US2729553A - Abrasive article - Google Patents

Description

United States Patent M 2,729,553 ABRASIVE ARTICLE James E. Price, Abington, Pa., assignor to Simonds Abrasive Company, Philadelphia, Pa., a corporation oi Pennsylvania No Drawing. Applicatien March 6, 1952, Serial No. 275,222

. 6 Claims. (Cl. 51298) The present invention relates to a novel abrasive body possessing improved properties; and, more particularly, it relates to an abrasive body of superior mechanical strength which high strength is maintained over long periods of time. The invention also relates to a novel method for preparing the abrasive product.

The present application is a continuation-in-part of application Serial Number 211,193 filed February 15, 1951, now abandoned.

Abrasive bodies, that is, dense, rigid structures having abrading properties, such as grinding wheels and the like, are well known. In such bodies abrasive grains are bound into a dense, rigid structure by means of a thermosetting resin binder in the final, infusible, insoluble state. It is also common practice to incorporate a finely-divided filling material in the resin binder. Because of the formation of water in the resin during the curing of the body, that is, during the conversion of the resin to the insoluble, infusible state, it has been the practice to incorporate in the mixture, as part of the filler, a dehydrating agent prior to shaping and curing thereof. This dehydrating agent takes up the water formed preventing the abrasive body from swelling and distorting.

The dehydrating agent normally employed for this pur pose is quicklime (CaO), although magnesium oxide (MgO) may be used. At least a portion of the quicklime reacts with the water to form hydrated lime, Ca(OH)2, so that in the final product at least a portion of the lime is present as calcium hydroxide. While the incorporation of quicklime solved the problem of swelling during the manufacture of the abrasive article, and increased to some extent, the strength of the article, a secondary problem arose in that it has been found that, with such abrasive bodies containing lime, in time, par ticularly under conditions of high humidity as is common in shops where such abrasive bodies are employed, the mechanical strength decreases to the point where the use of the article must be discontinued. Moreover, because of this decreased strength, the use of such abrasive bodies, particularly when the abrasive body is a grinding wheel, becomes hazardous. In addition, it has been found that very strict control of the quicklime must be maintained to prevent the formation of an unsatisfactory product. In other words, the quicklime of commerce generaly loses about l3% of its weight on ignition. Such quicklime had to be fired prior to use to reduce its ignition loss to less than 1%, usually 0.5% before it could be employed in the preparation of abrasive bodies. Various attempts to remedy the foregoing difficulties in the past have not proved successful.

It is a principal object of the present invention to provide an abrasive body whose mechanical strength does not decrease with time.

Another object of the invention is to provide an abrasive body possessing a higher mechanical strength than those heretofore available.

Further objects including the provision of a novel method for making abrasive bodies will be apparent from a consideration of the following specification and claims.

The abrasive body of the present invention comprises abrasive grains bound into a rigid structure by a binding phase which comprises a thermosetting resin in the 2,729,553 Ratented Jan. 3, 1956 final, infusible, insoluble state, and finely-divided filler comprising an alkaline earth metal fluoride selected from the group consisting of the calcium, magnesium and barium fluorides, and an alkaline earth metal compound selected from the group consisting of lime and magnesia. Herein, in connection with the final abrasive product, the terms lime and magnesia refer to the oxide or hydroxide as well as to mixtures thereof, since, as will be pointed out hereinafter, the proportion of the initial oxide employed as dehydrating agent which is converted to the hydrated form will vary depending upon various factors, and since, from the standpoint of the present invention, it is immaterial what proportion of the original oxide is present as such or as the hydrated form.

The present invention is based upon the discovery that the incorporation of at least one of the stated alkaline earth metal fluorides in the binding phase of an abrasive body containing a thermosetting resin and calcium oxide and/or magnesium oxide, as a dehydrating agent, provides a product which possesses an improved mechanical strength, and which maintains its high mechanical strength over long periods of time even. when used under conditions of high humidity. While the exact reasons for this are not fully understood, the following theory is advanced by Way of explanation. As indicated above, the calcium or magnesium oxide functions as a dehydrating agent by virtue of its ability to combine chemically with Water to produce the corresponding hydroxide. The hydroxide formed both during the manufacture of the abrasive body, due to the formation of water by the resin during curing thereof, and during the products use, particularly under conditions of high humidity, is believed adversely to afleet the resin, reducing its mechanical strength. It is believed that the finely-divided alkaline earth metal fluoride dispersed throughout the inding phase of the present product neutralizes the hydroxide or otherwise eliminates its deleterious influence on the resin component. At any rate, as stated, the presence of the alkaline earth metal fluoride enhances the mechanical strength of the finished product and also results in a product which maintains its high mechanical strength over long periods of time. Moreover, it has been found that when the alkaline earth metal fluoride is incorporated in the binding phase the quicklime, which is preferably employed as dehydrating agent, need not be rigidly controlled as to ignition loss as previously, and that the high mechanical strength and maintenance thereof can be achieved even if the quicklime of commerce is employed Without preliminary calcination.

The preparation of the abrasive product of the invention will present no problem to those skilled in the art since, as is well known, the general procedure involves the mixing of the abrasive grains with the binding phase, and the pressing of the resulting mixture into the desired shape and the curing of the shaped body by heat to convert the resin into the insoluble, infusible state. However, the important feature insofar as the method of the present invention is concerned, is the thorough distribution of the stated alkaline earth metal fluoride, in finely-divided form, throughout the binding phase.

The abrasive grains from which the abrasive body is prepared may be selected from a wide variety of materials well known in the art. The particular abrasive grain selected will, of course, depend upon the use intended for the abrasive body and upon the properties desired. Examples of abrasive grain are fused alumina, emery, corundum, diamond, the various carbides such as silicon carbide, boron carbide, tungsten carbide, tantalum carbide, and the like. The size of the abrasive grain may also vary widely depending upon the properties desired in the final product. The selection of any particular material for use as an abrasive grain and the particle size distribution thereof, are considerations well known in the art and will present no problem to those skilled in the art. The proportion of abrasive grain in the product will vary somewhat as known to those skilled in the art. Generally, the abrasive grain may make up as low as about 40% of the final abrasive product, and generally, it will range between about 60% and about 96%, by weight of the product. Preferably, the abrasive grains make up between about 65% and about 90% of the product. The remainder of the product comprises the hereinafter-described binding phase.

The resin'employed in the binding phase of the abrasive body will,as stated, be of the thermosetting type so that it may be converted by heat, and also under pressure if desired, into 'a form which is no longer fusible at high temperatures and which is no longer soluble in ordinary solvents. There is a wide variety of such resins available as is well known in the art and examples of such materials are the phenol-aldehyde resins, particularly the phenol-formaldehyde resins; the resorcinobaldehyde resins, particularly the resorcinol-formaldehyde resins; the urea-aldehyde resins, particularly the urea-formaldehyde resins; the melamine-formaldehyde resins; the furfuryl alcohol resins; furfuraldehyde resins; furfuryl alcohol-fhrfuraldehyde resins; the alkyd resins; and the like, as well as various mixtures of such resins. Of the various resins available the thermosetting phenol-formaldehyde resins are preferred. In preparing the product of the invention, the resin will, of course, be in the initial state of condensation or polymerization so that it can be rendered fluid to facilitate the formation of the continuous binding matrix, and also, in 'certain situations, to facili- *tate the shaping of the body. The initial resin may be in powdered condition or in the liquid state, or a mixture of powdered and liquid resins may be employed. Powdered (resins are preferred. In addition, resin-forming ingredients may be employed in making up the mixture, as for example when furfural is employed to Wet the abrasive grain, or when phenols, for instance commercial cresylic acid, are employed to wet the binding ingredients when a powdered resin is employed. In such situations, heat subsequently applied. during curing causes these ingredients to enter into and become part of the resin binding phase. In the binding phase of the product of the present invention the resin will generally comprise between about 33% and about 80%, by weight, thereof, and preferably, the proportion of resin in the binding phase will be between about 45% and about 60%. It will be understood that there may be incorporated in the binding phase, or in the resin, a small amount of a curing catalyst to facilitate conversion of the resin into the final, infusible, insoluble state. For example, when phenol-aldehyde resins are employed, hexamethylenetetramine may be incorporated therein to provide'a convertible resin and to facilitate conversion thereof to the final, infusible, insoluble state. i

"As indicated above, the. product of the invention is made up of two main components, namely the discontinuous phase of abrasive grain and the continuous phase, or matrix, termed the binding phase. The binding phase comprises the described thermosetting resin and a finelydivided filler at least a portion of which is lime and/or magnesia and at least a substantial portion of which is the stated alkaline earth metal'fluoride. Referring specifically to thefdehydrating agent employed in preparing theproduct, calcium oxide (quicklime) is the preferred material. While magnesium oxide may be employed alone, it is when employed, generally used in conjunction with quicklime, the latter making up at least half of the combined compounds. With respect to the alkaline earth metal fluoride, the preferred compound is magnesium fluoride. Thu s, in the bindingphase of the preferred product of the invention, the finely-divided filler. will wee i ated;

divided form. Examples of such materials are cryolite,

clays, quartz, calcium carbonate, calcium sulphate, the alkali metal fluoborates, iron sulfide, various metal oxides, such as chromium oxide, finely-divided metals, and the like. The filler, in addition to the lime, most generally employed in the binding phase of abrasive bodies is finely-divided cryolite, and such material is the preferred material for making up any balance of the filler in the binding phase of the present product.

The filler will generally make up between about 20% and about 67%, preferably between about 40% and about 55%, of the binding phase, and in the product of the present invention the alkaline earth metal fluoride will make up at least about 10%, generally at least about 20% of the filler, and preferably at least about 50% of the filler will be the finely-divided alkaline earth metal fluoride, the remainder being the lime and/or magnesia and any other filler material as mentioned above. Along with the lime and/or magnesia, the alkaline earth metal may make up substantially all of the filler. The filler, including the lime and/or magnesia and alkaline earth metal fluoride, as stated, will be finely-divided and generally it will possess a particle size less than about mesh and preferably less than about 200 mesh.

As stated above, lime and/or magnesia will be present in the binding phase. Although the dehydrating agent employed in the preparation of the article will be calcium and/ or magnesium oxide, at least a portion thereof will be converted to the hydroxide during the preparation of the product, and additional oxide may be converted to the hydroxide after the preparation of the product and during its use due to moisture in the atmosphere. The amount of oxide in the product converted to the hydroxide will depend upon various factors including the proportion of oxide employed, the amount of water formed during the conversion of the resin to the final, infusible, insoluble state, the humidity and other moisture conditions encountered in the products manufacture, storage and use, and the length of time during which the product is subjected to such conditions. Since the advantages of the present invention are gained Whether a large proportion of the oxide has been converted to the hydroxide or Whether a small portion of the oxide has been converted leaving the balance thereof in a condition potentially convertible to the hydroxide after the product has been manufactured, this component of the binding phase is referred to generically herein and in the claims as lime and/ or magnesia to include both the oxide and the hydroxide of calcium and/ or magnesium as the case may be. In the preparation of the binding phase, the amount of oxide employed will usually range from about 7% to about 75% of the filler and thus in the product of the invention, the lime and/or magnesia will make up between about 7%. and about 75% (calculated as the oxide) of the filler. Preferably, the

lime and/or magnesia makes up between about 10% and about 5 0% of the filler.

In preparing the product of the invention, a moldable mixture comprising the abrasive grain and the binding phase is prepared. A wide variety of procedures is available for preparing this moldable mixture, so long as the finely-divided alkaline earth metal fluoride is thoroughlydistributed in the mixture,v and in accordance withfthe present invention, any of these procedures may be employed. In general it may be stated that the method comprises mixing abrasive grain, an initial thermosetting resin and a finely-divided filler comprising calcium oxide and/ or magnesium oxide and the alkaline earth metal fluoride, and shaping the mixture underv pressure. For example, a dry mixture of the various materialsmay be madeby mix.- ing the abrasive grain, powdered resin, filler, including the alkaline earth metal fluoride and calcium oxide and/or 1 magnesium oxide, together. in the desired proportions, following whieh themixture is. pressed into the desiredshape,

either under heat in which case the resin is at least par' tially converted to the infusible, insoluble state, or at ordinary temperatures following which the shaped body is subjected to a heating cycle to convert the resin. Or the wheel, and the wheel is then heated from room temperature to 360 F. over a period of four hours and is held at this temperature for an additional 16 hours. The result ing grinding wheel possesses high mechanical strength and resin, in a liquid condition, can be mixed with the abrasive has been found not to lose this strength upon standing in grain, and filler, including the alkaline earth metal fluoride an atmosphere of high humidity over a long period of time. and the calcium oxide and/or magnesium oxide, in which EXAMPLF H case the resulting plastic mixture can be pressed into the A desired shape, either under heat and pressure, or the mix- P i of a dryipowdered Phembformaldeh? ture may be first formed into the desired shape following resm (ctmslsimg of a mixture of aqua} parts by Weight which the shaped article is subjected to a heating cycle. Bakelite BR14740 Monsanio Resin 766) are mlxed Furthermore, the abrasive grains may be wetted with a vilth 37 Parts of P fluonde.and i i of resin or resin Component, in the liquid state or other clum oxide. This binding phase mixture is divided into liquid, and the thus wetted grain may then be mixed with parts each of WhlCh is mixed with a dltferentarnount or additional resin, or resin component, in the powdered abraswe gram of the Same type as employed m Example state, and also with the filler, including the alkaline earth as follows:

metal fluoride and the calcium oxide and/or magnesium oxide, and the resulting mixture then molded as previously Mix 1 Mix 2 stated.

The conversion of the resin into the final infusible, in- Grain g Fermi soluble stage will present no problem to those skilled in nindnigbir'gsffjjjjr 14 10 the art, since various methods for acomplishing this are well known As indicated above, the conversion, or at The pmcedure employed in preparing each mix i h 1 wit ur ura an t1e a ition o creosote oi. heat and Pressure} The generally R f method of Each of the above mixes is further divided into parts Converting the resin to the Insoluble, lnfuslble Stage, 110W- and molded into abrasive bodies following the procedure ever, comprises first, the shaping of the miX into the set forth in Example I, each product, however, difiering desired form, as in a press, following which the shaped as to density as follows; article is subjected to a heating cycle in which heat is a plied until the resin is converted. Such a curing cycle vt ill usually comprise slowly heating the shaped article to Product 1a 1b 16 26 i 20 the curing temperature and maintaining the article at this Density: 1b [cu in 0870 0900 0940 0920 0960 temperature for an extended period of time. As is known, the exact curing temperature will vary depending upon the a particular resin selected. Generally, particularly with b j of the i ai 5 of g the phenol-formaldehyde resins, the curing temperature r0 transversey lmme latey f z to employed will be above about F. and may go as high determine mechanical strength, and each u as tes-e furas about F. ther after aging for three days at 110 F. and 98 a rela- The preparation of the product of the invention will be 40 twe humldlty to dslermme h 108.8 strength i more clearly understood from a consideration of the fol- 3 2252 of thesa tests are glven m Table I heremafter lowing specific examples which are given for the pu ose of illustration and are not intended to limit the sec; of Abraswe bodies were piepareci followmg the p the invention in any Way tical procedure as set forth in section A hereof, us ng,

however, 37 parts of cryolite in place of the magnesium EXAMPLE I fluoride. In this case also one group of products (desigparts, by weight, of a dry, powdered, thermosetting herein as gmlip contained 86% of abrasive phenol-formaldehyde resin (nown as Bakelite BR14740) gram and bmdmgfhase, and the other gYOuP are mixed with 41 parts, by Weight, of fine1y divided of products (designated herein as group 4-) contained 84% nesium fluoride having a particle size of 200 mesh and 9 50 of abraswe, gram a of Pmdmg phase The Prod parts, by weight, of calcium id ucts also differed in density as 1n the case of the products Furfural is added to the abrasive grain (fused alumina, prfipared m semen A hereof as follows :1 25% by weight, of which was #10 grit, 25% of which was #12 grit, 25% of which was #14 grit and 25% of Product 3b 3c 4b which was #16 grit) in a Hobart-type mixer until each of the grains has been wetted with the furfural. The furfural Density in -0870 -0900 W40 -0920 is in an amount equivalent to 30 cc. per pound of dry binding phase mixture. To 84 parts, by weight, of the Each of these products was tested immediately after wetted grain are added 16 parts of the dry binder mixture preparation for mechanical strength and each was again in a tumbling barrel. To the resulting mixture is then tested after aging for 3 days at F. and 98% relative added creosote oil in the amount of about 15cc. per pound humidity to determine the loss in strength. of dry binder mixture to form a moldable mass. The data from the foregoing tests are set forth in the The mixture is then pressed in the form of a grinding following table:

Table 1 Product la 1b 11'- 3a 3b 30 2a 2b 4a 4b gensityJbJcuailll .0870 .0000 .0940 .0870 .0900 .0040 .0920 .0950 .0020 .0900 a, 570 3,910 4,040 3,310 3,880 4,440 4,300 5, 020 4,020 5, 020

in 3,540 3,840 4, 590 2, 280 2,400 3,500 4,230 5, 080 3,10 4,410 Change in strength, percent 1 2 1 -31 ---37 -21 -1.5 +1.0 -26 12 :7 EXAMPLE III Following the procedure of section A under Example made, using, however, quicklimes having ignition losses this case the proportions of grain and binding phase is 84% and 16% respectively, and the samples are pressed to a density of .0960. This product is designated as product 10a.

of 0.3% 097%, 1.45% and 3.5% respectively. (These Samples of this prodllct are tested immediately after products are designated therein as 5a, 5b, 5c and 5d, repreparation mechamcal strengtoh and Samples f' spectively.) These were tested immediately after presi gfi i f igg f i i 98% lame paring and also after aging for 3 days at 110 F. and 98% i g from gi i i 22 at f th th relative humidity to determine the loss, if any, in strength. fonbwin table 1 g es ar 5 or m e The results are given in Table II hereinafter set forth. g T M In Following the procedure under section B of Example a 6 II for product 4b (37 parts of cryolite in place of mag- Product nesium fluoride) four diflerent abrasive bodies were made using also quicklime having ignition losses of 0.3 0.97%, 7a 7b 8b 9a 1.45% and 3.5%, respectively. These products are desig- Hated herein as 6b, 6C and p These Density, 10/00. in .0900 .0980 .0940 .0900 .0920 .0870 products were tested for mechanical strength immediately v l s 4 4 A after preparationand also after aging for 3 days at 110 5135 ifififi g 5090 L670 2960 F. a d '1 aging 3 days t110 F., g relame humldlty to determne the loss In R. H.1,:ll; ./S?1. 111.... 4,330 4,050 4,140 4,295 4,170 2,745

ange in s reng per- The results of the foregoing tests are set forth in Table 8- '6 6- 5 -3 II below:

Table II Product 50 5b 5c 5d 6a 6b 6c 6d Density, 10 00. in .0900 .0900 .0900 .090 .0900 .0900 .0900 .0900 Ignition loss of CaO, percent. 0.3 0.97 l. 3. 5 0.3 0. 97 1. 45' 3. 5 Transverse modulus as prepared, lb./sq. in 4,830 4,700 4,880 4, 270 4-, 740 4,370 4,000 4,000 Transverse modulus after aging 3 days at 110 F., 98 percent R lb./sq. in. 4, 930 4, 050 4, 800 4,200 3,900 3,930 4,000 3, 050 Change in strength, percent... +2.0 1.0 -.5 -.2 17.0 10.0 12.5 -9.0

EXAMPLE IV EXAMPLE V parts of powdered thermosetting phenol- Abrasive products in the form of bars are prepared formaldeh de resin e ual arts of Bakelite BR14740 and of Moiilsanto Resgnqmm am mixed with 37 parts y 40 following the procedure set fOIt h III Example II, using, weight of finely-divided barium fluoride and 8.5 parts however 37 parts 9f finelydwlded calm-um fluoliide of calcium oxide, the fluoride and oxide passing through $5 3 gggg i zgi z ig ig g i fi i g gg ggs a 200 mesh screen. This binding phase mixture is divided are 5 5 and 16% respecfigely and the i are to g} g i g gggf gg ig g gyg g $222 322 5 52? .45 pressed to a denslty of .0960. The product 18 designated herein as 11a. amp 1e as follows Upon testing the product in the same manner as in the M. 7 M 8 9 previous examples, the following data are obtained:

1X 1X 1X Percent Percent Percent Table IV Grain 82 84 86 Binding phase 18 16 14 The procedure employed in preparing each mix is the Pmd'lct same as in Example I including the wetting of the grain with furfural and the addition of creosote T fifi v ai iiada sysiasaajisiisaii.1ii:::':::::::::::::: 5% Each of the above mixes is further divided into parts 'lransver se modulus after aging3 days at 110 F 98% R H and molded into abrasive bodies following the procedure f i'g g g gig set forth in Example I, each product, however, differing as i to density as follows:

Product 7a 7b 8a 8b 9a EXAMPLE VI Abrasive products in the form of bars are prepared Density m 0980 0940 0960 0920 0870 following the procedure of Example II using 37 parts of magnesium fluoride, and, in one case (designated 12a), Samples of each or the products, made in the form of Q bars, are broken transversely immediately after preparariplaclfg is 01 g i f i g i fi tion to determinemechanical strength, and samples of Q maineslum 0X1 6 W1 an m ano er c each are tested after aging for three days at 1100 R and natedproduct 13a)replac1ng 0.85 parts of calcium oxldc 98% relative humidity to determine the loss in strength. with a like l fi f The results of these tests are given in Table III herein- The Propomons of abraslve gram and bmdmg Phase after set forth, are 84% and 16% respect vely, and the products are 13. Abrasive bodies are prepared following the identical. P e se 0 a dQHS iY 0960- procedure asset forth in sectionA hereof using, however, Upon. testing samples of'the products as in the foregoing 37. parts of cryolite in place of-the barium fluoride. In examples, the following data are obtained:

amazes 1 Although the average loss in strength for samples is low, the root mean square deviation among the various samples is relatively high.

Considerable modification is possible in the selection of the components of the present product as well as in the particular procedure employed in making the product without departing from the scope of the invention.

I claim:

1. An abrasive body comprising abrasive grains bound in a binding phase comprising between about 33% to about 80% of a thermosettiug resin in the infusible, in soluble state, and between about 20% and about 67% of a finely-divided filler of which at least about 10% is an alkaline earth metal fluoride selected from the group consisting of the calcium, magnesium and barium fluorides and of which at least about 7% is an alkaline earth metal compound selected from the group consisting of magnesia and lime.

2. The product of claim 1 wherein at least about 20% of the filler is magnesium fluoride and wherein at least about 10% of the filler is lime.

3. The product of claim 2 wherein at least about of the filler is magnesium fluoride.

4. An abrasive body comprising abrasive grains bound in a binding phase comprising between about 33% to about of a phenol-aldehyde resin in the infusible, insoluble state, and between about 20% and about 67% of a finely-divided filler of which at least about 10% is magnesium fluoride and of which at least about 7% is lime.

5. The product of claim 4 wherein at least about 20% of the filler is magnesium fluoride.

6. The product of claim 5 wherein the phenol-aldehyde resin comprises a phenol-formaldehyde resin.

References Cited in the file of this patent UNITED STATES PATENTS 2,022,893 Martin Dec. 3, 1935 2,168,281 Sanford Aug. 1, 1939 2,249,279 Kistler July 15, 1941 2,308,983 Kistler Jan. 19, 1943 2,400,036 Wooddell et al May 7, 1946 2,422,153 Wooddell et al June 10, 1947

Claims (1)

1. AN ABRASIVE BODY COMPRISING ABRASIVE GRAINS BOUND IN A BINDING PHASE COMPRISING BETWEEN ABOUT 33% TO ABOUT 80% OF A THERMOSETTING RESIN IN THE INFUSIBLE, INSOLUBLE STATE, AND BETWEEN ABOUT 20% AND ABOUT 67% OF A FINELY-DIVIDED FILLER OF WHICH AT LEAST ABOUT 10% IS AN ALKALINE EARTH METAL FLUORIDE SELECTED FROM THE GROUP CONSISTING OF THE CALCIUM, MAGNESIUM AND BARIUM FLUORIDES AND OF WHICH AT LEAST ABOUT 7% I AN ALKALINE EARTH METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF MAGNESIA AND LIME.