US2398890A - Reinforced abrasive article and method of making same - Google Patents

Description

' April 23, 1946. I HOWARD 2,398,890 1 1 REINFORCED ABRAsIvE ARTICLE AND METHOD QF mm sAMEj Filed Sept. 22, 1945 Invenir; L

A'LMEc How/920g v Patented Apr. 23, 1946 UNITED STAT- E sameness ABRASIVE METHOD or MAKINGSAME were me Elmer E. nowaranuiralo, N. Y sasslgnor toThe Carborundum Company, Niagara Falls, N. Y., acorporation of Delaware Application September-22,1943, sesame. 503,338

- 1 Claims. Cl. 519209 f;

This invention relates to bonded abrasivearticles andthe method of making same. More particularly it relates to abrasive articles in which the abrasive portions of the articles. are supported by rigid means, such as backing plates or side plates secured to the flat face of the abrasive sections and to methods of molding the abrasive portions and securing them to the rigid reinforcing means. The invention has as an object the making of a superior reinforced abrasive article able to withstand very severe usa e. and to a novel method of making such article distinguishedby its economy andease of practice. Other objects of the invention will become apparent as the description proceeds.

It is common in the art in the making of disc shaped grinding wheels adapted to be mounted for grinding with the flat side face of the wheel to employ a rigid metal supporting and reinforcing plate secured to one flat-side face of the wheel as by being adhesively. mounted thereon with a resilient tie bond interposed between the, backing plate and the abrasive.,,Such resilient,

. and-:the assembly c for a suflicient length oltime 'to effect .thexcure and vulcanization of the tie bond and the cure and hardening of the added layers of adhesive,

subjected to heats-rid seam if such are employed. A reinforced bonded abrasive article made. in this manner requires extensive finishing steps after theabovedescribed by use of suitable cutting or dressing tools the y various-grinding surfaces, of the wheel are flni a wheel stronger, safenandotherwis'e superiorto steps necessary in the-prior art,.and inso doing cuts down the cost of the finished article to a efiect and allows differential expansion between the backing and the abrasive which otherwise would impose severe stresses upon the abrasive and might ultimately result in the fracture thereof. l p

In the making of such prior art reinforced abrasive articles such as disc shaped grinding wheels, the abrasive portions have been molded and the bond has been vitrified, in the case of ceramic bonded abrasives, and cured in the case of abrasive portions bonded with organic binders such as rubber, synthetic resins, or shellac. The thus preformed abrasive body has then been mounted upon the reinforcing backing. This has useless is much less than that resulting fromprior -artmethods.. i I

plate. In suchflnlshing operation the assembled 'tionship with reference to the backing plate.

- by. use of production methods to assemble an were initially finished to the desired shape and -size.. 1

number offlnished wheels having crackedsbrar process of bonding the abrasive to the reinforcing wheel is mounted one. lathe by meanscontacting the center arbor 'hole in the, backingplate, and

ished to size and are located in the desired rela- Such steps are necessary because it is not possible abrasive article on a backing plateso that all of its surfaces bear the correct relationship @tothe i backing plate, even thoughthe abrasive article By-use of the method of the present invention that made by prior art methods is produced; In 1 addition, such methodobviates theme of several marked extent; Furthermore. by practiced the present. invention it has been found thatthe sive sections and other defect rendering Briefly; the method of the present invention i consists in assembling upon aremforcing plate,

whose bonding surface has been suitably prepared, a layer'of un'vulcanizeditie bond both of ,f

:whose surfaces may have beencoated with suit- 1 able adhesives, 0n the top of theupper surface been done by suitably cleaning and preparing the face of the abrasive to be secured to the backing, and by preparing the backing for its reception. The latter is straightened, the surface thereof to be secured to the abrasive is sand-blasted, and the backing is again straightened. The abrasive, a layer of tie bond, and the reinforcing backing, with orv without added layers of suitable cement between metal backing and tie bond and tie bond and abrasive are then assembled in that order.

of an intimate mixture of abrasive grain and a l relatively low temperature cure binder such as 1 then subjected to pressure so that it is comtie bondyandyif added adhesive is employed on tween it and the backing, to cure such adhesive layers. The composition of thetie bond used is of the tie bond thereis placed a suitable amount" rubber, synthetic resin, or shellac. Such mixture pactedand brought to the desired shape andthe whole assemblyis then heated for such length of time as to curethe abrasive bond,=vulcanize the the tie-bond betweenit and the abrasive andbesuch that itis toughfandresilientafter' theproi longed heating betwecn approximately 300 and plate 2.

. 400- Fj which is necessary to cure the abrasive be carried out.

The abrasive article shown in Figure 1 by way of illustration consists of a bonded abrasive annulus I, secured to a reinforced backing plate 2.

Plate 2 may be made of iron, steel or other suitable metal. Backing plate 2 may also, if desired, be made of other material, such asa molded resin, which has sufficient strength and shock resistance in the particular wheel in which it is employed, and which also has sufllcient resistance to heat that it is not materially aflected by the heating necessary to cure the abrasive bond and *vulcanize the tie bond. Backing member 2. in the modification shown in Figure 1, is secured to abrasive annulus I by means of-interposed layers of. cement 3, resilient tie bond 4, and layer of ce-' ':ment 5, occurring in the finished article in the' :direction from backing! toward abrasive I in the order named. Backing member 2 is provided with acentral hole 6 thereinfor the reception of the arbor ofthe grinding machine, and with holes 1 for the reception of bolts holding the wheel onto a mounting plate on the grinding machine.

' In forming the'abrasive article of Figure 1, the

- apparatus shown in Figure 2 may be conveniently either in the cold, in which case hot plates 10 and I8 act merely as spacers for the time being or, ii. desired, the initial compacting may take place with the parts in heated condition, the heat being supplied by circulating steam through the bores within the hot plates.

After the assembly has been initially compressed either in hot or cold condition, it is then subjected to heat for a suitable length of time to cure the bond for the abrasive, the tie bond, and the adhesive layers, thus uniting the backing plate, tie bond, and bonded abrasive portions of the article intimately into a. unitary structure. The last recited heating step for the purpose of curing tie bond and abrasive bond may be, if desired, carried out in the same press which was employed for, the initial pressing step, or, alternaused. .Such apparatus consists of a press, of

which only'portions of the bottom platen 8 and the top press plunger 0 are shown inthe figure. Aihot plate 10 is placed ontopof platen 0 and I on top ofJhot plate It! there is placed a mold assembly consisting of a bottom plate H having a central hole l2itherethrough, and a mold barrel *13 surrounding the bottom plate. A backing plate 2, having its'top surface suitably prepared ."and coated with ailayerof adhesive 3, and having a sheet of resilient tie bond 4 of therequired shape and size positioned thereon, the upper surface of the tie bond being coated with a'layer 5 of adhesive, is then placed within mold barrel l3 on topof mold plate II. Interior mold part M, which is in the nature of a core, and which has on its bottom end a centrally projecting pin 15, is

' then introduced into the assembly so that pin l5 fits into hole I2. .A suitable amount of an intimate mixture I 6,

of abrasive grain and low temperature cure bond,

such as a synthetic resin, is then introduced into n the mold in the space between mold barrel I3 and core I 4 and is distributed soas to have. a maximum uniformity as regard to degree of com- *paction and the height to whichit extends above adhesive layer 5 at every location within the mold. Plunger H, which is in the form of anannulus having inner and outer diameterssuch as the annulus fits the space between moldbarrel l3 and core 14 within close tolerances, is then assembled in the mold. The upper hot plate I8 is placedon .top of mold part ILand press plunger 9 is then brought down under a. predetermined pressure to compact the mixture N5 of grain and bond to a predetermined degree and to force it firmly against layer 5 of adhesive, which in turn, together with tie bond {and layer of adhesive 3 are firmly compressed in the direction toward the backing lsuch initial compression may take place tively, the mold may be removed from the press and heated, for instance, by being charged into V maintain the assembly under moderate compacting pressure during the cure; this may be accomplished in the press, or if the cure takes place in an oven, by suitable weights or clamps 0n the mold or wheel. I

The following example, which is illustrative only, is typical of procedures followed and compositions of the materials employed in carrying out the present invention: I

A steel reinforcing backing is straightened and is cleaned and sand-blasted on that side which is to be secured to the tie bond. The sand-blasted surface is then coated with a cement having good adhesive properties for the backing plate and the type of tie bond employed. In this instance the cement used on the steel backing consists of the following ingredients in the indicated ratios:

Phenol formaldehyde resin such as Bakelite resin BR2417 grams 25.0 V Ethylsulfate cc 16.6 l-chloro-lnitropropane cc 4.2 Methylethylketone cc 67.0 o-Dichlorobenzene cc 22.0 Compound X grams 10.0

Compound X consists of the following inis a synthetic rubber composed of butadiene with acrylic acid "Hycar O. R." of a copolymer nitrile. I

Nevoll is a liquid coal tar derivative having a specific gravity of approximately 1.10, which functions as a rubber softener and dispersing agent.

Such coated backing plate has then placed upon it a layer of resilient tie bond material, which is usually to of an inch in thickness. Such tie bond, which may be provided with a, plurality of perforations extending therethrough in accordance with the teaching of application Serial No. 492,057, filed June 24, 1943, by Arthur G.

heated tosuch temperatures and for such lengths cure the abrasive a, cement which has been found suitable for bonding the tie bond to the mixture of abrasive grain and organic bond. Such cement is one consisting of 75 of a liquid phenol-aldehyde condensaof time as are necessary to bond and the tie bond. i i Instead of the AmeripolPtie-bondjabove disclosed, one made of Buna S,'which isra copolymer of butadiene andstyrene, may be used; Buna S may be cured atthesame temperature-as Amerij pol," and has substantially the same qualities insofar'as strength and resilience are concerned.

tion product such as Bakelite resin BC5763 with r 25% of a finely divided clay added as a filler. The cement mixture may be thinned if'necessary with a small amount of a resin solvent such as furfural or alcohol. The tie bond thus coated on its top surface and cleaned on its bottom surface is placed on the top cement coated face of the backing, and the backing plate with the attached tie bond is placed in the mold with the backing plate on the bottom. a

. A suitable amount of a. mixture of grainjja'n d 1 Besides-the synthetic resin bond employed for the abrasive in the example above, other low low temperature cure bond is then charged into. mold space lying between core I and mold barrel l5. Such abrasive-bond mixture may be prepared in accordance with Martin Re. Patent No. 19,318. In accordance with this method a predetermined amount of-abrasive grain of suitable mesh size is wet with a relatively small amount of resin solvent which may be, for example, furfural. The thus treated grain is then mixed with asuitable quantity of a powdered synthetic resin, such as an A stage phenolaaldehyde condensation product, in the amount, for example, of by weight of the mixture. The ingredients are mixed quickly to keep the mix to be used with oily grindingfiuids.

BunaS, however, is not oil resistant, and so unless protected by an oil resistant coating it is not advisable toemploy it in wheels which are Other elastomers, synthetic or natural, may alsobe employed as the tie bond in the ,wheel. Suchelastomers must, like the cement layers,.have adequate hot and cold strength and not be adverse- 1y affected by the curing treatment employed for from balling up, after whichthe mixture is ready for charging into the mold. After such step,

the mold is closed by having plunger ll placed thereon, and the assembly is cold pressed at,

for example, a pressure of 2000 pounds per square inch of abrasive mix. The resin abrasive bond, cement layers, and tie bond are then removed from the mold and cured by heating the assembly under a moderate pressure "for a maximum of 55 hours, 46 hours of such period being consumed in raising the temperature to approximately 400 F. After a hold of 9 hours at this temperature, the wheel assembly is cooled in stages to room temperature. With the exception of a, slight dressing operation necessary to re,- move the outer glaze from the grinding surface, the wheel is in wholly finished condition after its cure. i i

\ It is to be understood that the procedureset out in the above example is capable of numerous variations. It is possible to employ the tie bond alone Without layers 3 and '5 of cement thereon to secure the abrasive to the backing. It is'also possibleto employ the first named cement, namements must have satisfactory hot and cold strengths when employed between the specific elements to be adhered together, and must, possess sufiicient heat resistance so as not to be deleteriously affected to any marked extent when the abrasivebond. The molding pressure .used is capable ofvariation, the particular one em,- ployedbeing that yielding the desired grade of wheel. i

temperature bonds such as natural rubber, synthetic rubber, and shellac may be employed, all

of which have a curing temperature ofapproximately 325 F. If a natural rubber or natural with the above abrasive bonds, it would as a result of; heating at approximately 325 F be cured to a hard inflexible condition, but a tie bond composed'eitherof Ameripol or Buna S remains sufficiently resilient aftersuch heattreatment so that-it will perform its intended function. When shellacis used as thebond forthe f abrasive the preparation of the abrasive-bond mixture and the molding thereof may conveniently be carried out in" accordance with thedisclosures of the Martin Patents Re. 17,739 and Re. 17,740. A typical curing cycle for the resulting 'molded abrasive shellac mixture, the cement layers, and the tie bond consists of heating the wheel assembly mately 325! F. for a period of 6 days.

Reinforced abrasive artlclesscoming withi'nthe scope of this invention, for example, discshaped' I grinding wheels, are distinguished from prior art reinforced abrasive articlesby their strength and safety. Because the molding of the abrasive and the compacting of such abrasive, the resilienttie bond, and the intermediatelayersof cement, if r jsuch are-used, against the rigid backing alltake place at the same time, the maximum possible strength is developed at each interface. The bond employed for the abrasiveandithe cement layer on the top of the resilient tie bond mingle at the interface and become practically one. ,The

1 abrasive granuleswhen; compacted against such 7 abrasive portion of the present wheel is thus Q "uppercement layerand/or the tie bond are free to adjust themselves. under the relatively high pressure employed, e. g. 2000 p. s. 1., and thus assume positions where they are most-intimately in contact with the uppercement layer and/or the tie bond. At the same time the tie blind and cement, if such is used, flow under the; pressure into the most intimate contact with the abrasive mix. A wheel madein this manner has the grit at the bottom of the abrasive slightly out, of a plane, because of the self-adjustment of the abrasive mix and tie bond; This contrasts with a premolded and cured abrasive wherein the face adjacent'the tie bond lies in a plane, since it was in contact with plane faces of the mold. The

wheel. assembly to .an undesirable extent.

4 a :keyed to the tie bond much more thoroughly than that in prior art wheels.

This becomes apparent when priorart-processes are considered; .In making reinforced wheels by premoldihg and curing the :abrasiveyportion and I :then securing it to a backing by means of an interposed tie bond, only moderate pressures can beqemployed to press" the abrasive against the tie bond and the tie bond against theloackingr The pressure employedin thisprocess islimited to a :,value not materially above 300 p. s. i. by the fact @that the .prebonded abrasive is :readily "broken undervpressure, particularly if it #iS slightly I :warped, and. bythe'fact that, higher pressures result in the. extrusion of the tie bond'from the The use of a mold surrounding the, assembly to pre- I Y vent such extrusion is not feasible because of the --practical impossibility of finishing the abrasive portion to sufliciently close tolerances to allow it toseal the mold against such extrusion of the tie bond. Because of theninherent limitation of the former method to the use of low'pressures foreifecting assembly of the parts, thebonds bea other, atypical wheel of the present invention did not fail until it reached a surface speed of 25,000 feet per minute. of breaking speeds reached by reinforced *wheels made by premolding the abrasive and then securing it to a backing, and still further exceeds the minimum breaking surface speed perminute, im-

, posed by safety requirements, forthis type of wheel.

g The method of the present invention shows marked advantages over prior art methods in that by its use fewer operatingsteps are necessary to produce a finished wheel. Molding of the abrasive portion takes place simultaneously with mounting of the backing and the resilient tie bond. Thus the separate preparation'and'iinish- .-ing of the abrasive are avoided. Furthermore,

except for the light dressing above noted no finishing of the abrasive, after the assembly has been finally mounted and the parts cured, is necessary. On the other hand, when theabrasive is molded and cured separately and then is mounted upon the backing plate with an interposed tie bond,it is necessary to 'finishthe abrasive extensively to locate all its surfaces in the y, desired relationship with .respect to the backing and to bring the wheel to final balance. The

sive grain and low temperature cure bond (onto a layer of substantially uncured tie bond comprisins an elastomer in sheet form which is vulcanizable to a permanently tough and resilient condition mounted on a'strong rigid reinforcing backing, and heating the assembly of backing, tie bond, and molded abrasive until the abrasive bond becomes hard and relatively inflexible and the tie bond becomes cured and bonded to the abrasive and the backing but remains tough and resilient.

2. The method of making reinforced abrasive articles'comprising preparing a mixture of abrasive grain and a bond therefor having a curing temperature lying between 300 and 400 F., pressing andmolding such mixture of grain and bond onto a layer of substantially uncured tie bond comprising an elastomer in sheet form which is vulcanizable to a permanently tough and resilient condition assembled on astrong rigid backing plate, such molding and pressing serving to compress the abrasive grain and bond strongly against the tie bond and the backing plate, and heating the assembly of backing plate, tie bond, and abrasive at temperatures between 300 and 400 F. until the abrasive bond becomes cured to a hard and relatively inflexible condition and the tie bond becomes cured and bonded to the abrasive and backing plate but remains tough and resilient.

3. The method of making reinforced abrasive articles comprising preparing a mixture of. abra- This i much in excess sive grain and a bond therefor curable at temperatures between 300 and 400 F., pressing and molding the mixture of abrasive grain and bond onto a layer of substantially uncured tie bond in sheet form comprising a copolymer of butadiene sive grain and a bond therefor curable at 'tem-,

peratures between 300 and 400 F., pressing and molding such mixture of abrasive grain and bond onto a substantially uncured layer of tie bond in sheet form, such tie bond comprising a oomethod of the present invention is :flexible, since within the limits of compositions of tie bond-cements, and abrasive bonds noted above, thesame steps are followed regardlessof what-different compositions of such parts are employed.

While the preferred embodiment of the reinforced abrasivearticle and its process of manufacture have been described above in detail, it is g to be understood that the inventionis notlimited to allof the described details, but that it may be otherwise embodied within the scope of the following claims.

I claim:

i. Th method of making reinforced abrasive tarticles comprising pressing a mixture of abrapolymer of butadiene with acrylic acid nitrile and being vulcanizable to a permanently tough and resilient condition, said tie bond being assembled on a strong rigid backing plate, and heating the assembly of backing'plate, tie bond, and molded abrasive at temperatures between 300 and 400 F. until the abrasive bond becomes cured .to a

hard relatively inflexible condition and the tie bond becomes cured and 'bondedto theabrasive and the backing plate but remains tough and resilient.

5. The method of making reinforced abrasive articles comprising preparing a mixture of abrasive grain and a bond therefor curable at temperatures between 300 and 400 F., pressing and molding such mixture of abrasive grain and bond ejaiseaseo a -5 backing'plate. and heating the assemblyot backcondition'and the tie bond becomes cured and ing plate, tie bond, and molded abrasive at temperatures between 300 and.400 F. until the abrasive bond becomes cured to a hard relativel inflexible condition and the tie bfond becomes cured 6. The method of making reinforced abrasive bonded to the abrasive andthe backing but re mains tough and resilient.

and bonded to the abrasive and the backing plate but remains tough andresilient. y

articles comprising preparing. a mixtureotabra sive grain and a synthetic resin bond, pressing; and molding the mixture oi abrasive grain and bond onto a layer of substantially uncuredtie'j bond vulcanizable to apermanently' tonghfand, resilient condition and comprisinga copolymegfoi butadiene .and' a 'copolym'er'lzabl res n in i'sheet' formi assembled on astro'n'g "rigid'rei'niorcing backing, and heating the assemblybf bacldngg tie' I bond,fand molded abrasive for a period'oi at-lea 50 hours; a substantialp rtion of. themea'ting cycle being carried out at a temperature b iwgen 325 and 400 Fl, and; then cooling thea'rti'cletlie heating cycle being. /'such that theabrasivebond becomes cured to and relativelfinneziible i '7. The method of making reinforced abrasive articles comprising preparing a mixture or abrasive grain and a. shellac bond, pressing and mold ing the mixture of abrasive grain and bond onto a layer oifsubstantiallyuncuredtie bond vulcan .izable to a permanently tough and-resilient. con-f dition and comprising -a,?cop'olymer of buta diene and a copolymeri zable resin in sheet form asseme bled on a strong rigid reinforcing backingyand a, heatingvthe assemb1y oi,backin g, tie bond; "and; mol n's an ma, sub- I y H heatinfg cycle being car 'riedout at atemperature 'of atleast 3 25*F.,andthen cooling -the"article,'f tg lie heating'cycle being suchthat; the abrasive. bond becomes cured to a 1 hard andrrelatively inflexible condition and the tie .bond becomes. cured, and bonded to the abrasive butremai'ns tough and resilient;

molded abrasive for stantial portion "or .the

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