US 3637146 A
A hammermill for wood pulp fiberizing has rotary blades, the front faces of which are bevelled so that pulp impacted by the rotors tends to slide from the rotors, avoiding repeated impacts of pulp on pulp, thereby minimizing pulp clots.
Description (OCR text may contain errors)
nitd States Patent anlra Jan. 25, 1972 54] HAMMERMILL CONSTRUCTION FOREIGN PATENTS OR APPLICATIONS  Inventor: Charles T. Banks, Neenah, Wis. 645,098 10/1950 Great Britain ..24l/l9l  Assignee: Kimberly-Clark Corporation, Neenah, Primary Examiner Donald Kelly AttorneyDaniel J. Hanlon, Jr. and Raymond J. Miller  Filed: Oct. 27, 1969 A hammermill for wood pulp fiberizing has rotary blades, the  Cl 241/194 241/3 front faces of which are bevelled so that pulp impacted by the [5H f 5302c 13/04 B026 13/28 rotors tends to slide from the rotors, avoiding repeated im-  1mm all Search 41/186, 191, 194, 195, 3 Pacts of pulp on pulp, thereby minimizing pulp clots  References Cited 5 Claims, 5 Drawing Figures UNITED STATES PATENTS 2,803,634 8/l957 Chayen ..24l/195 X IIAMMERMILL CONSTRUCTION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates particularly to the fiberizing of pulp, such as wood pulp, by hammermill action. In one specific aspect the invention is concerned with the structural arrangement of the hammers for pulp working hammermills.
2. The invention With Relation to the Prior Art Cellulosic fluff is commonly produced from wood pulp fibers. The fibers are provided from the pulp mill as dried, hard pulp board sheets. These sheets are fed to a hammermill or a hammermill attrition mill sequence, or fiber picking devices for breaking of the sheet to the fluff condition.
I have found that, while hammermills, and hammermills followed by attrition mills, are useful for the purpose, the fluff product contains nits or small hard clots of fibers. Such clots apparently tend to be present in any fiber fluff product and are undesirable as they provide for nonuniformity and, for example, decrease the efficiency of the fluff as an absorbent medium. In fiuffs produced by the action of a hammermill, whether the mill is provided with a screen or is followed by other fiberizing equipment, I have found that the action of the hammers carried by the rotor exerts a material influence on the presence in the final product of fiber clots. Specifically, I have found that the hammer for a hammermill, when acting on pulp board sheets, should be bevelled to provide for a sliding action of the pulp fibers on the hammers adjacent the hammer periphery. By providing for a sliding action, successive fibers are apparently urged toward the housing of the mill rather than being impelled directly on one another. Apparently also, such sliding overcomes to a significant extent the clotting tendency, and the extent of improvement increases with the angle of bevel of the hammers. I have also found, however, that the bevel angle materially affects power consumption in the fiberizing action and, for many purposes, a moderate bevel is preferred.
It is, then, one object of the present invention to provide a novel hammer structure for a pulp working hammerrnill.
It is another object of the present invention to provide an improved method of forming fluff from a pulp board sheet. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description and accompanying drawings wherein:
FIG. 1 is an elevational view partially in section illustrating a hammermill embodying the invention;
FIGS. 2 and 3 are fragmentary views in side and front elevation respectively of a hammer structure useful in the arrangement of FIG. 1; and
FIGS. 4 and 5 illustrate hammers having, respectively, relatively small and relatively large angles for fiber contact.
THE INVENTION IN DETAIL As shown in FIG. I, a sheet of pulpboard l is fed longitudinally in the direction of the arrow by a feed unitindicated generally at 2 and constituted by toothed feed rolls 3, 4. The pulpboard 1 is a relatively hard coarse sheet material and commonly is fed in the dry condition to the hammermill generally designated at 5. The mill in this instance is comprised of an upper housing portion 6, a lower housing portion 7, and a cutter bar arrangement 8, which together define a cylindrical spacing. The sheet 1 is fed between the bar 8 and housing portion 6 which define the housing inlet. A shaft 9 disposed centrally within the cylindrical spacing of mill 5 mounts a rotor 10 which is provided with a plurality of radially projecting hammers or heads 11 retained by bolts 12. Heads or hammers 111 act on the entering sheet 1 to break it into fine pieces, preferably individual fibers, and to direct the fibers to the indicated outlet between the housing portions 6 and 7. In the present instance the mill is not equipped internally with a screen and, in common practice, the mill would be followed by an attrition mill or like device to insure fine fluffing action. Alternatively, as in the device illustrated in U.S. Pat. No.
3,170,640 issued Feb. 23, 1965, a screen may be provided across the outlet indicated by the arrow in FIG. I. In any event, the arrangement as thus far generally described is known to the art.
The hammers 11 are suitably simply rectangular bars of greater length and width than thickness. l have found that these blades or hammers II should be bevelled as indicated at 13, and that such will minimize fiber clot formation. Apparently as the rotor urges the blades in counterclockwise rotation (FIG. I) to break up the entering sheet, there is a tendency for fibers to cling to the blades. When the blade structure is such that the blade face presented to the fibers is radial, or approximately so, this clinging of the fibers is acute and the impact of newly entering fibers on fibers carried by a blade is sufficient to pound the fibers into a clot. Such clot, once formed, is difiicult to break because of the natural tendency of the fibers to cling together. Particularly is this so if the fibers are impacted while they contain a small quantity of moisture. For example, the tendency to clot is greater under conditions of high humidity and high temperatures.
To minimize the clotting action I provide the forward face 13 of the blade 11 (FIG. 1) with a rectilinear bevel so that, as the pulp is engaged in the sweep of the rotor, the fibers tend to slide on the hammers and to be directed to the periphery of the outlet of the housing defined between the portions 6 and 7. A small angle of about 15 (FIG. 4) provides a long bevel and such is effective, the blade narrowing in width to the periphery to reduce the clotting action. A larger angle of about 45 is much more effective in minimizing nit formation. However, at 45 there is greater power input required to effect the same fiberizing action. Accordingly, I prefer that the bevel angle be between about 25 and 35 and most suitably about 30. At this latter angle clotting appears to be unobjectionable for most uses of the fluff, and power consumption is not unduly high. In fact, in my testing I have found that at a bevel angle of about 30 the power consumption is about half of that at 45. Accordingly, while the greater angle results in somewhat improved fiberizing and is warranted for some purposes, the economics and product quality at a somewhat lower bevel angle are usually quite suitable.
The bevel joins (FIGS. 2, 4 and 5)) the forward face of the blade and the peripheral face and is preferably of such a length as to extend over at least one-quarter of the working forward face (FIG. 5). It may suitabiy be much longer (FIG. 4). In general, I have found that the bevel should preferably be as long as the peripherally extending face as this provides for good blade balance and strength. As illustrated in FIG. 4, the
bevelled front face may be twice or more the length of the peripherally extending blade face.
As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.
I. In combination, in a hammermilll having an inlet, an outlet and a blade carrying rotor interposed between the inlet and outlet, blades on said rotor serving as hammers and which sweep across said inlet in their rotation to fiberize pulp introduced at the inlet and direct it to the outlet, each of said blades having a front face for engaging said pulp and which face is rectilinearly bevelled at an angle of between 15 and about 45 from the periphery of the blade and narrows in width toward the blade periphery to urge pulp in a sliding action toward the periphery.
2. The combination according to claim 1 in which the bevel angle is between about 25 and 35.
3. The combination according to claim I in which the bevel angle is about 30.
4. The combination according to claim 1 in which the front face of the blade in the bevel area is at least as long as the peripheral face of the blade.
5. The combination according to claim 4 in which the front face of the blade in the bevel area is twice that of the peripheral face.
Disclaimer 3,637,146.0harles T. Banks, Neenah, Wis. HAMMERMILL CONSTRUC- TION. Patent dated Jan. 25, 1972. Disclaimer filed Aug. 13, 1973, by the assignee, Kimberly-Clark Corporation. Hereby enters this disclaimer to claims 1, 2, 3, 4 and 5 of said patent.
[Ofiioial Gazette October 30, 1973.]