Abrasive tool making process – material – or composition – With inorganic material
Reexamination Certificate
2002-08-14
2003-07-08
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
C051S295000, C051S298000, C051S308000, C051S309000, C051S293000
Reexamination Certificate
active
06589304
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of bonding a porous abrasive solid mass to a desired member and a method of manufacturing a grindstone or grinding wheel. More particularly, the present invention is concerned with techniques for preventing an adhesive from penetrating into pores of the porous abrasive solid mass when the porous abrasive solid mass is bonded to the base member.
2. Discussion of the Related Art
There is known a grinding wheel including: a base disk; and a multiplicity of abrasive segment chips which are fixed to the base disk so as to be arranged on a circle whose center corresponds to the axis of the base disk. In a grinding operation with this grinding wheel, the base disk is rotated about the axis, so that a workpiece is ground by the abrasive segment chips. One example of such a grinding wheel is disclosed in JP-A-H11-300626 (publication of unexamined Japanese Patent Application laid open in 1999). In such a grinding wheel, it is common that the abrasive segment chips are bonded to the base disk with an epoxy resin adhesive or other adhesive as in the example disclosed in JP-A-H10-316952 (publication of unexamined Japanese Patent Application laid open in 1998).
However, where each of the abrasive segment chips has a porous abrasive structure such as a vitrified CBN abrasive structure in which super abrasive grains of cubic-crystal boron nitride are held together by a vitrified bond, the adhesive used for bonding the abrasive segment chips to the base disk is likely to penetrate into pores of the porous abrasive structure, thereby deteriorating a grinding capacity of the grinding wheel.
FIG. 6
shows a segment-chip-type grinding wheel
100
in which a multiplicity of arcuate abrasive segment chips
104
are disposed on an outer circumferential surface of a base disk
102
having an axis O, with a minimized gap between each adjacent pair of the abrasive segment chips
104
as viewed in a circumferential direction of the base disk
102
. The arcuate abrasive segment chips
104
are bonded to each other and also to the outer circumferential surface of the base disk
102
by a suitable adhesive
105
. Owing to the minimized gap between each adjacent pair of the abrasive segment chips
104
, the abrasive segment chips
104
can be successively brought into contact with a workpiece, thereby making it possible to grind the workpiece with a high machining accuracy. However, if each of the abrasive segment chips
104
has a porous abrasive structure in which abrasive grains
106
are held together by bond bridges
108
as a boding agent and in which a multiplicity of pores
110
are formed between the abrasive grains
106
, as shown in
FIG. 7
, the adhesive
105
is likely to penetrate into the pores
110
after the adhesive
105
is applied to the abrasive segment chips
104
. That is, since the adhesive
105
inherently has a certain degree of fluidity before the adhesive
105
is hardened or cured, the adhesive
106
very probably penetrates into the pores
110
, whereby a volume ratio of the pores
110
to the abrasive grains
106
is reduced, particularly, in circumferentially opposite end portions of each abrasive segment chip
104
.
Thus, the actual volume ratio of the pores
110
to the abrasive grains
106
tends to be smaller than a target volume ratio which is predetermined depending upon a kind of workpiece to be ground by the grinding wheel
100
and a desired grinding condition in which the workpiece is ground by the grinding wheel
100
. Each abrasive segment chip
104
has, in its opposite end portions, relatively dense abrasive structure portions in which the volume ratio of the pores
110
to the abrasive grains
106
is relatively small, so that the dense abrasive structure portions of the abrasive segment chips
104
are intermittently brought into contact with the workpiece during a grinding operation with the grinding wheel
100
. The dense abrasive structure portions provide a larger grinding resistance than the other portions. Further, the dense abrasive structure portions are poor in a so-called self-sharpening capability or spontaneous edge-forming capability for spontaneously restoring sharpness of each abrasive grain
106
. Therefore, the opposite end portions of each abrasive segment chip
104
(that are located near joint lines at which each abrasive segment chip
104
is bonded to the adjacent abrasive segment chips
104
) are likely to be worn in a larger amount than the other portions, and are likely to be broken with a larger possibility than the other portions, so that the abrasive segment chips
104
are brought into contact with the workpiece in an intermittent manner rather than in a successive manner. The intermittent contact of the abrasive segment chips
104
with the workpiece causes a periodic vibration, which might cooperate with a proper vibration of a grinding machine to cause a resonance vibration, thereby deteriorating a machining accuracy.
In general, the adhesive tends to penetrate into the pores located in a radially inner portion of each abrasive segment chip
104
(at which portion each abrasive segment chip
104
is bonded to the base disk
102
), as well as into the pores located in the circumferentially opposite end portions of each abrasive segment chip
104
. That is, each abrasive segment chip
104
has the relatively dense abrasive structure portion also in its radially inner portion. As the outside diameter of the grinding wheel
100
is reduced, namely, as a radially outer portion of each abrasive segment chip
104
is worn as a result of repeated use of the grinding wheel
100
, the dense abrasive structure portion is eventually exposed to an outer circumferential surface of each abrasive segment chip
104
, so that the dense abrasive structure portion is brought into contact with the workpiece, for thereby causing glazing on the outer circumferential surface of each abrasive segment chip
104
and accordingly deteriorating a machining accuracy. This problem is encountered not only in the segment-chip-type grinding wheel
100
as shown in
FIG. 6
but also in other type of grinding wheels such as a tubular-body-type grinding wheel
124
as shown in
FIG. 8
in which a tubular abrasive body
120
as the porous abrasive solid mass is bonded to an arbor
122
as the base member with an adhesive.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide techniques for preventing an adhesive which is used for bonding a porous abrasive solid mass to a desired member, from penetrating into pores of the porous abrasive solid mass, so as to avoid deterioration of a grinding capacity of the abrasive solid mass. This object of the invention may be achieved according to any one of the first through twelfth aspects of the invention which are described below.
The first aspect of this invention provides a method of bonding an abrasive solid mass to a desired member with an adhesive, wherein the abrasive solid mass has a porous abrasive structure in which a multiplicity of abrasive grains are held together by a bonding agent, the method comprising: a sealing-film forming step of forming a sealing film on a surface of the abrasive solid mass, for preventing the adhesive from penetrating into pores which are located between the abrasive grains in the porous abrasive structure. It is noted that the above-described desired member may be provided by a base member such as a base disk or cylindrical base body, or may be provided by another abrasive solid mass.
According to the second aspect of the invention, the method defined in the first aspect of the invention further comprising a bonding step of bonding the abrasive solid mass to the desired member with the adhesive, by heating the adhesive up to a predetermined setting temperature, wherein the sealing film is formed of a material having a softening point or temperature which is lower than a softening point or temperature of the bonding agent and which is higher than the
Kondo Tomoharu
Nakagawa Toshimichi
Yoshida Kazumasa
Marcheschi Michael
Noritake Co. Ltd.
Oliff & Berridg,e PLC
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