US2307698A - Manufacture of abrasive articles - Google Patents

Description

Jan..5, 1943. R. L. MELTON ET AL 2,307,698

MANUFACTURE OF ABRASIVE ARTiCLES Filed May 20, 1942 2 Sheets-Sheet l Ma an-far; Ran/E L. NELTON flLBEET 4. BALL e4 yMono BEN/YER y Tne R. L. MELTQN ET AL MANUFACTURE OF ABRASIVE ARTICLES 2 Sheets-Sheet Filed May 20, 1942 7 1mm 2 1 m2 w M R Patented Jan. 5, 1943 a OFFICE MANUFACTURE OF ABRASIVE ARTICLES Romie L. Melton, Niagara Falls, Albert L.- Ball, Lewiston, and Raymond C. Benner, Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application May 20, 1942, Serial No. 443,762

12 Claims.

This invention relates to the manufacture of abrasive articles and especially to a process of making abrasive webs or sheets of felted, fibrous material in which the abrasive element is distributed internally or the fibrous structure. More particularly, it is concerned with a method of pro- .lecting or otherwise introducing the abrasive grains into the web by means of electrical forces whereby the fibrous structure of the web is distended to open up the interstices between adjoiningfibers simultaneously with the introduction of the abrasive particles so as to provide a more ready reception and deeper penetration of the] abrasive material internally of the web. At the same time, when the abrasiveparticles are elongated in shape the projection of the abrasive particles by electrical forbes orients the particles as they enter the fibrous structure so as to deposit the abrasive particles within the web with their long axes oriented with respect to the web surface, resulting in an improved cutting behavior of the finished product. The invention further relates to the formation of flexible abrasive webs in the above manner in which various modifying agents are incorporated in the web to impart specific desired properties to all or portions of the web structure.

So-called coated abrasive articles, such as abrasive paper and cloth, discs and the like, are old and well known in the art, but the present invention should not be confused with such articles since it deals with a product which differs therefrom by the absence of the conventional backing. The present product represents-an improvement over such articles by reason of the elimination of the backing and may be used for many purposes for which abrasive paper is adapted as well as in applications for which the conventional abrasive paper is not suited. In addition, its fibrous structure lends a strength and durability to th final product not to be expected in a backless product.

Felted fibrous web material has been made by building up a layer of the desired thickness from a plurality of superimposed thin membranes. Such felted fibrous webs have also been made in which abrasive particles have been introduced into the webs at the time of making and also in which the finished webs have been employed as supports for a top facing of abrasive grains adhesively secured to the surface. The abrasive material has been added to the fibrous material by sifting it onto the web at the time of making or by blowing the abrasive grainsinto the web with a blast of air. Abrasive particles of smaller incorporation of the abrasive powder in a liquid adhesive which then carries the abrasive particles into the web as the adhesive penetrates the web.

It is an object of the present invention to provide an improved process of introducing abrasive material internally of the web whereby the abrasive particles can be caused to be presented to the web so as to penetrat more deeply without undue disturbance or disruption of the fibrous structure in the operation, and moreover, the abrasive particles can be placed within the web structure in oriented position. At the same time the present invention serves to simultaneously prepare the fibrous web for afavorable reception of the abrasive material into the web.

In accordance with the present invention, a loosely interwoven, felted fibrous web is first formed by any suitable procedure. For example, such a web may be formed by superimposing, a plurality of thin carded fibrous membranes upon a moving support in suflicient number to build up a loose, uncompacted web of the desired thickness. While the web is in its uncompacted state it is passed through an electrostatic field whereupon the electrostatic forces of the fieldcause the fibrous structure of the web to become-distended and the interstices formed by tile adjoining interlocked fibers to be opened up to a position favorable for the introduction of abrasive material internally of the web. While the fibrous web is in the above distended condition, abrasive particles are introduced into the electrostatic field whereupon the action of the electric field upon the abrasive material causes it to become electrically charged and projected into the opened fibrous web structure. Particles of granular abrasive material in crushed form often have an irregular shape of a substantially elongated nature in which the major or lengthwise axis of the granule is considerably greater, sometimes mounting to several times, the length of the minor axis. During the projection ofsuch abrasive grains into the web the individual particles of the abrasive become oriented in a direction depending upon the position of the electrode toward which the abrasive particles are attracted. The orientation of such elongated abrasive particles is usually such that the grains are projected into the web with their long axes substantially normal to the surface of the web, although the orientation may also be such that the grains are presented with their long axes at any controlled degree of obliqueness to the web surface. By the interjection of sizes have been included in such web material by the fibrous web between the sourc of abrasive 2 I 'a,so7,eee

particles within the electrostatic field and the electrode toward which the particles are attracted the abrasive particles become projected and oriented in the desired direction internally or the fibrous web. By reason of their orientation and also because of the opened-11p, distended condi.--

tion of the fibrous structure at the point of projection the abrasive particles are presented to the web so as to cause a minimum disruption or disturbance of the. fibers and the maximum amount of penetration oi the web After the fibrous web has been thus loaded with abrasive grain a suitable adhesive binder is applied to the web audit is compacted to the desired density.

Moreover, modifying agents such as waterproofing compounds, anti-friction agents, fiexibillzers, adhesives and other fillers may be incorporated in the web atthe time of making in order to render the web resistant to water or impart other specific desirable propertie'sto all or 2 abrasive particles into the web and the compact-- ing thereof a Figure 3 is an enlarged vertical cross-section of a modified form 01 the apparatus shown in Figure 2; and t Figure 4 is a vertical cross-sectional view on a greatly exaggerated scale showing a portion of a slots a they are shielded irom any undesirable external influences, such as strong air currents, by the surrounding sidewalls l3 and IS. The

conveyor belt II is provided with a smooth outer surface and is supported at the opposite ends thereof by the rolls and I, which are driven by any suitable means (not shown). The speed of the belt is synchronized with the rate of feed of the membranes so as to prevent any appreclable strain or pull on the fiimsy membranes during their deposition.

The individual laps e. e, I and a are applied successively to form a composite layer of proper thickness and character. The number and arrangement oi the carding assemblies will depend upon the desired thickness and type of fibrous v web produced.

After the loosely ielted,-uncompacted web II has been built up to the required thickness it is ready to be conveyed to the apparatusior introducing the abrasive material into the web. The web I8 is fed onto a moving conveyor belt I9, which is supported by the synchronously driven rolls 2! and 2 I, and delivered through the electrostatic field 22 for distending the web and projecting theabrasive grains into the web, from which the web is conducted immediately between the adhesive binder- applyin rolls 23, 24.

As the uncompacted fibrous web moves into the electrostatic field 22' created between electrodes 23 and 2! which extend the full width of the web I. and are. positioned above and below .the moving web, the individual fibers tend to become disarranged and are shifted irom their nor- T1131 parallel position (assumed as a result oi the carding operation) so as to assume partially upright or upended positions. The individual fibers are caused to intertwlne to a greater degree and thereby produce a firm, homogeneous, interlockfibrous abrasive-loaded web formed by the meth- 4t) 1118 structure which will be non-lamellar in final with abrasive grains incorporated "therein and bonded with a suitable adhesive. The particular apparatus shown comprises aplurality or carding machines, suitably spaced apart and'consisting 01' carding rolls 2, stripper rolls 3 and combat 4, adapted to form and deliver a number of ii brous membrances or laps I, i, I and I to the moving conveyor l I.

The carded membranes or laps are delivered from the carding machines as fiimsy webs of independent fibers generally parallel and loosely adhering together. The carded membranes may consist of any animal, vegetable ctr-synthetic fibrous material capable of being carded into yarn or sheet form. While cotton fibers have proven to be highly satisfactory for the present process, other fibers suggested for use are such natural fibers as wool, jute, flax and the like, or anyoi the newer synthetic fibers such as glass wool, resinous or synthetic rubber fibers. Also, instead of having all the fibers oi the same material, one or more of the fibrous membranes may be a ditferent fiber than the rest. Although only iour carder assemblies are shown inFigure 1. any number of carders may be used depending upon the ratus for accomplishing this distending action and for projecting the abrasive grains into the web and orienting the abrasive particles therein are shown in greater detail in Figure 2 01. the drawings. The electrically charged electrodes and the particular manner in which they are positioned and used tor the distention oi the fibrous web and the deposition of the abrasive grains into the web is clearly depicted. The fibrous web ll passes from the conveyor belt I. into the electrostatic field 22 which is created between electrodes 23 and 25. As it enters the electrostatic field the electrical forces thereof cause the fibrous structure to become distended and the individual fibers thereof to be partially upended so as to open up the interstices between adjoining fibers and prepare the web for a more favorable reception and penetration of the granular mate-- rial. Simultaneously, abrasive grains are fed in a constant stream from a hopper 28 by means 0! a regulating roll 21 and adjustable gate 2| onto a moving conveyor belt 20 which is supported by end rolls 2! and II, roll 2! of which also constitutes one electrode ,0! the electrode pair. The abrasive granules II are carried on the belt 29 into the electrostatic field 22 where they receive an electrostatic charge, become oriented, and are projected into the distended branes. As the membranes ass through the fibrous web. The excess abrasive grains pass The electrostatic means and associated appaover the end of the conveyor belt and drop into a suitable receptacle l2.

An auxiliary or secondary electrode 38 having the some polarity as the electrode is option ally positioned beneath the moving grain-carryingbelt 29 to serve as a precharging electrode for imparting an electrical charge to the abrasive granules preparatory to their entering the electrostatic projecting field 22.

The source of electromotive force for creating m the electrostatic field, the effective potential of which is 20,000 volts or more, is not specifically shown in the drawings, but is indicated by the.

positive (-1-) and negative rsymbols and connected to theelectrodes 28, 33 and 23 by the connecting lead wires 34 and 35, respectively.

The revolving cylinder electrodes 23 and 25 are connected to the source of electromotive power through a slip ring of well known type connected brush contacts 12, flexible connectors 43 and slip rings 44. The source of electromotive force may produce a continuous unidirectional cur- I rent, an intermittent unidirectional current, or

an alternating current depending upon the. par- 2 -ticular requirements. The eflects of direct current and alternating current electrostatic fields will be described hereinafter in greater detail.

when a unidirectional current source is utilized connected to the positive terminal and the lower electrodes 25, 33 be connected to the negativeterminal. However, if desired, the polarity of the electrodes may be reversed, and as a safety The character and construction of the lower electrodes 25 and 33, and particularly electrode 25, are of great importance in the operation of the apparatus and, preferably, are shielded by 40 some "poorly conducting material.

The materials so used should be low enough in conductance that not enough current can flow along or through it to cause arcing between the upper and lower electrodes, yes it should'be sufficiently to conductive to allow a small leakage current. to

supply electrical charges to the abrasive particles in order that they may be oriented so'that their lengthwise axes are normal to the web direction and most suitable for projection into the fibrous structure and also for distension and preparation of the fibrous structure for recepelectrode 82 and thehollow metallic tube or lining ll of electrode 25. In speaking of a poorly conducting material this expression is used to highly insulating materials such as hard rubber, varnished cambric or the like, which are such good insulators at the voltage preferably used with the present apparatus that the leakage cur-' rent which flows through them is insufilcient to electrically charge the abrasive particles or influence the fibruus vveb on the other hand.

For this purpose molded materials, such as those sold under the trade names of Micarta and Bakelite" have been found to be most satisfactory. However, other materials such as dry,

'knot-i'ree wood can also be used. While these materials are so poorly conducting that they will After the fibrous web has been suillciently and negative reference characters. lower electrode I is constructed similar-to elecat ground potential and thus does not need to be encased by a poorly conducting sheath,

Figure 3 illustratesa modified form of electro- I static apparatus for dlstending the fibrous weband orienting and projecting the abrasive particles into the distended web. This apparatus differs from that shown in Figures 1 and 2 in'that the uncompacted fibrous web is fed from a carrier belt such as belt ll shownin Figure 1 onto a horizontal secondary carrier belt 0 which is supported by end rolls ii and 52 and-is driven I at the same speed as that of the web in order to the metallic rings 40 and ll .by means of 20 not to exert any appreciable strain upon the -uncompacted fibrous web. The guide rolls 53 and it placed at or adjacent the opposite ends I do not serve as a compressing means. As the web ll passes along the carrier belt BI it passes through an electrostatic field it created between the electrode 56 positioned beneath the upper surface of the carrier belt and the screen grid electrode 51 positioned above the carrier belt but suitably spaced therefrom. This electro-- static field is produced by a source of electromotive force, the eflective potential of which is measure it is desirable that-the'upper or bare 3s 3 Vo m re. not specifically shown in metal electrode be grounded.

the drawings, but indicated by the positive The trode a of Figure 2 and consists of a metallic plate 58 shielded by a poorly conducting material 89, and connected to thc'source of electromotive force by connecting wire I. The upper electrode consists of a screen grid which pernuts the passage and distribution of gravity-fed abrasive grain therethrough into the electrostatic fleld and is connected to the source of electromotive force by connecting wire 6|. Abrasive. grain i2 is fed from a supply hopper l3 equipped with grain feeding control gate 64 and roll 65 for depositing a steady controlled stream or abrasive grain through the auxiliary screen it which serves to additionally distribute the grains evenly over the entire area of the screen grid electrode II. v

p In employing an electrostatic field to project the abrasive particles into the web it has been found that in projecting the larger grit sizes the unidirectional electromotive force is particularly eilective since it serves to distend and distinguish between such materials as metals, 00 carbon. or the like, which are relatively good conductors of electricity. on'the one hand, and

open up the interstices of the web structure and" This double action of the electrostatic field of opening the web and orienting the abrasive grains serves to permit a larger quantity of abra- "sive to be effectively distributed throughout the internal structure of the web. On the other smes, whereby the web structure is not distended in the degree accomplished by the unidirectional current'field and is desirable .in the making or certain finegrlt products.

- loaded with abrasive grain in the manner described,'it is ready to be consolidated to a greaterdensity for added strength. At the same time 'it is desirable to incorporate a liquid adhesive binder within said web to bond the compacted fibers and abrasive grains and product a'web of greater density having a strength comparable to The abrasive-laden fibrous web is conducted from the electrostatic fieldibetweena pair of 1 hesive binder, determined. by the adiustably spacedscraper bar H, is applied to the web. The adhesive is transferred to roll 2| from roll I! by means of transfer roll 12. Roll 23 is adjustably spaced with respect to the adhesive roll 24 and applies suflicient pressure to finally compact the loose fibrous web as well as aid in forcing the binder to permeate into and throughout the web oriented therein so that the majority of the individual grains are substantially in a perp ndicular position with respect to the surface line of the fibrous web, and moreover are distributed throughout the interior of the web.

4 While the preferred embodiments of the invention have been specifically illustrated and dethat of cloth. 4

scribed, it is to be understood that the invention may be otherwise embodied and practiced within the scope of the appended claims.

1 We claim: I 1. A method of-making flexible, fibrous abrasite web material having abrasive particles included therein which comprises depositing a plurality of thin carded, fibrous membranes in superposed relationship upon a suitable moving supp rt to form a felted fibrous web, passing said fibrous web through an electrostatic field to disi .tend and open up the fibrous structure of said structure. The surface of roll 24 should be covcred with a resilient layer of absorbing material.

In Figure 3 the adhesive pick-up roll ll serves also to apply the adhesive to the fibrous web without the requirement of transfer rolls and serves also to cooperate with pressure roll 14 to suitably compact the web to the desired density and force the adhesive to permeate and penetrate into the fibrous web structure.

The adhesive binder used to permeate and assist in maintaining the consolidated condition of the web is preferably one of a flexible or resilient nature-such as latex, flexibilized animal or vegetable glue, plasticized vinyl resin, plasticized urea formaldehyde resin, and the like. Such flexible adhesives permit the retention of the natural pliable character of the interlocked fibrous structure. 1

Also, in practicing the invention anyof the abrasive materials in common use may be employed, such as silicon carbide, fused aluminum oxide, fiint, corundum, emery, rouge and similar substances. The size of the abrasive particles may vary from the finest polishing or bufilng powders to the coarser grit sizes used in grinding.

After the web is compacted and the proper amount of adhesive binder applied therethrough, it is passed over a suction drum l5 and idler roll 16 to a suitable chamber where it is dried or cured. This chamber contains an endless conveyor 11 which serves to festoon the web onto supporting sticks 18 and to transport these sticks and looped material to the moving rack 19. The speed of the moving rack 18. is so adjusted that the adhesive binder is properly set or cured by the time it reaches the end of the chamber. When the abrasive web material is taken down from the drying rack it is wound into rolls or cut into sheets suitable for use.

Figure 4 is a greatly enlarged vertical crosssection of a fragment of an abrasive-included fibrous web made according to the present in- 7 vention, in which web the individual fibers 80 of the fibrous structure are interlocked and interwoven about the abrasive granules 8|, firmly anchoring them in place. The abrasive granules 8i have been projected into the fibrous web and 7 web, introducing abrasive granules into said electrostatic field and thereby orienting and projecting said particles by means of the electrical charge collected thereon into the interstices of the-fibrous web, applying adhesive to the abrasive-laden fibrous web and compacting the web to the desired density.

2. A method of making flexible, fibrous abrasive web material having abrasive particles in cluded therein which comprises depositing a plurality of thin carded, fibrous membranes in superposed relationship upon a suitable moving support to form a felted fibrous web, passing said fibrous web into an electrostatic field, introduclng abrasive particles into said electrostatic 'field, projecting said particles into the web by means .of the electrostatic forces of said field, applying-adhesive to the abrasive-laden fibrous web and compacting the web to the. desired density.

3. A method of making flexible, fibrous abrasive web material having abrasive particles included therein which comprises forming an uncompacted web of felted, fibrous material, passing said uncompacted fibrous web through an electrostatic field, introducingabrasive particles into said electrostatic field so as to electrically charge and project the particles internally of the loose fibrous web, applying adhesive to the abrasive-laden web and compacting the web to the desired density.

4. A method of making flexible fibrous abrasive web material having abrasive particles included therein which comprises forming an uncompacted web of felted fibrous material, passing said uncompacted fibrous web through an electrostatic field, introducing abrasive particles into said electrostatic field so as to electrically charge and orient the particles, projecting said oriented particles internally of the loose fibrous web, .applying adhesive to the abrasive-laden web and compacting the web 'to the desired density.

5. A method of making flexible, fibrous abrasive web material having abrasive particles included therein which comprises forming a loosely felted web from a plurality of superimposed thin carded fibrous membranes, passing said fibrous web through an electrostatic field, introducing abrasive particles into said electrostatic field so as to electrically charge and project the particles internally of the loose. fibrous web, applying adhesive to the abrasive-laden fibrous web and compacting the web to the desired density.

6. A method of making flexible, fibrous abrasive web material having abrasive particles included internally thereof which comprises forming an uncompacted web of felted, fibrous material, passing said uncompacted fibrous web through an electrostatic field to distend and open up the fibrous structure of said web, feeding abrasive particles upon a moving support, carrying said abrasive grains into said electrostatic field and projecting said abrasive particles internally of the fibrous web while the fibrous structure of said web is in distended condition, immediately thereafter applying adhesive to the abrasive-laden web and compacting the web to the desired density.

7. A method of making flexible, fibrous abrasive web material having abrasive particles included internally thereof which comprises forming an uncompacted web of felted, fibrous material, passing said uncompacted fibrous web through an electrostatic field to distend and open up the fibrous structure of said web, feeding abrasive particles by gravity through a screen into said electrostatic field to orient said abrasive particles, introducing the oriented abrasive particles into the distended fibrous structure of said web, applying adhesive to the abrasive-laden fibrous web and compacting the web to the desired density. v

8. In the process of making flexible, fibrous abrasive webs having abrasive particles included internally thereof the steps which comprise passing an uncompacted fibrous web material through an electrostatic field to distend and open up the fibrous structure thereof and simultaneously projecting abrasive particles into the web by means of electrostatic forces while said web is in a distended condition.

9. An abrasive article comprised of a flexible, felted fibrous web of cardable fibers having abrasive particles included internally of said web and held in position therein by an adhesive binder,

substantially all of said abrasive par-ticles" being oriented within said web.-

10. A felted fibrous, abrasive web composed of a plurality of superimposed thin carded fibrous membranes adhesively compacted together and having abrasive particles distributed throughout the interior of said Web structure and oriented therein.

11. A felted fibrous, abrasive web composed of a plurality of superimposed thin carded fibrous membranes adhesively compacted together and having abrasive particles distributed throughout the interior of said web structure and oriented therein with their major axes substantially all normal to the surface of the fibrous web.

12. A felted fibrous, abrasive web composed of a plurality of superimposed thin carded fibrous membranes adhesively compacted together and having abrasive particles distributed throughout the interior of said web structure and oriented therein with their major axes lying obliquely to the surface of the web,

ROMIE L. MELTON. ALBERT L. BALL. RAYMOND C. BENNER.

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