GB2309184A

GB2309184A - Grinding wheels

Info

Publication number: GB2309184A
Application number: GB9700570A
Authority: GB
Inventors: Fuko Murai
Original assignee: Musashi Seimitsu Industry Co Ltd
Current assignee: Musashi Seimitsu Industry Co Ltd
Priority date: 1996-01-16
Filing date: 1997-01-13
Publication date: 1997-07-23
Also published as: JPH09193024A; GB9700570D0; ID15830A

Description

GRINDING WHEEL BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a grinding wheel to be used for grinding operation, and particularly to a grinding wheel having a plurality of grinding members on its peripheral grinding surface.

Description of the Prior Art Conventionally, diamond abrasive particles or cubic boron nitride (CBN) abrasive particles such as Borazon (commercially available from General Electric Company, U.S.A.) are often used for the grinding members on the grinding wheel. These particles are useful because they are extremely hard and their grinding loss is small; however, as they are expensive, not the whole body of a grinding wheel is formed of such material. More particularly, arcuate grinding members containing the above abrasive particles have been affixed to the outer circumference of a disk-shaped grinding wheel body made of, for example, a carbon steel, pig iron, an aluminum alloy or others.

On the circumference of the grinding wheel small gaps are defined between adjacent grinding members affixed to the outer circumference of the grinding wheel body. These gaps extend parallel to the rotational axis of the grinding wheel. The gaps are provided in consideration of thermal expansion of the grinding wheel body due to heat produced during the grinding and thermal contraction of the grinding wheel body due to stop of the grinding operation. These gaps 123 absorb thermal expansion and contraction and function to suppress load that may be applied to the grinding members. Moreover, as the case may be, a bonding agent is filled in the gaps 123 for affixing the grinding members to the outer circumference of the grinding wheel body.

Such a grinding wheel is disclosed, for instance, in Japanese Patent Laid-Open Publication No. Hei-3-104566 published May 1, 1991.

When a workpiece is ground with the grinding wheel as described above, the surface to be ground is finished to become a very smooth surface, because diamond abrasive particles or cubic boron nitride (CBN) abrasive particles are used for the grinding members of the grinding wheel.

In such grinding wheel, however, ground chips produced by the grinding will enter the gaps for absorbing thermal expansion and contraction. The ground chips that have entered and deposited in the gaps will come into contact with the surface being ground of a workpiece and reduce the grinding quality.

It is thus required to remove periodically such ground chips deposited in the gaps to prevent deterioration of the grinding quality and precision. However, this periodic removal of deposited ground chips in the gaps results in stopping of the grinding operation during the exchange of the grinding wheel, and hence reduces the grinding efficiency.

SUMMARY OF THE INVENTION The object of the present invention is to solve the problems as mentioned above, and to provide a grinding wheel which can prevent drop of the grinding efficiency while maintaining a high grinding precision.

According to the present invention, there is provided a grinding wheel comprising a disk-shaped grinding wheel body for mounting to a rotating shaft, and a plurality of adjoining arcuate grinding members affixed to and along an outer circumference of the grinding wheel body, wherein the grinding members have circumferential end faces slanting with respect to the direction of width of the disk-shaped grinding wheel body and a gap is defined between adjacent end faces of adjoining grinding members, said gap also slanting with respect to the direction of width.

The slanting of the gap is effective to promote removal of ground chips deposited therein because the slanting of the gap enables the ground chips in the gap to be subjected to a component, along the gap, of the rotational force of the grinding wheel, which component force acts on the ground chips to expel the same out of the gap.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view of the grinding wheel according to an embodiment of the invention; Figure 2 is a view, as seen from radially outside, of a portion of the grinding wheel of Figure 1; Figure 3 is an explanatory view of a portion of the grinding wheel, showing particularly grinding members; Figure 4 is a plan view showing a state before the grinding using the grinding wheel of Figure 1; Figure 5 is a plan view showing a state during the grinding using the grinding wheel of Figure 1; Figure 6 shows a modified embodiment of the invention; Figure 7 shows a further modified embodiment of the invention; Figure 8 shows a still further modified embodiment of the invention; Figure 9 shows a grinding wheel having grinding members of dual-layer structure; Figure 10 is a front view of a conventional grinding wheel; and Figure 11 is a view showing a portion of the conventional grinding wheel of Figure 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will now be described with reference to Figures 1 through 6.

Figure 1 shows a grinding wheel 1 in a preferred embodiment of the present invention. The grinding wheel 1 comprises a disk-shaped grinding wheel body 11 with a central mounting hole 12 to be attached to a rotation shaft not shown, and a plurality of arcuate grinding members 21 affixed to and along the outer circumference of the grinding wheel body 11. The grinding wheel body 11 is made of, for example, a carbon steel, pig iron, an aluminum alloy or others. On the other hand, each of the grinding members 21 constituting a cylindrical grinding surface 25 is molded by binding abrasive particles of diamond or cubic boron nitride (CBN) such as Borazon (commercially available from General Electric Company, U.S.A.) with a sintering method using a vitrified binder.As shown in Figure 2, the shape of the grinding members 21 is, when viewed from radially outside of the grinding wheel, a parallelogram having opposite end faces 22 slanting with respect to the direction of the width w of the grinding wheel body or with respect to the circumferential direction of the grinding wheel body. The grinding members 21 are affixed, as shown in Figure 3, to the circumferential surface of the grinding wheel body 11 by means of an adhesive or the like. Here, uniform gaps 23 are defined between adjoining grinding members 21. It is to be noted that the gaps 23 extend obliquely to the direction of width of the grinding wheel body 11.This is a unique feature of the present invention, which is different from the feature of the conventional grinding wheel shown in Figures 10 and 11, in which the grinding wheel 101 comprises a wheel body 111 and grinding members 121 having therebetween gaps 123 extending in parallel with the rotational axis of the grinding wheel.

Next, referring to Figure 4 and Figure 5, a method for grinding a grinding surface 52 of a workpiece 51 with said grinding wheel 1 will be described.

Figure 4 shows a state of a grinding device 31 having the grinding wheel 1 prior to the grinding of a workpiece 51. The grinding device 31 comprises the grinding wheel 1, a rotation shaft 32 fitted in the mounting hole 12 of the grinding wheel 1, fixing members 33, 34 disposed at opposite sides of the grinding wheel with respect to the axial direction for holding the grinding wheel 1, and a nut 35 for keeping the grinding wheel 1 held between the fixing members 33, 34 by screw engagement with a male screw 32a formed at an end portion of the rotation shaft 32. The workpiece 51 is, for example, a shaft member such as cam shaft, and is supported by a workpiece support (not shown).

For the grinding operation using the grinding device 31, the grinding device 31 is disposed so that the grinding wheel 1 faces the surface 52 to be ground of the workpiece 51, and the rotation shaft 32 is driven to rotate the grinding wheel 1. Then, the grinding device 31 approaches the workpiece 51, and as shown in Figure 5, the grinding is carried out when the grinding wheel 1 comes in contact with the surface 52 of the workpiece 51. During this grinding operation, ground chips of the workpiece 51 may enter the gaps 23 between adjoining grinding members 21 on the grinding wheel 1.However, as the end faces 22 of the grinding members 21 in the circumferential direction thereof extend so as to be slanting in the width direction, ground chips that have entered the gaps 23 during the grinding operation are forced to be moved to the outside along the slanting gaps 23 due to a component of the rotational force of the grinding wheel 1 that is turning at high speed. It is to be noted that if the gaps 23 extended as in the case of Figures 10 and 11, no such component force would be produced to expel the ground chips from within the gaps. When a prescribed amount of the surface 52 of the workpiece 51 is removed by the grinding, the grinding device 31 returns to the initial position to terminate the grinding. Thus, the grinding wheel described above is effective to prevent ground chips from depositing in the gaps 23.

While, in the embodiment described above, the end faces 22 of each grinding member 21 slant in the same direction, they may slant in mutually opposite directions as shown in Figure 6. By the slanting of the end faces 22 in the opposite directions, ground chips that have entered the gaps 23 are subjected to components of the rotational force along the different slanting directions and are forced to move out of the gaps 23 therealong.

Figure 7 shows another embodiment of the present invention, in which the slanting gaps 23 do not extend linearly but extend curvilinearly. The gaps 23 may curve concavely in the same circumferential direction as shown.

Alternatively, the gaps 23 may be concave in the opposite circumferential direction as shown in Figure 8. The embodiment of Figure 8 is a combination of the embodiment of Figure 6 and the curved configuration of the gaps 23.

Figure 9 shows an embodiment of the invention in which each grinding member 21 has a dual layer structure comprising an outer layer 21a and an inner layer 21b. The outer layer 21a is made of the same material as the grinding members 21 described before, and the inner layer 21b may be made of a conventional grinding wheel material containing an aluminium oxide (alumina), for example. The inner layer 21b is provided to prevent direct contact of the grinding wheel body 11 with the workpiece being ground in the event of an accidental damage of the outer layer 21a.

The diameter of the grinding wheel 1 is generally in the range from 200 to 1200 millimeters. The width of the gaps 23 is from 1 to 3 millimeters. The depth of the gaps 23 is about 3 millimeters. This means that the radial thickness of the grinding members 21 is about 3 millimeters. The adhesive used for attaching the grinding members 21 to the grinding wheel body 11 is typically an epoxy resin adhesive. The same adhesive may be used for attaching the outer and inner layers 21a and 21b shown in Figure 9. The cross-sectional shape of the gaps 23 is typically rectangular but may be semi-circular or radially outwardly diverging trapezoidal.

Tests were conducted for comparing the grinding performance of a grinding wheel according to the present invention with that of the conventional grinding wheel with the following results.

Conditions of the tests 1. Rotational speed of the grinding wheel: 4280 rpm 2. Workpiece: Cam shaft (largest cam diameter 36.5 mm) 3. Workpiece mounting shaft speed: 60 rpm 4. Grinding wheel: 80-M-200 CBN (Product of Noritake Co., Ltd. Japan) 5. Amount of grinding: 3 mm 6. Angle formed between the gaps and the circumferential line of the wheel: 45C Maximum surface roughness of the ground surfaces of the cams TABLE

The invention Conventional (pm) (pom) 1. 1st cam after 2.087 2.375 truing-dressing 2. 800th cam after 4.125 3.300 truing-dressing 3. 1120th cam after 3.862 3.637 truing-dressing 4. 1280th cam after 4.362 4.337 truing-dressing It will be noted from the above comparison table that there is no substantial difference in the maximum surface roughnesses between the cam surfaces ground by the grinding wheel of the invention and by the conventional grinding wheel.

However, there was a remarkable difference in the time required for obtaining the above listed surface roughnesses. More specifically, in the case of using the grinding wheel of the invention, the time needed for grinding each cam was 22 seconds, while in the case of using the conventional grinding wheel, the time need for grinding each cam was 30 seconds.

It was found that there was no substantial difference in grinding the exact profile of each cam between the grinding wheel of the invention and the conventional grinding wheel. However, there was a remarkable difference in the quality of the ground surface. More specifically, in all of the cases 1 to 4 in the above table, cam surfaces ground by the grinding wheel of the invention did not have any grinding burn and minute cracks, whereas cam surfaces ground by the conventional grinding wheel had sometimes a grinding burn and minute cracks. This difference is considered to be obtained because ground chips are prevented from depositing in the gaps in the present invention.

According to the present invention described above, the gaps between adjacent arcuate grinding members are formed to slant in the width direction of the grinding wheel, so that ground chips that have entered the gaps during the grinding are moved outside the gaps along the slanting gaps by a component, along the gaps, of the rotational force of the grinding wheel turning at high speed. Therefore, ground chips do not deposit in the gaps, whereby a high grinding efficiency is achieved. Moreover, as ground chips do not deposit in the gaps, no work for the removal of ground chips is necessary so that decrease of the grinding operation due to the chip removal work can be avoided.

Claims

What is claimed is:

1. A grinding wheel comprising: a disk-shaped grinding wheel body; a plurality of arcuate grinding members fixed to an outer circumference of the grinding wheel body and each having opposite circumferential end faces extending obliquely to the direction of axial width of the grinding wheel body; and the end faces of circumferentially adjoining grinding members defining slanting gaps that extend obliquely to said direction of axial width.

2. The grinding wheel according to claim 1, wherein said gaps extend linearly.

3. The grinding wheel according to claim 1, wherein said gaps extend curvilinearly.

4. The grinding wheel according to claim 1 or claim 2, wherein said gaps at opposite ends of each of the grinding members extend in parallel.

5. The grinding wheel according to any one of claims 1 to 3, wherein said gaps at opposite ends of each of the grinding members extend obliquely with opposition inclinations.

6. The grinding wheel according to any preceding claim, wherein each of said grinding members comprises a radially outer layer and a radially inner layer.

7. The grinding wheel according to any preceding claim, wherein said gaps have a width of from 1 to 3 millimetres.

8. The grinding wheel according to any preceding claim wherein said gaps have a depth of about 3 millimetres.

9. A grinding wheel substantially as any one described herein with reference to figures 2, 3, 4 and 5, or figure 6, or figure 7, or figure 8, or figure 9.