Air jet screening machine and method for operating an air jet screening machine

Abstract

The invention illustrates and describes an air jet screening machine (24), in particular for laboratory operation, having a screen passage housing (29) into which a screen (5) that is able to be covered by a screen cover (6) is insertable, wherein the screen (5) has a screen base (8) and, in the inserted state of the screen (5), the screen passage housing (29) delimits a screen passage space (9) below the screen base (8), having a slotted nozzle (20) that is rotatable about a vertical centre axis, wherein the slotted nozzle (20) is arranged below the screen base (8) in the inserted state of the screen (5) in the screen passage space (9), having a rotary drive (37) for the slotted nozzle (20) and having an air feed to the slotted nozzle (20) and an air duct through the screen passage housing (29) out of the screen passage space (9). According to the invention, a weighing unit (30) comprising the screen passage housing (29) and a force measuring device having at least one force transducer (26) are provided, wherein the weight force of the weighing unit (30) is transmissible to the force transducer (26) and the weight force and / or the weight of the weighing unit (30) is able to be determined by means of the force measuring device.

Description

[0001] Air jet screening machine and method for operating an air jet screening machine

[0002] The invention relates to an air jet sieve machine, particularly for laboratory use, with a sieve passage housing into which a sieve can be covered with a sieve lid, wherein the sieve has a sieve base and the sieve passage housing, in the inserted state of the sieve, defines a sieve passage space below the sieve base, with a slot nozzle rotatable about a vertical central axis, wherein the slot nozzle, in the inserted state of the sieve, is arranged in the sieve passage space below the sieve base, with a rotary drive for the slot nozzle and with an air supply to the slot nozzle and an air discharge through the sieve passage housing from the sieve passage space.

[0003] Furthermore, the present invention relates to a method for operating an air jet sieve machine, in particular for particle size analysis, wherein the air jet sieve machine has a sieve passage housing into which at least one sieve can be covered with a sieve lid and which, in the inserted state of a sieve, defines a sieve passage space below a sieve base of the sieve, and wherein the air jet sieve machine has a slot nozzle rotatable about a vertical central axis and a rotary drive for the slot nozzle, an air supply to the slot nozzle and an air discharge through the housing from the sieve passage space, a control and evaluation device and a force measuring device with at least one force sensor, in particular a load cell.

[0004] Finally, the present invention relates to a further method for operating an air jet screening machine, wherein an air supply to a slot nozzle of the air jet screening machine and / or an air discharge from a screen passage chamber is carried out through a screen passage housing of the air jet screening machine via at least one stationary air inlet part, in particular connected to a machine frame, and / or at least one stationary air outlet part, in particular connected to a machine frame, and at least one seal is provided in the airflow path between the screen passage housing and the air inlet part and / or the air outlet part.

[0005] Sieving machines of this type and methods for operating such sieving machines are used particularly in connection with analytical sieving. They are especially used to determine the fineness and particle size distribution of dry, powdered materials. Automation of analytical sieving aims to prevent operator errors and achieve high measurement accuracy and reproducibility.

[0006] Air jet screening machines have a housing onto which a screen can be mounted. The screen typically consists of a frame with a flat screen base made of mesh. The screening chamber above the screen base is closed with a lid during screening. Below the screen, the housing has a space. A slot nozzle, rotatable around the vertical central axis of the screen, is located in this space. During screening, air is blown from below against the screen through the uniformly rotating slot nozzle, or the space below the screen is vacuumed by a powerful suction unit. The airflow cleans the mesh of the screen and agitates the material lying on the screen. Fine particles of the material are carried along by the air jet and transported as throughput through the mesh from top to bottom into the space below the screen. The throughput can then be vacuumed out.The particles are separated via a cyclone and collected in a sample vial. Coarse particles larger than the mesh size of the respective sieve cannot pass through the sieve plate and remain on the sieve plate as residue after sieving.

[0007] To determine a particle size distribution curve, several sieving operations must be performed using sieves with different mesh sizes. The coarse fraction remaining on the sieve after the first sieving, the sieve residue, is subjected to further sieving. The sieve with the first mesh size is removed from the sieving machine, and a second sieve with a larger mesh size is inserted. The sieve residue from the first sieving is fed to the second sieve, and a second sieving is carried out. The remaining sieve residue from the second sieving is then fed to a third sieving. Depending on the requirements, several sieving operations can be performed in the desired particle size increments using sieves with different mesh sizes. After each sieving operation, the sieve residue must be weighed to determine the particle size distribution curve.However, material can also be weighed and sieved anew for each sieving. Manually weighing the sieve sample, collecting and manually weighing the sieve residue, and calculating the particle size distribution curve in sieve analyses require considerable time and personnel resources.

[0008] To simplify and thus increase the economics of operating air jet screening machines, it is already known in the art to determine the mass or weight of the screen residue using load cells and its gravitational force. For example, DE 44 19 153 A1 discloses a generic air jet screening machine in which a load cell with its force application point on the central axis of the screen is arranged below the housing. The known air jet screening machine has a three-armed support which is attached to the load cell at the force application point by a connecting element and carries a lifting ring via rods for receiving a test screen, which is inserted into the lifting ring via an elastic support ring. The load cell is mounted on a mounting part which carries an adjustment device that allows the load cell, together with the lifting ring, to be moved or positioned relative to the housing in the direction of the central axis of the screen.The adjustment device can be designed as a motor with a threaded spindle engaging in the housing. During sieving, the receiving part with the load cell and bracket, and thus also the lifting ring, is in a lowered position, i.e., a rest position, with the lifting ring disengaged from the support ring on the test sieve. The test sieve therefore rests positively on a seat surface of the housing with its support ring. After sieving is complete, the receiving part and the components attached to it are raised by the adjustment device so that the lifting ring engages with the support ring and lifts the test sieve from its seat on the housing. The load cell can then determine the total weight of the test sieve, the sieve residue, and the lifting ring with its bracket, and, together with the empty weight of the test sieve determined before sieving, calculate the quantity of the sieve residue.

[0009] The lifting of the test sieve from the housing of the air jet sieve machine, which defines the sieve passage area, as known from DE 44 19 153 A1, is structurally complex and prone to malfunctions due to the precise engagement of the lifting ring and support ring required for lifting the test sieve. In particular, inserting the test sieve into the lifting ring via the support ring requires increased time and complicates the operation of the known air jet sieve machine. Furthermore, the automatic lifting of the test sieve required for determining the mass of the sieve residue is time-consuming, which is a disadvantage, especially when determining a particle size distribution curve based on multiple sieving operations in the desired particle size increments using sieves with different mesh sizes.The prior art method also requires determining the blank weight of the test sieve before sieving, which increases the time and manual effort involved in determining the mass of the sieve residue. Another significant disadvantage of the known embodiment is that sample particles fall through the sieve mesh when the sieve rests on the lifting frame. Therefore, the known air jet sieve machine can only determine the weight of the sieve residue; the mass of sample particles that fall through the sieve mesh cannot be determined with the load cell.

[0010] The object of the present invention is to provide an air jet screening machine and a method for operating an air jet screening machine of the type mentioned above, which are characterized by a high degree of automation and high measurement accuracy, as well as low time and manual effort in determining the mass of the screen residue. Furthermore, the air jet screening machine should have a simple design and allow for the weight determination of the screen residue with a high degree of user-friendliness. Finally, a simple method for determining the screening time of a screening process and for screen identification should be provided.

[0011] The aforementioned problems are solved by an air jet screening machine with the features of claim 1, by a method for operating an air jet screening machine with the features of claim 13, and by a method for operating an air jet screening machine with the features of claim 14. Advantageous embodiments of the invention are the subject of the dependent claims.

[0012] To solve the aforementioned problems, the invention provides for an air jet screening machine of the type mentioned at the outset, comprising a weighing unit encompassing the screen housing and a force measuring device or weighing device with at least one force sensor, wherein the weight of the weighing unit, in particular the screen housing, is transferable to the force sensor and the weight and / or the weight of the weighing unit can be determined with the force measuring device. According to the invention, the screen housing is a component of the mass of a weighing unit, which is determined with the force measuring device provided according to the invention. In contrast to the air jet screening machine known from DE 44 19 153 A1, the invention provides for the measurement or determination of the weight and / or the weight of the screen housing.

[0013] A first method according to the invention for operating an air jet sieve machine, in particular for particle size analysis, accordingly provides the following process steps:

[0014] Determination of the weight force and / or weight of a weighing unit comprising the sieve passage housing with the force measuring device and, preferably,

[0015] Determination of the weight of a sieve residue taking into account the determined weight force and / or the determined weight of the weighing unit.

[0016] The air jet sieve machine according to the invention and the method according to the invention for operating an air jet sieve machine, in particular for particle size analysis, is associated with process, cost and handling advantages.

[0017] In particular, it is advantageous that, according to the invention, the mass of the weighing unit can be derived together with the mass of the complete sample via the force transducer. Integrating a weighing function into the air jet sieve machine eliminates the need for weighing with an external scale, resulting in a smaller footprint and lower equipment costs compared to weighing with an external scale. Furthermore, integrating a weighing function into the air jet sieve machine avoids interface problems associated with using external scales and reduces maintenance requirements. Finally, an external scale often represents a non-validated process component, which is also a disadvantage when weighing with an external scale.

[0018] The measurement of the weight force of the weighing unit, or the determination of the weight of the weighing unit, as provided for in the invention, enables automated weight determination of the sieve residue in a structurally simple manner with low susceptibility to malfunctions and high ease of use. By determining the weight force and / or the weight of the weighing unit with the force transducer, a very precise weight determination of the sieve residue is possible, resulting in significant time savings, especially compared to manual weighing of the sieve residue.

[0019] The weighing unit of the air jet sieve machine according to the invention comprises in particular a sieve passage housing of the air jet sieve machine, which limits the sieve passage space, and optionally further components connected to the sieve passage housing, the masses of which are recorded together with the mass of the sieve passage housing when weighing the weighing unit.

[0020] In particular, when determining the weight of the weighing unit, the mass of a sieve inserted into the sieve passage housing, if applicable the mass of a sieve cover and / or the mass of a sieve sample placed on the sieve as well as parts of the sieve passage can be taken into account and / or measured or determined.

[0021] According to the invention, the handling of the sieve and sample can be carried out together with the handling of the weighing unit, in particular together with the sieve housing. This simplifies handling and reduces the risk of sample carryover, spillage, and sample loss during transfer to transfer vessels. The use of transfer vessels is provided for in the prior art when external precision balances with a typically small weighing platform and / or draft shield are used.

[0022] In contrast to the method known from DE 44 19 153 A1, in which the sieve must be lifted from the housing by a lifting device to determine the weight of the sieve residue, the invention provides a weighing unit that includes or comprises the sieve housing and optionally further components and component groups, wherein the weight force of the weighing unit is transmitted to the force transducer and the weight force and / or the weight of the weighing unit is determined by the force measuring device. By weighing the sieve housing as part of the weighing unit, optionally together with a sieve inserted into the housing and further optionally with a sieve sample inserted into the sieve and / or with the sieve residue, the method according to the invention eliminates the need for mechanically lifting the sieve with an adjustment device, which also leads to a shorter time for determining the weight of the sieve residue.According to the invention, the determination of the weight force and / or the weight of the weighing unit using the force sensor of the weighing device can be performed discontinuously, either before or after the sieve has been inserted into the sieve housing of the weighing unit, optionally with a sieve cover. The method according to the invention thus also enables a simple determination of the weight of the sieve and, optionally, the sieve cover.

[0023] The method according to the invention may in particular comprise the following process steps:

[0024] First, the empty weight of the weighing unit, which includes the sieve housing, is determined in a first process step before a sieve is inserted into the housing. The weight of the weighing unit is then transferred to the force sensor. The determined weight, or the weight of the weighing unit, can be stored in a memory of the force measuring device.

[0025] Subsequently, in a second process step, a sieve without a sieve cover can be inserted into the sieve housing of the weighing unit, and the total weight of the weighing unit with the sieve inserted can be determined. For this purpose, the weight of the weighing unit, together with the weight of the sieve inserted into the sieve housing, is transmitted to the force transducer. The total weight of the weighing unit with the sieve inserted into the sieve housing can be stored in a memory of the force measuring device. By subtracting the mass of the tare weight of the weighing unit determined in the first process step before inserting the sieve into the sieve housing, the tare weight of the sieve can be determined. This subtraction can be achieved by taring the resulting weighing system or by balancing the weights.

[0026] In a third process step, a sample or material to be screened can be placed onto the screen inserted into the screen housing of the weighing unit. The total weight of the weighing unit, including the screen, the material placed on the screen, and any material particles that have fallen through the screen onto the screen housing, can then be determined again. From this total weight, the weight of the material being screened is calculated by subtracting the empty weight of the weighing unit (determined in the first process step) and the weight of the screen (determined in the second process step). The subtraction of these previous masses can be achieved by taring the resulting weighing system or by balancing the weights. The weight of the material being screened can then be stored in the force measuring device's memory.

[0027] In a fourth process step, the sieve cover can then be placed on the sieve, and the total weight of the weighing unit, including the sieve inserted into the sieve housing, the material being screened, the material already passing through the sieve, and the sieve cover, can be determined. This process involves transmitting the combined weight of the weighing unit, the sieve, the material being screened, and the sieve cover to the force sensor. The total weight can also be stored in the weighing device's memory. Before placing any of the masses of the sieve, sample, and cover on the device, all other masses of the weighing unit can be subtracted by prior taring, so that only the weight relevant to the respective process step can be displayed or stored.

[0028] The fifth process step involves sieving. The space below the sieve base can be vacuumed using a powerful suction unit. The air drawn in flows through the slot nozzle, which rotates close to the sieve base. This causes the material being sieved to be agitated by the incoming air and distributed evenly across the entire sieve surface. The airflow reorients the particles on the sieve surface, and particles smaller than the sieve mesh size are either vacuumed up or separated by a cyclone and collected in a sample vial.

[0029] At the end of the sieving process with a rotating slot nozzle, a tapping sieve can be provided to transmit, in particular, vertical tapping impulses to the sieve and / or sieve cover in order to complete the passage of the material through the sieve. Tapping is generally performed to loosen sample adhesions from the sieve or cover that are caused by residual moisture or remain above the sieve mesh due to electrostatic adhesion. A further aspect of the present invention, which may be subordinate, i.e., realizable independently of the features described above, relates to a sieve cover for a sieving machine, in particular for an air jet sieving machine, with the preamble features of claim 1, wherein the sieve cover is made of or comprises a conductive antistatic plastic (ESD plastic).This reduces or completely prevents sample particles from adhering to the sieve lid due to electrostatic effects. Conversely, a statically charged sieve lid can act like a magnet for light, powdery sample components. Sample adhesion to the sieve lid can distort the results of the weight force determination. While it is possible to at least partially remove sample particles adhering to a statically charged sieve lid by tapping, this method is less user-friendly.

[0030] An embodiment in which an airflow is conveyed to the slot nozzle via the air supply using a turbomachine is not excluded.

[0031] During the sieving process, a large portion of the sieve material is carried away from the sieve chamber along with the air extracted from the sieve housing. Some of this material can accumulate on the housing base, parts of the slot nozzle, and, if applicable, in a discharge duct provided and / or formed on the sieve housing (through which the air is extracted along with the sieve material). These particles are then present in the weighing unit at the end of the sieving process.

[0032] To easily determine the sieve residue on the sieve base after the sieving process without manual weighing, a sixth process step involves determining the weight of the weighing unit, including any sieve residue deposited in and / or on the sieve housing or on machine parts connected to the sieve housing, the sieve with its lid inserted into the sieve housing, and the sieve residue remaining on the sieve base. The total weight can then be stored in the weighing device's memory. A tare function can then be implemented so that the weight is zero before the sieve, lid, and residue are removed from the sieve housing. Upon subsequent removal of the sieve, lid, and residue, a negative return weight is obtained.Finally, in a seventh process step, the sieve containing the sieve residue and sieve lid is lifted from the weighing unit to determine the weight of the sieve residue. The weight of the sieve residue is then calculated by subtracting the previously determined weight of the sieve and sieve lid (determined in the sixth process step) from the total weight of the weighing unit (including any deposited sieve residue), the sieve with its lid, and the sieve residue. Manual weighing of the sieve with the sieve residue and, if applicable, the sieve lid is not necessary. If taring as described above is performed at the end of the sixth process step, the mass of the sieve residue can then be determined from the negative return weighing value using the known weight of the sieve and lid.

[0033] The method according to the invention thus enables the determination of the weight of the sieve residue in a convenient manner with high accuracy of weight determination and with high ease of use.

[0034] Preferably, the force and / or weight of the weighing unit is determined using the force sensor before and after the completion of a screening process, i.e., before and after the rotation of the slot nozzle has ceased. However, it is also possible to continuously determine the force and / or weight of the weighing unit during the screening process. As the screening process continues, the force and / or weight of the weighing unit decreases due to the discharge of the screen material from the screen housing. In this context, a control and / or evaluation unit of the air jet screen machine can be configured to automatically terminate a screening process when a predetermined weight or force value of the weighing unit, and thus a predetermined screening duration, is reached.If the weighing signal does not change or only changes insignificantly over a certain period of time, the control and / or evaluation unit can also automatically terminate a sieving process.

[0035] Furthermore, the operator of the air jet screening machine can easily determine from the weight or force value output by the force measuring device whether a screen is inserted into the screen housing or not. This simplifies the process for the operator and allows for a straightforward plausibility check. A precise weight or force value can correlate with a specific screen weight, thus enabling the conclusion that a particular screen has been inserted into the screen housing.In this context, automatic control of the air jet sieve machine can be provided depending on the weight force determined by the force measuring device and / or the determined weight of the weighing unit, in particular such that sieving is only carried out when a weight or force value is reached that corresponds to or exceeds the weight or force value of the weighing unit with the sieve in place.

[0036] To enable sieve identification based on the specific weight force and / or the specific weight of the weighing unit, it is also preferable to use sieves with different mesh sizes and different sieve weights. This allows each sieve to be assigned a specific sieve weight that uniquely identifies the respective sieve.

[0037] Particularly preferably, the weight of the weighing unit can be determined independently of the weight of the machine frame and of components of the air jet screening machine connected to the machine frame. The term "independently decoupled" in the context of the invention means that only the weight of the weighing unit is measured, and the mass of the machine frame and other components connected to the machine frame, in particular a machine housing and / or a base plate of the screening machine and / or a rotary drive for the slot nozzle, are not taken into account when determining the weight of the weighing unit. The machine frame serves to secure the geometric position of machine elements and machine equipment, to absorb loads, forces, and moments occurring during the machine's operation, and to accommodate functional assemblies.Components that are connected to the machine frame will be referred to as "stationary" below.

[0038] A "stationary" machine part is, in particular, a machine part that is directly or indirectly rigidly connected to a machine frame, a machine housing, and / or a base plate of the air jet screening machine. The force transducer can have at least one deformable, in particular bendable and / or deflectable, measuring element, wherein the measuring element is connected to a machine frame of the air jet screening machine and wherein the weight force of the weighing unit is transmitted to the measuring element, and the measuring element is deformed and / or deflected as a result of the transmission of the weight force. The force measuring device comprises a force transducer with a measuring element and control and / or evaluation electronics, in particular signal processing electronics, for converting a measurement signal from the force transducer into a weight or force value.The measuring body can be rigidly connected to or attached to a machine part of the machine frame, for example, a frame component, a base plate, or a machine housing. When the weight of the weighing unit is applied to the measuring body, it deforms and / or deflects from its rest position. A measurement variable dependent on the state of deformation / deflection of the measuring body is then recorded to determine the weight force or weight transferred from the weighing unit to the measuring body.

[0039] Weight determination is preferably carried out using a load cell. The load cell contains a spring element as the measuring body, which is rigidly connected at one end to the machine frame or to a component of the screening machine that is rigidly connected to the machine frame. A force application point for the weight of the weighing unit can then be provided at the other, free end of the measuring body to introduce the weight of the weighing unit into the load cell. This force application causes a slight elastic deformation or change in geometry, in particular a deflection, of the measuring body. As a result, the electrical resistance of the strain gauges changes proportionally to the deformation caused by the applied weight of the weighing unit. Using signal conditioning electronics, the electrical resistance of the strain gauges can be measured, and the resulting signal can be output as a weight or force value.

[0040] The measuring element can, in principle, be formed by any component of the sieving machine according to the invention, which is rigidly connected, directly or indirectly, to a stationary machine part or to the machine frame and whose geometry changes under the influence of the weight or weight force of the weighing unit, or which is slightly elastically deformed under the influence of the weight or weight force of the weighing unit. Elastic deformation of the component is then detected by strain gauges and converted into an electrical signal.

[0041] In particular, the component can be a substantially rigid pipeline connected to the weighing unit, especially the screen housing, and to the machine frame or a component of the screening machine rigidly connected to the machine frame. The supply of air to the slot nozzle and / or the discharge of air from the screen housing, together with the screen opening, can be carried out via the pipeline, which forms a spring element or measuring element of a load cell. The pipeline can be rigidly connected at one end to the weighing unit, especially the screen housing, and at the other end to the machine frame or a component of the screening machine connected to the machine frame, especially a fixed air inlet and / or a fixed air outlet, and must exhibit sufficiently high elasticity so that the geometry of the pipeline changes under the influence of the weight or load.The weight of the weighing unit changes. Elastic deformation of the pipeline is then detected by strain gauges and converted into an electrical signal. At least one pipe connection between the weighing device and a stationary part of the screening machine allows the supply of air to the slot nozzle and / or the exhaust of air from the screen passage housing to be carried out together with the screen passage without sealing elements in the area of ​​the air supply and / or air exhaust, which further simplifies the machine's design.

[0042] Force measurement can be based on the principle of a beam balance and include a position-measuring system that determines the deflection of a beam arm when subjected to the weight of the weighing unit. This enables high precision in weight determination, repeatability, speed, and temperature compensation.

[0043] Electromechanical force compensation is also possible and advantageous. Scales or load cells with electromagnetic force compensation are fundamentally based on beam balances. However, in electromagnetic force compensation, the counterforce to the load on the reference side is generated using a coil acting as an electromagnet and a permanent magnet into which the coil is immersed. A lever system reduces the load to such an extent that it can be compensated by the electromagnet. A position sensor, often optical, on the lifting beam controls the current in the coil used for force compensation via a control amplifier. A shunt with high long-term stability and a low temperature coefficient of electrical resistance converts the current, which is strictly proportional to the compensating force, into a voltage. This voltage is usually fed to an analog-to-digital converter.This enables subsequent digital processing of the measurement result. With such a load cell, high resolution and good reproducibility are possible, along with extremely short measurement times.

[0044] Furthermore, force measurement can be based on the well-known vibrating string measuring principle, whereby electromagnetic oscillations are measured on a resonating body.

[0045] Instead of strain gauge-based force sensors, piezoelectric sensors can also be used. These consist of crystal discs with an electrode foil mounted between them. When a force is applied, a charge is generated, which can be detected using a charge amplifier. The charge is proportional to the applied weight force.

[0046] An embodiment in which the force measuring device forms a functionally and / or structurally independent unit within the screening machine is not excluded. The force measuring device can then be used within the screening machine as a turnkey component. The integration of a force measuring device as an accessory and / or retrofit component into the screening machine is also not excluded.

[0047] Preferably, the air jet screening machine has a machine housing in which the weighing unit is integrated or which encloses the weighing unit. The weighing unit forms a mass unit integrated into the air jet screening machine, which can be weighed with the force measuring device provided according to the invention independently of a machine frame or other stationary components of the air jet screening machine, in particular those connected to the machine frame.

[0048] When determining the weight force and / or the weight of the weighing unit with the force transducer, the weight force of the screen passage housing together with the weight force of the slot nozzle, and, preferably, the weight force of a drive shaft of the slot nozzle, as well as, more preferably, the weight force of a shaft bearing of the drive shaft and / or optionally the weight force of coupling parts of a shaft coupling, as well as optionally the weight force of other components or machine parts that are connected to the screen passage housing and are a mass component of the total mass of the weighing unit, can be transferred to the force transducer.

[0049] The slot nozzle can be mounted on the screen housing or on a component connected to the screen housing. When measuring the weight of the weighing unit, the mass of the screen housing, together with the masses of the slot nozzle, and, preferably, a drive shaft of the slot nozzle, as well as, optionally, coupling parts of a drive coupling connected to the drive shaft, are recorded, and the weights of the aforementioned components are transmitted to the force transducer of the force measuring device. The weight of the weighing unit then includes the weight of the screen housing and the weight of the slot nozzle mounted on the housing, as well as, preferably, the weight of a drive shaft of the slot nozzle and, optionally, the weight of coupling parts for connecting the drive shaft to a rotary drive for the slot nozzle.

[0050] Force bypasses can adversely affect the accuracy of the force and / or weight determination of the weighing unit. Therefore, it is preferably ensured that the weight force of the weighing unit is transmitted to the force transducer at least substantially free of force bypasses that partially divert the weight force of the weighing unit to the machine frame and into the force transducer. Force bypasses can occur at connection points between the weighing unit and stationary machine parts.

[0051] In particular, when determining the weight force and / or the weight of the weighing unit, a force shunt decoupling of the weighing unit from the rotary drive is provided.

[0052] In this context, it can be provided that the slot nozzle is connected to the rotary drive via a drive shaft with a shaft coupling, and that the determination of the weight force and / or the weight of the weighing unit takes place in the disengaged state of the shaft coupling. This eliminates a power bypass of the rotary drive from the mass balance. For example, a jaw coupling can be provided that can be switched from a coupled state during sieving to a disengaged state when determining the weight force and / or the weight of the weighing unit. In the disengaged state, the mechanical connection between the drive shaft and the rotary drive via the shaft coupling is then interrupted. In the disengaged state, the jaws of a jaw coupling can be released, so that no friction or force transmission occurs between the coupling components.

[0053] The air supply to the slot nozzle and / or the air discharge from the sieve passage through the housing can be carried out via at least one stationary machine part, wherein, preferably, when determining the weight force and / or the weight of the weighing unit with the force transducer, a force shunt decoupling of the weighing unit from the stationary machine part is provided.

[0054] Particularly preferably, the air supply to the slot nozzle is carried out via at least one stationary air inlet part connected to a machine frame and / or the air discharge from the screen passage chamber through the screen passage housing via at least one stationary air outlet part connected to a machine frame, wherein, when determining the weight force and / or the weight of the weighing unit with the force transducer, a force shunt decoupling of the weighing unit from the air inlet part and / or air outlet part may be provided.

[0055] The air supply to the weighing unit can be via an inlet channel and / or the air discharge from the weighing unit can be via an outlet channel, wherein the inlet channel can be formed in a stationary air inlet section and / or the outlet channel in a stationary air outlet section of the screening machine, and wherein, during the transmission of the weight force of the weighing unit to the force transducer, a force bypass decoupling of the weighing unit from the air inlet section and / or the air outlet section can be provided. According to the invention, force bypasses are preferably prevented by connecting the weighing unit to stationary machine parts, i.e., to a machine frame or machine base, in particular a base plate and / or an outer machine housing, through which the air supply or discharge takes place. This contributes to high accuracy in force and / or weight determination.The air supply to the slot nozzle can be via a supply channel and / or the air discharge from the screen passage chamber and the screen passage housing can be via a discharge duct, wherein the supply channel can be formed in an air supply section connected to the weighing unit, in particular the screen passage housing, and the discharge duct can be formed in an air discharge section connected to the weighing unit, in particular the screen passage housing. The mass of the air supply section and / or the mass of the air discharge section, together with the masses of the screen passage housing and other machine parts connected to the screen passage housing, in particular the slot nozzle and optionally a drive shaft of the slot nozzle as well as coupling parts of a shaft coupling, can be introduced into or transferred to the force transducer during force and / or weight determination of the weighing unit.

[0056] The feed channel to the slot nozzle and the discharge chute can also be formed by a housing wall of the screen passage housing.

[0057] The transmission of the closing force of a sealing agent to the weighing unit can lead to a change in the value determined by the force sensor for the weight force and / or the weight of the weighing unit.

[0058] When determining the weight force and / or the weight of the weighing unit with the force transducer, a force shunt decoupling of the weighing unit from a stationary air inlet part and / or from a stationary air outlet part is preferably provided.

[0059] In particular, air is supplied to the weighing unit via at least one stationary air inlet part connected to a machine frame and / or air is discharged from the weighing unit via at least one stationary air outlet part connected to a machine frame, wherein, when determining the weight force and / or the weight of the weighing unit with the force transducer, a force shunt decoupling of the weighing unit from the air inlet part and / or air outlet part is provided.

[0060] In particular, a force shunt decoupling is provided between a stationary air inlet part and a supply line connected to and / or formed on the screen passage housing for supplying air to the slot nozzle and / or between a stationary air outlet part and a discharge line connected to and / or formed on the screen passage housing for the air discharge from the screen passage space via the screen passage housing.

[0061] At least one activatable seal can be provided between the weighing unit, in particular the feed line, and the stationary air inlet part and / or between the weighing unit, in particular the discharge line, and the stationary air outlet part, wherein the weighing unit is sealedly connected to the air inlet part and / or the air outlet part in an activated state of the seal, and wherein, when determining the weight force and / or the weight of the weighing unit with the force transducer, the weighing unit is decoupled from the air inlet part and / or the air outlet part by means of a force shunt, in particular spatially separated, in a non-activated state of the seal.

[0062] An "activatable" seal within the meaning of the invention is, in particular, a seal that can be inflated radially, laterally, or axially with a fluid such as air or a liquid, such as a pneumatic seal, expansion seal, roll-out seal, pneumatically or hydraulically activated profile, or inflatable seal. In these seals, the closing force is applied by the fluid pressure. A peristaltic pump can preferably be provided for supplying the fluid to the seal and generating sufficient fluid pressure. This pump is preferably connected to or mounted on the machine frame of the screening machine. The peristaltic pump is preferably not a component of the weighing unit.Channels can be formed in a feed line leading to the slot nozzle and / or in a discharge line leading from the screen passage chamber and the screen passage housing of the weighing unit in order to direct an activation fluid to the seal or to drain it away from the seal.

[0063] Instead of inflatable seals, actuator-operated sealing elements can also be provided, whereby the closing force can be generated by motor or magnet.

[0064] Furthermore, seals can be provided which have an elastically deformable sealing element that, under vacuum, particularly during screening, presses against a sealing surface and releases a sealing gap after the vacuum generation has ceased. A closing force support for the seal is preferably provided on a stationary machine part of the air jet screening machine according to the invention.

[0065] If, in particular, activatable seals are provided on opposite sides of the weighing unit, the closing forces can cancel each other out in the closed state of the seals, so that a "force bypass decoupling" in the sense of the invention can also be present in the sealed state.

[0066] Furthermore, it is possible to determine the sealing and / or contact forces of the seal that act on the weighing unit in the sealed state and to take them into account when determining the force and / or weight of the weighing unit in order to determine the actual weight of the weighing unit as accurately as possible.

[0067] In particular, the activatable seal can have at least one sealing element which, by axial sliding, radial or lateral constriction, axial or radial or lateral inflation, squeezing or sliding, or by axial and / or radial coupling due to the elastic deformation of a sealing agent when there is negative pressure in the air supply or air discharge, leads to a sealing effect between a movable machine part of the weighing unit and a stationary machine part of the air jet sieve machine.

[0068] An embodiment in which the air supply to the slot nozzle and / or the air discharge from the sieve passage space through the housing is carried out via highly elastic hose connections is not excluded, so that the air supply to the slot nozzle and / or the air discharge from the sieve passage space through the housing is again decoupled by force by way of a bypass.

[0069] A further aspect of the present invention relates to a method for operating an air jet screen machine, wherein air is supplied to a slot nozzle of the air jet screen machine via at least one stationary air inlet part and / or air is discharged from a screen passage chamber through a screen passage housing of the air jet screen machine via at least one stationary air outlet part, and at least one seal is provided in the airflow path between the screen passage housing and the air inlet part and / or the air outlet part, wherein the seal, in an activated state, seals the screen passage housing and the air inlet part and / or the air outlet part together, and the screen passage housing and the air inlet part and / or the air outlet part are decoupled by force by way of a non-activated state of the seal.

[0070] By activating the seal, a pressure force is transferred to the weighing unit, leading to a change in the weight force and / or the weight of the weighing unit as determined by the force measuring device. This change in weight force and / or weight of the weighing unit allows conclusions to be drawn about the closed state of the seal and the presence of any leakage in the pressure system formed by the weighing unit.

[0071] The weight force and / or the weight of the weighing unit can be determined with a force measuring device having at least one force transducer, in particular a load cell, wherein the activation state and / or the closing force of the seal is preferably automatically determined from the determined weight force and / or the determined weight of the weighing unit.

[0072] In principle, the pressure force or closing force of the seal on the weighing unit can also be determined in terms of height and is then taken into account accordingly with the weight force and / or the determined weight of the weighing unit determined by the force measuring device in order to determine the actual weight force and / or the actual weight of the weighing unit.

[0073] For a force-by-shutoff decoupling of the weighing unit from at least one stationary machine part of the screening machine, through which the air supply to the slot nozzle and / or the air discharge from the screen passage through the housing is carried out, in particular for a force-by-shutoff decoupling of the weighing unit from a stationary air inlet part and / or stationary air outlet part, a seal can also be provided which has a very low deformation resistance such that the weighing unit is preferably at least substantially force-by-shutoff decoupled from the stationary machine part when the seal is in its closed state. For example, the seal can be made of an elastomer material with low hardness. The sealant then permanently seals the transition between the weighing unit and the stationary machine part.The formulation "at least substantially force-by-side decoupled" within the meaning of the invention comprises a force by-side influence through the connection of the weighing unit with the stationary machine part via the sealing means on the weight force and / or the determined weight of the weighing unit determined by the weighing device of less than 10%, preferably less than 5%, of the actual value of the weight force and / or the weight of the weighing unit in the case of complete force by-side decoupling or separation of the weighing unit from the stationary machine part.

[0074] The reading or display accuracy of the weight and / or force value output by the force measuring device can range between 0.001 g and 0.01 g. "At least substantially force-by-circuit decoupled" within the meaning of the invention can be achieved if the deviation of the actual value of the weight force and / or the weight of the weighing unit from the weight and / or force value determined by the weighing device is less than 5, preferably less than 3, weighing units.

[0075] Sample carryover, sample transfer, moisture, adhesions, electrostatic effects, interference from electromagnetic radiation, wind, vibrations, temperature, and hysteresis can all influence the weighing result, sometimes exceeding the weighing accuracy many times over. Therefore, the reading or display accuracy of the weight and / or force value output by the force measuring device can range from 0.01 g to 0.1 g.

[0076] In an alternative embodiment, a non-contact seal can be provided for force-by-circuit decoupling of the weighing unit from at least one stationary machine part of the screening machine, through which the air supply to the slot nozzle and / or the air discharge from the screen passage through the housing is carried out, in particular for force-by-circuit decoupling of the weighing unit from a stationary air inlet part and / or stationary air outlet part. The non-contact seal is arranged in the flow path of the supplied or discharged air between the weighing unit, in particular a supply line and / or a discharge line connected to the screen passage housing, and the stationary machine part of the screening machine, in particular a stationary air inlet part and / or a stationary air outlet part.A labyrinth or gap seal, for example, can be used as a non-contact seal, whereby the sealing effect is achieved by extending the flow path through the gap to be sealed.

[0077] Alternatively, the flow path between the weighing unit, in particular a feed line and / or a discharge line connected to the screen passage housing, and a stationary machine part of the screening machine, in particular a stationary air inlet part and / or stationary air outlet part, can also be unsealed or seal-free.

[0078] Further details, features, and advantages of the subject matter of the invention will become apparent from the dependent claims and from the following description of the accompanying drawing, in which exemplary preferred embodiments of the invention are shown. Structurally and / or functionally identical components of the illustrated embodiments are identified by the same reference numerals. The drawing shows:

[0079] Fig. 1 shows a schematic representation of an air jet screening system with an air jet screening machine known from the prior art;

[0080] Fig. 2 shows a schematic representation of an air jet screening system with an air jet screening machine according to the invention;

[0081] Fig. 3 shows a schematic representation of a method according to the invention for operating an air jet sieve machine according to the invention;

[0082] Fig. 4 shows a schematic top view of an arrangement with a screen passage housing of an air jet screen machine according to the invention and with an air supply to the screen passage housing and an air discharge from the screen passage housing;

[0083] Fig. 5 shows a schematic representation of the force-by-circuit decoupling of a weighing unit of an air jet sieve machine according to the invention from stationary machine parts using activatable seals in the open or non-activated state of the seals;

[0084] Fig. 6 shows a schematic representation of the force-by-circuit decoupling of a weighing unit of an air jet sieve machine according to the invention from a stationary machine part, wherein a non-contact seal is provided between the weighing unit and the stationary machine part;

[0085] Fig. 7 shows a schematic representation of the air supply to a screen passage housing of an air jet screen machine according to the invention, wherein a substantially rigid supply line forms an uninterrupted supply channel for supplying an airflow to a slot nozzle of the air jet screen machine;

[0086] Fig. 8 shows a schematic representation of the transmission of a pressure force from an activatable seal to a weighing unit of an air jet sieve machine according to the invention in the closed state of the seal.

[0087] Fig. 1 shows an air jet screening system 1 with an air jet screening machine 2 known from the prior art. The air jet screening machine 2 has a housing unit 3 with a screen passage housing 4, onto which a screen 5 with a screen cover 6 can be placed for a screening operation. The screening chamber 7 above a screen base 8 is closed by the screen cover 6 during a screening operation. Below the screen base 8, the screen passage housing 4 has a screen passage chamber 9. A slot nozzle 10, rotatable about a vertical central axis of the screen 5, is arranged in the screen passage chamber 9.

[0088] During sieving, an airflow 11 is directed upwards through the rotating slot nozzle 10 against the sieve base 8. To generate the airflow 11, a suction device 12 with a suction unit 13 and an upstream filter 14 is provided. The sieve passage 9 is vacuumed by the suction unit 13. The extracted airflow 11 then flows through the slot nozzle 10, causing the material 15 to be sieved to be agitated by the incoming air and distributed evenly over the sieve surface.The airflow 11 reorients particles on the sieve surface, and particles smaller than the mesh size of the sieve 5 are drawn off by the suction unit 13 along with the airflow 11. These particles, forming a sieve passage 20, pass from the sieve passage chamber 9 through the sieve passage housing 4 and via an outlet channel 17 formed on a stationary machine part 16 into a cyclone 18, where they are separated from the airflow 11 and collected in a sample vial 19. The outlet channel 17 forms a suction port (not shown). The airflow 11 is drawn in by the suction unit 13 via this suction port.

[0089] The airflow 11 is supplied to the slot nozzle 10 via a supply channel 21 formed in the machine part 16. The airflow 11 passes through the supply channel 21 to the slot nozzle 10, exits through the slot nozzle 10 into the sieve passage chamber 9 and flows upwards through the sieve base 8 of the sieve 5.

[0090] The slot nozzle 10 is driven by a rotary drive 22, which is connected to the slot nozzle 10 via a drive shaft 23 and a shaft coupling not shown.

[0091] Components that are functionally identical and / or structurally identical or similar to the embodiments described in Figures 2 to 8 below are marked with the same reference numerals.

[0092] Figure 2 schematically shows an air jet screening system 23 with an air jet screening machine 24, wherein a force transducer 26 of a force measuring device is integrated into the air jet screening machine 24 and attached directly or indirectly to a machine frame 25 of the air jet screening machine 24. The force transducer 26 is a load cell. The machine frame 25 is shown schematically in Figure 2. The machine frame 25 can, in particular, have frame components that are rigidly connected to each other and, preferably, to a base plate of the air jet screening machine 24 (not shown) and / or a machine housing (not shown).

[0093] In the illustrated embodiment, the force application point 27 of the force transducer 26 is, by way of example, arranged below a housing edge 28 of a screen housing 29. The force transducer 26 is formed by a measuring body with strain gauges, wherein one end of the measuring body is attached to the machine frame 25 and the force application point 27 for the weight force of a weighing unit 30 encompassing the screen housing 29 is provided at the other, free end of the measuring body. In Fig. 2, the encompassing system boundary of the weighing unit 30 is schematically shown as a dashed line. Due to the force applied by the weighing unit 30 to the force transducer 26, a slight deflection or deformation of the measuring body and the connected strain gauges occurs. The electrical resistance of the strain gauges changes proportionally due to this deformation.Using a signal processing electronics 51, the electrical resistance of the strain gauges can be measured, and the resulting signal can be output as a weight or force value.

[0094] The drive shaft 32 can be supported directly or indirectly on a housing base 38 of the screen housing 29. The total mass of the weighing unit 30 then comprises the mass of the screen housing 29, the mass of a slot nozzle 31, the mass of a drive shaft 32 with shaft bearing 33, the mass of one or more coupling parts 35 of a detachable shaft coupling 34 with coupling parts 35, 36, via which the drive shaft 32 can be coupled to a stationary rotary drive 37 connected to the machine frame 25, and optionally the masses of other structural or machine parts that are connected to the screen housing 29 and whose weight force is introduced into the force transducer 26 during the determination of the weight or force value of the weighing unit 30.

[0095] The mass of the rotary drive 37 is not a component of the mass of the weighing unit 30.

[0096] The sieve housing 29 is connected to a supply line 39 for the air supply to the slot nozzle 31 via a supply channel 40 and to a discharge line 41 for the air discharge from the sieve chamber 9 and the sieve housing 29 via a discharge shaft 42. The supply line 39 and the discharge line 41 are also integral components of the weighing unit 30.

[0097] A stationary air inlet part 43, connected to the machine frame 25, forms an inlet channel 44 for supplying air to the feed line 39 and thus to the slot nozzle 31. A stationary air outlet part 45, also connected to the machine frame 25, forms an outlet channel 46 for exhausting air from the screen passage chamber 9 and the screen passage housing 29 via the exhaust chute 42. A suction line 47 is connected to the air outlet part 45, through which the airflow 11 is extracted by a suction device 12 (not shown), as described above with reference to Fig. 1. The air inlet part 43 and the air outlet part 45 are not integral components of the weighing unit 30.

[0098] The air supply for the airflow 11 is routed through a silencer 48, which is connected to the air inlet part 43. A screen 5 with a screen cover 6, which has a screen base 8, is mounted on the screen passage housing 29. A screen seal 50 is provided to seal the screen 5 against the screen passage housing 29.

[0099] When determining the weight force and / or the weight of the weighing unit 30, the weight force of the weighing unit 30 is transmitted to the force transducer 26. In this process, the weight force of the sieve passage housing 29, together with the weight forces of the slot nozzle 31, the drive shaft 32, the shaft bearing 33, the coupling part 35 of the shaft coupling 34, as well as the feed line 39 forming the feed channel 40 and the discharge line 41 forming the discharge chute 42, can be transmitted to the force transducer 26.

[0100] To decouple the weighing unit 30 from the rotary drive 33 by means of a force shunt, the determination of the weight force and / or the weight of the weighing unit 30 is carried out in the disengaged state of the shaft coupling 34. For example, the shaft coupling 34 can be a jaw coupling whose jaws are disengaged for force shunt decoupling.

[0101] Furthermore, when determining the weight force and / or the weight of the weighing unit 30, a force-by-shutoff decoupling of the weighing unit 30 from the stationary air inlet part 43 and the stationary air outlet part 46 is provided. For this purpose, the air inlet part 43 can be connected to the feed line 39 connected to the screen passage housing 29 and / or the air outlet part 46 to the discharge line 41 connected to the screen passage housing 29 can be connected via activatable seals 49.

[0102] The activatable seals 49 are preferably inflatable seals or actuator-adjustable seals, wherein the feed line 39, in an activated inflated or actuator-adjusted state of the seal 49, is sealed to the stationary air inlet part 43 and / or the discharge line 41 is sealed to the stationary air outlet part 45. In a non-activated state of the seals 49, the weighing unit 30 is decoupled from the stationary air inlet part 43 and / or the stationary air outlet part 45 by means of a force bypass. In the non-activated state of the seals 49, the feed line 39 is not sealed to the stationary air inlet part 43 and the discharge line 41 is not sealed to the air outlet part 45, and weighing takes place. During a sieving process with a rotating slot nozzle 31, the seals 49 are in the activated state.

[0103] The force transducer 28 is connected to a signal conditioning electronics 51 to measure the electrical resistance of strain gauges of the force transducer 26 and to output the signal resulting from the transmission of the weight force of the weighing unit 30 to the force transducer 26 as a force value or weight value.

[0104] Fig. 3 schematically shows the process sequence for operating the air jet sieve machine 24 from Fig. 2, in particular for particle size analysis, wherein the process comprises the following steps:

[0105] First, the empty weight of the weighing unit 30 is determined before a sieve 5 is inserted into the sieve passage housing 29 of the weighing unit 30 (Fig. 3A). The weight of the weighing unit 30 is then transmitted to the force transducer 26. The determined weight, or the determined weight of the weighing unit 30, can be stored in a memory of the force measuring device.

[0106] Subsequently, in a second process step (Fig. 3B), a sieve 5 without a sieve cover 6 can be inserted into the sieve passage housing 29 of the weighing unit 30, and the total weight of the weighing unit 30 with the sieve 5 inserted into the sieve passage housing 29 can be determined. For this purpose, a force transmission of the weight of the weighing unit 30 together with the weight of the sieve 5 inserted into the sieve passage housing 29 is provided to the force transducer 26. The total weight can be stored. From the determined total weight, the sieve weight is obtained by subtracting the empty weight of the weighing unit 30 before the insertion of a sieve 5.

[0107] In a third process step (Fig. 3C), a material 15 is placed onto the sieve 5. The total weight of the weighing unit 30, including the sieve 5 and the material 15 placed on the sieve 5, can then be determined again. From this total weight, the weight of the material 15 is calculated by subtracting the stored weight of the weighing unit 30 and the stored weight of the sieve 5. The weight of the material 15 can then be stored. In a fourth process step (Fig. 3D), the sieve cover 6 can be placed on the sieve 5, and the total weight of the weighing unit 30, including the sieve 55, the material 15 placed on the sieve 5, the material 20 already passed through the sieve 5, and the sieve cover 6 placed on the sieve 5, can be determined. Here too, it is possible to store the total weight in the memory of the force measuring device.

[0108] In a fifth process step (Fig. 3E), a sieving process as described above now follows. At the end of the sieving process with a rotating slot nozzle 31, a preferably manually performed tapping sieve can be provided to transfer vertical tapping impulses to the sieve 5 and / or sieve cover 6 in order to complete the sieve passage 20.

[0109] During the sieving process, a large portion of the sieve material 20 is carried away from the sieve passage chamber 9 by the air discharged from the sieve passage housing 29. Parts of the sieve material 20 may be deposited on the housing base 38, parts of the slot nozzle 31, and possibly in the discharge duct 42, through which the air is discharged from the sieve passage housing 29, and are not carried away from the weighing unit 30 by the airflow 11.

[0110] To easily determine the sieve residue 50a on the sieve base 8 of the sieve 5 after completion of the sieving process without manual sieve weighing, a sixth process step (Fig. 3F) is provided to determine the total weight of the weighing unit 30 with any sieve residue 20 deposited in and / or on the sieve passage housing 29 or on machine parts connected to the sieve passage housing 29, the sieve 5 with sieve cover 6 inserted into the sieve passage housing 29, and the sieve residue 50a remaining on the sieve base 8. The total weight can then be stored.

[0111] Finally, in a seventh process step (Fig. 3g), the sieve 5 with the sieve residue 50a and sieve cover 6 is lifted from the weighing unit 30 to determine the weight of the sieve residue 50a. The weight of the sieve residue 50a is then calculated by subtracting the previously determined weight of the sieve 5 and the sieve cover 6, as determined in the sixth process step, from the total weight of the weighing unit 30 with any deposited sieve passage residues 20, sieve 5 with sieve cover 6, and sieve residue 50a. Manual weighing of the sieve residue 50a is not provided. Fig. 4 shows an embodiment in which the air supply to the slot nozzle 31 and the air discharge from the sieve passage housing 29 are located on the same side of the housing as the sieve passage 20.Accordingly, the feed line 39 to the slot nozzle 31, which forms the feed channel 40, and the discharge line 41, which forms the discharge chute 42, are located on the same side of the housing. The feed channel 40 can be connected to an inlet channel 44 via an activatable seal 49, and the discharge chute 42 can be connected to an outlet channel 46 via an activatable seal 49. The inlet channel 44 and the outlet channel 46 can be formed in a stationary machine part 52 connected to the machine frame 25. In this case, the inlet channel 44 and the outlet channel 46 are located on the same side of the housing. It is also possible for the inlet channel 44 and the outlet channel 46 to be formed in separate, stationary machine parts.The air supply to the slot nozzle 31 and the air discharge from the screen passage housing 29 together with the screen passage 20 on the same side of the housing and the symmetrical arrangement of the air supply and air discharge enable a compact design.

[0112] Fig. 5 schematically and partially shows the construction of an air jet screening machine 53 with a force transducer 26 of a force measuring device, wherein the weight force of a weighing unit 30 can be transmitted to the force transducer 26 and the weight force and / or the weight of the weighing unit 30 can be determined with the force measuring device. For the functional construction of the air jet screening machine 53, reference is made to the embodiment of the air jet screening machine 24 described with reference to Figs. 2 and 3A-G.

[0113] The force transducer 26 is arranged below a weighing unit 30, which is shown schematically. The force transducer 26 is a load cell.

[0114] The force application point 27 of the force transducer 26 is located below a feed line 39 connected to a screen housing 29, leading to the slot nozzle 31. The feed line 39 is formed and / or attached to the screen housing 29 and is an integral part of the mass of the weighing unit 30. The force transducer 26 is arranged below the weighing unit 30, so that when determining the weight force and / or the weight of the weighing unit 30 with the force measuring device, the weight force of the weighing unit 30 is introduced into the force transducer 26 from above. The force transducer 26 is formed by a measuring body with strain gauges, wherein one end of the measuring body is attached to a stationary air inlet part 43 connected to a machine frame 25, and the force application point 27 for the weight force of the weighing unit 30 is provided at the other, free end of the measuring body.This force application causes a slight deflection or deformation of the measuring body and the associated strain gauges. This deformation causes a proportional change in the electrical resistance of the strain gauges. Using signal conditioning electronics (not shown), the electrical resistance of the strain gauges can be measured, and the resulting signal can be output as a weight or force value.

[0115] As can be further seen from Fig. 5, during the determination of the weight force and / or the weight of the weighing unit 30 with the force transducer 26, a force shunt decoupling of the weighing unit 30 from a rotary drive 37 for a drive shaft 32 of the slot nozzle 31 is provided. For a sieving operation, the rotary drive 37 can be connected to the drive shaft 32 via a detachable coupling (not shown) to enable the rotation of the slot nozzle 31 during a sieving operation. However, when determining the weight force and / or the weight of the weighing unit 30 with the force transducer 26, the coupling connection between the drive shaft 32 and the rotary drive 37 is interrupted, thus achieving force shunt decoupling.

[0116] A shaft bearing can be provided on the sieve passage housing 29, but is also not shown in Fig. 5.

[0117] As can be further seen from Fig. 5, a discharge line 41 is formed and / or attached to the sieve passage housing 29, which forms a discharge shaft 42 and is a mass component of the mass of the weighing unit 30.

[0118] During sieving, an airflow from the sieve passage chamber 9 is discharged through the sieve passage housing 29, along with the sieve passage, via the discharge duct 42. An air outlet duct 46 connects to the discharge duct 42 and is formed in a stationary air outlet section 45. The air outlet section 45 is connected to the machine frame 25. The air inlet section 43 and the air outlet section 45 can also be formed in one piece and, preferably, arranged side by side on the same side of the sieve passage housing 29, as shown schematically in Fig. 4.

[0119] For force-by-circuit decoupling of the supply line 39 from the stationary air inlet part 43 and / or for force-by-circuit decoupling of the discharge line 41 from the stationary air outlet part 45, activatable seals 49 can be provided, which can be pneumatically or hydraulically inflated and thus brought into a sealed or activated state. The supply of an airflow 54 to the seals 49 for activation of the seals 49 can be effected via air channels 55, which can be formed in the air inlet part 43 and the air outlet part 45. Preferably, a peristaltic pump 55a is provided, which draws in ambient air and supplies both seals 49 with air.

[0120] Fig. 5 shows the seals 49 in a non-activated state, in which the weighing unit 30 is spatially separated from the air inlet part 43 and the air outlet part 45 and thus decoupled from force bypass. In the activated state of the seals 49, i.e., in the sealing state, the feed line 39 is sealed to the stationary air inlet part 43 and the discharge line 41 is sealed to the stationary air outlet part 45, so that false air ingress during the sieving process can be prevented.

[0121] Alternatively, the seals 49 can also be adjustable seals that can be moved or adjusted from a non-sealing state to a sealing state by an actuator. In the non-sealing state, the feed line 39 is spatially separated from the stationary air inlet part 43, and the discharge line 41 is spatially separated from the stationary air outlet part 45, so that no weight force can be transmitted and a force bypass decoupling is achieved during the weight (force) determination of the weighing unit 30. In the sealing state during the sieving process, however, the feed line 39 is sealed to the stationary air inlet part 43, and the discharge line 41 is sealed to the stationary air outlet part 45, and thus physically connected.

[0122] Fig. 6 shows, by way of example only for the air inlet side and schematically with reference to Fig. 5, the use of non-contact seals in an air jet sieve 56 to achieve force decoupling of the weighing unit 30 from stationary machine parts, in particular a feed line 39 from a stationary air inlet part 43, during the determination of the weight force and / or weight of a weighing unit 30. A non-contact seal can be designed as a gap or labyrinth seal. A corresponding non-contact seal can be provided between a discharge line 41 described above with reference to Fig. 5 and a stationary air outlet part 45.

[0123] An embodiment in which no seal is provided between the weighing unit 30 and stationary machine parts, in particular between a feed line 39 of the weighing unit 30 and a stationary air inlet part 43 and / or a discharge line 41 of the weighing unit 30 and a stationary air outlet part 45, is not excluded, so that a free space exists and the flow transition is always unsealed.

[0124] Alternatively, activatable seals can be provided which have an elastically deformable sealing element in order to achieve force-by-shutoff decoupling of the weighing unit 30 from stationary machine parts, in particular a feed line 39 leading to the slot nozzle 31 from a stationary air inlet part 43 and / or a discharge line 41 leading from the screen passage chamber 9 from a stationary air outlet part 45, during the determination of the weight force and / or the weight of a weighing unit 30. Due to the airflow during the air supply to the slot nozzle 31 and / or the air discharge from the screen passage chamber 9 via the screen passage housing 29, the sealing element can be elastically deformed, so that the sealing element is converted from a non-activated open state to an activated sealing state, in which the sealing element is pressed against the feed line 39 and / or the air inlet part 43 or the screen passage chamber 9.seals against the discharge line 41 and / or the air outlet part 45 and prevents the passage of false air.

[0125] Fig. 7 shows, by way of example for the air inlet side and schematically with reference to Fig. 6, an embodiment of an air jet sieve 57 in which a substantially rigid feed line 59 forms a continuous feed channel 58 for supplying an airflow to a slot nozzle 31, wherein the feed line 59 is rigidly connected at one end to a sieve housing 29 and at the other end to a machine frame 25. Strain gauges 60 are preferably arranged opposite each other on the feed line 59. The feed line 59 together with the strain gauges 60 forms a load cell. When the weight force of a weighing unit 30 comprising the sieve housing 29 is introduced into the feed line 59 as described above, a slight deflection or deformation of the feed line 59 and the connected strain gauges 60 occurs.The deformation causes the electrical resistance of the strain gauges 60 to change proportionally. Using signal conditioning electronics (not shown), the electrical resistance of the strain gauges 60 can be measured, and the resulting signal can be output as a weight or force value.

[0126] Fig. 8 shows, in a highly schematic and exemplary manner for the air inlet side of the air jet sieve machine 53 shown in Fig. 5, the activated state of the seal 49 between the stationary air inlet part 43 and the feed line 39 to the slot nozzle 31. The seal 49 can be an inflatable seal or an actuator-operated seal.

[0127] Fig. 8 schematically shows, in only a partial representation with reference to Fig. 5, the transmission of a compressive force 61 or closing force in the activated sealing state of an activatable seal 49 to the feed line 39 and thus to the weighing unit 30, whereby the transmission of the compressive force 61 leads to a change in the weight or force value determined by the force transducer 26. The force transducer 26 is deformed by the force transmission from the weighing unit 30, whereby the deformation can be measured by strain gauges via a signal processing electronics by means of a change in the electrical resistance of the strain gauges proportional to the deformation.The transmission of the pressure force 61 to the weighing unit 30 results in a change in the electrical resistance of the strain gauges on the force transducer 26, so that, based on the determined weight or force value, a conclusion can be drawn about the sealing condition of the seal 49.

[0128] The air jet screening machine 53 can have a control and / or evaluation device which, upon reaching a specific weight or force value, preferably automatically, detects an activated sealing state of the seal 49 and / or a specific pressure force 61 or sealing force and outputs a corresponding signal. Depending on this, the operation of the air jet screening machine 53 can be controlled, in particular such that a screening process can only be initiated upon reaching a predetermined pressure force 61 or sealing force.

[0129] Figures 5 and 8 show the sealing with activatable sealing elements 49 at a vertical separation line. Sealing at a horizontal or axial separation line, or at an inclined separation line, is also possible.

[0130] Reference symbol list:

[0131] 1 Air jet screening system 35 33 Shaft bearing

[0132] 2 Air jet screening machine 34 Shaft coupling

[0133] 3 Housing unit 35 Coupling part

[0134] 4 sieve passage housings 36 coupling part

[0135] 5 sieve 37 rotary drive

[0136] 6 sieve covers 40 38 housing base

[0137] 7 Sieve chamber 39 Feed line

[0138] 8 sieve tray 40 feed channel

[0139] 9 Sieve passage room 41 Discharge line

[0140] 10 slot nozzles 42 discharge chute

[0141] 11 Airflow 45 43 Air intake part

[0142] 12 Extraction device 44 Inlet channel

[0143] 13 Suction cups 45 Air outlet part

[0144] 14 filters 46 outlet channel

[0145] 15 sieved material 47 suction line

[0146] 16 Machine part 50 48 Silencer

[0147] 17 Outlet channel 49 Seal

[0148] 18 Cyclone 50 Screen seal

[0149] 19 Sample glass 50a Sieve residue

[0150] 20 Sieve pass 51 Signal processing electronics

[0151] 21 Feed channel 55 52 Machine part

[0152] 22 Rotary drive 53 Air jet screening machine

[0153] 23 Air jet sieve system 54 Airflow

[0154] 24 Air jet sieve machine 55 Air duct

[0155] 25 Machine part 55a Pump

[0156] 26 Force transducers 60 56 Air jet sieve machine

[0157] 27 Force application point 57 Air jet screening machine

[0158] 28 Housing edge 58 Feed channel

[0159] 29 Sieve housing 59 Feed line

[0160] 30 weighing units, 60 strain gauges

[0161] 31 Slot nozzle 65 61 Pressure force

[0162] 32 Drive shaft

Claims

Patent claims:

1. Air jet sieve machine (24), particularly for laboratory use, comprising a sieve passage housing (29) into which a sieve (5) that can be covered with a sieve cover (6) can be inserted, wherein the sieve (5) has a sieve base (8) and the sieve passage housing (29), in the inserted state of the sieve (5), defines a sieve passage space (9) below the sieve base (8), comprising a slot nozzle (20) rotatable about a vertical central axis, wherein the slot nozzle (20) is arranged in the sieve passage space (9) below the sieve base (8) in the inserted state of the sieve (5), comprising a rotary drive (37) for the slot nozzle (20) and an air supply to the slot nozzle (20) and an air discharge through the sieve passage housing (29) from the sieve passage space (9), characterized in that a weighing unit comprising the sieve passage housing (29) (30) and a force measuring device with at least one force sensor (26) is provided,wherein the weight force of the weighing unit (30) can be transmitted to the force transducer (26) and the weight force and / or the weight of the weighing unit (30) can be determined with the force measuring device.

2. Air jet sieve machine (24) according to claim 1 , characterized in that the weight force and / or the weight of the weighing unit (30) can be determined mass-decoupled from the weight force of a machine frame (25) of the air jet sieve machine (24).

3. Air jet sieve machine (24) according to claim 1 or 2, characterized in that the force transducer (26) has at least one deformable, in particular bendable, and / or deflectable measuring body, wherein the measuring body is connected to a machine frame (25) of the air jet sieve machine (24) for force transmission and wherein the weight force of the weighing unit (30) is transferred to the measuring body and the measuring body is deformed and / or deflected as a result of the transfer of the weight force.

4. Air jet sieve machine (24) according to one of the preceding claims, characterized in that a machine housing is provided and that the weighing unit (30) is integrated into the machine housing.

5. Air jet sieve machine (24) according to one of the preceding claims, characterized in that the mass of the weighing unit (30) is the mass of the Slot nozzle (20) and, preferably, the mass of a drive shaft (32) of the slot nozzle (20), and, further preferably, the mass of a shaft bearing (33) of the drive shaft (32).

6. Air jet sieve machine (24) according to one of the preceding claims, characterized in that the weight force of the weighing unit (30) can preferably be transmitted to the force transducer (26) at least substantially free of force bypasses.

7. Air jet sieve machine (24) according to one of the preceding claims, characterized in that when determining the weight force and / or the weight of the weighing unit (30) with the force transducer (26) a force shunt decoupling of the weighing unit (30) from the rotary drive (37) is provided.

8. Air jet sieve machine (24) according to one of the preceding claims, characterized in that the slot nozzle (20) is connected to the rotary drive (37) via a drive shaft (32) with shaft coupling (34) and that the determination of the weight force and / or the weight of the weighing unit (30) with the force transducer (26) is carried out in the uncoupled state of the shaft coupling (34).

9. Air jet sieve machine (24) according to one of the preceding claims, characterized in that the air supply to the weighing unit (30) is provided via at least one stationary air inlet part (43) connected to a machine frame (25) and / or the air discharge from the weighing unit (30) is provided via at least one stationary air outlet part (45) connected to a machine frame (25), wherein, when determining the weight force and / or the weight of the weighing unit (30) with the force transducer (26), a force shunt decoupling of the weighing unit (30) from the air inlet part (43) and / or air outlet part (45) is provided.

10. Air jet sieve machine (24) according to claim 9, characterized in that at least one activatable seal (49) is provided between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45), wherein the weighing unit (30) is sealedly connected to the air inlet part (43) and / or the air outlet part (45) in an activated state of the seal (49), and wherein the weighing unit (30) is in a non-activated state when determining the weight force and / or the weight of the weighing unit (30) with the force transducer (26). the seal (49) is decoupled from the air inlet part (43) and / or the air outlet part (45) by means of a force bypass.

11. Air jet sieve machine (24) according to claim 9, characterized in that at least one seal (49) is provided between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45), which has a low resistance to deformation such that the weighing unit (30) is preferably at least substantially decoupled from the air inlet part (43) and / or the air outlet part (45) in a sealing state of the seal (49).

12. Air jet sieve machine (24) according to claim 9, characterized in that at least one non-contact seal is provided between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45) or that the air passage between the weighing unit (30) and the air inlet part (43) and / or the air outlet part (45) is unsealed.

13. Method for operating an air jet sieve machine (24), in particular for particle size analysis, wherein the air jet sieve machine (24) has a sieve passage housing (29) into which at least one sieve (5) can be covered with a sieve cover (6) can be inserted and which, in the inserted state of a sieve (5), defines a sieve passage space (9) below a sieve bottom (8) of the sieve (5), and wherein the air jet sieve machine (24) has a slot nozzle (20) rotatable about a vertical central axis and a rotary drive (37) for the slot nozzle (20), an air supply to the slot nozzle (20) and an air discharge through the sieve passage housing (29) from the sieve passage space (9), a control and evaluation device and a force measuring device with at least one force sensor (26), in particular a load cell, in particular for operating an air jet sieve machine (24) according to one of the preceding claims, wherein the method includes: Determination of the weight force and / or the weight of a weighing unit (30) comprising the sieve passage housing (29) with the force measuring device and, preferably, Determination of the weight of a sieve residue (50a) taking into account the determined weight force and / or the determined weight of the weighing unit (30).

14. Method for operating an air jet screening machine, in particular an air jet screening machine (24) according to one of the preceding claims, in particular a method according to claim 13, wherein an air supply to a slot nozzle (20) of the air jet screening machine (24) and / or an air discharge from a screen passage chamber (9) through a screen passage housing (29) of the air jet screening machine (24) is effected via at least one stationary air inlet part (43) and / or at least one stationary air outlet part (45) and at least one seal (49) is provided in the airflow path between the screen passage housing (29) and the air inlet part (43) and / or the air outlet part (45),wherein the seal (49) in an activated state seals the screen passage housing (29) and the air inlet part (43) and / or the air outlet part (45) together and the screen passage housing (29) and the air inlet part (43) and / or the air outlet part (45) are decoupled by force in a non-activated state of the seal (49).

15. Method according to claim 14, characterized in that the weight force and / or the weight of the weighing unit (30) is determined with a force measuring device having at least one force transducer (26), in particular a load cell, wherein the activation state and / or the closing force of the seal (49) is preferably automatically determined from the determined weight force and / or the determined weight of the weighing unit (30).

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