Method for producing an improved vitreous bonded abrasive article and the article produced thereby

A method is provided that produces grinding wheels which exhibit improved burn reduction or prevention, lower power consumption and increased penetration of metalworking fluid into the grinding zone in high metal removal rate grinding operations such as for example creep feed grinding. The method comprises the steps of preparing a blend, cold pressing the blend in a mold to the desired shape, size and density to form a cold molded article, removing the cold molded article from the mold and firing the cold molded article to produce the vitreous bonded abrasive article wherein the blend comprises aluminum oxide abrasive grains, non-metallic, inorganic, thermally conductive, solid particles having higher thermal conductivity than the abrasive grains and a particle size at least twice that of the abrasive grains, a vitreous matrix precursor which forms a vitreous matrix having a bond with the thermally conductive, solid particles that is weaker than the bond with the abrasive grains and an organic, open cell producing, solid pore inducer that produces spring back of the cold molded article (i.e. green molding) that is at least equal to the smallest particle size of the article size range of the pore inducer.

FIELD OF INVENTION 
This invention relates to a method for producing vitreous bonded abrasive 
articles. More particularly this invention relates to a method for 
producing vitreous bonded abrasive articles, still more particularly 
grinding wheels, containing thermally conductive solid particles for 
improved grinding performance. 
BACKGROUND OF THE INVENTION 
Grinding operations on structural materials (e.g. metallic and ceramic 
workpieces) typically involves contacting the structural material 
workpiece with an abrasive article (e.g. grinding wheel) to remove 
material from and shape the workpiece. Such grinding operations generally 
involve the input of large amounts of energy (i.e. grinding energy) into 
the removal of material from the workpiece and often employ high rotating 
speeds for the abrasive article (e.g. grinding wheel) and/or the 
workpiece. In some grinding operations it is known to rotate both the 
grinding wheel and the workpiece. Where high material removal rates, 
workpieces that are especially tough or hard, high grinding wheel speeds 
and deep cuts are employed the amount of energy applied to the grinding 
operation can be and often is very high. This energy in large measure 
translates into heat that is mostly applied to the workpiece and grinding 
wheel. The heat often has a detrimental effect on both the grinding wheel 
and the workpiece. Excessive heat generated during grinding can and often 
does result in burning of metallic workpieces (ie the formation of a 
yellow brownish or dark brown to black discoloration on the ground surface 
of the workpiece). Burning of the metallic workpiece results in a scrapped 
part. Often the effects of excessive heat generated during grinding can be 
distortion of the workpiece, out of tolerance parts, changes in the 
surface appearance and properties of the ground part (e.g. surface 
hardening effects), excessive break down of the grinding wheel, loss of 
grinding performance and efficiency, loss of productivity and increase 
costs. 
Creep feed, snagging and cut off grinding operations are high heat 
generating processes because of the desire for high metal removal rates 
(i.e. cubic inches of metal removed per unit of time). In snagging and cut 
off grinding operations the burning of the metal part due to the high 
generation of heat is not critical because the metal part is in a rough 
condition after the snagging and cut off operations and is subject to 
subsequent shaping and finishing steps. The creep feed grinding operation 
also generates large amounts of heat because of the desire for high metal 
removal rates in the shaping of the metallic workpiece. However burning of 
the metallic piece (i.e. the formation of a yellow brown, brownish or 
brownish black discoloration on the surface) during creep feed grinding 
operations is a very undesirable condition resulting in the scrapping of 
the workpiece or article. Additionally, excessive heat generated in a 
creep feed grinding operation can cause distortion of the part, alteration 
of the surface appearance and surface properties of the part (e.g. change 
the surface hardness of the part) and cause the production of an out of 
tolerance part. Typically in the creep feed grinding operation the 
metallic workpiece, article or part is fed into a rotating grinding wheel 
which remains in one location. The rate at which the workpiece is fed into 
the grinding wheel and the depth of cut are established to maximize the 
metal removal rate consistent with the desires to produce quality parts, 
reduce scrap, achieve high grinding efficiency and lower grinding 
operation costs. Thus the higher the metal removal rate, the greater the 
G-ratio (i.e. amount of metal removed per unit of grinding wheel lost) 
without burning the part the greater the efficiency and productivity and 
the lower the cost of the creep feed grinding operations. Creep feed 
grinding is used for example in the production of gears. In the production 
of gears, formed grinding wheels (i.e. wheels having a particular shape) 
are often used in the creep feed grinding process. It is therefore 
important that such shaped wheels retain their shape for as long as 
possible consistent with the other desirable conditions of the creep feed 
grinding operation (e.g. high metal removal rate, high G-ratio, low heat 
production and non-burning of workpiece). Although the burning of metallic 
workpieces and excessive heat generation are of major concern in creep 
feed grinding operations they are also important concerns in other 
grinding operations for shaping metallic workpieces to produce useful 
articles. Such other grinding operations include, for example, surface, 
internal, plunge and roll grinding operations. Thus it is important and 
highly desirable to have grinding wheels which produce or contribute to 
low heat generation during grinding and reduce or eliminate part burn or 
the risk of part burn while providing high grinding efficiencies and 
performance, long wheel life and high productivity to reduce grinding 
operation costs. 
It is known to employ metalworking fluids (e.g. water based or oils) in 
grinding operations to improve grinding performance and efficiency. These 
fluids are, in many cases, known to reduce friction and remove heat during 
the grinding operation. Reduction of friction by the fluids can reduce the 
heat generated during grinding. The ability of these fluids to reduce 
friction (i.e. friction between the workpiece and the grinding wheel 
and/or components thereof) and remove heat during grinding can depend upon 
such factors as the composition of the fluid and the ability of the fluid 
to penetrate into the grinding zone or interface (i.e. the area of contact 
between the grinding wheel and the workpiece during grinding). Many 
metalworking fluids are known to be effective in many grinding operations 
and have been found to be of value in mild (i.e. low heat generating) 
grinding operations to improve grinding efficiency or performance. However 
in severe (i.e. high heat producing) grinding operations (e.g. creep feed 
grinding) they are often found to be of limited, if any, effectiveness in 
reducing or preventing part burn when high metal removal rates are sought. 
In such severe grinding operations it has been found that the metalworking 
fluids often exhibit poor penetration into the grinding interface, i.e., 
the region within which material removal occurs, to reduce friction and 
remove heat. 
In the art it is known that different grinding operations (e.g. surface vs 
internal vs roll vs plunge vs snagging vs cut off vs creep feed grinding) 
involve different conditions. Such operations therefore often employ for 
example different forces, speeds, temperatures, infeed rates, metal 
removal rates and workpiece materials. Some grinding operations (e.g. 
finish grinding or surface grinding) may employ mild physical conditions 
involving low forces, low feed rates and low metal removal rates etc. 
Other grinding operations (e.g. creep feed, plunge and cut off grinding) 
may employ severe physical conditions involving high forces, high feed 
rates and high metal removal rates etc. Thus it is known to produce 
grinding wheels tailored to particular grinding operations and/or 
workpiece materials. Such wheels may differ in composition (i.e. amount 
and kind of abrasive grit, bonding material binding together the abrasive 
grit and additives) and/or structure depending upon their end use. The 
wheel structure may vary in the amount and type of porosity it contains. 
The porosity of a grinding wheel, particularly a vitreous bonded grinding 
wheel, can be of an open and/or closed cell structure. In the open cell 
porosity the cells or pores are interconnected much like the pores of a 
sponge or open celled foam. In the closed cell porosity the cells or pores 
are not interconnected and remain as separated totally enclosed voids much 
like closed cell foam. Closed cell, rather than open cell, porosity is 
generally found in resin bonded grinding wheels. The pore structure of a 
vitreous bonded grinding wheel can serve a number of functions including, 
for example, controlling the physical strength of the wheel, controlling 
the breakdown of the wheel to present fresh cutting edges, the elimination 
of swarf and providing means for getting metalworking fluid to the 
grinding zone. In a vitreous bonded grinding wheel having an open pore 
structure it is known to have an essentially random distribution of pore 
or cell sizes (i.e. some pores being large and other pores being small) 
and in some cases a random distribution of pores. Thus vitreous bonded 
grinding wheels can have a heterogeneous open pore structure with respect 
to pore size and in some cases pore distribution. Pore sizes larger than 
the abrasive grain average size may be found. Grinding wheels, 
particularly resin bonded grinding wheels, are known in the art to include 
thermally conducting particles (e.g. metal particles) to act as heat sinks 
and improve the dissipation of heat from the grinding wheel. In the case 
of resin bonded grinding wheels the dissipation of heat from the wheel by 
such thermally conducting particles serves to protect the poor thermally 
conducting resin bond from thermally induced breakdown and thus helps 
protect (i.e. preserve) the strength of the wheel during grinding. 
In the grinding process and in particular a grinding operation under severe 
physical conditions, as are encountered in creep feed grinding operations, 
using an open cell porosity vitreous bonded grinding wheel, the open pore 
structure of the wheel can serve as a significant avenue or means by which 
metalworking fluid can penetrate into the grinding zone or interface and 
by which metalworking fluid can be captured by the wheel during grinding 
to reduce friction and remove heat generated during grinding. Such 
reduction in friction and dissipation of heat are significant factors in 
reducing or preventing grinding burn of the metallic workpiece, increasing 
performance and efficiency and lowering the power or energy needed for the 
grinding operation. These improvements in turn can lead to higher metal 
removal rates, increased productivity and lower grinding operation costs 
Vitreous bonded grinding wheels in the prior art are known to be less than 
desirable in preventing or reducing grinding burn of metallic workpieces 
under severe physical grinding (e.g. high metal removal rate) conditions 
even when the grinding operation is carried out in the presence of a 
metalworking fluid. Thus grinding burn obtained with prior art vitreous 
bonded grinding wheels under severe physical conditions is known in the 
art. In many cases, in the art, grinding burn is overcome by reducing the 
severity of the physical grinding conditions (e.g. reducing metal removal 
rate and/or infeed rate and/or wheel speed etc.) leading to a loss of 
productivity and increased grinding costs. Additionally the excessive heat 
generated during grinding under severe physical conditions with prior art 
vitreous bonded grinding wheels is often known to lead to scrapped metal 
parts because of out of tolerance conditions and/or adverse changes in 
surface appearance and/or properties (e.g. reduction or increase in 
surface hardness) of the parts. Improvements in vitreous bonded grinding 
wheels, particularly for use under severe physical grinding conditions, 
which reduce or prevent grinding burn of metallic workpieces, reduce power 
or energy consumption during grinding, improve grinding performance and 
efficiency and increase grinding productivity therefore are needed and 
desirable. This invention seeks to overcome these and other problems of 
prior art vitreous bonded grinding wheels, particularly those vitreous 
bonded grinding wheels used under severe physical conditions in a grinding 
operation and provide vitreous bonded grinding wheels with improved 
grinding performance, and improved penetration of metalworking fluids into 
the grinding zone for reducing or preventing grinding burn of metal 
workpieces and in reducing the energy or power used in the grinding 
operation. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a method for producing a 
vitreous bonded abrasive article, particularly a grinding wheel, that 
exhibits reduced or no grinding burn on metal workpieces, during grinding 
at high metal removal rates. 
Another object of this invention is to provide a method for producing a 
vitreous bonded abrasive article, particularly a grinding wheel, which 
uses lower energy or power during the grinding of metal workpieces at high 
metal removal rate. 
A further object of this invention is to provide a method for producing a 
vitreous bonded abrasive article, particularly a grinding wheel, 
permitting improved penetration of a metal working fluid into the grinding 
zone or interface. 
It is a still further object of this invention to provide a method for 
producing a vitreous bonded abrasive article, particularly a grinding 
wheel, that improves the removal of grinding heat generated during the 
grinding of a metal workpiece at high metal removal rates. 
These and other objects, as will become apparent to one skilled in the art 
from the following description and accompanying claims, are achieved by a 
method for producing an improved vitreous bonded abrasive article, more 
especially a vitreous bonded grinding wheel, comprising the steps of 
preparing a blend, cold pressing the blend in a mold to the desired shape, 
size and density to form a cold molded article, removing the cold molded 
article from the mold and firing the cold molded article to produce the 
vitreous bonded abrasive article wherein the blend comprises: a) aluminum 
oxide abrasive grains, b) non-metallic, inorganic, thermally conductive, 
solid particles having a thermal conductivity greater than the thermal 
conductivity of the abrasive grains and an average particle size at least 
twice the average particle size of the abrasive grains, c) a vitreous 
matrix precursor which forms a vitreous matrix that binds together the 
abrasive grains and forms a bond with the thermally conductive solid 
particles that is weaker than the bond the matrix forms with the abrasive 
grains and d) an organic, open cell producing, solid pore inducer that, 
subsequent to the pressing step, produces spring back of the cold molded 
article in an amount at least equal to the smallest particle size of the 
particle size range of the pore inducer. 
The grinding wheel produced by the method of this invention exhibits 
improved penetration of metalworking fluid into the grinding zone for 
greater removal of the heat generated during grinding to thereby reduce or 
eliminate grinding burn of metal workpieces, especially during high metal 
removal rate grinding operations such as for example creep feed grinding. 
This improved penetration of metalworking fluid into the grinding zone 
aids in maximizing friction reduction between the metal workpiece and the 
grinding wheel and components thereof. The thermally conductive solid 
particles of the grinding wheel produced by the method according to this 
invention can act as heat sinks to further assist in removing heat from 
the grinding zone to reduce or prevent grinding burn of the metal 
workpiece.

DESCRIPTION OF THE INVENTION 
There has been found in accordance with this invention a method for 
producing an improved vitreous bonded grinding wheel that overcomes many 
of the problems occurring with prior art grinding wheels during grinding 
operations on metal workpieces, particularly where such grinding 
operations are carried out at high metal removal rates. Such high metal 
removal rates while varying with the nature of the metal workpiece are 
especially known in the grinding art in grinding operations commonly 
called creep feed and plunge grinding. In creep feed and plunge grinding 
the grinding operation is carried out under conditions (e.g. feed rates, 
depth of cuts and wheel speed) to maximize the amount of metal removed 
from the metal workpiece during a single grinding contact between the 
wheel and the metal workpiece (i.e. a single grinding pass). During the 
grinding of metal workpieces or parts, particularly at high metal removal 
rates, it is known in the art that excessive heat can be generated, even 
with the use of metalworking fluids, that produces a discoloration of the 
ground metal surface, and sometimes the surrounding area, commonly known 
as burn. This discoloration is quite visible upon inspection of the ground 
part and is often a yellow brown to brown to brownish black color which 
renders the part as scrap. Further the burn can indicate detrimental 
changes in the physical properties of the surface of the part in the 
region of the burn (e.g. detrimental changes in hardness) and may also 
indicate changes in the composition of the metal in the region of the 
burn. In addition to burn it is known in the art to require high power or 
energy consumption during grinding at high metal removal rates with 
vitreous bonded grinding wheels. Such high power or energy consumption 
often impacts the efficiency and cost of the grinding operation. These and 
other problems were attacked and solutions sought in arriving at the 
invention disclosed and claimed herein. 
Vitreous bonded abrasive articles, e.g. grinding wheels, are made from 
blends that contain ingredients to produce voids, i.e. pores, in the fired 
or vitrified article. These pores are of an open cell or closed cell 
structure. The vitreous bonded abrasive article may have only open cell 
pores or only closed cell pores or a mixture of open cell and closed cell 
pores. Open cell pores are generally produced by the decomposition of an 
organic constituent of the blend whereas closed cell pores are generally 
produced by the addition of non-decomposing bubble-like particles to the 
blend. In the production of vitreous bonded abrasive articles, e.g. 
grinding wheels, the components of the vitreous bonded abrasive article 
formulation are combined into a uniform mixture or blend, that mixture or 
blend placed in a suitable mold at room temperature, the blend in the mold 
compressed at room temperature to a desired density, nominal dimensions 
and shape, the self sustaining cold molded article (i.e. green molding) 
removed from the mold and dried and the dried green molding then fired 
under appropriate conditions to produce the vitrified abrasive article or 
grinding wheel. The blends, for producing vitreous bonded abrasive 
articles, which contain organic, open cell producing pore inducers provide 
green moldings which may or may not exhibit spring back upon removing the 
green molding (ie cold molded article) from the mold immediately after 
pressing. Spring back is the growth (i.e. increase) in thickness of the 
cold molded article or green molding (e.g. green wheel) over a short 
period of time after the pressure from pressing is released and the cold 
molded article or green molding is immediately removed from the mold. This 
growth decreases with time and eventually essentially reaches zero. Thus, 
for example, the blend in the mold may be pressed to form a cold molded 
article having a nominal thickness of 1 inch. Upon releasing the pressure 
and removing the green molding from the mold the green molding may have a 
measured thickness let us say of 1.001 inches and at, for example, 5 
minutes after being removed from the mold may have a thickness of 1.005 
inches. This increase in thickness is a phenomenon called spring back. 
Generally spring back is an undesirable occurrence because it indicates 
that the green molding has a thickness greater than that desired for 
firing the molding or article. There has however been unexpectedly 
discovered a method, that produces an improved vitreous bonded abrasive 
article, employing a step of preparing a blend wherein the blend contains 
organic, open cell producing, solid pore inducers that produce green 
moldings exhibiting spring back, particularly spring back in an amount at 
least equal to the smallest particle size of the particle size range of 
the organic pore inducer, to produce improved vitreous bonded abrasive 
articles, e.g. grinding wheels, that during a metal abrading, e.g. 
grinding, operation a) prevent or reduce metal burn at high metal removal 
rates and high infeed rates, b) exhibit lower power consumption and c) 
exhibit increased penetration of grinding (ie metal working) fluid into 
the interface between a grinding wheel and the workpiece (i.e. grinding 
zone). 
In one aspect of this invention there is provided a method for producing an 
improved vitreous bonded abrasive article, more especially a vitreous 
bonded grinding wheel, comprising the steps of preparing a blend, cold 
pressing the blend in a mold to the desired shape, size and density to 
form a cold molded article, removing the cold molded article from the mold 
and firing the cold molded article to produce the vitreous bonded abrasive 
article wherein the blend comprises: a) aluminum oxide abrasive grains, b) 
non-metallic, inorganic, thermally conductive, solid particles having a 
thermal conductivity greater than the thermal conductivity of the abrasive 
grains and an average particle size at least twice the average particle 
size of the abrasive grains, c) a vitreous matrix precursor which forms a 
matrix that binds together the abrasive grains and forms a bond with the 
thermally conductive, solid particles that is weaker than the bond the 
matrix forms with the abrasive grains and d) an organic, open cell 
producing, solid pore inducer that, subsequent to the pressing step, 
produces spring back of the cold molded article in an amount at least 
equal to the smallest particle size of the particle size range of the pore 
inducer. 
There may be employed as the abrasive grain in the method in accordance 
with this invention various types or kinds of aluminum oxide (i.e. 
alumina) abrasive grains individually or in combination or mixture. 
Thus, there is provided in accordance with one practice of the method of 
this invention a blend wherein the abrasive grain comprises sol-gel 
alumina abrasive grains. In accordance with another practice of the method 
of this invention there is provided a blend wherein the abrasive grains 
comprise sintered sol-gel alumina abrasive grains. In a still further 
practice in accordance with the method of this invention there is provided 
a blend wherein the abrasive grain comprises fused alumina abrasive 
grains. There may be provided in accordance with the practice of the 
method of this invention a blend wherein the abrasive grain comprises a 
mixture of sol-gel alumina and fused alumina abrasive grains. In another 
practice in accordance with the method of this invention there is provided 
a blend wherein the abrasive grain comprises a mixture of sintered sol-gel 
alumina and fused alumina abrasive grains. This invention may also be 
practiced to provide in accordance therewith a blend whose abrasive grains 
comprises a mixture of sintered sol-gel alumina and fused alumina abrasive 
grains of different sizes. 
There is contemplated a method for producing a vitreous bonded abrasive 
article comprising the steps of preparing a blend, cold pressing the blend 
in a mold to the desired shape, size and density to form a cold molded 
article, removing the cold molded article from the mold and firing the 
cold molded article to produce the vitreous bonded abrasive article 
wherein the abrasive grain and thermally conductive, solid particles, 
respectively, of the blend are a) abrasive grain comprising sintered 
sol-gel alumina abrasive grains and the non-metallic, inorganic, thermally 
conductive, solid particles are silicon carbide particles having an 
average particle size of at least twice the average particle size of the 
sintered sol-gel alumina abrasive grains or b) abrasive grains comprising 
a mixture of sintered sol-gel alumina abrasive grains and fused alumina 
abrasive grains and the non-metallic, inorganic, thermally conductive, 
solid particles are silicon carbide particles having an average particle 
size of at least twice the average particle size of both the sintered 
sol-gel alumina and the fused alumina abrasive grains or c) abrasive grain 
comprising fused alumina abrasive grains and the non-metallic, inorganic, 
thermally conductive, solid particles are silicon carbide particles having 
an average particle size of at least twice the average particle size of 
the fused alumina abrasive grain. 
There may be provided in accordance with this invention a method for 
producing a vitreous bonded abrasive article, preferably a grinding wheel, 
comprising the steps of preparing a blend, cold pressing the blend in a 
mold to the desired shape, size and density to form a cold molded article, 
removing the cold molded article from the mold and firing the cold molded 
article to produce the vitreous bonded abrasive article wherein the blend 
comprises: a) sintered sol-gel alumina abrasive grains, the non-metallic, 
inorganic, thermally conductive, solid particles are silicon carbide 
particles having an average particle size of at least twice, preferably in 
the range of from about 2 to 10 times, the average particle size of the 
sintered sol-gel alumina abrasive grains and an organic, open cell 
producing, solid pore inducer that, subsequent to the pressing step, 
produces spring back of the cold molded article in an amount at least 
equal to the smallest particle size of the particle size range of the pore 
inducer or b) a mixture of sintered sol-gel alumina abrasive grains and 
fused alumina abrasive grains, the non-metallic, inorganic, thermally 
conductive, solid particles are silicon carbide particles having an 
average particle size of at least twice, preferably in the range of from 
about 2 to 10 times, the average particle size of both the sintered 
sol-gel alumina abrasive grains and the fused alumina abrasive grains and 
an organic, open cell producing, solid pore inducer that, subsequent to 
the pressing step, produces spring back of the cold molded article in an 
amount at least equal to the smallest particle size of the particle size 
range of the pore inducer. 
The abrasive grains of the vitreous bonded abrasive article produced in 
accordance with the method of this invention are aluminum oxide abrasive 
grains. Aluminum oxide abrasive grains, also called alumina abrasive 
grains herein, usable in the practice of this invention include for 
example, but are not limited to, sol-gel alumina, sintered sol-gel 
alumina, sintered alumina and fused alumina abrasive grains of 
conventional size well known in the art. Abrasive grain or grit sizes in 
the range of about 24 to 220, preferably 36 to 150, mesh US Standard Sieve 
Sizes, are usable in the practice of this invention. Mixtures of alumina 
abrasive grains differing in composition and/or grain or grit sizes are 
usable in the practice of this invention. Thus, for example, there may be 
used a mixture of sintered sol-gel alumina and fused alumina of the same 
or different grit sizes, mixtures of sol-gel alumina and sintered sol-gel 
alumina of the same or different grit sizes, mixtures of sintered sol-gel 
alumina of different grit sizes and mixtures of fused alumina of different 
grit sizes. 
Sol-gel and sintered sol-gel alumina abrasive grains usable in the practice 
of this invention are well known and described in the art. Various sol-gel 
alumina and sintered sol-gel alumina abrasive grains usable in this 
invention, including their composition and method of manufacture, have 
been described in U.S. Pat. Nos. 4,314,827 to Leitheiser et.al., 4,518,397 
to Leitheiser et.al., 4,623,364 to Cottringer et.al., 4,744,802 to 
Schwabel, 4,770,671 to Monive et.al., 4,881,951 to Wood et.al., 4,898,597 
to Hay et.al. and 5,282,875 to Wool et.al. Preferably the sintered sol-gel 
abrasive grit usable in the method of this invention is a sintered 
sol-gel, polycrystalline, high density (i.e. at least 95% of theoretical 
density) alpha alumina abrasive grit, more preferably a sintered sol-gel, 
submicron, polycrystalline, high density (i.e. at least 95% of theoretical 
density) alpha alumina abrasive grit. Mixtures having a weight ratio of 
sintered sol-gel alumina to fused alumina abrasive grains in the range of 
from 90/10 to 10/90, preferable 10/90 to 75/25 may be used in the practice 
of the method of this invention. 
There are employed in the method, disclosed and claimed herein, 
non-metallic, inorganic, thermally conductive,solid particles having a 
thermal conductivity greater than the thermal conductivity of the abrasive 
grains and an average particle size at least twice the average particle 
size of the abrasive grain or each of the abrasive grain types of the 
abrasive grains. Where a mixture of abrasive grains of different grit 
sizes are used, the non-metallic, inorganic, thermally conductive, solid 
particles have an average particle size at least twice the average 
particle size of the abrasive grain having the largest grit size. These 
thermally conductive solid particles are held by the vitreous matrix with 
a binding force or strength weaker than the strength of the bond between 
the abrasive grain and the vitreous matrix. Thus the thermally conductive, 
solid particles are not part of the vitreous matrix and are more readily 
lost from the abrasive article (e.g. grinding wheel) during grinding of a 
workpiece (e.g. metal workpiece) than are the abrasive grains and 
therefore do not significantly take part in or contribute to the cutting 
action of the abrasive article or grinding wheel. The thermally 
conductive, solid particles, having a thermal conductivity greater than 
the thermal conductivity of the abrasive grains, act as heat sinks to 
conduct heat away from the grinding zone (i.e. interface between the 
grinding wheel and workpiece during grinding) and to distribute and 
dissipate the heat in and from the grinding wheel to thereby assist in 
reducing or preventing the risk of a) burn of the metal workpiece and b) 
thermally induced breakdown of the grinding wheel. The relatively large 
size of the thermally conductive, solid particles provides a large heat 
sink potential. 
Various non-metallic, inorganic, thermally conductive, solid particles are 
usable in the practice of this invention. Such thermally conductive, solid 
particles include, for example, but not limited to silicon carbide, 
hexagonal boron nitride, graphite, zirconia and titanium carbide. There 
may be employed non-metallic, inorganic, thermally conductive, solid 
particles having an average particle size range of from about 10 to 80, 
preferably 10 to 46 mesh or grit, US Standard Sieve Sizes. 
In accordance with the method of the invention disclosed and claimed herein 
there is employed a vitreous matrix precursor forming a vitreous matrix 
binding together the abrasive grains and forming a bond between the 
vitreous matrix and the non-metallic, inorganic, thermally conductive, 
solid particle that is weaker than the bond between the vitreous matrix 
and the abrasive grain without destroying or substantially altering the 
size, composition and properties of the non-metallic, inorganic, thermally 
conductive, solid particles. The weak bond between the vitreous matrix and 
the thermally conductive, solid particles allows these particles to more 
readily break out of the abrasive article (e.g. grinding wheel), during 
grinding, than does the abrasive. It is desired that the vitreous matrix 
precursor composition does not react with the abrasive grain in a manner 
that would have a detrimental effect upon the structure and properties of 
the abrasive grain. 
The vitreous matrix precursor composition employed in this invention is a 
mixture of materials that, upon firing forms a vitreous matrix binding 
together the abrasive grains of the abrasive article. This vitreous 
matrix, also known in the art as a vitreous phase, vitreous bond, ceramic 
bond or glass bond, may be formed from a combination or mixture of oxides 
and silicates that upon being heated to a high temperature (e.g. firing 
temperature) reacts and/or fuses or may be formed from particles of frit 
that are fused together. Frit is a well known particle form of a vitreous, 
ceramic or glassy material, produced from oxides and silicates, that upon 
being heated to a high temperature fuses to form a continuous vitreous 
matrix. Primarily the oxides and silicates in the vitreous matrix 
precursor composition may be materials such as metal oxides, metal 
silicates and silica. The vitreous matrix may, for example have an oxide 
based composition including silicon dioxide, titanium oxide, aluminum 
oxide, iron oxide, potassium oxide, sodium, oxide, calcium oxide, barium 
oxide, boric oxide and magnesium oxide. Temperatures, for example, in the 
range of from 1000.degree. F. to 2500.degree. F. may be used, in the 
practice of this invention, for producing the vitreous matrix binding 
together the abrasive grains. Such heating is commonly referred to as a 
firing step or firing and is usually carried out in a kiln or furnace 
where the temperatures and times that are employed in firing the abrasive 
article are controlled or variably controlled in accordance with such 
factors as size and shape of the article, the composition and structure of 
the abrasive grain and the composition of the vitreous matrix precursor. 
Firing conditions well known in the art may be employed in the practice of 
this invention. 
Pore inducers are organic or inorganic materials that create open or closed 
cell porosity in the vitreous bonded abrasive article, depending upon the 
pore inducer material being used. Generally closed cell porosity is 
produced by inorganic pore inducers because such materials are usually 
preformed hollow particles whose shape may be retained, upon firing the 
vitreous bonded abrasive article, to form separated, non-interconnected 
closed cell pores or voids in the abrasive article. Closed cell pore 
inducers find particular use in resin bonded grinding wheels, but are also 
known to be used in vitreous bonded grinding wheels. Open cell porosity in 
vitreous bonded abrasive articles is produced by organic pore inducers 
that decompose during firing of the abrasive article to create open, 
interconnected voids, cells or pores in the vitreous bonded article. The 
open cell porosity is employed in the practice of this invention. Open 
cell porosity in vitreous bonded grinding wheels can provide the means by 
which metalworking fluids, employed in grinding operations, may penetrate 
into the grinding wheel and into the grinding zone during grinding. 
Effective penetration of a metalworking fluid into the grinding wheel and 
grinding zone assists in the utilization of the heat removing and 
dissipation function of the metalworking fluid during the grinding 
process. Metalworking fluid may enter and be captured by the open pore 
structure of a vitreous bonded grinding wheel and subsequently carried 
into the grinding zone. Alternatively the open pore structure of the 
grinding wheel, on the face of the wheel engaging the workpiece surface 
during grinding, creates the clearance for metalworking fluid to enter the 
grinding zone. The open pore structure of a vitreous bonded grinding 
wheel, formed by organic pore inducers, is generally in the art only 
controlled as to the amount of the porosity in the wheel (e.g. volume of 
porosity). Thus there often results an open pore structure having a very 
wide range of pore sizes and a non-uniform distribution of pores in the 
abrasive article. A number of materials, well known in the art, may be 
employed as the organic, open cell producing, solid pore producers or 
inducers, in the practice of this invention, to create porosity in the 
vitreous bonded abrasive article made in accordance with the method of 
this invention. Such organic pore inducers can include, for example, but 
are not limited to such materials as crushed nut shells, synthetic 
polymers, resins and wood flour. Solid organic pore inducers are generally 
easier to work with in making vitreous bonded abrasive articles and are 
therefore preferred in the practice of this invention. The organic, open 
cell producing, solid pore inducer preferably used in this invention is 
crushed nut shells. 
It is known to use various additives in the making of vitreous bonded 
abrasive articles, both to assist in and improve the ease of making the 
article and increase the performance of the article. Such additives may 
include lubricants, fillers, temporary binders and processing aids. These 
additives, in amounts well known in the art, may be used in the practice 
of this invention for their intended purpose. 
The blend in accordance with the method of this invention may have a wide 
range of amounts of a) abrasive grains, b) vitreous matrix precursor, c) 
non-metallic, inorganic, thermally conductive, solid particles and d) 
organic, open cell producing, solid pore inducer adjusted to various 
intended uses of the vitreous bonded abrasive article produced by the 
method of this invention. Thus the vitreous bonded abrasive article 
produced by the method disclosed and claimed herein may, for example, 
have, but is not limited to, an abrasive grain content in the range of 
from about 30 to about 60 volume percent, a vitreous matrix content in the 
range of from about 2 to about 36 volume percent, a non-metallic, 
inorganic, thermally conductive, solid particle content in the range of 
from about 2 to 30 volume percent and a porosity in the range of from 
about 20 to about 60 volume percent. Preferably the vitreous bonded 
abrasive article produced by the method in accordance with this invention 
has an abrasive grain content in the range of from about 32 to about 50 
volume percent, a vitreous matrix content in the range of from about 3 to 
about 26 volume percent, a non-metallic, inorganic, thermally conductive, 
solid particle content in the range of from about 4 to about 20 volume 
percent and a porosity in the range of from about 32 to about 61 volume 
percent. 
Apparatus well known in the art for making vitreous bonded abrasive 
articles may be used in the method of this invention. Conventional 
blending and mixing techniques, conditions and equipment well known in the 
art may be used. Techniques, conditions and equipment well known in the 
art for pressing the blend to produce a cold molded article can be 
employed. Drying of the cold molded article prior to firing may be used to 
remove water or organic solvents usually introduced into the article with 
the temporary binder. After drying, the cold molded article, usually 
termed the green article or wheel, may be subjected to high temperatures, 
e.g. 1000.degree. F. to 2500.degree. F., to form the vitreous matrix 
holding together the abrasive grain and thus the vitreous bonded abrasive 
article. This firing step is usually carried out in a kiln where the 
atmosphere, temperature and the time conditions for heating the article 
are controlled or variably controlled. Firing conditions well known in the 
art may be used in the practice of this invention. 
The vitreous bonded abrasive article produced by the method invention 
disclosed and claimed herein is preferably a vitreous bonded grinding 
wheel for use in high metal removal rate grinding of metal workpieces, 
more preferably a vitreous bonded grinding wheel particularly adapted for 
use in a creep feed grinding operation. 
This invention will now be further described in the following non-limiting 
examples wherein, unless otherwise specified, the amounts and percentages 
of materials are by weight, temperatures are in degrees Fahrenheit, time 
is in minutes, linear measurements are in inches, mesh or grit is in US 
Standard Sieve Sizes and wherein 
1) Cubitron 321 is a sol-gel alumina abrasive grain in accordance with the 
disclosure and claims of U.S. Pat. No. 4,881,951 issued Nov. 21, 1989 and 
obtained from the Minnesota Mining and Manufacturing Company (Cubitron is 
a registered trademark of the Minnesota Mining and Manufacturing Company); 
2) Bond A (vitreous matrix precursor) has a mole % oxide based composition 
of SiO.sub.2 63.28; TiO.sub.2 0.32; Al.sub.2 O.sub.3 10.99; Fe.sub.2 
O.sub.3 0.13; B.sub.2 O.sub.3 5.11; K.sub.2 O 3.81; Na.sub.2 O 4.20; 
Li.sub.2 O 4.48; CaO 3.88; MgO 3.04 and BaO 0.26; 
3) Vinsol is a pine resin obtained from Hercules Inc. (Vinsol is a 
registered trademark of Hercules Inc.); 
4) 3029 UF Resin is a 65% by weight urea formaldehyde resin 35% by weight 
water composition; 
5) Crunchlets CR10 are sugar/starch particles having a weight ratio of 
sugar to starch of 78.5 to 21.5 and a particle size in the range of from 
10 to 30 mesh, obtained from Custom Industries Inc. (Crunchlets is a 
registered trademark of Custom Industries Inc.); 
6) Crunchlets CR20 are sugar/starch particles having a weight ratio of 
sugar to starch of 78.5 to 21.5 and a particle size in the range of from 
16 to 45 mesh, obtained from Custom Industries Inc. 
7) Dual Screen Aggregates AD-7 is a ground vegetable shell material having 
a particle size ranging from -35 to +60 mesh obtained from Agrashell Inc.; 
8) Dual Screen Aggregates AD 10.5 is a ground vegetable shell material 
having a particle size ranging from -60 to +200 mesh obtained from 
Agrashell Inc. and 
9) Rhinolox Bubble Alumina AB 20/36 are bubbled alumina particles (i.e. 
hollow spheres of alumina) having a size smaller than 20 mesh but larger 
than 36 mesh (US Standard Sieve Size) obtained from Rhina-Schmelzwerk GMBH 
of Germany (Rhinolox is a registered trademark of Rhina-Schmelzwerk GMBH). 
The components of the formulations or blends in the examples below were 
combined in the following manner and in accordance with the percentages 
listed. Where two or more grains of different chemical compositions, 
physical structure or size were used they were blended together prior to 
the following steps. The abrasive grain, 3029 UF Resin and ethylene glycol 
were blended together until uniform coating of the abrasive grains was 
achieved. To the resulting mixture was added a combination of the bond 
(vitreous matrix precursor) and dextrin powder with mixing and mixing 
continued until a uniform mixture was obtained. Vinsol was then added to 
the mixture with agitation and agitation continued until a uniform blend 
was produced. Pore inducer particles as called for by the formulation were 
added to the blend with agitation and agitation continued to form a 
uniform mixture. The silicon-carbide particles were than added and mixed 
into the resulting blend and mixing continued until a uniform blend was 
obtained. This blend or mixture was then screened to remove undesirable 
lumps and a predetermined amount of the screened mixture or blend was 
placed and evenly distributed in a steel mold having the size and shape 
for producing the desired vitreous bonded abrasive article. The blend in 
the mold was then pressed at room temperature to compact it into the 
desired shape and dimensions. This compacted blend or cold molded article, 
commonly called a green article (e.g. green wheel), was then removed from 
the mold and subjected to a drying cycle by heating it from room 
temperature to 275.degree. F. over 13 hours and then ambient air cooled 
back to room temperature. Upon cooling to room temperature the dried green 
wheel was given a firing cycle in air wherein it was heated from room 
temperature to 1650.degree. F. over 11 hours, held at 1650.degree. F. for 
12 hours, heated from 1650.degree. F. to 2100.degree. F. over 6.5 hours 
and held at 2100.degree. F. for 3 hours. Thereafter the wheel was cooled 
in ambient air to room temperature over 27.4 hours and finished to its 
final dimensions. 
EXAMPLE NO. 1 
______________________________________ 
Cubitron 321 abrasive (80 grit) 
22.8 
White Fused Alumina abrasive (80 grit) 
53.1 
Bond A 8.6 
Vinsol 1.4 
Ethylene Glycol 0.5 
3129 UF Resin 2.8 
Black Silicon Carbide (24 grit) 
3.2 
Crunchlets CR 20 6.8 
Dextrin 0.8 
______________________________________ 
Finished wheel size 16.times.1.times.5 inches 
EXAMPLE NO. 2 
______________________________________ 
Cubitron 321 abrasive (60 grit) 
36.0 
White Fused Alumina abrasive (60 grit) 
36.0 
Bond A 10.2 
Vinsol 1.4 
Ethylene Glycol 0.6 
3029 UF Resin 3.0 
AB 20/36 Alumina Bubbles 
4.8 
Crunchlets CR 10 6.8 
Dextrin 1.2 
______________________________________ 
Finished wheel dimensions 19.times.2.times.8 inches Examples 1 and 2 are 
comparison formulations and the grinding wheels produced therewith are 
comparison grinding wheels. 
EXAMPLE NO. 3 
______________________________________ 
Cubitron 321 abrasive (80 grit) 
23.5 
White Fused Alumina abrasive (80 grit) 
54.9 
Bond A 8.9 
Vinsol 1.5 
Ethylene Glycol 0.5 
3029 UF Resin 2.9 
Black Silicon Carbide (24 grit) 
3.3 
Dual Screen Aggregates AD 7 
2.4 
Dual Screen Aggregates AD 10.5 
1.3 
Dextrin 0.9 
______________________________________ 
Finished wheel dimensions 16.times.1.times.5 inches 
EXAMPLE NO. 4 
______________________________________ 
Cubitron 321 abrasive (60 grit) 
37.3 
White Fused Alumina abrasive (60 grit) 
37.3 
Bond A 10.6 
Vinsol 1.5 
Ethylene Glycol 0.6 
3029 UF Resin 3.1 
Silicon Carbide (24 grit) 
5.0 
Dual Screen Aggregate AD 7 
2.2 
Dual Screen Aggregate AD 10.5 
1.3 
Dextrin 1.2 
______________________________________ 
Finished wheel dimensions 19.times.2.times.8 inches 
EXAMPLE NO. 5 
______________________________________ 
Cubitron 321 abrasive (60 grit) 
36.5 
White Fused Alumina abrasive (60 grit) 
36.5 
Bond A 12.0 
Vinsol 1.5 
Ethylene Glycol 0.7 
3029 UF Resin 3.4 
Silicon Carbide (24 grit) 
4.9 
Dual Screen Aggregates AD 7 
2.2 
Dual Screen Aggregates AD 10.5 
1.2 
Dextrin 1.2 
______________________________________ 
Finished wheel dimensions 19.times.2.times.8 inches Examples Nos 3 to 5 are 
in accordance with this invention 
Spring Back Measurement 
Procedure: The required amount of the blended vitreous bonded abrasive 
article formulation was placed in a 13/8 inch wide by 5 inch long by 1 
inch deep room temperature steel mold having a 13/8.times.5 inch open face 
and the mold placed in a press at room temperature. A force of 37 tons was 
then applied to the 13/8.times.5 inch face of the mixture in the mold for 
2 minutes. The force on the mixture was then released and the self 
sustaining (i.e. green) molding removed from the mold. Metal plates 
13/8.times.5.times.0.010 inches were immediately placed on each side of 
the cold pressed molding and the thickness of the sandwich of metal plates 
and molding was measured with a micrometer. Thickness measurements were 
again made at 2 minutes and 8 minutes after removing the green molding 
from the mold. The thickness of the metal plates was then deducted from 
the thickness of the sandwich to obtain the thickness of the bar. Using 
this procedure 240.3 grams of the formulation of Example 1 and 232.7 grams 
of the formulation of Example 3 were cold pressed into bars for spring 
back measurements. Example 1 and 3 formulations were used at the same 
volume in the mold. 
Results 
______________________________________ 
Thickness of test bar (inches) after 
Formulation 
0 min. 2 min. 8 min. 
______________________________________ 
Example 1 0.989 0.989 0.989 
Example 3 0.993 0.997 1.001 
______________________________________ 
Spring back (inches) after 
Formulation 
0 min. 2 min. 8 min. 
______________________________________ 
Example 1 0 0 0 
Example 3 0 0.004 0.008 
______________________________________ 
The formulation of Example 1 is a comparison formulation containing an 
organic, open cell producing pore inducer not producing spring back and 
the formulation of Example 3 is a vitreous bonded abrasive article 
formulation in accordance with the method of this invention containing an 
organic, open cell producing pore inducer producing spring back. 
Grinding tests were conducted with the vitreous bonded grinding wheels 
produced from the formulations of Examples 1 to 5. Wheels produced in 
accordance with Examples Nos. 1 and 3 were tested and compared in the 
following continuous creep feed grinding test number 1 and wheels produced 
in accordance with Examples 2, 4, and 5 were tested in a production 
grinding test number 2 described below. Grinding wheels using the 
formulations or blends of Examples 3, 4, and 5 were produced in accordance 
with the method of this invention, whereas grinding wheels using the 
formulations of Examples 1 and 2 were not. 
Grinding Test No. 1 
Procedure: The wheels were tested using continuous creep feed grinding 
under the conditions described below. Each wheel was dressed 200 um 
(micrometers) before testing, the dressed wheel having a form to produce a 
root truncation profile in a workpiece. The ground workpiece geometry is 
shown in FIG. 1. The depth of cut was held constant at 1 mm (millimeter). 
A feed rate of 800 mm/min (minute) was selected as the starting point of 
the test and the feed rate was then increased in steps of 100 mm/min until 
burn or breakdown of the 0.5 mm radius of the root truncation profile 
occurred. The power drain on the grinding wheel spindle motor was 
monitored during the test and a shadowgraph used to measure the actual 
size of the 0.5 mm radius. Workpiece burn (yellowish brown discoloration) 
of the ground surface was visually monitored during grinding. Grinding was 
carried out using a coolant. 
Conditions: Wheel Speed 20 meters/second; Depth of cut 1 millimeter; Width 
of cut 12 millimeters; Length of cut 60 millimeters; Dresser feed rate 1 
micrometer per revolution; Dresser speed ratio +0.8; Workpiece material 
Rene 80 casting (nickel alloy); Coolant Cimperial 22 DB at 3% (a 3% 
aqueous metalworking fluid obtained from Cincinnati Milacron 
Inc.--Cimperial is a registered trademark of Cincinnati Milacron Inc.). 
Grinding Test No. 1 Results 
______________________________________ 
Example 1 Example 3 
Table Speed Break- Break- 
(mm/min) Burn down* Power** 
Burn down* Power** 
______________________________________ 
800 yes no 5.07 no no 4.80 
900 yes no 6.45 no no 5.59 
1000 yes no 6.27 no no 5.60 
1100 yes no 6.81 no yes 6.08 
1200 yes no 7.27 no yes 6.23 
1300 yes no 7.16 -- -- -- 
1400 yes yes 7.78 -- -- -- 
______________________________________ 
*Form breakdown on the 0.5 mm radius 
**kW 
Grinding Test No. 2 
This grinding test was conducted in a production creep feed grinding 
operation on titanium ductile casting alloy jet engine parts using an ELB 
Creep Feed Grinder, the grinding wheels produced using the formulations of 
Example Nos. 2, 4 and 5 and Syntilo 9930 10% aqueous solution metalworking 
fluid obtained from Castrol Industries Inc. The test was performed to 
evaluate the grinding performance, under production conditions, of 
vitreous bonded grinding wheels produced in accordance with the method of 
this invention. The following results were obtained. 
Grinding Wheel 
______________________________________ 
Example 2 
Example 4 Example 5 
______________________________________ 
Wheel Speed (SFPM)* 
4725 6000 5500 
Table Feed Rate (in/min) 
8.0 6.0 6.0 
Number of Passes** 
2 1 1 
Depth of Cut (inches) 
0.030 0.050 0.050 
Total Machine Cycle Time 
120 58 58 
(sec) 
Machine Cycle Time per 
60 29 29 
Part (sec) 
______________________________________ 
*Surface feet per minute 
**The number of times contact was made between the wheel and the workpiec 
to achieve the desired grinding result. 
Discussion of Grinding Tests Results 
In grinding test number 1 the vitreous bonded grinding wheel produced by 
the method in accordance with this invention, as produced using the 
formulation of Example No. 3, exhibited no burn of the metal workpiece 
over a table speed (i.e. feed rate) of from 800 to 1200 millimeters per 
minute whereas the comparison wheel, produced using the formulation of 
Example No. 1 and having the same abrasive and same bond as in Example No. 
3, exhibited burn of the metal workpiece over the entire table speed range 
of 800 to 1200 millimeters per minute. The power required for grinding, in 
test number 1, with the wheel produced in accordance with the method of 
this invention, using the formulation of Example No. 3, was lower at each 
of the table speeds over the table speed range of 800 to 1200 millimeters 
per minute than the comparison wheel produced using the formulation of 
Example No. 1. Thus the vitreous bonded grinding wheel produced by the 
method in accordance with this invention exhibited improved grinding 
performance over the comparison wheel by reducing or preventing burn of 
the metal workpiece and at the same time using less power during grinding. 
The advantage of the vitreous bonded abrasive grinding wheels produced by 
the method in accordance with this invention is exemplified in test number 
2 by the performance of the wheels produced using the formulations of 
Example Nos. 4 and 5. Test number 2 was in essence a real life test since 
it was carried out in a production creep feed grinding operation under 
production conditions. What test number 2 has shown is that the vitreous 
bonded grinding wheel produced by the method in accordance with this 
invention, as produced using the formulations of Example Nos. 4 and 5, out 
performed the comparison wheel, produced using the formulation of Example 
2 having the same abrasive and bond as in Example Nos. 4 and 5, by 
reducing the number of passes needed to grind the part, achieving 
significantly greater depth of cut, significantly reducing the total 
machine cycle time and significantly reducing the machine cycle time per 
part while not producing burn of the expensive titanium part. Such 
improved performance translates into reduced grinding cost and increased 
productivity.