PULVERMÜHLE

Description

Technical field of the invention

[0001] The present invention relates to the field of powder grinding. State of the art

[0002] Powders used in the pharmaceutical, chemical and food industries typically have an average grain diameter of between 10 and 500 microns, and are produced by grinding raw powders whose grains have an average diameter of, for example, between 100 microns and several millimeters.

[0003] The grain size involved requires the use of suitable grinding devices.

[0004] Among the suitable mills - so-called mechanical mills - there are spindle mills which have two parallel discs each equipped with grinding elements, typically in the form of rods, directed towards the adjacent disc. These grinding elements are intended to impact the product grains during a relative rotation of the two discs.

[0005] There are also screen mills that combine two different principles of grain size reduction: the impact of the rotor on the grains and the forced passage of the grains through the screen openings.

[0006] There are several types of screen mills, which differ mainly in their shape and rotation speed. These are mainly: the conical screen crusher which comprises a rotor with a vertical axis fitted with blades cooperating with a coaxial conical screen, the hammer crusher which comprises a rotor with a horizontal axis fitted with blades and a semi-cylindrical screen with the same axis as the rotor, and the oscillating crusher whose rotor with a horizontal or vertical axis has the particularity of being located very close to the semi-cylindrical screen and of carrying out back and forth movements at a low speed.

[0007] All the aforementioned devices have in common the fact that they have a casing supporting a first rotary grinding member and a second grinding member fixed relative to the casing, the first and second grinding members being spaced from each other and cooperating to grind the powder, each of said first and second members generally being made of an electrically conductive material.

[0008] With these devices, grinding results from both impacts and compression / shearing forces experienced by the raw powder grains, one or other of these mechanical effects being more or less significant depending on the type of device considered.

[0009] To ensure sufficient impact forces, the rotation speed of the rotating part of powder mills is generally very high, in the order of 20 to more than 200 meters per second.

[0010] Also, to ensure sufficient compression / shear forces, the spacing between the grinding members is very limited, of the order of a few tenths of a millimeter to a few millimeters.

[0011] Given the high relative speeds and the short distances between static and rotating parts, mechanical contact between these parts, caused for example by the presence of a metallic foreign body entering the mill, must absolutely be avoided because such contact, in addition to risking damage to the equipment, would cause pollution of the ground product. Such mechanical contacts can also present safety problems in production, since they can generate sparks and / or a local increase in temperature that can ignite the powder-gas mixture and cause an explosion.

[0012] To date, foreign body detection modules are sometimes installed upstream of grinding equipment, but this solution considerably increases the cost and space requirements of the installations. Vibration measurements also make it possible in certain cases to stop the mill quickly in the presence of foreign bodies, but these systems are regularly disrupted by normal vibrations caused by the grinding process itself. The following documents present examples of prior art foreign body detection modules: WO 2014 / 066921 A1, DE 12 46 366 B, WO 2008 / 129183 A2 and EP 1 981 641 B1. Summary of the invention

[0013] An aim of the present invention is therefore to propose a powder grinder which makes it possible to solve the aforementioned problem and which makes it possible in particular to detect conductive foreign bodies, for example metallic ones, which may be present in the mill and thus ensure the stability and quality of the grinding process by stopping the equipment.

[0014] According to the invention, this object is achieved by the subject matter of the independent claims. The more specific aspects of the present invention are described in the dependent claims as well as in the description.

[0015] More specifically, an object of the invention is achieved by means of a mechanical powder grinder, in particular a spindle grinder or a sieve grinder, in particular a conical sieve grinder or a hammer grinder or an oscillating grinder, comprising a casing supporting a first rotary grinding member and a second grinding member fixed relative to the casing, the first and second grinding members being separated from each other by a gap and cooperating to grind the powder, each of said first and second members being made of an electrically conductive material, and the grinder being characterized in that it is provided with an electrical control circuit making at least one primary electrical connection between the first and second grinding members, said electrical circuit comprising at least one device for measuring an electrical parameter of said circuit,and the crusher further comprises a processing device configured to detect an additional connection between the two crushing members, in particular due to the presence of a foreign body between said members, from the measured value of said parameter.,

[0016] In the grinder according to the invention, the gap between the two grinding members forms a grinding zone within which the powder is compressed and / or sheared and / or shocked.

[0017] In normal operation of the mill, there is no direct mechanical contact between the first and second grinding members. In particular in the gap forming the grinding zone, the two members do not touch each other but cooperate to grind the powder. The cooperation between them consists of a relative movement which stirs and projects the powder, so as to subject it, between the two members, to the aforementioned compression / shearing and / or impact forces.

[0018] In the electrical control circuit according to the invention, the first and second grinding members form, so to speak, the two terminals of a switch.

[0019] In normal operation, the switch is open: there is no direct mechanical contact between the first and second grinding members and, in the grinding zone, the gap between them is free or filled with non-conductive materials. There is therefore no additional electrical connection between the grinding members, in addition to the primary electrical connection(s). The gap between the two members can be likened to an infinite resistance.

[0020] When there is contact between the two grinding members via a conductive foreign body (indirect contact) or when there is direct contact linked for example to a deformation of the grinder, the switch is closed: in this case there is an additional electrical connection between the grinding members, linked in particular to the presence of a conductive interposing body between these members. The resistance of this additional electrical connection between the first and second grinding members depends on the nature of the contact made: if for example the interposing body is very conductive, then the resistance is zero or almost zero.

[0021] The electrical control circuit associated with the measuring device makes it possible in particular to evaluate the relative insulation - or the equivalent resistance - between the first and second grinding organs.

[0022] According to the invention, the processing device is also configured to detect, from the value of the measured parameter, a connection anomaly on the electrical control circuit, and this an anomaly of the primary electrical connection. A connection anomaly may for example correspond to an absence of one of the grinding members, or to poor contact at the level of the primary electrical connection (cut electrical wire, poor connection, etc.).

[0023] The electrical parameter measured by the measuring device may be a voltage, a resistance or a current intensity. It is representative of the equivalent resistance between the first and second grinding members, in other words, variations in this parameter can be deduced from variations in the equivalent resistance between the first and second grinding members.

[0024] According to one example, the two grinding members are physically separated by at least one electrically insulating element, so that the primary electrical connection(s) constitute the only passages for an electric current between this grinding member and the second, during normal operation of the grinder.

[0025] More specifically, at least one of the grinding members can thus be electrically isolated from the casing, i.e. physically separated from the latter and from the other grinding member by at least one electrically insulating element. In the present application, and to facilitate understanding, such a member will be referred to as “electrically isolated”, although it is not, in itself, totally isolated.

[0026] Advantageously, the fixed grinding member is electrically insulated.

[0027] In particular, in the aforementioned case of a screen crusher, the screen may be the electrically insulated member of the casing.

[0028] As a variant or in addition, the first rotating grinding member can also be electrically insulated.

[0029] According to one example, the first and second grinding members are physically separated from each other by at least one intermediate piece made of non-conductive material, in particular synthetic material, in particular a polymer material, even more particularly an elastomer material.

[0030] In a particular embodiment, such an intermediate part may also have a sealing function, for example to prevent powder from being able to bypass the sieve or to avoid retention zones.

[0031] According to one example, the first and second grinding members are physically separated from each other by at least one non-conductive coating.

[0032] If it is the static grinding member (fixed relative to the casing) which is electrically insulated, then such a non-conductive coating can in particular be applied directly to said fixed member and / or to a part of the casing supporting this member.

[0033] More specifically, an electrically insulated member as explained above may be physically separated from the housing and the other grinding member by a non-conductive intermediate piece and / or a non-conductive coating.

[0034] According to the invention, a primary electrical connection is made via at least one resistive element. In other words, the electrical control circuit integrates at least one resistive element between the first and second grinding members.

[0035] The resistive element usually has a fixed and known resistance.

[0036] For safety reasons, a grinding element electrically isolated from the housing must be connected to earth. Such a connection allows electrostatic discharge and prevents sparks and possible explosions that may result. The element is therefore advantageously connected to earth via such a resistive element which allows a safe discharge of the isolated element.

[0037] The resistance value of the resistive element must in this case be below a certain limit value beyond which the discharge would no longer be sufficiently rapid and effective. For example, the resistive element has a resistance R between 1 ohm and 1 megaohm.

[0038] According to one example, a resistive element of the control circuit is formed by at least one intermediate part and / or at least one coating inserted between the first and second grinding members.

[0039] The control circuit is governed by Ohm's law (U = R * I) and can therefore be characterized in different ways using a corresponding measuring device.

[0040] In one example, the measuring device is an ohmmeter.

[0041] Alternatively, a current measurement with an ammeter, a voltage measurement with a voltmeter or any other suitable measurement can be considered.

[0042] According to the invention, the measuring device is mounted in parallel with a resistive element of the primary electrical connection.

[0043] According to an example not included in the invention, the resistive element can be located on a first branch of the circuit forming a primary electrical connection between the two grinding members and the measuring device can be located on a second branch of the circuit connected respectively to two points of said first branch located on either side of the resistive element. The measuring device and the resistive element are then connected to each grinding member by the same contact point. In this case, however, in the event of an anomaly in the electrical connection, the measured resistance is the same as during normal operation, even in the presence, for example, of a conductive foreign body between the two grinding members. In other words, in this configuration, the detection system does not make it possible to identify an unwanted electrical contact between the two grinding members, in the event of a failure of the electrical assembly.

[0044] According to the invention, the resistive element is mounted on a first branch of the electrical circuit connected to a first contact point of a grinding member and the measuring device is mounted on a second branch of the electrical circuit mounted in parallel with the first branch and connected to a second contact point of the same grinding member, spaced from the first contact point.

[0045] This additional contact makes it possible to detect a possible connection problem with the double contact grinding member or to detect if the member in question is missing.

[0046] According to a particular example of the invention, the grinder is a screen grinder, for example a conical screen grinder. In this case, the screen forms the second grinding member, fixed relative to the housing.

[0047] This sieve can have openings of any shape, including round and / or square.

[0048] This sieve can also be a grater with openings containing a spout.

[0049] According to one example, the maximum width of the gap between the first and second grinding members is between two tenths of a millimeter and ten millimeters.

[0050] According to another aspect, the invention relates to a method for controlling a powder grinder as defined above, in particular a method for detecting electrically conductive foreign bodies in such a powder grinder and / or for detecting an additional connection between the grinding members of such a grinder, the method comprising at least the steps in which: a parameter representative of the electrical control circuit is measured, from the measured value of said parameter, an additional connection is detected, by direct or indirect contact, between the two grinding members.

[0051] According to one example, from the measured value of said parameter, the presence of a connection anomaly in the electrical control circuit is further detected. Brief description of the drawings

[0052] The features and advantages of the present invention will appear in more detail in the context of the description which follows with an example of embodiment given for illustrative and non-limiting purposes with reference to the three attached drawings which represent: There figure 1 schematically illustrates a powder grinder according to a first embodiment of the invention; The figure 2 is an electrical circuit equivalent to the assembly of the figure 1 , in normal operation of the crusher; The figure 3 is an electrical circuit equivalent to the assembly of the figure 1 , in the case of additional contact between the two grinding members; The figure 4 is an electrical circuit equivalent to the assembly of the figure 1, in the event of a connection anomaly in the control circuit; The Figure 5 schematically illustrates a powder grinder according to an example not included in the invention. Detailed description

[0053] There figure 1 illustrates a powder mill 10 according to a first embodiment of the invention. This is a conical sieve mill but the invention is not limited to this type of mill and can be implemented in an equivalent manner on any other powder mill, in particular a sieve or pin mill.

[0054] In the example illustrated on the figure 1 , the crusher 10 includes a metal casing 20 comprising an external wall 22, for example substantially tubular, delimiting an enclosure 24 of axis Z, and an internal part 26 secured to the external wall 22 and projecting inside the enclosure 24, said internal part comprising at least one support portion 28 located along the axis Z, inside the enclosure 24 delimited by the casing 20, a sieve 30 and a rotor 40 forming two grinding members which cooperate with each other to grind together raw powder introduced from above into the grinder 10.

[0055] The raw powder processed by such a grinder 10 typically consists of grains whose average diameter is, for example, between 500 microns and 20 millimeters. The powder, once ground, is formed of grains whose average diameter is between 100 microns and 5 millimeters.

[0056] Examples of materials that can be ground include active ingredients or excipients for the manufacture of medicines, food products such as lactose, or any other powders for pharmaceutical, chemical or food use.

[0057] The sieve 30, fixed relative to the casing 20, delimits inside the enclosure 24 an upstream part 12 and a downstream part 14 of the grinder. The upstream part 12 receives the raw powder to be ground and the downstream part 14 receives the ground powder after it has passed through the sieve 30.

[0058] In the example, the sieve 30 has a truncated cone shape, with axis Z1. Its perforated wall 32 is inclined at an angle a of, for example, between 20 and 60° relative to this axis Z1. The sieve 30 is arranged inside the casing 20 with its axis Z1 vertical, parallel to - and generally coincident with - the axis Z of the enclosure 24. Its widest end 30a is located upwards, and thus towards a device for supplying the powder to be ground (not illustrated), which may comprise, for example, a valve or a metering wheel. At its lower end 30b, the sieve 30 is supported by the support portion 28 of the casing 20.

[0059] The wall 32 of the sieve 30 is provided with a plurality of openings (not visible in the figure), of any shape, in particular round or square, intended to allow the passage of powder grains of defined maximum diameter. The internal face 32a of the sieve 30 may be smooth or the openings may comprise a beak projecting towards the inside of the sieve, forming a grater.

[0060] The rotor 40, movable relative to the casing 20 and therefore relative to the sieve 30, is housed in the interior space 36 delimited by the wall 32 of the sieve 30.

[0061] It is formed of a plurality of blades 42 secured to a hub 44 mounted to rotate around its axis Z2 and also supported by the support portion 28 of the casing 20. The means for setting the rotor in motion (motor, transmission), well known to those skilled in the art, are integrated into this support portion 28 or offset from the crusher and are not shown in the figure 1 .

[0062] The rotor 40 is arranged coaxially with the screen 30. Each blade 32 is arranged so that one of its edges is permanently flush at a distance d with the internal wall 32a of the screen 32 during rotation.

[0063] The rotor 40 is therefore not in contact with the sieve 30 and a gap 60 of width d is maintained between the two grinding members 30, 40. In the example, the sieve 30 defines, at its lower end 30b, an opening 38 through which the hub 44 of the rotor 40 passes - without contact.

[0064] When the mill 10 is in operation, grains of raw powder are poured by gravity into the upstream part 12 of the mill, onto the rotor / sieve assembly, by the feed device.

[0065] With the rapid rotation of the rotor 40, the grains are projected at high speed against the internal face 32a of the wall 32 of the sieve 30. The grains also undergo compression and shear forces between the blades 42 of the rotor 40 and the wall 32 of the sieve 30. Under the effect of the shocks and the compression / shear forces, the grains are broken up, and their average diameter is reduced, allowing them to pass through the openings of the sieve 30 towards the downstream part 14 of the mill 10 where they will be recovered.

[0066] According to the invention, the grinder 10 is provided with a detection system 70 making it possible to detect an undesirable electrical contact between the two grinding members 30, 40, in particular due to the interposition, between them, of an electrically conductive foreign body, for example a metallic body (for example a screw, a bolt, etc.) present in the raw powder.

[0067] The detection system 70 comprises an electrical control circuit 72 configured to make at least one primary electrical connection between the first and second grinding members 30, 40 and comprising at least one measuring device 90 allowing the measurement of an electrical parameter of the circuit, in particular a multimeter, an ohmmeter, an ammeter or a voltmeter.

[0068] The detection system 70 further comprises a processing device 92 configured to detect an additional connection between the two grinding members 30, 40 from the value thus measured by the measuring device 90.

[0069] The two grinding members 30, 40 are electrically separated from each other by electrically insulating elements, so that the primary electrical connection(s) constitute the only passages for an electric current between the two members, during normal operation of the grinder.

[0070] In particular, at least one of the rotor 40 and the sieve 30 is electrically insulated from the casing 20. In the particular example illustrated, it is the sieve 30 which is insulated from the casing 20, by electrically non-conductive intermediate parts, in particular made of synthetic material, in particular a polymer material, even more particularly an elastomer material.

[0071] In the particular example illustrated, at least one first intermediate piece 50 is interposed laterally between the external wall 22 of the casing 20 and the upper end 30a of the sieve 30. This intermediate piece 50 has an electrical insulation function, but it can also allow the sieve 30 to be fixed relative to the casing 20, and / or ensure sealing between the sieve 30 and the casing 20. The raw powder to be ground is thus prevented from passing directly into the downstream part 14 of the mill 10 without having passed through the sieve 30. Advantageously, the first intermediate piece 50 is arranged to border the upper end 30a of the sieve 30 over its entire periphery and thus forms a closed contour. It may for example be an annular-shaped piece. The first intermediate piece 50 may for example be fixed to the sieve 30 and to the casing 20 by gluing.

[0072] As a variant, the crusher 10 could comprise a plurality of first intermediate parts 50 at the periphery of the screen 30, making it possible to isolate the screen 30 from the external wall 22 of the casing 20. In this case, other means can be implemented to ensure the necessary sealing.

[0073] As illustrated in the figure 1 , the screen 30 is also isolated from the support portion 28 of the casing 20, at its lower end 30b, by at least one second intermediate piece 52 made of non-conductive material. In the example, the second intermediate piece 52 is arranged on the upper face of the support portion 28, and the lower end 30b of the screen 30 rests and is advantageously fixed, for example by gluing, on said second intermediate piece 52.

[0074] As an alternative or in addition to the aforementioned intermediate parts 50, 52, the insulation can also be provided by a non-conductive coating. In the example, such a coating would be applied in particular to the screen 30 and / or to the parts of the casing holding this part (here in particular the support portion 28 and / or the external wall 22 of the casing 20).

[0075] The rotor 40 is mounted directly on the support portion 28, and therefore in electrical contact with this portion 28 and the entire casing 20.

[0076] In the particular example shown in the figure 1 , the electrical control circuit 72 comprises a first branch 74 connected to a first contact point B1 of the sieve 30 on the one hand and to a contact point A1 of the casing 20 on the other hand. The first branch 74 includes a resistive element 80 or grounding resistor, of resistance R, by means of which the sieve 30 is connected to ground.

[0077] The resistance R is preferably between 1 ohm and 1 megaohm to allow a sufficiently rapid and effective electrical discharge if necessary.

[0078] The measuring device 90 is here connected in parallel with the resistive element 80, on a second branch 76 of the electrical circuit 72 connected to a second contact point B2 of the sieve 30, spaced from the first contact point B1, and to the point A1 of the casing 20.

[0079] The connection point A1 to the casing 20 is, due to the electrical contact between the rotor 40 and the casing 20, also electrically connected to the rotor 40.

[0080] In normal operation of the crusher 10, the gap 60 of width d separates the rotor 40 and the screen 30, so that an electric current cannot pass directly from one to the other through said gap. In the electrical control circuit 72, the gap 60 is thus equivalent to an open switch or to an infinite resistance R AB. figure 2illustrates the electrical diagram equivalent to the assembly of the figure 1 , in normal operation.

[0081] The device 90 is for example an ohmmeter, configured to measure a resistance corresponding to the equivalent resistance between points B1 and A1 obtained by relation (1) R eq = 1 1 R 1 + 1 R 2

[0082] With : R1 the resistance of the first branch 74 of the circuit, assimilated to the resistance R of the element 80, R2 the resistance R AB between the two grinding members at the level of the gap 60, Req the equivalent resistance measured by the measuring device 90.

[0083] In normal operation of the crusher 10, the resistance R2 is infinite, and the equivalent resistance R eq is substantially equal to R1 and therefore to the resistance R of the resistive element 80 (Equivalent diagram of the figure 2 ).

[0084] When a metallic foreign body is interposed between the blades 42 of the rotor 40 and the wall 32 of the sieve 30, this body forms an additional contact 99 between the two grinding members 30, 40. The body lets the current pass and forms a resistive element of resistance R AB close to 0 (the element being metallic and therefore conductive). In this case, the equivalent resistance R eq measured by the ohmmeter 90 is also close to 0 (Equivalent diagram of the figure 3 ). The situation is similar in the case of direct contact between the blades 42 of the rotor 40 and the wall 32 of the sieve 30.

[0085] In the case of poor contact at point B1 and / or B2, or in the absence of sieve 30, the measuring device 90 detects an infinite resistance Req. (Equivalent diagram of the figure 4 )

[0086] The measurement results are transmitted to the processing device 92 configured to detect, from the measured equivalent resistance value, the presence of an additional electrical contact between the grinding members 30, 40. The processing device 92 communicates with the automaton (not shown) which controls the grinder 10, so that an alarm and / or a total shutdown of the grinder 10 can be triggered in the event of an abnormal measurement.

[0087] There Figure 5 illustrates a grinder according to an example not included in the invention. Contrary to what has been described previously in connection with the figure 1 , the measuring device 90 is here mounted directly at the terminals of the resistive element 80. The resistive element 80 and the measuring device 90 are therefore connected to the same contact point B1 of the sieve 30.

[0088] In this case, in normal operation of the crusher 10, the measuring device 90 detects a resistance equal to the resistance R of the resistive element 80. In the presence of an electrical contact between the two crushing members 30, 40, the measured resistance is zero. A connection anomaly is not detected in this case.

[0089] The embodiments described above are not limiting of the present invention and numerous variants could be envisaged, in particular: The measuring device may, for example, be a multimeter, an ammeter or a voltmeter, or any other suitable device. The grinding members may be adapted to the type of powder mill in question. The element electrically insulated from the housing may be the movable grinding member, or both grinding members may be electrically insulated from the housing.

Claims

1. Mechanical powder grinder (10), in particular spindle grinder or sieve grinder, in particular conical sieve grinder or hammer grinder or oscillating grinder, comprising a housing (20) supporting a first rotating grinding member (40) and a second grinding member (30) fixed relative to the housing (20), the first and second grinding members (30, 40) being separated from each other by a gap (60) and co-operating in said gap to grind the powder, each of said first and second members (30, 40) being made of an electrically conductive material, and the grinder (10) is provided with an electrical control circuit (72) making at least one primary electrical connection between the first and second grinding members (30, 40), said electrical circuit (72) comprising at least one device (90) for measuring an electrical parameter of said circuit (72), and the grinder (10) further comprises a processing device (92) configured to detect an additional connection (99) between the two grinding members (30, 40), in particular due to the presence of a foreign body between said members, on the basis of the measured value of said parameter, and a primary electrical connection is made via at least one resistive element (80), characterized in that the resistive element (80) is mounted on a first branch (74) of the electrical circuit (72) connected to a first contact point (B1) of a grinding member (30) and said measuring device (90) is mounted on a second branch (76) of the electrical circuit (72) connected in parallel with the first branch (74) and connected to a second contact point (B2) of the same grinding member (30), spaced apart from the first contact point (B1).

2. Grinder (10) according to claim 1, wherein at least one of the grinding members (30, 40) is grounded via said resistive element (80).

3. Grinder (10) according to claim 2, wherein the fixed second grinding member (30) is grounded via said resistive element (80).

4. Grinder (10) according to any one of the claims 1 to 3, wherein the measuring device (90) is connected in parallel with said resistive element (80).

5. Grinder (10) according to any one of the claims 1 to 4, wherein the measuring device (90) is an ohmmeter.

6. Grinder (10) according to any one of the claims 1 to 5, wherein the first and second grinding members (30, 40) are physically separated from each other by at least one intermediate part (50, 52) made of a non-conductive material, in particular a synthetic material, in particular a polymer material, even more particularly an elastomer material.

7. Grinder (10) according to any one of the claims 1 to 6, wherein the first and second grinding members (30, 40) are physically separated from each other by at least one non-conductive covering.

8. Grinder (10) according to claim 2 and any one of the claims 1 to 5, wherein a resistive element (80) of the control circuit (72) is formed by at least one intermediate part (50, 52) and / or at least one covering interposed between the first and second grinding members (30, 40).

9. Grinder (10) according to any one of the claims 1 to 8, wherein the second fixed grinding member (30) is a sieve.

10. Grinder (10) according to any one of the claims 1 to 9, wherein the maximum width (d) of the gap (60) between the first and second grinding members (30, 40) is between two tenths of a millimeter and ten millimeters.

11. Method for control of a powder grinder (10) according to any one of the claims 1 to 10, in particular a method of detecting electrically conductive foreign bodies in such a powder grinder and / or of detecting an additional connection between the grinding members of such a grinder, the method comprising at least the steps of: - measuring a parameter representative of the electrical control circuit (72), - detecting, on the basis of the measured value of said parameter, an additional connection, by direct or indirect contact, between the two grinding members (30, 40).

12. Control method according to claim 11, wherein, on the basis of the measured value of said parameter, the presence of a connection anomaly in the electrical control circuit (72) is also detected.