PRECISION METERING UNIT FOR FINE/GRAINED POWDERS

Abstract

A fine grain powder metering unit for fine-grained powders combines the volumetric metering mode with the weighing mode, using for pre-metering 95-99% of the required quantity a volumetric drawer which is then emptied into the tray of a precision scale where a low-flow feeder feeds the powder for metering the final 1-5%, so as to combine the advantages of both metering modes and quickly achieve a metering with high accuracy and repeatability, automatically and with a simple and reliable structure.

Claims

1. Metering unit for fine-grained powders including a hopper for loading the powder, a support provided with a vertical hole in correspondence with a bottom outlet of said hopper which is mounted on said support, a volumetric drawer provided with a volumetric metering chamber, said volumetric drawer being mobile back and forth through the support between a filling position, in which said volumetric metering chamber is filled by the powder that descends by gravity from the hopper through said vertical hole in the support, and an emptying position, in which the volumetric metering chamber is emptied of the powder that descends by gravity through a hole formed in a plate on which the support is mounted, and actuator means (11) that provide the volumetric drawer with said back and forth motion, wherein it further includes a final metering chamber, placed under said plate and communicating with the volumetric metering chamber through a second hole formed in the plate in correspondence with said filling position, a metering tube that extends through said final metering chamber so as to protrude in front with its end in correspondence with said emptying position, said metering tube being provided with a slot for the entry of the powder formed in its portion contained in the final metering chamber, a variable-speed motor that turns the metering tube, a weighing tray placed in correspondence with the emptying position so as to receive the powder from the volumetric metering chamber and from the metering tube, a scale that carries the weighing tray and constantly records the exact weight of the powder contained therein; second actuator means which empty the weighing tray into a discharge pipe, and a control unit operatively connected to said scale, to both the actuator means and to said variable-speed motor so as to control the operation of the actuator means and of the motor on the basis of the weight of the powder detected by the scale.

2. Metering unit according to claim 1, wherein the internal surface of the metering tube has a slight flare towards its end with a taper (α) of a few degrees.

3. Metering unit according to claim 1, wherein a small plate is placed between the volumetric drawer and the plate, said small plate being provided with passages in correspondence with the holes formed in the plate.

4. Metering unit according to claim 1, wherein the weighing tray is mounted on the scale so as to rotate around a horizontal transversal axis and is provided with a front spout.

5. Metering unit according to claim 1, wherein the variable-speed motor rotates the metering tube at a speed between 0 and 120 rpm.

6. Metering unit according to claim 1, wherein the metering tube protrudes from the rear of the final metering chamber to connect to the variable-speed motor.

7. Metering unit according to claim 1, wherein the metering tube is rotatably mounted on the final metering chamber by means of sealing rings.

8. Metering unit according to claim 1, wherein the volumetric drawer consists of a drawer body in which an elongated vertical opening is formed that houses a slider sliding therein under the action of an adjustment screw that engages a longitudinal threaded hole formed in said slider, the volumetric metering chamber being defined by the space between the rear end of the slider and the rear end of said elongated vertical opening.

9. Metering unit according to claim 3, wherein the weighing tray is mounted on the scale so as to rotate around a horizontal transversal axis and is provided with a front spout.

10. Metering unit according to claim 3, wherein the variable-speed motor rotates the metering tube at a speed between 0 and 120 rpm.

11. Metering unit according to claim 4, wherein the variable-speed motor rotates the metering tube at a speed between 0 and 120 rpm.

12. Metering unit according to claim 3, wherein the metering tube protrudes from the rear of the final metering chamber to connect to the variable-speed motor.

13. Metering unit according to claim 4, wherein the metering tube protrudes from the rear of the final metering chamber to connect to the variable-speed motor.

14. Metering unit according to claim 5, wherein the metering tube protrudes from the rear of the final metering chamber to connect to the variable-speed motor.

15. Metering unit according to claim 3, wherein the volumetric drawer consists of a drawer body in which an elongated vertical opening is formed that houses a slider sliding therein under the action of an adjustment screw that engages a longitudinal threaded hole formed in said slider, the volumetric metering chamber being defined by the space between the rear end of the slider and the rear end of said elongated vertical opening.

16. Metering unit according to claim 4, wherein the volumetric drawer consists of a drawer body in which an elongated vertical opening is formed that houses a slider sliding therein under the action of an adjustment screw that engages a longitudinal threaded hole formed in said slider, the volumetric metering chamber being defined by the space between the rear end of the slider and the rear end of said elongated vertical opening.

17. Metering unit according to claim 5, wherein the volumetric drawer consists of a drawer body in which an elongated vertical opening is formed that houses a slider sliding therein under the action of an adjustment screw that engages a longitudinal threaded hole formed in said slider, the volumetric metering chamber being defined by the space between the rear end of the slider and the rear end of said elongated vertical opening.

18. Metering unit according to claim 6, wherein the volumetric drawer consists of a drawer body in which an elongated vertical opening is formed that houses a slider sliding therein under the action of an adjustment screw that engages a longitudinal threaded hole formed in said slider, the volumetric metering chamber being defined by the space between the rear end of the slider and the rear end of said elongated vertical opening.

19. Metering unit according to claim 7, wherein the volumetric drawer consists of a drawer body in which an elongated vertical opening is formed that houses a slider sliding therein under the action of an adjustment screw that engages a longitudinal threaded hole formed in said slider, the volumetric metering chamber being defined by the space between the rear end of the slider and the rear end of said elongated vertical opening.

20. Metering unit according to claim 3, wherein the internal surface of the metering tube has a flare towards its end with a taper (α) of 6°.

Description

[0009] Further advantages and characteristics of the metering unit according to the present invention will be evident to those skilled in the art from the following detailed and not limiting description of a preferred embodiment thereof with reference to the annexed drawings in which:

[0010] FIG. 1 is a top perspective view of the metering unit;

[0011] FIG. 2 is an exploded top perspective view of the upper portion of the metering unit;

[0012] FIG. 3 is a top plan view of the portion of FIG. 2 in assembled condition and with the volumetric drawer in the filling position;

[0013] FIG. 4 is a vertical sectional view along line IV-IV of FIG. 3;

[0014] FIG. 5 is a view equal to FIG. 3 but with a different section line;

[0015] FIG. 6 is a vertical sectional view along line VI-VI of FIG. 5;

[0016] FIG. 7 is a view similar to FIG. 3 but with the volumetric drawer in the emptying position; and

[0017] FIG. 8 is a vertical sectional view along line VIII-VIII of FIG. 7.

[0018] Referring to FIGS. 1 to 6, there is seen that a metering unit according to the present invention comprises a support structure substantially made up of two sides 1 carrying between them an upper plate 2 shaped as a horizontal T and a lower plate 3 extending forward, as well as a scale 4 located behind the lower plate 3 and a first actuator cylinder 5 located above scale 4. The other components of the metering unit are all mounted directly or indirectly on plates 2, 3 and scale 4.

[0019] More specifically, the lower plate 3 carries a discharge pipe 6 which receives the precise dose of gunpowder from a weighing tray 7 mounted on scale 4 so that it rotates around a horizontal transversal axis, under the action of the first actuator cylinder 5, between the filling position shown in FIG. 1 and an emptying position (not shown) where the powder is poured into the discharge pipe 6 through a front spout 7a of tray 7.

[0020] A hopper 8 for loading the gunpowder, either manually or by means of a tube connected to an external automatic feeder, is mounted on a support 9 having a substantially inverted U-shaped cross-section. In this way, a volumetric drawer 10, described in detail below, can slide longitudinally back and forth through said support 9 which is fixed on the upper face of the horizontal arm of the upper plate 2. The longitudinal reciprocating motion of drawer 10 is provided by a second actuator cylinder 11, which is mounted on the rear face of the upper plate 2 and is connected to drawer 10 through a first hole 2a in the vertical arm of the upper plate 2.

[0021] A second hole 2b is formed in the horizontal arm of the upper plate 2 at the bottom outlet of hopper 8 to connect it, through a vertical hole 9a in support 9 and drawer 10, with a final metering chamber 12 which is mounted on the bottom face of the horizontal arm of the upper plate 2. In this way, the gunpowder coming down from hopper 8 first fills said chamber 12 and then drawer 10.

[0022] A metering tube 13, better described later, extends longitudinally through chamber 12 so that it protrudes in front above tray 7 and from the rear to connect to a variable speed motor 14 which rotates it. Also motor 14 is mounted on the rear face of the upper plate 2, below the second actuator cylinder 11, and is connected to tube 13 through a third hole 2c in the vertical arm of the upper plate 2.

[0023] A fourth hole 2d is formed in the horizontal arm of the upper plate 2 at tray 7, and receives a cane 15 that extends downwards to a position adjacent to the front end of the metering tube 13. Finally, a control unit 16 is mounted on the side face of the vertical arm of the upper plate 2 and is operationally connected to scale 4, motor 14 and the two actuator cylinders 5, 11.

[0024] The volumetric drawer 10 consists of a drawer body 10a in which there is formed an elongated vertical opening 10b housing a slider 10c that slides longitudinally under the action of a front adjustment screw 10d, which engages a longitudinal threaded hole obtained in slider 10c. The space between the rear end of slider 10c and the rear end of opening 10b defines the volumetric metering chamber 10e, whose length can thus be varied through the adjustment screw 10d according to the amount of gunpowder to be metered.

[0025] The volumetric drawer 10 is therefore adjusted to typically reach a quantity of gunpowder equal to about 95-99% of the quantity to be metered: for example, for a quantity of 4000 mg chamber 10e can be sized to receive 3970 mg with a tolerance of ±20 mg, so that the final metering involves only a quantity between 10 and 50 mg. This final quantity is loaded into tray 7 by the metering tube 13, which is provided with a filling slot 13a in the portion at the final metering chamber 12, on which tube 13 is rotatably mounted being supported by sealing rings 12a.

[0026] The gunpowder then enters tube 13 through slot 13a and proceeds towards the front end of tube 13 due to the rotation given by motor 14 and, preferably, also thanks to a slight flare of the internal surface of tube 13 which may have a taper α of some degrees (e.g. 6°) so that the powder proceeds along a surface with a small inclination towards the front end of tube 13 (FIG. 6).

[0027] From the description above, and with the help of FIGS. 7 and 8, the simple and effective operation of this metering unit is readily understood.

[0028] As mentioned above, the volumetric metering chamber 10e is filled with the powder that descends by gravity from hopper 8 through hole 9a in support 9 (FIG. 4), after which the second actuator cylinder 11 pushes the volumetric drawer 10 forward until chamber 10e is brought to cane 15 (FIG. 8), so that the quantity of powder metered in chamber l0e is emptied into the weighing tray 7. The scale 4 checks the exact weight of the powder present in tray 7 and sends the data to the control unit 16 which drives motor 14 which turns the metering tube 13 at a preset speed (e.g. the speed of motor 14 can vary between 0 and 120 rpm).

[0029] The gunpowder, coming from the final metering chamber 12 through slot 13a, then starts to flow out from tube 13 and falls into tray 7. The scale 4 continuously sends the powder weight value to the control unit 16, which reduces the rotation speed of motor 14 (and therefore of tube 13) as the detected weight approaches the preset weight, until it comes to a complete stop when the detected weight is exactly the desired one.

[0030] The exact dose of gunpowder present in the weighing tray 7 is then automatically emptied into the discharge pipe 6 through spout 7a by means of the first actuator cylinder 5, as mentioned above, tray 7 is then brought back to the filling position by cylinder 5, the volumetric drawer 10 is brought back to the filling position by the second actuator cylinder 11, and at this point the metering unit is ready to perform the next cycle.

[0031] Note that the volumetric drawer 10 preferably does not rest directly on the upper plate 2 but on a small plate 17 placed between them (FIG. 2), which is obviously provided with passages 17a and 17b respectively at the holes 2b and 2d of the upper plate 2. The purpose of the small plate 17 is to prevent the wear of plate 2, which is typically made of a light and relatively soft metal such as aluminum so as not to make it too heavy, due to the sliding of the volumetric drawer 10, which is typically made of a harder and heavier material to ensure the seal of chamber 10e and the closure of hole 9a during its reciprocating motion.

[0032] It is therefore evident that with the metering unit according to the present invention it is possible to quickly achieve a metering with high precision and repeatability, in an automatic way and with a simple and reliable structure.

[0033] It is clear that the embodiment of the metering unit according to the invention described and illustrated above is only an example susceptible of numerous variations. In particular, the type and arrangement of the actuator means that drive tray 7, drawer 10 and tube 13 can vary somewhat according to specific construction requirements as long as the functionality described above is maintained.