Abstract:
A briquetting die set comprises first and second mating cylindrical dies. The first die has a plurality of adjacent recesses surrounded by a wall having an upper rim. At least a portion of the upper rim of each recess is common to an adjacent recess and has a relatively small radius of curvature. The second mating die has mirror image recesses thereon. When the first and second dies are brought into mating relationship, the upper rims of the first and second plurality of recesses mate with each other in substantially line contact to form a briquetting cavity.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the formation of briquettes from fibers, and more particularly, to a high speed briquetting die for forming a plurality of fiber briquettes. 
     BACKGROUND OF THE INVENTION 
     Readily dispersible fibers may be utilized in the construction of fiber reinforced materials such as plastic and cementitious panels used in the building trades as a filler and reinforcing medium. For example, the fibers may be dispersed in an aqueous cementitious slurry and then formed into the panels. It is important for the fibers to be readily dispersible into the slurry so that the fibers are separated from one another and distributed evenly throughout the slurry. It is also important that the fibers be provided to the panel manufacturer in a form that is easily transportable, flowable, and meterable. 
     The fibers may be supplied in the form of small pellets or briquettes. Prior attempts at making briquettes in flat or rotary dies have resulted either in substantial wastage or the formation of webs between individual briquettes that are hard and glassified. These hard glassified webs do not easily dissolve and disperse in the cementitious slurries. A die and method of manufacturing briquettes that eliminates the hard and glassified web between the individual pellets or briquettes is needed. 
     SUMMARY OF THE INVENTION 
     The present invention therefor provides a briquetting die set that comprises a first die and a second mating die. Preferably, the first and second dies are cylindrical in shape with die forming recesses formed on the circumferential faces of each of the first and second dies. The first die has a first plurality of adjacent recesses therein. Each of these recesses is surrounded by a wall having an upper rim, at least a portion of which is common to an adjacent recess and that has a relatively small radius of curvature. The second mating die has a second plurality of recesses therein that are formed in the mirror image of the recesses in the first die. Again, each of the second plurality of recesses has an upper rim, at least a portion of which is common to an adjacent recess and has a relatively small radius of curvature. The upper rims of the first and second plurality of recesses mate with each other in a substantially line contact as said first and second dies are rotated and brought into mating relationship. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description when taken conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side elevation view of first and second mating dies constructed in accordance with the present invention used to produce briquettes of easily dispersible fiber; 
         FIG. 2  is an isometric view of the apparatus shown in  FIG. 1 ; 
         FIG. 3  is an enlarged view of a surface of one of the dies showing the briquette-forming recesses constructed in accordance with the present invention; 
         FIG. 4  is a cross-sectional view taken along section line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a cross-sectional view taken along section line  5 - 5  of  FIG. 3 ; 
         FIG. 6  is a cross-sectional view taken along section line  6 - 6  of  FIG. 3 ; 
         FIG. 7  is a cross-sectional view taken along section line  7 - 7  of  FIG. 3 ; 
         FIG. 8  is a schematic view of the recesses formed in the surfaces of the dies before they are completely machined; and 
         FIG. 9  is a schematic view of a plurality of briquettes manufactured with the briquetting dies of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 2 , a first die  10  and a second die  12  are mounted on a support frame generally designated  14 . Each of the dies is mounted for rotation about axes  16  and  18 , respectively. The dies  10  and  12  are cylindrical and preferably of equal diameter. The axes  16  and  18  are spaced by a distance such that the circumferential surfaces  20  and  22  of dies  10  and  12  mate in substantially tangential relationship at the briquetting location or nip  24  between the two dies. Cellulose fiber  30 , preferably in the form of an air laid mat, is fed by opposing conveyors  32  and  34  to the nip  24  between the two dies  10  and  12 . Each of the dies contains a plurality of recesses  36  on their respective circumferential faces. The dies are rotated so that a recess on one die mates with a recess on the opposing die to form cavities in the shape of a flattened cylindroid. These cavities receive the cellulose fibers  30  as the dies rotate and form the fibers into briquettes  40 . 
     Referring to  FIGS. 2 and 3 , the recesses  36  are formed in a circumferential array around each of the dies  10  and  12 . The recesses in the second or mating die  12  are the mirror image of the recesses created in the first die  10 . Recesses  36  in a preferred embodiment are formed in two rows  42  and  44  around the circumference of the dies. While only two rows are shown, one of ordinary skill will understand that any number of side by side rows may be employed, limited only by the width of the circular die and the constraints in building and operating an apparatus on which the dies are mounted. 
     The recesses  36  will now be described in more detail only in conjunction with  FIG. 3  and the upper die  10 . It is to be understood, however, that the dies on the lower die are formed in exactly the same manner and, as stated above, are formed in the mirror image of those on the upper die  10 . Each of the recesses  36  in plan view are preferably racetrack shaped. That is, the recesses have elongated, substantially parallel sides with curved end portions that approximate a semicircle. Each of the recesses has an upper rim  50  that lies on the original circumferential surface of the cylindrical die  10 . The recesses  36  extend radially inwardly from the upper rims  50 . Preferably, the lateral dimension of each racetrack-shaped recess is about twice the circumferential width of the recess along the upper rim. Preferably, each recess has smoothly contoured sides that blend smoothly with each other at the bottom or radially inwardly portion of the recesses  36 . It is preferred that the maximum depth of the recess be on the order of 50% or less of its circumferential width, although other depths may be employed as desired. It is preferred that the length of the recesses range from 10 mm to 60 mm, preferably 21 mm, the width of the recesses range from 5 mm to 50 mm, preferably 7 mm, and the depth range from 1 mm to 30 mm, but preferably not greater than 50% of the length. The bottom of the recesses are radiused into the sidewalls. The radius of the rims  50  is preferably 1.0 mm or less. A small radius on the rim causes the fiber to flow laterally (circumferentially and crosswise) so as to minimize the web thickness between briquettes. These dimensions may also vary depending on the end use of the briquette. 
     The upper rims of the recesses are formed to eliminate any substantial lands or smooth areas at the surface of the circumferential surface of the die so as to eliminate regions in which fiber can be compacted into hard, glassified mats. Thus, each of the lateral portions of the rims in each of the rows  42  and  44  are shared with the next adjacent recess. The recesses of the second row  44  are offset in the circumferential direction by one-half the circumferential width of the recesses so that the curved end portions  52  of one row  42  is nested between the curved end portions  54  of the recesses of the adjacent row  40 . In addition, two rows of offset troughs  56  are formed laterally outwardly from each of rows  42  and  44 . These troughs  56  have circularly shaped end portions  58  that are circumferentially offset from adjacent recesses in rows  44  and  42 , respectively. The troughs  56  open onto opposite sides of the die  10  and are not used to form briquettes. It is necessary for these troughs to be formed, however, so that the curved portions of the rims  50  of the recesses  36  meet the circumferential surface along lines  60 . 
     Referring to  FIGS. 4 and 5 , rims  50  between recesses  36  essentially meet at a line or knife edge, but are preferably rounded to a relatively small radius, as set forth above. Referring now to  FIG. 8 , the schematic depiction of the recesses  36  are shown before they are completely milled. Recesses  36  are formed by a milling machine having a hemispherical milling tool. This tool, however, leaves large triangularly shaped lands  64  between adjacent rows of recesses  36 . If these lands  64  are allowed to remain on the circumferential surface of the die, as fibers are fed through the die, they will be compacted in hard mats at the lands. Thus, the edges  62  of the lands  64  may be hand milled so that the edges recede toward the center point of the lands  64  joining the edges  62  from adjacent recesses as shown in  FIG. 3 . This milling is preferably accomplished with a computer numerically controlled (cnc) milling machine. This milled surface  64  is shown in the cross sections of  FIGS. 6 and 7  taken across the region that was a land prior to being additionally milled to cause the edges  62  of the lands  64  to retreat toward each other and form a virtual line between adjacent curved end portions of recesses  36 . 
     As shown in  FIG. 9 , the briquettes are in the shape of an oblate or flattened cylindroid. Referring to  FIG. 4 , the preferred cross-section of one side of a forming recess for this briquette is shown. It will be understood that the briquette formed by this recess has a flattened cross-section in its minor dimension. 
     Referring now to  FIG. 9 , a ribbon of briquettes  70  formed in the recesses  36  are shown. The briquettes  70  are compacted, but are readily separated and dispersed when placed in an aqueous slurry. The bands  72  of material between the briquettes are formed in the regions where the upper rims  50  of adjacent recesses meet. The bands are paper thin (although shown as having some thickness) and allow the briquettes to be easily separated from each other without any hard glassified mats of fiber remaining. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.