US3481723A - Abrasive grinding wheel - Google Patents

Description

Dec. 2, 1969 s. s. KISTLER ET AL 3,481,723

ABRASIVE GRINDING WHEEL Filed March 2, 1965 @E PES. FEEL- 11m n.

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United States Patent O 3,481,723 ABRASIVE GRINDING WHEEL Samuel S. Kistler, Salt Lake City, Utah, and Charles V. Rue, Tifin, Ohio, assignors, by mesne assignments, to International Telephone and Telegraph Corporation, New York, N.Y., a corporation of Delaware Filed Mar. 2, 1965, Ser. No. 436,543 Int. Cl. C08h 17/12 U.S. Cl. 51-298 9 Claims ABSTRACT F THE DISCLOSURE An abrasive grinding wheel comprising an abrasive matrix containing from about 40% to about 64% by volume of a plurality of dense, hard abrasive grains bonded in a bonding matrix of which the predominant proportion of the abrasive grains have a preshaped cylindrical configuration and a cross section of a controlled cross sectional area ranging from 500 to about 20,000 square mils and wherein the ratio of the peripheral length squared to the cross sectional area is within the range of from 13:1 to about 100:1.

The present invention broadly pertains to abrasive articles, and more particularly to improved grinding wheels of a type employed for snagging steel, incorporating therein abrasive grains of a preshaped cylindrical configuration.

Heavy-duty grinding wheels of the type to which the present invention is applicable are in widespread commercial use, such as for snagging steel billets. Conventionally, snagging-type grinding wheels comprise an abrasive mass which consists of a suitable bonding agent in which a plurality of abrasive grains are tenaciously bonded. Snagging wheels may additionally include suitable reinforcing elements for strengthening the wheel, as well as various filler materials serving as extenders and also as modifying agents, to achieve optimum grinding characteristics. It has been conventional in the past to derive the abrasive grains for use in such snagging wheels from naturally occurring minerals or ores, such as natural corundum or emery, by crushing and screening the material to provide granules of the appropriate mesh size. Alternatively, abrasive grains have 4been derived from a crushing or grinding of fused bricks or pigs derived from an electric furnace such as fused alumina or silicon carbide pigs which subsequently are screened, providing a wide range in nominal sizes of abrasive grains.

It will =be apparent from the techniques heretofore known that no effective means is provided for controlling the specific configurations of the resultant abrasive grains, other than resorting to variations in the techniques employed for crushing the crude products into relatively finesized particles. To this end, various attempts have been made to effect modifications in the particle configuration by alternatively adopting crushing rolls, crushing hammers, jaw or gyrocrushers, or by introducing a mulling or ball milling of the splintery particles derived from the crushing operation to effect a reshaping thereof. In essence, then, the techniques for making abrasive grains have been relatively dormant over an extended period of time, with the developments being restricted primarily to variations in crushing and mulling techniques to provide modifications in grain configuration. The techniques heretofore known have all been subject to the inherent disadvantage of producing a relatively high quantity of unusable fines, substantially detracting from the economy in the manufacture of abrasive grains. In addition, the resultant abrasive grains produced are characterized as being of a generally uncontrolled configuration and nonuniform in shape, as well as incorporating residual in- Mice ternal stresses and incipient cracks or fissures therein, resulting in a substantial reduction in their physical properties.

It is accordingly a principal object of the present invention to provide improved abrasive grinding wheels incorporating an abrasive matrix containing a controlled proportion of abrasive particles, at least the predominant portion of which are of a preshaped cylindrical configuration of controlled size and configuratio-n, which overcomes the problems and disadvantages associated with grinding wheels of' similar type heretofore known.

Another object of the present invention is to provide an improved abrasive grinding `wheel incorporating preshaped cylindrical abrasive grains that provides for a significant improvement in the efficiency of grinding expressed in terms of speed of metal removal, as well as the amount of metal removed per pound of abrasive material consumed.

Still another object of the present invention is to provide abrasive grinding wheels incorporating therein abrasive grains of a preshaped cylindrical configuration which enables the adaptation of Specific abrasive compositions to an increased variety of grinding operations, substantially enhancing the flexibility and versatility of the abrasive material.

A further object of the present invention is to provide an improved abrasive grinding wheel which, through careful and controlled modifications in the shape and size of the preshaped cylindrical abrasive grains and the composition thereof, provides for optimum grinding efiiciency for any one specific grinding operation, providing substantial improvements in the economy and simplicity of metal removal.

Yet still a further object of the present invention is to provide an improved grinding wheel which, through careful control of the size and configuration of the preshaped cylindrical abrasive grains, permits controlled changes in the cutting speed of the grinding wheel, enabling the attainment of optimum economy of any one specific abrasive finishing operation.

Yet still another object of the present invention is to provide an improved abrasive grinding wheel and method of making the grinding wheel and abrasive grains thereof, providing for simplification and increased economy and versatility over the techniques and grinding wheels heretofore known.

The foregoing and other objects and advantages of the present invention are achieved by forming an abrasive grinding wheel from about 40% up to about 64%, by volume, of a plurality of dense, hard abrasive grains tenaciously bonded by a suitable bonding agent. The predominant portion of the abrasive grains in the abrasive matrix are of a preshaped cylindrical shape having a controlled geometrical configuration and having a cross-sectional area preferably of from about 500 to about 20,000 square mils. The cross-sectional configuration of the abrasive grains is controlled so as to provide a ratio of the square of the peripheral length of the cross section to the area of the cross section within a range from about 13:1 up to about :1. The length of each of the abrasive grains exceeds the maximum width of its cross section, and preferably does not exceed a length greater than about 5 times its width, with a length-to-width ratio of about 3 :1 being preferred in most instances.

The foregoing and other objects and advantages of the present invention will become apparent upon a reading of the following description and the examples provided, taken in conjunction with the drawings, wherein:

FIGURE 1 is a perspective view of a typical abrasive grinding wheel to which the present invention is applicable;

FIGS. 2-16 are perspective views of a variety of typical abrasive-grain configurations which can be satisfactorily employed in accordance with the practice of the present invention; and

FIG. 17 is a graphical portrayal of the effect of variations in the perimeter squared to area ratio of the crosssectional configuration of abrasive grains on the rate of metal removal and on the efficiency of the grinding operation.

Referring now in detail to the drawings, a typical grinding wheel is illustrated in FIG. 1 consisting of a cylindrically shaped body 20 containing a plurality of the preshaped cylindrical abrasive grains tenaciously bonded by a suitable bonding agent. The wheel is suitably supported for rotation by means of a pair of clamping plates 22 which are secured to a drive shaft 24 for rotatably supporting and driving the grinding `wheel in a manner well known in the art.

The advantages achieved in accordance with the discovery of the present invention are obtained regardless of the specific type of bonding agent or matrix employed for forming the abrasive matrix. In accordance with the practice of the present invention, the lbond may be of the vitrified, resinoid, shellac, rubber, silicate, magnesium, oxychloride type or metallic type. Conventionally, the bonding agent employed in manufacturing heavy-duty grinding wheels such as snagging wheels consists of suitable thermosetting resins including urea formaldehyde and phenol-aldehyde, of which the condensation product of phenol and formaldehyde is the most common and preferred material. The bonding agent and abrasive grains are conventionally employed in proportions such that the resultant abrasive matrix comprises from about 40% up to about 64% by volume of the abrasive grains, with the 4balance thereof consisting of the bonding agent, reinforcing elements, filler materials, pores and plasticizers, and the like. Filler materials suitable for inclusion in the abrasive matrix include powdered cryolite, metallic sulphides, and other filler materials of the types well known in the art which are either inert or which improve the cutting efficiency of the resultant abrasive grinding wheel. When thermosetting-type bonding materials are employed, modifications can `be achieved by adding small quantities of other resinous materials such as epoxy resins, vinyl resins, and the like, as well as cross-linking aids such as hexamethylene tetramine, or paraformaldehyde, as well as suitable plasticizers including furfuraldehyde and propylene sulfite. The particular composition of the bonding agent, as well as the inclusion or omission of various filler materials of the types well known in the art, is not critical in order to obtain the benefits of the present invention.

cordance with the typical embodiments illustrated in FIGS. 2-16. In order to achieve the benefits of the present invention, it has been discovered that the cross-sectional configuration must be controlled within a particular range, in order to provide the desired grinding characteristics of the resultant abrasive grinding wheel. As will be noted in FIGS. 2-16, each of the abrasive grains is of a preshaped cylindrical shape wherein the term cylindrical as herein employed is defined as a volume encompassed within an enclosed surface generated by the movement of a straight line parallel to a fixed straight line. Accordingly, the preshaped abrasive grains are all of a generally prismatic configuration, wherein the length thereof as measured along the longitudinal axis of the abrasive grain is greater than the maximum width of the abrasive grain as measured across a cross section of the grain taken in a plane perpendicular to the longitudinal axis thereof. It has been found that, to provide cutting rates and grinding efficiency within a range applicable to most grinding operations, it is important that the crosssectional area of the abrasive grains be controlled within a range from about 500 square mils up to about 20,000 square mils. It is also important that the particular configuration of the cross section of the abrasive grains is controlled so as to provide a ratio of perimeter squared to the area of the cross section taken in a plane perpendicular to the longitudinal axis of the grain greater than about 13:1 up to about 100:1.

The foregoing perimeter squared-to-area ratio relationship, which has been found important in order to achieve the benefits of the present invention, can be readily computed for any particular abrasive grain crosssectional configuration. This relationship has been discovered as indicative of the cutting speed of the abrasive, other variables being constant, such that (as the ratio increases) the cutting speed of the grinding wheel also increases. Conversely, as this ratio decreases, approaching a ratio of 13:1 as a lower limit, the cutting speed of a grinding wheel decreases in terms of weight of metal removed per unit time. While the reason for this relationship between perimeter squared to area and cutting speed is not completely understood at this time, it is Abelieved that at least a portion thereof is attributable to the increased length of the cutting edges made available for contact with the work being ground, resulting in a more rapid cutting action, lwhile concurrently evidencing a reduction in the physical strength of the abrasive grain and an increase in its wear characteristics. Accordingly, for any one specific grinding operation, it is now possible, in accordance with the practice of the present invention, to substantially enhance the abrasive characteristics of any particular composition while concurrently con trolling the speed of the cutting action of the abrasive matrix, to provide optimum efficiency and economy for a specific job. By virtue of the foregoing, a tailoring of grinding wheels to specific jobs is now feasible which heretofore was believed impossible or impractical with abrasive materials of the types heretofore known.

Typical examples of preshaped cylindrical abrasive grains, within the definition as hereinabove set forth, are illustrated in FIGS. 2-16. An abrasive grain 216 is illustrated in FIG. 2 which is of a right-triangular configuration. Similarly, an abrasive grain 28 is illustrated in FIG. 3 which also is of a right-triangular configuration, but wherein the hypotenuse thereof is concave, lfurther increasing the ratio of perimeter squared to area, as may be desired. An elliptical cross-sectional shaped abrasive grain 30 is illustrated in FIG. 4, while a generally rectangular abrasive grain 32 having rounded side edges is illustrated in FIG. 5. An abrasive `grain 34 is illustrated in FIG. 6 which is of a general dumbbell cross-sectional configuration, while an abrasive grain 36 is shown in FIGURE 7 which has a thin rectangular cross-sectional shape. Alternative forms of suitable abrasive grains typical of those satisfactory for use in accordance with the practice of the present invention include the L-shaped abrasive grain 38 shown in FIG. 8, the kidney-shaped abrasive grain 40 shown in FIG. 9, the abrasive grain 42 having a cross-sectional configuration in the form of a cross shown in FIG. 10, an abrasive grain 44 of a generally rectangular cross-sectional configuration formed with a V-shaped surface along one side thereof illustrated in FIG. ll, and FIG. 12 is illustrative of an abrasive grain having a plurality of longitudinally extending edges as defined 'by a cross-sectional configuration in the form of an X. A generally rectangular-shaped abrasive grain 48 is shown in FIG. 13 wherein one side thereof is of a convex configuration and the opposite side thereof is of a concave configuration. A cross-sectional shape generally of a keyhole configuration is illustrated by an abrasive grain S0 illustrated in FIG. 14, while a U-shaped and H-shaped cross-sectional configuration is illustrated by the abrasive grains 52 and 54 as illustrated in FIGS. 15 and 16, respectively.

It will be understood that the various cross-sectional configurations as typified by the abrasive grains illustrated in FIGS. 2-16 are intended to be illustrative of the various congurations feasible, and are in no way to be construed as limiting of other suitable shapes which can be satisfactorily employed, provided that the crosssectional configuration is one providing a perimeter squared to cross-sectional area ratio Within a range of from about 13:1 up to about 100:1. For example, the abrasive grain 32, as illustrated in FIG. 5, which is of a generally rectangular configuration having roundedside edges, can be made having a total Width of 0.120 and a thickness of 0.020" providing a cross-sectional area of 2,314 square mils. The specific cross-sectional shape has a perimeter of 263 mils providing a perimeter squared per area ratio of 29.9. Similarly, the L-shaped abrasive grain 38 illustrated in FIG. 8, when shaped so as to provide a cross section such that the long side edge of the L is 0.080" long and with a thickness of each leg of 0.040, provides a cross section of 4,800 square mils. The perimeter squared to area relationship of this L- shaped configuration is about 21.3.

It will be noted that, in accordance with the definition of the cross-sectional configuration of the preshaped cylindrical abrasive grains employed in accordance lwith'the practice of the present invention, it is not necessary that the ends of the abrasive grains be cut in a plane perpendicular to the longitudinal axis of the grains. Accordingly, the end edges of the abrasive grains may be cut on a bias, or may be chamfered as desired, without materially affecting the grinding characteristics thereof in comparison to grains the ends of which are precut in a plane perpendicular to the longitudinal axis.

It Will be further noted, from the typical configurations illustrated in FIGS. 2-16, that the abrasive grains are of substantially uniform cross section throughout their length. For the purposes of the present invention, it has been found that the length of the abrasive grain should exceed the maximum width of its cross section as measured along a plane perpendicular to the longitudinal axis of the grain, and may range upwards therefrom to any convenient length. Conventionally, abrasive grains having a length-to-Width ratio of greater than 1 up to about 5:1 are preferred, while ratios of about 3:1 have been found particularly effective in providing an efficient abrasive. Lengths substantially above about 5 times the maximum Width of the a-brasive grains result in difiiculty in some instances in a packing of the abrasive grains to form an abrasive matrix incorporating the requisite quantity of abrasive material. Nevertheless, in some instances unique grindin-g action is achieved when the abrasive grains are of a length substantially in excess of a lengthto-width ratio of about 5:1.

As an illustration of the effect of the length-to-diameter ratio on the grinding characteristics of an abrasive grinding wheel incorporating the preshaped cylindrical grains in accordance with the practice of the present invention, a test was conducted in which all variables were kept constant, with the exception of the length-to-diameter ratio. Grains of the same geometrical cross-sectional coniiguration and area were employed having a maximum diameter of .090 and were all of about 1/2 length, providing a length-to-diameter ratio of about 5.6. A second abrasive grinding test Wheel was made employing the same abrasive grains which were only 1A" long, providing therewith a length-to-diameter ratio of about 2.8. The test results obtained on the two grinding wheels employed for snagging stainless steel billets are set forth in Table( l.

The wheel wear W, as will be noted in Table 1 and as expressed in terms of cubic inches per hour, was almost twice as high for the shorter abrasive grains as for the longer grains. The shorter grains, however, effected a higher rate of steel removal S, expressed in terms of pounds of steel removed per hour, providing a ratio of steel removed to wheel wear S/ W of 2.27 for the short grains in comparison to 3.31 for the longer grains. In terms of grinding efiiciency, the longer grains provided an efiiciency of 268 in comparison to 222 for the shorter grains. The foregoing test data illustrate the effect of the length-to-width ratio on the grinding characteristics of abrasive grinding wheels and can be varied in combination with the composition, size and configuration within the limits hereinbefore set forth to achieve optimum performance for a specific grinding situation.

The formation of the abrasive grains can be achieved by any one of a variety of techniques, including extrusion, pelletizing, casting, 'California-type pellet milling, molding, etc., of which the extrusion technique constitutes the preferred method. In addition, the composition of the abrasive grains can be varied, consistent with the specific material to be ground, to provide the desired abrasive characteristics and abrasive finishing action to achieve optimum ef'liciency. To further illustrate the various abrasive compositions which can be employed in accordance with the practice of the present invention, the following examples are provided. It will be understood that the compositions as disclosed in the following examples are provided for illustrative purposes and are not intended to be limiting of the scope of the invention as herein disclosed and as defined in the subjoined claims.

EXAMPLE 1 Composition: Percent by wt. A1203 EXAMPLE 2 Composition: Percent by wt.

TiOz 5 The alumina and titanium dioxide constituents are milled and extruded in the Same manner as described in Example l, and the resultant green abrasive pellets are fired to a pyrometric cone #30, forming dense hard abrasive pellets.

EXAMPLE 3 Composition: Percent by wt. A1203 96 M1102 2 TiO3 2 The alumina, manganese dioxide and titanium dioxide constituents are milled to a particle size of less than about 2 microns and are subsequently mixed with an organic binding agent and extruded in accordance wtih the procedure as set forth in Example l. The resultant green abrasive grains are thereafter fired to a pyrometric cone #121/2, forming dense, hard, abrasive grains of a controlled cylindrical configuration.

The constituents are milled, extruded and fired under the same conditions as set forth in Example 3, forming dense, hard, abrasive grains of a preshaped cylindrical configuration halving a controlled cross-sectional shape and a controlled length.

EXAMPLE Composition: Percent by wt. A1203 49 ZrSiO., 47 Mn02 2 TiO2 2 The several constituents comprising the abrasive mixture are prepared, employing the same procedure as set forth in Example 3, with the exception that the green extruded abrasive pellets formed are fired to a pyrometric cone #14.

EXAMPLE 6 Composition: Percent by wt. ZrSiO4 93 Bentonite 3 MnOz 2 Ti02 2 The several constituents are milled and extruded in accordance with the same procedure as set forth in Example 3, except that the resultant green abrasive pellets are fired to a pyrometric cone 16.

EXAMPLE 7 Composition: Percent by wt. SiC 90 Silicon 10 The silicon carbide and silicon constituents are milled to a particle size preferably less than about 5 microns and are thereafter extruded and subsequently fired to a pyrometric cone in a nitrogen atmosphere, forming dense, hard, abrasive pellets comprising about 87% silicon carbide and 13% silicon nitride which are of the requisite size and configuration.

EXAMPLE 8 Composition: Percent by Wt. A1203 60 SiC Bentonite 10 The constituents are milled and extruded in accordance with the procedure as set forth in Example 7, except that the resultant green abrasive pellets are fired to a pyrometric cone #15 in either a neutral or a reducing atmosphere.

It will be apparent from the foregoing examples that the specific composition of the abrasive grains may include any of those well known in the art, and in each case substantial improvements are obtained in their abrasive finishing characteristics over grains of the same composition of an irregular, uncontrolled, slivery configuration derived from a crushing of either the crude product or fused CTI bricks or pigs. The specific composition of the abrasive grain employed, as Well as the specific cross-sectional configuration and length of the abrasive grain, and the cross sectional area thereof, are controlled consistent with the intended end use to which the abrasive grinding wheel is to be employed. The tailoring of a grinding wheel to a specific grinding `operation for any specic abrasive composition is facilitated by the general relationship, as graphically portrayed in FIG. 17. As shown in FIG. 17, the rate of metal removal S increases as the perimeter squared to area ratio of the grain increases. This relationship is indicated by the upper curve in the graph illustrated in FIG. 17, which is based on the grinding of a type 302 stainless steel billet. Corresponding relationships can be derived for alternative metals at the same or different grinding wheel surface speeds. The efficiency of the grinding wheel, as indicated by the lower curve of the graph, also increases, but at a lesser rate as the ratio of perimeter squared to cross-sectional area increases.

The foregoing discovery, in -accordance with the practice of the present invention, enables the appropriate selection of the abrasive grain conguration for any specific grinding operation, to achieve optimum efficiency and economy. As a generalization, grinding wheels incorporating abrasive grains having a ratio of their perimeter squared to cross-sectional area less than 14:1 can be classified as slow-cutting grains which provide for a relatively low wheel Wear rate and a moderate rate of metal removal in a grinding operation. Abrasive grains within the aforementioned classification accordingly are best adapted in those situations Iwherein rate of metal removal per unit time is not critical in comparison to providing a wheel of a substantially greater useful operating life. On the other hand, abrasive grains having a perimeter squared per crosssectional area ratio ranging from about 14:1 up to about 20:1 are classified as being of an intermediate cutting rate, providing thereby a relatively rapid rate of metal removal which is accompanied by an increasing greater wear rate of the grinding wheel. Abrasive grains having a ratio of perimeter squared per cross-sectional area ratio of greater than 10:1 and up to `about 100:1 are classified as fast-cutting abrasive grains, providing the most rapid rate of metal removal, which is accompanied also by a high rate of wheel wear.

As will be noted, the efficiency of the abrasive grains of the intermediate and fast-cutting classification increases slightly from a perimeter squared to cross-sectional area ratio 14:1 to the upper ratio of 100:1. Accordingly, the importance andeconomics of rate of metal removal for a given grinding operation can be optimized by forming an abrasive grinding wheel wherein the individual `abrasive grains, or at least the predominant portion of abrasive grains employed, are of a controlled cross-sectional c011- fguration providing a perimeter squared to cross-sectional area ratio consistent with the cutting speed desired.

While it will be apparent that the preferred embodiments of the invention disclosed are Iwell calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. An abrasive grinding wheel comprising an abrasive mass containing from about 40% to about v64% by volume of a plurality of dense, hard, abrasive grains tenaciously bonded in 4a bonding matrix; said abrasive grains consisting essentially of an abrasive material selected from the group consisting of aluminum oxide, zirconium oxide, zirconium silicate, silicon carbide, titanium oxide, manganese oxide, bentonite, silicon and mixtures thereof; the predominant portion of said grains having -a preshaped cylindrical shape with a cross section of a controlled geometrical configuration and an area of from about 500 to about 20,000 square mils, said grains having a length greater than the maximum width of said cross section, said configuration of said cross section controlled to provide a ratio of peripheral length square to cross-sectional area of from 20:1 to about 100:1.

2. The abrasive grinding wheel as defined in claim 1, wherein said grains consist essentially f about 100% alumina.

3. The abrasive grinding wheel as dened in claim 1, wherein said grains consist essentially of :about 95% alumina and about titanium dioxide.

4. The abrasive grinding wheel as defined in claim 1, wherein said grains consist essentially of about 96% alumina, :about 2% manganese dioxide, and about 2% titanium dioxide.

5. The abrasive grinding wheel as dened in claim 1, wherein said grains consist essentially of about 91% alumina, about 5% zirconium dioxide, about 2% manganese dioxide, and about 2% titanium dioxide.

6. The abrasive grinding wheel as dened in claim 1, wherein said grains consist essentially of about 49% alumina, about 47% zirconium silicate, about 2% manganese dioxide, and about 2% titanium dioxide.

7. The abrasive grinding wheel as delned in claim 1, wherein said grains consist essentially of about 93% zirconium silicate, about 3% bentonite, about 2% manganese dioxide, and about 2% titanium dioxide.

8. The abrasive grinding -wheel as dened in claim 1, wherein said grains consist essentially of about 87% silicon carbide and about 13% silicon nitride,

9. The abrasive grinding wheel as defined in claim 1, wherein said grains consist essentially of about 60% alumina, about silicon carbide, and about 10% bentonite.

References Cited UNITED STATES PATENTS 90,824 `6/ 1869 Dickinson.

2,347,537 4/1944 Benner et al.

2,947,124 8/ 1960 Madigan el; al.

2,978,850 4/1961 GleSZeI'.

3,079,243 2/1963 Ueltz 51-298 3,183,071 5/1965 Rue et al 51-298 2,877,103 3/1959 Lane 51-298 3,387,957 6/1968 Howard 51--298 DONALD I. ARNOLD, Primary Examiner U.S. Cl. X.R.

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