US2376342A - Manufacture of abrasives - Google Patents

Description

MayyZvZ, 1945.

R. F. CARLTON MANUFACTURE '0F ABRASIVES May 22 1945- R. P. CARLTON 2,376,342

MANUFACTURE OF ABRASIVES original Filed Jan. 20, 19 so 5 sheets-sheet 5 May 22 1945 R. P. CARLTON 2,376,342

MANUFACTURE OF ABRASIVES Original Filed Jan. 20' 19 30 5 Sheets-Sheet 4 R. P. CARLTON 2,376,34

MANUFACTURE OF ABRASIVES May 22 1945.

` Original Filed Jan. 20' 19 30 5 Sheets-Sheet 5 fw@ f..

Patented May 22, 1945 UNITED STATES PATENT OFFICE MANUFACTURER OF ABRASIVES Original application January 20, 1930, Serial No. 422,065. Divided and this application July 8, 1941, Serial No. 401,484

.6 Claims.

This invention relates in general to coated articles and to the art of coating, and more particularly to an improved method of and apparatus for applying pulverulent coatings to suitably adhesively coated surfaces, and While the invention nds particular utility in the art of making iiexible abrasives, and is, therefore, described and illustrated for this purpose, it finds a wide eld of utility for analogous purposes.

This application is a division of my copending application Serial Number 422,065, filed January i0, 950, now Patent No. 2,318,570, granted May It is well known that in the art of making sandpaper, emery paper or cloth and similar abrasive articles, a flexible or in some cases, a rigid, backing of paper, cloth,vwood or the like is employed, to which is applied a coating of an adhesive substance, such as animal or vegetable glue, or where a waterproof article is desired, the backing may be coated with any of the now well known waterproof adhesives of the Okie Patents 1,565,027, 1,565,028, of December 8, 1925, or 1,581,657 of April 20, 1926, for this purpose, and while the coating is still wet or unset, a suitable abrasive material such as garnet, corundum, sand or the like is applied thereto. The grains of abrasive substance are usually applied by gravity upon the upper adhesive coated surface of the backing, and they lie in the adhesive material in hap-` hazard fashion due to the elongated nature of the abrasive particles, and in a large degree, the facets or cuttings edges of the individual grains or grits often lie flat upon or are embedded in the adhesive coating in such a manner that in some instances their best cutting edges never come into contact with the work or at best are brought inefflciently into contact therewith. The invention here has as one of its objects to measurably increase the number of grits whose longer or greater dimensions are in a plane perpendicular to the surface of the backing, thereby to present more efiiciently the cutting edges to the work, and increase the cutting ability and life of the abrasive article.

It will be understood that in ordinarily depositing mineral, that is, pulverulent abrasive material solely under the force of gravity onto a backing, it acquires a velocity due to the action of gravity. As the grits pass through the intervening air space, there will be caused some change in their positions en route to the sheet or backing, but ordinarily neither the velocity given to the grits or the effect of the air on them is suicient to cause them to become aligned so as to assume positions substantially perpendicular to the backing. It is, therefore, necessary that independent force be applied to the grits, and I have found that by passing the grits through a static field of electric energy or of electro-magnetic energy or by mechanically imparting this force to the grits a much greater number of the individual particles will assume erect positions on the backing, which will enhance its cutting ability. As will later appear, my invention, in its several forms, is capable of application for operation in conjunction with gravity methods of applying the grit, inasmuch as under certain conditions, and for some purposes, it is desirable to employ both gravity and one of the forms of my invention in conjunction in order to attain a desired form of abrasive article.

In carrying out this invention, I iind it desirable to employ a conveyor for conducting the mineral at rest relative to the conveyor by relatively slow speed to a point adjacent to which the independent force is applied for projecting the particles of grit onto the backing. I find that by then applying this independent force, be it mechanical or electrostatic or electro-magnetic, I am able to impart a high velocity to the particle so that any force of gravity acting on the particle, whether in the same direction, in a counter direction, or in a direction angularly to that at which the force is applied, will be relatively small compared to this force applied. It is possible with the present invention to apply the force directly counter to gravity, that is, by bringing the grits beneath the backing or by applying the force in some other direction as long as the force of gravity and the eiiect of air is reduced below a point which will interfere with the result desired, namely, the projection of the grits with their longitudinal dimensions ultimately perpendicular or substantially so with respect to the backing.

The principal objects and advantages of this invention reside in the provision of an improved abrasive coated article, such, for example, as sandpaper, emery cloth, or the like, wherein the abrasive grits or grains lie in position on the backing for increasing the cutting eiect and durability of the abrasive article; the provision of an improved abrasive article wherein the abrasive grits are disposed so that their cutting facets are presented in position to more eciently engage the work and thereby produce a sharper article; the provision of an improved abrasive article wherein the abrasive grains or grits are applied thereto with their longer or greater dimension substantally perpendicular to the plane of the backing;

the provision of an improved abrasive article which may be flexible or rigid, as desired, and which may or may not be made waterproof, that is, suitable for employment in a water abrading operation.

This invention further includes as objects and advantages thereof, the provision of an improved method of and apparatus for manufacturing abrasive articles; the provision of an improved method of and apparatus for applying pulverulent material to one surface of a backing irrespective of the force of gravity, that is, against the normal tendency of the force of gravity; the provision of an improved method of and apparatus for propelling a pulverulent material, such as a grit or an abrasive grain, against an adhesive coated surface; the provision of an improved method of and apparatus for the purpose set forth and including electrically operated means for acting on an abrasive grain or pulverulent material and causing it to advance onto the adhesive coated backing irrespective of the force of gravity; the provision of an improved method of and apparatus for causing the particles of pulverulent material to impinge upon and assume a position in the adhesive coated surface substantially normal or perpendicular to the surface of the backing; the provision of an improved method of and apparatus for propelling a pulverulent 'material onto a moving sheet in a direction transversely to the plane of movement thereof and in a direction substantially counter to gravity; the provision of an improved method of and apparatus for making abrasive articles, such as sandpaper and the like, which includes the application of a grit to the under side of the backing; the provision of an improved apparatus which includes means for feeding and applying a pulverulent material counter to the force of gravity and simultaneously with movement of the backing; the provision of an improved means for moving a web of paper and applying an adhesive thereto and including means arranged below and for operating synchronously with for applying a pulverulent material to the under side of said moving backing; and the provision of an apparatus of the character described wherein improved electrostatic or electro-magnetic means may be employed, acting on the abrasive material and causing it to move at an accelerated speed toward the sheet so as to cause it to impinge thereon in the adhesive coating and thereby present the cutting edges of the abrasive grits away from the surface of the backing and thus increase the cutting ability and life of the abrasive article.

I have also found my invention useful as a modifying step in the employment of the conventional gravity process for applying grit in the manufacture of sandpaper or other abrasive and, therefore, additional objects of this invention reside in the provision of an improved method f interposing an additional step which will apply abrasive grains either before or after the application of grits by gravity in the usual manner,

it being understood that the step of applying grit irrespective of gravity by an electro-magnetic or electrostatic means may be employed somewhere in the process of manufacture, `the essential purpose being to increase the number of grits whose cutting facets are presented away from the backing and thereby to enhance the cutting ability of the finished article.

The apparatus of this invention includes a number of alternative forms for mechanically or electrically carrying out the steps of the process, and to this end is provided an improved pneumatic means and improved vibrator structure for mechanically propelling the pulverulent material and improved electro-magnetic structure for acting on the mineral and causing it to move in a cloud toward the adhesive coated surface of the moving web or backing.

The foregoing and such other objects and advantages as may appear or be pointed out as this description proceeds are attained in the structures illustrated in the accompanying drawings in which:

Figure 1 is a schematic view illustrating one form of apparatus for carrying out the process of this invention;

Figure 2 is a view similar to Figure l of an alternative form of the invention;

Figures 3, 4 and 5 are further alternative forms of the invention which include the electrical feature;

Figure 6 is a further alternative form of the l apparatus of this invention of employing me chanical vibrating means;

Figure 7 is an enlarged schematic view illustrating a portion of an abrasive article made in accordance with this invention;

Figures 8 and 9 are additional alternative forms of apparatus for carrying out further steps of thev process of this invention; and

Figure 8a is a fragmentary schematic view of another alternative form of apparatus;

Figure l0 is a further alternative form of apparatus for carrying out one of the methods of this invention.

The method of the present invention includes as steps thereof the feeding of a web or strip of paper or other fabric at a predetermined rate of speed, applying an adhesive substance to the under side of the sheet, or applying the adhesive coating to one side and then moving the sheet with the coated side out, and simultaneously with the movement of the coated sheet, causing a grit or abrasive material to be applied to this side. The sheet or web of paper may be moved so that the adhesive coated side is either presented downwardly or at any angle thereto. The movement of the abrasive grains onto the under side of the backing is done irrespective of the force of gravity and, in fact, directly counter to gravity, and preferably done by imparting relatively high velocity to the abrasive material, thus causing it to impinge upon the adhesive coating. In View of the fact that the abrasive grains are projected through an intervening space from a suitable carrier onto the adhesive coated side irrespective of or counter to the force of gravity, the grains, which are usually somewhat elongated, will assume a position in transit so that the longer dimension thereof will take a position normal to the surface of the backing, thus causing the grains to stand on the surface rather than lie flat in greater percentage than when they are deposited by gravity. It is to be understood that this movement of the grains and deposition of them on the coated surface may be carried out in a number of ways, either by vibration, by an air blast, or by electrostatic or electro-magnetic means` In the alternative forms of this invention later to be described, the method involved includes combining a gravity deposition of mineral on the adhesively coated moving backing with the step of applying the grits irrespective of gravity, this being particularly useful in some of the heavier grits wherein it may be `found that the force susceptible of application by an electrostatic or an electro-magnetic means is not sufficiently active on the available area of the individual grits to cause an entirely satisfactory result or to move enough of the grits into the sheet to attain the desired end. In this invention it may be required to apply some of the grit by gravity and later apply some of the grit by one of the methods of this invention or vice versa, but, in any event, the number of grits in the entire finished article whch stand erect on the backing will be measurably increased over the ordinary methods heretofore employed for depositing grit on a backing for forming an abrasive article.

This invention produces a very satisfactory piece of sandpaper in which the cutting ability `is measurably increased and by the deposition of the grains of sand or grit irrespective of the force of gravity, it is possible to produce an orientation of the mineral as desired and to control the thickness of the abrasive coating much more readily than where gravity alone is relied upon or employed for depositing the grains on the sheet.

The apparatus of this invention may take any one of `the forms shown in the drawings, and in the form of the invention shown in Figure l, air pressure is resorted to for producing the mineral cloud and for projecting the mineral onto the moving web.

Referring now more particularly to Figure 1, the flexible backing of paper or cloth or other fabric is trained or fed over a series of rollers 6, 6, and over one of a pair of the squeeze rollers indicated at 1, the other roller B of said pair being in contact with an adhesive material contained in a tray or tank 9 by which an adhesive coating is applied to one side of the moving web. After receiving the adhesive coating, the web 5 is trained over rollers I0 and II and is brought back over a roller I2 so that the adhesive coated surface of said web is presented downwardly. The web may then be trained over rollers I3, I3, and fed to a suction drum I4, whence it passes into festoons for drying.

'I'he mineral is supplied from a hopper I6 and a conventional outlet I1 which feeds a layer I8 of mineral to a moving conveyor I9. This conveyor I9 is preferably porous and passes over the feeding rollers and 2| yand is adapted to move at a suitable rate of speed to supply a sufficient quantity of abrasive grain. In some cases, it has been found advantageous to move the conveyor at a speed substantially the same rate of speed as the web l5, although these speeds are, of course, variables. The rollers 20 and 2l are mounted in the ends of a suitable frame 22, and this frame may be raised and lowered so as to vary the distance between mineral conveyor I9 and the moving web I5. This frame 22 may be supported Xedly at one end, as indicated at 23. and the other end may be raised and lowered by a toggle arrangement 24 activated by a threaded rod 25. Below the conveyor I9 and at the movable end thereof, that is, adjacent to the web I5, there is provided a second conveyor 2B which serves to conduct away excess mineral which ows over the end of the conveyor I9 and which may be returned in any suitable manner to the mineral hopper.

Below the upper flight of the conveyor I9, there are provided two air troughs 21. These air troughs are provided with flat upper walls Cil 28, having slots 29 therein, said slots extending across the width of conveyor I9 and the troughs themselves being connected to a suitable Source of air under pressure.

These troughs form in effect elongated jets or nozzles and when so placed below the conveyor belt or frame 22, a small quantity of air is emitted at high velocity which passes through the porous belt or conveyor.

It will be understood that when a blast or blasts of air are delivered from the troughs 21, this blast of air passes through the porous conveyor I9 and blows the mineral from the conveyor against the under side of the jght I5 so that the mineral is caused to strike into the adhesive at a relatively high velocity and become impinged therein. Owing to the projecting of the mineral in this manner through the intervening air space, the individual particles of grit or abrasive material are caused to assume a position parallel to their trajectory, that is, with their longer dimension perpendicular to the surface of the flight I5. In view of the fact that most of the particles of mineral are somewhat elongated, due to the manner of production of the same, they will naturally assume this position in movement from the conveyor I9 to the adhesive coated surface of the backing. As they arrive at the adhesive material, they impinge, themselves thereon and will thus stand erect in the adhesive, thus forming a sharper contour for abrasive purposes. By varying the rate of speed of the moving backing relatively to the speed of the conveyor and by varying the distance between the conveyor and theI backing and the velocity of the air stream, and by increasing or reducing the number of such jets and the quantity of adhesive applied, any reasonable desired thickness of grit layer may be produced during the process and without stopping the apparatus. It will be understood that the excess mineral carried by the conveyor may be dumped into the conveyor 2B and returned by any suitable means to the hopper IG.

Referring now to Figure 2, there is provided the same general arrangement of moving backingy having the night 30 adhesively coated from the squeeze rollers 3l.

Below the flight 3f) there is provided a mineral feeding conveyor I9a, receiving pulverulent material from the hopper I6a.

The conveyor I9a is mounted for movement toward and away from the flight 30 similar to the conveyor I9 and, therefore, this structure has not been shown in Figure 2.

As the mineral flows from the hopper Ia it does not always assume a smooth or even distribution on the conveyor |90., and, therefore, it may be desirable to provide a pair of charged electrodes 32, one arranged above and one below the conveyor I9a, for the purpose of spreading the mineral evenly on the conveyor belt. The conveyor I9a in this instance may be non-porous.

When charged electrodes are put in this position they act in principle the same as the charged electrodes used for coating the mineral on the backing. An electrical charge or difference of potential is set up between the electrodes 32. The voltage or difference in potentiall between those electrodes is maintained great enough to produce a strong electrostatic eld, but not so great as to break down the insulation between the plates. which insulation may be the dielectric strength of the air or the dielectric strength of the air plus the dielectric strength of any insulating material which may be used to wrap the electrodes.

As the mineral on the conveyor enters the static field between the plates the mineral particles take on the charge of the lower plate, and are repelled to the upper plate where they lose their charge and take on the opposite charge of the upper plate. At this point they are repelled to the lower plate. Since new mineral is being conveyed by the conveyor into the field continuously the static fields soon become supersaturated with mineral particles, and an equilibrium is reached where as many particles are thrown out of the static field as are brought in by the conveyor. By having a down-turned end 32a of the upper electrode the mineral particles that are thrown out of the static field are deflected evenly on the conveyor belt so that a smooth coating of abrasive grit is rst placed on the conveyor.

The use of an electrostatic field for getting a smooth coating of mineral on the conveyor belt is not necessary to the invention but is an additional means of obtaining evenly distributed abrasive coatings, and is also a means for avoiding the use of any excess mineral on the conveyor. When the mineral is evenly coated on the conveyor at the time it is being coated, streaks, thin spots, etc., in the finished product are reduced.

At the same approximate point at which troughs 21 are provided in Figure 1 there are here provided electrically charged electrodes 33 and 34, the electrode 34 being located below the upper flight of the conveyor belt |9a and electrode 33 being disposed above the flight 30 of the backing. A sufficient difference of potential is maintained at electrodes 33 and 34 to produce a strong electrostatic eld, similarly to that referred to above. This electrostatic iield moves the mineral from the belt ISa to the underside, which is the adhesive coated surface of the flight 30.

As the mineral enters the electrostatic eld between the electrodes 33 and 34 it becomes charged with the charge of the lower plate, and is here propelled to the upper plate 33.

It will be observed that in this method of coating the mineral is applied by a force other than gravity. In all other methods of coating sandpaper, known to me, the velocity of the particle is either in whole or part given to it by the force of gravity. In the case of this electrostatic coating the particles are oriented in the electrostatic field so that there is a tendency for the long dimension of the mineral to be perpendicular to the electrode plates, and also perpendicular to the web 30, which is being coated. The finished sandpaper product, therefore, contains a substantial percentage of the particles of mineral standing on end rather than laying dat, thereby increasing the cutting properties of the abrasive article.

Excess mineral is dumped onto the conveyor 35, whence it may be returned to the hopper |6a.

Referring now to the alternative form of the invention shown in Figure 3, there are provided the squeeze rollers 36 which apply adhesive to one surface of the moving paper web 31, and the adhesive coated surface thereof is presented downwardly in the flight 33.

In this instance there is provided a hopper 39, having a curved outlet spout 40 whose outlet 4| is presented below the moving web 38. The hopper may be provided with a bracket 42 whereby to receive a threaded member 43, said bracket engaging a guide post 44. In this manner, the hopper may be raised or lowered so as to vary the distance of the outlet 4| from the flight 38 of the backing. A suitable screen 45 may or may not be provided over the outlet so as to cause the distribution of the mineral contained in the hopper. In this instance, the mineral flows by gravity to they outlet 4|, but does not pass from the outlet to the adhesive coated backing by gravity, but under the effect of the static charge established between the electrode 46 and the hopper or the screen 45 of said hopper.

The operation of the invention here is much like that of Figure 2, the screen 45 serving the purpose of distributing the mineral and at the same time preventing the large body of mineral in the hopper from forcing it against the coated surface of the backing.

Referring now to the form of the invention shown in Figure 4, there is provided the adhesive coating rollers 41, applying an adhesive coating to one surface of the moving web 48. This web 48 is trained over rollers 49 and 50 so that flight 5| thereof between said rollers is presented in a plane tangential to the surface of a conveyor drum 52 whose lineal velocity is suflicient to furnish the required amount of mineral. This drum is fed from a hopper 53 and forms one electrode of the electrostatic system. The other electrode is indicated at 54 and is disposed above the flight 5|. As mineral issues from the gate 55 of the hopper, the drum rotating in the direction of the arrow A, the mineral is carried to a point adjacent to the flight 5|, whereupon the electrostatic charge set up between the drum 52 and the electrode 54 will cause a projection of the mineral from the drum onto the coated surface of the flight 5|.

Referring now to the alternative form of the invention shown in Figure 5, there is employed here electro-magnetic means or a permanent magnet means for moving the grits toward the adhesively coated web. The adhesively coated web is shown at 12 and is fed from a roll 13 over an adhesive coating roller 14. The horizontal flight of the web 12 passes beneath magnet 15 which may be either an electro-magnet upon which a variable voltage may be imposed or a permanent magnet.

Immediately below the magnet 15 and the flight 12 of the web, there is provided a source of supply for the mineral, that is, the abrasive material, indicated at 16. This source includes an outlet 11, and the distance between the outlet 11 and the moving web 12 may be varied as desired, or the intensity of the electro-magnet, where one is employed, may be varied for changing the thickness of the abrasive coating. The web passes over an idler 18 whence it is fed to festoons not shown.

Referring now to the form of the invention shown in Figure 6, the moving web 56 is trained over a series of rollers similar to the arrangement shown in Figures 1 and 2 so that a horizontal flight 51 of the paper backing is provided, having an adhesive coating on the under side thereof. Squeeze rollers 58 engage the paper backing for applying an adhesive thereto.

In this form of the invention, a mechanical vibrating means is provided which serves to propel the mineral, that is, the grit, from the gritfeeding conveyor 59, which latter receives mineral from the hopper 60, having a gate 6|. The

conveyor 59 is trained over rollers 62 and 63 mounted in a suitable frame 64, which latter may be mounted for adjustment toward and away from the flight 51 similarly to the conveyor I9 of Figure l. The conveyor 59 extends below and is separated from the flight 51 of the paper web and travels at substantially the same speed as the paper web.

The conveyor 59 passes between sets of pinch rollers, one above and one below the upper ight of the conveyor 59, as indicated by 65 and 66, and also beneath a pinch roller 61 which bears on the roller 62. The pinch rollers 65 and 66 tend to distribute the mineral evenly over the surface of the conveyor and are so spaced from the rollers 62 and 61 that the portion of the belt 59 between the rollers 65 and 66, and 62 and 61 is permitted to lie slack, whereas the remaining part of the conveyor is substantially taut. This arrangement tends to limit the vibration of the conveyor belt to the zone of application of the mineral to the paper backing, as indicated at 68.

Beneath the portion 68 of the belt 59, there is provided a revolving batter 69 operating on a shaft carried in suitable bearings in the frame 64 and provided with a plurality of radial arms 19 which upon rotation rigidly strike the under side of the portion 68 of the belt, thus throwing or projecting the mineral content thereof against the under side of the adhesive coated paper backing, much in the manner in which the air stream blows the mineral or grit against the paper backing as shown in Figure l. The batter 69 may be driven in any desired manner from a separate source of power or may be connected suitably with the rollers driving the belt 59, but geared to operate at a greater rate of speed. The rollers 65 and 66 and the roller 61 are separately driven from the belt 59 s0 as to produce the tautness in the belt, except the flight of the belt indicated at 68.

In Figure 7, there is illustrated an article made in accordance with the present invention. The backing is shown at 8|] to which an adhesive coating 8l has been applied, and the grits, greatly enlarged, are indicated at 82, and it is noted that they stand on end in the adhesive coating, thus causing their sharper edges to project beyond the upper or outer surface of the coating, thereby enhancing the cutting ability and increasing the life of the abrasive article. While the article shown in Figure 7 is purely schematic, it will be understood that the mineral actually does take a position substantially normal to the backing and, while all of the grits may not take this position, a large number of the same do, and the cutting qualities of the abrasive article are thus greatly increased. Furthermore, by so disposing the grits, it permits of the application of an additional sizing coat or coats to the back and to the front or cutting face of the abrasive material without completely burying the grits and as a thicker coat of adhesive may thus be employed on the cutting face of the abrasive material, the engagement of the adhesive material with the abrasive material is greatly enhanced, thus further tending to increase the life of the abrasive article. Such a sizing coat is indicated at 83.

As previously pointed out, where the electrostatic or electro-magnetic methods are resorted to in some of the coarser grades of abrasive devices made, it may be found that the electrostatic or magnetic field into which the particles are conducted may not exert on each individual particle f suiicient force to cause proper orientation of the particles, for the reason that the electrostatic effect is substantially proportional to the area of the particle, and the coarser the particle, the smaller the area of eifect per weight. Therefore, as larger gits or sizes of particles are employed, increased force is required to move the particle, and for some purposes, insuicient increase in force results because of the reduced area per weight. Therefore, in such cases, a form of the invention, as shown in Figure 8, may be resorted to wherein the mineral is applied to the adhesively coated backing in part by gravity and in part by electrostatic or electro-magnetic means,

In View of the fact that the electrostatic and electro-magnetic means may for some purposes be alternatively employed, I have illustrated in Figure 8 merely the electrostatic elements, though it will be understood that the electro-magnetic means of Figure 5 may be employed in the same manner.

Referring in detail to Figure 8, I have illustrated a web of paper 84 coming oil a roll 85 and passing through an adhesive coating device illustrated in general at 86. The web 84 is thence trained over rollers 81, 81a, so that it has a substantially horizontal flight 81h, which receives grits in the desired amount from an ordinary conveyor 88, said conveyor receiving grits `from the hopper 89. The web of paper thence is carried downwardly to a horizontal flight by the provision of rollers 9|, 9|, and adjacent one end of this iiight, I provide the conveyor 92 receiving additional grits from the hopper 93, which may be adjustably mounted similar to the conveyors hereinabove described, said conveyor 92 passing beneath the flight 90 of the paper web. As the web passes over the rollers 81a and 9|, a quantity of the mineral deposited from the conveyor 88 onto the web will drop off, and, for conveying away this excess mineral, I provide a transversely running conveyor 92a arranged between the flight .90 and the conveyor 92. Beneath the upper flight of the conveyor 92 and above the flight 90 of the web 84, I provide electrostatic electrodes 94 and 95, or may provide an electro-magnet similar to that shown in Figure 5 which will cause grit coming from the hopper 93 to be applied counter to the force of gravity onto the under surface of the flight 90. A conveyor 95a may be employed for carrying off the excess mineral from the conveyor 92,

In the operation of this form of the invention, it will be understood that Va desired proportion of mineral applied by gravity to that applied by force other than gravity may be determined by actual operation so that the desired quantity of the abrasive grits is properly applied to the paper web.

It may be necessary in some of the very coarse grains to additionally apply grit to the moving web, and this may be done by providing an additional conveyor similar to that indicated at 92 and additional electrodes, or may be accomplished by additionally applying by gravity grits at the point indicated at 96, this arrangement being shown in Figure 8a and the grits being applied to an upper ight 91 of the paper web just before it passes on to the iestoons.

Figure 9 illustrates the alternative forms suggested in connection with Figure 8, that is, wherein electrostatic or electro-magnetic means, or any other means counter to gravity, is employed for applying the grits, and in Figure 9 the paper web is indicated at 96a having a horizontal flight 91a disposed below a conveyor 98a. In this instance, the grits are deposited from the `conveyor 98a by gravity, and the orientation of the grits is assisted by a plate electrode 98. 'Ihe paper web may then be carried in position so as to provide a horizontal flight 99, and an electrostatic or electro-magnetic or other grit applying means for applying grit counter to gravity may be employed at one or more points as indicated at A and B, wherein the conveyors and |0| convey grit from suitable hoppers |02 and |03, and electrodes |04, |04 and |05, |05 serve to apply the grit.

Referring now in detail to Figure 10, there is further illustrated there an apparatus for applying the grit to the adhesively coated backing by an electro-magnetic means. In this form of the invention a moving web is provided indicated at |06, this web being a flexible strip of paper which is suitably adhesively coated by a mechanism indicated generally at |01.

The moving web thus adhesively coated is carried over a roller |08, thence over a roller |09, said roller |09 being mounted on a shaft carried in a bearing arm or arms ||0 pivotally mounted at whereby the roller |09 may be raised and lowered in the substantially vertical plane of the arrows H2, thus permitting the lower flight ||3 of the paper web to be elevated or depressed, as the case may be.

Mineral is deposited from a hopper I4 onto a conveyor 5 trained over rollers ||6 and lla, the upper flight of said conveyor passing beneath the roller |09 `and the moving web and conveying mineral, that is, the grit, to a point adjacent to the roller |09.

Preferably immediately below the axis of the roller |09 and below the upper night of the conveyor ||5 I provide an electro-magnet ||8 which is so mounted that its magnetic flux passes through the conveyor and causes the mineral particles to stand erect, as indicated at ll9, as they move along with the upper flight of the conveyor. While the mineral particles are thus 'standing erect they come into contact with the adhesively coated side of the paper backing and are thus picked up by it and conveyed away, the backing being trained over rollers and carried to the festoons similarly to the other forms of the invention. It will be observed that the angularity of the lower stretch H3 of the paper web is such that it lies upwardly to the conveyor ||5. In this way the particles of grit adhering to the paper are not knocked down by other particles remaining on the conveyor, it being understood that the grit is fed somewhat in excess of the required amount so that an adequate amount will be deposited on the adhesively coated side of the backing. The excess mineral drops olf the conveyor and is carried to a collecting means by a conveyor |2I.

It will be understood that by varying the amount of mineral fed from the hopper, the strength of the electro-magnet, that is, the strength of the flow current transferred, and the position of adjustment of the roller |09, the assembly may all be properly correlated for obtaining the desired grade of finished article.

It may be desirable that a certain amount of pressure be exerted on the erect particles of mineral so as to cause them to impinge upon the adhesively coated side of the paper and thus, by manipulation of the arms H0, an adjustment of the pressure of the roller |09 may be attained.

It will be understood that while the electrostatic and electro-magnetic means for coating counter to gravity are illustrated in Figures 8 and 9, the mechanical means hereinabove described may be conveniently employed in these locations without departing from the spirit of the invention. However, the reason the electro-magnetic and electrostatic elements are particularly shown here is that the difficulty of counter coating successfully with the coarser grains is more likely to arise with these elements than With the vibrator or air blast heretofore described.

I wish to point out that where the expressions "electro-magnetic and electrostatic are employed in the specification, I refer to the employment as well of a permanent magnet or some other form of static charge or magnetic charge which will perform the function.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. The method of manufacturing an abrasive article having a backing and a grit layer, which includes as steps thereof applying an adhesive to one side of the backing, bringing the coated side of the backing into proximity to a quantity of grit, providing an electrical force acting on the grit for causing it to stand erect in relation to the backing material, and bringing the grit while thus erect into embedding contact with said adhesive by a differently applied mechanically embedding force.

2. In the method of making sandpaper or the like, the steps which comprise adhesively coating a web, directing said web with the adhesively coated surface downward and presenting the same adjacent a surface over which a layer of abrasive particles have been distributed, synchronizing the movement of the web and the distributed layer of abrasive and then transferring the abrasive to the adhesive.

3. In the method of making sandpaper or the like, the steps which comprise adhesively coating a web, directing said web with the adhesively coated surface downward and presenting the same adjacent a surface over which a layer of abrasive particles have been distributed, synchronizing the movement of the web and the distributed layer of abrasive and then transferring the abrasive to the adhesive by contacting the adhesive with the abrasive and removing the abrasively coated web from the zone of contact.

4. In the manufacture of granular coated webs, the method comprising positioning from a layer thereof in a deposition zone elongated granular particles upon an adhesive coated web, with the major axes of the particles substantially uniformly oriented at an angle with respect to the surface of the web by moving the web into the deposition Zone where said web is mounted in a position to face downwarly while in said zone, and supporting the freshly coated web with respect to the horizontal with the particle coated side down and in a position to have the particles thereof clear the layer in the deposition zone.

5. In the manufacture of granular coated webs, the method comprising positioning from a layer thereof in a deposition zone elongated granular particles upon an adhesive coated web, with the major axes of the particles substantially uniformly oriented at an angle with respect to the surface of the web by moving the web into the deposition zone where said web is mounted in a position to face downwardly while in said zone, orienting substantially all of the particles with their axes substantially in parallelism with each other and substantially normal with respect to the surface of the web and supporting the freshly coated web with respect to the horizontal that the oriented particles hang vertically downward and in a position to have the particles thereof clear the layer in the deposition zone.

6. In the manufacture of abrasives upon a downwardly faced adhesive backing, the steps which include directing, depositing and orienting abrasive particles to form an alerading4 surface by subjecting the particles, during attachment thereof to the backing, to the combined actions of a contacting mechanical embedding force and 5 an electrical force.

RICHARD PAUL CARLTON.

Certificate of Correction Patent No. 2,376,342. May 22, 1945. RICHARD PAUL CARLTON It is hereby certified that errors appear in the printed speciiication of the above'pff "i numbered patent requiring correction as follows: Page 1, first column, line 28, fo`r`-L substance read Substances llne 33, for cuttings read cutting page 2, second column,

line 30, strike out and after invention and insert the same after apparatus 1n line 32; page 3, rst column, line 7, for into read ortto; line 12, for Whch read which; and second column, line 30, after the syllable pinge strike out the comma; page 5, second column, line 4, for gits read grits; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofce.

Signed and sealed this 22nd day of October, A. D. 1946.

LESLIE FRAZER.

First Assistant Commissioner of Patents.

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