US2467596A - Manufacture of abrasive wheels - Google Patents

Description

April 19, 1949. w. R'. PRATT 2,467,596

MANUFACTURE OF ABRASIVE WHEELS Filed Nov. 8, 1946 M! iapnflfipary INVENTOR.

Patented Apr. 19, 1949 MANUFACTURE OF ABRASIVE WHEELS Willard R. Pratt, Lcs Angeles, Calif., assigllor to Bevil Company, San Francisco, Calil'., a copartnership Application November 8, 1946, Serial No. 708,613

6 Claims. 1

This invention has to do with improved methods for the manufacture of abrasive wheels of the general form embodying a metallic center or core carrying an abrasive rim. Particularly the invention is concerned with considerations having to do with the bonding of the rim to the core, and where the rim may be composed of preformer individual segments, with the inter bonding of those segments to form an integrated rim annulus.

At the outset it may be observed that the invention deals with abrasive wheels having sintered rims, by which I mean rim compositions formed for example of pulverulent metal containing uniformly distributed diamond particles, integrated by heating to a temperature of incipient fusion or sintering of metallic particles, and at which the composition at all times remains essentially solid, though perhaps slightly plastic at the maximum temperature to which it is subjected.

Considering first the problem of. bond formation between the core and the heated essentially solid rim, my primary concern is to create a fusion formed bond while exteriorly confining the rim and expanding the core into tight or even penetrating engagement with the rim. Difficulties have arisen however because of the fact that upon expansion of the core, the rim material is bodily displaced or expanded against the confining medium or mold with such force as not infrequently to rupture the mold.

The invention afiords a solution of the dimculty by permitting an expansion range for both the core and rim within an initial and considerable expansion range, and final confinement against further expansion of the rim at a point insuch relation to the temperature rise that the core to rim bond formation will occur while the rim is strongly pressed between the core and mold, but without the latter being subjected to breaking pressure. The considerations thus taken into account for the bonding of sintered rims to their cores has given rise to advantages and facilities unattainable by any of the various practices heretofore used or proposed for abrasive wheel manufacture.

In accordance with the invention, the core and rim are placed in a mold, the material of which is specially regarded as to its co-eflicient of expansion relative to the expansion properties of the core. Preferably I use a graphite mold, because of the low coefficient of expansion of graphite, of sufficient, but not necessarily of excessive wall thickness, to withstand the highest pressure to be transmitted by the rim. The rim 2 material is placed in the mold about the core in such relation that the rim material occupies less than the radial distance between the mold wall and core. Thus clearance space initially may exist beyond either or both the inner and outer edges of the rim.

Thereafter, as the assembly is heated, the resultant expansion of the core, or core and rim, is accommodated throughout an initial range in taking up, so to speak, the clearance space or spaces. In the course of the expansion, the solid rim is radially displaced or compressed, ultimately to a point of pressing strongly against the circular mold wall because of the pressure transmitting qualities of the sintered rim material. However, since such pressure exertion against the mold occurs only toward the end of the expansion range, such pressure will not assume a rupturing magnitude.

Since dimensional relationships are of significance, it may be preferred to first sinter the rim material before placing it in the mold for bonding to the core, with the advantage that having been compacted and presintered, the rim will have reached more accurately predeterminable and stable physical and dimensional characteristics.

It is contemplated that the rim may-be composed of preformed segments to be placed in annular arrangement about the core. The aforementioned advantages obtain in this instance, with the further effects of the core expansion to displace or crowd the segments toward their interengagement, and resultant tight pressure of one against the other as where the segments are themselves to be bonded together. Other features and objects of the invention are directed to the maintenance or placement in the 1 interfaces between either or both the core and rim, and between rim segments, of a relatively low melting temperature metal which is subjected to compression by the expansion forces of the core and rim, and which melts to form an alloy bond between the interface surfaces.

More complete understanding of the invention will be had from the following detailed description throughout which reference is had'to the accompanying drawing, in which:

Fig. l is a sectional view showing the core and abrasive rim within a typical form of mold assembly;

Fig. 2 is a cross-section on line 22 of Fig. 1; and

Fig. 3 is a view similar to Fig. 2 illustrating a variational procedure contemplated by the invention.

It is contemplated that theabrasive rim initially and before bondage to the core, may be formed as a complete annulus, or as segments to be placed in the mold in annular arrangement about the core. Fig. 2 shows the rim II to consist of a preformed annular compact, composed typically of finely divided nickel (passing a 325 mesh screen) containing a uniform distribution of small diamond particles. The compact ini-' tially will have been formed under high pressure to assume a self-sustaining shape, and desirably may have been heated to sintering temperature, resulting in a preformed annulus having, by reason of itssintered condition, the advantages of more accurate predetermination of its dimension and other physical characteristics.

. 4 terial, the latter having at its sintering temperature sufilcient plasticity to permit its penetra tion by the core. but without having the free mobility of a fiuid.

For purposes of the bond formation between the core and rim. provision is made for making available at the cote-rim interface a metal The rim II is placed in amold assembly ii about a care if, typically in the form of a circular steel disc whose thickness is less than the rim thickness. The mold assembly comprises a pair of identical mating sections I! and II, the latter of which has a cylindrical bore ll receiving the corresponding size lower portionila of the section above. The rim II is received within opposed annular recesses ll within the end faces of the mold sections, while the core if is flatly engaged between the mold surfaces ll surrounded by the recesses. One mold section may carry an axial projection ll receivable through opening II in the disc within bore of the companionsection, to accurately center the core with relation to mold wall surface ll.

As previously explained, the rim II is pre-I formed'to occupy, when first placed in the mold. a space less than the radial distance between therim of the core Iland the mold wall Ii. Thus as shown in Fig. 2, the rim may have clearances at either or both fl and 22, respectively between the rim and core, and between the rim and mold wall. The amount of clearancein anygiven instance will depend upon such considerations as the diameter of the wheel and the expansion characteristics of the core, or the diiferential expansion, upon heating, of the core, and mold.

Using a graphite mold, having relatively low coefiicient of expansion, thetendencyupon heat ing the assembly will be for the steel core to expand and ultimately close such clearance spaces as will initially have existed at either or both the inside and outside of the rim. p

With the rim and core placed in the mold in the condition illustrated by Figs. 1 and 2, the,

mold assembly is placed in a furnace and heated to a temperature which will not exceed the sintering temperature of the rim composition, andwill therefore permit the rim to at all times remain an initially solid mass. Pressure may or may not be applied to the rimand disc during the heating.. Pressure, if desired, may be applied in any suitable mannenas by means of plunger fl bear-' ing against the "upper mold section. As the heating and temperature rise progress, the core I ll expands, together with some expansion of the rim II, to completely close the clearance spaces at II and If, this condition preferably. being reached as the maximum temperature is approached, so that subsequent expansion will bring the core into. tightly pressed engagement with the rim, and the'rim into tightlypressed engagement with the mold surface II, but withas into alloy solution. Of course the effectiveness whose melting temperature is low with relation to the melting point of the rim matrix metal. in this case typically nickel, so that at the rim aintering temperature, the interface metal will melt and form a bonding alloy solution with the core and rim metals. Bestlresults are obtained using the low melting temperature metal in a very thin form, as for-example by electroplating on the rim surface of the core, or by applying to either the rim or core surfaces at the interface a thin coating of the metal, or by insertion of a thin foil of the metal between the interface surfaces. Excellent bonds have been obtained by inserting within .the interface space a foil of copper, or copper-containing alloy, the thickness of the foil being not in excessof about 0.002 inch. Upon heating, the foil melts and goes lntoalloy solution with-the interface metals at a relatively low temperature, within the range of from 150031'Lto 2000 I".. thus enabling the bond to be formed at such low temperatures and without having to reach the relatively high temperatures required for alloy formation at the interface in the absence of the low melting temperature metal. Upon examination of the resulting bond, the copper or copper alloy. will be hand to have virtually disappeared by having gone of the bond formation is further increased by the fact that the core expansion will have kept the foil under tight compression between the core and remain as the copper melts and alloys with so the interface metals.

out the exertion of such excessive pressure as will rupture the mold. Preferably the parts will be so dimensionally related that at the highest temperature and point of maximum-expansion, the

Fig. 3 illustrates the adaptation of the invention for bonding to the rim a preformed segmental rim. Here therim fl is shown to be composed of segments I0 preformed as self-m taining compacts, which as in the case of the first described rim l0, may initially have been sintered. The egm nts are placed inthe mold about the core 11 with clearances'at 20 or II, or both, respectively at the inside andoutside of the segments. The arcuate dimensions of the latter may be such that the and surfaces at 30 of adiacent segments may initially be inclose proxq imity or ultimately brought into pressed interengagement upon expansion of the core and by virtue of the degree of mobility which the compacts have at sintering temperature.

As before, relatively low temperature melting metal, e. g. coper foil, is inserted within the interface at 20, and where bonds are to be formed between the segments. themselves, thevpfoil may rim between the core and the mold wall, are

essentially the same as in the am described instance.

I claim:

core will have slightlypenetrated the l m ma i 1. The method of makin abrasive wheels that includes, placing a metallic core within-and in annularly spaced relation to the wall of a mold, placing between said core and wall a relatively high melting temperature rim compact composed of abrasive particles and matrix metal and occupying less than the radial distance between said core and wall, heating the mold. core and rim to a temperature below the melting temperature of the compact and at which the compact remains an essentially solid mass to resist expansion of the core, producing b said heating radial expansion of the core into tight engagement with the solid rim and resultant strongly pressed engagement oi the rim against said mold wall, and simultaneously forming a fused bond between said core and rim in the presence of a relatively low melting temperature metal between said core and rim.

2. The method of making abrasive wheels that includes, placing a metallic core within and in annularly spaced relation to the wall of a mold, placing between said core and wall a relatively high melting temperature rim compact composed of abrasive particles and matrix metal and comprising a plurality of individual segments occupying less than the radial distance between said core and wall, heating the mold, core and rim to a temperature below the melting temperature of the compact and at which the. compact remains an essentially solid mass to resist expansion of the core, producing by said heating radial expansion of the core into tight engagement with the solid rim and resultant strongly pressed engagement of the rim against said mold wall, and

simultaneously bonding said segments together and to said core in the presence of a relatively low melting temperature metal tightly pressed by -said core expansion between the segments and core and which forms an alloy with the core.

3. The method of making abrasive wheels that includes, placing a metallic core within and in annuiarly spaced relation to the wall of a mold, placing between said core and wall a rim compact composed of abrasive particles and matrix metal and occupying less than the radial distance between said core and wall, maintaining between the core and rim a relatively low melting temperature metal, heating the mold, core and rim to a temperature below the melting temperature of the compact and at which the compact remains an essentially solid mass to resist expansion of the core, producing by said heating radial expansion of the core to tightly press said low melting temperature metal between the core and rim and to strongly press the rim against said mold wall, and simultaneously melting said low melting temperature metal to form at the interface between said core and rim a bond composed of alloy of said low melting temperature metal and the core and rim metals.

4. Th method of making abrasive wheels that includes, placing a metallic core within and in annulary spaced relation to the wall of a mold, placing between said core and walla rim compact composed of abrasive particles and matrix metal and occupying less than the radial distance between said core and wall, maintaining between the core and rim a foil-like layer of relatively low melting temperature metal, heating the mold, core and rim to a temperature below the melting temperature of the compact and at which the compact remains an essentially solid mass to resist expansion of the core, producing by .said

9 heating radial expansion of thecore to tightly press said low melting temperature metal between the core and rim and to strongly press the rim against said mold wall, and simultaneously melting said low melting temperature metal to form at the interface between said core and rim a bond composed of alloy or said low melting teml erature metal and the core and rim metals.

5. The method oi making abrasive wheels that includes, placing a metallic core within and in annularly spaced relation to the wall of a mold, placing between said core and wall a rim compact composed of abrasive particles and matrix metaLand comprising a plurality of individual segments occupying less than the radial distance between said core and wall, maintaining between said segments and between the segments and rim a relatively low melting temperature metal, heating the mold, core and rim to a temperature below the melting temperatureof the compact and at which the compact remains anessentially solid mass to resist expansion of the core, producing radial expansion of the core to tightly press said low melting temperature metal between the core and rim and to strongly press the rim against said mold wall, and simultaneously melting said low melting temperature metal to form at the interfaces between the segments and between the core and segments bonds composed of alloy of said low melting temperature metal and the core and rim metals.

6. The method of making abrasive wheels that includes placing a metallic core within and in annularly spaced relation to the wall of a mold, placing between said core and walla rim compact composed of abrasive particles and matrix metal and comprising a plurality of individual S m O pying less than the radial distance between said core and wall, placing between the segments and between the segments and rim relatively low melting temperature metal foil, heating the mold, core and rim to a temperature belowthe melting temperature of the compact and at which the compact remains an essentially solid mass to resist expansion of the core, producing by said heating radial expansion of the core to tightly press said low melting temperature metal between the core and rim and to strongly press the rim against said mold wall, and simultaneously melting said foil to form at the interfaces between the segments and between the core and segments bonds composed of alloy, of said low melting temperature metal and the core and rim metals. WILLARD R. PRATT.

REFERENCES CITED The following references are of record in the iiie of this patent:

UNITED STATES PATENTS F. T. Van Syckel, The Welding Journal, August, 1941, pages 527 and 529.

Tool Tipping Data," The Welding Journal, an 1943, page 61, Engineering Data Sheet No.

Images