GB2578327A

GB2578327A - Apparatus and method for forming a helical type flight

Info

Publication number: GB2578327A
Application number: GB1817301.3A
Authority: GB
Inventors: Clift Mcgregor Duncan
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-10-24
Filing date: 2018-10-24
Publication date: 2020-05-06
Also published as: GB201817301D0; WO2020084292A1

Abstract

Apparatus for forming a helical screw flight segment comprises first and second support members 26, 28 arranged for: · axial movement in a direction of a main axis (X-X); · movement perpendicular to the main axis (X -X); and · rotational movement about a rotational axis extending parallel with the main axis (X-X) The arrangement is such that the rotational movement of the first or second support member (26, 28) can be effected by lateral movement of the respective support member in a direction perpendicular to the main axis (X - X). In operation of an embodiment, a blank 14 side edges (20, 22, Figure 4) are positioned within respective pairs of clamping jaws 26A, 26B when the blank 14 is in a plane which is at right angles to the main axis X-X. One support member 28 is axially locked while the other 26 is moved axially. Axial actuator 46 and lateral actuators 74-78 are actuated to draw apart side edges (20, 22) in the X-X direction and simultaneously drawn them together in the direction perpendicular to the X-X direction, such that lateral and rotational adjustments occur.

Description

APPARATUS AND METHOD FOR FORMING A HELICAL TYPE FLIGHT

TECHNICAL FIELD

The present invention relates to an apparatus for and method of forming a helical type flight. The flights so formed may find application in screw conveyors, auger drills, mixing devices, turbines, propellers, ground anchors and screw piles.

BACKGROUND OF THE INVENTION

Helical flights referred to herein are of the type having a central bore which may encircle a circular central shaft and to be secured thereto in any manner, such as by welding, brazing, etc. It is important that a screw flight is of accurate and uniform pitch in order to obtain certain mechanical advantages in operation.

An optimum configuration for a flight is of a true helix. A true helix has perfect symmetry and uniform pitch angle throughout. This means that the tangential slope angle of the helix must be consistent and that the surface of the helix flight is normal to the axis on all radii. When these conditions are fulfilled the leading and trailing ends of a screw flight are axially aligned and their edges are substantially perpendicular to the centre axis.

A known method of manufacturing conventional screw flight segments is a tension method where a flight blank in the form of an annular disc with a sector removed is placed in jaws and clamped along its sector edges, and the jaws are driven axially in opposite directions. In this way, the disc is stretched or pulled to a distance so as to form a helix of the desired length and pitch. When the blank is extended axially it contracts radially. Although this characteristic is not particularly significant for short pitch helices where the pitch is less than approximately one third of the outside diameter of the helix, it presents a problem when the pitch exceeds approximately one third of the outside diameter of the helix. In this case, the regular helical geometry becomes inconsistently distorted during stretching and a true helix is not obtained. This is because the helix blank is subjected to significantly misaligned longitudinal forces due to the divergence of their connection points on the sector edges by 40 degrees or more for a 100% pitch. Without additional measures to counteract the effect of such misalignment, misshapen helices result. The misalignment of the axes of the pulling and restraining forces is in proportion to the sector angle which is proportional to the pitch. The resultant vector force is neither aligned to, nor parallel with, the central axis of the helical flight being formed.

US 3485116 discloses an apparatus for forming a sectional spiral flight using the tension method wherein the apparatus comprises opposing edge clamping members, which, in addition to being moveable axially relative to one another, are swivelly mounted in order to be allowed to freely or passively follow the line of bend imparted to the disc during the pulling. In this way, the leading and trailing edges of the blank are allowed to partially rotate about a fixed axis extending parallel to the central axis of the blank during stretching. However, the apparatus does not provide an optimum configuration for a flight which is of a true helix.

Another tension method of manufacturing a screw flight is disclosed in W02017/156587, wherein an apparatus for forming a helical flight comprises first and second support heads arranged for relative axial movement with respect to one another in a direction of a main axis and for rotational movement about a rotational axis which extends in a direction generally parallel to the main axis. The support heads are further configured to freely or passively move laterally in a direction of respective lateral axes to follow the line of bend imparted to the disc during the pulling. This apparatus also does not provide a true helical flight.

An object of the present invention is to provide an alternative and/or improved method of and apparatus for forming a helical flight. In addition, this invention is aimed at forming true helices with pitches of 100% of OD or greater.

SUMMARY OF THE INVENTION

One aspect of the present invention accordingly provides an apparatus for use in the formation of a helical screw flight, the apparatus comprising: first and second support members, arranged for: relative axial movement with respect to one another in a direction of a main axis; lateral movement in a direction generally perpendicular to the main axis; rotational movement about at least one rotational axis which extends in a direction generally parallel with the main axis; the arrangement being such that the rotational movement of the first or second support member about its' at least one rotational axis can be effected by the lateral movement of the respective support member in a direction generally perpendicular to the main axis.

In one embodiment, the first and second support members can be rotated about a first common rotational axis.

In one embodiment, the position of the at least one rotational axis can be adjusted whilst remaining generally parallel with the main axis.

In one embodiment, the first and second support members can be rotated about respective second rotational axes which extend in a direction generally parallel with the first common rotational axis and the main axis.

In one embodiment, the rotational movement of the first or second support member can be effected in response to actuation of at least one lateral drive.

In one embodiment, the lateral movements of the respective first and second support members can be in opposite directions towards the main axis.

In one embodiment, the second rotational axes of the respective first and second support members can be moved simultaneously towards each other and the main axis.

In one embodiment, the lateral and rotational movements of one support member can be effected simultaneously.

In one embodiment, the combined lateral and rotational movements of one support member can be effected simultaneously with the combined lateral and rotational movements of another support member.

In one embodiment, the axial, lateral and rotational movements of one support member can be effected simultaneously.

In one embodiment, the first or second support member is fixed in position with regard to axial movement. The axially fixed support member may be arranged for lateral movement and rotational movement. The other support member is preferably arranged for axial, lateral and rotational movement.

In one embodiment, the support members are operatively connected to one or more drives for effecting one or more of the axial, lateral and rotational movements in response to actuation of the drive. The axial and lateral movements of one support member can conveniently be effected by actuation of separate or different drives.

In one embodiment, the first and/or second support member is in the form of a plate having an upper end and a lower end relative to the base of the apparatus. The support member may be pivotally connected at, or in the region of, its lower end about a pivot axis which extends in a direction generally parallel with the main axis. When the pivot or rotational axis provided at the lower end region of the support member is moved laterally towards or away from the main axis in a direction generally perpendicular to the main axis, the support member can rotate about this (second) rotational axis. Thus, the position of the second rotational axis of the support member will adjust while remaining parallel with the main axis during flight formation. At the same time, the support members can rotate about a common rotational axis which is the centre point of the aperture or hole in the blank and the centre axis of the flight. When the support member is moved laterally and rotates about the rotational axis in the lower end region, the upper end region of the support member moves in a generally upwardly or downwardly direction relative to the base of the apparatus. It will be appreciated that the position of the common (first) rotational axis of the first and second support members will also adjust while remaining parallel with the main axis during flight formation.

The support members may be provided with engaging means for engaging sector edges of a blank. The engaging means may comprise a pair of opposing clamping jaws for holding an edge margin of the removed sector of the blank which is to be shaped. The clamping jaws are designed to allow the edge margins of the sector blanks to be held firmly during the various movements of the support members.

In one embodiment, at least one of the first and second support members is connected to a respective lateral member adapted for lateral movement in a direction generally perpendicular to the main axis whereby lateral movement of the lateral member causes rotational movement of the support member. The lateral movement of the lateral member causes a corresponding movement of the rotational axes of the support member. The support member is preferably pivotally connected to the lateral member so that upon movement of the lateral member, the support member pivots about this second pivot or rotational axis which extends in a direction generally parallel with the main axis. The presence of the additional common first rotational axis of the support members allows the rotational movement to occur in a controlled, precisely directed manner.

In one embodiment, the lateral member comprises a movable carriage or plate. The carriage is preferably adapted for sliding movement in a direction generally perpendicular to the main axis. Guide means may be provided for the lateral carriage to allow the carriage to move in the perpendicular or cross-wise direction relative to the main axis.

In a preferred embodiment, the guide means comprises a track that extends in the direction of lateral movement of the lateral member and means for engaging the track. In a preferred embodiment, at least two parallel tracks are provided. The track may be provided in the surface on which the lateral member moves and the engaging means may be provided on the lateral member, or vice versa. In one embodiment, the lateral member is provided on its underside with one or more projections for engaging the track.

In a preferred embodiment, stabilizing means are provided so that yawing or tilting of the lateral member about its' vertical axis from moment forces during forming is avoided. The stabilizing means may take the form of engaging means between the lateral member and the surface on which the lateral member moves. Preferably, the stabilizing means is such that there is minimum friction during the application of moment forces in operation. The stabilizing means may take the form of, for example, spur gears engaged with matching racks. The spur gears are conveniently keyed or locked onto opposite ends of a shaft extending through the lateral member to engage with a pair of matching racks.

The support member may be connected to an axial member adapted for axial movement in a direction of the main axis. In one embodiment, the axial member comprises a moveable plate or carriage. The axial plate or carriage is preferably adapted for relative axial sliding movement.

Guide means for the axial carriage may be provided to allow the axial carriage to move in a direction of the main axis. The guide means may be provided on the base of the apparatus on which the axial carriage moves and/or on the movable axial carriage. The guide means may comprise at least one elongate opening or slot extending longitudinally in the base or frame adapted to receive a projection provided on the movable carriage. The projection may alternatively be provided on the base and the elongate opening or slot provided on the movable carriage. In this way, the movement of the axial carriage is confined solely to axial motion in line with the longitudinal axis of the apparatus (the "main axisff).

In a preferred embodiment, the lateral member is mounted on the axial member for lateral movement in a single plane. In this way, the movement of the lateral member is synchronized with the movement of the axial member.

In a preferred embodiment, the axial, lateral and pivotal movements of one support member are effected simultaneously. In an alternative embodiment, the axial movement is effected in a first step and the lateral and rotational movements are effected simultaneously in a second step, or vice versa.

Another aspect of the present invention includes a method for the manufacture of a helical flight comprising: providing a flight blank in the form of an annular disc with a sector removed; engaging the blank at its sector edges with first and second support members, arranged for: relative axial movement with respect to one another in a direction of a main axis; lateral movement in a direction generally perpendicular to the main axis; rotational movement about at least one rotational axis which extends in a direction generally parallel with the main axis; effecting axial movement of at least one of the first and second support members; effecting lateral movement of the first and second support members towards the main axis; effecting rotational movement of the first and second support members; whereby the rotational movement of the first and/or second support member is effected by lateral movement of the respective support member or of the at least one rotational axis of the respective support member in a direction generally perpendicular to the main axis.

In one embodiment, the first and second support members are rotated about a first common rotational axis.

In one embodiment, the position of the at least one rotational axis is adjusted whilst remaining generally parallel with the main axis.

In one embodiment, the first and second support members are rotated about respective second rotational axes which extend in a direction generally parallel with the first common rotational axis and the main axis.

In one embodiment, actuation of a lateral drive causes the rotational movement of the first or second support member about its' rotational axis.

In one embodiment, the first and second support members move in opposite directions towards each other and the main axis simultaneously.

In a preferred embodiment, the axial, lateral and rotational movements of one support member are effected at the same time as the lateral and rotational movements of another support member.

A further aspect of the present invention includes a helical flight segment formed by the method of the present invention. Such formed flight segments may form part of a continuous screw comprising several conjoined segments, typical of Archimedean screws used in screw conveyors or auger drills. Alternatively, formed flights might be used singly as in some mixing devices, propellers, turbines, ground anchors and screw piles.

The application of controlled (i.e., active, rather than passive) axial, lateral and rotational movements of the support members according to the present invention provides a more effective forming method than those described in the prior art which rely at least in part on free (passive) lateral or rotational movements. In particular, the use of controlled rotational forces that counter-rotate about the centre axis of the helix during flight formation has been found to result in the formation of a true helical flight. This is especially the case where the pitch is above 20% of the flight diameter of the helix. Furthermore, the present invention allows large helices formed of thick material suitable for heavy industry and demanding geotechnical purposes to be formed.

Other aspects, features and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which illustrate, by way of example, principles of the inventions disclosed.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of apparatus according to the present invention in an initial stage; Figure 2 is a front end view of the apparatus of Figure 1; Figure 3 is a top plan view of the apparatus of Figure 1 at a final stage; Figure 4 (a), (b) and (c) are respective plan views of a helix blank at stages initial, midway and final; and Figure 5 (a), (b) and (c) are respective side views of the helical segments in Figures 4 (a), (b) and (c).

DETAILED DESCRIPTION OF THE INVENTION

With reference to the Figures of the drawings, there is illustrated one embodiment of apparatus (10) for use in the formation of a flight (12) of helical configuration. As shown in detail in Figures 4 and 5, the flight (12) is formed from a blank (14) which is a generally annular body in the form of a generally circular disc-like member having an outer peripheral edge (16), an inner or central hole having an inner peripheral edge (18) with a sector removed after making two cuts radially through the annulus. The blank after the sector is removed has opposed side edges (20, 22). The edges (20, 22) extend radially with respect to a central point (C) of the hole (Figure 4(a)) and as such are slightly inclined with respect to one another.

The blank (14) may be formed from any suitable material such as metals, including steel, and may have some resilience or elastic deformation properties. The thickness of the blank will vary depending on the end use of the helical flight which is to be formed. By way of example, it may be in the region of between about 1 mm and about 60 mm, such as between about 5 mm and about 50 mm. The internal diameter of the blank is chosen to match the external diameter of a shaft to which the helical flight to be formed is to be mounted. The external diameter is also chosen for the required end-use purpose and may be in the range from about 5 cm to about 5 meters, such as from about 20 cm to about 2 meters. An example of a design program is provided as follows: Helix OD 1200mm, Helix ID 350 mm, Pitch 900 mm, Thickness 35 mm, Strength 355 Mpa (minimum yield), Edge length 425 mm; Blank OD 1302 mm, Blank ID 452 mm, Sector Angle 28 degrees.

With reference to Figures 1-3, the apparatus (10) includes a base (24) having an upper surface lying in a generally horizontal plane on which are mounted first (26) and second (28) support members which in use are adapted to hold the blank (14) in the region of the side edges (20, 22). In the initial position shown in Figures 1 and 2, the support members (26, 28) are at an angle to each other that corresponds to the angle (30) formed by the sector edges (20, 22) of the particular blank to be used. The first and second support members (26, 28) comprise respective pairs of opposing jaw frames (26A, 26B, 28A, 28B) for mounting clamping jaws. The clamping jaws include respective blank grippers or holders (30, 32) (shown in Figure 3) provided in gripper slots (86) which are adapted to grip or hold the blank (14) in the region of side edge (20, 22). The jaw frames can be adjusted to be held in clamping or release position either manually or mechanically by side actuators (34, 36) in the form of bolts or by hydraulic or electro-mechanical means. The clamping force on the jaws is such as to allow rotation of the gripped sector edges without causing uneven local bending. The force on the jaws to tighten or loosen them may be managed by electronic or digital means.

The first and second support members (26, 28) are mounted inclined relative to each other on the same horizontal plane and are axially displaceable arranged for movement in the direction of the main axis X-X in response to actuation of the drive. Either of the first and second support members (26, 28) may be locked so as to be inhibited from movement in the direction of the main axis X-X while the other support member is unlocked or mobilized for movement. The choice of which support member (26, 28) is locked/unlocked is dependent on the direction of the formed flight to be formed: clockwise in the case of the first or right-hand axial carriage being mobilized or anticlockwise in the case of the second or left-hand axial carriage being mobilized.

Right and left side axial members (38, 40) are in sliding contact with the apparatus base (24) by mechanical connection of the respective parts. The base (24) is provided with projections (42) of T shape profile which slideably engage in T shaped slots (44) in the base of the axial members (38, 40). The axial members (38, 40) are in the form of a plate and are able to be driven by any suitable type of linear drive technology, but these are shown here as being driveable by respective hydraulic operable cylinders (46, 48) with a piston at the sides of the plates to move the plates (38, 40) to and fro. In other embodiments the axial plates (38, 40) may be guided by any suitable type of mechanical linear guidance mechanism.

The upper surface of each axial plate (38, 40) is provided with two parallel slots (50), extending perpendicular to the slots (44) provided in the base of the axial member (38, 40) and to the main axis X-X, which serve as mounting and guide means for a lateral carriage member (52, 54). Projections in the form of T-bars, lugs or bolts extend from the underside of the carriage (52, 54) and locate in the slots (50) and are slideable along the slots (50) to guide linearly and to restrain uplift.

The first and second support members (26, 28) are arranged for lateral displacement in a direction Y-Y generally perpendicular to the main axis X-X. The lateral displacement can be effected as follows. For example, as shown the lower ends of the support members (26, 28) are pivotally mounted on hinge pins (56, 58) about a pivot axis (60, 62) that is parallel to the main axis X-X. The hinge pins (56, 58) extend through apertures in the lower region of the support members (26, 28). The upper ends of the support members (26, 28) are connected to articulating lateral actuators (72, 74).

Upon lateral movement of the support members (26, 28) towards the main axis X-X, the pivot axis (60, 62) (Figure 2) of each member moves generally in the same horizontal plane. At the same time, the support members (26, 28) pivot about a common axis, which is the centre axis C-C of the flight (Figure 5). The upper ends of the support members move towards each other and towards the main axis X-X and also move in a generally upwardly direction during the lateral movement permitted by the use of articulating connectors (68, 70) on lateral actuator (72, 74).

Thus, when pivot axis (60) of the right side support member (26) is moved towards the main axis, the right side support member (26) pivots about the pivot axis (60) to rotate in a clockwise direction about pivot axis (60) and common rotational axis (C-C) when viewed from the front end. In the same way, when pivot axis (62) of the left side support member (28) is moved towards the main axis, the left side support member (28) pivots about the pivot axis (62) and common rotational axis (C-C) to rotate in an anticlockwise direction. Between the initial position of the blank and the final stage of the formed flight, the position of the common centre rotational axis (C-C) moves in a direction vertically relative to the base of the apparatus.

As shown in Figures 1-3, the first and second support members (26, 28) are operatively connected to respective axial (46, 48) and lateral (76, 72, 78, 74) drives. The drives are electro-mechanical actuators or may be actuators in the form of a hydraulic or pneumatic cylinder with a ram which is connected to the movable carriage. Right and left side articulating lateral actuators (72, 74) connected to the upper end regions of respective right and left support members (26, 28) allow this end region of the support member to move upwardly or downwardly as the support member rotates. The axial drives (46, 48) are attached to fixed actuator supports (92, 94). The lateral drives (72, 76, 70, 78) are attached to actuator supports (96, 98, 100, 102) that can move axially.

Figure 3 illustrates the apparatus of the invention in a final position. Here the first (26A, 26B) and second (28A, 28B) pairs of clamping jaws of the respective first and second support members (26, 28) are at spaced apart locations. At an initial positon, the support members (26, 28) are at the left hand side for production of a right-hand helical flight. In this initial position the respective pairs of clamping jaws (26A, 26B, 28A, 28B) in the first and second support members (26, 28) are in alignment and the initial circular disc (14) is positioned with its respective edges held in those jaws. Right side axial actuator (46) acts on the right side axial carriage or plate (38). At the same time, right and left lateral actuators (76, 78) act on the right and left side lateral carriages (52, 54) and right and left side articulating actuators (72, 74) act on the right and left side support members (26, 28). Figure 3 then shows the final position where the right side axial carriage (38) has been displaced to the right and the lateral carriages (52, 54) have been displaced to the centre so that opposed side edges (20, 22) lie in approximately the same plane (see Figure 4 c), thereby having caused the deformation of the disc (14) towards formation of the helical flight (12). For the production of a left-hand helical flight, the first and second support members (26, 28) would be in a corresponding initial position at the right hand side of the apparatus. In this initial position, the pair of clamping jaws (26A, 26B) in the unlocked or movable carriage or plate (26) are in alignment with the second pair of clamping jaws (28A, 28B) in the locked or immobilized carriage (28). Then, in operation, the movable carriage (26) in this case moves towards the left and at the same time the lateral carriages (52, 54) move towards the centre, to the final position.

A mechanism for restraining the lateral members (38, 40) from tilting about their respective vertical axes is provided in the form of spur gears (80) keyed to opposite ends of a shaft (82) that extends through each lateral member (52, 54) engaged with matching racks (84) provided on the upper surface of the axial members (38, 40). Such an arrangement has less friction under high loading from the forming process compared to the methods making use of sliding components. Figures 1 and 2 show a single pair of spur gears/pinions for each lateral member (52, 54) but there may be more than a single pair so deployed.

In operation of one embodiment of the apparatus in accordance with the first aspect of the invention, a blank (14) is installed with the apparatus (10) in the initial or preforming position shown in Figures 1 and 2. The support heads (26, 28) are angularly inclined with respect to each other. In this position the side edges (20, 22) are positioned within respective pairs of clamping jaws (26A, 26B, 28A, 28B), and the blank (14) is in a plane which is at right angles to the main axis X-X. The second or left side support member (28) is locked in axial position while the first or right side support member (26) is mobilized for axial movement. The right side axial actuator (46) and the right side-and left side-lateral actuators (76, 72, 78, 74) are then actuated so that the side edges (20, 22) are drawn or pulled apart in the direction of the main axis X-X and simultaneously the side edges (20, 22) are drawn or pulled together in the direction perpendicular to the main axis X-X during which lateral and rotational adjustment occurs. During these movements, the blank (14) is formed into the true helix profile.

The mobilization of the lateral (52, 54) and axial (38, 40) members and support members (26, 28) is synchronized by a programmable digital controller which is housed in an electronic cabinet (88).

The stages in forming a helical flight from a blank are shown in Figures 4 and 5. The blank (14) is an annular disc of flat malleable metal plate that is cut twice radially through the annulus. The sector so formed is removed as shown. Rotational motion is induced by the reduction of the sector angle (30) as the blank (14) changes in form from flat to helical.

The blank diameter and sector arc length decrease as the pitch increases. The arc in stage 1 (Figures 4 (a) and 5 (a)) is the difference between the outside circumference of the flat blank, including the sector arc, and the projected circumference of the fully formed helix in stage 3 (Figures 4 (c) and 5 (c)). The sector angle in stage 1 is the product of 360° and the percentage of the arc in the whole circumference. The edges (20, 22) are of constant length.

The blank outside and inside diameters and the sector angle are extrapolated from the dimensions of the flight to be formed.

During formation of the flight the blank is drawn or pulled in the direction of the axis X-X beyond the point at which the required helix is achieved. When the pulling motion of the drive ceases the arrangement can be such that the profile is caused to be drawn back to the desired helix profile by reversing the direction of travel of the support member in a controlled manner to a predetermined set distance. This relieves the retained elastic-tension ("spring-back") caused by the initial forming process.

The apparatus and method for forming a helical flight according to the invention provide a novel combination of axial, lateral and rotational forming forces that operate in a simple, reliable and precise manner to obtain a flight of a true helix.

Definitions The following definitions shall apply throughout the specification and the appended claims.

Within the context of the present application, the terms "comprises" and "comprising" are interpreted to mean "includes, among other things". These terms are not intended to be construed as "consists of only".

Unless otherwise stated or indicated, the terms such as "front", "rear", "upper", "lower", "side", "horizontal", "vertical", and the like, are used as words of convenience to provide reference points and are not to be construed as limiting terms.

The term "about" means plus or minus 20%, more preferably plus or minus 100/0, even more preferably plus or minus 5%, most preferably plus or minus 2%.

Within this specification embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention.

It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art.

Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications are covered by the appended claims.

Claims

CLAIMS1. An apparatus for use in the formation of a helical screw flight, the apparatus comprising: first and second support members, arranged for: axial movement in a direction of a main axis; movement in a direction generally perpendicular to the main axis; rotational movement about at least one rotational axis which extends in a direction generally parallel with the main axis; the arrangement being such that the rotational movement of the first or second support member can be effected by lateral movement of the respective support member in a direction generally perpendicular to the main axis.
2. An apparatus according to claim 1, wherein the first and second support members can be rotated about a first common rotational axis.
3. An apparatus according to claim 1 or claim 2, wherein the first and second support members can be rotated about respective second rotational axes.
4. An apparatus according to any one of the preceding claims, wherein the rotational movement of the first or second support member can be effected in response to actuation of a lateral drive.
5. An apparatus according to any one of the preceding claims, wherein the movements of the respective first and second support members in a direction generally perpendicular to the main axis can be in opposite directions towards each other and the main axis.
6. An apparatus according to claim 3, wherein the second rotational axes of the respective first and second support members can be moved simultaneously towards each other and the main axis.
7. An apparatus according to any one of the preceding claims, wherein the lateral and rotational movements of one support member can be effected simultaneously.
8. An apparatus according to any one of the preceding claims, wherein the combined lateral and rotational movements of one support member can be effected simultaneously with the combined lateral and rotational movements of another support member.
9. An apparatus according to any one of the preceding claims, wherein the first and second support members can independently be fixed in position with regard to axial movement.
10. An apparatus according to claim any one of the preceding claims, wherein the axial and lateral movements of one of the support members can be effected by a separate or different drive.
11. A method for forming a helical screw flight segment, the method comprising: providing a flight blank in the form of an annular disc with a sector removed; engaging the blank at its sector edges with first and second support members, arranged for: axial movement in a direction of a main axis; lateral movement in a direction generally perpendicular to the main axis; rotational movement about at least one rotational axis which extends in a direction generally parallel with the main axis; effecting axial movement of at least one of the first and second support members; effecting lateral movement of the first and second support members towards the main axis; effecting rotational movement the first and second support members; whereby the rotational movement of the first or second support member is effected by movement of the respective support member in a direction generally perpendicular to the main axis.
12. A method according to claim 11, wherein actuation of a lateral drive causes the rotational movement of the first or second support member.
13. A method according to any one of claims 1 to 12, wherein the first and second support members move in opposite directions towards each other and the main axis simultaneously.
14. A method according to any one of claims 1 to 13, wherein the lateral and rotational movements of one support member are effected in tandem with the respective lateral and rotational movements of another support member.