous materials, the following table suggests the preferable slot dimensions and curvatures for typical materials:

In the above "table, the width values are for the radial width of 'the slot, while the length and radius values have reference to the inner shorter sides of the slots. The ends of the slots are preferably defined by radial lines-taken from the axis of the curve, although these ends may be rounded. The curved slots may not have to be truly arcuate, general conformation to the shapes suggested, being adequate in some instances.

A good general rule is that the slots should have lengths just slightly longer than the average fiber length of the material being defibered', and the radius of their curvatures should be less for softer and more flexible fibers and greater for harder and stiffer fibers.

In some instances it may be desirable to provide circumferential rows of the curved slots with groups of the slots reversed at one ormore points in one or more rows, as suggested in the case of the groups II and I2 illustrated by the drawings. In such instances the slots should also progressively rotate circumferentially of the screen to assure passage of the fibers regardless of their orientation. That is to say, there should be an almost infinite varying of the rotative positions of the slots circumferentially of the screen, to accommodate the fibers regardless of their angle of attack respecting the slots.

Another variation is suggested by the groups Ila and 12a in Fig. 4 wherein the respective groups are relatively offset in directions axially of the screen to avoid the formation of circumferential blanks extending the complete circumferential extent of the screen. Such offsetting may be for more than two groups only if desired, or it may be combined with the other arrangements disclosed herein. This prevents a condition wherein fibers might ride on circumferential blanks and be unable to escape prior to some fragmenting by the hammers, and thereby increases the efficiency of the invention even further.

The screen may be made by punching a steel plate in the usual fashion. With this mode of manufacture the invention enjoys the advantage that the necessary curved shapes of the punches, greatly enhances the punches deflection rigidity and this reduces punch breakages. This advantage is not enjoyed when manufacturing screens having longitudinally straight slots.

The described use of the new screen involves a new method in that the new and unexpected results described are obtained when deflbering fibrous material. While the screen may have advantages when using a hammer mill to disintegrate non-fibrous materials, the described results are, of course, tied with the treatment of fibrous substances. The features of the invention also provide an entirely new hammer mill having new characteristics providing for the new and unexpected results described herein. No prior art hammer mill could provide these results.

Since the present invention embraces the idea of using curved slots to prevent the escape of straight and relatively rigid material such as small pieces of undefibered leather, asbestos or other fibrous material, with the deflbered material sucked through these slots by bending them to conform therewith in shape, fibers being comparatively flexible, care should be taken to assure a good draft through the screen. Commercial hammer mills are not arranged with the hopper box, connecting the screen with the suction source, in an air tight manner, but in the case of this invention these parts are preferably made airtight so that all the air is sucked through the screen without bypassing it through leaks.

If it is desired to make the screen to include more than a semi-cylinder, it may be made in two parts to permit its installation, in which event it may be even made as a complete cylinder in the case of special equipment. Available sidefeeding hammer mills may easily be redesigned to use a screen that is more than a semi-cylinder. Thus in Fig. 2 the screen includes a radially separable section la connecting with the hopper box 4 through an extension 4a with interconnection established through large openings l3 through which the fibers may be sucked, a gasket l4 making this extension air-tight with the main portion. This increase in the circumferential extent of the screen is of advantage in increasing the efliciency of the invention. The illustrated arrangement of the two-part screen idea is not to be considered as being the only possible design. Another way of doing this would be to have the longitudinal joint at the bottom of the screen with either or both sides extended above the level of the shaft 6. This would permit installation of the screen while providing increased effi ciency. Also, it might be preferable to have the entire screen connecting directly with the suction box to prevent fiber entrapment such as might occur if pockets are formed by the machine parts in the suction path of the fibers.

To simplify the drawings Figs. 3 and 4 do not show the screens completely covered with the perforations but it is to be understood that in practice the screen will have as many perforations as is structurally possible. The drawings cannot be made with the perforations to scale without confusing the disclosure; and therefore the perforations are shown in larger proportionate sizes respecting the screen, than they actually are.

I claim:

1. A curved hammer mill screen having a plurality of screening perforations comprising longitudinally curved slots defining transversely curved passages adapted to retard the passing of long pieces too rigid to flex and conform to the shapes of said curved passages and to pass such pieces when they are flexible enough to flex and conform to said shapes, said slots extending circumferentially around said screen with progressively rotated orientations.

2. A curved hammer mill screen having a plurality of screening perforations comprising longitudinally curved slots defining transversely curved passages adapted to retard the passing of long pieces too rigid to flex and conform to the shapes of said curved passages and to pass such pieces when they are flexible enough to flex and conform to said shapes, said slots extending circumferentially around said screen with progressively rotated orientations, and with said slots adjacent the circumferential center of said screen at least approximately aligned circumferentially respecting said screen.

3. A curved hammer mill screen having a plurality of screening perforations comprising longitudinally curved slots defining transversely curved passages adapted to retard the passing of long pieces too rigid to flex and conform to the shapes of said curved passages and to pass such pieces when they are flexible enough to flex and conform to said shapes, said slots extending circumferentially around said screen with progressively rotated orientations, in groups wherein said orientations are rotatively reversed.

4. A curved hammer mill screen having a plurality of screening perforations comprising longitudinally curved slo'ts defining transversely shapes of said curved passages and to pass such pieces when they are flexible enough to flex and conform to said shapes, said slots extending cir- I cumferentially around said screen with progressively rotated orientations in groups wherein said orientations are rotatively reversed and with said slots adjacent thecircumferential center of said screen at least approximately aligned circumferentially respecting said screen.

A curved hammer mill screen having a plurality of screening perforations comprising longitudinally curved slotsQ defining transversely curved passages adapted to retard the passing of long pieces-too rigid to flex and conform to the shapes of said curved passages and to pass such pieces when they are flexible enough to flex and conform to said shapes, said slots having widths ranging from A4 to /2 of an inch, inner side lengths ranging from /2 to 2 inches and an inner curvature radius ranging from T55 to 2 inches, said slots extending circumferentially around said screen with progressively rotated orientations rotatively reversing at least once.

6. A curved hammer mill screen having a plurality of screening perforations comprising longitudinally curved slots defining transversely curved passages adapted to retard the passing of long pieces too rigid to flex and conform to the shapes of said curved passages and to pass such pieces when they are flexible enough to flex and conform to said shapes, said slots having Widths ranging from to /2 of an inch, inner side lengths ranging from A2 to 2 inches and an inner curvature radius ranging from $5 to 2 inches, said slots extending circumferentially around said screen with progressively rotated orientations rotatively reversing at least once near the center of said screen and there being oriented at least approximately circumferentially respecting said screen. I

'7. A curved hammer mill screen having a plurality of screening perforations comprising slots arranged in circumferential rows with progressively rotated orientations in said rows.

8. A curved hammer mill screen having a plurality of screening perforations comprising slots arranged in circumferential rows with progressively rotated orientations in said rows, with said slots adjacent the circumferential center of said screen oriented substantially circumferentially respecting said screen.

9. A curved hammer mill screen having-a plurality of screening perforations comprising slots arranged in circumferential rows with progressively rotated orientations in said rows, said slots defining passages transversely curved within the flexibility limits of separated, previously intermatted, fibers.

} 10. A curved hammer mill screen having a plurality of screening perforations comprising slots arranged in circumferential rows with progressively rotated orientations in said rows, said slots defining passages transversely curved within the flexibility limits of separated, previously intermatted, fibers, and said orientations extending circumferentially respecting said screen. 11. A curved hammer mill screen having a plurality of screening perforations comprising slots arranged in circumferential rows with progressively rotated orientations in said rows, saidslots defining passages transversely curved within the flexibility limits of separated, previously intermatted, fibers, and said orientations extending circumferentially respecting said screen, and said slots rotatively reversing at least once in their said progressively rotated orientations in said rows.

THOMAS W. LEP'KOWSKI.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 8,601 Wheeler Dec. 16, 1851 97,584 Allen Dec. 7, 1869 255,325 Oastler Mar. 21, 1882 1,807,197 Clement 'May 26, 1931 2,460,938 Koehne Feb. 8, 1949 2,474,314 Koehne June 28, 1949 FOREIGN PATENTS Number Country Date 132 Great Britain of 1871 39,216 Germany Apr. 22, 1887

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