Spiral jet mill and method for grinding grinding material in a spiral jet mill

Abstract

The invention relates to a spiral jet mill (1) having a grinding chamber (10) which is defined by a bottom (11), a cover (12) and a wall (13) connecting the bottom (11) and the cover (12) and having a plurality of grinding gas nozzles (14) which pass through the wall (13) and are connected to a grinding gas source, wherein a switchable closing mechanism (15) is provided corresponding to at least a portion of the grinding gas nozzles (14) with which the connection to the grinding gas source can be opened and closed independently. Furthermore, the invention relates to a method for grinding a grinding material in a spiral jet mill.

Description

Technical Field

[0001] This invention relates to a spiral jet mill having a grinding chamber defined by a bottom, a cover, and a wall connecting the bottom and the cover, and having a plurality of grinding gas nozzles that pass through the wall and are connected to a grinding gas source. Furthermore, the invention relates to a method for grinding abrasive material in such a spiral jet mill, wherein the abrasive material is introduced into the spiral jet mill and a grinding gas flow from the plurality of grinding gas nozzles passing through the wall is applied into the spiral jet mill. Background Technology

[0002] The type of spiral jet mill mentioned at the beginning has been known for a long time and is currently widely used in industrial applications requiring particles with a diameter of less than approximately 10 µm, particularly in the pharmaceutical, specialty chemical, and fine chemical industries. The spiral jet mill works by subjecting the abrasive material entering the grinding chamber to a powerful, accelerated abrasive gas flow from nozzles that pass through the wall of the chamber. Since the abrasive gas nozzles are typically angled approximately tangentially towards the grinding chamber, a spiral flow of the incoming abrasive gas is created within the chamber. The supplied abrasive material is captured and accelerated by the gas jet and pulverized through inter-particle collisions. The abrasive material with the desired particle size is discharged from the grinding chamber along with the depressurized abrasive gas at the center of rotation of the spiral flow, while coarser particles are further ground. Therefore, the spiral jet mill eliminates the need to move internal components within the grinding chamber, produces exceptionally fine abrasive material with a relatively narrow particle size distribution and minimal mechanical wear. However, while spiral jet mills possess the aforementioned advantages, they also have drawbacks. Specifically, their energy input is relatively high, and adjusting the optimal operating point is complex because many influencing parameters, such as the size of the grinding chamber, the entry angle of the grinding gas nozzle, the mass flow rate of the grinding gas, or the properties of the product, can vary considerably, especially depending on the grinding material. For example, the basic design of such a spiral jet mill can be found in EP 3 613 508 A1.

[0003] To date, in existing technologies, grinding intensity and grinding effect are achieved by adjusting the mass flow rate or pressure of the grinding gas. This is done by placing a throttle valve in the central supply line of the grinding gas between the grinding gas source and the spiral jet mill, or by adjusting the grinding gas source itself, such as a compressor. For example, see WO 2019 / 155038A1, WO 2017 / 042341 A1, US 2004211849, and WO 2013 / 156465 A1. However, it has been proven that as the grinding gas pressure continuously decreases, the velocity of the grinding gas entering the grinding chamber at the grinding gas nozzle outlet also decreases, which has a very significant negative impact on the grinding effect and grinding efficiency, requiring improvement.

[0004] CN 203990833 U also discloses a jet mill in which two air nozzles arranged in opposite positions are combined with a vertically upward bottom nozzle. At the start of the grinding process, the application of compressed air from a common air supply line to the compressor is regulated by independent regulating valves and flow measurement devices arranged at the nozzles, ensuring that the airflow from all three nozzles is identical. Only when this equilibrium is reached is the material supply port opened, where the opening cross-section can be varied to match the grinding material. This is very complex and difficult to use for varying grinding tasks. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide a spiral jet mill and a method for grinding bulk materials in the spiral jet mill, which achieves significantly improved grinding efficiency and higher output despite improved adjustability of the grinding process.

[0006] To achieve the above objectives, the present invention proposes a design scheme for a spiral jet mill and a method thereof.

[0007] According to a proposal of the present invention, an embodiment of a spiral jet mill is provided, wherein at least a portion of the present grinding gas nozzles are respectively provided with an on / off shut-off mechanism, by which the connection to the grinding gas source can be opened and closed independently of other shut-off mechanisms.

[0008] Therefore, according to the present invention, a spiral jet mill is provided, wherein the installed grinding gas nozzles can be individually connected or disconnected by opening or closing corresponding closing mechanisms and opening or closing the connection between the corresponding grinding gas nozzles and the grinding gas source. Thus, in the spiral jet mill according to the present invention, the flow rate of the grinding gas entering the grinding chamber can be adjusted solely by the number of nozzles connected and the cross-section of the nozzles used for grinding gas entry. In this case, regardless of the number of currently open closing mechanisms and corresponding grinding gas nozzles, the optimal maximum operating pressure of the grinding gas source is always present, and the grinding gas enters the grinding chamber at an optimal high speed through the open grinding gas nozzles. Even if the number of open closing mechanisms and corresponding grinding gas nozzles decreases or increases, the grinding gas pressure at the grinding gas nozzles does not change, nor does the discharge velocity into the grinding chamber. Therefore, compared to current spiral jet mills employing pressure regulation, both grinding effect and efficiency are significantly improved.

[0009] Within the scope of this invention, at least a portion of the grinding gas nozzle is equipped with a corresponding switchable shut-off mechanism in accordance with the method of this invention.

[0010] Therefore, according to the present invention, at least a portion of the grinding gas nozzles are each provided with an on / off shut-off mechanism, by which the respective connections from the grinding gas nozzles to the grinding gas source can be independently opened and closed to connect and disconnect the grinding gas nozzles. Each grinding gas nozzle equipped with a corresponding shut-off mechanism can be connected to the grinding gas source independently of other grinding gas nozzles by correspondingly operating the corresponding shut-off mechanism to the open position to introduce grinding gas into the grinding chamber, or disconnected from the grinding gas source by operating the relevant shut-off mechanism to prevent any grinding gas from being introduced into the grinding chamber. In this way, the grinding gas flow can be changed by increasing the number of grinding gas nozzles connected to the grinding gas source and introducing grinding gas into the grinding chamber by correspondingly opening the corresponding shut-off mechanisms, or by respectively closing the corresponding shut-off mechanisms.

[0011] According to one suggestion of the invention, all the grinding gas nozzles of the spiral jet mill according to the invention can each be equipped with a corresponding switchable shut-off mechanism to turn them on or off as needed.

[0012] In the context of this invention, stop valves, ball valves, gate valves and similar shut-off devices are particularly considered as shut-off mechanisms that allow for rapid switching between open and closed states.

[0013] According to another suggestion of the invention, the grinding gas source is connected to these grinding gas nozzles via independent supply lines each leading to a separate grinding gas nozzle, wherein an on / off shut-off mechanism is disposed in the supply line. This allows for a space-saving arrangement of the shut-off mechanism and ensures that each individual grinding gas nozzle corresponds to an individually controllable supply of grinding gas from the grinding gas source.

[0014] A particular advantage of the spiral jet mill according to the invention is that, apart from modifying the supply of grinding gas to each grinding gas nozzle and integrating the corresponding shut-off mechanism, the rest of the spiral jet mill components, especially the grinding chamber defined by the bottom, the cover, the wall connecting the bottom and the cover, and the corresponding grinding material supply openings and discharge openings, remain unchanged, so that the design according to the invention can also be implemented as part of the modification or retrofit of an existing spiral jet mill.

[0015] The spiral jet mill according to the invention comprises one, but preferably multiple, grinding gas nozzles distributed on the outer periphery of the wall, wherein, according to one suggestion of the invention, in particular 3 to 40 such grinding gas nozzles are provided, which are distributed on the outer periphery of the wall at regular intervals or in groups.

[0016] According to the present invention, the grinding gas nozzle can be configured as a Laval nozzle, which can generate a particularly high discharge velocity of the grinding gas into the grinding chamber, which is beneficial to the grinding effect. Until now, the grinding gas nozzle has only been configured as a Laval nozzle under very difficult circumstances, because in the conventional adjustment of the applied grinding gas pressure in a spiral jet grinder, the optimal operating point of the Laval nozzle can only be utilized to a very limited extent. However, in the design according to the present invention, since there is no need to adjust the existing grinding gas pressure, the optimal operating point of the Laval nozzle can almost always be utilized, and the grinding gas can be accelerated to several times the speed of sound, thereby achieving the best grinding effect.

[0017] According to another suggestion of the invention, a control device is provided for independently controlling the closing mechanism to control each closing mechanism and the corresponding grinding gas nozzle to open or close in a manner suitable for each respective adjustment purpose.

[0018] According to the invention, the shut-off mechanism is preferably switchable only between a fully open state and a fully closed state (on / off). However, the switching of the shut-off mechanism can be performed as part of the pre-setting process for the grinding task before starting the spiral jet mill, but it can also be performed during the operation of the spiral jet mill to adjust various process parameters. For example, depending on the type and hardness of the grinding material and / or the internal pressure of the grinding chamber, the individual grinding gas nozzles of the spiral jet mill according to the invention can be turned on or off based on the desired degree of pulverization.

[0019] According to another suggestion, the spiral jet grinder according to the invention can also be formed with cylindrical walls, thus defining a corresponding cylindrical grinding chamber between the bottom and the cover, into which grinding gas nozzles, each switchable by a corresponding closing mechanism, converge at a predetermined entry angle. In this case, the bottom and the cover can be flat or arched, so that the grinding chamber is cylindrical or lenticular in shape accordingly.

[0020] Furthermore, the cover of the spiral jet mill according to the invention may be configured to have a supply opening for feeding abrasive material into the grinding chamber and a discharge opening for discharging abrasive material ground in the grinding chamber.

[0021] The method according to the invention for grinding abrasive materials in a spiral jet mill is based on the fact that the spiral jet mill has a grinding chamber defined by a bottom, a cover, and walls, the abrasive material is introduced into the grinding chamber, and a grinding gas flow is applied to the grinding chamber from a plurality of grinding gas nozzles passing through the walls. According to the invention, the grinding gas flow is adjusted by changing the number of grinding gas nozzles to which the grinding gas flow is applied.

[0022] In existing spiral jet mills, the grinding process is typically regulated by adjusting, in particular throttling, the flow rate of the grinding gas through a central supply device. This inevitably leads to pressure and velocity losses at all the grinding gas nozzles. In contrast, in the method according to the invention, the flow rate of the grinding gas entering the grinding chamber can be matched by the number of grinding gas nozzles to which the grinding gas flow is applied, wherein the grinding gas exiting from the grinding gas nozzles to which the grinding gas flow is applied always flows into the grinding chamber at maximum pressure and maximum velocity.

[0023] As shown within the scope of this invention, the spiral jet mill is thus adjusted / controlled within a wider range than currently permitted by the prior art.

[0024] The present invention particularly provides for opening the grinding gas nozzle and applying the grinding gas flow individually and independently of other grinding gas nozzles, or closing it to disconnect it from the grinding gas flow. This opening or closing can be achieved, in particular, by switchable closing mechanisms corresponding to the grinding gas nozzles, arranged in grinding gas supply lines that lead separately to each individual grinding gas nozzle.

[0025] According to another suggestion of the invention, the flow rate of the grinding gas entering the grinding chamber per unit time is adjusted by changing the number of grinding gas nozzles to which the grinding gas flow is applied, so that the grinding process in the spiral jet mill can be particularly effectively and variably matched to the special properties of the grinding material and the respective grinding tasks according to the method of the invention.

[0026] The application or disconnection of the grinding gas flow at each grinding gas nozzle, depending on the required adjustment, can be performed in almost any configuration.

[0027] According to one suggestion of the invention, viewed from the outer periphery of the wall, the grinding gas nozzles are opened or closed alternately in a regular sequence, for example, in an alternating pattern of open-close-open-close. Alternatively, grinding gas flow can be uniformly applied to or disconnected from adjacent grinding gas nozzles, for example, by opening two or more adjacent grinding gas nozzles and correspondingly closing a subsequent number of adjacent grinding gas nozzles.

[0028] According to another suggestion of the invention, viewed from the outer periphery of the wall, a certain number of adjacent, successive grinding gas nozzles can be closed in a fan-shaped manner, while the remaining grinding gas nozzles are opened. The number of grinding gas nozzles in the closed fan and the corresponding number of the remaining open grinding gas nozzles can be freely selected.

[0029] Therefore, the method of the present invention has the characteristic of a very wide adjustment range. However, it is crucial that the supply of grinding gas is not subject to inefficient throttling; instead, the maximum operating pressure of the grinding gas source is applied to each individual grinding gas nozzle, whether the grinding gas nozzles are open and simultaneously applying grinding gas flow, or closed and disconnected from the grinding gas flow.

[0030] Therefore, the pulverizing effect and pulverizing intensity achievable in the spiral jet mill of the present invention are not adjusted by regulating the grinding gas source, but rather by opening and closing individual grinding gas nozzles and applying grinding gas to them. The total grinding gas flow introduced into the grinding chamber is set by varying the number of grinding gas nozzles to which the grinding gas flow is applied; however, the grinding gas pressure in front of each individual grinding gas nozzle is kept as high as possible, so that the achievable discharge velocity of the grinding gas entering the grinding chamber through the grinding gas nozzles to which the grinding gas flow is applied is also kept correspondingly high, thereby effectively utilizing the kinetic energy of the grinding gas.

[0031] In its simplest form, the nozzle cross-section of the abrasive gas nozzle used can be cylindrical or conical. However, in an extended embodiment of the invention, they can also be formed as Laval nozzles, capable of accelerating the discharged abrasive gas to speeds in the range of one to several times the supersonic speed.

[0032] In particular, according to another suggestion of the invention, the grinding gas nozzle is opened or closed when the grinding gas flow is applied to the grinding chamber, so that the spiral jet grinder can be smoothly adjusted even during operation, in order to respond to changes in other influencing parameters or disturbance variables, for example, during operation.

[0033] The opening or closing of the grinding gas nozzle is preferably determined based on the desired particle size, the hardness of the grinding material, and / or the pressure of the grinding chamber, and can be selected by those skilled in the art as required. Attached Figure Description

[0034] Other design options and details of the invention are explained below with the aid of the accompanying drawings, which illustrate embodiments. In the drawings:

[0035] Figure 1 A top view of the spiral jet mill according to the present invention is shown in schematic diagram;

[0036] Figure 2 A cross-sectional view through the spiral jet mill shown in Figure 1 is shown in an enlarged view;

[0037] Figure 3 The abrasive material supply device of the spiral jet mill according to the present invention is shown in a larger magnified view of FIG1. Detailed Implementation

[0038] The figure shows a strongly simplified schematic diagram of a spiral jet mill 1 for grinding abrasive materials, which is used, for example, in the pharmaceutical, specialty chemical and fine chemical industries, for grinding granular solids.

[0039] In this context, particulate solids are understood to be, for example, iron oxides, especially α-, β-, γ-, and / or δ-FeOOH phases and / or Fe(OH)2 phases, molten iron phases, and their mixtures and intermediate phases. Modified hematite α-Fe2O3, γ-Fe2O3 magnetite, magnetite, manganese ferrite or zinc ferrite, such as rutile or anatase modified titanium dioxide or titanium dioxide as a rutile mixed-phase pigment, chromium oxide, zinc oxide, zinc sulfide, ultramarin, nickel titanium dioxide or chromium-antimony titanium dioxide, cobalt blue, cobalt green, chromium oxide, or carbon-based substances such as carbon black, graphite, or graphene. Inorganic pigments in the above categories are particularly preferred.

[0040] The spiral jet mill 1 includes a cylindrical enclosed grinding chamber 10 defined by a bottom 11, a cover 12 spaced apart from the bottom 11, and a wall 13 connecting the bottom 11 and the cover 12. Therefore, the wall 13 is also cylindrical. The grinding chamber 10 can also be lenticular in shape due to the corresponding arches of the bottom 11 and / or the cover 12.

[0041] The wall 13 is penetrated by a plurality of grinding gas nozzles 14, four in this example, which converge into the grinding chamber 10 at a predetermined entry angle approximately tangentially.

[0042] The grinding gas nozzle 14 is connected to a grinding gas source (not shown), such as a compressor, via a supply unit 16 (shown only), and is supplied with a corresponding grinding gas flow, such as compressed air. The grinding gas enters the grinding chamber 10 approximately tangentially through the grinding gas nozzle, and in the exemplary embodiment shown, generates a spiral counterclockwise grinding gas flow within the grinding chamber 10.

[0043] The grinding material is fed from the corresponding storage container through a funnel 121 via a supply opening 120 located at an eccentric position within the cover 12 area and seen in more detail in Figure 3. The material is then accelerated in the ejector tube 123 and introduced into the grinding chamber 10 by an airflow ejected from the ejector nozzle 122. Here, the grinding material is captured and entrained by the spirally surrounding grinding airflow, where the required crushing and grinding occurs due to the resulting acceleration force and the collision of different parts of the material. Once the grinding material is below the desired particle size, it accumulates in the central region of the grinding chamber 10 due to the reduced centrifugal force in the spiral airflow, and is discharged from here, along with the depressurized grinding gas, through a central discharge opening 125 also arranged in the cover 12 from the spiral jet mill 1, possibly using a filter or cyclone separator not shown here.

[0044] Essentially, in order to regulate the grinding process within the grinding chamber 10, each individual grinding gas nozzle 14 has a separate, independently controllable shut-off mechanism 15 within its grinding gas supply section 16. This allows for the arbitrary application of grinding gas flow to and activation of each individual grinding gas nozzle 14, or the disconnection from the grinding gas flow and corresponding deactivation. When the shut-off mechanism 15 is open, the corresponding grinding gas nozzle 14 receives grinding gas from its source; conversely, when the corresponding shut-off mechanism 15 is closed, the corresponding grinding gas nozzle 14 is disconnected from the grinding gas. For example, the shut-off mechanism 15 can be formed by a shut-off valve that can switch between open and closed positions.

[0045] In this way, a continuous high working pressure of grinding gas from the grinding gas source can be applied to all gas supply lines 16, and by opening one or all of the closing mechanisms 15, a corresponding number of corresponding grinding gas nozzles 14 can be activated, and then the grinding gas flow can enter the grinding chamber 10 from the grinding gas nozzle at a constant pressure and a corresponding constant maximum speed.

[0046] By altering the total grinding airflow entering the grinding chamber 10, the pulverizing action and intensity of the spiral jet mill 1 can be adjusted using the switching of a single grinding gas nozzle 14 without reducing the discharge velocity of the grinding gas entering the grinding chamber 10. This allows for the most efficient use of the grinding gas and significantly improves the energy efficiency of the spiral jet mill 1.

[0047] Before and during operation of the helical jet mill, the number of opening and closing mechanisms 15 and the corresponding grinding gas nozzles 14 can be arbitrarily changed. For example, in the illustrated embodiment, the grinding gas flow can be applied to one of every two grinding gas nozzles 14 by opening the corresponding closing mechanism 15, but it is also possible to open only one grinding gas nozzle 14, or open three adjacent grinding gas nozzles 14, or open all grinding gas nozzles 14. The same applies to helical jet mills 1 with more or fewer grinding gas nozzles, wherein, in this invention, a number of 3 to 40 such grinding gas nozzles 10 is particularly suitable. The control of each closing mechanism 15, as required, can advantageously be performed by a corresponding control device, for example, according to the specifications of an electronic device controller.

[0048] Compared to currently used implementations of spiral jet mills, the design of the spiral jet mill 1 shown is modified only in the area supplying grinding gas to each individual grinding gas nozzle 14. Each individual grinding gas nozzle 14 is equipped with a separate gas supply line 16, in which an independently switchable shut-off mechanism 15 is provided. In contrast, the pre-distributor and pressure regulator commonly used for supplying grinding gas can be omitted.

[0049] Compared to the current method of regulating the grinding gas pressure to control the flow rate of grinding gas entering the grinding chamber 10, the design described above achieves an ideally constant high pressure at the inlet of the grinding gas nozzle. This allows the grinding gas nozzle to be constructed not only as a cylinder or cone, but also as a Laval nozzle. By opening and closing the individual grinding gas nozzles described above, and possibly by matching the discharge flow of the grinding material, the pressure in the grinding chamber 10 can be matched, but a constant high pressure is always applied at the open grinding gas nozzle. Therefore, each open grinding gas nozzle can always operate within its optimal operating range, which, especially when using the Laval nozzle design, ensures highly energy-efficient operation because the outlet velocity of the grinding gas can reach several times the speed of sound, while the jet divergence is minimal. This results in a significantly more energy-efficient grinding effect.

[0050] By maintaining a constant grinding gas pressure and the pressure inside the grinding chamber 10, energy loss that is detrimental to grinding can be reliably avoided due to compression shocks or large jet divergence caused by the grinding gas nozzle 14, which is formed as a Laval nozzle, operating above or below the optimal operating point.

[0051] Even when using, for example, a cylindrical grinding gas nozzle 14, high-efficiency grinding can also be achieved by limiting the number of grinding gas nozzles 14 that are activated and opened under a predetermined flow rate of grinding material, thereby increasing the outlet velocity of the grinding gas entering the grinding chamber 10 to the speed of sound.

[0052] When flow restriction is traditionally achieved by adjusting the pressure of the grinding gas, the pressure of the grinding gas applied at the nozzle inevitably decreases, leading to a reduction in the velocity of the grinding gas flow exiting the nozzle and a deterioration of the energy balance. In the flow regulation described above, which involves reducing the amount of grinding gas applied at the available grinding gas nozzle 14, the flow rate of the grinding gas is also reduced to the required level, but maximum pressure remains at the open grinding gas nozzle 14, thus maintaining the maximum velocity of the discharged grinding gas. This significantly improves the currently unavoidable low-energy-efficiency operation of spiral jet mills.

[0053] The spiral jet mill and method described above can be implemented not only in newly constructed spiral jet mills, but also in existing spiral jet mills based on the prior art with relatively simple modifications.

[0054] Explanation of reference numerals in the attached figures

[0055] 1: Spiral jet mill

[0056] 10: Grinding Chamber

[0057] 11: Bottom

[0058] 12: Lid

[0059] 13: wall

[0060] 14: Grinding gas nozzle

[0061] 15: Closure of the institution

[0062] 16: Gas supply pipeline

[0063] 120: Supply Opening

[0064] 121: Funnel

[0065] 122: Injector nozzle

[0066] 123: Injector tube

[0067] 125: Discharge opening

Claims

1. A spiral jet mill (1) having a grinding chamber (10) defined by a bottom (11), a lid (12) and a wall (13) connecting the bottom (11) and the lid (12) and having a plurality of grinding gas nozzles (14) passing through the wall (13) and connected to a source of grinding gas, characterized in that, A switchable closing mechanism (15) is provided corresponding to at least some of the abrasive gas nozzles (14), with which the connection to the abrasive gas source can be opened and closed independently, wherein, in order to adjust the abrasive gas flow, the abrasive gas flow rate into the grinding chamber (10) per unit of time can be changed by changing the number of abrasive gas nozzles (14) to which the abrasive gas flow is applied, wherein the abrasive gas pressure at the abrasive gas nozzles and the discharge rate into the grinding chamber do not change even if the number of open closing mechanisms and corresponding abrasive gas nozzles decreases or increases.

2. A spiral jet mill (1) according to claim 1, characterized in that A switchable closing mechanism (15) is provided corresponding to each abrasive gas nozzle (14).

3. A spiral jet mill (1) according to claim 1 or 2, characterized in that The abrasive gas source communicates with the abrasive gas nozzles (14) via a gas supply line (16) leading to each of the abrasive gas nozzles (14), wherein a switchable closing mechanism (15) is provided in the gas supply line (16).

4. The spiral jet mill (1) according to claim 1, characterized in that, The number of abrasive gas nozzles (14) is from 3 to 40.

5. The spiral jet mill according to claim 1, characterized in that, The abrasive gas nozzles (14) are formed as Laval nozzles.

6. The spiral jet mill (1) according to claim 1, characterized in that A control device is provided for independently controlling the closing mechanisms (15).

7. The spiral jet mill (1) according to claim 1, characterized in that, The wall (13) is formed as a cylinder.

8. The spiral jet mill (1) according to claim 1, characterized in that, The lid (12) has a supply opening (120) for supplying abrasive material into the grinding chamber (10) and a discharge opening (125) for discharging the ground abrasive material from the grinding chamber (10).

9. Method for grinding a grinding material in a spiral jet mill (1), wherein the spiral jet mill (1) has a grinding chamber (10) defined by a bottom (11), a lid (12) and a wall (13), a grinding material is introduced into the grinding chamber and a grinding gas stream from a plurality of grinding gas nozzles (14) through the wall (13) is applied into the grinding chamber, characterized in that, The number of abrasive gas nozzles (14) to which the abrasive gas flow is applied is changed in order to adjust the abrasive gas flow, wherein, in order to adjust the abrasive gas flow, the abrasive gas flow rate into the grinding chamber (10) per unit of time is changed by changing the number of abrasive gas nozzles (14) to which the abrasive gas flow is applied, wherein the abrasive gas pressure at the abrasive gas nozzles and the discharge rate into the grinding chamber do not change even if the number of abrasive gas nozzles to which the abrasive gas flow is applied decreases or increases.

10. The method of claim 9, wherein, An abrasive gas nozzle (14) is opened and supplied with an abrasive gas flow individually and independently of the other abrasive gas nozzles (14), or is closed and disconnected from the abrasive gas flow.

11. The method according to claim 9 or 10, characterized in that, The abrasive gas nozzles (14) are alternately opened or closed in a regular sequence as seen around the outer circumference of the wall (13).

12. The method of claim 9 or 10, wherein, A certain number of adjacent abrasive gas nozzles (14) are closed or opened as seen around the outer circumference of the wall (13).

13. The method of claim 9, wherein, The abrasive gas nozzles (14) are opened or closed during the application of the abrasive gas flow to the grinding chamber (10).

14. The method of claim 9, wherein, The abrasive gas flow is introduced into the grinding chamber (10) from the abrasive gas nozzles (14) at supersonic speed.

15. The method of claim 9, wherein, The opening or closing of the abrasive gas nozzles (14) is varied depending on the desired abrasive material grain size, the abrasive material hardness and / or the pressure in the grinding chamber (10).

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