Technical Field

The invention relates to a screw feeder for delivering a metered flow of particulate material via an auger screw, that has a reduced number of openings and therefore less risk of contamination.

Background

Screw feeders are devices that receive particulate material into a hopper, and deliver the particulate material in a controlled manner at a constant rate from a screw, sometimes called an auger, usually positioned at the base of the hopper. Typically, the particulate material is gravity-fed to the auger, which is often facilitated by an agitator, to keep the particulate material in a flowable condition whilst located in the hopper.

Such feeders are generally capable of handling a wide variety of particulate material, such as free-flowing material (e.g. salt, corn, sugar) flushing (e.g. fly ash, gypsum, aerosil), fluidizable (e.g. cocoa, graphite, activated carbon), cohesive (e.g. titanium dioxide, tricalcium citrate, stearates), adhesive (e.g. pigments, carbon black), abrasive (e.g. quartz sand, silicon carbide, tungsten carbide), compressible (e.g. chalk), fragile (e.g. flakes, instant coffee) and sticky (e.g. fruits). Such feeders are used widely in the food industry and are particularly used where controlled quantities of high-value particulate foodstuffs are processed, such as particulate flavourings. In the food industry, contamination of the foodstuffs is therefore and essential consideration in the choice of screw feeder.

The particulate material is carried along by the thread of the auger screw, and out of the hopper in a metered manner.

Such screw feeders may operate on a gravimetric or volumetric basis. Gravimetric requires a weighing device to ensure that a specific quantity of flow of particulate material leaves the feeder via the auger, whereas volumetric is naturally provided by the speed of operation of the auger.

The auger, and if present, the agitator, are typically mounted on a horizontal shaft, that is driven by a motor that is external to the hopper. The drive shafts therefore extend from the motor to enter the hopper through a motor side of the hopper, necessitating the provision of shaft seals. In known screw feeders the auger screw, mounted on an auger shaft, and passes through the opposite side of the hopper, so that it can deliver the fixed quantity of particulate material from the side of the hopper opposite to the motor side. This arrangement helps to ensure that particulate material from the hopper is guided away from the motor by the auger, to leave the hopper through the opposite side away from the motor, and does not flow towards the motor, where it could cause mechanical damage. In such an arrangement there is typically a further shaft seal on this product-outlet side of the hopper.

Such devices often also have hoppers with a removable panel in the side wall opposing the motor side, to expose the internals of the hopper and allow the removal of the auger screw and its auger shaft, and also the agitator if present. This provides a convenient access point for cleaning and maintenance in the side wall of the hopper. Examples of known screw feeders of this type are the DSR103 from Brabender Technologie, the FEEDOS™ S from Gericke and the range of feeders available from Rospen.

However, it has been found that such access panels have seals, e.g. silicone, that tend to degrade, possibly contaminating the particulate material or allowing it to leak from the hopper.

Identification of these problems gives rise to the need for further improvements in this area.

Detailed Description of the Invention

In a first aspect, the invention relates to a screw feeder for delivering a metered flow of particulate material, the screw feeder comprising a hopper for receiving a supply of particulate material, the hopper having a surrounding side wall and a base, an auger screw positioned in the hopper to receive particulate material from above and mounted on a auger shaft, the auger shaft being rotatably drivable by an auger motor positioned external to the hopper, wherein the auger shaft passes through a motor-side opening in the side wall of the hopper, such that in use the auger screw can rotate on the auger shaft to deliver a metered flow of particulate material through the motor-side opening.

Thus, the auger and auger shaft do not pass through the hopper wall other than through the motor-side opening. The metered flow of particulate material therefore also leaves the hopper via the motor-side opening in the side wall of the hopper. Therefore the number of openings in the hopper is reduced as there is no need for an opening in the opposing outer side wall, and thus reducing the possibility of contamination of any metered particulate material from failing drive seals.

In general the auger screw is positioned adjacent to the base of the hopper. This is so that it can receive the particulate material held in the hopper by gravity, and once contained within the thread of the auger, the particulate material is transported out of the hopper by the auger.

Generally the auger will be horizontal, and be mounted on a horizontal auger shaft, although deviations from this are possible.

Preferably the screw feeder comprises a tubular outer casing, extending from the motorside opening, and through which the auger shaft passes.

Preferably the auger screw passes through the motor-side opening so that a portion of the auger screw is external to the hopper. This helps to ensure that the flow of particulate material out of the motor-side opening remains controlled and metered accurately. In this embodiment the auger screw is within the hopper but also extends out of the hopper through the motor-side opening.

Preferably the auger screw that is external to the hopper is located within the tubular outer casing that extends from the motor-side opening in the hopper, the tubular casing having an internal surface and an external surface, the internal surface being dimensioned to come into close contact with the auger screw. Typically the internal surface will be tubular with a characteristic diameter.

By “close contact” is meant that the screw approached but does not come into contact with the internal surface, e.g. leaving a gap of a couple of millimetres or less, e.g. 0.5 mm.

Once the metered flow of particulate material leaves the hopper, it can fall away from the auger under gravity, to be received below. This is a convenient means for delivering the metered flow of particulate material. Thus, preferably the metered flow of particulate material is directed to leave the hopper via the motor-side opening and subsequently fall under gravity. In one preferred embodiment, the tubular outer casing contains an opening positioned to permit metered flow of particulate material to fall through the opening under gravity to be received below.

Preferably the auger shaft also has mounted thereon a reverse-sense auger screw, the reverse-sense auger screw positioned between the motor and the auger screw and within the tubular outer casing, the reverse-sense auger screw being dimensioned to come into close contact with the internal surface of the tubular outer casing. The reverse-sense auger screw acts to direct any metered particulate material away from the motor, thus ensuring that particulate material does not get transported to the motor.

In a particularly preferred embodiment, the opening in the tubular outer casing is located between the auger screw and the reverse-sense auger screw. This has the effect that the particulate material is directed towards the opening from either side, and that accurate metering is achieved.

In a preferred embodiment the tubular outer casing extends beyond the auger screw towards the motor, in which extended portion the internal surface has a reduced diameter that is less than that of the auger screw. The reduction in diameter helps to ensure that any particulate material directed towards the motor by the auger is prevented from passing into this reduced diameter region and prevented from entering the motor.

The reduced diameter portion can further be combined with the reverse-sense auger to provide even greater prevention of the passage of particulate material to the motor. When so combined it is preferred that the reverse sense auger is positioned on the hopper-side of the reduction in diameter. Thus, in one embodiment, the reverse-sense auger has the same diameter as the auger, and the reduction in diameter occurs immediately on the motor-side of the reverse-sense auger.

Advantageously, the change in diameter is a step-change, and this step change can be conveniently provided by a union of two tubular outer casings having different internal diameters. Such a union preferably comprises a labyrinth mating between facing flanges of the joined tubular outer casing, as this helps further to prevent the passage of particulate material. In a preferred embodiment, the auger shaft comprises a horseshoe spacer, which comprises a vertical slot to allow the ejection under gravity of any undesirable particulate material traveling towards the motor, or any undesirable material travelling from the motor towards the hopper. The horseshow spacer may be located in any convenient position around the drive shaft, but is conveniently located to the motor side of any reduced diameter portion, so as to present a last degree of protection against undesirable movement of particulate material.

The invention will now be illustrated, with reference to the following figures, in which:

Figure 1 is a perspective view of a screw feeder according to the present invention.

Figure 2 is a side sectional view of the screw feeder shown in figure 1.

Figure 3 is a side sectional view through the auger shaft of the screw feeder shown in figures 1 and 2.

Figure 4 is a perspective view of a portion of the screw feeder shown in figures 1 to 3, illustrating internal detail.

Turning to the figures, figures 1 and 2 show a screw feeder 10 comprising a hopper 12 comprising an auger screw 14 mounted on an auger shaft 16 driven by an auger motor 18. The hopper 12 also comprises an agitator 20 mounted on an agitator shaft 22 driven by an agitator motor 24. The hopper 12 has a motor-side wall 26, an opposing outer side wall 28 a rear wall 27 a front wall 29 and a base 30. The side walls 26, 27, 28, 29 together form a hopper opening 32 at the top for receiving particulate material. The auger screw 14 is positioned horizontally and adjacent the base 30 of the hopper 12.

Auger shaft 16 passes from the auger motor 18 through the motor-side wall 26 through a motor-side opening 34. The auger screw 14 passes through the motor-side opening 34 so that a portion of the auger screw 14 is external to the hopper 12. It will be noted that opposing outer side wall 28 contains no openings or joins and is a clean sheet of material.

Extending from the motor-side opening 34 is a tubular casing 36 which contains the auger screw 14 and auger shaft 16. The tubular casing 36 has an internal diameter that provides a surface that is in close contact with the auger screw 14. The tubular outer casing 36 comprises an opening 38 to allow the metered flow of particulate material to fall through the opening 38 under gravity to be received below.

In use, particulate material is deposited into the hopper opening 32, and agitator 20 rotates on the agitator shaft 22 to ensure that the particulate material remain in a loosened and free- flowing state. The auger motor 18 acts to rotate the auger shaft 16 so that the auger 14 rotates such that metered particulate material contained within the thread of the auger 14 is moved towards and out of the motor-side opening 34. The metered particulate material continues to travel along the tubular casing 26 until it reaches the opening 38, where it falls away from the auger under gravity to be received below through hole 40.

Arrow 39 shows the direction of movement of the metered particulate material as it passes out of opening 38.

As most clearly shown in figure 3, also mounted on the auger shaft 16 is a reverse-sense auger screw 42, the reverse-sense auger screw 42 being positioned between the auger motor 18 and the auger screw 14 and within the tubular outer casing 36. The reverse-sense auger screw 42 is dimensioned to come into close contact with the internal surface of the tubular outer casing 36. As the auger shaft 16 rotates to transport metered particulate material to the opening 38, if any manages to be transported past the opening 38, it will encounter the reverse-sense auger screw 42, which acts to redirect any metered particulate material back towards the opening 38.

Also as shown in figure 3, the tubular outer casing 36 extends beyond the auger screw 14 towards the motor 18, in which there is a step-change in diameter, provided by a union 47 of the tubular outer casing 36 and a narrowed tubular casing 48 that has an internal diameter that is smaller than that of the auger 14. This step-change in internal diameter ensures that any metered particulate material that manages to pass the reverse-sense auger screw 42 will be unable to pass the step-change and thus travel onwards to the auger motor 18. Additionally, the space created by the step change, allows the reverse-sense auger screw 42 to snugly fit, ensuring close contact between the reverse-sense auger screw 42 and the internal space of the tubular outer casing 42 at the point of the step-change in diameter.

Arrow 41 shows the direction the metered particulate material would have to travel in order to pass the step-change in diameter. It will also be noted that the union 47 comprises a labyrinth mating between facing flanges of the tubular outer casing 36 and the narrowed tubular casing 48. This acts to ensure that no metered particulate material manages to escape through the union 47.

Thus, although particulate material is initially directed along the auger shaft 16 in the direction of the auger motor 18 by the auger 14, the arrangement ensures that none of the particulate material makes it to the motor 18, and all of it leaves via the opening 38. Additionally, as the opposing outer side wall 28 contains no openings or joins and is a clean sheet of material, there is no prospect of contamination of the particulate material from any seals.

Figure 4 is a perspective view of the internals of the screw feeder 10, and shows where the tubular outer casing 36 pass through metal casing 52 that contains motors 18, 24. For clarity, the auger shaft 16 is not shown. Immediately on the inside of metal casing 52 is positioned a horseshoe spacer 50 which comprises an open vertical slot 54 around the lower region of the circumference of the horseshoe spacer 50. This slot provides an additional ability for any particulate material travelling towards the motor to be ejected by falling under gravity through the vertical slot 54. Additionally, it provides for the ejection of any undesirable material travelling from the motor 18 towards the particulate material contained within the hopper 12.