RU2778253C2 - Method for increasing the productivity of mills - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: invention relates to devices for grinding the product. A method is proposed to increase the productivity of the mill, according to which, after installing the optimal wear geometry of the grinding units through normal operation of the mill, the optimal wear geometry is preserved by applying a thin wear-resistant protective coating to the surface of the grinding units.

EFFECT: invention provides an increase in the productivity of mills.

10 cl, 4 dwg

Description

The present invention relates to a method for increasing the productivity of mills, in which the optimal wear geometry of the mills is preserved by applying a protective coating and thereby reducing the need for frequent repairs of the mills and increasing their productivity.

Technical field

The grinding action of grinding tools is influenced in particular by wear phenomena. The harder the crushed particles, the greater the material removal or, accordingly, the wear of the grinding tool, which, in turn, affects the throughput and productivity of the mill. The specific energy consumption in the grinding process depends on wear. In this case, the energy consumption is described by the so-called "U-shaped curve", in which the energy consumption first decreases, then passes into a constant phase, and, finally, as the grinding aggregates wear out, it sharply increases.

State of the art

Currently, various methods are used to reduce the cost of grinding processes, as well as to stabilize the productivity and throughput of mills. Thus, for example, worn-out grinding aggregates or grinding bodies are replaced or subjected to repair welding, and in both cases the original geometry of the grinding aggregates is restored.

Improving wear protection and minimizing mill wear results in increased mill availability, reduced downtime and extended maintenance intervals. At the present time, in particular, three different groups of materials are used to protect grinding aggregates from wear.

Thus, grinding parts made of high-chromium cast iron have proven themselves as standard materials for everyday use. These materials have very high abrasion resistance, so that with a total hardness of 630 to 800 HV20 uniform predictable wear is obtained and it becomes possible to plan the overhaul intervals accordingly. The service life of these materials can be further increased by hardfacing.

In the most general case, cast steel grinding tools can be made more wear resistant by hardfacing. When surfacing, a high-alloyed material is applied as a protective coating to heavily loaded parts. The materials to be welded contain chromium and carbon, and, depending on the desired wear resistance, additional carbide-forming substances are used, such as niobium, vanadium or other substances.

The third group of materials includes grinding parts made of multilayer castings. In this case, two or more materials are structurally combined into a composite material. The grinding tools preferably consist of a metal matrix composite material, the ceramic profiles being embedded in nodular cast iron. In this way, particularly hard and wear-resistant grinding tools are obtained.

Thus, DE 39 21 419 A1 describes a roller mill in which the grinding surfaces of the grinding rollers and the working surface of the millstone are protected by bonded ceramic segments. The grinding media are reinforced by installing segments of a much more wear-resistant material, which increases the service life of the grinding media.

DE 203 21 584 U1 describes a roller mill comprising a grinding chamber with a rotating work surface of a millstone and grinding rollers rolling along it. To ensure exceptionally high operational reliability, six grinding rollers are positioned to form a 3×2 roller mill. In accordance with the modular principle, it is thus possible, in the event of malfunctions or breakage of wear parts of the rollers, to stop the rollers of the roller mill for a short time and turn the pair of rollers outwards. The roller mill can then be operated further with four grinding rollers while the grinding rollers turned outwards are repaired. This avoids interruptions in production.

The measures described above, which provide an increase in the wear resistance of grinding aggregates or, accordingly, the reliability of production, are successfully used today. However, even today, the wear of grinding media in grinding processes is a factor that determines the quality and cost, so there is still a need to find ways and means to reduce the wear of grinding aggregates or, accordingly, grinding media.

Statement of the problem and description of the invention

The object of the present invention is to propose a method that makes it possible to increase the service life of grinding aggregates or, respectively, grinding bodies beyond the limits known from the prior art.

This problem is solved thanks to a method for increasing the productivity of mills, which first includes the step of setting the optimal wear geometry of the grinding aggregates through normal operation of the mill. The optimal wear geometry occurs when the specific energy consumption of the mill at a given throughput reaches a minimum. Achievement of optimum wear geometry is monitored and determined by continuous measurement and recording of energy consumption. The optimum wear geometry is then preserved by applying a thin, wear-resistant protective coating to the surface of the grinding aggregates or grinding media, in particular grinding rolls and grinding plates.

All known methods can be used to apply a wear resistant protective coating. Preferably, a thin wear resistant protective coating is applied by hardfacing or laser cladding.

As material for the wear-resistant protective coating, hard alloys or hard materials based on carbides, such as, for example, WC, CrC, TiC, VC, TaC and NbC, can be used, and in a preferred embodiment of the present invention, hard alloys are applied, which, depending on the desired wear resistance is alloyed with appropriate carbide-forming substances.

The method according to the invention is particularly suitable for vertical roller mills, in which the grinding aggregates or grinding media to be coated are grinding rollers and grinding plates.

The thickness of the applied wear-resistant protective coating is preferably 1 to 5 mm.

The subject of the invention is also grinding bodies, on the surface of which there are grinding surfaces coated with a thin wear-resistant protective coating. According to the invention, the grinding media have an optimal wear geometry, which is determined during the grinding process by continuous measurement and recording of the energy consumption and which is defined as the geometry at which the minimum energy consumption is achieved for a given throughput.

In a preferred embodiment, the wear resistant protective coating is a welded coating.

In yet another preferred embodiment of the present invention, it is provided that the grinding media are parts of a vertical roller mill and the coated surfaces are the grinding surfaces of the grinding rolls and grinding plates. Preferably, the thickness of the layer of thin wear-resistant protective coating is from 1 to 5 mm.

The present invention is based on the fact and idea that the grinding media or grinding aggregates in most of the known grinding processes at some point form an optimal wear geometry, which becomes possible only as a result of wear of the grinding media and is automatically set after a certain time of operation of the mill. In this case, the energy consumption is described by the so-called "U-shaped curve", in which the energy consumption first decreases, then passes into a constant phase and, finally, with greater wear of the grinding aggregates, it sharply increases. Thus, the achievement of the optimal wear geometry can be judged by the energy consumption. The optimum wear geometry is achieved when the energy consumption is kept to a minimum at a constant throughput. This state, in which the quality of the product also remains at a constant level, corresponds to the state that is optimal for the grinding process.

With a longer operation due to progressive wear, the geometry of the grinding media changes, and the energy consumption increases with a simultaneous drop in productivity. Starting from a certain wear geometry, the wear of the grinding media increases so rapidly that the grinding media must be repaired or replaced if it is necessary to ensure a qualitatively and quantitatively balanced grinding operation. At this stage, the mill is particularly prone to production downtime, as vibration peaks occur during the uneven grinding process, making it necessary to interrupt continuous production in order to prevent a complete failure of the mill. As a result, the availability of the mill falls, the quality of the product decreases, and the yield of the product drops sharply. This state is reached after a certain period of operation with all modern grinding methods and must be eliminated by repair or replacement of grinding media, since further operation of the mill in this state no longer makes economic sense.

The present invention is based on the idea of preserving the ideal state, in which the grinding media have an optimal wear geometry, and thus increasing the productivity (yield, costs and quality) of the ground product. Since this state is reflected in the form of reaching a minimum energy consumption, by continuously measuring and recording the energy consumption in a simple way, the optimal time for conservation of the corresponding geometry can be determined in a simple way. According to the invention, at a specified time, a thin wear-resistant protective coating is applied to the wear-prone part of the surface of the grinding aggregates or grinding bodies, so that the geometry of the grinding bodies is not changed, while the wear resistance of the surface is increased, and thereby the geometry is preserved. Now, during further operation of the mill, the geometry does not change as quickly as compared to the unpreserved geometry, so that the ideal state is maintained longer, and the mill can be operated without additional shutdown for a longer time.

By reusing said method, the plant can be continuously operated in the optimal geometry range for a long time. In particular, the operation can additionally be monitored by means of regular wear measurements and, depending on the wear condition of the grinding media, the necessary restoration or conservation measures can be taken to obtain an ideal wear geometry and ensure continuous operation.

The invention is explained in more detail below on the basis of a numerical example of a cement mill. According to conservative estimates, the measures described above should increase the availability of the mill by more than 5%, which, therefore, corresponds to an increase in productivity of 5%. With a capacity of 200 t/h, this corresponds to an additional capacity of 86400 t/year, which, with a realistic profit of 12 €/t, corresponds to an additional revenue of 1.036.800 €. At the same time, with a typical energy consumption of 28 kWh/t, continuous operation with optimal wear geometry can save at least 3% on energy costs, which, with an energy cost of approx. 0.15 €/kWh and an annual output of 1, 5 million tons (in the calculation, a load of 90% was assumed) corresponds to the amount of 189.000 €.

Brief description of the drawings

The preferred embodiments of the invention are described below with the aid of the drawings, which are for illustration only and should not be construed as limiting. The drawings show the following:

fig. 1 is a sectional view of a fragment of a vertical roller mill;

fig. 2 is a sectional view of a fragment of a vertical roller mill;

fig. 3 is a sectional view of a fragment of a roll of a vertical roller mill; and

fig. 4 is another sectional view of a fragment of a vertical roller mill roll.

Description of Preferred Embodiments

Below the invention is explained in detail with the help of the drawings described above.

In FIG. 1 shows a sectional view of a fragment of a vertical roller mill used, for example, in the cement industry. The stationary cylindrical grinding roller 1, made with the possibility of rotation, is pressed with spring force against the mill bowl driven into rotation or, accordingly, the working surface 4 of the millstone, and the working surface 4 of the millstone in the area against which the grinding rollers 1 are pressed is reinforced by means of grinding plates 2. The grinding aggregates or, respectively, the grinding media (grinding rollers 1 and grinding plates 2) are in their original state and have a smooth, undamaged profile 5, 6.

In FIG. 2 shows the same device as in Fig. 1, but after long-term grinding operation, the grinding rolls 1 and grinding plates 2 now having typical wear profiles 7, 8.

In FIG. 3 is a sectional view of a grinding roll 1, wherein the grinding roll 1 has reached its optimum wear profile 7 . In this drawing, the original profile 5 is shown in dotted lines.

Finally, in FIG. 4 using the same drawing as in FIG. 3 shows a grinding roll 1 whose optimum wear profile 7 has now been preserved by means of a thin wear-resistant protective coating 9, which in this case is shown in dotted lines.

In the case of grinding plates 2, an optimum wear profile is also established, which is preserved in the same way by means of a thin wear-resistant protective coating. An additional drawing showing grinding plates 2 having an optimal wear profile similar to the wear profile of grinding rolls 1 is not shown here.

As stated at the outset, the drawings described above are for illustration only and should not be construed as limiting. Thus, the principle based on the idea underlying the invention can be used in relation to any other mill, on the wearing parts of which, during operation, an optimal wear geometry is also established. The execution of the wear-resistant protective coating is also not limited to hardfacing, but can be made by any other known method, it only has to be ensured that the appropriate time for conservation of the optimal wear geometry is chosen in order to optimally take advantage of the advantages of the present invention.

Thus, the present invention can preferably be combined with other known methods for improving the wear resistance of grinding aggregates or, accordingly, ensuring production reliability. If, for example, as described in DE 203 21 584 U1, the grinding rolls can be turned outward during operation of the mill practically without stopping production, optimum wear profiles on the surfaces of the grinding rolls can be maintained without production downtime, in which case the overhaul interval for the mill is simultaneously increased.

List of reference symbols

1 grinding roller

2 grinding plates

3 grinding chamber

4 working surface of the millstone

5 initial profile (grinding roll)

6 initial profile (grinding plate)

7 wear profile (grinding roll)

8 wear profile (grinding plate)

9 wear-resistant protective coating

Claims (32)

1. A method for increasing the productivity of mills, including the following steps: setting the optimum wear geometry of the grinding aggregates by means of normal mill operation, the optimum wear geometry occurring when the specific energy consumption of the mill at a given throughput reaches a minimum, and - preservation of optimal wear geometry, characterized in that the achievement of the optimal wear geometry is controlled during the grinding process by continuously measuring and recording the energy consumption, and the preservation of the optimal wear geometry is performed by applying a thin wear-resistant protective coating (9) to the surface of the grinding units (1, 2). 2. The method according to claim 1, characterized in that application of a thin wear-resistant protective coating (9) is carried out by surfacing. 3. The method according to claim 1 or 2, characterized in that the material for the wear-resistant protective coating (9) is selected from the group consisting of hard alloy, WC, CrC, TiC, VC, TaC and NbC. 4. The method according to one of paragraphs. 1-3, characterized in that hard alloy coating is applied as a thin wear-resistant protective coating (9). 5. The method according to one of paragraphs. 1-4, characterized in that the mill is a vertical roller mill and the grinding aggregates or grinding bodies to be covered are grinding rollers (1) and grinding plates (2). 6. The method according to one of paragraphs. 1-5, characterized in that the thickness of the layer of thin wear-resistant protective coating (9) is from 1 to 5 mm. 7. Grinding bodies, on the surface of which there are grinding surfaces covered with a thin wear-resistant protective coating (9), characterized in that the grinding media have an optimal wear geometry, wherein the optimum wear geometry of the grinding media (1, 2) is determined during the grinding process by continuous measurement and recording of energy consumption and is set as a geometry in which, at a given throughput, a minimum energy consumption is ensured. 8. Grinding bodies according to claim 7, characterized in that wear-resistant protective coating (9) is a welded coating. 9. Grinding bodies according to claim 7 or 8, characterized in that the grinding bodies are a part of the vertical roller mill, and the coated surfaces are the grinding surfaces of the grinding rollers (1) and grinding plates (2). 10. Grinding body according to one of paragraphs. 7-9, characterized in that the thickness of the layer of thin wear-resistant protective coating (9) is from 1 to 5 mm.

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