US2084513A - Abrasive article - Google Patents

Description

June 22, 1937. F. J. TONE ABRASIVE ARTICLE Original Filed Feb. 7, 1928 lNVENTOR Patented June fi, 1937 ABRASIVE ARTICLE Frank J. Tone, Niagara Falls, N. Y assignor, by mesne assignments, to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Continuation of application Serial No. 252,468,

February 7, 1928. This application September Y 26, 1930, Serial No. 484,545.

Renewed October 8 Claims. (01. 51-207) The present invention relates to abrasive devices, and particularly to wheels, and pertains especially to abrasive wheels of such large size that they cannot be conveniently or economically molded and burned as an integral wheel, but is not limited to such particular application. The

invention constitutes a continuation of my ap-' rliizcation Serial No. 252,468, filed February 7,

10 More particularly 'the invention is especially applicable to the manufacture of pulp grinding wheels in connection with which it will be specifically described, but it is to be understood that I toform a pulp wheel as an integral mass from an abrasive mix, due to the fact that the bond employed is generally a ceramic bond which :must be fired to a high temperature to mature. It is extremely diificult to iire such a large mass 5 and to secure the necessary heat penetration;

moreover, such a mass in the green state cannot be conveniently handled without likelihood of damage, and in firing it is apt to slough away or warp. If other bonds are used in the abrasive 30 mix, it is difii'acult to secure uniform curing throughout the entire mass.

Consequently, where artificial abrasives have been employed, the wheel has been formed of segments which are burned individually and as- 35 sembled into the completed wheel. The general practice heretofore has been to provide a' metal drum or cylinder to which the abrasive segments 4 are secured and which forms a necessary part of the wheel assembly. Due to the fact, however, 40 that metal cylinders and the abrasive segments have widelydiiierent coefiicients of thermal expansion, stresses are produced in such a wheel necessitating the use of some compensating arrangement to prevent breakage of the wheel over 45 the temperature range to which the wheels are subjected to use. Ordinarily this temperature range is between -40 F. and 212 F. In such a wheel the metal drum is a'very expensive part of the assembly. It costs several hundred dol- 50 lars, at least, and considerably more if it is made of a material that will resist corrosion for periods up to seven years, which is the length of time manufactured abrasive wheels last in pulp grinding operations. 1

55 The abrasive manufacturer assembles the segments on the metal drum, and the assembly is shipped to the user. The user operates the wheel until most of the abrasive has been worn ofi, when he returns the drum to the abrasive manufacturer to have the abrasive segments replaced. The metal drum, of course, adds materially to the shipping weight of the wheel as well as to the initial cost, and the freight cost of returning such a large metal cylinder to the abrasive manufacturer is a further item of expense in the use of such wheels.- In addition to this, the user of the wheels must have one or more spare wheels in stock at all times, so that operation of the mill will not be shut down during the time that a metal drum is in the hands of the abrasive manupreformed segments or members of abrasive material which are cemented together by a cement, the tensile strength of which is great enough to hold the segments togetheragainst the centrifugal and other forces incident to the operation of grinding, whereby the use of a metal supporting drum is rendered unnecessary. The elimination of the metal drum in the wheel assem bly efiects a saving of from eight hundred to eighteen hundred dollars in the initial cost of' a large pulp wheel, and a pulp wheel embodying the present invention will furnish the abrasive user with about one and one-half times as much abrasive for the same cost as a pulp wheel having abrasive segments on a metal drum; moreover, due to the elimination of themetal drum, the handling of the wheels is much easier.

The elimination of the metal supporting drum, however, introduces several serious problems into the successful use. of the wheel, all of which are eliminated in the present invention. These wheels are shipped into territories and are used in places where the temperature not infrequently gets as low as 40 F. In the operation of grinding pulp, the wheels are exposed to the action of water at about the boiling point. The wheel must be constructed so as to eliminate stresses or strains suflicient to produce any rup-' ture thereof over this temperature range.

The material used for joining the segments must not only have a tensile strength great enough to hold the segments together against the centrifugal and other forces incident to the operation of grinding, but it also should have I a modulus .of elasticity such as to cause the joint to compress or to stretch readily when the abraimpose any undue strain on the wheel. According to the present invention, there is provided an abrasive wheel in which this relation of the joint material to the bonded abrasive material exists.

The invention may be described in connection with the accompanying drawing in which Figure l is an elevation of a composite abrasive wheel embodying my invention;

Figure 2 is a section along the plane of line II-II of Figure 1;

Figure 3 is a plan view of the abrasive wheel;

Figure 4 is a vertical section showing the composite abrasive wheel with its mounting; and

Figure 5 is a plan view of the composite abrasive wheel containing a plurality of rings which are composed of different materials, the said rings having difierent abrasive properties and different physical properties in other respects.

The abrasive wheel shown in Figures 1 to 4 is made up of a number of segments 2 arranged in circumferentially extending rows 3, d and 5.

The segments-or blocks 2 are united by joints I designated 6,1, 8 and 9. The end faces of the outer row of segments 3 and 5 are cut away to leave the projections it which are engaged by the end clamping plates M, by means of which the wheel is mounted on a shaft R2. The wheel,

as made by the abrasive wheel maker, is shown in Figures 1, 2 and 3, and the purchaser or user of the wheel mounts it as shown in Figure 4. It will be observed that the manner of mounting does not require the use of any internal cylinder or other internal support, the two end plates providing the only means for supporting thewheel on the shaft. According to the preferred construction of the wheel, the segments in one row are staggered or offset with respect to the segments-in the adjacent rows whereby the joints do not extend continuously transversely across the wheel. r 7

The segments 2 are made of bonded abrasive grains. The bonding material used for bonding the grains maybe of any suitable kind, as for instance ceramic bonds, rubber, resins or the like. In the case of ceramic bonded segments, the

' blocks are molded and then fired in a kiln, after thermal expansion; A material that has a relatively high modulus -of elasticity should have, in

I have found that synthetic resins possessing these properties are highly satisfactory for this purpose. Such'synthetic resins should have incorporated therein some inert filling material, and the character of the joint can be varied by varying the percent of inert filling material with respect to the amount of synthetic resin used.

As an example, one composition suitable for the purpose is as follows:

Composition:

Percent by weight Fused quartz 200 mesh and/or finer (inert filler) 70 A stage phenolic resin Water 20 This material possesses the following properties:

Coefiicient of thermal expansion 3 l0- /C. Modulus of elasticity 0.9 10 #/sq. in.

Another example of a synthetic resin is as follows:

Composition: 4

Percent by weight Inert filler fused quartz 200 mesh and/or finer 8i Glycerol-phthalic anhydrite resin 16 A third example comprises: Percent by weight Inert filler 240 mesh and/or finer '86 A stage phenolic resin 14 This mixture has the following physical properties:

Coemcient of expansion--- 9Xl0- /C. Modulus of elasticity 2.7 10 #/sq. in.

Still another example of suitable material comprises: Percent by weight Fused quartz 200'mesh and/or finer 68.3

Water 12.2

This material has the following physical characteristics:

Modulus of elasticity l.8 l0 #/sq. in.

Coefici'ent of thermal expansion 'l.6 10-/C.-

Theoretically, in the above mixes, it would be desirable to have the moduli of elasticity reversed in order; however, a modulus of elasticity of 2.7' 10 is low enough for a cement having a coefiicient' of expansion of 9x10- and consequently it is immaterial that those cements with lower coefficients of expansion have lower moduli of elasticity.

I have also found that the characteristics of hard rubber can be modified to adapt it to the cementing of abrasive segments in a wheel of this nature, or for the cementing of abrasive articles having different coeflicients of thermal expansion and elasticity. A typical example is:

Parts by weight Rubber 10.6 Sulphur. 2.5

, Silicon carbide at a fineness or approxiinately 500 mesh 90c When this mixis cured to the extent required {by the percentage of sulphur given above, it is satisfactory a joint materizd for or using a different abrasive material.

grade wheel having a specific type of bond and a specific type of abrasive,'but it would not necessarily be applicable to a wheel of a different grade of abrasive, or having a different bond This composition, when cured, has'the following properties:

Tensile strength 2,000 lbs. per sq. in. Coeflicient of thermal expansion 20x 10- /C. Modulus of elasticity 1.5 10 /sq. in.

In order to provide cement suitable for other materials, it is only necessary to vary the composition as given above, in accordance with the following general trends until the desired properties are obtained.

The inert filler, being of relatively low coeflicient of thermal expansion with respect'to the rubber sulphur compound, serves to reduce the coeflicient of thermal expansion of the joint mav terial in proportion to the amount present. Consequently, by increasing the amount of inert filler from the percentage given above, the coefllcient of thermal expansion of the joint material is lowered while the modulus of elasticity is slightly increased. Generally stated, the modulus of elascarbide, as the inert filler. For instance, alumina v or quartz, as noted above in the synthetic resin cements, can be employed.

The inert filler preferably has a coefiicient of thermal expansion not substantially greater than that of fused quartz, which is about .5 10' per degree centigrade.

The following specific methods of joining mem bers to make a unitary structure are given where rubber is employed by way of illustration and are not intended to limit the invention to the specific materials or manipulative details disclosed, nor are they intended to limit the process to the specific steps or sequence of steps.

The abrasive surfaces that are to be joined are first primed with the rubber compound softened with a volatile softener, such as benzol. The ratio of benzol to, rubber compound may be varied as required, but it has been found that two parts of benzol and one part of the rubber compound form a priming material that may be applied easily by brushing and leaves a satisfactory coating of rubber compound on the abrasive surface after the solvent has evaporated.- If a thicker coating of rubber compound thanthat produced by one application, either by brushing or by spraying, is desired, additional coats of the solvent-softener compound maybe applied. Sufllcient time should elapse between coatings to permit the solvent to evaporate completely before a subsequent coat is applied.

' The blocks or rings of-bonded abrasive material are then positioned'with a sheet of the joint material, of the desired thickness and of the area of the block or ring, between them. Pressure is applied to force thejointmaterial into intimate contactwith the surfaces it lies between, and heat is applied tocure the joint material.

Figure illustrates a two-part abrasive wheel in which the two parts l3 and I! have different grinding characteristics. For example, the ring l3 may be intended for rapid cutting, this-ring hold together coarse grain consisting of fused alumina. The ring l4 may be made of finer grains of silicon carbide bonded with rubber or phenol condensation product resin. The coefiicient of expansion of a rubber bond is in general greater than that of a highly siliceous bond. The two rings are cured separately according to the methods suitable for the two types of bond respectively. The two rings are then united by means of a cement whose coeflicient of expansion and resiliency are such that the abrasive materials in the respective rings will not suffer undue stress under the extreme temperature and speed conditions to which they are subjected.

The composite wheel structure provided by the present invention comprises, generally stated, a

plurality of segments which are set in and held together by a web or skeleton of cementitious material which holds the blocks together against the centrifugal and other stresses incident to operation, and the thermal expansion of which and modulus of elasticity of which are adjusted in accordance with the abrasive employed whereby the structure is free of any strains over the temperature range to which it is subjected under normal conditions.

The invention, therefore, provides a practical way in which a substantially solid body of abrasive material can be employed without metal supporting drums. Pulp wheels made in accordance with the present invention have been satisfactorily employed over extended periods of time. The initial cost of such wheels has been proven much less than the cost of wheels employing metal reinforcing drums. The joint material is resistant to the action of hot water, so that the rate of disintegration of the joints is not excessive in proportion to the rate of disintegration of the abrasive blocks themselves.

The cements above described being somewhat elastic, apparently allow a certain amount of yield in the structure, whereby the blocks can adjust themselves under the strains set up upon operation of the wheel; moreover, joints of the materials disclosed herein have a tensile strength at least 200#/sq. inch after continuous immersion in boiling water for periods of four weeks or more.

While T have described my invention with particular reference to pulp wheels, it will be understood that the invention is not so limited but may be used in the manufacture of other composite abrasive articles.

r claim:

1. An abrasive wheel, comprising a plurality of preformed shapes of bonded abrasive material and having cementitious joints between the abrasive shapes composed of a phenolic condensation resin binder together with at least 70% by weight of the total of fused quartz ground 200 mesh and finer, said cementitious joint material being characterized by a coemcient of thermal expansion approximately that of the bonded abrasive and a modulus of elasticity in the order of about 1 x10 to 3 x 10 pounds per square inch, and forming joints with the abrasive shapes having a tensile strength of at least 200 pounds per square inch aftercontlnuous immersion in boiling water for four-weeks.

2. An abrasive wheel, comprising a plurality of preformed shapes of bonded abrasive material and having cementitious joints between the abrasive shapes composed of a synthetic resin binder together with at least 70% by weight of a finely divided inert filler having a relatively low coefficient of thermal expansion, said cementitious joint material being characterized by a low modulus of elasticity with respect to that of the bonded. abrasive.

3. An abrasive wheel, comprising a plurality of preformed shapes of bonded abrasive material and having cementitious joints between the abrasive shapes composed of a synthetic resin binder and a finely divided inert filler, said cementitious joint material being characterized by a coefiicient of thermal expansion of the same order as that of the bonded abrasive and a modulus of elasticity lower than that of the bonded abrasive, and forming joints with the abrasive shapes having a tensile strength of at least 200 pounds per square inch after continuous immersion in boiling water for four weeks.

4. An abrasive wheel, comprising a plurality of preformed shapes of bonded abrasive material and having cementitious joints between the abrasive shapes composed of a hard rubber binder together with a finely divided inert filler having a thermal expansion lower than that of the hard rubber.

5. An abrasive wheel, comprising a plurality of preformed shapes of bonded abrasive material and having cementitious joints between the a'brasive shapes composed of a hard rubber binder together with a finely divided inert filler having a thermal expansion lower than that of the hard rubber, the rubber and filler being so proportioned, that the cementitious joint material has a coefiicient of thermal expansion approximating that of the bonded abrasive and a modulus of elasticity lower than that of the bonded abrasive,

aoeatra and forming joints with the a rasive shapes having a tensile strength of at least 200 pounds per square inch after continuous immersion in boiling water for four weeks. I

6. An abrasive wheel comprising a plurality of preformed shapes of bonded abrasive material and, having cementitious joints between the abrasive shapes composed of a synthetic resin binder Y together with a finely divided inert filler havin a coefficient of thermal expansion not substantially greater than that of fused quartz, the binder and filler being so proportioned that the cementitious-joint material has a coefiicient of expansion approximating that of the bonded abrasive and a modulus of elasticity lower than that of the bonded abrasive.

'7. An abrasive wheel comprising a plurality of preformed shapes of bonded abrasive material and having cementitious joints between the abrasive shapes composed of a phenolic condensation resin binder together with at least about 68% by weight of the total oi finely divided fused quartz.

8. An abrasive wheel comprising a plurality of preformed shapes of bonded abrasive material and having cementitious joints between'the abrasive shapes composed of a synthetic resin binder together with an inert filler having a coeficient of thermal expansion not substantially greater than that of fused quartz, the binder and filler being so proportioned that the cementitious joint material has a coeficient of expansion approximating that of the bonded abrasive and a modulus of elasticity lower than that of the bonded abrasive.

FRANK J. TONE.

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