A WEAR RESISTANT COMPOSITION FOR MANUFACTURING

WEAR RESISTANT COMPONENT USED FOR MAKING GRINDING ROLL OR TABLE LINER FOR VERTICAL ROLLER MILL AND METHOD TO MANUFACTURE THE SAME

Field of Invention

The present invention relates to vertical roller mill. More particularly it relates to wear resistant components of the vertical roller mill. Even more particularly, it relates to wear resistant composition for manufacturing of the wear resistant components for making grinding roll or table liner 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 example, 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, 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 Ball and Race 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. The principal on which such roller mills operate is that the rollers are driven by an arrangement on a track, which is formed by the table liners. The material to be crushed falls on the track and is crushed between the roller and the table liner. It is then taken out by other peripheral arrangement.

Various kinds of grinding rollers and table liners are available in market. Some of them are discussed herein below: Weld over lay grinding rolls and table liners: In the weld over lay grinding rolls and table liners, wear resistant hard weld alloy is deposited over mild steel cast rolls or base of table liners by the process of welding. The base of grinding roll and table liner is generally made by conventional casting process in mild steel. The thickness of weld may vary depending on the life desired also depending on various other factors.

Hi-Cr and other wear resistant grades grinding rolls and table liners:

In these kinds of rolls and table liners, the complete grinding roll or the complete table liner 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, or the non-wear or non- performing areas, which is never ground, but also that it has to be annealed in order to machine the fitment areas of Hi-Cr material. 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. These kinds of grinding rolls were normally used with the conventional Ni- hard and Hi-Cr table liners.

In aforesaid grinding rolls and table liners inserts are missing. In some of the grinding rollers and table liners, inserts are provided as a wear resistant component. These inserts are made of hard and wear resistant material. Several attempts have been made in the past to make grinding rolls and table liners with first casting inserts separately and then fixing them by mechanical forces, wedges, bolt and many other methods.

Several types of inserts have also been made, by not using metal inserts and also using other inserts, examples of which are metal oxide powder, alumina grain cakes etc.

Several other attempts have also been made to cast inserts differently, one of the examples being impregnating the metal inserts by ceramic grains.

Several patents are available in the field of wear resistant material. Some of them are discussed herein below:

US Pat. No. 3,502,447 discloses dense, homogeneous compositions having an average grain size less than about 10 microns. The compositions comprise: (1) 30-87% by vol. of alumina, aluminum nitride, zirconia, or mixtures thereof; (2) 10-60% by vol. of a nitride of titanium tantalum, zirconium, hafnium, nobidium, or mixtures thereof; and (3) 3- 15% by vol. of a metal component having: 50-80% by vol. of tungsten, molybdenum, or mixtures thereof, and 20-50% by vol. of nickel, iron, cobalt, or mixtures thereof.

US Pat. No. 3,565,643 discloses dense compositions having an average grain size less than about 10 microns and containing from 20- 80 volume percent alumina; 10 to 78 volume percent of a metalline selected from the group consisting of titanium carbide, titanium nitride, zirconium carbide, zirconium nitride, niobium carbide, nobium nitride, tantalum carbide, tantalum nitride, and mixtures thereof; and 2 to 30 volume percent of an intermetallic selected from the group consisting of iron aluminide, iron titanide, cobalt aluminide, cobalt titanide, nickel aluminide, nickel titanide, tungsten aluminide, molybdenum aluminide, niobium aluminide, tantalum aluminide, titanium aluminide, zirconium aluminide, and mixtures thereof.

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 Pat. No. 8,147,980 discloses a metal matrix ceramic composite wear part (MMCC) comprising a wearing portion formed by a ceramic cake impregnated by metal, wherein the ceramic cake comprises: at least one ceramic grain including alumina, and carbide grains including a carbide material selected from the group consisting of boron carbide, silicon carbide and tungsten carbide, wherein the ceramic cake comprises about 1 to about 4% by weight of a fine ceramic powder, expressed in weight of the ceramic grains.

Indian Pat. Application No. 276/ UM/2005 discloses a method for the manufacture of a wear resistant metallic part comprising introducing mineral grains at the wearing surface, said mineral grains comprising a mixture of zirconia, alumina and titanium oxide. Even though aforesaid varieties of wear resistant materials are available, still there is a need of further improvements in the wear resistant material to make them more efficient and economic.

Objects of the Invention

The primary object of the present invention is to provide an improved wear resistant material to be used in wear resistant components of the vertical roller mill.

Another object of the invention is to provide an improved wear resistant material to be used in wear resistant components of the vertical roller mill which is economic. Yet another object of the invention is to provide an improved wear resistant material to be used in wear resistant components of the vertical roller mill which is long lasting.

Still another object of the invention is to provide an improved wear resistant material to be used in wear resistant components of the vertical roller mill which is easy to manufacture.

Statement of the Invention Accordingly to achieve the foregoing objects, present invention provides composition for manufacturing wear resistant component used for making grinding roll or table liner for vertical roller mill, the composition comprising: - 50.0-70.0% by volume of Aluminum Oxide (A1203);

- 25.0-39.0% by volume of Zirconium Oxide (Zr02); - 0.10-0.9% by volume of Titanium Oxide (Ti02);

- 0.10-0.9% by volume of Silica (Si02);

- 0.10-0.5% by volume of Iron Oxide (Fe203);

- 0.03-0.09% by volume of Sodium Oxide (Na20);

- 0.05-0.09% by volume of Calcium Oxide (CaO);

- 5.0-8.0% by volume of Magnesium Oxide (MgO); and

- 0.5-2.0% by volume of Yttrium Oxide (Y203).

The present invention also provides a cake being used for manufacturing wear resistant component used for making grinding roll or table liner for vertical roller mill, the cake comprising:

- 85-98% by volume of the composition as defined above; and

- 2-15% by volume of binder.

The present invention further provides a method of manufacturing a cake being used for manufacturing wear resistant component used for making grinding roll or table liner for vertical roller mill, the method comprising:

- mixing 85-98% by volume of the composition as defined above and 2- 15% by volume of binder to obtain a mixture;

- putting the mixture into a mould of desired shape as per requirement of design;

- vibrating the mould by vibrator to stable and settle the mixture in the mould; and

- heating the mould in oven at temperature between 60°C- 180°C for a period between 50-300 seconds to form the cake. Furthermore, the present invention provides a wear resistant component used for making a grinding roller for vertical roller mill, the wear resistant component comprising:

- 2-10% by volume of the cake as defined above and 90-98% by volume of metal.

Further, the present invention provides the process of making wear resistant component with the use of above wear resistant component, used in manufacturing grinding roll of a roller mill as one of the embodiments. The process of manufacturing the wear resistant component includes following steps: preparing a mould for the wear resistant component according to the shape and design required; placing the bottom plate out of the pair of plates to be used, inside the mould; putting the cake as discussed above, wherein the cake is put inside the mould in such a way that the cake get supported by the pair of plates; putting the top plate; closing the mould; pouring the metal inside the mould through runner bar provided, as is done in normal foundry practice;

Performing hot shake out on the mould hen component achieves a surface temperature of 350-750° C, followed by heat treatment. Since the proposed composition uses high level of Magnesium Oxide (MgO), hot shake of the mould becomes possible. The advantages of this are firstly, the different coefficient of thermal expansion/ contraction factors of cake, the plate and the metal do not interfere with one another hence cracking of the mould is overcome. And with this step, significant amount of energy is saved since for heat treatment the starting temeperature of the mould is 350 C instead in case of prior art in which the mould were cooled and then were given heat treatment.

This wear resistant component after the heat treatment is fettled to bring it to desired shape and further used as an insert to manufacture grinding roller through known foundry casting (either through static casting or centrifugal casting.)

In another embodiment, the cake is used directly as an insert to cast grinding roller or table liner with a high chrome wear resistant, by normal foundry practice. In this case too, hot shake out technique should be adopted. Further heat treatment, fettling and machining processes are also adopted, as required in normal foundry practice.

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 examples.

The present invention provides improved wear resistant material which is used in the wear resistant components used for making grinding roll or table liner for the vertical roller mills. The wear resistance components mainly include a cake, which can be used to make a grinding roll or a table liner, directly, or it could be an insert, which is first made with the help of the cake so produced, and then the insert is used to manufacture grinding roll. It is pertinent to mention that the use of wear resistant material is not limited to manufacturing of the wear resistant components of the vertical roller mill, but can also be used for products of other applications.

The wear resistant material (composition) proposed by the present invention includes the following ingredients:

According to one of the preferred embodiment of the present invention the composition comprises the following combination:

Ingredients of composition Volume percentage in

composition

Aluminum Oxide (A1203) 59.0%

Zirconium Oxide (Zr02) 32.85%

Titanium Oxide (Ti02) 0.35%

Silica (Si02) 0.45%

Iron Oxide (Fe203) 0.25%

Sodium Oxide (Na20) 0.08%

Calcium Oxide (CaO) 1.02%

Magnesium Oxide (MgO) 5.20%

Yttrium Oxide (Y203) 0.80%

According to another preferred embodiment of the present invention the composition comprises the following combination:

In another embodiment, the composition can be coated by Titanium nitride (TiN). TiN is normally used to harden and protect cutting and sliding surfaces. This gives the abrasive grains further hardness to improve it's wear characteristics. There are several other variants of TiN such as titanium carbon nitride (TiCN), titanium aluminium nitride (TiAIN or AlTiN), and titanium aluminum carbon nitride, which may also be used individually or in alternating layers with TiN. The wear resistant component of the grinding roller and table liner used in roller mill is made of the composition as proposed by the present invention. For manufacturing the wear resistance component, the composition of the present invention is first converted into cake form.

A cake mainly includes the following ingredients:

- 85-98% by volume of the composition as proposed by the present invention; and

- 2- 15% by volume of binder.

According to the preferred embodiment of the invention the cake comprises 95% by volume of the composition as proposed by the present invention and 5% by volume of alumina based inorganic binder.

In the above embodiment, because of the nature of binder, and ratio of mix of binder, and mix of grains, the method to produce the cake is simpler. It does not need any gasification, thereby reducing cost and effort, like is being used in some other conventional approaches.

The binder is an alumina based inorganic binder, having the below properties.

Compressive Strength (psi) 3000

Flexural Strength (psi) 1 100

Thermal Expansion (x 10-6/°F) 4.5

Thermal Cond. (BTU in/hr. in ft2) 15

Dielectric Strength (volts/mil) 200

Volume Resistivity (ohm - cm) 108 Manufacturing steps involved in the production of the cake includes following steps:

- mixing the composition as proposed in the present invention and binder to obtain a mixture;

- putting the mixture into a mould made of wood/ rubber silicone of desired shape as per requirement of design;

- vibrating the mould by vibrator to stabilize and settle the mixture in the mould; and

- heating the mould in oven at temperature between 60°C- 180°C for a period between 50-300 seconds to form the cake. The temperature and time period varies depending Upon the type and size of mill.

The cake could be the wear resistant component, and in another embodiment, the cake can be used to make another wear resistant component. This wear resistant component used for making grinding roll for vertical roller mill is made from the cake as described hereinbefore. The wear resistant component includes 2- 10% by volume of the cake and 90-98% by volume of metal:

A sand mould is prepared for the wear resistant component, according to the shape and design required. A pair of plates is also made which helps in supporting the cake in the wear resistant component mould. First the bottom plate is placed in the mould, and then the cake is placed. Then, the top plate is placed and the mould is closed and is poured with metal by normal foundry process. The mould is broken to get the wear resistant component. The advantage of the plates is that it does not let the cake move from it's specific position inside the wear resistant component. The preferred volume of the ingredients of wear resistant component includes 5% by volume of the cake and 95% by volume of metal. Preferred metal is high chromium steel (Hi-Cr).

Further, the present invention provides the process of making wear resistant component with the use of above wear resistant component, used in manufacturing grinding roll of a roller mill as one of the embodiments. The process of manufacturing the wear resistant component includes following steps: preparing a mould for the wear resistant component according to the shape and design required; placing the bottom plate out of the pair of plates to be used, inside the mould; putting the cake as discussed above, wherein the cake is put inside the mould in such a way that the cake get supported by the pair of plates; putting the top plate; closing the mould; pouring the metal inside the mould through runner bar provided, as is done in normal foundry practice;

Performing hot shake out on the mould when component achieves a surface temperature of 350-750° C, followed by heat treatment. Since the proposed composition uses high level of Magnesium Oxide (MgO), hot shake of the mould becomes possible. The advantages of this are firstly, the different coefficient of thermal expansion /contraction factors of cake, the plate and the metal do not interfere with one another hence cracking of the mould is overcome. And with this step, significant amount of energy is saved since for heat treatment the starting temperature of the mould is 350 C instead in case of prior art in which the mould were cooled and then were given heat treatment.

This wear resistant component after the heat treatment is fettled to bring it to desired shape and further used as an insert to manufacture grinding roller through known foundry casting (either through static casting or centrifugal casting.)

In another embodiment, the cake is used directly as an insert to cast grinding roller or table liner with a high chrome wear resistant by normal foundry practice. This wear resistant component is then put into a mould/ die and the roller is cast either centrifu gaily or by static method followed by hot shake out technique. Further heat treatment is given to the mould. Table liners, grinding rollers or other components can be cast with the ceramic . cake directly put in the mould.

Both the types of wear resistant components are placed such that it forms the periphery of the grinding roll or table liner, which gets exposed to wear the most.

Examples;

Example 1: Ingredients 59.00% by volume of Aluminum Oxide (A1203); 32.85% by volume of Zirconium Oxide (Zr02); 0.35% by volume of Titanium Oxide (Ti02); 0.45% by volume of Silica (Si02); 0.25% by volume of Iron Oxide (Fe203); 0.08% by volume of Sodium Oxide (Na20); 1.02% by volume of Calcium Oxide (CaO); 5.20% by volume of Magnesium Oxide (MgO); and 0.80% by volume of Yttrium Oxide (Y203) are coated with Titanium nitride (TiN). It is then mixed with the help of alumina based inorganic binder to make the mixture. . The weight of ingredients is kept 85% and weight of binder is kept 15%. The mixture is then put into a mould of desired shape as per requirement. The mould is then vibrated by vibrator to stable and settle the mixture in the mould. The mould is heated in oven at temperature at 120°C for a period of 100 seconds to form the cake.

A sand mould is prepared for the wear resistant component, according to the shape and design required. A pair of plates is also made which helps in supporting the cake in the wear resistant component mould. First the plates are placed in the mould, and then the 5% by volume cake is placed between the plates. Then, the mould is closed and is poured with 95% by volume of high chromium steel (Hi-Cr) by normal foundry process. The advantage of the plates is that it does not let the cake move from it's specific position inside the wear resistant component. The mould is broken when surface temperature of wear resistant component reaches 700° C and is put directly into furnace for heat treatment, before the surface temperature drops below 400 C. The component is then heated in oven at temperature at 1700°C to prepare wear resistant component used for making grinding roll for the vertical roller mill. The grinding roller is then prepared with known foundry practice. Example 2:

Ingredients 60.00% by volume of Aluminum Oxide (A1203); 31% by volume of Zirconium Oxide (Zr02); 0.15% by volume of Titanium Oxide (Ti02); 0.35% by volume of Silica (Si02); 0.15% by volume of Iron Oxide (Fe203); 0.03% by volume of Sodium Oxide (Na20); 0.09% by volume of Calcium Oxide (CaO); 7.52% by volume of Magnesium Oxide (MgO); and 0.71% by volume of Yttrium Oxide (Y203) are mixed with the help of alumina based inorganic binder to make the mixture. The weight of ingredients is kept 87% and weight of binder is kept 13%. The mixture is then put into a mould of desired shape as per requirement. The mould is then vibrated by vibrator to stable and settle the mixture in the mould. The mould is heated in oven at temperature at 140°C for a period of 150 seconds to form the cake.

A sand mould is prepared for the table liner, according to the shape and design required. The cake so built is placed inside the mould and Hi-Cr material is poured by known foundry practice. The cake is forming 8% of the total weight of table liner and the rest being Hi-Cr metal. The mould is broken by hot shake out method to get the table liner., which is followed by heat treatment and fettling get the table liner.

Example 3:

Ingredients 69.00% by volume of Aluminum Oxide (A1203); 25% by volume of Zirconium Oxide (Zr02); 0.1% by volume of Titanium Oxide (Ti02); 0.1% by volume of Silica (Si02); 0.1% by volume of Iron Oxide (Fe203); 0.04% by volume of Sodium Oxide (Na20); 0.06% by volume of Calcium Oxide (CaO); 5.0% by volume of Magnesium Oxide (MgO); and 0.6% by volume of Yttrium Oxide (Y203) are mixed with the help of alumina based inorganic binder to make the mixture. The mixture is coated with Titanium nitride (TiN). The weight of ingredients is kept 89% and weight of binder is kept 1 1%. The mixture is then put into a mould of desired shape as per requirement. The mould is then vibrated by vibrator to stable and settle the mixture in the mould. The mould is heated in oven at temperature at 145°C for a period of 1 10 seconds to form the cake.

A sand mould is prepared for the wear resistant component, according to the shape and design required. A pair of plates is also made which helps in supporting the cake in the wear resistant component mould. First the plates are placed in the mould, and then the 7% by volume cake is placed. Then, the mould is closed and is poured with 93% by volume of high chromium steel (Hi-Cr) by normal foundry process. The mould is' broken to get the wear resistant component. The advantage of the plates is that it does not let the cake move from it's specific position inside the wear resistant component. The mould is heated in oven at temperature between 1770°C to prepare wear resistant component used for making grinding roll or table liner for the vertical roller mill.

Example 4:

Ingredients 50.00% by volume of Aluminum Oxide (A1203); 39% by volume of Zirconium Oxide (Zr02); 0.7% by volume of Titanium Oxide

(Ti02); 0.7% by volume of Silica (Si02); 0.5% by volume of Iron Oxide (Fe203); 0.04%'by volume of Sodium Oxide (Na20); 0.06% by volume of Calcium Oxide (CaO); 8.0% by volume of Magnesium Oxide (MgO); and 1.0% by volume of Yttrium Oxide (Y203) are mixed with the help of alumina based inorganic binder to make the mixture. The mixture is coated with Titanium nitride (TiN). The weight of ingredients is kept 86% and weight of binder is kept 14%. The mixture is then put into a mould of desired shape as per requirement. The mould is then vibrated by vibrator to stable and settle the mixture in the mould. The mould is heated in oven at temperature at 135°C for a period of 125 seconds to form the cake.

A sand mould is prepared for the wear resistant component, according to the shape and design required. A pair of plates is also made which helps in supporting the cake in the wear resistant component mould. First the plates are placed in the mould, and then the 6% by volume cake is placed. Then, the mould is closed and is poured with 94% by volume of high chromium steel (Hi-Cr) by normal foundry process. The mould is broken to get the wear resistant component. The advantage of the plates is that it does not let the cake move from it's specific position inside the wear resistant component. The mould is heated in oven at temperature between 1790°C to prepare wear resistant component used for making grinding roll or table liner for the vertical roller mill.

Advantages of the present invention The composition proposed by the present invention ensures increased life of the wear resistant component which not only saves material cost but also help in saving the cost of replacing the wear resistant component. Furthermore, the time which is consumed in doing so, the mills are also non-operational, and therefore increasing the life of wear resistant component also decreases the downtime of the mill/ equipment and increases the productivity of the plant. The nature of binder and ratio of mix of binder, and mix of grains, the method to produce the cake is simpler. It does not need any gasification, thereby reducing cost and effort. Due to use of higher quantum of Magnesium Oxide the refractoriness of the cake increases. Due to use of higher quantum of Magnesium Oxide, the process of manufacturing wear resistant component can be performed at the higher temperature up to 1800°C. Use of Titanium oxide in lesser quantum ensures cost saving and avoidance of cracking as the Titanium oxide has limitation of the cracking. Coating of the grains by various kinds of coating increases the life of the grains and further the cake and wear resistant component. Use of plates while making the insert ensures that the cake remains in right position in the insert. This is very important, as the wear resistant component should be at the wearing surface, and the cake is most likely to shift if we normally cast the component, while the ceramic cake is resting inside. Adopting the hot shake out technique saves the possibility, and thus reduces rejection, of cracking of wear resistant component because of variable coefficient of thermal expansion /contraction of Hi-Cr metal, the cake and the plates. It also saves energy in doing the heat treatment process as we start the process from 350° C and energy is not wasted in bringing the temperature from room temperature to 350 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 arid details may be made therein without departing from the spirit and scope of the invention.