US 2475517 A
Description (OCR text may contain errors)
July 5, 1949. K. G. RlEs ErAL BRASIVE ARTICLE 0F ANUFACTURE Filed Aug. 13, 1946 ill" `resinoid composition. 'molded resinoid centers made of the thinness l Patented July 5, 1949 ABRASIVE ARTICLE OF MANUFACTURE Kernell G. Ries, George J. Goepi'ert, and George J. Easter, Niagara Falls, N. Y., asslgnors to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application YAugust 13, 1946, Serial No. 690,180
This invention relatesA to abrasive articles of manufacture and to methods of making the same.
More particularly, it relates to abrasive grinding wheels of the type which comprise a resinoid bonded abrasive annulus or rim bonded to the periphery of a nonabrasive supporting center.
The invention is especially adapted to the making of diamond abrasive cutting off wheels of the aforesaid described structural type which are relatively thin, the resinoid bonded diamond annulus and the non-abrasive supporting center of the wheel usually having an overall thickness Ino greater than nl, to 11; of an inch and often less. The invention will therefore be primarily described as it pertains tothe making of such -thin diamond cutting of! wheels, although it 1s i to be understood that it is similarly applicable to thev manufacture of abrasive Wheels of like construction embodying other abrasive materials such as silicon carbide, fused aluminum oxide,
4 Claims. (Cl. 51--206) boron carbide, and other hard granular sub.- l
stances of abrading or cutting abilit It has been common practice heretofore to make abrasive Wheels of the herein-described type with the non-abrasive center of molded Abrasive wheels with necessary to render them satisfactory for cutting off purposes vhave been subject yto frequent failure because of insuflicient strength of the molded center. Eiforts to meet thisdeiiciency in strength by the provision of layers of paper or organic cloth materials as reinforcement for the molded resinoid supporting centers have been but partially satisfactory. Although such centers have l shown some degree of increase in strength, they have had` a marked tendency to become warped or distorted during manufacture so that the resulting abrasive wheels have not run trueand have not only vprovided a wasteful cut but have been uneven often to the extent of absolute v failure. It is also essential in a satisfactory wheel that the non-abrasive center of the wheel closely approximate in thermal coefficient of expansion that of the bonded abrasive annulus or rim. Furthermore. the shrinkage of the supporting center during the curing of the wheel should match the shrinkage of the abrasive rim in order to provide a high strength of union of the two `and a resulting sound structure. Complete satisfaction in all the above respects has not been obtained by the abrasive wheel constructions provided by the prior art.
It is an object of the present invention to pro- Avide thin abrasive cutting olf wheels comprising 55 come warped or distorted. A still further object is the provision of an abrasive'wheel of the described type in which the thermal coefficient of expansion and the shrinkage characteristics of `the non-abrasive supporting center will be of the same order of magnitude as the thermal coefficient of expansion and shrinkage characteristics of the abrasive annulus. Other objects and advantages accruing from practice of the present invention will become apparent as the description proceeds.
In accordance with the present invention, we have found that an improved abrasive cutting-off wheel comprising an abrasive rim or annulus secured to a non-abrasive supporting center is obtained when the non-'abrasive supporting oenter of the wheel comprises a laminated structure in which one or more of the laminations of the supporting center is composed of glass fibers such as fiber glass cloth, the laminations of the supporting center being compacted and held together by impregnation with the `proper amount of a resinoid binder. Such wheels have been found to be not only of'increased strength but also, vby the control of the amount of resin in `respect to the glass fiber laminations, the shrinkage characteristics and also-the thermal coemoient of expansion can be controlled so as to approximate the same characteristics in the bonded abrasive annulus', thereby providing increased strength and durability to the resulting article. We have 'further found that abrasive Wheels of the dewarpage or distortion during manufacture and use by the inclusion of one or more laminations of wire screen in the laminated structure of the center. The ber glass cloth, due to its inorganic nature, is believed to serve the function of reducing the thermal expansion and shrinkage of theI laminated center to the point where it approaches the thermal expansion and shrinkage characteristics of the abrasive annulus. provided always that the amount of impregnating resin is maintained low enough not to offset this advantage. The presence of glass fibers in the supporting center serves the additional advantage of providing a structure having a low water and moisture vapor sensitivity, which feature is particularly valuable in cutting ci! wheels since many cutting of! operations are performed on machines dewarp threads of the remaining laminations of woven glass cloth.
In order that the invention may be better understood, reference is made to the' accompanying drawing which is presented for illustrative,
purposes, and in which y Figure 1 is a vertical sectional diagrammatic view of a molding set-up adapted for making abrasive wheels in accordance with the present invention, and showing the mold set-up as it is charged preparatory to compacting and forming the abrasive wheel structure;
Figure 2 is a plan view of an abrasive wheel made in accordance with the present invention;
Figure 3 is a vertical sectional view taken on the line 3-3 of'Figure 2. The thickness ci the wheel structure as shown in Figures 1 and 3 is shown in highly exaggerated form for the purpose of more clearly bringing out the actual construction of the article.
In the making of thin abrasive cutting off Wheels having a non-abrasive supporting center and a peripherally bonded abrasive rim structure oi the herein-described type, it is first necessary to obtain or prepare the individual resin-lled sheet material which is to go into the laminated center structure. These plies of sheet material nhas been found that charging of the glass bei cloth with a heat-hardenable resin amounting to from 4060% by weight of the glass cloth provides shrinkage characteristics and a thermal cog efficient of expansion of the material which are of the same order of magnitude as the shrinkage characteristics 'and thermal coefiicient of expansion or resoinoid bonded abrasive bodies of the type used in making abrasive wheels with which l the present linvention is concerned. The determination of the amount of resin to be used in any specific Wheel structure will be dependent upon the shrinkage and thermal expansion characteristics of the resin bonded abrasive annulus, and will be one comparable thereto in those properties. For example, a resinoid iilled laminate comprising several laminations of glass iiber cloth containing 47.3% by weight of phenol formaldehyde resin has a thermal coeilicient of expansion u from 26 C.-to 100 C. of l8.47 10/C. and a y curing shrinkage in inches per inch of .0024. These iigures compare favorably with a thermal coefncient of expansion between 26 C. and 100 C. of 18.22x10*/C. and a curingl shrinkage in g5 inches per inch of .0017 for a resin bonded abrasive body of the type used in Example I below. The thermal c oeflicients of expansion and curing shrinkage in inches per inch are given in Table I below for glass liber cloth lled with 30 diierent percentages by weight of a heat-hardenable phenol formaldehyde condenastion product. Also shown for purposes of comparison therewith is the thermal coefiicient of expansion and the shrinkage characteristics for an ordinary cotton cloth filled with 50% by weight of the same resin, showing the much greater expansion and shrinkage properties of such material.
Table I Per Cent by Th rmai cosin- Gunn T 0f Ba Weight "I aienta ci e ansion shrink g 8&0 Remarks ygb Immgmt 26 o. toxioo" o. inches/:nen
ing Resin 1 Woven glass ber 42. 0 14.39X10/ C... 0. 0018 Low thermal coeiiieient of E ansion and curing shrinkage. Satiscioth. factory for use with resin bon ed abrasive bodies. 2 Do 46. 6 17.94Xl0/ C..- 0. 0022 Do. 3 Do 54. 0 l9.60XI/ O--- 0. 0022 Do. 4 Ordinary cotton 60 30.27X10/ C... 0.0050 High thermal coeiileient oi Expansion and curing shrinkage. Unsatisiiber cloth. factory for use with resin bonded abrasive bodies.
are prepared by filling the layers of glass bers such as glass cloth with an uncured resinoid binder such as phenol formaldehyde condensation product resins as, for example, that known and sold by the Bakelite Corporation under the designation Bakelite No. BR2428.
The resin can be prepared for lling and applied in,the following manner: 30 parts by weight of powdered Bakelite resin No. BR2428 is dissolved in a solvent mixture consisting of 40 parts by weight of acetone and 20 parts by weight of ethyl alcohol. The resulting resin solution is then applied to the glass cloth by any of the well known ways such as dipping, spraying, brushing, or the like, angl the solvents removed by heating at 150 F. for 1/2 hour.
The preparation of the above sheet material requires a control of the resin to fiber weight ratio in order that the amount of resin will not be sumcient to increase the thermal Vcoefficient of expansion and the shrinkage characteristics of the resin-filled material to such an extent that they will be appreciably higher than those characteristics are for the particular bonded abrasivev annulus of the abrasive article in which the resin-loaded materials are to be embodied. It
- As previously stated we have found that abrasive wheels embodying a laminated center comprising one or more layers of glass fibers can be improved greatly in stability against warpage or distortion by the inclusion in the laminated 55 center of one or more plies of wire screen. A wire screen material which has been found satisfactory for that purpose is x 65 mesh size stainless steel wire screen, which is usually given a light sizing of a resin such as the resins used to 60 lill the glass fiber laminations prior to its incorporation in the laminated center. 40 x 40 mesh size tinned wire screen has also been used with satisfactory results.
After the preliminary preparation of the indi- 05 vidual resin-filled iam'inaticns of ber glass cloth as previously described, the abrasive wheels are made in the following manner. Referring to Figure 1, a, mold set-up comprising a disc-shaped base plate 4 is provided with a central arbor pin.
5 and an annular mold ring 6 which closely iits over the periphery of the base plate l. The annular mold ring 8 is held in the proper position by means of shims II placed at` suitable intervals beneath the mold ring. The resin lled sheets of glass cloth 1 and the layer or layers o! 5 resin sized wire screen l are cut or died out to the desired size and shape, assembled in the desired order, and placed over the arbor pin l' so as to rest on the base plate I. In the example shown in Figure 1, these laminations comprise two layers of resin impregnated glass cloth l porting center of the wheel and an outer annular,y
ring I ntting around the inner disc plunger I and having an outside diameter equal to the 4diameter of the wheel to be made. The outer annular ring I0 is usually slightly thicker, e. g., .001 to .002", than the inner top plunger 9 and the base plate 4 is depressed on equal amount about the periphery so that the abrasive bonded rim when compacted will be a few thousandths of an inch thicker than the supporting center structure. After the laminations for the center structure have been placed in the mold the top plunger disc 9 is placed over the arbor pin 5 on top of the laminations to hold them compressed together. The space between the thusly positioned laminations of the supporting center and the annular mold ring 6 is then filled with the desired abrasive mixture I4 of granular abrasive material and resinoid binder. The annular ring I0 of the top mold plunger is then placed in position and the entire assembly placed between top and bottom platens il4 and l2 of a hot press, the press being heated by steam passed through conduits I3 in the press platens. The mold contents are` subjected to heat and pressure to simultaneously compact and unite the individual layers of the laminated central structure, compact the annular abrasive rim, and securely bond lthe thusly compacted rim to the compressed support- 'ing center. The thusly molded abrasive wheel is given a further oven cure `to finally mature the resinoid binder.
While the abrasive wheels have been described above as being made by forming the laminated supporting center simultaneously with the molding and securing thereto of the bonded abrasive annulus, it is not essential that this exact procedure be followed. The laminated center can be preformed as a separate step with the abra- 0 sive rim subsequently molded and secured to the periphery of the preformed center without departing from the scope of the present invention.
In order that the present invention may be -further explained, the following specific examples are given:
Example I A diamond abrasive cutting off wheel 3" in diameter witha l/V' arbor and having a thickness of s1, of an inch was made as follows: Fiber glass cloth of the type designated as Fibreglas cloth ESS-12--261 having a thread count of 14 x 20 was secured from The Spaulding Fibre Co.
of Buffalo, N. Y., filled with an uncured resin of the phenol formaldehyde type, said resin being present to the extent of 47.3% by weight of the total weight of the resin nlled cloth. This resin filled fibre glass cloth was .033 inch thick. Bolting grade 65 x 65 mesh stainless mesh wire screen sold by the Buffalo Wire Company of Buffalo, N. Y., and lightly sized with a phenolic resin similar to that used for filling the glass cloth was used in the laminate. Two disc-shaped pieces of resin filled nbre glass cloth as described above and one disc-shaped piece of stainless steel wire for Example I except for the fact screen was omitted from V abrasive wheels of the types of center structures, such wheels are lim- Lwheels using molded resinoid cloth were cut with a y" arbor hole anda diameter of approximately 21/2". These discshaped pieces were assembled with the wire screendisposed between the two layers oi' resin filled glass cloth and placed in a mold such as shown in Figure 1 in the manner previously described. An abrasive mixture consisting of Parts by weight mesh size diamond bort 50 Liquid phenolic resin (sold by The Bakelite Corporation under the designation Bakelite No. XR7534) .Powdered phenolic aldehyde resin (sold by The Bakelite Corporation under the designation Bakelite N BR2428") 22 Powdered cryolite filler 25 Eample II A diamond labrasive cutting oil? wheel 3" in diameter with 1/2" arbor and al, thickness was made in accordance with the procedure set forth that the Wire the laminated supporting center.
While we have found that thin abrasive cutting oil wheels of small size comprising a resinoid bonded abrasive annulus or rim secured to a nonabrasive-center embodying one or more lamina'- Itions of glass fiber as the center support are imprioved in performance and durability over prior art employing other ited in respect to the size of wheel which can be made without warping orv distortion. For that reason most satisfactory results have been obtained bythe inclusion of one or more layers of wire screen in the central supporting structure in order to minimize or eliminate the warping tendency which becomes greater as the diameter size of the wheel increases. or the wire screen further improves the wheel by additionally strengthening it against breakage during use. The wire screen also aids in securing the abrasive annulus to the central support by reason of the projection of the ends of the wire strands of the layer or layers of screen a slight distance into the molded abrasive annulus.
The tremendous improvement in the perform'- y ance of abrasive wheelsv of the present invention wheels having a thickness of .032 inch as compared to the performance of similar abrasive centers or steel centers in the cutting oi'f oi l/g inch diameter rods of a very hard ceramic resistor material. The operation was conductedwet using water as the cool- F. for 30 minutes. The
The presence` 7 ant with a wheel operating speed of 12,000 ERM.
ter amounting to 40% to 60% by weight of the resin-tiled glass fabric of said center, said sup- Tablc Il had Wheel lgi Comparison ot Percentage oi Pieces Out Nm Thlok- Type oi Supporting Center Abrasive Annulus m No. oi Pieces out by Improved Wheelx100 ne i out o. oi Pieces Cut by Standard Wheel i Inch'r M 1aed Reim msm le senese 'ma a v i mm1 I Abrasive oem non No. 1. M00 100% (swam 2 .032 Staci- Reinlgdlin N Aiairasive Mix 6, 500 190%.
o on o. 3 .032 Laminations oi Fiber Glass Same as Wheel No. i 1o 75o 530%, 4 cs2 Leckifihnd WimrrberE non s when N z I m a ons o ame s c. oxen anewire semen. '30 775% Having described the invention in detail, it is ydesired to claim:
about 20x 10/ C. and a. curing shrinkage in the neighborhood of .002" per inch, said wheel being substantially fiat and free from distortion and having an overall thickness less than; of an inch.
2. An abrasive cutting of! wheel comprising an annular vresinoid-bonded diamond-containing rim secured to the outer periphery of a central supporting plate of resin-filled laminated ilbrous structure, the fibrous laminations thereof? comprising at least one layer of fibrous glass fabric and at least one layer of wire screen, the resin content of the nonabrasive center amounting to 40% to 60% by weight of the resin-filled glass fabric of said center, said supporting center having a. thermal coefilclent of expansion between normal room temperature and 100 C. from about 14 l0/ C. to about 20X10/ C. and a curing shrinkage in the neighborhood of i002" per inch, said wheel being substantially ilat and free from distortion and having an overall thickness less than 1*; of an inch.
3. An abrasive cutting oil wheel comprising an annular resinoid-bonded abrasive rim secured to' the outer periphery of a central supporting plate of resin-filled laminated fibrous structure, the fibrous laminations thereof comprising a layer of wire screen between two layers of ilbrous glass UNITED STATES PATEN'IB Number' Name Date 1,977,952 Ofienbacher -a Oct. 23, 1934 2,069,116 Sanford Jan. 26, 1937 2,138,882 Roble Dec. 6, 1939 FOREIGN PATENTS Number Country Date 522.040 Great Britain June 6, 1940 fabric, the resin content of the non-abrasive cenporting center having a thermal coemcient of expansion between normal room temperature and 100 C. from about `14 10"/ C. Ito about 20X10/ C. and a curing shrinkage in the neighborhood of .002 per inch, said wheel being substantially flat and free from distortion and livling an overall thickness less than 1*: of an 4. An abrasive cutting off wheel comprising an annular reslnoid-bonded diamond-containing rim secured to the outer periphery of a central supporting plate of resin-filled laminated fibrous structure. the ilbrous laminations thereof coinprising a layer of wire screen between two layers of fibrous glass fabric, the resin content o! the non-abrasive center amounting to 40% to 60% by weight of the resin-filled glass fabric of said center, said supporting center having a thermal coeillcient of expansion between normal room temperature and C. from about l4Xl0/ C. to about -2f0 10/ C. and a curing shrinkage inthe neighborhood of .002" per inch, said wheel being substantially flat and free from distortion and having an overall thickness less than of an inch.
. KERNELL G. RIES.
GEORGE J. GOEPFERT. GEORGE J. EASTER.
REFERENCES CITED The following referenices are of record in the me of this patent: