U.S. patent application number 11/289296 was filed with the patent office on 2006-06-29 for vitrified grinding stone and method of manufacturing the same.
This patent application is currently assigned to BOSCH CORPORATION. Invention is credited to Hideo Furukawa, Masatoshi Kishimoto, Osamu Kubota, Naoyuki Ukai, Takayuki Yui.
Application Number | 20060137256 11/289296 |
Document ID | / |
Family ID | 33487349 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060137256 |
Kind Code |
A1 |
Yui; Takayuki ; et
al. |
June 29, 2006 |
Vitrified grinding stone and method of manufacturing the same
Abstract
A vitrified grinding stone includes an abrasive grain and a
vitrified binder. The vitrified grinding stone has a porosity, a
degree of concentration of abrasive grains and an abrasive grain
diameter according to a preset processing efficiency and a
processing precision of grinding.
Inventors: |
Yui; Takayuki;
(Higashimatsuyama-shi, JP) ; Kubota; Osamu;
(Higashimatsuyama-shi, JP) ; Furukawa; Hideo;
(Higashimatsuyama-shi, JP) ; Kishimoto; Masatoshi;
(Nagoya-shi, JP) ; Ukai; Naoyuki; (Nagoya-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
BOSCH CORPORATION
Tokyo
JP
NORITAKE CO., LTD.
Nagoya-shi
JP
NORITAKE SUPER ABRASIVE CO., LTD.
Ukiha-gun
JP
|
Family ID: |
33487349 |
Appl. No.: |
11/289296 |
Filed: |
November 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP04/07754 |
May 28, 2004 |
|
|
|
11289296 |
Nov 30, 2005 |
|
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Current U.S.
Class: |
51/295 |
Current CPC
Class: |
B24D 18/00 20130101;
B24D 3/18 20130101 |
Class at
Publication: |
051/295 |
International
Class: |
B24D 11/00 20060101
B24D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2003 |
JP |
2003-155149 |
Claims
1. A vitrified grinding stone comprising: an abrasive grain; and a
vitrified binder, wherein the vitrified grinding stone has a
porosity, a degree of concentration of abrasive grains and an
abrasive grain diameter according to a preset processing efficiency
and a processing precision of grinding.
2. The vitrified grinding stone according to claim 1, wherein when
said processing precision of grinding ranges from 0.1 to 1.6 Rz
(.mu.m), the processing efficiency of grinding ranges from 0.1 to
2.0 mm.sup.3/(mmsec).
3. The vitrified grinding stone according to claim 1, wherein said
porosity ranges from 30 to 70 volume percent with respect to a
volume of the whole grinding stone.
4. The vitrified grinding stone according to claim 1, wherein said
porosity comprises a forced porosity based on burnout pores formed
by burning out a pore-forming material.
5. The vitrified grinding stone according to claim 4, wherein said
forced porosity ranges from 5 to 35 volume percent with respect to
a volume of the whole grinding stone.
6. The vitrified grinding stone according to claim 4, wherein said
pore-forming material has a size 0.1 to 3 times the average grain
diameter of the abrasive grain.
7. The vitrified grinding stone according to any of claims 1,
wherein a ratio of pores having a size 1 to 3 times an average
grain diameter of the abrasive grain in a volume of whole pores
ranges from 20 to 70 volume percent.
8. The vitrified grinding stone according to claim 1, wherein a
ratio of pores having a size 0.1 to 1 time an average grain
diameter of the abrasive grain in a volume of whole pores ranges
from 30 to 70 volume percent.
9. The vitrified grinding stone according to claim 4, wherein said
pore-forming material is a polymer compound.
10. The vitrified grinding stone according to of claim 1, wherein
said abrasive grain has an average grain diameter ranging from 10
to 90 .mu.m.
11. The vitrified grinding stone according to claim 1, wherein said
degree of concentration of abrasive grains ranges from 50 to
160.
12. The vitrified grinding stone according to claim 1, wherein said
abrasive grain is a cubic boron nitride abrasive grain.
13. A vitrified grinding stone comprising: an abrasive grain; and a
vitrified binder, wherein a ratio of pores having a size 1 to 3
times an average grain diameter of the abrasive grain in a volume
of whole pores ranges from 20 to 70 volume percent.
14. A vitrified grinding stone comprising: an abrasive grain; and a
vitrified binder, wherein a ratio of pores having a size 0.1 to 1
time an average grain diameter of the abrasive grain in a volume of
whole pores ranges from 30 to 70 volume percent.
15. The vitrified grinding stone according to claim 13, wherein
said abrasive grain has an average grain diameter ranging from 10
to 90 .mu.m.
16. The vitrified grinding stone according to claim 13, wherein the
degree of concentration of said abrasive grains ranges from 50 to
160.
17. A method of manufacturing a vitrified grinding stone comprising
an abrasive grain and a vitrified binder, the method comprising:
setting a processing efficiency and a processing precision of
grinding; and setting a porosity, a degree of concentration of
abrasive grains and an abrasive grain diameter according to the
processing efficiency and the processing precision.
18. The method of manufacturing according to claim 17, wherein said
processing precision of grinding is set within a range of 0.1 to
1.6 Rz (.mu.m) and said processing efficiency of grinding is set
within a range of 0.1 to 2.0 mm.sup.3/(mmsec).
19. The method of manufacturing according to claim 17, wherein said
porosity is set within a range of 30 to 70 volume percent with
respect to a whole volume of the grinding stone.
20. The method of manufacturing according to claim 17, wherein said
porosity comprises a forced porosity based on burnout pores formed
by burning out a pore-forming material.
21. The method of manufacturing according to claim 20, wherein said
forced porosity is set within a range of 5 to 35 volume percent
with respect to a whole volume of the grinding stone.
22. The method of manufacturing according to claim 20, wherein a
pore-forming material having a size 0.1 to 3 times an average grain
diameter of the abrasive grain is employed as said pore-forming
material.
23. The method of manufacturing according to claim 17, wherein a
polymer compound is employed as said pore-forming material.
24. The method of manufacturing according to claim 17, wherein an
abrasive grain having an average grain diameter ranging from 10 to
90 .mu.m is employed as said abrasive grain.
25. The method of manufacturing according to claim 17, wherein said
degree of concentration of abrasive grains is set within a range of
50 to 160.
26. The method of manufacturing according to claim 17, wherein a
cubic boron nitride abrasive grain is employed as said abrasive
grain.
27. The vitrified grinding stone according to claim 14, wherein
said abrasive grain has an average grain diameter ranging from 10
to 90 .mu.m.
28. The vitrified grinding stone according to claim 2, wherein said
porosity ranges from 30 to 70 volume percent with respect to a
volume of the whole grinding stone.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C.
.sctn. 119 to Japanese Patent Application No. 2003-155149, filed
May 30, 2003, entitled "VITRIFIED GRINDING STONE AND A METHOD OF
MANUFACTURING THE SAME". The contents of this application are
incorporated herein by reference in their entirety. The present
application is a continuation-in part of PCT/JP2004/007754 which
was filed May 28, 2004. The contents of PCT/JP2004/007754 are
incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a vitrified grinding stone
and a method of manufacturing the vitrified grinding stone.
[0004] 2. Discussion of the Background
[0005] Since the degree of binding and composition of vitrified
grinding stones are readily adjusted and they afford resistance to
water, alkali, and oil, they are widely employed in grinding and
polishing operations, including precision grinding.
[0006] For example, in small-diameter internal grinding, in which
the inner surfaces of small-diameter nozzles such as engine
injection nozzles are ground, the peripheral speed of the grinding
stone is limited and the quill rigidity becomes low. Thus, in order
to maintain good grinding, it is required to make the diameter of
the grinding stone as large as possible. For such reasons, grinding
stones having diameters close to those of the inner diameter of the
object being processed are employed in small-diameter internal
grinding. However, in such grinding, the chip length increases and
clogging tends to occur. These tendencies are particularly marked
when the grinding efficiency is increased.
[0007] FIGS. 2A-2C show the relation between the effective cutting
edge spacing of the grinding stone and the chip pocket in internal
grinding. To prevent clogging and increase processing efficiency
during grinding, the method (FIG. 2B) of increasing the abrasive
grain diameter and increasing the size of the effective cutting
edge spacing We and chip pocket P relative to the norm (FIG. 2A) is
conceivable. However, in this method, since the effective cutting
edge spacing We is broadened, the processing precision (surface
roughness) ends up decreasing. On the other hand, to increase
processing precision, the method of reducing the abrasive grain
diameter and decreasing the size of the effective cutting edge
spacing We and chip pocket P relative to the norm (FIG. 2A) is also
conceivable (FIG. 2C). However, in this method, since the volume of
chip pocket P is reduced, the chip pocket ends up quickly filling
with chips of the ground products. When grinding is further
continued in this state, the grinding stone clogs, causing fusion.
Due to this tradeoff between the improvement of the processing
efficiency and that of processing precision of grinding, it has
been difficult to simultaneously achieve both.
[0008] Conventionally, attempts have been made to simultaneously
achieve processing efficiency and processing precision of grinding.
For example, the method of decreasing the degree of concentration
of abrasive grains given by the ratio of abrasive grains present in
the grinding stone to increase processing efficiency and processing
precision of grinding has been conceived. However, when the degree
of concentration of abrasive grains is reduced, the binding
property between abrasive grains decreases, causing a problem in
the binding of abrasive grains. Further, the dispersion of abrasive
grains decreases, causing a problem that abrasive grains cannot be
uniformly dispersed in the grinding stone. Thus, in methods of
reducing the degree of concentration of the abrasive grains, it has
been difficult to achieve both processing efficiency and processing
precision of grinding.
[0009] The method of replacing a portion of the cBN abrasive grains
with a hollow inorganic substance is also known. Japanese
Unexamined Patent Publication (KOKAI) Showa No. 62-251077 discloses
such method. The contents of this application are incorporated
herein by reference in their entirety. In this method, a hollow
inorganic substance is pulverized during grinding to form pores,
which would be expected to produce an effect similar to that of
chip pockets. However, in grinding stones in which a portion of the
cBN abrasive grains is replaced with a hollow inorganic substance
and the degree of concentration is made about 100, dispersion of
the abrasive grains deteriorates due to the decreased degree of
concentration, making it difficult to obtain grinding stones in
which the abrasive grains are uniformly dispersed. Further, since
the hollow inorganic substance is also held by a vitrified binder,
the vitrified binder that originally should have held the cBN
abrasive grains ends up being trapped in the hollow inorganic
substance. Thus, when employing a hollow inorganic substance, it
becomes necessary to use more vitrified binder than usual,
resulting in a drawback in the form of decreased porosity. Further,
when the hollow inorganic substance is damaged during grinding, the
vitrified binder used to bind the hollow inorganic substance ends
up remaining in the grinding stone, resulting in a drawback in the
form of impaired grinding.
[0010] Methods of forming pores by employing organic pore-forming
materials such as walnuts, wood chips and the like are known. The
pore-forming materials are incorporated into a molded product prior
to calcination and burned out during calcination, yielding pores in
the grinding stone obtained after calcination. The use of such a
pore-forming material is desirable in that it does not have the
drawbacks encountered when fillers such as a hollow inorganic
material are incorporated into the grinding stone and permits the
achievement of a low degree of concentration.
[0011] However, depending on the type of pore-forming material
employed, there is a drawback in that shrinking tends to occur to a
greater degree than in common grinding stones in which common
alumina-based (A-based) abrassive grains employing WA abrasive
grains (white alumina abrasive grains) and the like are used
because the abrasive grains are not oxides and a large quantity of
vitrified binder is employed. There are further drawbacks in that
the use of conventional pore-forming materials makes it hard to
uniformly disperse the pores and is unsuited to vitrified cBN
grinding stones in which more uniform distribution of abrasive
grains is required than in common grinding stones.
[0012] In recent years, for the purpose of improving conventional
pore-forming materials, methods of reducing shrinkage due to
calcination and uniformly dispersing pores even when manufacturing
vitrified grinding stones in which the degree of concentration of
abrasive grains is made less than 200 have been known. For example,
Japanese Unexamined Patent Publication (KOKAI) No. 2000-317844
discloses such method. The contents of this application are
incorporated herein by reference in their entirety. The grinding
stones obtained by such methods afford advantages in that, even
when the degree of concentration is small, less than 200, the
grinding ratio is high, grinding burns and fusion tend not to
occur, and it is easy to use.
[0013] However, even in the aforementioned method, when the degree
of concentration is further lowered, that is, when pore-forming
materials having a diameter greater than the average grain diameter
of the abrasive grains are employed, the spacing between individual
abrasive grains widens and thus the effective cutting edge spacing
increases. As a result, there is a problem in that good processing
precision cannot be maintained. The above-cited method also
presents the problem of inadequate uniformity of pores and abrasive
grains in the grinding stone. Accordingly, there is a need for
further improvement in the above-cited method for maintaining good
processing efficiency and processing precision even in grinding
stones in which the degree of concentration has been further
reduced.
SUMMARY OF THE INVENTION
[0014] According to one aspect of the present invention, a
vitrified grinding stone includes an abrasive grain and a vitrified
binder. The vitrified grinding stone has a porosity, a degree of
concentration of abrasive grains and an abrasive grain diameter
according to a preset processing efficiency and a processing
precision of grinding.
[0015] According to another aspect of the present invention, a
vitrified grinding stone includes an abrasive grain and a vitrified
binder. A ratio of pores having a size 1 to 3 times an average
grain diameter of the abrasive grain in a volume of whole pores
ranges from 20 to 70 volume percent.
[0016] According to yet another aspect of the present invention, a
vitrified grinding stone includes an abrasive grain and a vitrified
binder. A a ratio of pores having a size 0.1 to 1 time an average
grain diameter of the abrasive grain in a volume of whole pores
ranges from 30 to 70 volume percent.
[0017] According to further aspect of the present invention, a
method of manufacturing a vitrified grinding stone which has an
abrasive grain and a vitrified binder includes setting a processing
efficiency and a processing precision of grinding, and setting a
porosity, a degree of concentration of abrasive grains and an
abrasive grain diameter according to the processing efficiency and
the processing precision.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0019] FIG. 1 is an enlarged schematic cross-sectional view of the
vitrified grinding stone according to an embodiment of the present
invention;
[0020] FIGS. 2A-2C are drawings showing the relation between the
effective cutting edge spacing We and the chip pocket P in a
grinding stone during internal grinding;
[0021] FIG. 3 is an enlarged schematic cross-sectional view showing
the structure of a grinding stone manufactured using a conventional
burnout material;
[0022] FIG. 4 is an enlarged schematic explanatory drawing showing
the structure of a grinding stone manufactured without using a
burnout material;
[0023] FIG. 5 is an explanatory drawing showing the relation
between the grinding efficiency ratio and the effective cutting
edge spacing in the grinding stone according to an embodiment of
the present invention and a conventional grinding stone;
[0024] FIG. 6 is an explanatory drawing descriptive of the
arrangement of abrasive grains and the effective cutting edge
spacing in an embodiment of the present invention;
[0025] FIG. 7 is a drawing showing the grinding efficiency ratio
when the effective cutting edge spacing is 0.1 mm in an embodiment
of the present invention and a comparative example;
[0026] FIGS. 8A to 8C show the results (power consumption, surface
roughness, and abrasion) when internal grinding was conducted at a
grinding processing efficiency of 0.3 mm.sup.3/(mmsec) with the
grinding stones of Examples 1 to 3 and Comparative Example 2;
and
[0027] FIGS. 9A to 9C show the results (power consumption, surface
roughness, and abrasion) when internal grinding was conducted at a
grinding processing efficiency of 0.7 mm.sup.3/(mmsec) with the
grinding stones of Examples 1 and 2.
DESCRIPTION OF THE EMBODIMENTS
[0028] The embodiments will now be described with reference to the
accompanying drawings, wherein like reference numerals designate
corresponding or identical elements throughout the various
drawings.
[0029] The present inventors conducted extensive research into the
relation between the effective cutting edge spacing of abrasive
grains and chip pocket volume for the purpose of achieving both
processing efficiency and processing precision of grinding. As a
result, they discovered that presetting the processing efficiency
and processing precision of grinding and then setting the porosity,
degree of concentration of abrasive grains, and abrasive grain
diameter based on the preset processing efficiency and processing
precision of grinding resulted in a method permitting improvement
in both grinding efficiency and processing surface roughness. The
vitrified grinding stone according to the embodiment of the present
invention and manufacturing method thereof will be described in
greater detail below.
[Vitrified Grinding Stone]
<Processing Efficiency and Processing Precision of
Grinding>
[0030] The grinding stone according to the embodiment of the
present invention has a porosity, a degree of concentration of
abrasive grains, and an abrasive grain diameter based on the preset
processing efficiency and processing precision of grinding. The
processing efficiency of grinding is given as the amount of
grinding per second for a grinding stone width of 1 mm and is
normally denoted in units of mm.sup.3/(mmsec). The processing
precision of grinding can be denoted as a surface roughness and is
normally denoted as a ten-point average roughness Rz (.mu.m).
[0031] For example, in internal grinding, when attempting to
achieve a processing precision of grinding of less than or equal to
1 Rz (.mu.m), the conventional limit of processing efficiency of
grinding is about 0.3 mm.sup.3/(mmsec). By contrast, in the
grinding stone according to the embodiment of the present
invention, it is possible to achieve a processing efficiency of
grinding of greater than or equal to 0.3 mm.sup.3/(mmsec) even at a
grinding precision of less than or equal to 1 Rz (.mu.m). More
specifically, even when the processing precision of grinding is set
to 0.1 to 1.6 Rz (.mu.m), preferably 0.2 to 1.0 Rz (.mu.m), and
more preferably 0.3 to 0.5 Rz (.mu.m), the processing efficiency of
grinding can be set to 0.1 to 2.0 mm.sup.3/(mmsec), preferably 0.2
to 1.0 mm.sup.3/(mmsec), and more preferably 0.3 to 0.7
mm.sup.3/(mmsec).
[0032] Here, the relation between the grinding efficiency ratio and
the effective cutting edge spacing, We, is shown in FIG. 5 to
describe the relation between the above-mentioned processing
efficiency of grinding and the effective cutting edge spacing, We.
As shown in FIG. 5, for example, when a conventional grinding stone
has an effective cutting edge spacing of 0.1 mm, the grinding
efficiency ratio is less than 2. By contrast, when the grinding
stone according to the embodiment of the present invention has an
effective cutting edge spacing of 0.1 mm, it is possible to make
the grinding efficiency ratio greater than or equal to 2
(preferably greater than or equal to 2.5, and more preferably
greater than or equal to 3.0). (FIG. 5 shows an example where the
grinding efficiency ratio is greater than or equal to 3 when the
effective cutting edge spacing is 0.1 mm.) In the grinding stone
according to the embodiment of the present invention abrasive
grains of prescribed size (preferably 10 to 90 .mu.m) are selected,
and the abrasive grains are not positioned next to one another in
the manner of a conventional grinding stone (see FIG. 2), but are
arranged uniformly as shown in FIG. 6, maintaining a certain
effective cutting edge spacing. Thus, the grinding stone according
to the embodiment of the present invention achieves good processing
efficiency (grinding efficiency ratio) while maintaining a
prescribed processing precision of grinding.
<Porosity>
[0033] In the present Specification, the term "porosity" means the
ratio of the volume of pores (space) without abrasive grains,
binder, and other fillers and the like, to the volume of the whole
grinding stone. In the present invention, the porosity is comprised
of a forced porosity and a natural porosity. Here, the term "forced
porosity" means the ratio of the volume of burnout pores--formed by
burning out a pore-forming material when a molded product
containing at least an abrasive grain, a vitrified binder, and a
pore-forming material is calcined in a calcination step--to the
volume of whole pores. The term "natural porosity" refers to the
porosity calculated by subtracting the above forced porosity from
the total porosity, and is the ratio occupied in the molded product
of gap portions in the abrasive grain, vitrified binder, and
pore-forming material prior to calcination.
[0034] In the vitrified grinding stone according to the embodiment
of the present invention, the porosity suitably falls within a
range of 30 to 70 volume percent, preferably 40 to 60 volume
percent, and more preferably 45 to 55 volume percent, of the volume
of the whole grinding stone. When the porosity is greater than or
equal to 30 volume percent, fusion is not caused due to inadequate
volume of chip pockets and clogging during grinding. Since the
pore-forming material is burned out during the calcination in the
embodiment of the present invention, better porosity can be ensured
than in grinding stones in which a pore-forming material is not
employed; porosities of up to 70 volume percent can be
obtained.
[0035] Within this porosity, the forced porosity suitably falls
within a range of 5 to 35 volume percent, preferably 20 to 35
volume percent, and more preferably 25 to 35 volume percent, of the
volume of the whole grinding stone. In the vitrified grinding stone
according to the embodiment of the present invention, the forced
pores formed by the pore-forming material primarily contribute to
the improvement of the processing efficiency of grinding. When the
forced porosity is greater than or equal to 5 volume percent,
grinding can be carried out well. When the forced porosity is less
than or equal to 35 volume percent, grinding stones can be
manufactured stably.
[0036] In the vitrified grinding stone according to the embodiment
of the present invention, the size of the forced pores formed by
burning out the pore-forming material greatly affects grinding
stone performance. For example, the smaller the forced pores, the
greater the dispersion of abrasive grains and pores in the grinding
stone. Since increasing dispersion of the abrasive grains and the
pores stabilizes the cutting edge spacing, the chip discharge
performance increases and power consumption during grinding
decreases, which are advantageous with regard to production
efficiency. Further, since the strength of the grinding stone
increases, abrasion of the grinding stone due to grinding
decreases, resulting in good durability. The vitrified grinding
stone according to the embodiment of the present invention can be
one comprising pores (including both forced pores and natural
pores) having a size 1 to 3 times the average grain diameter of the
abrasive grains in a ratio of 20 to 70 volume percent, preferably
30 to 60 volume percent, and more preferably 30 to 50 volume
percent, with respect to the volume of whole pores. The vitrified
grinding stone according to the embodiment of the present invention
can be one comprising pores having a size 0.1 to 1 time the average
grain diameter of the abrasive grains in a ratio of 30 to 70 volume
percent, preferably 40 to 70 volume percent, and more preferably 50
to 70 volume percent, with respect to the volume of whole pores.
The ratio of pores having a desired size can be adjusted by
suitably setting the size and quantity added of the pore-forming
material employed. The ratio of pores having a desired size can be
calculated by slicing the grinding stone, measuring the
cross-section with a microscope capable of three-dimensional
measurement to obtain three-dimensional data, and then analyzing
the cross-sectional shape.
<Pore-Forming Material>
[0037] The pore-forming material employed in the embodiment of the
present invention is not specifically limited, other than that it
be a material that can be burned out in calcination. It is
preferable to use a pore-forming material having a burnout starting
temperature greater than or equal to the transition temperature of
the vitrified binder described further below, and having a burnout
ending temperature lower than the maximum temperature within the
calcination temperature range of the vitrified binder.
[0038] For example, it is suitable to use a pore-forming material
having a burnout starting temperature at least 5.degree. C. (more
preferably at least 10.degree. C., and further preferably at least
20.degree. C.) greater than the transition temperature of the
vitrified binder, and having a burnout ending temperature at least
5.degree. C. (more preferably at least 10.degree. C., and further
preferably at least 20.degree. C.) lower than the maximum
temperature within the calcinations temperature range of the
grinding stone starting materials including the vitrified
binder.
[0039] The pore-forming material desirably has a strength so as to
preclude pulverization during stirring of the manufacturing
starting materials in the process of manufacturing the grinding
stone. Any pore-forming material having a strength so as to
preclude pulverization during stirring may be employed, whether it
be solid or hollow.
[0040] The specific gravity of the pore-forming material is
desirably greater than or equal to 1 (for example, 1 to 2.5,
preferably 1 to 1.5). When the specific gravity of the pore-forming
material is greater than or equal to 1, it does not float on the
starting materials during stirring and can be uniformly dispersed
in the starting materials.
[0041] The size of the pore-forming material is preferably selected
according to the size of the desired forced pores. As set forth
above, the smaller the forced pores, the lower the power
consumption during grinding and the greater the advantage afforded
in the form of production efficiency. Further, the smaller the
forced pores, the greater the strength of the grinding stone and
the less the abrasion of the grinding stone during grinding,
resulting in good durability. However, when the forced pore
diameter becomes excessively small, the processing efficiency
during grinding drops. From the above perspectives, the size of the
pore-forming material is suitable from 0.1 to 3 times the average
grain diameter of the abrasive grains. In particular, from the
perspective of power consumption during grinding and grinding stone
durability, the size of the pore-forming material is preferably
from 0.16 to 1 time the average grain diameter of the abrasive
grains. For example, when employing cBN abrasive grains as an
abrasive grain, when the average grain diameter of the abrasive
grains is 22 to 36 .mu.m, a pore-forming material about 3.5 to 36
.mu.m in size can be employed.
[0042] The shape of the pore-forming material is not specifically
limited. However, an abrasive grain having a true spherical shape
that can be dispersed well during the manufacturing process is
preferred.
[0043] The content, as volume percentage, of the pore-forming
material in the starting materials is preferably 10 to 50 percent,
more preferably 15 to 45 percent, and further preferably 15 to 40
percent. When the volume percentage is greater than or equal to 10
percent, an effect by the formation of burnout pores can be
achieved. When the volume percentage is less than or equal to 50
percent, a grinding stone of suitable strength and durability can
be manufactured.
[0044] Specific examples of pore-forming materials are: polymer
compounds such as polymethyl acrylate and polymethyl methacrylate,
and carbonaceous compounds containing 90 mass percent or more of
carbon. The use of polymethyl methacrylate as a pore-forming
material is preferred.
<Abrasive Grains>
[0045] The grain diameter of the abrasive grain employed in the
embodiment of the present invention can be suitably determined in
view of the relation between the porosity and the degree of
concentration based on the above-described processing efficiency
and processing precision of grinding. For example, within the
above-stated ranges of grinding efficiency and processing precision
of grinding, it is suitable to use abrasive grains having an
average grain diameter ranging from 10 to 90 .mu.m, preferably 18
to 60 .mu.m, more preferably 20 to 55 .mu.m, and most preferably 25
to 45 .mu.m. With abrasive grains having an average grain diameter
of greater than or equal to 10 .mu.m, there is no problem with
adhesion between abrasive grains and processing efficiency of
grinding does not drop sharply. With abrasive grains having an
average grain diameter of less than or equal to 90 .mu.m, a
prescribed cutting edge spacing can be maintained and processing
precision can be improved.
[0046] The type of abrasive grain is not specifically limited other
than that the average grain diameter falls within the above-stated
range. For example, cBN abrasive grains, A-based (alumina-based),
and C-based (silicon carbide-based) abrasive grains can be
employed. When grinding the inner surface of a high-precision
component, cBN abrasive grains are preferably employed. One type of
abrasive grain may be employed alone, or two or more types may be
mixed for use.
[0047] When employing cBN abrasive grains as an abrasive grain, one
or more types of common abrasive grains and hollow inorganic
materials may be employed as a filler as needed. However, in that
case, the quantity of filler employed is suitably adjusted so that
the degree of concentration of the cBN abrasive grains ranges from
50 to 160.
[0048] Further, when employing diamond abrasive grains as an
abrasive grain, it is desirable to suitably set the types of
vitrified binder and pore-forming material and manufacturing
conditions such as the calcination temperature to prevent
deterioration of the diamond abrasive grains.
[0049] The degree of concentration of the abrasive grains is
suitably from 50 to 160, preferably from 75 to 150, and more
preferably from 100 to 125. Here, the term "degree of
concentration" means the ratio of abrasive grains in the grinding
stone. For example, in the case of diamond abrasive grains, 4.4
ct/cm.sup.3 is the degree of concentration of 100 corresponding to
25 volume percent. Accordingly, the degree of concentration of 200
corresponds to 50 volume percent. When abrasive grains having a
different density from diamond abrasive grains are employed, the
difference in density from diamond abrasive grains is taken into
account and the degree of concentration is established in
accordance with the above. When the abrasive grains are cBN
abrasive grains, in the same manner as diamond abrasive grains, the
degree of concentration of 100 corresponds to about 25 volume
percent and the degree of concentration of 200 to about 50 volume
percent.
[0050] In the embodiment of the present invention, the degree of
concentration is adjusted within a relatively low range of 50 to
160 as well as the porosity is adjusted within a range of 30 to 70
volume percent, as mentioned above, to maintain or increase a
prescribed chip pocket volume and prevent clogging and fusion of
the grinding stone during high-efficiency grinding.
<Vitrified Binder>
[0051] In the embodiment of the present invention, the vitrified
binder can be suitably selected based on the type of abrasive
grain. For example, when manufacturing a vitrified cBN grinding
stone employing cBN abrasive grains as an abrasive grain, the
vitrified binder can be, for example, borosilicate glass or
crystallized glass. An example of crystallized glass is one from
which willemite has been precipitated. To achieve adequate holding
strength, the coefficient of thermal expansion of the vitrified
binder desirably falls within a range of .+-.2.times.10.sup.-6
(1/K) (room temperature to 500.degree. C.) with respect to the
coefficient of thermal expansion of the abrasive grains.
[0052] When employing a vitrified binder for superabrasive grains
as a vitrified binder, the temperature for calcining grinding stone
starting materials containing binder is selected based on the type
of the vitrified binder for superabrasive grains employed. Since
the transition temperature of the vitrified binder for
superabrasive grains is lower than the transition temperature of
vitrified binders for common abrasive grains, the temperature of
calcining grinding stone starting materials containing vitrified
binder for superabrasive grains preferably falls within a range of
650 to 1,000.degree. C., more preferably within a range of 700 to
950.degree. C. At greater than or equal to 650.degree. C., a
grinding stone having a certain strength even after calcination is
obtained. At less than or equal to 1,000.degree. C., the
superabrasive grains do not deteriorate.
[0053] An example of a preferred composition of the vitrified
binder for superabrasive grains is SiO.sub.2:40 to 70 mass percent,
Al.sub.2O.sub.3:10 to 20 mass percent, B.sub.2O.sub.3:10 to 20 mass
percent, M.sup.1O:2 to 10 mass percent, and M.sup.2.sub.2O:2 to 10
weight percent. Here, M.sup.1 denotes one or more metals selected
from alkaline earth metals, and M.sup.2 denotes one or more metals
selected from alkali metals.
[0054] The content of vitrified binder can be suitably selected.
For example, the content thereof may fall within a range of 13 to
35 volume percent, preferably within a range of 18 to 22 volume
percent, with respect to the volume of the starting materials.
[0055] In the vitrified grinding stone according to the embodiment
of the present invention, it suffices for at least the portion
contributing to grinding to have the above-stated composition.
Accordingly, the vitrified grinding stone according to the
embodiment of the present invention includes, for example, those in
which a vitrified grinding stone portion containing abrasive grains
and vitrified binder is provided on a support surface made of
ceramic not containing abrasive grains.
[0056] Further, when the grinding stone according to the embodiment
of the present invention is a vitrified superabrasive grain
grinding stone, the additives normally employed in vitrified
superabrasive grain grinding stones, such as embrittling agents and
solid lubricants, can be incorporated in suitable quantity as
desired.
[0057] The vitrified grinding stone according to the embodiment of
the present invention may be wheel-shaped, cylinder-shaped,
rectangle-shaped and the like.
[Method of Manufacturing Vitrified Grinding Stone]
[0058] The method of manufacturing vitrified grinding stones
according to the embodiment of the present invention will be
described in greater detail below.
[0059] The manufacturing method according to the embodiment of the
present invention comprises steps of setting a processing
efficiency and a processing precision of grinding, and setting a
porosity, a degree of concentration of abrasive grains and an
abrasive grain diameter based on the processing efficiency and
processing precision. As regards the processing efficiency and
processing precision of grinding, porosity, degree of concentration
of abrasive grains, and abrasive grain diameter, those regarding
the above-described vitrified grinding stone may be employed
without alteration. Further, the abrasive grains, vitrified binder,
and pore-forming material employed in the vitrified grinding stone
according to the embodiment of the present invention set forth
above may be suitably employed as the abrasive grains, vitrified
binder, and pore-forming material in the manufacturing method
according to the embodiment of the present invention.
[0060] The manufacturing method according to the embodiment of the
present invention may comprise a calcinations step in which a
molded product containing at least an abrasive grain, vitrified
binder, and a pore-forming material is calcined to burn out the
pore-forming material. In the manufacturing method according to the
embodiment of the present invention, the method of calcining a
molded product containing at least an abrasive grain, vitrified
binder, and a pore-forming material is preferably one in which the
molded product is calcined by maintaining it at a certain
temperature for a certain period to burn out the pore-forming
material. Such a method is preferable in that the pore-forming
material burns out before the vitrified binder melts in the
calcination step, preventing calcination shrinkage and disruption
of the abrasive grain distribution caused by the binder and
abrasive grains moving about freely.
[0061] The period of maintaining mentioned above is preferably long
enough for the aforementioned pore-forming material contained in
the molded product to burn out. A period adequate for the
pore-forming material to burn out can be suitably set based on the
shape and dimensions of the grinding stone being manufactured.
[0062] When maintaining the aforementioned molded product at the
calcination temperature of the vitrified binder, it is maintained
at a certain temperature falling within the range of the
calcination temperature. So long as the temperature remains within
this calcination temperature range, variation in the temperature
(for example, a rise in temperature over time) is permissible.
[0063] The temperature that is maintained for a certain period
during calcination is preferably greater than or equal to the
burnout ending temperature of the pore-forming material (preferably
a temperature at least 5.degree. C. greater than the burnout ending
temperature, more preferably a temperature at least 10.degree. C.
greater than the burnout ending temperature). The temperature of
calcining the molded product (maximum temperature during
calcination) can be a temperature within the calcination
temperature range of the vitrified binder as well as higher than or
equal to the burnout ending temperature of the pore-forming
material.
[0064] In the manufacturing method according to the embodiment of
the present invention, the dimension of the molded product in the
course of calcining the molded product is preferably a dimension so
as to permit adequate burnout of the pore-forming material
employed. For example, in the case of a molded product in the form
of a rectangular parallelepiped, the thickness (the dimension in
which the rectangular parallelepiped is the thinnest) can be set to
less than or equal to 10 mm (preferably less than or equal to 5 mm,
more preferably less than or equal to 3 mm). As a further example,
when the molded product is in the shape of a cylinder, the edge
thickness (the thickness of the cylinder wall) can be made less
than or equal to 10 mm (preferably less than or equal to 5 mm, more
preferably less than or equal to 3 mm).
[0065] In the manufacturing method according to the embodiment of
the present invention, the atmosphere during calcination is one in
which the pore-forming material burns adequately. When the
pore-forming material is carbonaceous, an atmosphere containing
oxygen can be employed with air normally being adequate.
[0066] In the manufacturing method according to the embodiment of
the present invention, the step yielding the molded product can be
inserted before the calcination step.
[0067] The molded product is preferably obtained by mixing and
stirring starting materials comprising at least abrasive grains, a
vitrified binder powder, and a pore-forming material with a primary
binder such as an adhesive paste to obtain a mixture in which each
of the components has been uniformly dispersed, and molding this
mixture by pressing and drying.
[0068] When manufacturing a vitrified superabrasive grain grinding
stone, desired additives such as embrittling agents, solid
lubricants, and molding adjuvants that are commonly employed in
vitrified superabrasive grain grinding stones may be incorporated
into the above starting materials in suitable quantity.
[0069] The vitrified grinding stone obtained by the above
manufacturing method can be employed as a grinding stone in various
grinding devices. Even when the diameter of the object being ground
is small, high processing efficiency and processing precision of
grinding are achieved. Thus, it is suited to use in internal
grinding. Examples of applications of the grinding stone of
according to the embodiment the present invention include grinding
of the inner surfaces and sheet surfaces of the injection nozzles
of fuel injection devices and pressure regulators, and internal
grinding of the inner and outer wheels of bearings.
EXAMPLES
[0070] Examples according to the embodiment of the present
invention will specifically described below. Vitrified grinding
stones of Examples and Comparative Examples described below are
wheel-shaped ones.
[0071] Suitable modification of the materials, quantities employed,
ratios, processing contents, and processing sequences described in
Examples is possible without departing from the spirit of the
present invention. Accordingly, the scope of the present invention
must not be restrictively interpreted to the specific examples
below.
1. Manufacturing of Grinding Stone and Structure Thereof.
[0072] Starting materials of the following blend shown in Examples
1 to 3 and Comparative Examples 1 and 2 were press molded and
calcined in air for 24 hours at 900.degree. C. (during which they
were maintained at 900.degree. C. for one hour) to obtain vitrified
grinding stones. In Example 1, when the decrease in mass was
measured under the condition of raising a temperature of 10.degree.
C./min, the burnout starting temperature (a reduction of 10 mass
percent) of polymethyl methacrylate was found to be 300.degree. C.
and the burnout ending temperature (a reduction of 90 mass percent)
was found to be 500.degree. C. The transition temperature of the
vitrified binder employed was 550.degree. C. and the specific
calcination temperature was 850 to 950.degree. C.s. TABLE-US-00001
<Starting materials of Example 1 and blend thereof> cBN
abrasive grain 55.1 volume parts (average grain diameter: 30 .mu.m
(#600), degree of concentration: 160) Polymethyl methacrylate 17.4
volume parts (average grain diameter: 30 .mu.m, true specific
gravity: 1.2) Vitrified binder 27.5 volume parts Adhesive paste
14.5 volume parts
[0073] TABLE-US-00002 <Structure of grinding stone of Example 1
after calcination> cBN abrasive grain 40.0 volume parts Pore
40.0 volume parts Burnout pore (forced pore): 10.0 volume parts
Natural pore: 30.0 volume parts Ratio of pores having a size 1 to 3
times the average grain diameter of abrasive grain: 37 volume
percent Vitrified binder 20.0 volume parts
[0074] TABLE-US-00003 <Starting materials of Example 2 and blend
thereof> cBN abrasive grain 55.1 volume parts (average grain
diameter: 30 .mu.m (#600), degree of concentration: 160) Polymethyl
methacrylate 17.4 volume parts (average grain diameter: 5 .mu.m,
true specific gravity: 1.2) Vitrified binder 27.5 volume parts
Adhesive paste 14.5 volume parts
[0075] TABLE-US-00004 <Structure of grinding stone of Example 2
after calcination> cBN abrasive grain 40.0 volume parts Pore
40.0 volume parts Burnout pore (forced pore): 10.0 volume parts
Natural pore: 30.0 volume parts Ratio of pores having a size 0.1 to
1 time the average grain diameter of abrasive grain: 67 volume
percent Vitrified binder 20.0 volume parts
[0076] TABLE-US-00005 <Starting materials of Example 3 and blend
thereof> cBN abrasive grain 56.5 volume parts (average grain
diameter: 30 .mu.m (#600), degree of concentration: 160) Polymethyl
methacrylate 21.0 volume parts (average grain diameter: 5 .mu.m,
true specific gravity: 1.2) Vitrified binder 22.5 volume parts
Adhesive paste 14.5 volume parts
[0077] TABLE-US-00006 <Structure of grinding stone of Example 3
after calcination> cBN abrasive grain 40.0 volume parts Pore
40.0 volume parts Burnout pore (forced pore): 14.0 volume parts
Natural pore: 30.0 volume parts Vitrified binder 16.0 volume
parts
[0078] TABLE-US-00007 <Starting materials of Comparative Example
1 and blend thereof> cBN abrasive grain 55.1 volume parts
(average grain diameter: 30 .mu.m (#600), degree of concentration:
160) Carbonaceous beads (150 .mu.m) 17.4 volume parts Vitrified
binder 27.5 volume parts Adhesive paste 14.5 volume parts
[0079] TABLE-US-00008 <Structure of grinding stone of
Comparative Example 1 after calcination> cBN abrasive grain 43.7
volume parts Pore 40.0 volume parts Burnout pore (forced pore):
10.0 volume parts Natural pore: 30.0 volume parts Vitrified binder
16.3 volume parts
[0080] TABLE-US-00009 <Starting materials of Comparative Example
2 and blend thereof> cBN abrasive grain 69.2 volume parts
(average grain diameter: 30 .mu.m, degree of concentration: 180)
Vitrified binder 30.8 volume parts Adhesive paste 14.3 volume
parts
[0081] TABLE-US-00010 <Structure of grinding stone of
Comparative Example 2 after calcination> cBN abrasive grain 45.0
volume parts Pore (natural pore) 35.0 volume parts Vitrified binder
20.0 volume parts
[0082] FIGS. 1, 3 and 4 are enlarged schematic cross-sectional
views of the structures of the grinding stones of Example 1 and
Comparative Examples 1 and 2 obtained after calcination. As shown
in FIG. 1, the grinding stone according to the embodiment of the
present invention is a grinding stone in which cBN abrasive grains
1 are bonded by vitrified binder 3, and burnout pores (forced
pores) 2 and natural pores 4 are present. As shown in FIG. 3, the
grinding stone of Comparative Example 1 is a grinding stone in
which cBN abrasive grains 21 and burnout pores 22 are bonded by
vitrified binder 23, and pores 24 are present. As shown in FIG. 4,
the grinding stone of Comparative Example 2 is a grinding stone in
which cBN abrasive grains 31 are bonded by vitrified binder 32, and
pores 33 are present.
[0083] When the structure of the grinding stone according to the
embodiment of the present invention is compared to those of the
grinding stones of Comparative Examples, the grinding stone of
Example 1 shown in FIG. 1 has more uniformly dispersed abrasive
grains and pores and greater porosity than the grinding stones of
Comparative Examples 1 and 2. By contrast, the grinding stone of
Comparative Example 1 shown in FIG. 3, despite having good
porosity, has nonuniformly dispersed abrasive grains. The grinding
stone of Comparative Example 2 shown in FIG. 4 has nonuniform
abrasive grains and low porosity. This reveals that the grinding
stone according to the embodiment of the present invention is a
grinding stone having good chip pocket size while maintaining a
certain effective cutting edge spacing.
2. Evaluation of Vitrified Grinding Stone (1)
[0084] The grinding stones obtained in Example 1 and Comparative
Examples 1 and 2 were used to conduct internal grinding and the
relation between grinding efficiency ratio and the size of the
effective cutting edge spacing was examined. FIG. 7 gives the
results. The ground objects, the processing conditions, and the
dressing conditions are given below. TABLE-US-00011 <Ground
object> Material SCM415 Dimension Internal diameter .phi. 3.95
mm Grinding allowance .phi.0.05 mm
[0085] TABLE-US-00012 <Processing condition> Machine employed
Grinder for internal grinding Grinding type Wet oscillation
grinding Peripheral speed of grinding stone 22.6 m/s Peripheral
speed of ground object 0.5 m/s Grinding efficiency ratio 1-3.2
Oscillation Done Grinding oil Oil-based
[0086] TABLE-US-00013 <Dressing condition> Dresser .phi.50
square column rotary Dress depth of cut .phi. 1 .mu.m/pass Lead
0.004 mm/rev
[0087] In FIG. 7, for an identical effective cutting edge spacing
We (0.1 mm), it was possible to conduct normal grinding to a
grinding efficiency ratio up to 3.2 in Example 1. By contrast, it
was only possible to conduct normal grinding to a grinding
efficiency ratio up to 1.9 in Comparative Examples 1 and 2. This
reveals that for an identical processing precision of grinding, the
vitrified grinding stone according to the embodiment of the present
invention affords a processing efficiency of grinding of about 1.7
times that of conventional grinding stones.
3. Evaluation of Vitrified Grinding Stone (2)
[0088] Internal grinding was conducted at a processing efficiency
of grinding of 0.3 mm.sup.3/(mm sec) with the grinding stones
obtained in Examples 1 to 3 and Comparative Example 2, and the
power consumption, surface roughness, and abrasion were examined.
The change in power consumption is shown in FIG. 8A, the results of
surface roughness measurement are shown in FIG. 8B, and the results
of abrasion measurement are shown in FIG. 8C. The grinding stones
obtained in Examples 1 and 2 were used to conduct internal grinding
at a grinding efficiency of 0.7 mm.sup.3/(mm sec), and the power
consumption, surface roughness, and abrasion were examined. The
change in power consumption is shown in FIG. 9A, the results of
surface roughness measurement are shown in FIG. 9B, and the results
of abrasion measurement are shown in FIG. 9C. However, the grinding
stone of Comparative Example 2 underwent fusion during processing
immediately after dressing, precluding subsequent evaluations.
TABLE-US-00014 <Ground object> Material SUJ-2 Dimension
Internal diameter .phi. 28.3 mm Grinding allowance .phi.0.36 mm
[0089] TABLE-US-00015 <Processing condition> Machine employed
Grinder for internal grinding Grinding type Wet oscillation
grinding Peripheral speed of grinding stone 45 m/s Peripheral speed
of ground object 1.25 m/s Oscillation Done Grinding oil
Water-soluble
[0090] TABLE-US-00016 <Dressing condition> Dresser .phi.25
square column rotary Dress depth of cut .phi. 4 .mu.m/pass Lead
0.030 mm/rev
(i) Power Consumption
[0091] As shown in FIG. 8A, the grinding stone of Comparative
Example 2 exhibited extremely high power consumption during initial
grinding and fused, precluding subsequent grinding. By contrast, as
shown in FIGS. 8A and 9A, the grinding stones of Examples 1 to 3
exhibited low levels of power consumption that were maintained
stably during grinding without fusion, permitting continuous
grinding.
(ii) Surface Roughness
[0092] As shown in FIG. 8B, the grinding stones of Examples 1 to 3
achieved a processing precision of grinding of less than or equal
to 0.7 Rz (.mu.m) at a processing efficiency of grinding of 0.3
mm.sup.3/(mmsec).
[0093] Further, as shown in FIG. 9B, the grinding stones of
Examples 1 and 2 achieved a processing precision of grinding of
less than or equal to 0.8 Rz (.mu.m) at a processing efficiency of
grinding of 0.7 mm.sup.3/(mmsec).
(iii) Abrasion
[0094] Comparing Examples 1 and 2 as shown in FIGS. 8C and 9C, the
grinding stone of Example 2, which had a pore-forming material of
smaller diameter (that is, smaller forced pores), had greater
strength and thus underwent less abrasion. Comparing Examples 2 and
3, in which a pore-forming material of identical diameter was
employed, as shown in FIG. 8C, the grinding stone of Example 2,
which contained more binder, was harder and thus underwent less
abrasion.
[0095] As set forth above, the vitrified grinding stone according
to the embodiment of the present invention has a porosity, degree
of concentration of abrasive grains, and abrasive grain diameter
that are based on preset processing efficiency and processing
precision of grinding. Thus, the grinding stone according to the
embodiment of the present invention affords precision processing of
roughness of surfaces being processed while improving processing
efficiency of grinding, formerly considered to be contradicting
indicators of grinding stones.
[0096] In the method of manufacturing a vitrified grinding stone
according to the embodiment of the present invention, the
processing efficiency and processing precision of grinding are
preset. Based on the processing efficiency and processing precision
of grinding, the porosity, degree of concentration of abrasive
grains, and abrasive grain diameter are set. Thus, the method of
manufacturing according to the embodiment of the present invention
permits uniform distribution of abrasive grains and pores within
the grinding stone, thereby permitting the manufacturing of
grinding stones affording both processing efficiency and processing
precision of grinding.
[0097] According to the embodiments of the present invention, a
vitrified grinding stone in which a prescribed porosity is
maintained and the pores and abrasive grains are uniformly disposed
even when small-diameter abrasive grains are employed is
provided.
[0098] According to the embodiments of the present invention, a
method of manufacturing vitrified grinding stones capable of
maintaining a prescribed porosity in the grinding stone and
achieving uniform dispersion of abrasive grains and pores in the
grinding stone even when small-diameter abrasive grains are
employed is provided.
[0099] In the embodiments of the present invention, the processing
efficiency and processing precision of grinding are preset. Thus,
the embodiments of the present invention can provide both a
vitrified grinding stone having a porosity, degree of concentration
of abrasive grains, and abrasive grain diameter based on the
aforementioned processing efficiency and processing precision of
grinding, and a method of manufacturing the same. For example, the
embodiments of the present invention can provide a grinding stone
having good processing precision of less than or equal to 1.0 Rz
(.mu.m) even at a processing efficiency of grinding of greater than
or equal to 0.3 mm.sup.3/(mmsec). Further, the embodiments of the
present invention can provide a grinding stone in which abrasive
grains and pores are uniformly dispersed and the degree of
concentration is maintained at 50 to 160 with a porosity of 30 to
70 volume percent by containing a forced porosity of 5 to 35 volume
percent based on burnout pores even when small-diameter abrasive
grains having an average grain diameter of 10 to 90 .mu.m are
employed. As a result, the embodiments of the present invention
affords a uniform cutting edge spacing comparable to that of
large-diameter abrasive grains even when employing small-diameter
abrasive grains, and maintains the chip pocket volume. Thus, it
provides both a vitrified grinding stone in which clogging tends
not to occur during grinding, fusion is prevented, and both
grinding processing efficiency and grinding processing precision
are achieved, and a method of manufacturing the same.
[0100] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *