GB2614557A

GB2614557A - Screw feeder

Info

Publication number: GB2614557A
Application number: GB2200155.6A
Authority: GB
Inventors: Apps Dan; Smith Chris
Original assignee: KMG Systems Ltd
Current assignee: KMG Systems Ltd
Priority date: 2022-01-07
Filing date: 2022-01-07
Publication date: 2023-07-12
Also published as: WO2023131790A1

Abstract

A screw feeder 10 for delivering a metered flow of particulate material in direction 39 has a hopper 12 for receiving a supply of particulate material via opening 32. Hopper 12, comprising a surrounding side walls 26, 28 and base, also has an outlet 38 for delivering particulate material. At least one drive shaft 16 for mounting a rotatable particulate material transport tool / auger 14, is rotatably drivable by motor 18, positioned external to hopper 12. Drive shaft 16 passes through a motor-side opening 34 in a side wall 26 of hopper 12 and extends into hopper 12, such that the rotatable particulate material transport tool 14 can rotate inside the hopper 12 to facilitate the metered flow in direction 39. Drive shaft 16 passes through a tubular outer casing 36 with an internal and external surfaces and also having also mounted thereon a reverse-sense screw 42 that is dimensioned to come into close contact with the internal surface of the tubular outer casing 36; thereby directing the flow of any particulate material to flow in the direction away from motor 18 and towards hopper 12 during metered flow of particulate material out of hopper 12. Internal surface of casing 36 may have a reduced diameter between motor 18 and reverse sense screw 42. Hopper 12 may also comprise an agitator (20, Fig 1), driven by motor (24) via agitator shaft 22 and associated with motor side opening 43 and tubular casing 37. Motors 18, (24) are encased in metal casing 62.

Description

Screw Feeder

Technical Field

The invention relates to a screw feeder for delivering a metered flow of particulate material via an auger screw, that has no need for drive seals.

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 FEEDOSTm 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 outlet for delivering the metered flow of particulate material, and at least one drive shaft for mounting a rotatable particulate material transport tool, the drive shaft being rotatably drivable by a motor positioned external to the hopper, wherein the drive shaft passes through a motor-side opening in the side wall of the hopper and extends into the hopper, such that the rotatable particulate material transport tool can rotate inside the hopper in use to facilitate the metered flow, and wherein the drive shaft passes through a tubular outer casing, the tubular casing having an internal surface and an external surface, the drive shaft having also mounted thereon a reverse-sense screw that is dimensioned to come into close contact with the internal surface of the tubular outer casing, the sense of the screw being such that it directs the flow of any particulate material to flow in the direction away from the motor towards the hopper during metered flow of particulate material out of the hopper.

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.

Thus, the reverse-sense screw acts to prevent any particulate material from passing along any drive shaft towards the motor driving the shaft. Thus drive seals can be omitted completely, so that contamination of the particulate material from degradation of such seals is prevented.

In general the tubular outer casing extends from the hopper side wall towards the motor, although it could also pass through the side wall and enter the hopper by a small distance.

In a first embodiment, the rotatable particulate material transport tool can be an agitator, the drive shaft being an agitator shaft, operable to facilitate metered flow by maintaining the particulate material in a free-flowing state but not delivering metered flow from the hopper.

Such an agitator may take a variety of forms, such as paddles, a ribbon thread or a screw thread. However, its function is not to deliver particulate material from the hopper, but instead is to maintain the stored particulate material in a free-flowing state, so that it can descend freely under gravity, to an auger screw positioned below.

In this embodiment, the reverse-sense screw may be positioned in any convenient location within the tubular outer casing, however it has been found to be usefully positioned such that it is adjacent to or passes through the side wall of the hopper. In this way the reverse-sense screw prevents particulate material from entering the tubular casing at all.

In a second embodiment, the rotatable particulate material transport tool is an auger screw, positioned in the hopper to receive particulate material from above, the drive shaft being an auger shaft 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 in side wall of the hopper, which is also the outlet.

Thus, the auger and auger shaft do not pass through the hopper wall other than through the motor-side opening, and act to direct particulate material in the direction towards the motor. 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 this embodiment, the reverse-sense auger screw is positioned between the motor and the auger screw and within the tubular outer casing. The reverse-sense auger screw acts to prevent the transport of any metered particulate material, thus ensuring that particulate material does not get transported to the motor.

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 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. Thus the auger screw is within the hopper but also extends out of the hopper through the motor-side opening. The auger screw may therefore be partially encased within the tubular outer casing, and in which case it is also in close contact with the internal diameter thereof.

Thus, the auger screw that is external to the hopper is preferably located within the tubular outer casing that extends from the motor-side opening in the hopper.

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. 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.

Preferably, the screw feeder comprises both the first and second embodiments, so that both the auger shaft and agitator shaft each comprise a reverse-sense screw.

Although the reverse-sense screw provides a very high degree of prevention of flow of particulate material towards the motor, additional steps may be taken to further reduce such undesirable migration.

In one preferred embodiment the tubular outer casing has a reduction in diameter, preferably located between the motor and the reverse-sense screw. The reduction in diameter helps to ensure that any particulate material directed towards the motor is prevented from passing into this reduced diameter region and prevented from entering the motor.

The reduced diameter portion can be optimally combined with the reverse-sense auger to provide even greater prevention of the passage of particulate material to the motor. Thus, in one embodiment, 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 also 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 another preferred embodiment, the drive shaft comprises an increased diameter portion, located between the motor and the reverse-sense screw. Preferably the increased diameter portion is greater in diameter than the internal surface of the tubular outer casing. In order to achieve this, the tubular outer casing comprises a corresponding region of increased internal diameter, in order to accommodate the increased diameter portion of the drive shaft. With this arrangement, the drive shaft presents a physical barrier to any particulate material that manages to migrate past the reverse-sense screw. The only way that particulate material may pass the increased diameter portion is to pass between the tubular outer casing and the increased diameter portion, which can optimally be arranged to provide a very close contact therebetween, thus providing a significant impedance to particulate material migration and protecting the motor further.

Such an increase in internal diameter is conveniently provided by a union of two tubular outer casings having an increased internal diameter at the point of their union. Such a union also 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 and/or the agitator 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 or reverse-sense auger, 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 side sectional view through the agitator shaft of the screw feeder shown in figures 1 and 2.

Figure 5 is a perspective view of a portion of the screw feeder shown in figures 1 to 4, 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, being a rotatable particulate material transport tool, mounted on an auger shaft 16 driven by an auger motor 18. The hopper 12 also comprises an agitator 20, also being a rotatable particulate material transport tool, 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, which also acts as the outlet for the metered particulate material, 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.

Agitator shaft 22 passes from the agitator motor 24 through the motor-side wall 26 through a motor-side opening 35. The agitator shaft 22 also comprises a reverse-sense screw 43 that is located adjacent to the motor-side opening 35.

Extending from the motor-side opening 35 is a tubular casing 37 which contains the reverse-sense screw 43 and agitator shaft 22 and has an internal diameter that is in close contact with the reverse-sense screw 43.

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.

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.

Arrow 39 shows the direction of movement of the metered particulate material as it passes out of 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 particulate material would have to travel in order to pass the step-change in internal 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 pulled 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.

As most clearly shown in figure 4, the agitator shaft 22 comprises an increased diameter portion 50 that has a diameter that is greater than that of the internal diameter of the agitator shaft 22. The tubular outer casing 22 comprises a corresponding region of increased internal diameter 52, in order to accommodate the increased diameter portion of the agitator shaft. The region of increased internal diameter 52 is provided by a union 57 of joined tubular outer casing 37, the union 57 comprising a labyrinth mating between facing flanges of the joined tubular outer casing 37.

Arrow 25 shows the direction of travel of any particulate material that enters the region covered by the reverse-sense screw 43.

Arrows 54 show the direction the particulate material would have to travel in order to pass the increased diameter portion.

Figure 5 is a perspective view of the internals of the screw feeder 10, and shows where the tubular outer casing 36 pass through metal casing 62 that contains motors 18, 24. For clarity, the auger shaft 16 is not shown. Immediately on the inside of metal casing 62 is positioned a horseshoe spacer 60 which comprises an open vertical slot 64 around the lower region of the circumference of the horseshoe spacer 60. 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 64. Additionally, it provides for the ejection of any undesirable material travelling from the motor 18 towards the particulate material contained within the hopper 12.

Claims

Claims 1 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 outlet for delivering the metered flow of particulate material, and at least one drive shaft for mounting a rotatable particulate material transport tool, the drive shaft being rotatably drivable by a motor positioned external to the hopper, wherein the drive shaft passes through a motor-side opening in the side wall of the hopper and extends into the hopper, such that the rotatable particulate material transport tool can rotate inside the hopper in use to facilitate the metered flow, and wherein the drive shaft passes through a tubular outer casing the tubular casing having an internal surface and an external surface, the drive shaft having also mounted thereon a reverse-sense screw that is dimensioned to come into close contact with the internal surface of the tubular outer casing, the sense of the screw being such that it directs the flow of any particulate material to flow in the direction away from the motor towards the hopper during metered flow of particulate material out of the hopper.
2. A screw feeder according to claim 1, wherein the tubular outer casing extends from the hopper side wall towards the motor.
3 A screw feeder according to claim 1 or claim 2, wherein the rotatable particulate material transport tool is an agitator, the drive shaft being an agitator shaft, operable to facilitate metered flow by maintaining the particulate material in a free-flowing state but not deliver metered flow from the hopper.
4. A screw feeder according to claim 3, wherein the reverse-sense screw is adjacent to or passes through the side wall of the hopper.
A screw feeder according to any one of the preceding claims, wherein the rotatable particulate material transport tool is an auger screw, positioned in the hopper to receive particulate material from above, the drive shaft being an auger shaft such that in use the auger screw can rotate on the auger shaft to deliver a metered flow of particulate material through a motor-side opening in side wall of the hopper.
6. A screw feeder according to claim 5, wherein the reverse-sense screw is positioned between the motor and the auger screw and within the tubular casing.
7. A screw feeder according to claim 5 or claim 6, wherein the auger screw is positioned adjacent to the base of the hopper.
8. A screw feeder according to any one of claims 5 to 7, wherein the auger screw passes through the motor-side opening so that a portion of the auger screw is external to the hopper.
9. A screw feeder according to claim 8, wherein the auger screw that is located external to the hopper is located within the tubular outer casing, 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.
10. A screw feeder according to claims 3 and 5, wherein both the auger shaft and agitator shaft each comprise a reverse-sense screw.
11. A screw feeder according to any one of the preceding claims, wherein the metered flow of particulate material is directed to leave the hopper via the motor-side opening, which also acts as the outlet, and subsequently fall under gravity.
12. A screw feeder according to claim 11, wherein the tubular outer casing comprises an opening to allow the metered flow of particulate material to fall through the opening under gravity to be received below.
13. A screw feeder according to claim 12, wherein the opening in the tubular outer casing is located between the auger screw and the reverse-sense auger screw.
14. A screw feeder according to any one of the preceding claims, wherein the internal surface of the tubular outer casing has a reduction in diameter, preferably located between the motor and the reverse-sense screw.
15. A screw feeder according to claim 14, wherein the reduction in diameter occurs immediately on the motor-side of the reverse-sense auger.
16. A screw feeder according to any one of claims 14 to 15, wherein the change in diameter is a step-change.
17. A screw feeder according to any one of claims 14 to 17, wherein the change in diameter is provided by a union of joined tubular outer casing, the union comprising a labyrinth mating between facing flanges of the joined tubular outer casing.
18. A screw feeder according to any one of the preceding claims, wherein the drive shaft comprises an increased diameter portion, located between the motor and the reverse-sense screw.
19 A screw feeder according to claim 18, wherein the increased diameter portion is greater in diameter than the internal surface of the tubular outer casing and the tubular outer casing comprises a corresponding region of increased internal diameter, in order to accommodate the increased diameter portion of the drive shaft.
20. A screw feeder according to claim 19, wherein the region of increased internal diameter is provided by a union of joined tubular outer casing, the union comprising a labyrinth mating between facing flanges of the joined tubular outer casing.
21 A screw feeder according to any one of the preceding claims, wherein the at least one drive 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.