US2246362A - Abrasive disk - Google Patents

Description

.June W', 1941. l R, Q KEHQE 5TM. 2,246,362

ABRAS IVE DISK Filed Feb. 8, 1940 W 5)/ A TTO RNEY.

atenteoi .lune '17, 1941 ABRASIVE DISK Richard D. Kehoe, Hadlyme, Conn., and Robert B'. Eastty, Montclair, and William H. Sayre, Essex Fells, N. J.

Application February s, 1940, serial No. eri-,soz

1 Claim.

This invention relates to attrition wherein solids are rendered into a state of finer particle subdivision by being subjected to abrasion, or,A wearing away. Devices used in this art comprise mills,'reners, abraders, jordans, beaters, attrition mills, and Vthe like, characterized by two or more opposed abrasion surfaces, of which at least one rotates or is moved relative to the others, although theA surfaces 'do not actually touch.' The material to be attrited passes between the surfaces and is thus partly acted upon by the surfaces and partly by its particles being rubbed against each other under the pressure exerted on them by the working abrasion surfaces.

The invention was primarily designed to apply to refinersand attrition mills as used in the paper industry for the attainment and conditioning of.

fibers that form the basisonsheets or felts. However, the invention has much wider usefulness, for it. can be used in treating cork', scrap rubber, leather, grain and so on.

It has been customary in the' paper industry to make the abrasion surfaces of the mills, which. herein will be referred to generically'as refiners, of cast iron but .these have proved to be unsatisfactory because of excessive wear. As wear takes place, the working abradingsurfaces have to be adjusted closer together with the result that' less eflicient abrasion results, and what is worse,- greater power input is required for the continued rotation of the surfaces, `Moreover, at relatively body having a matrix of 'relative soft but tough metal that is wearable under "the operating conditions in the rener with relative harder abrasive grains set in the tough, matrix.. The objecthere is to cause the exposed surfaces of the matrix to wear faster than the general wear on the grains so that they always project outwardly from the surface of the matrix a` multitude of short intervals, the'reflners have to be stopped and the working surfaces in them renewedat the loss of valuable operati g time and'expense. So one of the objects of this nvention is to devise for refiners an Yabrasion unit or surface element that will far outwear theburrent ones with the resultant saving in needfor repeated adjustment of the rener surfaces; avoidance of -fiuctuating power input, of fluctuating efficiencies, and of 4 repair time and expense.

It has been proposed heretofore in refiners, to apply to the working surfaces, an inset of some abrading material such as sandstone and as carborundum. But these have not been satisfactory for a variety of reasons. Sandstone wears too rapidly, and like carborundum', it has a tendency to break or chip off in pieces, or even chunks. These broken-off pieces may wreck the jagged protuberances, which to use a rather picturesque word will be called `pimples. These make excellent abraders. As they wear, as theyv inevitably must, they tend to drop out from the matrix 4leaving a jagged crater with projecting prongs,"or .again more picturesquely, af' pock-V mark. Thus, this combination of. pimpleand Dock-mark has been found to be highly e'icient in their abrasion capabilities and yet .thetotal wear of the inset itself is almost negligible.- Indeed, experience has shown that such an -inset has operated for as much' as"500 hours without`- needing replacement.

The matrix material must be moldable andV of tough material in order to vembed the abrasive' grains in it, which Ymeans thatthe matrix may be softer ormore wearable than is generallyJ desired for such an inset. In order to overcome this deliciencyzit :is proposed to embed in it primary abrasive grains of one size, and placed-` in the interstices between them areV secondary grains of a smaller size. Thesmaller secondary grains seem-to protect the surface ofthe matrix from excessive wear, and yet permit .it to wear sufficiently to assure a continuous exposure of the pimples and peck-marks above referred t'o..

The/larger or primary abrading' grains preferj ably should constitute at least half of the total whole machine, and at least the break in the 5 working abrasion surface results thereafter in uneven and inefcient abrasion. Again, in abrasion insets of'this kind,there is a tendency for the abrasion surfaces to wear smooth and thus become highly inefficient. Therefore, it is grains used. It may be important in some industries, to use abrasive grains of a material that is inert to alkalis or acids, and particularly to corrosion, for stray grains that escape from the inset might discolor or otherwise harm the producttreated. To that end, it is preferred to use fused aluminum oxide (A1203) of the types known `to the trade as Aloxite, Alundum and so on.`

And finally, since the abrasive grains are so much more expensive'than the matrix, it is def sired' to confine the grains to a relatively thin zone along' the exposed surface of the abrading\ element. To that end, it is preferable to sprinkle them on the bottom of the sand mold in which the inset is to be cast. Then the molten matrix material is poured. Then, when the cast element or block is removed, it is found that substantially all of the abrasive grains are adjacent to the surface of it where they can be of most effectiveness, with a minimum of them dispersed in the body of the vmatrix where they would be valueless. More particularly, then, the invention comprises surfaces used in attrition made up of a matrix of a softer metal in which are embedded adjacent to the attriting surface of the inset, grains or nuggets of fused abrasive material. The grains used are of at least two sizes of which one does the major part of the abrading while the other protects the matrix against excessive wear.

An embodiment of the invention that has proved satisfactory has been chosen for illustration in the drawing but it is to be understood that this has been chosen for illustrative purposes since the invention obviously is capable of other embodiments.

In the drawing- Fig. 1 shows in perspective an abrading inset unit see'n from the rear.

Fig. 2 is a view upon a carrying disk with abrading insets assembled thereon.

Fig. 3 shows a portion of an abrading inset unit in enlarged scale.

Fig. 4 is a further enlarged cross-sectional view of a portion of an abrading inset unit.

Fig. 5 is still further enlarged to show abrading bodies supercially embedded in the matrix of an abrading inset unit or body.

The embodiment chosen for illustrating tnis invention is what is known as an attrition mill and is of the general-type as shown in more detail in patents such as that to Daniels #1,814,587 and to Farley et al. #1,984,869. Such a mill comprises essentially two disks having opposed working faces, of which either one or both are rotated. Stock to be treated is fed between the disks and escapes from a casing housing the disks, in treating condition.

In these particular patents, the disks are arranged to have secured to their working faces, insets of more abrasive material than that of the disks themselves, although it has been widely customary to use the disks themselves to do the abrading. This invention directs itself, however, to that type of disks or cooperating elements that carry abrading elements or units that are supplemental to the disks.

To that end, this invention is specifically embodied in a circular ring segment or other shaped inset I of which a plurality, when placed together end to end, form a`ring. Each segment is made up of a main body or block portion or matrix of some moldable materiall that is extremely tough so as to withstand tendencies to break, when used in an attrition mill. Such materials include cast iron, brass, bronze, aluminum, and so on.`

Each segment or inset is provided with means for attaching it to its carrying rotating disk II, such as apertures I2 therethrough and squared recesses I3 for countersinking the heads of bolts that pass through the apertures I2 to bolt the segments to the disk. To aid in centering the segments in or on the disk, chipping strips or ears I4 are provided that are arranged to frictionally engage the flange or rim I on the periphery of the carrying disk. A depression Illa is provided on the back of the inset I0 (see Fig. 1) that can be filled with lead or other weighting material in order to balance the segments when in place. The disks rotate at such va speed that the weight of all the segments must be equalized, and this is done by the amount of lead placed in these depressions.

v The working surface of the segment I0 is made up of grooves I6 and lands I1 that are more or less customary now on the working surfaces of disks in an attrition mill. These grooves I6, it will be noticed, are non-radial and non-tangential, but at an angle in between the two. Also, it is to be noticed that each groove is broken, or a bridge I8 is provided to prevent stock from bypassing abrasion by too-ready exit from the mill. In cross-section, the segment I0 shows its top or working surface to be crenelated or toothed (see Fig. 4) like a rack for a gear, whereby a greater surface area is exposed to the stock being treated than would be the case if the working surface were flat.

Embedded in the working surface of the main body of the segment or inset I0 are abrasive grains of at least two sizes I9 and 20 with one size I9 being larger than the 'other 20. The smaller size 20 is selected to be small enough to lie in the interstices between the larger grains I9. 'Ihese grains are embedded in the main body in a manner that the working surface thereof serves as a matrix for the grains.

The grains are chosen for their abrasiveness and preferably are of fused aluminum oxide or corundum, as produced, for instance, in an electric furnace. Carefully sized grains are chosen. The larger or primary abrasive grains are to be of a size best suited to do the abrading work desired of them, and in practice to date, what is known in the abrasive art as grain size No. 8, has proved to be satisfactory. Next is chosen a grain size for the secondary work which is more particularly to ft in between the primary grains and thus to form a protective bridging between the larger grains to protect the softer but tougher matrix material of the segment. For this purpose, what is known in the abrasive art as grain size No. 12 has proved itself satisfactory although grain size No. 16 can be used. Also, a combination of both No. 12 and No. 16 is effective.

However, as the larger sized grains are depended upon to do the major part of the abrasion, they` should comprise the major proportion of the total grains, that is to say, not less than 50% by surface area of the inset. In Fig. 5 the grain I9 may correspond to the standard grain 'size No. 8, and the grain 20 to the standard sizes I2 and I6 respectively. That is to say, the sizes employed are of a granular character, substantially to the exclusion of fines. Whereas the size of primary and secondary grains have been mentioned, they may be changed to suit local conditions. That is, if a coarser grind is desired, larger primary abrading grains are used, with a. size of secondary grains that will fill in between the primary grains to protect the matrix against wear at a rate faster than is needed to expose fresh surfaces of abrading grains. The primary and secondary grains thus form a bridging or crust or armor for the matrix material but which is not sufficiently impervious to wear for it is planned to use some wear on the matrix for exposing fresh abrasive grains to the stock being treated as the primary abrasive grains wear away and fall out. As this happens, the secondary grains are bound to do some abrading. So also some abrading will be done by the crater with its jagged surrounding prongs left when a primary grain falls out of its setting. And to a lesser extent, the same thing will happen when a secondary grain wears and falls out.

Since the abrasive grains are expensive as compared to the matrix material, it is desired to use-no more of them than is necessary, so to that end, the distribution is confined to a relatively thin surface zone Z adjacent thev working face of the segments, but care is taken that the grains well cover all of the exposed surfaces of the segment including the lands and valleys of the grooved areas of them. This is accomplished by way of example as shown in patents to Bowers No. 1,403,005 and to Edmondson No. 1,893,539, although other methods may be used.

While the embodiment chosen for illustration is what is called an attrition mill wherein the abrading surfaces are represented by opposing disks, which disks carry the novel type of insets herein described, it should be understood that the shape and size of the inset will be modied as necessary to nt them into whatever elements are to carry them. For instance, in the refiner or jordan type of mill, there is a cone shaped rotor called a plug, adjustably mounted Within a correspondingly shaped shell. In such a machine the insets may take the form of strips or bars disposed on the surface of the plug substantially axially thereof, and on the inner side of the shell.

While in the embodiment herein shown, two

specified grain sizes are used as abrading elements, it should be understood that it is Within the scope of this invention to use other than the specified grain sizes; or else more than just two grain sizes, or on the other hand, substantially not more than just one grain size provided for the surfaces of the inset units.

We claim:

An abrasion element for attrition mills and the like comprising a bonding matrix of mold able metal havingv a crenelated wor'king surface provided with a series of grooves and intervening land portions, the material of said matrix being substantially continuous in the innerregions thereof and having relatively hard long- Wearing abrasive grains at least partially embedded therein solely in the surface regions thereof both in the bottom and side walls of the grooves and in the land portions, said grains including a plurality of relatively large primary abrasive bodies of a substantially uniform size land a plurality of relatively small secondary abrasive bodies of a smaller uniform size occupying the intervening spaces existing between the primary bodies, said grains substantially coextensively covering the metal surface of the moldable matrix with the outermost grains of both sizes projecting outwardly therefrom in directions substantially normal to the surface 30 thereof. l

RICHARD D. KEHOE. ROBERT B. EASTTY. WILLIAM H. SAYRE.

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