EP3793741B1 - Method for improving the productivity of grinding plants - Google Patents

Description

The present invention relates to a method for improving the productivity of grinding plants, the optimum wear geometry of grinding plants being preserved by applying a protective layer, and thus the susceptibility to repair of the plants being reduced and their productivity being improved.

BACKGROUND OF THE INVENTION

The comminution effect of grinding tools is particularly influenced by signs of wear. The harder the particles to be ground, the greater the material removal or wear on the grinding tool, which in turn influences the throughput and product quality of the grinding plant. The specific energy requirement during the grinding process changes depending on wear. The energy requirement runs through a so-called "bathtub curve", with the energy requirement initially decreasing, then transitioning into a constant phase and finally rising steeply as the wear of the grinding aggregates progresses.

STATE OF THE ART

Various techniques are currently being used to reduce the costs of grinding processes and to stabilize product quality and mill throughput. For example, worn grinding aggregates or grinding bodies are replaced or subjected to repair welding, with the original geometry of the grinding aggregates being restored in both cases.

Improving wear protection and minimizing wear and tear on grinding plants leads to increased plant availability, reduced downtime and longer maintenance intervals. Today, three different groups of materials in particular are used to protect the grinding aggregates from wear.

Grinding parts made of chrome cast iron have proven themselves as standard materials in daily use. These materials have very good resistance to abrasion, so that with a consistent hardness of 630 to 800 HV20 uniform, predictable wear and can plan the repair intervals accordingly. The service life of these materials can be further increased by build-up welding.

In general, grinding tools made of cast steel can be made more wear-resistant by build-up welding. During build-up welding, a high-alloy material is applied to highly stressed components as surface protection. The welding materials contain chromium and carbon, with other carbide-forming substances such as niobium, vanadium or others being used depending on the desired wear resistance.

The third group of materials includes the grinding parts made of compound casting. Two or more materials are constructively combined to form a composite material. The grinding tools are preferably made of a metal matrix composite material, with ceramic shaped pieces being embedded in a ductile cast iron. In this way, particularly hard and wear-resistant grinding tools are obtained.

So will in the DE 39 21 419 A1 describes a roller mill in which the grinding surfaces of the grinding rollers and the grinding track are protected by integrated ceramic segments. The grinding media are armored by applying the segments made of a much more wear-resistant material, which increases the service life of the grinding media.

In the DE 203 21 584 U1 describes a roller mill which has a grinding chamber with a rotating grinding track and grinding rollers rolling thereon. In order to ensure an extraordinarily high level of operational reliability, six grinding rollers are arranged in a 3 x 2 roller mill. According to the modular system, there is the possibility that in the event of operational disruptions or damage to the wearing parts of the rollers, the roller mill will be stopped briefly and a pair of rollers will be swung out. The roller mill can then continue to be operated with four grinding rollers while the grinding rollers that have been swiveled out are being repaired. In this way, a production stop can be avoided.

In the WO2016101952 discloses a method for forming a wear surface on a roller body and correspondingly a grinding roller comprising a grinding surface coated with a thin anti-wear layer.

The measures described above to increase the wear resistance of grinding aggregates and to ensure production are successful today deployed. Nevertheless, even today the wear of the grinding bodies in the grinding processes is a quality and cost-determining factor, so that there is still a need to find possibilities and methods to reduce the wear of grinding aggregates or grinding bodies.

OBJECT AND DESCRIPTION OF THE INVENTION

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

The task is solved by a method for improving the productivity of grinding plants, which initially includes the step of setting the optimal wear geometry of the grinding aggregates by conventional operation of the grinding plant. The wear geometry is optimal when the specific energy requirement of the grinding plant reaches a minimum for a given throughput. The achievement of the optimal wear geometry is controlled and determined by continuous measurement and recording of the energy requirement. The optimal wear geometry is then preserved by applying a thin wear protection layer to the surface of the grinding aggregates or grinding bodies, in particular grinding rollers and grinding plates.

All known methods can be used for applying the wear protection layer. The thin anti-wear layer is preferably applied by build-up welding or laser cladding.

Hard metals or carbidic hard materials, such as WC, CrC, TiC, VC, TaC and NbC, can be used as the material for the wear protection layer, with hard metals being applied in a preferred embodiment of the present invention, which are doped with appropriate carbide-forming substances depending on the desired wear resistance become.

The method according to the invention is particularly suitable for vertical roller grinding plants, the grinding aggregates or grinding media to be coated being grinding rollers and grinding plates.

The layer thickness of the applied anti-wear layer is preferably 1 to 5 mm.

The invention also relates to grinding bodies which have grinding surfaces coated on the surface with a thin anti-wear layer. According to the invention, the grinding bodies have an optimal wear geometry, which is determined by continuous measurement and recording of the energy requirement during the grinding process and is defined as the geometry at which a minimum of the energy requirement is achieved for a given throughput.

In an advantageous embodiment, the wear protection layer is a build-up welded layer.

A further advantageous embodiment of the present invention provides that the grinding bodies are parts of a vertical roller grinding system and the coated surfaces are the grinding surfaces of grinding rollers and grinding plates. The layer thickness of the thin anti-wear layer is advantageously 1 to 5 mm.

The present invention is based on the finding and the idea that the grinding media or grinding aggregates in most known grinding processes eventually form an optimal wear geometry that is only made possible by the wear of the grinding media and that adjusts itself automatically after a certain period of operation of the grinding plant. The energy requirement runs through what is known as a "bathtub curve", with the energy requirement initially decreasing, then transitioning into a constant phase and finally rising steeply as the grinding aggregates wear out. Thus, the achievement of the optimal wear geometry can be read from the energy consumption. The optimal wear geometry is reached when the energy consumption is at a minimum with a constant throughput. This condition, in which the product quality also remains at a constant level, corresponds to the optimum for the grinding process.

With longer periods of operation, the geometry of the grinding media changes due to progressive wear and the energy requirement increases while productivity decreases at the same time. Above a certain wear geometry, wear increases Grinding media so rapidly that the grinding media must be repaired or replaced if a qualitatively and quantitatively balanced grinding operation is to be guaranteed. At this stage, the grinding plant is particularly susceptible to production interruptions, as vibration peaks occur if the grinding process is not smooth, which means that continuous production must be interrupted in order to prevent a total breakdown of the plant. The result is that plant availability decreases, product quality decreases and product yield drops drastically. With all current grinding technologies, this state is reached after a certain period of operation and must be remedied by repairing or replacing the grinding media, since continued operation of the system at this point no longer makes economic sense.

The present invention is based on the idea of preserving the ideal state, in which the grinding media have their optimum wear geometry, and thus improving the productivity (yield, costs and quality) of the product to be ground. Since this state is reflected in the achievement of a minimum of the energy requirement, the optimal point in time for conservation of the corresponding geometry can be determined in a simple manner by continuous measurement and recording of the energy requirement. According to the invention, a thin anti-wear layer is applied at this time to the part of the surface of the grinding aggregates or grinding media that is susceptible to wear, so that the geometry of the grinding media is not changed, while the wear resistance of the surface is increased and the geometry is thereby preserved. With continued operation of the plant, the geometry will now change less quickly in comparison to a geometry that has not been conserved, so that the ideal state is retained for longer and the grinding plant can be operated over a longer period of time without additional downtime.

Repeated application of this process allows the system to be operated continuously in the optimum geometry range over a long period of time. In particular, the operation can also be monitored by regular wear measurements and depending on the state of wear of the grinding media the necessary regeneration or preservation measures can be taken to maintain the optimal wear geometry and to enable continuous operation.

The invention is to be explained in more detail below using a numerical example for a grinding plant for cement. According to conservative estimates, the measures described above should improve the availability of the grinding plant by more than 5%, which corresponds to a productivity increase of 5%. With a production of 200 t/h, this corresponds to an additional production of 86,400 t/a, which would correspond to an additional income of 1,036,800 € with a realistic profit of 12 €/t. At the same time, with a typical energy requirement of 28 kWh/t, continuous operation with optimal wear geometry would save an estimated at least 3% in energy costs, which corresponds to energy costs of approx. 0.15 €/kWh for an annual production of 1.5 million tons (90% utilization was calculated ) would correspond to €189,000.

BRIEF DESCRIPTION OF THE DRAWINGS

Figur 1

eine Schnittdarstellung eines Ausschnitts einer Vertikal-Rollenmahlanlage,

Figur 2

eine Schnittdarstellung eines Ausschnitts einer Vertikal-Rollenmahlanlage,

Figur 3

eine Schnittdarstellung eines Ausschnitts einer Walze einer Vertikal-Rollenmahlanlage und

Figur 4

eine weitere Schnittdarstellung eines Ausschnitts einer Walze einer Vertikal-Rollenmahlanlage.

Preferred embodiments of the invention are described below with reference to drawings, which are only intended as explanations and are not to be interpreted as restrictive. In the drawings show:

figure 1

a sectional view of a section of a vertical roller mill,

figure 2

a sectional view of a section of a vertical roller mill,

figure 3

a sectional view of a section of a roller of a vertical roller mill and

figure 4

another sectional view of a section of a roller of a vertical roller mill.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is explained in detail below with reference to the drawings listed above.

The figure 1 is a sectional view of a section of a vertical roller grinding plant, such as that used in the cement industry. A stationary, rotatable cylindrical grinding roller 1 is resiliently pressed against a rotary driven grinding table or grinding track 4, the grinding track 4 being reinforced with grinding plates 2 in the area against which the grinding rollers 1 are pressed. The grinding aggregates or grinding media (grinding rollers 1 and grinding plates 2) are in their original state and have a smooth, intact profile 5, 6.

The figure 2 shows the same arrangement as figure 1 after prolonged grinding operation, with the grinding rollers 1 and also the grinding plates 2 now showing their typical wear profiles 7, 8.

In the figure 3 a section of a grinding roller 1 can be seen in a sectional view, with the grinding roller 1 having reached its optimal wear profile 7 . The original profile 5 is drawn in dashed lines in this representation.

The figure 4 finally shows in the same representation as figure 3 the grinding roller 1, whose optimal wear profile 7 is now preserved with a thin wear protection layer 9, which is shown in dashed lines in the present case.

The grinding plates 2 also have an optimal wear profile, which is preserved in the same way with a thin wear protection layer. An additional graphic representation of the grinding plates 2, which have a comparable optimum wear profile to the grinding rollers 1, was omitted at this point.

As mentioned at the outset, the drawings described above are intended to be illustrative only and not limiting. That's how it can be The principle of the idea according to the invention can be applied to any other grinding plant in which an optimal wear geometry is also established during operation on its wearing parts. Also, the formation of the wear protection layer is not limited to build-up welding, but can be realized by any other known technique, it only having to be ensured that the right point in time for the preservation of the optimal wear geometry is selected in order to exploit the optimum of the advantages of the present invention .

Thus, the present invention can advantageously also be combined with other known methods for increasing the wear resistance of grinding aggregates or for safeguarding production. If, for example, as in the DE 203 21 584 U1 described, grinding rollers can be swiveled out during operation of the plant virtually without stopping production, the optimal wear profiles on the surfaces of the grinding rollers can be preserved without resulting in a loss of production, whereby the repair interval for the plant is then extended at the same time.

Reference List

1

grinding roller

2

grinding plate

3

grinding room

4

grinding track

5

Original profile (grinding roller)

6

Original profile (grinding plate)

7

wear profile (grinding roller)

8th

wear profile (grinding plate)

9

wear protection layer

Claims (10)

1. A method for improving the productivity of grinding plants, the method comprising the steps of:

   - reaching the optimum wear geometry of the grinding units by conventional operation of the grinding plant, the optimum wear geometry being present when the specific energy requirement of the grinding plant reaches a minimum at a prespecified throughput, and

   - preserving the optimal wear geometry,

   wherein the energy requirement is continuously measured and recorded during the grinding method to verify when the optimal wear geometry is reached, and the optimal wear geometry is preserved by applying a thin wear protection layer (9) to the surface of the grinding units (1, 2).
2. The method according to claim 1,
   characterized in that
   the thin wear protection layer (9) is applied by means of buildup welding.
3. The method according to claim 1 or 2,
   characterized in that
   the material for the wear protection layer (9) is selected from the group comprising hard metal, WC, CrC, TiC, VC, TaC and NbC.
4. The method according to any one of claims 1 to 3,
   characterized in that
   a hard metal layer is applied as a thin wear protection layer (9).
5. The method according to any one of claims 1 to 4,
   characterized in that
   the grinding plant is a vertical roller grinding plant, and the grinding units or grinding elements to be coated are grinding rollers (1) and grinding plates (2).
6. The method according to any one of claims 1 to 5,
   characterized in that
   the layer thickness of the thin wear protection layer (9) is 1 to 5 mm.
7. Grinding elements having grinding surfaces which are coated with a thin wear protection layer (9),
   wherein the grinding elements have an optimal wear geometry, characterized in that the optimal wear geometry of the grinding elements (1, 2) is determined by continuous measurement and recording of the energy requirement during the grinding process, and is defined as the geometry for which a minimum of the energy requirement is reached at a prespecified throughput.
8. The grinding elements according to claim 7,
   characterized in that
   the wear protection layer (9) is a buildup-welded layer.
9. The grinding elements according to claim 7 or 8,
   characterized in that
   the grinding elements are part of a vertical roller grinding plant, and the coated surfaces are the grinding surfaces of grinding rollers (1) and grinding plates (2).
10. The grinding elements according to any one of claims 7 to 9,
    characterized in that
    the layer thickness of the thin wear protection layer (9) is 1 to 5 mm.

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