A GRINDING ROLL FOR VERTICAL ROLLER MILL AND METHOD OF MANUFACTURING THE SAME

FIELD OF INVENTION

The present invention relates to vertical roller mill. It particularly relates to wear resistant components of the vertical roller mill. More specifically it relates to grinding roll for the vertical roller mill.

BACKGROUND OF THE INVENTION AND PRIOR ART

In industries, various kinds of equipments, which are called mills, are used to crush or grind materials. For examples, coal is ground in thermal power plants, limestone, coal and clinker is ground in cement plants and various others like gold, zinc, iron are crushed in mining industries before they are purified. There are various kinds of mills being used in such industries. A few examples are Horizontal mill, which is a rotary drum kind of a structure having wear resistant liners to protect the shell of the mill,

l diaphragms to separate various chambers of the mill, and grinding media balls/rods to crush the material. The mill is rotated at the critical speed by way of which balls rise to the top and fall by weight of its gravity and hence help in crushing.

Other example of mill includes E-mill which has a bottom ring, a top ring and hollow balls. The balls revolve on the track of the ring crushing the material to be crushed. There are other peripherals and methods to take out the crushed material.

Another type of mill is roller mill. Roller mills have gained a firm footing in many industrial branches for the size reduction of bulk materials. Roller mills are also known as bowl mills or vertical roller mills. The advantages of mills for size reduction are not only their high throughput rates but also the high quality of the final product with respect to particle size and size distribution as well as their energy demand. Roller mills are typically used in coal fired power plants and cement plants. In power plants they are used for grinding coal and in cement plants for raw material size reduction as well as for grinding coal. Lately there has been a growing demand for these types of mills for finished cement grinding and the grinding of granulated blast furnace slag. In addition there are several further applications in other branches of industry that make use of the advantages offered by roller mills. In the vertical roller mill, besides the peripheral arrangement which takes out the crushed material, the two main wear resistant components are grinding rollers and table liners.

Various kinds of grinding rollers are available in market. Some of them are discussed herein below: i. Weld over lay grinding rolls:

In the weld over lay grinding rolls, wear resistant hard weld alloy is deposited over mild steel cast rolls by the process of welding. The thickness of weld may vary depending on the life desired also depending on various other factors. ii. Hi-Cr grinding rolls:

In the hi-Cr rolls, the complete grinding roll is cast from a wear resistant and hard grade of High Chrome. However, it has the limitation that not only expensive Hi-Cr material is wasted in the core, which is never ground, but also that it has to be annealed in order to machine the core of Hi-Cr material. iii. Ni-hard bi metallic grinding rolls:

In the Ni-hard bi metallic rolls, the outer surface which helps in grinding (and is consumed) is cast in wear resistant and hard Ni-hard grade through centrifugal casting process, where as the core is in cast iron, which is not only cheaper but also is easier to machine.

In aforesaid grinding rolls inserts are missing. In some of the grind rollers, inserts are provided as a wear resistant component. These inserts are made of hard and wear resistant material.

Several patents are available in the field of grinding rollers. Some of them are discussed herein below:

US Pat. No. 5,114,082 discloses rolling mill comprising grinding rollers and a grinding path each having a fastening body of ferrous material for attaching a grinding surface including a cladding of wear- resistant segments made from a ceramic compound and tightly fixed to said fastening bodies, the segments having outer faces which form the entire grinding surfaces, and in which said fastening bodies of said grinding rollers and said grinding path facing the grinding rollers have a step-like configuration in axial section which support the segments of the cladding for positively fixing said segments against dynamic stressing forces in the radial direction of the grinding surfaces of the rolling mill.

US Publ. No. 2007/0215733 discloses grinding rolls in particular for high-pressure roller mills or rolling presses for pressure grinding a granular material not only with a wear-resistant coating but also with a face armour plating in the area of the roller annular edge, which has a long service life due to the high wear resistance thereof and whose production and repair are, in general, relatively simple and inexpensive. For this purpose, the inventive face armour plating consists of a plurality of prefabricated hard bodies which are circularly arranged side by side in such a way that the circular face edge of the roller is formed, said hard bodies are disposed ,on said circular shoulder of a roll shell such that said hard bodies are placed axially and radially against said circular shoulder of the roll shell and are movably assembled with the roll shell.

Further development has happened in the above category, where inventions have happened and people have tried to impregnate the insert used with cakes, made of harder material like alumina grains etc.

In conventional grinding roll inserts are placed inside the roll in such a manner that they form the periphery of the roll. But this kind of construction leads to maximum wearing of the roll which ultimately reduces the working life span of the roll. Hence it is a need to develop new or improved kind of grinding roll which can take care of the problem associated with the wear life of the roll.

OBJECTS OF THE INVENTION

The primary object of the present invention is to provide a grinding roll to be used in vertical roller mill which is having long lasting wear life.

Another object of the invention is to provide a grinding roll to be used in vertical roller mill which is economic.

Still another object of the invention is to provide a grinding roll to be used in vertical roller mill which is easy to manufacture.

STATEMENT OF THE INVENTION

Accordingly to achieve the foregoing objectives, the present invention provides a grinding roll for vertical roller mill, the grinding roll comprising: roll body having inner periphery and outer periphery; at least one insert being placed inside the roll body; characterized in that the insert is placed inside the roll body such that the insert is near to the inner periphery of roll body and away from the outer periphery of roll body, the insert does not make part of the inner periphery and outer periphery of roll body and gap between the insert and outer periphery of the roll body is filled by hard facing or welding.

The present invention also provides a method of manufacturing a grinding roll for vertical roller mill, the grinding roll comprises roll body having inner periphery and outer periphery and at least one insert being placed inside the roll body, the method comprising: placing the insert inside the roll body such that the insert is near to the inner periphery of roll body and away from the outer periphery of roll body, the insert does not make part of the inner periphery and outer periphery of roll body; filling gap between the insert and inner periphery of the roll body by spheroidal graphite cast iron; and filling gap between the insert and oiiter periphery of the roll body by hard facing or welding.

BRIEF DESCRIPTION OF THE DRAWING

Fig.1 : Shows perspective view of grinding roll for vertical roller mill in accordance to present invention.

Fig. 2 : Shows sectional view of grinding roll for vertical roller mill in accordance to present invention.

Fig. 3 : Shows top view of grinding roll for vertical roller mill in accordance to present invention.

Fig. 4 : Shows exploded sectional view of grinding roll for vertical roller mill in accordance to present invention.

DETAILED DESCRIPTION OF THE INVENTION The invention and its further features and advantages are explained in more detail on the basis of the exemplary embodiments schematically represented in the figures.

Meaning of Reference numerals in figures:

1. Grinding roll

2. Roll body

3. Outer periphery of the roll body

4. Inner periphery of the roll body

5. Insert

6. Insert part made of wear resistant material

7. Insert part made of metal

8. Weld or hard facing surface

9. Part of roll body made of metal

Referring to figures 1 and 2, which illustrate grinding roll (1) for the vertical roller mills in accordance to present invention. The grinding roll (1) includes roll body (2) and one or more inserts (5).

The roll body (2) comprises an inner periphery (3) and outer periphery (4). The roll body (2) is made of metal preferably of spheroidal graphite cast iron. Referring to figures 2 and 4, the insert (5) is placed inside the roll body (2). The insert (5) includes a part (6) made of wear resistant material. The part (6) is generally made of ceramic material. The part (6) is surrounded by metal part (7). The metal part (7) is generally made of high chromium steel. In figure 2, plurality of inserts (5) placed adjacent to each other are shown.

The insert (5) is placed in the roll body (2) in such a way that the insert (5) does not make the part of inner periphery (4) and outer periphery (3) of the roll body (2). The insert (5) is placed away from the outer periphery (3) of the roll body (2) and near to the inner periphery (4) of the roll body (2), but not even on the periphery of the inner periphery (4).

The gap between the insert (3) and the outer periphery (3) of the roll body (2) is filled by way of hard facing or welding. The hard facing or welding is done with a wear resistant high chromium welding wire. It not only provides an additional wear life but also enhances the binding strength of the insert (5) around the grinding roll (1). The hard facing is done to a minimum thickness of 3 mm and go up to 30 mm, depending on the output in terms of life required versus the cost to be incurred. In another embodiment, the hard facing is done only in the surface which is prone to high wear and not in the areas which is prone to comparatively low wear.

Gap between the insert (5) and inner periphery (4) of the roll body (2) is filled by spheroidal graphite cast iron.

The present invention also provides the method of manufacturing grinding roll. Firstly the inserts (5) are placed adjacent to each other inside the roll body (2) such that the insert (5) is near to the inner periphery (4) of roll body and away from the outer periphery (3) of roll body. The insert (5) does not make part of the inner periphery and outer periphery of roll body (2). Then the gap between the insert (5) and inner periphery (4) of the roll body is filled by spheroidal graphite cast iron. The gap between the insert (5) and outer periphery (3) of the roll body by hard facing or welding.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be understood by those skilled in the relevant art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.