EP4371670A1 - Powder crusher - Google Patents

Abstract

The invention relates to a mechanical powder mill (10) comprising a casing (20) supporting a first rotary grinding member (40) and a second grinding member (30) fixed relative to the casing (20), each of said first and second members (30, 40) being made of an electrically conductive material. According to the invention, the grinder (10) comprises an electrical control circuit (72) making at least one primary electrical connection between the first and the second grinding member (30, 40), and comprising at least one measuring device ( 90) of an electrical parameter of said circuit (72). The crusher (10) further comprises a processing device (92) configured to detect an additional connection between the two grinding members (30, 40), in particular due to the presence of a foreign body between said members, from of the measured value of said parameter.

Description

Technical field of the invention

The present invention relates to the field of powder grinding.

State of the art

Powders used in the pharmaceutical, chemical or even food industries typically have an average grain diameter of between 10 and 500 microns, and come from the grinding of raw powders whose grains have an average diameter of, for example, between 100 microns and several millimeters. .

The size of the grains involved requires the use of suitable grinding devices.

Among the suitable crushers - called mechanical crushers - we find spindle crushers which comprise two parallel discs each provided 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 relative rotation of the two discs.

There are also screen mills which 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 openings of the screen.

• le broyeur à tamis conique qui comporte un rotor d'axe vertical muni de pales coopérant avec un tamis coaxial de forme conique,
• le broyeur à marteaux qui comporte un rotor d'axe horizontal muni de pales et un tamis semi-cylindrique de même axe que le rotor, et
• le broyeur oscillant dont le rotor d'axe horizontal ou vertical a la particularité d'être situé très proche du tamis semi-cylindrique et de réaliser des mouvements d'aller-retour avec une vitesse faible.

There are several types of screen mills which differ mainly by their shape and their rotation speed. We mainly find:

• the conical screen crusher which comprises a rotor with a vertical axis provided with blades cooperating with a coaxial screen of conical shape,
• the hammer mill which comprises a rotor with a horizontal axis provided with blades and a semi-cylindrical screen with the same axis as the rotor, and
• the oscillating crusher whose horizontal or vertical axis rotor 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.

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

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

To ensure sufficient impact forces, the rotation speed of the rotating member of powder crushers is generally very high, of the order of 20 to more than 200 meters per second.

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.

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 more risk of causing 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 which can ignite the powder-gas mixture and cause an explosion.

To date, foreign body detection modules are sometimes installed upstream of grinding equipment, but this solution considerably increases the cost and size 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.

Summary of the invention

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

According to the invention, this aim is achieved thanks to the subject matter of the independent claims. More specific aspects of the present invention are described in the dependent claims as well as in the description.

More specifically, an aim of the invention is achieved thanks to a mechanical powder mill, in particular a spindle mill or screen mill, in particular a conical screen mill or hammer mill or oscillating mill, 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 providing at least one primary electrical connection between the first and the second grinding member, 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 grinding members, in particular due to the presence of a foreign body between said members, to from the measured value of said parameter.

In the crusher 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.

In normal operation of the crusher, there is no direct mechanical contact between the first and the second grinding member. In particular in the gap forming the grinding zone, the two organs 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 organs, to the aforementioned compression/shearing forces and/or shocks.

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.

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 organs can be compared to an infinite resistance.

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

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 the second grinding member.

Advantageously, the processing device can also be configured to detect, from the value of the measured parameter, a connection anomaly on the electrical control circuit, and in particular an anomaly of the primary electrical connection. A connection anomaly can, for example, correspond to the absence of one of the grinding elements, or to poor contact at the primary electrical connection (cut electrical wire, poor connection, etc.).

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

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

More specifically, at least one of the grinding members can thus be electrically isolated from the casing, that is to say physically separated from the latter and from the other grinding member by at least one electrical insulating element. In the present application, and for ease of understanding, such an organ will be called “electrically isolated”, although it is not, in itself, totally isolated.

Advantageously, the fixed grinding member is electrically insulated.

In particular, in the aforementioned case of a screen mill, the screen can be the member electrically insulated from the casing.

As a variant or in addition, the first rotary grinding member can also be electrically insulated.

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

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

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

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.

More specifically, an electrically insulated member as explained above can be physically separated from the casing and the other grinding member by a non-conductive intermediate part and/or a non-conductive coating.

According to one example, 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 the second grinding member.

The resistive element generally has a fixed and known resistance.

For safety reasons, a grinding member electrically isolated from the casing must be connected to earth. Such a connection allows electrostatic discharge and avoids sparks and possible explosions which could arise from it. The member is therefore advantageously connected to earth via such a resistive element which allows secure discharge of the isolated member.

The resistance value of the resistive element must in this case be less than a certain limit value beyond which the discharge would no longer be sufficiently rapid and effective. According to one example, the resistive element has a resistance R of between 1 ohm and 1 megaohm.

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 interposed between the first and the second grinding member.

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

According to one example, the measuring device is an ohmmeter.

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

According to one example, the measuring device is mounted in parallel with a resistive element of the primary electrical connection.

More specifically, 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 resistance measured is the same as during normal operation, even in the presence, for example, of a conductive foreign body between the two organs. grinding. In other words, in this configuration, the detection system does not make it possible to identify unwanted electrical contact between the two grinding members, in the event of failure of the electrical assembly.

According to another more advantageous example, 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 of the first branch and connected to a second contact point of the same grinding member, spaced from the first contact point.

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.

According to a particular example of the invention, the mill is a screen mill, for example a conical screen mill. In this case, the screen forms the second grinding member, fixed relative to the casing.

This sieve can have openings of any shape, in particular round and/or square.

This sieve can also be a grater with openings having a spout.

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

• on mesure un paramètre représentatif du circuit électrique de contrôle,
• à partir de la valeur mesurée dudit paramètre, on détecte une connexion additionnelle, par contact direct ou indirect, entre les deux organes de broyage.

According to another aspect, the invention relates to a method for controlling a powder mill as defined above, in particular a method for detecting electrically conductive foreign bodies in such a powder mill and/or for detecting an additional connection between the grinding members of such a crusher, the process 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.

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

• La figure 1 illustre schématiquement un broyeur de poudre selon un premier mode de mise en oeuvre de l'invention ;
• La figure 2 est un circuit électrique équivalent au montage de la figure 1, en fonctionnement normal du broyeur ;
• La figure 3 est un circuit électrique équivalent au montage de la figure 1, dans le cas d'un contact additionnel entre les deux organes de broyage ;
• La figure 4 est un circuit électrique équivalent au montage de la figure 1, dans un cas d'anomalie de connexion dans le circuit de contrôle ;
• La figure 5 illustre schématiquement un broyeur de poudre selon un deuxième mode de mise en oeuvre de l'invention.

The particularities and advantages of the present invention will appear in more detail in the context of the description which follows with an exemplary embodiment given by way of illustration and not limitation with reference to the three attached drawings which represent:

• There figure 1 schematically illustrates a powder mill according to a first mode of implementation of the invention;
• There figure 2 is an electrical circuit equivalent to the assembly of the figure 1 , in normal operation of the crusher;
• There 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;
• There figure 4 is an electrical circuit equivalent to the assembly of the figure 1 , in the case of a connection anomaly in the control circuit;
• There Figure 5 schematically illustrates a powder mill according to a second mode of implementation of the invention.

detailed description

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.

• un carter métallique 20 comportant une paroi externe 22 par exemple sensiblement tubulaire délimitant une enceinte 24 d'axe Z, et une partie interne 26 solidaire de la paroi externe 22 et faisant saillie à l'intérieur de l'enceinte 24, ladite partie interne comprenant au moins une portion de support 28 située le long de l'axe Z,
• à l'intérieur de l'enceinte 24 délimitée par le carter 20, un tamis 30 et un rotor 40 formant deux organes de broyage qui coopèrent l'un avec l'autre pour broyer entre eux de la poudre brute introduite par le dessus dans le broyeur 10.

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 Z axis,
• 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 the raw powder introduced from above into the crusher 10.

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 crushed, is formed of grains whose average diameter is between 100 microns and 5 millimeters.

As examples of materials that can thus be ground, we can cite active ingredients or excipients intended for the manufacture of medicines, food products such as lactose for example or any other powders for pharmaceutical, chemical or food use.

The screen 30, fixed relative to the casing 20, defines inside the enclosure 24 an upstream part 12 and a downstream part 14 of the crusher. The upstream part 12 receives the raw powder to be crushed and the downstream part 14 receives the crushed powder after it has passed through the sieve 30.

In the example, the sieve 30 has a frustoconical shape, with axis Z1. Its wall 32, perforated, is inclined by an angle α comprised for example between 20 and 60° relative to this axis Z1. The screen 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 include for example a valve or a dosing wheel. At its lower end 30b, the screen 30 is supported by the support portion 28 of the casing 20.

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 grains of powder of defined maximum diameter. The internal face 32a of the sieve 30 may be smooth or the openings may include a nozzle projecting towards the inside of the sieve, forming a rasp.

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

It is formed of a plurality of blades 42 secured to a hub 44 rotatably mounted 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 outside the crusher and are not shown on the figure 1 .

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

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

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.

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 shocks and compression/shearing forces, the grains are split, and their average diameter is reduced, letting them pass through the openings of the sieve 30 towards the downstream part 14 of the crusher 10 where they will be recovered.

In accordance with the invention, the grinder 10 is provided with a detection system 70 making it possible to detect unwanted electrical contact between the two grinding members 30, 40, in particular due to the interposition, between them, of a foreign body electrical conductor, for example a metallic body (e.g. a screw, bolt, etc.) present in the raw powder.

The detection system 70 comprises an electrical control circuit 72 configured to make at least one primary electrical connection between the first and the second grinding member 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.

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.

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

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

In the particular example illustrated, at least a first intermediate part 50 is interposed laterally between the external wall 22 of the casing 20 and the upper end 30a of the screen 30. This intermediate part 50 has an electrical insulation function, but it can also allow the fixing of the sieve 30 relative to the casing 20, and/or ensure the seal between the sieve 30 and the casing 20. The raw powder to be crushed is thus prevented from passing directly into the downstream part 14 of the crusher 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 part. The first intermediate part 50 can for example be fixed to the screen 30 and to the casing 20 by gluing.

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. works to ensure the necessary sealing.

As illustrated on 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 of non-conductive material. In the example, the second intermediate piece 52 is placed 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.

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

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.

In the particular example shown on 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, through which the screen 30 is connected to the ground.

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

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 point A1 of the casing 20.

The point A1 of connection 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.

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 . There figure 2 illustrates the electrical diagram equivalent to the assembly of the figure 1 , in normal operation.

Avec :

• R1 la résistance de la première branche 74 du circuit, assimilée à la résistance R de l'élément 80,
• R2 la résistance R_AB entre les deux organes de broyage au niveau de l'interstice 60,
• Req la résistance équivalente mesurée par le dispositif de mesure 90.

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) $${\mathrm{R}}_{\mathrm{eq}}=\frac{1}{\frac{1}{R1}+\frac{1}{\mathrm{R}2}}$$

With :

• R1 the resistance of the first branch 74 of the circuit, assimilated to the resistance R of 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.

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 ).

When a metallic foreign body is interposed between the blades 42 of the rotor 40 and the wall 32 of the screen 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 with 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 screen 30.

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 )

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 illustrated) which controls the crusher 10, so that an alarm and/or a total shutdown of the crusher 10 can be caused in the event of an abnormal measurement.

There Figure 5 illustrates a crusher according to a second embodiment of the invention. Contrary to what was previously described in connection with there figure 1 , the measuring device 90 is here mounted directly to 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.

In this case, in normal operation of the grinder 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 grinding members 30, 40, the resistance measured is zero. In this case, a connection anomaly is not detected.

• Le dispositif de mesure peut par exemple être un multimètre, un ampèremètre ou un voltmètre ou tout autre dispositif adapté.
• Les organes de broyage peuvent être adaptés au type de broyeur de poudre considéré.
• L'élément isolé électriquement du carter peut être l'organe de broyage mobile, ou les deux organes de broyage peuvent être isolés électriquement du carter.

The embodiments described above are not limiting to the present invention and numerous variants could be considered, in particular:

• The measuring device can for example be a multimeter, an ammeter or a voltmeter or any other suitable device.
• The grinding members can be adapted to the type of powder mill considered.
• The element electrically insulated from the casing may be the movable grinding member, or the two grinding members may be electrically insulated from the casing.

Claims (14)

Mechanical powder mill (10), in particular a spindle mill or screen mill, in particular a conical screen mill or hammer mill or oscillating mill, comprising a housing (20) supporting a first rotary grinding member (40) and a second grinding member (30) fixed relative to the casing (20), the first and second grinding members (30, 40) being separated from each other by a gap (60) and cooperating 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) being characterized in that it is provided with an electrical control circuit (72) carrying out at least a primary electrical connection between the first and the second grinding member (30, 40), said electrical circuit (72) comprising at least one measuring device (90) of 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, from of the measured value of said parameter. Grinder (10) according to claim 1, in which a primary electrical connection is made via at least one resistive element (80). Grinder (10) according to claim 2, wherein at least one of the grinding members (30, 40) is connected to earth via said resistive element (80). Grinder (10) according to claim 3, wherein the second fixed grinding member (30) is connected to earth via said resistive element (80). Grinder (10) according to any one of claims 2 to 4, wherein the measuring device (90) is mounted in parallel with said resistive element (80). Grinder (10) according to any one of claims 2 to 5, in which the resistive element (80) is mounted on a first branch (74) of the electrical circuit (72) connected to a first contact point (B1) d a grinding member (30) and the measuring device (90) are mounted on a second branch (76) of the electrical circuit (72) mounted in parallel with the first branch (74) and connected to a second contact point ( B2) of the same grinding member (30), spaced from the first point of contact (B1). Grinder (10) according to any one of claims 1 to 6, in which the measuring device (90) is an ohmmeter. Crusher (10) according to any one of claims 1 to 7, in which the first and the second grinding member (30, 40) are physically separated from each other by at least one intermediate part (50, 52 ) made of non-conductive material, in particular of synthetic material, in particular a polymer material, even more particularly an elastomeric material. Grinder (10) according to any one of claims 1 to 8, wherein the first and second grinding members (30, 40) are physically separated from each other by at least one non-conductive coating. Grinder (10) according to claim 2 and any one of claims 1 to 7, in which a resistive element (80) of the control circuit (72) is formed by at least one intermediate part (50, 52) and/or at least one coating interposed between the first and the second grinding member (30, 40). Crusher (10) according to any one of claims 1 to 10, wherein the second fixed grinding member (30) is a sieve. Crusher (10) according to any one of claims 1 to 11, in which the maximum width (d) of the gap (60) between the first and the second grinding member (30, 40) is between two tenths of millimeters and ten millimeters. Method for controlling a powder mill (10) according to any one of claims 1 to 12, in particular method for detecting electrically conductive foreign bodies in such a powder mill and/or for detecting an additional connection between the grinding members of such a crusher, the process comprising at least the steps in which: - a parameter representative of the electrical control circuit (72) is measured, - from the measured value of said parameter, an additional connection is detected, by direct or indirect contact, between the two grinding members (30, 40). Control method according to claim 13, in which from the measured value of said parameter, the presence of a connection anomaly in the electrical control circuit (72) is further detected.

Images