Description of the Prior Art As well known to those skilled in the art, diamond tools are typically classified into three types: metal bond tools, resinoid tools and vitrified,tools. Of the above diamond tools, both the metal bond and resinoid tools have been more widely used than the vitrified tools. The metal bond tools are suitable for grinding relatively rough surfaces, while the resinoid tools are suitable for grinding relatively fine surfaces.

However, such metal bond tools or resinoid tools are not suitable for rapidly grinding hard surfaces of materials with high abrasion resistance, such as super-precision machine parts, electronic parts and optical parts. Therefore, wheel-

type vitrified diamond tools and CBN (cubic boron nitride) tools are proposed and used for grinding such hard surfaces.

Such vitrified diamond tools or CBN tools are provided with both excellent grinding ability and high economical efficiency, thus having been more widely and effectively used.

The inventor of this invention proposed a method of producing vitrified diamond tools in Korean Patent Appln. No.

96-20014. Vitrified diamond tools, which are produced through the above method, have both excellent grinding ability and high economical efficiency and effectively resist against static pressure, but they are fragile, thus being easily broken even by low impact and being rarely used for general use.

Another problem of the above vitrified diamond tools resides in that it is necessary to separately dress a ground surface using resinoid tools in a grinding process.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a vitrified diamond wheel with both excellent grinding ability and high impact resistance.

Another object of the present invention is to provide a

vitrified diamond wheel which removes a process of separately dressing a ground surface in a grinding process.

In an embodiment, the present invention provides a vitrified diamond wheel, comprising: a wheel-type iron shank; and a vitrified layer provided on the top surface of the iron shank, the vitrified layer including: a grinding member made of vitrified diamond; and inside and outside protection rings provided at inside and outside edges of the grinding member for protecting the grinding member from impact.

In another embodiment, the present invention provides a vitrified diamond wheel, comprising: a wheel-type iron shank; and a plurality of vitrified grinding pieces provided on the top surface of the iron shank, each of the grinding pieces including: a grinding member made of vitrified diamond; and a protection ring provided at the edge of the grinding member for protecting the grinding member from impact.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a perspective view of a vitrified diamond wheel in accordance with the primary embodiment of the present

invention; Fig. 2 is a sectional view of the vitrified diamond wheel taken along the line A-A of Fig. 2; Fig. 3 is a sectional view of a vitrified diamond wheel in accordance with the primary embodiment of the present invention having another structure of the grinding member; Figs. 4a and 4b are views of a vitrified diamond wheel in accordance with the second embodiment of the present invention, in which: Fig. 4a is a plane view of the wheel; and Fig. 4b is a perspective view of a grinding piece of the wheel; Figs. 5a and 5b are views of a vitrified diamond wheel in accordance with the third embodiment of the present invention, in which: Fig. 5a is a plane view of the, wheel; and Fig. 5b is a perspective view of a grinding piece of the wheel; and Figs. 6a and 6b are views of a vitrified diamond wheel in accordance with the fourth embodiment of the present invention, in which: Fig. 6a is a plane view of the wheel; and Fig. 6b is a perspective view of a grinding piece of the wheel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Figs. 1 and 2 are perspective and sectional views of a vitrified diamond wheel in accordance with the primary embodiment of the present invention, respectively. As shown in the drawings, the vitrified diamond wheel 10 of this invention comprises a wheel-type iron shank 2 and an annular vitrified layer provided on the top surface of the iron shank 2.

The above vitrified layer includes an annular grinding member 3, which is made of vitrified diamond. The annular grinding member 3 is tightly sided by two impact protection rings 4 and 5 at the inside and outside edges. Each of the two impact protection rings 4 and 5 is securely attached to both the iron shank 2 and the grinding member 3. In order to detachably mount the diamond wheel 10 to the rotating shaft (not shown) of a grinding machine and allow the wheel 10 to rotate with the shaft, a plurality of bolt holes 6 are formed at the center of the iron shank 2. The resinoid diamond of the inside and outside protection rings 4 and 5 preferably contains 45% of epoxy resin, 45% of diamond particle and 10 % of graphite. However, it should be understood that polyamide resin or phenol resin may be substituted for epoxy resin of the above resinoid diamond without affecting the operational function of the diamond wheel 10 of this invention.

In addition, the material of the two protection rings 4 and 5 may be changed in accordance with materials to be ground or characteristics of grinding processes. That is, when it is expected that the resulting diamond wheel 10 may be used in a high impact grinding process, one of the two rings 4 and 5 is preferably made of resinoid diamond, with the other ring being formed of metal bond diamond. On the other hand, when the resulting diamond wheel 10 may be used in a higher impact grinding process, both the two rings 4 and 5 may be made of metal bond diamond.

In the operation of the above vitrified diamond wheel 10, the wheel 10 rotates and grinds the surface of a material to be ground, thus smoothing the surface. In such a grinding process, the surface of material is mainly ground by the grinding member 3 made of vitrified diamond, while the grinding member 3 is protected by the two protection rings 4 and 5.

When the diamond wheel 10 is provided with at least one protection ring, made of resinoid diamond, at the inside or outside edge of the annular grinding member 3, the resinoid diamond ring finely rubs the ground surface in a grinding process, thus removing a dressing process from the grinding process.

Fig. 3 is a sectional view of a vitrified diamond wheel in accordance with the primary embodiment of the present

invention having another structure of the grinding member. As shown in Fig. 3, the annular grinding member 3 of the vitrified diamond wheel 10 consists of a plurality of sectorial vitrified pieces 7.

Figs. 4a to 6b are views of vitrified diamond wheels in accordance with the second to fourth embodiments of the present invention. In the drawings, Figs. 4a, 5a and 6a are plan views of the diamond wheels according to the three embodiments, respectively, while Figs. 4b, 5b and 6b are perspective views of the grinding pieces of the diamond wheels, respectively.

In the second embodiment of Figs. 4a and 4b, the vitrified diamond wheel 20 comprises a wheel-type iron shank 21 and a plurality of sectorial vitrified pieces 22. The above vitrified pieces 22 are radially and securely mounted on the top surface of the iron shank 21. Each of the.vitrified pieces 22 comprises a grinding member 23, which is made of vitrified diamond and is surrounded by an impact protection ring 24.

In the third embodiment of Figs. 5a and 5b, the vitrified diamond wheel 30 comprises a wheel-type iron shank 31 and a plurality of circular vitrified pieces 32. The above vitrified pieces 32 are securely mounted on the top surface of the iron shank 31. Each of the vitrified pieces 32 comprises a grinding member 33, which is made of vitrified diamond and

is surrounded by an impact protection ring 34.

In the fourth embodiment of Figs. 6a and 6b, the vitrified diamond wheel 40 comprises a wheel-type iron shank 41 and a plurality of rectangular vitrified pieces 42. The above vitrified pieces 42 are also securely mounted on the top surface of the iron shank 41. Each of the vitrified pieces 42 also comprises a grinding member 43, which is made of vitrified diamond and is surrounded by an impact protection ring 44.

In the second to fourth embodiments, the impact protection rings 24, 34 and 44 may be preferably made of resinoid or metal bond diamond in accordance with materials to be ground or characteristics of grinding processes.

In the operation of the above vitrified diamond wheels 20, 30 and 40, the wheels rotate and grind the surfaces of materials to be ground, thus smoothing the surfaces. In such a grinding process, the surfaces of material are mainly ground by the grinding members 23, 33 and 43 made of vitrified diamond, while the grinding members 23, 33 and 43 are protected by the impact protection rings 24, 34 and 44, respectively. When the protection rings 24, 34 and 44 are made of resinoid diamond, the rings 24, 34 and 44 finely rub the ground surface in a grinding process, thus removing a dressing process from the grinding process.

As described above, the present invention provides a

vitrified diamond wheel. In the grinding operation of the above vitrified diamond wheel, the surface of material is mainly ground by the grinding member made of vitrified diamond, while the grinding member is protected by an impact protection ring. Therefore, the diamond wheel of this invention has excellent grinding ability and high impact resistance.

When the protection ring is made of resinoid diamond, the ring finely rubs the ground surface in a grinding process, thus removing a dressing process from the grinding process and improving productivity.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions or substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.