Archimedean screw apparatus

An Archimedean screw apparatus for use either in power generation or for the pumping or conveying of fluid material includes a screw body formed by a shaft and at least one helical flight that is located in a close-fitting channel structure. The screw body is rotatably mounted such that the flight is in frictional contact with in inner surface of the channel. The weight of the screw body is borne at least partially by the channel structure and is dissipated fully or partially along the length of channel structure. Hence, preferably the Screw both is either provided with only a single bearing located at one end of the shaft, the other end being left floating within the channel structure, or the screw body is not provided with any bearings and the shaft is connected directly to a drive mechanism or to part of a power generating apparatus.

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

Not applicable.

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an Archimedean screw apparatus for use either in power generation or in the pumping or conveying of fluid material.

Conventionally, a modern Archimedean screw apparatus comprises a screw body having a rotatable shaft around which is secured one or more helical flights. The shaft is suspended at its ends between bearings, typically a drive-end bearing and a non drive-end bearing, in a close fitting trough and a small clearance is left between the flights and the trough or a liner located in the trough. In a pumping apparatus, the trough is either horizontal or inclined and the shaft is driven to pump material along the trough, from the bottom to the top if it is inclined. In contrast, in power generation the trough is inclined and fluid flows down the trough under gravity to rotate the screw body, which is linked to a generator. Power to or torque from the screw body is therefore transmitted by the shaft and it is important that the length and strength of the shaft are chosen so that the screw body is sufficiently strong to remain suspended without serious bending or deflection, which would create undue stresses in the screw body and cause contact with the trough. Hence, the longer the screw body the stronger it needs to be to withstand the bending moments to which it is subjected.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is to provide an Archimedean screw apparatus in which the bending loads on the screw body are removed or significantly reduced enabling the strength required in the screw body to be made substantially independent of its length.

According to the present invention there is provided an Archimedean screw apparatus comprising a screw body formed by a shaft and at least one helical flight located in a close-fitting channel structure, the screw body being rotatably mounted such that the flight is in frictional contact with an inner surface of the channel structure.

In this apparatus, as the flight or flights of the screw body are in contact with the inner surface of the channel structure the weight of the screw body is borne at least partially by the channel structure and is dissipated fully or partially along the length of channel structure. This means that the screw body can be made of lightweight materials, such as plastics and the like which also has the effect of reducing the load between the tips of the flight or flights and the inner surface of the channel structure.

Preferably, the channel structure comprises a trough, an open channel, a closed channel or a tube.

Preferably, the screw body comprises a plurality of up to seven flights. In practice, for ease of construction the screw body is most likely to be provided with three or four flights.

Preferably also, the screw body is provided with a single bearing located at one end of the shaft Advantageously, the other end of the screw body floats within the channel structure.

Alternatively, the shaft is connected directly to a drive mechanism or to part of a power generating apparatus.

Preferably also, means are provided to retain the screw body in position within the channel structure.

Preferably also, the screw body is either buoyant or is made at least partially from a buoyant material. This means that the screw body will tend to float, in use, in fluid material passing through the apparatus and allow a small passage of the fluid between tips of each flight and the adjacent inner surface of the channel that will lubricate the rotation of the screw body.

Advantageously, the means retaining the screw body in position comprises an anti-flotation means.

Preferably also, the inner surface of the channel structure is defined by a liner. Advantageously, the liner is detachable from the channel structure.

Further preferred but non-essential features of the various aspects of the present invention are further described in the dependent claims appended hereto.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIG. 1, a first embodiment of Archimedean screw apparatus1in accordance with the present invention comprises a screw body2which is located in a close-fitting channel structure3. The screw body2is formed by a shaft4and at least one helical flight5that is secured to or integrally formed with the shaft4, as is further described below. In all of the drawings, the screw body2is shown having three helical flights5. However, it should be appreciated that the screw body2of an apparatus in accordance with the invention may comprise one or any number of flights, typically seven being the optimal number for efficiency. However, for ease of construction in most practical applications of the apparatus1the screw body will comprise three or four flights5.

The channel structure3defines a channel with a semi-cylindrical inner surface6adjacent the screw body2that may be formed by a liner7located in the channel or, alternatively, the surface of the channel itself. The screw body2is rotatably mounted along its longitudinal axis A with the flights5in frictional contact with the inner surface6so that it runs under normal circumstances in contact with the channel structure3, which thereby provides longitudinal support and alignment to the screw body2. InFIG. 1the channel structure3comprises an open trough or channel but in the embodiment shown inFIG. 2the channel structure3comprises a cylindrical tube that completely encloses the screw body2, there being no discernible gap between the tips of the flights5and the liner7. In a modification, the liner7may be omitted and the screw body2mounted in direct frictional contact with the surface of the tube. In other embodiments, the channel structure3may comprise a trough, an open channel or a closed channel and various of these arrangements of channel structure3are shown inFIGS. 5 to 7.

FIG. 1shows an apparatus1suitable for the pumping or conveying of fluid material, by which is meant a readily flowing liquid or liquid-based material such as water, river water, sewage or like materials. Here, the shaft4is supported at its upper end in a drive-end bearing8and is linked via a coupling9to a drive unit10comprising gears and a motor. However, the lower, non-drive end of the shaft4is not supported in a bearing and effectively floats within the channel structure3.

In order to reduce the load on the channel structure3and to reduce friction created when the shaft4is rotated by the drive unit10, the screw body2can be made from lighter-weight material than would be possible in a conventional apparatus. This is because the screw body2is not subjected to the same bending moment along its length as a conventional screw body and dissipates its weight at least partly along the length of the channel structure3. In view of this in some embodiments it is possible to dispense with the bearing8and to couple the shaft4directly to the drive unit10or to a power generating unit. Alternatively, drive-end and non-drive end bearings can still be provided but the reduced load of the screw body2means that the bearing size and strength used can also be reduced, with consequent cost savings.

In the embodiments shown inFIGS. 1 and 2, the screw body2is fabricated from metal and comprises a hollow shaft4to the exterior of which three helical flights5are welded. In a modified, stronger arrangement, the helical flights5are pressed into the body of the shaft4and welded into position. However, the present invention opens up the possibility of the screw body2being made in many other ways and from lightweight materials such as plastics. The channel structure3, or at least the liner7, may also be made from similar materials and various of these are described below with reference toFIGS. 5 to 7. The screw body2may be made, for example, by fabrication, moulding, injection moulding, rotary moulding casting or from glass reinforced plastics. In such cases, the screw body2may be buoyant during use. This may be because it is a hollow structure and/or because it is made from a buoyant material. Such a screw body2has the advantage that it decreases the surface loadings on the tips11of the flights5of the screw body2leading to less friction and a reduction in wear of the flights5and the liner7or surface6of the channel structure3.

FIG. 3shows part of a screw body2wherein the shaft4and three flights5have been integrally moulded in one piece from a plastics material such as, for example, nylon, polyethylene or polypropylene, all of which have a high wear resistance. Conventional moulding techniques can be used for this purpose. As can be seen, the flights5are integrally formed with a central tube that forms the shaft4. In a modification as shown inFIG. 4, the tips11of the flights5are provided with separately produced ribs12that are secured to the tips11, for example by mechanical fixing, welding or bonding. The ribs12can be made of a more wear resistant material than the flights5as they are in frictional contact with the inner surface6of the channel structure3. Preferably, therefore, the ribs12are secured to the flights5so that they can be readily replaced should they become worn or damaged. The use of replaceable ribs12, either made or plastics or otherwise, could also be used with metal flights5. The use of plastics ribs12with such flights5will reduce the friction between the screw body2and the inner surface6of the channel structure3, particularly if a plastics liner7is also used.

The liner7is preferably removable from the channel structure3and therefore replaceable. It can be made of any suitable material and may, for example, be a moulded structure or a sheet that conforms to the contours of the inner surface6of the channel structure3. If the liner7is readily replaceable, in general it is better to use different plastics materials for the liner7and the flights7such that the liner7is sacrificial. This is because in many embodiments, it is easier and less expensive to replace a worn liner7than worn flights5or ribs12. However, in some embodiments it may be better if the plastics used for both the ribs12and the liner7are the same.

Reference will now be made toFIGS. 5 to 7which show alternative embodiments of channel structures3suitable for use in an apparatus according to the invention. InFIG. 5the channel structure comprises an outer concrete structure13formed with channel defining an angled inner surface14over which is laid a smooth concrete grout15that forms the semi-cylindrical channel surface6. Above the grout15on one side of the channel is a separate profile16, that can be made of metal or plastics and that also conforms to the outer profile of the screw body2. This profile16is secured to the channel structure3on the side where the flights5rise upward. During use of the apparatus1, the profile16acts as a baffle to retain liquid material passing through the apparatus1within the channel structure as it tends to be carried upwards by the flights5. The profile16is usually detachable from the channel structure3to provide access to the screw body2and the interior of the channel for maintenance purposes.

A second profile16may also be provided on the opposite side of the channel structure3and together they may act to retain the screw body2within the channel structure3, as in the present invention the screw body2is not necessarily held in position by bearings. This is important for two reasons. First, to prevent movement or removal of the screw body2by external forces or by unauthorized persons. Second, if the screw body2is buoyant when the apparatus is in use, the screw body2will tend to float away from the inner surface6of the channel structure and decrease the surface loadings on the tips of the flights11. However, it will be appreciated that the efficiency of the screw apparatus will suffer if the screw body2is permitted to float too far out of position. Hence the need for an anti-flotation means. This means may take the form of one or more profiles16or of a separate an anti-flotation bracket17, such as shown inFIG. 1, which is provided for the same reason. The bracket17holds the screw body2in place without necessarily conforming to the outer profile of the screw body2. It with be appreciated that with a tubular channel structure3, as shown inFIG. 2, in which the screw body2is closely fitted, such a profile16or bracket17would not be required, the structure3itself retaining the screw body2in position.

FIG. 6shows a channel structure3with a similar outer concrete structure13to that shown inFIG. 5except that the channel surface14is made semi-cylindrical. This surface is covered by a removable plastics liner18that can be either moulded to fit over the channel surface14or comprise a flexible sheet material that moulds itself to the surface14.

FIG. 7shows a channel structure3in the form of a U-shaped channel19, made or metal or plastics, in which the screw body2is a snug fit. The screw body2is located directly in contact with the bottom of the channel19, which is also provided with a detachable profile20and a removable lid21so that the screw body2is completely contained within the structure3. The lid21may also comprise an anti-flotation means that retains the screw body2in position.

In use, the screw body2rotates within the channel structure3and there tends to be a small passage of fluid material22between the tips of the flights5and the inner surface6of the channel structure3, as indicated by the arrows23inFIG. 8. There is an advantage in such a passage of fluid which is that it lubricates the tips11of the flights5as they move over the surface6. This leads to a lower frictional resistance and thus a lower wear rate of the flights5of the screw body2and/or ribs12and of the liner7or channel structure3in general.FIG. 8shows a screw apparatus when in use for power generation. Hence, the direction of flow of the fluid material22is downwards from an inlet24at the top of the channel structure3, through the screw apparatus itself, and out at the bottom, as indicated by the large arrows25. The fluid flow rotates the screw body2, which is linked to a generator (not shown). No bearings are shown inFIG. 8and none may be required but a bearing may be provided at an upper end of the screw body2to accommodate thrust load. It is not expected that any bearing would be required at the lower end of the screw body2.

A similar passage23of fluid material22will occur in all of the aforementioned embodiments. In those cases where the screw body2is buoyant, there may be a greater passage of fluid than in other cases but this can be controlled by use of an anti-flotation means such as the bracket17or by use of a tubular channel structure3, as shown inFIG. 2.

Hence, it will be appreciated that in an Archimedean screw apparatus according to the invention the bending loads on the screw body are removed or significantly reduced enabling the strength required in the screw body to be made substantially independent of its length. This means that the screw body can be made of lighter-weight material than hitherto, including plastics material, which make the production of such a screw body2both simple and relatively inexpensive.