Abrading – Rigid tool – Rotary cylinder
Reexamination Certificate
2003-03-03
2004-12-07
Hail, III, Joseph J. (Department: 3723)
Abrading
Rigid tool
Rotary cylinder
C451S541000, C451S542000, C451S546000, C451S547000
Reexamination Certificate
active
06827641
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to improvements in a grindstone or grinding wheel to be used in a thru-feed centerless grinding operation.
2. Discussion of the Related Art
As a type of industrial grindstone, there is known a grinding wheel which is to be brought into sliding contact with a workpiece while being rotated about its axis, so that a surface of the workpiece is ground by an abrasive layer which is provided by an outer circumferential surface of the grinding wheel. The abrasive layer has a longer service life where the abrasive layer is formed of so-called “super abrasive grains” such as diamond abrasive grains and CBN (cubic boron nitrides) abrasive grains, than where the abrasive layer is formed of standard abrasive grains such as alumina abrasive grains and silicone carbide abrasive grains. Where the abrasive layer is formed of the super abrasive grains, the abrasive layer has a relatively small thickness, in general, due to a relative expensiveness of the super abrasive grains. In recent years, the grinding wheel having the abrasive layer formed of the super abrasive grains is widely used, thereby contributing to an unmanned or automated grinding operation in a machining industry. Therefore, the grinding wheel of the super abrasive grains is employed in various fields of industry, and is an object of further research and development for further improvement of its grinding performance.
As an example of a grinding operation in which the above-described grinding wheel is employed, there is known a centerless grinding operation in which a cylindrical workpiece is not supported on its centers but rather by a work rest blade, a regulating wheel and the grinding wheel, so that the cylindrical workpiece is ground mainly at its outer circumferential surface by the grinding wheel.
FIG. 1
is a view illustrating a thru-feed centerless grinding operation in which cylindrical workpieces
14
are successively fed to a grinding zone in which each of the workpieces
14
is actually ground at its outer circumferential surface by the grinding wheel in the form of a segment-chip-type grinding wheel
10
. The workpieces
14
, which are disposed on the work rest blade
18
(which is positioned between the grinding wheel
10
and the regulating wheel
12
) and are guided by work rest guides
16
, are successively moved or fed in a predetermined feed direction, i.e., a longitudinal direction as indicated by the arrow, while being gripped by and between the grinding wheel
10
and the regulating wheel
12
. In this instance, the regulating wheel
12
and the grinding wheel
10
are rotated in the same direction, namely, the clockwise direction as seen in the above-described feed direction. Described more specifically, the regulating wheel
12
is rotated for rotating workpieces
14
at a relatively low speed, while the grinding wheel
10
is rotated at a relatively high speed, whereby the outer circumferential surfaces of the workpieces
14
are grounded by an abrasive layer provided by an outer circumferential surface of the grinding wheel
10
.
In the above-described thru-feed centerless grinding operation, the workpieces
14
are fed at a feed rate of, for example, about 5-10 m/min in the feed direction indicated by the arrow. The work rest guides
16
guiding the workpieces
14
are positioned in the upstream and downstream sides of the wheels
10
,
12
as viewed in the feed direction. Each of the work rest guides
16
is not held in contact with the wheels
10
,
12
but is necessarily spaced apart from the wheels
10
,
12
as viewed in the feed direction. Due to the spacing region between an upstream side one of the work rest guides
16
and the wheels
10
,
12
, each workpiece
14
fed in the feed direction could be momentarily shaken or oscillated in a direction perpendicular to the feed direction, when the workpiece
14
is passing an entrance of the grinding zone, i.e., an upstream end portion of the grinding wheel
10
. Upon initiation of contact of the workpiece
14
(at its forward end portion) with the grinding wheel
10
, the grinding wheel
10
receives at its upstream end portion an impact or shock from the workpiece
14
, thereby possibly causing a large amount of wear in the upstream end portion of the grinding wheel
10
. Similarly, due to the spacing region between a downstream side one of the work rest guides
16
and the wheels
10
,
12
, each workpiece
14
could be oscillated when the workpiece
14
is passing an exit of the grinding zone, i.e., a downstream end portion of the grinding wheel
10
. This shaking or oscillating motion of the workpiece
14
in the exit of the grinding zone is likely to cause a deterioration in a machining accuracy of the grinding operation.
SUMMARY OF THE INVENTION
The present invention was made in the light of the background art discussed above. It is therefore an object of the present invention to provide a cylindrical grindstone or grinding wheel which is capable of grinding a workpiece with a high degree of machining accuracy without suffering from a large amount of wear in its local portion. This object of the invention may be achieved according to any one of the first through tenth aspects of the invention which are described below.
The first aspect of this invention provides a grinding wheel comprising: a cylindrical main body having a grinding surface on an outer circumferential surface thereof; and a pair of synthetic resin layers disposed on respective axially opposite end faces of the cylindrical main body, each of the synthetic resin layers covering at least a radially outer end or peripheral portion of a corresponding one of the axially opposite end faces.
In the grinding wheel according to this first aspect of the invention, the synthetic resin layers are provided on the respective axially opposite end faces of the cylindrical main body such that each of the synthetic resin layers covers at least the radially outer end portion of the corresponding one of the axially opposite end faces. This arrangement is advantageous in the above-described thru-feed centerless grinding operation, because the synthetic resin layers serve to reduce the problematic oscillating motion of the workpiece upon its entrance into the grinding zone and also upon its exit from the grinding zone, thereby making it possible to grind the workpiece with a high degree of machining accuracy without suffering from a large amount of wear in a local portion of the grinding wheel.
According to the second aspect of the invention, in the grinding wheel defined in the first aspect of the invention, the cylindrical main body has an abrasive layer which constitutes a radially outermost layer thereof so that the abrasive layer provides the grinding surface.
According to the third aspect of the invention, in the grinding wheel defined in the second aspect of the invention, each of the synthetic resin layers has an elastic modulus lower than that of the abrasive layer.
According to the fourth aspect of the invention, in the grinding wheel defined in any one of the first through third aspects of the invention, the synthetic resin layers have respective elastic moduli which are different from each other.
In the thru-feed centerless grinding operation, a position of the regulating wheel relative to the grinding wheel may be adjusted such that a spacing distance between the two wheels is not constant as viewed in the feed direction. For example, the spacing distance may be larger in the entrance of the grinding zone, than in the exit of the grinding zone, so that the diameter of the workpiece is gradually reduced as the workpiece is fed through the grinding zone in the feed direction. In this case, the diameter of the workpiece is approximated to a target dimension by grinding the workpiece with the upstream end and intermediate portions of the grinding wheel, and then the diameter is reduced precisely to the target dimension by grinding the workpiece with the downstream end portion of the grinding w
Nomura Takashi
Yoshida Kazumasa
Grant Alvin J
Hail III Joseph J.
Noritake Co. Ltd.
Oliff & Berridg,e PLC
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