US2638413A - Abrasive articles - Google Patents

Description

Patented May 12, 1 953 Norman P. Robie, Hamburg, .N. .Y., assignorto Electro Refractories & Abrasives Corporation, a

. corporation of Delaware N Drawing. Application August 10, 1949,

:SerialNo.109',621;

60laims. (01. 51-298),

. This inventionrelates to abrasivearticlesand more particularly to grinding wheels ;bonded with thermo-setting resin. -A primary objectof my'invention is to produce abrasive bodies withsuperior cutting ability, which maybe-measured either in terms of away very rapidly. I have found that by the use of my invention it is possible to makethe work done per body during the useful lifeof the same; or in terms of rateofcut. Another'obj'ect is to provide an abrasive wheel whichis cooler during cutting "than the usual wheels;particu-' larly thosebonded withjsyntheticresins capable ofhighspeed operation.- {Another -objectis to increase the safety factor byreducin the tendency tobreak when the Wheel is used in severecutting applications. i

"My invention residesparticularly in the use of certain fillers which I have found it advantageous to incorporate inthe mixfrom' which the'body or'wheel ismade; Thesefillers are not in themselvesabra sives in the 'usual'sense, but greatly improve'the performance of the body. or wheel when it is in operation by modifyingand/cr extending the binder used therein. The use of fillers in such wheels is old in the"art,'the use of such materials'as' cryolite, clay, fine alumina, lead oxide, flint, rouge, lime or magnesium oxide having been described in patents or practiced more or less widely-in the industryw In some cases the selection of these, materials has been to secure some chemical reaction with the resin or with the water vapor released during thecur ing operation. The use of lubricating fillers such as graphite has also been suggested. The .fillers according to my' invention; are

chemicallyinert and do not possess the quality. of lubricity, hence they seem to fall into-a different category from theforegoingi My fillers-in common with some of the others, seem'to make. the abrasive articles or wheels containin them'somewhat denser and harder-than' whenthe fillers are left. out, -but theyvary sharply from a e e er e wheel ,orthe .metalsothat the wheel binds in the slot being cut, with the re-- sult that thewheel. seizes. and breaks. Further,

ifexcessive heat is generated, the bond disintegrates, causing chips to break out of the wheel edge. To avoid. these difficulties, such wheels wheels far stronger and more solid, and yet not secure excessive heating even when metal is removed-at a rapid rate. While my invention is highly applicable to cutoff wheels, it is not limited tothem, but is rather applicable to resin bonded wheels and abrasive articles of all sorts.

I have found that certainlead salts which are not reactive withphenolic resins and do not form lead phenolates, as'do those suggested by Kuz'mick in U. S. Patent #2,083,719, are un usually valuable fillers in phenolic resin bonded abrasives. These salts are the substantially insoluble and anhydrous lead salts of strong acids, including specifically lead chloride, lead fluoride, lead sulfate, lead flue-chloride and the like. I do not know why these fillers are so superior, but I have established by repeated tests in the laboratory and in the field that such is the case. I also know that they do not embrittle the resin by reaction therewith, as do oxidic compoulnds of lead. I

In the manufacture of abrasive articles in accordance with my invention, I have used my fillers in various amounts from as low as 3% of the mix by weight to as high as 30%. I prefer, however, to use from 10 to 25% with 20% as generally satisfactory.

.The abrasive employed may be of any desired-- type, such as aluminum oxide, corundum, emery,

diamonds. and the like. The binder may be of any thermo-setting resin of the type commonly used as binders in the abrasive industry such, for example, as phenolic or alkyd resins.

" fusible and soluble, heat reactive, heat hardening containing are.often maderelatively open or porous, which 1 Me a er e r r ur th they ea phenol-formaldehyde resin capable of heat hardening into an infusible, insoluble state. The phenol-formaldehyde resin is a two stage resin usually hexamethylenetetramine groundthereinto act as a hardening agent.

Preferably I use a plasticizer, which may be a solvent, a liquid resin or a solution of resin in accordance with the well known practice in the abrasive industry. The following maybe em--,

ployed'; cresol, furfuryl alcohol, furfural, liquid phenolic resins.

These materials are thoroughly mixed according to conventional practice and formed into. articles of desired shapes by either hot or cold be heated OroVen-baked in the usual manner to thermo -set the bond.

; In orderthat the method of manufacture may I preferably employ a finely powdered, less than 1% on mesh, less'than'15% on 325 mesh, initially be clearly understood, I give the following examples by Way of illustration and not limitation:

Example I 200 gra rnsof technical grade, finelyv powdered lead chloride is first mixed dry with 110 grams of powdered phenol formaldehyde resin of the A stage heat reactive variety (sold by the Var; cum Chemical Corporation under the number V1364). In a separate container I mix together 690 grams of fused aluminum; oxide abrasive grains using equal amounts of" grits 24; 3.0 andz36..

respectively. After these are well mixed, they are wet up with 8 cc. of cresolr and the mixture,

of powdered bond and filler is then added and thoroughly mixed in. The material thus prepared is then placed in a mold, levelled and Example II Azwheelin whichsiliconcarbide is used as the abrasivemay be made by employing the iollovh ing pe'rcentages of ingredients by weight:

"'S ilicpnfcarbide grain 64.4%. The grain may befir'ithe and 36' grain size, and preferablyequal'quantities of each size are used.

"Thib ondin g agz'ent may be the same asspecified 'in- Example I, and constitutes 12.6% of the finalprodiict.

Ladsulfate in powdered form is employed to the extent er -"2 of the weight of the final product The silicon carbide grain is wetted with a suitable plasticizer, for example 30 cc. oi cresol per poundor resin bond'use'd, before mixing with the leadsulfate filler'and' the resin powders, The material is'then molded to a density oiabout .9891"pound"per cubic inch and may then be cured or baked as desci'ibedin Exarnple'l.

The specific examples I have-given have been concer-nedchi'efly with cutoff wheels because due to their thinness, these can he tested with mininiuni requirement formaterial. I do not confine useo'f my fillers'to-such wheelshowever, but may use "them in portable wheels, snagging wheels, thread grinding wheels, or any other. type of abrasive in which synthetic resin bonds are-used. Their use in wheels containingnatural' on synthetic rubber in the bond is beneficial. The

fillers-may he used with any of the common types of abrasive including alumina or silicon carbide, and with' phenolic, alkyd or other thermosetting 1'esin's. Their use" is beneficial without regard to the type of plasticizer used. The Wheelsmay be made by either hot or cold pressing methods.

I mayadmix my fillers with other cheaper fillers,such as cryolite-or lime in order to extend their utility,'or I may use them unmixed. I have; in' general used them in powder form; such that 100% will pass through a 325 mesh sieve, but

their beneficial effect-is not primarily dependent upon size solong as they are 'of the order of fineness of 100' mesh or less.

In azseriesof comparative tests, I made wheels identical with one another except for. the filler used, as follows: a mix was made from 79% by weight of fused alumina grain comprising equal proportionsof. 24, 30 and 3 6'grit. This grain was wet up with a plasticizer in the usual way and a premixed lot of powder consisting of 14.2% by weight of reactive heat-hardenable phenolic resin, 5.9% filler and 0.87% lime was then mixed in and-the mi-xformed into-wheels having a density of 0.0866 pound pericubic inch. These wheels were then baked between batts, their temperature being raised to 360 F. and held at that temperature for over nine hours. The wheels. each of which was 16 x x 1 inches were then used. to, ma l ;e 25.. cuts through a 1 inch bar of eold rglled steel and the loss of abrasive determined-byweighing; the wheel before and after use. My, leadfluoride filler gave superior results as follows Grams Wheel Loss Filler Potassium 1110.

The other fillers. here chosen are those commonly used in suchabrasive articles, It islinown that theireiiectivenss. decreases, as the percentage fallsbelowthat use.d,,soth at.if for instance the volume of the cryolite and fiuoboratehad been. assrnall as the volumeofthe much denser lead salt, the results would have been even. more favorable to. my material.

In another. series, of. compaa ative. tests made with my fillers in comparison withlitharge, 69% weight ofiused aluminagrain, sized. as above. was similarly ,madeup into wheels using 11%. of. powdered r,esin.and.20% by Weight of filler. The wheels. in this case. were each'pressedto a density. of. 0.11.1oound per. cubicjinch Afterfbaking, they were. eachused tomake tencuts through 1 inch stainlesssteel rods and the. lossfo f weight of, each wheel measuredasbefore, The results are ive b ow Grams Filler Wheel Loss Load'cliloride, C. P 1 l0 1 ead chloride, techn 9 Lead sulfate, 0. P 10. 5 Lithargeftechnia l8. 5 Basicload sulfate 1 S 19 sta e at tests were: madeunder. drastic test, conditiens in which. it was-attempted. to. u -slic s fr m a. tou h our. inch square stainless steel bar. The wheels; madefwithaconvens el fi ers made nly; partial cuts. and: then,

beeau of thetremendous heatgenerated; seized:- crumbled and broker With-.wheelsrmade.

5 usinsmyleacl c lfl de and: lead. sulfate fillers se-made Sui-le t bas h ir h q -lawms table,

Grams Wheel- Loss oratory results, with superiority in pieces proc-. essed per wheel running 50% above normal in many instances.

Having thus described my invention in general terms and given a specific example of its application, I desire patent protection within the scope of the following claims:

1. A cutoff wheel comprising abrasive grains, from to 25% by Weight of an anhydrous lead salt of a strong acid selected from a group consisting of non-basic lead sulfate, a lead halide and mixtures thereof, and a thermo-set phenolic resin bond uniting said grains and said lead salt into an integral body, said lead salt being substantially insoluble in water and non-reactive with said bond and being substantially uniformly dispersed throughout said body.

2. As an intermediate article of manufacture, a shaped object for the manufacture of an abrasive body therefrom, said shaped object consisting of a compacted formed mixture of abrasive granules, a thermal setting phenol formaldehyde resin, and from 3% to 30% by weight of a finely divided lead salt of a strong acid, said salt being substantially insoluble in water and non-reactive With said bond and being a member of the group of compounds consisting of non-basic lead sulfate, lead halides and mixtures thereof.

3. An abrasive article comprising abrasive grains, an anhydrous lead salt of a strong acid in finely divided form, said salt being a member of the group consisting of non-basic lead sulfate, lead halides and mixtures thereof, and a phenoli resin thermo-set bond uniting said grains and said lead salt into an integral body, said lead salt being substantially insoluble in water and nonreactive With said bond and being substantially uniformly dispersed throughout said body, said lead salt comprising from 3% to 30% by weight of the article.

4. An abrasive article comprising abrasive grains, an anhydrous lead salt of a strong acid in finely divided form, said salt being a member of the group consisting of non-basic lead sulfate, lead halides and mixtures thereof, and a phenolic resin thermo-set bond uniting said grains and said lead salt into an integral body, said lead salt being substantially insoluble in water and nonreactive with said bond and being substantially uniformly dispersed throughout said body, lead salt comprising from 10% to 25% by weight of the article.

5. An abrasive article comprising abrasive grains, from 3% to 30% by weight of a lead halide in finely divided form and a phenolic resin thermo-set bond uniting said grains and said lead salt into an integral body, the lead salt being substantially uniformly dispersed throughout said body.

6. An abrasive article comprising abrasive grains, from 3% to 30% by weight of a non-basic lead sulfate in finely divided form and a phenolic resin thermo-set bond uniting said grains and said lead salt into an integral body, the lead salt being substantially uniformly dispersed through out said body.

NORMAN P. ROBIE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,083,719 Kuzmick et al. s June 15, 1937 2,273,891 Pollak et al Feb. 24, 1942 2,456,920 Coes Dec. 21, 1948

Claims (1)

1. 3. AN ABRASIVE ARTICLE COMPRISING ABRASIVE GRAINS, AN ANHYDROUS LEAD SALT OF A STRONG ACID IN FINELY DIVIDED FORM, SAID SALT BEING A MEMBER OF THE GROUP CONSISTING OF NON-BASIC LEAD SULFATE, LEAD HALIDES AND MIXTURES THEREOF, AND A PHENOLIC RESIN THERMO-SET BOND UNITING SAID GRAINS AND SAID LEAD SALT INTO AN INTEGRAL BODY, SAID LEAD SALT BEING SUBSTANTIALLY INSOLUBLE IN WATER AND NONREACTIVE WITH SAID BOND AND BEING SUBSTANTIALLY UNIFORMLY DISPERSED THROUGHOUT SAID BODY, SAID LEAD SALT COMPRISING FROM 3% TO 30% BY WEIGHT OF THE ARTICLE.