US2393267A - Method of making laminated abrasive articles - Google Patents

Description

INVENTORS NOE/VAN ems/E N. P. ROBIE ET AL Filed June 27, 1944 By faaer Eon E METHOD OF MAKING LAM INATED ABRASIVE ARTICLES Ja n. 22, 1946.

Patented Jan. 22, 1946 METHOD OF MAKING LAMINATED ABRASIVE ARTICLES Norman P. Roble, Lewiston, and Robert G. Rowe,

Niagara Falls, N.

assignors to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application June 27, 1944, Serial No. 542,327

7 Claims.

This invention relates to a method of making abrasive articles. More particularly it relates to a method of making abrasive articles composed of a plurality of layers of web material having abrasive particles included therein, coated on one face or both faces thereof, or both, in which such layers of web material are secured together by cured adhesive material.

One of the objects of the invention is the provision of a fast efficient method of producing abrasive articles made of such adheslvely secured laminae of web material. Another object is the production of such abrasive articles'wherein the adhesive is hardened to the optimum degree without damaging the fibres of the Web material due to prolonged heating. A further object is the production of such abrasive articles having more uniform properties throughout their extent than it is possible to obtain by practice of prior art methods. These and further objects will appear in the following description.

One type of article produced by the method of the present invention is that disclosed and claimed in the application of Melton et al., Ser. No. 408,936, filed August 30, 1941. Abrasive articles of this type consist of a plurality of layers of thin felted abrasive containing webs superimposed one on the other, said layers being adhesively united over certain portions of their contacting surfaces or over the whole of such surfaces. The abrasive containing fibrous Web material used in making the product in accordance with the present invention may be made in several ways. One method is that described in Patent No. 2,284,716, issued June 2, 1942, wherein a plurality of thin carded fibrous membranes are imposed upon each other to build up a web of loosely felted fibrous material on a traveling support. Abrasive grain is fed onto the fibrous membranes in variousstages of the building up of the final web, so that abrasive grain is distributed through such web. Thereafter the web is sized witha suitable adhesive such as glue. thermoplastic resins, thermosetting resins, latex, and synthetic rubberlike materials, and theweb .S then compacted to final thickness, after which the sizing adhesive is dried.

Various other methods may be employed to form such web with included .abrasive. Other such methods are those disclosed in application serial No. 375,517, filed January 22, 1941, and in Patent No. 2,284,739, issued June 2, 1942. Any )f the abrasive materials in common use may :e employed, such as silicon carbide, diamonds, Joron carbide, fused aluminum oxide, flint, co-

rundum, emery, rouge, andv similar substances. The size of the abrasive particles employed depends upon the use to which the final abrasive product is to be put and may vary from the finest polishing, or bufflng powders to the coarser grit sizes used in grinding.

Although the present invention will be described' in connection with abrasive articles formed from the above fibrous webs with included abrasive,'it is to-be understood that it displays similar advantages in making laminated abrasive products wherein the laminatlons are composed of webs of other material, such as paper fibers, having abrasive particles included therein, and that it may be practiced with webs of various materials such as cloth, paper and felted fibrous webs such as those above having abrasive particles only on the surface or surfaces thereof.

In the prior art, laminated abrasive products such as those made by the present invention have been produced by superimposing a, plurality of layers of abrasive coated or abrasive included sized webs, with or without additional coatings of additional adhesive in the form of a liquid film or as an impregnated sheet material, between the adjacent layers of the superimposed webs to act as a bonding agent. Such additional adhesives may be glue, natural or synthetic resins, rubber, latex, sodium silicate, shellac and the like. Such layers, which may have been cut to finished size before the laminating step are then subjected to a cold pressing operation to cause a preliminary adhesion between the layers, so as to permit handling of the resulting article. Following such cold pressing the article is heated in a hot press, the platens of which are heated either by steam or by electric resistance heating. With wheelsof any appreciable thickness, such as /1 inch or more, a considerable length of time in the hot press must be provided, particularly if such products are stacked between platens as is necessary in production methods. Extended heating in the hot press is necessary because of the low heat conductivity of the laminated material, even when compacted by being subjected to pressure in the order of ,1000 pounds per square inch. Usually from 1 to 2 hours in a hotpressis required when the articles are stacked, such time being determined by the time it takes the center products in the stack to reach the highest temperature which they could attain. If only a single article is hot pressed at one time, press time is determined by the time it takes the center portion of the article to reach such temperature. Such hot pressing operation accomplishes a partial curingof the sizing adhesive and of the added laminating layers of adhesive. ifsuch are used, and compacts the articles to their final density. It is jection of the relatively delicate fibers of the articles particularly in those portions in contact with or adjacent the platens to a high temperature for a long period, and results in weakening them. Furthermore, the sizing and laminating adhesives in the articles in portions which were in contact or near the press platens are much more fully cured than those in those portions distant from the platens. Thus any particular article so treated is not uniform in properties throughout its extent, and, if the articles are hot pressed in a stack, such articles are not uniform in properties from article to article, even after the final oven cure. The necessity for oven cure of the articles made by hot pressing by prior art methods is also a disadvantage since it adds to the time necessary to make the articles. Furthermore, the initial cost of the oven is considerable, and the cost of its operation and maintenance of such oven is substantial.

The method of the present invention overcomes the disadvantages inherent in the prior method involving the hot pressing of laminated abrasive products of the type described. The invention consists broadly in the subjection of laminated abrasive containing or abrasive coated webs to the action of a high frequency electric field while the article is held under pressure. The electric field accomplishes the cure of sizing and laminating adhesives in a manner which is uniform throughout the extent of the article. Such method of heating is fast, and because all portions of the article are heated to the same degree and the material of which the article is composed is of poor heat conductivity, it is possible to complete the cure of the adhesive upon removal of the article from the high frequency electric field merely by the heat stored in the article, thus dispensing with the use of an oven.

The invention will be more fully understood by reference to the accompanying drawing in which:

Figure l is a diagrammatic view of apparatus for adjusting the humidity of sized abrasive containing webs, for adhesive coating the resulting web, and for drying the adhesive coating and bringing the adhesive coated web to a uniform humidity.

Figure 2 is a diagrammatic view of further apparatus employed in the manufacture of laminated abrasive products herein contemplated and includes a fiying shear, a cold press for laminating cut portions of the web, and a beam press for dieing out the laminated sheet to size,

Figure 3 is a diagrammatic view of a press with high frequency electric heating means, and Figure 4 is a view in cross-section of a modified press in which the laminated articles are subjectcd to a high frequency electric field.

It is to he understood that the apparatus shown in the drawing described hereinafter is illustrative only of that used ln a preferred mode of carrying out the method of the present invention, and that certain elements of the apparatus here shown may be modified or omitted altogether as will be indicated.

In the apparatus shown in Figure 1, a sized or adhesive impregnated abrasive containing web i is shown being fed in the direction of the arrow into aconstant temperature, constant humidity. chamber 2 by-means of feed rolls 3 which forward the web to a festooning apparatus shown generally at 4. Following the storage of the web material in chamber 2 for a sufiicient length of time to dry the sizing or impregnating adhesive if it was not already dry and to bring it to a uniform humidity throughout its extent, it is then fed out to adhesive applying device 5, which applies a uniform coating of an additional laminating adhesive of the type above indicated, to the bottom face of the web. The thus coated web is then fed into a second constant temperature constant humidity chamber 6 by vacuum roll 1 and cpoperating feed rolls 8, which feed it to a .festooning and storage device generally indicated by the reference character 9.

The purpose of storing the web material in the constant humidity chambers 2 and 6 is to assure that the moisture content of the laminated abrasive products subsequently to be treated in the high frequency electric press will be uniform. This is important since the heating effect of the high frequency electric field upon such articles dependsupon their power factor, and the power factor of each article in turn depends upon its moisture content. Thus, if articles having different moisture contents are heated in multiple in the same high frequency electric field, those having the higher moisture content will be heated more highly than those with the lower moisture content, and the resulting articles will not be uniformly cured. "he invention is not confined to the heating of such articles in multiple, however, since it is important that the articles have a definite fixed moisture content even though cured singly. The adjustment of the moisture content to such desired definite value allows curing to be affected in a definite reproducible manner, by consideration only of the mass of the articles to be cured at one time, by applying a high frequency field of known intensity to such article or articles for a predetermined period of time, said time having been arrived at experimentally in the previous curing of similar articles to the desired degree.

' It is possible to dispense with the first humidity chamber 2, and to feed the air dried sized abrasive containing web directly to the adhesive coating means 5. In such case, humidity chamber 6 is relied upon to :bring the adhesive coated web material to a constant moisture content. It has been found preferable, however, first to adjust such moisture content by means of chamber 2, then to apply a uniform coating of adhesive by means 5. and to accomplish merely the drying of such adhesive and such further adjustment of moisture content in the web as may be necessary, in chamber 6. By so doing there is assured a sized, adhesive coated, abrasive containing web. shown as issuing from the exit end of chamber 8, and designated ill in Figure l, which has a uniform moisture content throughout its thickness and extent.

It has been found that a temperature of from to F. and a relative humidity of from 50 of web material having a uniform moisture Such values content of the desired amount. may obviously be varied within limits as desired. It is to :be understood'that other methods than festooning the material in a chamber may be employed to bring it to the desired moisture content. It may, for instance, be treated in a roll to accomplish this result or it may be sheared into fiat sheets and then subjected to an atmosphere of the requisite humidity. Constant moisture content throughout the laminated articles to be cured may also be substantially obtained by storage'of the laminated cold pressed slabs of laminated web material, or the cold pressed uncured articles themselves, in a constant temperature constant humidity atmosphere for a long enough period. It is preferred, however, to obtain such object by bringing the laminae themselves to such condition of constant moisture content.

In Figure 2 web It) is shown being fed to flying shear II by feed rolls l2. The processing, which follows the discharge of the web I!) from chamber 6 should take-place a relatively short I nected to the other of terminals 21, to which is connected a source of high frequency current (not shown). When a highfrequency electric current is connected to electrodes 23 and 24 and to electrode 25, there is set up between electrode 23 and electrode 25, and between electrode 25 and electrode 24, a high frequency electric field 'ofuniform strength throughout the space between them and thus throughout both articles being heated. Such high frequency electric field rapidly heats the sizing and laminating adhesives in the articles, causing them to reach ouring temperature in a relatively short time, in the order of 5 to 10 minutesat most. The articles so heated are subjected to pressure to cause the layers to become firmly attached to each other, and by compaction of the web material to cause the article to reach the desired density. The pressure employed depends upon various factors, such as thedensity desired and the degree to which the web I was compacted initially.

time thereafter, or at least such length of time should be such that the moisture content of the web is not substantially changed. Sheared lengths l3 of the abrasive containing web fall upon table I 4, upon which they are superimposed in the desired number that after being compacted it will yield a liminated slab of the desired thickness.

After a suiiicient number of sheared lengths l3 have been assembled, the pile is introduced into a cold press l5 and subjected to sufiiclent pressure to cause them to adhere sufilciently together to enable the resulting slab Hi to be handled as a unit. Slab I6 is then introduced into a :beam press I l, with which, by means of a clicker die IS, the operator cuts portions of the desired size and configuration from the slab. In the case of thinner articles, say 'A" thick or less, slab [6 may be made of the final required thickness of the articles, and the articles cut therefrom in the beam press are thus ready for pressing, curing, and finishing. If thicker articles are desired, it is generally preferred to make them by assembling a plurality of layers of the slab material cut from slab IS, the confronting parts being coated with a suitable adhesive prior to their assembly, such cut slab portions then being cold pressed together.

Laminated articles of the desired thickness, assembled as above, are then heated under pressure in a high frequency electric field. This may be accomplished by a high frequency electric press shown generally as IS in Figure 3. Such press consists generally of lower platen 20, upper platen 2|, and a pressure applying means such as a pneumatic or hydraulic cylinder 22. In commercial production it is preferred to heat and press a plurality of articles at one time; for. this purpose the arrangement shown in Figure 3 has provide suitable. The press frame, and upper and lower members 23 and 24, respectively, which contact the articles are made of metal, and, as shown, are connected to ground. Members 23 and 24, which constitute electrodes connected in parallel, are thus connected to the ground side of the high frequency electric source. Electrode 25, which may consist of a thin sheet. of metal of good conductivity, shown as 'being placed between two thick laminated articles 26 which are to be heated and cured. Electrode 25 is contalc,

In all cases, however, it is possible to attain a predetermined density. of finished article with a much lower pressure, when the articles are heated by a high frequency electric field, than when the curing is performed by means of steam or electric resistance heated hot presses. This is due to the fact that the high frequency electric field heats the articles uniformly throughout their extent, thus causing them to exhibit more uniform plastic tendencies than they do in the conventional hot press. that more than two articles may be so heated,

the number depending upon the size of the press,

amount of power available from the high frequency source, and the thickness of the articles heated and cured.

A relatively short heating period ina press such as shown in Figure 3, for example 5 to 10 minutes, is sufllcient to carr'y the cure of the adhesive or adhesives in the article forward enough so that the heat stored in the articles will, after their removal from the press, be sufiicient to complete the cure. In the steam or electric resistance heated platen hot presses,onthe other hand, the heating in the press of a comparable stack of similar articles hours, and, as has been said, an oven cure is required after completion of the hot pressing operation.

Articles cured by a press such as shown in Figure 3 usually change somewhat, particularly in a direction parallel to the faces of the platens or'electrodes, because of the slight flow of the material in that direction under heat and pressure. Where the articles are conventionally finished to final dimensions following cure and have the arbor hole, if the articles require it, punched through it later or have the arbor hole finished to final dimensions: if it was punched through before curing, this is not objectionable. In cases where it is desired that the articles after curing shall require little orno finishing, it-is preferred to use a press of the typeshown in Figure 4.

Such press consists of'upper and lower electrically insulating pressplatens 28 and 29, re-

spectively, and a pressure applying cylinder 30 acting upon the upper platen. A plurality of laminated articles 3 I, having arbor holes punched therethrough, are assembled-onxan accurately fitting ceramic arbor 32. It is preferable to coat the arbor and the contacting faces "of adjacent articles 3| with a parting composition such as grease, or any other conventional parting materials employed in the molding of resins. The

It is to be understood requires from 1%3-2 thus assembled stack of articles 3! is then placed In order to provide for the escape of the volatile materials in the articles, particularly the adhesive solvents, upon heating and curing the articles, mold barrel 33 is provided with a plurality of small vents 39. These vents are shown much exaggerated in diameter in Figure 4 for the sake of clarity of illustration. A vacuum chamber ll,

formed by cylindrical ceramic shell 4| and annular upper and lower sealing members 42, is formed about the mold barrel. Connection of such vacuum chamber to a vacuum pump (not shown) is eifectedby means of nipple 43 proiecting from shell I. Connection of the upper and lower metal electrodes to a source of high frequency alternating current is effected by means of electric cables Li and L: respectively.

Use of the apparatus shown in Figure 4 resuits in all'the advantages described in connection with the apparatus in Figure 3, and in addition assures that the products will be accurate and uniform, both as to outer diameter and as to location and diameter of the arbor hole. Because of the relatively light pressure employed in the operation, it is feasible to make platens 2| and 29 of the non-metallic electrically insulating'material shown. Metal platens may be employed, however, providing the top and bottom electrodes are well insulated from the press platens and frame.

For the purpose of illustration, the two following examples are given of methods by which the present invention may be carried out.

Example I Unsized abrasive included web material is made in accordance with the above-mentioned Patent No. 2,284,716. The web is then rewound, sized with casein adhesive in aconventional paper and cloth coating machine, and stored in a constant temperature constant humidity chamber. After the adhesive is suitably dry and the material reaches a uniform moisture content throughout its extent,-the wide roll is split to narrow rolls, and the smaller rolls sheared into sheets. Sufficient sheets are stacked to make a slab roughly inch thick when hot pressed, and the sheets cold pressed together to form a slab. Discs are cut from the resulting slabs, the discs are adhesively coated, and are then cold pressed together to make preformed laminated wheels.

The resulting wheels are inserted, in a stack, between the platens of a press, with a flat copper electrode between thev center articles in the stack. This electrode and the press (as the other electrode) are connected for 9 minutes to a radio frequency generator having an input of 4200 volts at 0.6 to 0.7 ampere, and with a frequency of 8 megacycles. Constant pressure is continually applied to the wheels, and at the end of 6 minutes the press is closed on the stops at around 500 lbs. per square inch pressure, which makes the thickness dimension 3 inches. At the end of approximately 9 minutes time the articles reach a temperature of 300 F. throughout their extent and the power is turned off. Cure of the articles is completed in the open, after removal of the articles from the press, by the heat stored in such articles.

Example II Fused alumina coated cloth, prepared by coating 80 mesh abrasive on one side of cloth drills by means of high grade glue, is coated on the nonabrasive side with 20 pounds per ream (480 sheet 9" x 11'') of casein glue containing solid glue dissolved in water. The casein glue is known commercially as Casco" glue. The casein glue coated abrasive cloth is then dried to a moisture content of approximately 1% in a constant temperature constant humidity chamber. Discs are cut from this sheet 3" in diameter with a arbor. These discs are then stacked into a pile approximately 2 inches high, and the pile is placed between two insulated copper electrodes in a hydraulic press. High frequency currents are applied to the electrodes while subjecting the disc pile to a pressure 360 lbs. per square inch for a total time of approximately five minutes. Cure of the articles is completed in the open after removal of the article from the press, by the heat stored in them by the heating in the high frequency electric field.

Having thus fully-disclosed our invention-and the preferred modes by which it is carried out, we desire toclaim as new the following:

1. The method of manufacturing laminated abrasive articles which comprises the steps of subjecting a web of material having abrasive grain affixed thereto in a constant temperature constant humidity atmosphere for a sumcient length of time to bring the material to the desired uniform moisture content throughout its extent, coating one face of the resulting web with a laminating coat of adhesive, again adjusting the moisture content of the web material by subjecting it in a constant temperature constant humidity atmosphere for a sumcient length of time to bring it to the desired moisture content, cutting blanks from the resulting web, superimposing such blanks, cold pressing such superimpwed blanks to form a laminated article, and further pressing the article while subjecting it to the action of a high frequency electric field whereby the adhesive throughout its extent becomes cured to the desired degree.

2. The method of manufacturing laminated abrasive articles, which comprises the steps of storing a web of felted fibrous material having impregnating adhesive and abrasive grain included therein in a constant temperature constant humidity atmosphere for a suficlent length of time to bring the web material to the desired uniform moisture content throughout its extent, coating one face of the resulting web with a laminating coat of adhesive, again adjusting the moisture content of the web material by storing it in a constant temperature constant humidity atmosphere for a sufficient length of time to bring it to the desired moisture content, cutting blanks from the resulting web, superimposing such blanks, cold pressing such superimposed blanks to form an article, and further pressing the article while subjecting it to the action of a high frequency electric field, whereby both the sizing and the laminating adhesives are heated and cured to the desired extent.

3. In a method of making laminated abrasive articles from sheet material comprising abrasive grain and a heat-softenable adhesive, the steps which comprise bringing each of a plurality of such sheets to the same uniform moisture content. superimposing such'sheets, and pressing the assemblage of sheets so formed while subjecting it to the action of a high frequency electric field capable of uniformly heating the assemblage and for a sufflcientlength of time to soften the adhesive and bond the sheets together.

4. In a method of making laminated abrasive articles from sheet material having impregnating adhesive and abrasive grain included therein, the steps which comprise bringing each of a plurality of such sheets to the same uniform moisture content, superimposing such sheets, and pressing the assemblage of sheets so formed while subjecting it to the action of a high frequency electric field capable of uniformly heating the -assemblage and for a sufficient length of time to soften the adhesive and bond the sheets together.

5. In a method of making laminated abrasive articles from sheet material having abrasive 6. In a method of making laminated abrasive grain and a heat-softenable adhesive aflixed to a surface thereof, the steps which comprise-bringing each of a plurality of such sheets to the same uniform moisture content, superimposing such sheets, and pressing the assemblage of sheets so formed while subjecting it to the action of a high frequency electric field capable of uniformly heating the assemblage and for a suflicient length of time to soften the adhesiv and bond the sheets together.

jecting a plurality .posing such sheets, and

ing impregnating adhesive and abrasive grain included therein, the steps which comprise subjecting a plurality of such sheets to an atmosphere of controlled humidity for a sufficient length of time to bring the sheet material to a desired uniform moisture content, superimposing such sheets, and pressing the assemblage of-sheets while subjecting it to the action of a high frequency electric field capable of uniformly heating the assemblage and for a suflicient length of time to' soften the adhesive and bond the sheets together, whereby the adhesive becomes uniformly cured throughout. c 7. In a method of making laminated abrasive articles from felted fibrous sheet material having impregnating adhesive and abrasive grain included therein, the steps which comprise subphere having a temperature of about 90-95 'F. and a, relative humidity of about 50-60% for a sufficient length of time to bring the sheet material to a uniform moisture content, superimpressing the assemblage of sheets while subjecting it to the action of a high frequency electric field capable of uniformly heating the assemblage and for a suflicient length of time to soften the adhesive and bond the sheets together, whereby the adhesive becomes uniformly cured throughout. 1

NORMAN P. ROBIE.

ROBERT G. ROWE.

of such sheets to an atmos- Certificate of Correction Patent No. 2,393,267. January 22, 1946.- NORMAN P. ROBIE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 5, line 31, after the word and period throughout. and before the signatures, insert the following claims:

8. In a method of making laminated abrasive articles from felted fibrous 7 sheet material having impregnating adhesive and abrasive grain included therein, the steps which comprise coating a number of such sheets with a laminating adhesive, subjecting a plurality of such sheets to an atmosphere of controlled humidity for a sufficient length of time to bring the sheet material and the laminatin adhesive to a desired uniform moisture content, cold pressing an assemb a e of a plurality of such sheets to form a slab, cutting an article fromthe res ting s ab, and pressing the article while subjecting it to the use of a h h frequency electric field capable of uniformly heating the assemblage and or a sufiicient length of time to soften the adhesiveand bond the sheets together, whereby the impregnating and the laminating adhesive are each heated and cured uniformly throughout.

9. In a method of making laminated abrasive articles from felted fibrous sheet material having impregnating adhesive and abrasive grain included therein the steps which comprise coating a surface of the said sheet material with a laminating adhesive comprising a solution of casein, drying the coated sheet material to a moisture content of approximately 7%, assembling a pluralitly of such sheets in superimposed relationship, and pressing the assemb age while subjecting it to the action of a high frequency electric field capable of uniformly heating the assemblage and for a suflicient length of time to soften the adhesive and bond the sheets together.

in the heading to the printed specification, line 9, for 7 Claims read 9 Claims; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record ofthe case in the Patent Office.

Signed and sealed this 17th day of February, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommzssioner of Patents.

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