Patent Application
20240157369
The present invention relates to the field of powder grinders.
The powders used in the pharmaceutical, chemical or food industries typically have an average grain diameter of between 10 and 500 microns, and are obtained by grinding raw powders whose grains have an average diameter of, for example, between 100 microns and several millimeters.
The size of the grains involved calls for the use of suitable grinding devices.
Among the suitable grinders—known as mechanical grinders—are pin grinders, which comprise two parallel disks, each fitted with grinding elements, typically in the form of rods or pins, directed towards the adjacent disk. These grinding elements are designed to impact the material grains when the two disks rotate relative to one another.
There are also sieve grinders 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 sieve openings.
There are several types of sieve grinders, differentiated mainly by their shape and rotation speed. The main ones are:
What all the above devices have in common is that they feature a casing supporting a first rotating grinding member and a second grinding member fixed relative to the casing, the first and second grinding members being spaced apart and co-operating to grind the powder, each of said first and second members generally being made of an electrically conductive material.
With these devices, grinding is the result of both impact and compression/shear 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.
To ensure sufficient impact forces, the rotational speed of the rotating part of powder grinders is generally very high, on the order of 20 to over 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 short distances between stationary and rotating parts, mechanical contact between these parts, caused, for example, by the presence of a metallic foreign body entering the grinder, must be absolutely avoided, as such contact would not only risk damaging the equipment, but would also pollute the ground product. Such mechanical contacts can also present production safety problems, since they can generate sparks and/or a local rise in temperature that can ignite the powder-gas mixture and cause an explosion.
To date, foreign body detection modules are sometimes installed upstream of the grinding equipment, but this solution considerably increases the cost and bulk of the installations. Vibration measurements can also be used in some cases to stop the grinder quickly in the presence of foreign bodies, but these systems are regularly disrupted by the normal vibrations caused by the grinding process itself.
One of the objects of the present invention is therefore to propose a powder grinder which solves the above-mentioned problem and, in particular, enables the detection of conductive foreign bodies, e.g. metallic, which may be present in the grinder, thus ensuring the stability and quality of the grinding process by stopping the equipment.
According to the invention, this object is attained by way of 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.
More specifically, an object of the invention is attained by means of a mechanical powder grinder, in particular pin grinder or sieve grinder, in particular conical sieve grinder or hammer grinder or oscillating grinder, comprising a casing supporting a first rotating 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 co-operating 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 grinder 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, from the measured value of said parameter.
In the grinder according to the invention, the gap between the two grinding members forms a grinding zone in which the powder is compressed and/or sheared and/or shocked.
In normal grinder operation, there is no direct mechanical contact between the first and second grinding members. Particularly in the gap forming the grinding zone, the two members do not touch but co-operate to grind the powder. The co-operation between them consists in a relative displacement that stirs and throws the powder, so as to subject it, between the two members, to the aforementioned compression/shearing and/or impact forces.
In the electrical control circuit according to the invention, the first and second grinding members form the two terminals of a switch, so to speak.
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 material. As a result, there is no additional electrical connection between the grinding members, over and above the primary electrical connection(s). The gap between the two members can be likened to an infinite resistance.
In the event of contact between the two grinding members via a conductive foreign body (indirect contact), or in the event of direct contact due, for example, to deformation of the grinder, the switch is closed: in this case, there is an additional electrical connection between the grinding members, due in particular to the presence of a conductive intermediate 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 intermediate body is highly conductive, then the resistance is zero or virtually zero.
In particular, the electrical control circuit associated with the measuring device makes it possible to evaluate the relative insulation—or equivalent resistance—between the first and second grinding members.
Advantageously, the processing device can also be configured to detect, from the measured parameter value, a connection anomaly on the electrical control circuit, and in particular an anomaly in the primary electrical connection. A connection anomaly may, for example, correspond to the absence of one of the grinding elements, or to poor contact in the primary electrical connection (cut 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 second grinding members. Said in another way, variations in this parameter can be deduced from variations in the equivalent resistance between the first and second grinding members.
In 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 electrical current between this grinding member and the second, during normal operation of the grinder.
More specifically, at least one of the grinding members can thus be electrically insulated 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 for ease of understanding, such a member will be referred to as “electrically insulated”, although it is not, in itself, totally insulated.
Advantageously, the fixed grinding member is electrically insulated.
In particular, in the aforementioned case of a sieve grinder, the sieve can be the member electrically insulated from the casing.
As an alternative or in addition, the first rotary grinding member can also be electrically insulated.
According to one example, the first and second grinding members are physically separated from each other by at least one intermediate part made of a non-conductive material, notably a synthetic material, in particular a polymer material, even more particularly an elastomer material.
In a particular embodiment, such an intermediate part can also have a sealing function, for example to prevent powder from bypassing the sieve or to avoid retention zones.
In one example, the first and second grinding members are physically separated from each other by at least one non-conductive covering.
If it is the static grinding member (fixed relative to the casing) that is electrically insulated, then such a non-conductive covering 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 covering.
In one example, a primary electrical connection is made via at least one resistive element. In other words, the electrical control circuit incorporates at least one resistive element between the first and second grinding members.
The resistive element generally has a fixed, known resistance.
For safety reasons, a grinding member that is electrically insulated from the casing must be grounded. Such a connection enables electrostatic discharge and avoids sparks and any resulting explosions. The member is therefore advantageously grounded via such a resistive element, which enables safe discharge of the insulated member.
In this case, the resistance value of the resistive element must be below a certain limit value, beyond which the discharge would no longer be sufficiently fast and effective. For 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 covering interposed between the first and second grinding members.
The electrical control circuit is governed by ohm's law (U=R*I) and can therefore be characterized in various 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 envisaged.
According to one example, the measuring device is connected 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. In this case, the measuring device and resistive element are connected to each grinding member via 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 of a conductive foreign body between the two grinding elements, for example. In other words, in this configuration, the detection system is unable to identify undesirable 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 connected in parallel with 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 any connection problems with the double-contact grinding member, or to detect whether the member in question is missing.
According to a particular example of the invention, the grinder is a sieve grinder, for example a conical sieve grinder. In this case, the sieve forms the second grinding member, fixed relative to the casing.
The sieve can have any shape of opening, especially round and/or square.
This sieve can also be a rasp with openings featuring a beak.
According to one example, the maximum width of the gap between the first and second grinding members is between 0.2 millimeter and 10 millimeters.
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:
According to one example, the measured value of said parameter is used furthermore to detect the presence of a connection anomaly in the electrical control circuit.
The features and advantages of the present invention will become apparent in greater detail in the description which follows, together with an illustrative and non-limiting example of an embodiment, with reference to the five drawings attached hereto, which show:
In the example shown in
The raw powder processed by such a grinder 10 is typically made up of grains with an average diameter of between 500 microns and 20 millimeters, for example. Once ground, the powder is made up of grains with an average diameter of between 100 microns and 5 millimeters.
Examples of materials that can be ground in this way include active ingredients or excipients for the manufacture of medicines, food products such as lactose, or any other powder for pharmaceutical, chemical or food use.
The sieve 30, fixed relative to the casing 20, delimits an upstream part 12 and a downstream part 14 of the grinder within the enclosure 24. 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.
In this example, the sieve 30 has a truncated cone shape with axis Z1. Its perforated wall 32 is inclined at an angle α of, for example, between 20 and 60° with respect to this axis Z1. The sieve 30 is arranged inside the casing 20 with its Z1 axis vertical, parallel to—and generally coincident with—the Z axis of the enclosure 24. Its widest end 30a faces upwards, and thus towards a device for feeding the powder to be ground (not shown), which may comprise a valve or a metering wheel, for example. At its lower end 30b, the sieve 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 on the figure), of any shape, in particular round or square, intended to allow the passage of powder grains of a defined maximum diameter. The inner face 32a of the sieve 30 may be smooth, or the openings may have a beak projecting towards the inside of the sieve, forming a rasp.
The rotor 40, movable relative to the casing 20 and therefore relative to the sieve 30, is accommodated in the interior space 36 delimited by the wall 32 of the sieve 30.
It is formed by a plurality of blades 42 integral with a hub 44 rotatably mounted about its axis Z2 and also supported by the support portion 28 of the casing 20. The means of moving the rotor (motor, transmission), well known to those skilled in the art, are integrated into this support portion 28 or mounted outside the grinder and are not shown in
The rotor 40 is arranged coaxially with the sieve 30. Each blade 32 is arranged so that one of its edges is permanently flush with the inner wall 32a of the sieve 32 at a distance d during rotation.
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 passes—without contact—the hub 44 of the rotor 40.
When the grinder 10 is in operation, raw powder grains are discharged by gravity into the upstream part 12 of the grinder, onto the rotor/screen assembly, via the feed device.
With the rapid rotation of rotor 40, the grains are thrown at high speed against the inner face 32a of the wall 32 of sieve 30. The grains are also subjected to compressive and shear forces between the blades 42 of the rotor 40 and the wall 32 of the sieve 30. As a result of the impact and compression/shearing forces, the grains are broken up and their average diameter is reduced, allowing them to pass through the openings in the sieve 30 to the downstream part 14 of the grinder 10, where they are collected.
In accordance with the invention, the grinder 10 is provided with a detection system 70 for detecting 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 metal 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 second grinding members 30, 40 and comprising at least one measuring device 90 for measuring an electrical parameter of the circuit, in particular a multimeter, an ohmmeter, an ammeter or a voltmeter.
The detection system 70 furthermore comprises a processing device 92 configured to detect an additional connection between the two grinding members 30, 40 on the basis of the value thus measured by the measuring device 90.
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 electrical current between the two members, during normal operation of the grinder.
In particular, at least one from among the rotor 40 and the screen 30 is electrically insulated from the casing 20. In the particular example shown, it is the sieve 30 that is insulated from the casing 20, by electrically non-conductive intermediate parts, notably made of synthetic material, in particular a polymer material, even more particularly an elastomer material.
In the particular example shown, at least one first intermediate piece 50 is interposed laterally between the outer wall 22 of the casing 20 and the upper end 30a of the sieve 30. This intermediate part 50 has an electrical insulation function, but it can also be used to secure the sieve 30 to the casing 20, 25 and/or to provide a seal 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 grinder 10 without having passed through the sieve 30. Advantageously, the first intermediate part 50 is designed to flank the upper end 30a of the sieve 30 around its entire periphery, thus forming a closed contour. This may be a part of annular shape, for example. The first intermediate part 50 can, for example, be fixed to the sieve 30 and to the casing 20 by gluing.
As a variant, the grinder 10 could comprise a plurality of first intermediate parts 50 at the periphery of the sieve 30, enabling the sieve 30 to be isolated from the outer wall 22 of the casing 20. In this case, other means may be used to ensure the necessary seal.
As shown in
As an alternative or in addition to the above-mentioned intermediate parts 50, 52, insulation can also be provided by a non-conductive covering. In the example, such a covering would be applied in particular to the sieve 30 and/or to the parts of the casing holding this part (here in particular the support portion 28 and/or the outer wall 22 of the casing 20).
The rotor 40 is itself mounted directly on the support portion 28, and is therefore in electrical contact with this portion 28 and the entire casing 20.
In the particular example shown in
The resistance R is preferably between 1 ohm and 1 megaohm to enable sufficiently rapid and effective electrical discharge if required.
Here, the measuring device 90 is 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 apart from the first contact point B1, and to point A1 of the casing 20.
Due to the electrical contact between rotor 40 and casing 20, the point A1 of connection to casing 20 is also electrically connected to rotor 40.
During normal operation of grinder 10, gap 60 of width d separates rotor 40 and sieve 30, so that an electric current cannot flow directly from one to the other through this gap. In the electrical control circuit 72, gap 60 is thus equivalent to an open switch or an infinite RAB resistance.
The device 90 is, for example, an ohmmeter, configured to measure a resistance corresponding to the equivalent resistance between the points B1 and A1 obtained through the relationship (1)
with:
In normal operation of the grinder 10, the resistance R2 is infinite, and the equivalent resistance Req is substantially equal to R1 and thus to the resistance R of the resistive element 80 (equivalent diagram of
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 allows the current to pass and forms a resistive element of RAB resistance close to 0 (the element being metallic and thus conducting). In this case, the equivalent resistance Req measured by the ohmmeter 90 is likewise close to 0 (equivalent diagram of
In the case of a 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 measurement results are transmitted to the processing device 92 configured to detect, on the basis of 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 controller (not illustrated) which controls the grinder 10, so that an alarm and/or a total stop of the grinder 10 can be triggered in the case of an aberrant measurement.
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. 20 In the presence of an electrical contact between the two grinding members 30, 40, the resistance measured is zero. A connection anomaly is not detected in this case.
The embodiments described above are not limiting for the present invention, and numerous variants may be envisaged, in particular:
| Number | Date | Country | Kind |
|---|---|---|---|
| . 001358/2022 | Nov 2022 | CH | national |
