US2027309A - Abrasive material - Google Patents

Description

Jan. 7, 1936. E. c. SCHACHT ABRASIVE MATERIAL Filed March 24, 1932 s Sheets-Sheet 1 Jan. 7, 1936. E, c. SCHACHT 2,027,309

'ABBASIVE MATERIAL Filed March 24, 1952 s Sheets-Sheet 2 awe/wh sew, W,)ur%

Jan. 7, 1936. E. c. SCHACHT 2,027,309

ABRASIVE MATERIAL Filed March 24, 1932 s Sheets-Shaet 5 distribution control which Patented-Jam 7,1936

UNITED STATES anaasrva m'rsamr.

Elmer C. Schacht, Troy, N. Y., assignor to Behr- Corporation, Troy, N. Y.. a corpora- Manning tion of Massachusetts Application March 24, 1932, Serial No. 601,001

1 Claim. (01. 51-185) This invention relates to the art of coating with finely divided or fragmentary material.

An object of the invention is to provide an abrasive article in which the abrasive particles are individually oriented thereon i. e., with their major axes arranged substantially perpendicularly to the carrier for the particles so that their sharpest portions are exposed.

A further object of the invention is to provide an abrasive article in which the particles are stratified in accordance with their size.

A further object of the invention is to provide an abrasive article in which the particles are secured to the base by means of adhesive and individually oriented and stratified according to their size.

The invention contemplates an arrangement or tribution or dispersion of the particles with reference to one another, and preferably also the proper positioning or orientation of each individual particle, .50 that in providing a coated surface of abrasive material, for instance, the particles are arranged with their major axes substantially perpendicular to the carrier with the result that the sharpest portion of each particle will be exposed.

The method and apparatus will be described in their application to the manufacture of an abrasive paper, such as sand paper, although it will be understood that while particularly useful in the manufacture of such material, the invention is not limited in broader aspects to this particular field.

Abrasive paper, by which is meant any abrasive sheet or strip material having an abrasive surface formed of abrasive particles, ordinarily consists of a backing or carrier of paper or fabric, or combined paper and fabric, which is first provided with an adhesive surface upon which the abrasive or cutting material, such as sand, is then deposited.

Abrasive paper is of two general types. In one type, the adhesive surface of the carrier or backing is completely covered with the abrasive grains or fragments. The individual grains are closely packed, so that virtually no portion of the backing surface is exposed. Such a coating of abrasive material is commonly called a closed coating. y

In the second type, the individual particles or grains are spaced apart as uniformly as possible over the surface, so that substantially all of the particles stand by themselves alone or as. units will effect proper disof the abrasive surface. Such a coating of abrasive material is termed an open. coating.

The open coating is considered preferable for abrasive paper in some usages, since it does not tend to load or become packed with the material which is abraded. In some cases, a closed coating, in which the inters 'ces between the individual grains are extremely small, and virtually non-existent, quickly becomes loaded or embedded with the material abraded, and this results in excessive friction and finally the burning of both the abrasive and abraded surfaces. Such loading and burning is especially noticeable when abrading soft materials or materials of a gummy or resinous nature. The open coating overcomes this objection, since in view of the substantial space around eachof the abrasive grains, the

abrasive surface does not become packed, and the 0 particles removed from an abraded object do not remain in the interstices between the individual grains.

In the manufacture of both types of coating, it is preferable to arrange or orient the individual grains so that their major axes are substantially perpendicular to the carrier with the result that their sharper and more pointed portions are exposed. Furthermore, in the formation of an open coating, it has always been a problem to obtain the desired arrangement or dispersion of the individual grains with reference to one another. This dispersion or spacing of the individual particles is a problem particularly important in the formation of an open coating, but the proper distribution of the particles as they are deposited upon the carrier is also important in the manufacture of a closed coating. In the manufacture of the closed coating, it is customary to drop or deposit upon the adhesively coated carrier a greater amount of abrasive than it can hold. The surplus is then removed. Consequently, the only control as to the amount of abrasive retained is the holding capacity of the adhesive. In order to control accurately the amount of abrasive applied on a closed coating,it is, therefore, important to see that the surface is uniformly covered, and due to this it is necessary that the particles be uniformly distributed at the instant the abrasive is applied to the adhesive. When the particles are simply dropped on the adhesively coated carrier and no dispersing method employed, the resultant surface reflects any irregularities which are present in the fall or passage of the sand, and these irregularities produce streaks or ridges in the coating. It has also been found that there is a tendency in dropping sand or other abrasive particles for the latter to bunch together and produce what is called a lumpy or bunchy coating which greatly impairs the cutting efiiciency of the sheet because there are created a multiplicity of small high areas which come in contact with the surface to be abraded. Obviously, these areas keep much of the abrasive out of contact with the surface being'abraded, and thus reduce the efficiency of the sheet.

It will be understood, therefore, that by the terms "dispersion or arrangement, as applied to the particles, is not meant any particular spacing of the particles relative to one another, since the particles are dispersed or arranged relative to one another regardless of whether an open or closed coating is being formed. So far as the method of this invention is concerned, thedifference between an open and closed coating resides solely in the extent or degree to which the electrostatic field is used, 1. e. a stronger field or different disposition of the same is employed to produce an open coating than a closed coating. But in the manufacture of both types of coating,

' the electrostatic field may be effectively employed to produce the desired arrangement or dispersion of particles in the abrasive stream.

Heretofore, it has been the common practice to supply the abrasive material, such as sand, from a hopper by means of a feed roll having associated therewith an adjustable gate which controls the feed of sand. In the use of coarser grades of sand or abrasive material, such a means for controlling its application has been found to be effective, to a certain extent, since coarse sands will not bind or pack between the gate and the feed roll and will flow uniformly between the gate and roll to produce an open coating upon the carrier. However, it has been observed that this expedient does not effectively guarantee the uniformity of particle distribution or the equalization of density throughout the different areas,

and, moreover, it has no effect upon the sharp ness of the abrasive surface produced, and does not have a tendency to arrange each individual particle so that its sharpest portion or point is exposed.

In the use of fine abrasive material, such as number 240 sand, 2. feed gate and roll or similar apparatus does not produce a uniform fiow, even though the gate andfeed roll surfaces are finely ground and brought extremely close together. The difiiculty is particularly due to the tendency of the sand to pack or bind in the gate. As a result, the abrasive surface is characterized by bare spots, blotches, bars and streaks.

Consequently, in the manufacture of abrasive paper from fine abrasive material, it is necessary to exercise extreme care to obtain a uniform flow of sand and to finely grind and adjust both the gate and feed roll.

The present invention seeks to provide an improved means for obtaining proper arrangement of the sand both with respect to the uniform dispersion or spacing of the particles relative to one another, and also with respect to the arrangement or orientation of each particle considered individually to arrange each particle with its major axis substantially perpendicular to the carrier and expose its sharpest portion.

The invention also contemplates an improved apparatus for carrying out this method.

. Essentially, the invention comprises the use of an electrical charge produced by an electrostatic field, which is arranged so as to influence the individual sand particles to obtain the proper distribution of the same over the surface, and

also preferably, to position each particle so that its sharpest and therefore most effective abrasive portion is exposed. 1

The invention also contemplates the use of the electrical field in such a manner that the stream of abrasive particles, as it fiows toward the car- 5 rier, is controlled by the electrical field so as to cause a uniform distribution of the same relatively to one another, and thus produce a misting of the particles over a much greater area and eliminate ridges and streaks as well as the bunehiness or lumping in the coating.

In providing the electrostatic field, the invention seeks to dispense with the necessity for accurately grinding and spacing the gate and feed roll. It has been found preferable to dispose the 15 field so that it will affect the sand as it travels toward the surface of the carrier to be coated, thus permitting the field to disperse the entire sand-shower. The method also contemplates the selecting oif from the dispersed or electrified 20 shower, as by means of a baiiie, any excess sand not desired, and permitting the remainder to drop with the particles in their properly dispersed relation and also individually oriented, i. e. sharpest points up, upon the adhesive surface. 25 By properly arranging the electrostatic field, the method will also maintain a predetermined relation between each particle and it is oriented, i. e., with its major axis disposed substantially perpendicular to the carrier, in the field until it is 30 united with the surface, thus obtaining exposure of the sharpest and most abrasive portion of each particle.

In carrying out the method, a supply of sand may be arranged in a hopper above an adhesively 35 surfaced carrier or backing. The hopper may, if desired, be provided with an adjustable gate and feed roll for controlling to a certain extent the showering of the sand upon the adhesive surface to be coated, although the sand may be dropped toward the carrier in surplus quantities. The electrostatic field is disposed between the carrier and gate, so that the sand must travel through or adjacent the field before it reaches the carrier.

The sand particles are each influenced by the electrical charge, which serves to fan or spread out and disperse the shower, maintaining the particles in substantially uniformly spaced relation until they reach the carrier. It will be found that the voltage or power of the field may be regulated to control the extent to which the par-- ticles are fanned out or dispersed, and, of course, a factor in this control will be the character of the coating desired. If a closed coating devoid of ridges or bunchiness is desired, the field will be of a character which will simply provide the uniform distribution necessary to prevent these defects. If an open coating is required, the field will be controlled so as to disperse the particles relatively to one another to a greater extent. If the sand is showered in surplus quantities, a bathe or diverting plate may be suitably arranged to divert from the normal path of the shower any portion thereof which it is desired to exclude from the carrier. The position of the baflle will, of course, vary depending upon the character of the coating desired, and the amount of sand being showered toward the carrier surface.

The particles not led off from the shower continue on to the carrier and fall upon its adhesive surface. Due to the dispersing action of the electrostatic field, the particles are deposited upon this surface in substantially uniformly spaced relation, thus providing an. ideal open coating.

when applied to an abrasive medium such as sand, the electrostatic field has been found to be extremely efficient, and even though the controlling gate is opened quite wide to overcome the packing tendency of fine sands, and to provide a flow in excess of that required to use a coating, the use of the field will properly disperse the entire shower from which maybe led off such excess portions as are not to be permitted to fall upon the adhesive surface. The use of such an excess fiow eliminates the necessity for maintaining the gate and feedroll accurately ground or adjusted, and moreover, the irregularities of sand fiow due to surface imperfections on the gate or roll have been found to be relatively small in relation to the large amount of sand flowing.

As will be understood, the deposition of the particles upon the carrier uninfluenced by any force which tends to oppose the effect of the electrostatic field, except, of course, the weight of the particles themselves, permits the field to effect desired control of position and the particles are, as a result, arranged upon the carrier under the influence of the field substantially unaffected by any other force.

Furthermore, it has been found that the resultant abrasive surface is much sharper'than a surface produced by simply dropping the material upon the carrier, even though attempts may be made to control the arrangement of the same by other media than electrical means.

In obtaining the proper orientation of each individual particle with its sharpest portion exposed, it is thought that the field causes substantially each particle to align itself so that its longest axis is virtually parallel to the lines of force of the field or, in other words, substantially perpendicular to the carrier surface. The rate of discharge of an electrostatic charge is dependent upon'the surface characteristics of the charged body, and the larger the radius of curvature, the slower the rate of discharge, and the sharper the point, the faster the rate of discharge. It is believed that this relation of the rate of discharge of the surface characteristic of the charged body, e. g. sand grain with a pointed abrasive portion, causes the sharpest points of the grains to orient themselves so as to discharge in the direction of the field, with a result that since the lines of force of the field intersect the carrier, the particles are deposited upon the surface with their sharpest points directed toward the electrostatic field, and away from the supporting surface. Consequently, the points are made to project outwardly, and the resultant coating is very much sharper than a coating made without the use of an electrical force for orienting or arranging each individual particle. such an arrangement or orientation of the par ticles is useful in either a closed or open coating, since it (1) increases the sharpness of the coating and enables faster and easier cutting, (2) minimizes heating and loading, and (3) increases the cutting life or capacity of the abrasive surface.

Moreover, it will be clear that the use of the electrostatic field in the formation of a closed coating prevents lumping or bunching of the sand by distributingthe same over the entire area or surface to be coated. It blends out the irregularities, which would otherwisedevelop in the stream due to lack of uniformity in the feed gate and to other factors which modify the effect of gravity, or other means which may be used to direct the stream to the carrier.

It will be understood, of course, that the elec- Obviously, of course,

particles known as (a) control, (b) undergrade,

and (c) overgrade; the control particles predominate. Ithas been found that the electrostatic field utilized in the manner herein described tends to stratify the particles and cause to locate on the top surface the larger particles,

that is, the particles having larger areas of cutting surface.

It will be understood, therefore, that the control or change of position of the various particles eifected by the field has three characteristics: First, the particles are oriented or turned by the lines of force, so that their major axes are substantially perpendicular to the carrier surface or parallel the lines .of force of the field with the result that the sharper surfaces of the abrasive coating are exposed. Second, the various particles are stratified so that the larger or more effective particles are on the surface. Third, the particles are dispersed to produce a more uniform coating, due to the fact that they are mutually repellent.

The dispersion of the particles is caused by the fact that, as they enter the field, they acquire a charge of the same polarity as one of the electrodes of the field, and since all of the particles have been graded to approximately the same size, although some are undergrade, some are overgrade and others are control particles, they all acquire a charge of approximately equal intensity and of the same polarity. Hence, all of the particles in any shower, as they pass through the field, are mutually repellent with substantially an equal repelling force, and thus arrange themselves so that they are substantially equidistant in all directions. 'This repellent action is effected not only as the particles pass through the field, but on the carrier.

It is preferred that the electrical field be arranged at the point of deposition of the particles, so that this control of position is exercised at the point of deposition and at the time the particles strike the carrier. As a consequence, the positions of the particles will be controlled before the adhesive has set and will be effected on the carrier as well as in the path of the particles to the carrier.

In practicing the method, various forms of apparatus may be employed, and in the accompanying drawings showing a preferred form:

Figure 1 is a vertical sectional view on substantially the line l-l of Figure2.

Figure 2 is a vertical sectional view on the line 2-2 of Figure 1.

Figure 3 is a horizontal sectional view on the line 3-3 of Figure 1, with the feed rollshown in elevation, and partly broken away.

Figure 4 is afragmentary sectional view on the line 44 of Figure 1.

Figure 5 is a cross sectional view of a modified form of discharge electrode.

Figure 6 is an elevational view of a modified form of discharge or high potential electrode haging its ends formed to eliminate end effect, an

Figure 7 is a top plan view of another form of discharge electrode.

Referring to the accompanying drawings for a more detailed description, l indicates the carrier or paper sheet which may befed in the direction of the arrows H by suitable means (not shown) over a roll l2 having end bearings in brackets l2 on the frame l3. As will be under stood, the paper has an adhesively coated top surface exposed to receive sand or other abrasive material dropped from a hopper IS, the lower end of which is partly closed by a feed roll I 4. A wall of the hopper terminates at l5, a short distance above the feed roll to provide a discharge opening for the sand, which may be entirely closed by means of a shut-01f gate l6 operable by means of a pair of rack bars I'l engaged by gears I8 upon a rock shaft IS, the latter carrying an operating lever and being-mounted in bearings 2| upon the wall of the hopper. The gate I6 is provided for the purpose of entirely shutting oif the supply of sandwhen desired, and a second regulating gate 22 for adjusting the size of the opening between the lower end of the gate l6 and the periphery of the sand roll is adjustably mounted in brackets 23 by means of adjusting rods 24 secured to an outwardly extending rib 25 upon the gate, and extending through openings in the bracket. Clamping nuts 26 on opposite sides of the bracket webs through which the bolts gate in any set position. As will be observed from Figure 4, the shut-oif gate I6 is arranged between the regulating gate and the hopper wall, and it fits closely in a slideway formed by strips 21 secured to the hopper by bolts 28. The regulating gate 22 is provided on its rear surface with ribs 29 which abut the face of the shut-01f gate and assist in providing a guideway for the same.

As the regulating gate is adjusted by means of the adjusting bolts 24, it, is adapted to slide in grooves 30 (Fig. 4) formed in the strips 21 secured to the hopper,

When sand or other finely divided abrasive material is arranged within the hopper, operation of the feed roll in the direction of the arrow 3| (Fig. 1) after the shut-01f gate has been opened and the regulating gate has been suitably adjusted, will cause the sand to drop downwardly in a shower toward the exposed adhesively coated surface of the carrier Ill.

The amount of sand discharged between the periphery of the sand roll and the end 22' of the adjusting gate 22, will, of course, depend upon the adjustment of the gate.

An electrostatic field may be formed by means of a tube connected, as by means of a lead wire 35, to a source of high voltage (not shown). The tube 36 may be supported at its ends by means of insulating posts 31 carried by brackets 33 upon the frame l3. The brackets 38 may be provided with elongated slots 40 receiving bolts 4| with clamping nuts 42, whereby the position of the electrode may be varied as desired. The zero or ground potential side of the field may be provided by means of the paper carrying roll l2 which may be formed of suitable material and connected with the ground, as by means of a lead 45." The field formed by the tube 35 and roll l2 may be varied in intensity and extent, as desired. For instance, it is possible to make a field of higher unit intensity by reducing the diameter of the tube 35, or a broader field and one of lower unit intensity, by increasing the diameter of the electrode 35. Moreover, the proximity of ground or 24 extend serve to secure the zero potential effects the field, and if desired, a

a pronounced effect upon the character of the 10 field, and that instead of .the tube 35, a solid rod may be employed if desired. In some instances, instead of a hollow tube, a wire brush, or a series of wires, such as piano wires, have been found to provide efiicient electrodes and to alter the 5 character of the electrostatic field to meet specialized conditions in the application of abrasive material.

Another modified form of electrode is shown in Figure 7, wherein the electrode is provided at 20 one end with a substantially horizontally extending rigid strip of metal, such as copper wire or brass, and at the other end, the lead 36' is directed substantially horizontally, and is exposed for the purpose of providing in effect an- 25 gularly bent ends of the electrode tube 35", which may be supported upon the insulating posts 31'. The strip and exposed lead wire being directed toward the sand shower at an angle of about 45 to the tube, serve to decrease end effect" and 30 to fan out the edge of the sand shower, which, as will be understood, in dropping upon the abrasive material passes through the field. As the sand enters the electrostatic field, the particles are dispersed, and in such dispersed relation are de- 35 posited upon the adhesive surface of the carrier Ill. The effect of the field is to fan out or spread the shower of sand, as illustrated in Figure I, and ordinarily it has been found that it is preferable to position the regulating gate 22, so that an excess or surplus amountof sand is discharged from the hopper. In order to divert from the normal path of flow such quantity as should not fall upon the carrier, a baflle or diverting plate 5| is positioned with its surface inclined upwardly toward the feed roll, and with one edge 52 entering the shower of sand. This baflle serves to direct a portion of the shower over its surface downwardly into a hopper 53, from which the sand may be removed as desired.

In order to provide suitable means for varying the position of the baflie, so that the amount of sand selected off from the shower may be accurately regulated, the baffle is provided with a pair of upstanding'slotted lugs 54, into the slots of which project clamping bolts 55 carried by adjusting arms 56 (Figure 3) which are positioned upon a cross head 51 having end blocks 58 slidably mounted in brackets 59 upon the frame 39. Ad-

justing screws 60 are threaded in walls 59' of the brackets 59 and have heads 6| swivelled in the boxes 58. As will be understood, manipulation of the screws 60 will guide the blocks and cross head 51 toward and from the sand shower, and

thus move the baflle horizontally. The angular" portionof the baflle may be varied at the clamping bolts 55, and as will be observed, the arms 56 are provided with a series of openings 56 so that their eifective length may be altered.

In Figure 5 there is shown a modified form of electrode comprising an electrified tube 62, which is arranged within a tube 63 of considerably larger diameter and in electrical contact with the electrified tube, by which it is supported. The outer tube considerably enlarges the effective diameter of the electrode, and as will be understood, broadens the field produced. The rod 62 may be connected to a source of high voltage in any suitable manner (not shown).

In operating the apparatus, the position of the battle will, of course, determine the portion of sand showered from the hopper which will be permitted to fall upon the adhesive surface. As has been explained, instead of bringing the end 22' of the gate close to'the feed roll, even with extremely fine sands, in order to determine the exact amount of sand necessary to make the coating desired, the gate is preferably opened sufliciently wide to overcome the packing tendencies of said sands and to obtain a uniform flow, which is in excess of that required to produce a satisfactory coating. The comparatively heavy flow of sand eliminates the necessity for keeping the gate and feed roll perfectly ground, because the irregularities in the sand flow due to surface imperfections on the gate or roll, are very small in proportion to the large amount of sand flowing. As the sand stream leaves the gate, it passes within the influence of the electrostatic field, and

. immediately causes a dispersion of the particles or a fanning out or widening of the stream or shower. As has been explained, this dispersion can be varied by changing the characteristics of the field by any of the means described. Moreover, varying the voltage controlling the field will control the dispersing action of the same. The adjustment of the baflle 5| will regulate the amount of the shower, which is diverted from the path toward the'surface to be coated, and in ordinary practice, it will be found that the control of the amount of grain applied and the character of the coating may be efiectively controlled by varying the voltage without making adjustments in the apparatus. As will be understood, the

abrasive material may be deposited in any degree of depth, from an extremely thin deposit approximately one particle thick to a thick deposit. And in any case the particles will not only be distributed with great uniformity, but will be individually oriented or deposited with their major axes at right angles to the abrasive surface.

As will be observed (Fig. 1) the abrasive coated carrier passes from the electrostatic field and is conducted away without mechanically or otherwise compacting the surface, thereby leaving the particles uniformly distributed and individually oriented in which condition they are, of course, maintained.

Since the tube 35 is sufliciently long (Fig. 2) to extend beyond the edges of the paper, the sand will be uniformly applied throughout the entire width of the same, and by properly regulating the speed of travel of the paper, the sand may be continuously applied as the paper travels over the roll 12 to a take-up roll (not shown).

By the expression adhesively retaining as used with reference to the retention of the particles upon the carrier, is meant the use of means other than electricity for retaining by adhesive action the coating material upon the carrier. By abrasive is meant any abrasive or coating material in fragmentary form; by carrier is meant any desired material or support on which the fragmentary or divided material may be superimposed or deposited; by controlled or regulated as applied to the supply or feed of finely divided material to the carrier is meant simply that the material is supplied in such a way as to be responsive to the action of the electrical field for the result desired, whether dispersion or orientation or both.

Obviously, numerous modifications may be made in the structure illustrated and described without departing from the invention, the essence of which is more definitely set forth in the following claim.

This application is a division of my co-pending application Serial No. 296,323, filed July 30, 1928.

What I claim is:

A new article of manufacture having abrasive particles positioned relative to one another by electric action, substantially all of the abrasive particles at the abrading surface being substantially uniformly spaced apart and having major and minor axes and being responsive to electric action, substantially all of said particles being positioned and supported in an adhesive with their major axes substantially perpendicular to the abrading surface.

ELMER C. SCHACHT.

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