FIELD OF INVENTION

[0001] The present invention concerns a method of and apparatus for forming helical flight segments, otherwise known in industry as "screw flights". It is particularly, but not exclusively, concerned with production of screw flights used in production of helical piles, augers and screw conveyors.

BACKGROUND

[0002] Helical piles, also known as "screw piles" in the industry are designed such that most of the axial capacity of the pile is generated through the bearing of a single screw flight, or of a plurality of screw flights, against the soil. The screw flights have to conform to "true helix" geometry. This means that 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. This is according to ICC-ES AC358 which establishes design and testing criteria for helical piles in accordance with this International Building Code.

[0003] Initial installation of a helical pile, or screw pile, is performed by applying a downward force and rotating the pile into the earth via the screw flight. Once the screw flight penetrates to a depth of about 50 to 100 cm, the pile shaft generally requires less applied axial force and installation is accomplished mostly by the downward force generated from the screw flight, similar to the effect of driving a screw into a block of wood. Therefore, screw flights perform a vital role in providing the downward force or thrust needed to advance the pile to the bearing depth. The screw flight geometry affects the rate of penetration, soil disturbance and torque to bearing capacity correlation. The optimum configuration is that of a true helix with perfect symmetry and with uniform pitch angle throughout the 360° revolution of the plate and all radial points extending across the plate lying perpendicular to the axis of a central shaft to which the screw flight is to be attached. When these conditions are fulfilled, the leading and trailing ends of a screw flight are axially aligned and their edges are substantially parallel to the central shaft.

[0004] A common fault in poorly formed screw flights is that the pitch at the periphery of the helix is greater than at the inside and the respective edge margins diverge instead of lying parallel. The consequences, in a helical pile, of a poorly-formed screw flight are that the screw flight severely disturbs the soil instead of precisely following the path of its leading edge, in a smooth sliding action. This might be compared with a cross threaded bolt as opposed to a bolt that is correctly aligned. The asynchronous path followed by a poorly formed screw flight results in loose disturbed soil with consequently reduced bearing capacity. A poorly formed screw flight will encounter more drag resistance in penetrating the soil than one conforming to a "true helix" and this increased drag resistance will adversely affect the torque to bearing capacity correlation, an important monitoring measurement used by installers of helical screw piles.

[0005] In contrast to typical helical (screw) piles, in the case of augers and screw conveyors a continuous helical flight encircles the central shaft and is welded or otherwise connected thereto. However, similar considerations apply as regards the importance of accurate helical geometry when helical flight sections are used to produce or repair helical augers or screw conveyors. While lightweight ribbon augers are typically produced by rolling from long flat bars to produce a continuous helical flight, other augers and screw conveyors for heavy duty purposes are either machined from solid bars or cast, but mostly they are fabricated by abutting a series of individual single pitch helical segments and welding these to each other and to the shaft. The present invention is therefore applicable to the latter, and to repair of sections of any auger or screw conveyor.

[0006] There are four known techniques for producing heavy duty segmental screw flights from annular shaped discs with a slot from the central hole to the periphery, otherwise referred to as "blanks" within the industry. The first is axial by stretching, namely pulling of the leading edge away from the trailing edge of the blank. This technique is exemplified in US 3,485, 1 16 where respective edge clamps are shown swivellably mounted to allow for rotation. It is therefore not mechanically compliant with the forming of a true helix as defined in paragraph [0002] above due to the swivelling arrangement which encourages misalignment of the leading and trailing edges and thus not conforming to the defined requirements of the code which states: "the leading and trailing ends of a screw flight are axially aligned and their edges are substantially parallel to the central shaft".

[0007] The second technique is of pressing the flat blank between matching helically shaped dies in a mechanical press. This has been the traditionally used method and is the most common method used universally today.

[0008] The third technique is a variant involving clamping inner and outer annular edges and effectively twisting the annulus by a rotary movement of the respective clamp and thereby incrementally bending the blank along radial lines to form a helical segment. This technique has not played a significant role in industry. It is described in US 4,596,064.

[0009] The fourth and most recent technique is by incremental pressing where the blank is guided and rotated to pass between a pair of directly opposed reciprocating dies. This causes controlled bending to occur in a precise manner along radii and the blank is formed into a helix by gradual bending at regular angular intervals. This method is accurate, typically under computer control, and can be used to form different pitches by adjusting the depth of penetration of the oppositely shaped reciprocating dies. It is described in PCT/AU 2012/000803, CA2840243A1 , CN103764526A, EP2729391A1 , and US 20140196515.

[0010] An object of the present invention is to provide alternative apparatus and method for forming a helical flight segment which provides required accuracy and reliability, but is simpler and requiring less power than the pressing techniques currently used. An additional objective is to form the blank into a finished screw flight in a single cycle (stroke) as opposed to multiple progressive or incremental cycles. A further objective is to avoid the cost of providing a range of dies to suit every product variation. Dies are expensive and are subject to high extents of wear. Dies have to be stored and changed for every variation in product size or pitch.

Oppositely configured dies are needed for clockwise (right hand) or anticlockwise (left hand) rotating screw flights. Besides the costs involved in holding different pairs of dies for each variant, there is also the significant cost of labour in having to change over from one set of dies to another set for every variant. Equally important is the time consumed to make these changes while relatively big expensive machinery lies idle.

SUMMARY OF THE INVENTION

[0011] The present invention provides apparatus for forming a helical flight segment from a flat circular disc having a central bore and a radial slot formed therein, hereinafter referred to also as the "blank". The apparatus is characterised by having two separate main components, typically in the form of plates or panels, although they do not necessarily have to be of that strict geometric form. Each of these components is able to clamp to an opposite edge of the slot in the blank which itself in an initial condition extends in a perpendicular disposition relative to the said plates, when in that form. These two components lie adjacent, namely side-by-side, each other and either one or both is/are capable of sliding parallel with the other. Within a common operational principle, there are three slightly different structural possibilities for such apparatus.

[0012] A first version of said apparatus comprises a stationary support having a substantially flat support surface and a movable carriage which is mounted side-by-side with the stationary support and has a substantially flat sliding surface facing the support surface, the carriage being mounted such that, in use, it is movable relative to and substantially parallel to the support surface with the sliding surface moving across the support surface, the stationary support and the movable carriage having respective clamping means for holding respective edge margins of the radial slot of the disc which is to be shaped, the edge margin clamped in the movable carriage being displaced relative to the edge margin clamped in the stationary support upon movement of the carriage relative to and parallel to the substantially flat support surface of the stationary support, thereby deforming the circular disc to a single pitch helical form. [0013] In a practical embodiment of this first version of said apparatus the stationary support typically comprises a machine frame and a stationary support plate secured to this frame, whereas the carriage typically comprises an axially shorter movable plate which is mounted side-by-side with the stationary plate. Appropriate guides keep the plates parallel and in contact, or in close proximity, one with the other as the movable plate slides across the stationary plate.

[0014] The sliding guides for the movable plate may be provided on the stationary support plate or, alternatively or additionally, axial sliding guides may be provided on the frame of the apparatus to keep both plates parallel one with the other.

[0015] A corresponding method involves clamping the first edge margin of the radial slot of the disc to the stationary support having the substantially flat support surface, clamping the second edge margin of the radial slot to the movable carriage which is disposed in close side- by-side relationship with the stationary support, and sliding said carriage across the flat support surface to thereby displace the second edge margin relative to the first edge margin and consequently deform the circular disc to a single pitch helical form.

[0016] A second version of said apparatus is similar in operation to the first version excepting that both of the said components, namely carriages or plates, are able to slide on guide means provided by the frame of the apparatus keeping both components with respective facing surfaces parallel one with the other. An advantage of this arrangement is that the components, namely carriages or plates, are able to slide axially in either direction relative to each other, thus allowing the margins of the slot in the blank to be pulled away from each other in either direction forming flights with either clockwise or anticlockwise helical forms.

[0017] A third version of the apparatus is also similar in operation to the first version excepting that there are two movable carriages, preferably in the form of plates and these are arranged at opposing sides of common central support which has opposing support surfaces. In practice the common central support would be a thin plate.

[0018] Accordingly, the apparatus provided by the present invention allows the helix to be formed by means of axial stretching of the margins of the slot in the blank plate away from each other. The blank is typically of steel, but any other malleable metal or other material is possible. In contrast to the old proposal, the present apparatus and method has been found to work very well in providing a good, namely well aligned, helical configuration. This results to a

considerable extent from the stability of the apparatus of the invention and the close side-by- side arrangement with the surface of the carriage, typically a moveable plate, moving across the stationary support surface or by respective surfaces of respective carriages sliding across each other while supported by the boundary frame of the apparatus. This means that lateral forces, likely to result in undesirable lateral components of deformation are adequately restrained.

[0019] Furthermore, the respective clamping means while necessarily having movable parts to carry out clamping function prior to operation and unclamping at the end, and having optional, indeed preferable, resilient bias in the direction of movement of the moveable plate, are themselves mounted in a non-rotatable, non-swivellable manner to the support and the moveable carriage, or to the respective movable carriages, respectively. This is to minimise any twisting forces on the clamped edge margins during operation of the apparatus in deforming the blank.

[0020] Drive means for moving each moveable carriage may take any suitable form, such as a feed screw engageable with a bracket mounted on the moveable carriage, or a hydraulic or pneumatic cylinder with a ram which is connected to the moveable carriage, or a rack and pinion arrangement, or a chain and sprocket arrangement.

[0021] Each moveable carriage may be directly mounted to the stationary plate or to the boundary frame of the apparatus in a manner permitting sliding of the sliding surface of the moveable plate across the support surface or the other carriage, respectively. In this respect, practical embodiments of the apparatus of the invention will typically have guide means provided on the stationary support or on the moveable carriage or on the machine frame or on any one or more of these to guide each moveable carriage such that its sliding surface slides across, and substantially parallel to, the stationary support surface or the other moveable carriage.

[0022] Typically, the stationary support is an elongate body. The guide means may then simply comprise at least one elongate opening extending longitudinally of said body and at least one corresponding projection provided on the movable moveable plate and locating slidably in said elongate opening. Alternatively, the guide means may comprise at least one elongate rail or channel extending longitudinally of said body and at least one corresponding slider provided on the movable moveable plate and engaging slidably with said elongate rail or channel.

However, other means of guiding may be provided in other embodiments. In this respect, the effectiveness of the apparatus depends on the movable carriage (which is typically in the form of a plate) and specifically the plane of the carriage in which the clamping means thereof is disposed, being maintained, during movement, close to or in sliding contact with the stationary support (also typically in the form of plate) or other moveable carriage, and more specifically close to the plane in which the clamping means of said stationary support or other carriage are provided. [0023] In preferred embodiments of the apparatus according to the invention a spacer plate between the support plate and movable carriage or between respective movable carriages may be provided as a means of keeping the surfaces of the support and carriage or respective carriages a fixed space apart. At the same time, this spacer plate advantageously serves to locate the radial slot of the blank which is to be deformed prior to operation commencing. Thus, the slot in the blank must have a slightly larger width than the thickness of the spacer plate so that the slot fits over the plate with clearance. The spacer plate also serves the important function of preventing interference by either one of the edges of the radial slot, if they are deformed imperfectly during the shaping process so as to project slightly beyond alignment with the other edge of the radial slot, from fouling and potentially damaging the clamping means of the other part, namely the stationary support or the movable moveable plate, respectively.

[0024] Embodiments of the apparatus of the invention may include means, such as scale markings on any suitable element of the apparatus, or electronic means, for measuring the extent of displacement of the blank slot margins from each other.

[0025] The clamping means in preferred embodiments of the invention comprise respective pairs of opposing clamping jaws. Said jaws may have rounded gripping edges allowing some rotation and local slippage of the blank margins while being effectively rotated about their radial axes during the helical segment forming operation. This helps to reduce the considerable lateral forces which would otherwise be brought to bear on any adjacent plate. These clamping jaws will typically be symmetrically configured in the sense that they will typically be equal and oppositely arranged on the two operating plates, respectively. Each jaw of each pair of jaws may also be symmetrically configured, but that is not always the case and will depend on the desired final configuration of helical flight and its dimensions of thickness and diameters.

[0026] Each of the clamping jaws is preferably mounted to the plates by a resilient mounting, such as an inserted cushion or spring. Such a resilient mounting is suitably made from elastic material.

[0027] The resilient mounting may suitably consists of or include a cushion in the form of a solid nylon block. Additionally or alternatively, such a resilient mounting may include

compressed fluid, or granular material, or a coiled spring, or a block of any other suitable resilient material, such as alternate layers of rubber and steel. The inserted cushions or springs ensure that adequate pressure is applied to hold the blank throughout the forming process, but are sufficiently yielding to allow the jaws to slide on the surface of the steel flight as it is forcibly rotated. Balanced distribution of the pressure is also important to a satisfactory forming operation. The resilient inserts, of whichever sort is chosen, may be electronically monitored so that the tightening of the jaws may be adjusted and controlled manually and/or or by

programmable technology.

[0028] The clamping jaws, in practical embodiments, each have at least one sloping surface extending at a predetermined angle relative to the plane of the direction of travel of the movable carriage (or the plane of the spacer plate when present) to accommodate a predetermined helical configuration to be produced from the circular disc. It is preferable that the clamping jaws should be releasably mounted to the plates so that differently configured jaws may be used to produce different helical flight configurations. For example, jaws of different profile, optionally tapering to different extent or segmental to accommodate possible variation in the forces and require displacement distance over the length of the jaws may be employed.

[0029] In any event, the apparatus of the invention preferably includes means to vary, select and/or control a clamping force applied to and applied by the opposing clamping jaws.

[0030] A further feature enabling such selection and control is that at least some of the clamping jaws may incorporate an insert, or a capping member or a roller.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a helix blank, namely a flat circular disc to be formed into a helical flight segment;

Figure 2 is a side view of the helix blank figure 1 ;

Figure 3 is a side elevation of a right-hand helical segment as formed from the disc of figures 1 and 2;

Figure 4 is a view of the same right-hand helical segment rotated through 180°;

Figure 5 is a schematic plan view of apparatus in accordance with the invention for forming a helical flight as in figures 3 and 4 from a helix blank as in figures 1 and 2;

Figures 6a and 6b are enlarged plan views illustrating an embodiment of jaw configuration for the apparatus of figure 5;

Figure 7 is a schematic plan view of an embodiment of apparatus in accordance with the invention with a helix blank mounted thereto in an initial position for forming a right-hand helical flight; Figure 8 is a similar view of the apparatus of figure 7 at the end of operation to form the right- hand helical flight;

Figure 9 is a schematic plan view, comparable to figure 7, of the same embodiment of apparatus with a helical blank mounted thereto in an initial position for forming a left-hand helical flight;

Figure 10 is a similar view of the apparatus of figure 9 at the end of operation to form the left- hand helical flight;

Figure 1 1 is a schematic partial perspective view of showing means of linear guidance for a moving plate in any of the embodiments of the apparatus of the invention;

Figure 12 is a side view of a further embodiment of apparatus in accordance with the second aspect of the invention;

Figure 12a is an end view of the apparatus of figure 12; Figure 13 is a plan view of the apparatus of figure 12;

Figure 14 is a side view of the embodiment of apparatus in accordance with the first aspect of the invention with a helix blank mounted in initial position ready for operation;

Figure 15 is a similar side view of the apparatus of figure 14 part way through use to deform the blank into a helical flight segment;

Figure 16 is a schematic perspective view of another modified embodiment of apparatus in accordance with the invention;

Figures 17a, 17b, 17c and 17d are schematic plan views of pairs of corresponding round nosed jaws for mounting to and use in embodiments of the apparatus of the invention for forming helical flight of different thickness;

Figure 18 is a schematic, fragmentary plan view showing how respective pairs of jaws are mounted in preferred embodiments of apparatus in accordance with the invention at an initial position ready for operation; and

Figure 19 is a similar schematic plan view of only one of the opposing pairs of jaws in figure 18 to illustrate use of the jaws in forming a screw flight into a desired true helical shape.

DETAILED DESCRIPTION

[0032] Figures 1 and 2 show a helix blank 20 which is to be formed into a helical flight segment using the apparatus and method of the invention. It consists of a flat circular disc of steel having a central bore 21 and a radial slot 22 formed therein. The thickness of the disc 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 5mm and 50mm. The internal diameter of the disc is chosen to match the external diameter of a shaft to which the helical flight to be formed is to be mounted, typically with a small annular clearance of, up to 2.5 mm. The external diameter is also chosen for the required end-use purpose. Typical outer diameters may be in the range from, say, 20cm to 200cm.

[0033] Figures 3 and 4 show the form of the helical flight segment 120 which can be produced from the blank 20 by the apparatus and method of the invention. The desired configuration is for an evenly formed, i.e. constant, pitch P where the leading and trailing edge surfaces 24, 25 lie substantially parallel to a nominal central shaft (not shown) to which an inner perimeter of the helical flight will be welded or otherwise connected during subsequent production of a helical pile or auger. In other words, all radial points extending across the helically formed plate ideally lying perpendicular to the axis of the nominal central shaft to which it is to be attached.

[0034] As shown schematically in figure 5, apparatus in accordance with the first aspect of the invention for producing the helical flight segment 120 from the helix blank 20 comprises a stationary support, which may take the form of an elongate, upright panel 30 and which has a substantially flat support surface 31 , and a movable carriage in the form of a plate 40 which is mounted side-by-side with the panel 30 and which has a substantially flat sliding surface 41 facing the support surface 31. As indicated by the arrow, the plate 40 is movable relative to the support 30 with the sliding surface 41 guided across the support surface 31. In fact, the plate 40 is slidably mounted onto the panel 30 in any suitable manner, although examples will be described later. This provides significant stability to the apparatus during operation in deforming the helix blank 20, which clearly requires considerable force. The mechanism may be likened to shears and a shearing action in that the sliding member is retained by or supported against the stationary member of the apparatus with lateral forces then being adequately restrained through the mechanical connection of these parts. The stationary panel 30 and the movable plate 40 have respective clamping means, designated generally by reference 50 and not shown in figure 5 in any detail, for holding respective edge margins 24, 25 of the radial slot 22 of the disc 20 which is to be shaped. In use, and as indicated, the leading edge margin 24 is clamped to the plate 40, and as the plate 40 moves, that edge 24 is displaced relative to the trailing edge margin 25 which is clamped to the stationary panel 30. This results in the blank 20 being deformed to a single pitch helical form 120. Deformation (the axial elongation) is proportional to the force applied (Hooke's law). Thus the helical elongation is evenly distributed throughout the helical flight, from leading edge to trailing edge, eliminating the need for forming dies in order to produce a true helical form.

[0035] The clamping means 50, in each case, namely on the stationary panel 30 and on the movable plate 40 comprise an opposing pair of jaws 51 , 52. These need to be shaped appropriately to avoid restraining the edge margins 24, 25 of the plate 20 during the deforming operation in a manner which would prevent the final product from having the required shape of a true (accurately configured, as previously explained) helical flight. The required shaping of the opposing jaws, namely the required slope for surfaces of the respective jaws, can be calculated on the basis of requirements of the final product, namely the thickness of the plate 20, 120, the projection (this is the radial extent of the plate 20, 120 between inner and outer diameter), and the helical pitch P required (this is the axial distance between the leading and trailing edges 24, 25 of the final helical flight 120). By way of example only, the angles of the slope of the respective jaws relative to a plane perpendicular to the direction of travel of the moveable plate 40 are shown as 10° for jaw 51 and 33° for jaw 52 in figures 5 and 6. These correspond to the tangential slope lines of the required helical form, 10° being the slope at the outer diameter, and 33° being the slope at the inner diameter of the plate 120. These tangential slope lines for the outer diameter edges and the inner diameter edges, respectively, are parallel to each other on the respective jaws and their angles to a plane perpendicular to the axis are equal

corresponding angles. The outer diameter of the trailing edge 25 is labelled 25a and the inner diameter of the trailing edge is labelled 25b, and is above as viewed in section in Figure 6b.

[0036] Figures 7 and 8 again illustrate the apparatus of the invention schematically, and for ease of reference the same reference numerals as previously are applied to equivalent parts. In this case the arrangement is shown to include first and second pairs of clamping jaws 50, 60 integrated in the stationary panel 30 but at spaced apart locations. In figure 7 the carriage plate 40 is shown at an initial position at the left hand side as required for production of a right-hand helical flight. In this initial position the respective pairs of clamping jaws 50 in the panel 30 and the movable plate 40 are in alignment and the initial circular disc 20 is positioned with its respective edges 25, 24 held in those jaws. Drive means in the form of a screw feed 70 is shown schematically acting by way of a bracket 42 provided with a threaded bore mounted on the movable plate 40. Figure 8 then shows the final position where the moveable plate 40 has been displaced to the right thereby having caused the deformation of the plate 20 to provide the helical flight 120. In figure 9, the movable plate 40 is shown in a corresponding initial position at the right hand side of the apparatus, as required for production of a left-hand helical flight. In this initial position the pair of clamping jaws 50 in the movable plate 40 are in alignment with the second pair of clamping jaws 60 in the panel 30. Then, in operation, the moveable plate 40, in this case moves towards the left, to the final position shown in figure 10. [0037] Figure 11 illustrates a stationary support panel 130 having two slots 132 for mounting clamping jaws (not shown) and a movable sliding plate 140 having a single slot 148 also for mounting clamping jaws (not shown). A mechanism for restraining the sliding plate 140 from tilting from its perpendicular relationship with the axis of its driven direction is shown which operates with much less frictional resistance than linear guides employing purely sliding means to restrain overturning. The mechanism employs intermeshing involute profiled spur gears 1 10, 112 on rolling bearings 111 , 1 13 which are provided on the movable plate 140 engaged with matching racks 1 14, 115 provided on a supporting frame of the machine (not shown). Such an arrangement eliminates virtually all friction compared to alternative methods making use of sliding components. The illustration depicts a single pair of intermeshing spur gears / pinions 110, 1 12 but depending on duty conditions there may be more than a single pair so deployed. Movement of the plate 140 in either direction relative to the stationary support 130 is again by means of a linear drive screw 170 engaging through a drive nut bracket 142 on the movable plate 140.

[0038] Figures 12 and 13 illustrate a variant structure for the apparatus of the invention in which two movable carriages, each in the form of plates 144, 146, and each mounting a respective pair of clamping jaws 154, 156, are slidably mounted to respective opposing elongate elements 101 of a base frame 100. These elongated elements 101 are connected at each end by cross members 102 to provide a stable and rigid frame 100. As best shown in figure 12a, the plates 144, 146 have mutually facing planar surfaces which slide relative to each other and may be in sliding contact with each other. The mutually remote surfaces of the respective plates 144, 146 are provided with projections of T shape profile which slidingly engage in T-shaped slots 103 in the base frame elements 101. The plates are able to be driven by any suitable type of linear drive technology, but are shown here as being driveable by respective linear drive screws 170 which extend through drive nut elements 172 provided in a lower extension of each plate 144, 146. In other embodiments such movable plates may be guided by any suitable type of mechanical linear guidance mechanism.

[0039] Also, in modified embodiments of the invention the movable carriage and the stationary support or the respective movable carriages may be configured or arranged relative to the supporting frame that the blank for forming the screw flight may be inserted on opposite sides of the jaws, namely inverted, for example extending below the apparatus in the initial position instead of being disposed primarily above the apparatus. This makes it possible to make left hand or right hand helical flight forms using the same apparatus and is useful as an alternative to providing apparatus similar to that illustrated in figures 7 and 8.

[0040] Figures 14 and 15 illustrate a different embodiment of apparatus in accordance with the first aspect of the invention. In this embodiment the stationary support 230 is provided as an upright, elongate panel with clamping jaws 251 , 252 in the plane of the panel, shown here at the right hand end. Again, the form of the clamping jaws is not shown in any detail here, but the jaws 251 , 252 are shown to be held in clamping position by bolts 256, and one edge of the plate 20, which is to be the trailing edge 25, is shown in section clamped in its initial position. The panel 230 is provided with two axially extending parallel slots 232 which serve as mounting and guide means for a moveable plate 240, the position of which is shown in broken lines as it is entirely overlapped by the panel 230. Thus, the carriage 240 is also in the form of a panel, extending in side-by-side relationship with the stationary panel 230. In axial extent the panel 240 is shorter than the panel 230. Projections in the form of pins or bolts 242 extend in a perpendicular direction through the moveable plate panel 240 and locate through the slots 232 and are slidable along said slots 232. They also maintain the moveable plate panel 240 in close adjacency to the far side of stationary panel 230, preferably in sliding contact with a support surface of the panel 230. Axial movement of the moveable plate 240 is again by means of a feed screw 270 mounted to a flange 234 at the end of the stationary panel 230 remote from the clamping jaws 251 , 252 and through a threaded bore 248 in the moveable plate 240. The moveable plate 240 is provided with a pair of clamping jaws 253, 254, comparable to the jaws on the stationary support panel 230, and clamped together with comparable bolts 257, and these are visible in broken lines in figure 15 where they are shown at a position where they have moved out of alignment with the jaws 251 , 252 (since in the initial position, shown in figure 14, they are in alignment). The other edge of the plate 20, which is to be the leading edge 24, is clamped into those jaws 253, 254 in the initial position, as shown in figure 14. Thus in this position the plate 20 is flat, as in figures 1 and 2.

[0041] Figure 16 illustrates another modified embodiment, also in accordance with the first aspect of the invention, with different drive means, namely a hydraulically operable cylinder 370 with a piston 372, to move the moveable plate 340 to and fro. During the course of movement a substantially flat surface 341 of the carriage, again in the form of a movable plate 340, is guided in sliding contact with the flat support surface 331 of the stationary support 330. As in the previous embodiment there are parallel elongate openings 332 in the support 330 and projections (not visible) from the sliding surface 341 of the movable plate 340 locate in and are guided along these elongate openings 332 during operation of the apparatus. The stationary support 330 and the movable plate 340 are again provided with clamping jaws 351 , 352 and 353, 354, respectively, which are only schematically shown here. Clamping bolts 356, 357 are shown. The support 340 carries scale markings 334 to indicate the initial position of the movable plate 340 and the distance which it has to be moved to achieve the required helical pitch by deformation of the plate 20, which is shown here in phantom in an initial clamped position. [0042] Figure 17 - a,b,c,d - illustrates four possible different configurations and jaw spacings for pairs of corresponding round nose jaws as used in practical embodiments in the various clamping jaws which have been illustrated schematically in the preceding figures. The different spacing between the opposing noses caters for different thicknesses of helix blanks 20.

[0043] The protruding edges of the flight 120, as shown in figure 6b, could foul the adjacent clamping members, 51 , 52 and 53, 54 (or in other embodiments 251 , 252 and 253, 254 or 351 , 352 and 353, 354, respectively) while attempting to travel past each other. Accordingly, in preferred embodiments an additional spacer plate 160 is provided along the surface of the stationary support panel 30, 230, 332 to prevent this occurring. Such a plate 160 is shown only in figures 18 and 19. It is not shown in the earlier figures illustrating practical embodiments to enable other parts to be more clearly visible. The presence of the plate 160 prevents damage to the machine by confining the edges of the plate 20 inside safe limits provided by the plate 160, as shown in figure 19. The spacer plate 160 is thinner than the width of the specified slot 22 in the blank (figure 1) and therefore also acts as a guide when locating the blank 20 into the clamps in the support 30 and the moveable plate 40.

[0044] Considerable lateral forces on the spacer plate 160 from the progressive rotation of the edges 24, 25 during forming of the flight, could be expected, but such forces are

considerably reduced in this design in two ways:

Firstly the gripping edges of the jaws 51 , 52 and 53, 54, respectively are rounded which allows some rotation and local slippage.

Secondly the pressure between the jaws and the plate 20 which is being deformed are evenly distributed and checked by resilient means, such as cushions or spring inserts, indicated generally by reference 164 in figures 18 in 19. These inserts, of whichever sort, may be electronically monitored so that the tightening of the jaws 51 and 52, and 53 and 54, respectively, may be accessed and managed manually or by programmable technology.

[0045] The clamping force on the jaws is simply shown in figures 18 and 19 as being provided by screws 56, 57, but may be provided by hydraulic or electro-mechanical means. Again, such forces on the jaws to tighten or loosen them may be managed by electronic or digital means.

[0046] The inserted cushions or springs 164 ensure that adequate pressure is applied to hold the blank 20 throughout the forming process, but are sufficiently yielding to allow the jaws to slide on the surface of the steel flight as it is forcibly rotated. Typically these inserts 164, when in the form of cushions, are made of elastic material such as solid nylon blocks. The resilience of the inserts 164 will vary to suit differences in size and other properties of the blanks 20. Selection of inserts of correct resilience may be facilitated by colour coding. [0047] The inserts 164 may utilise any material or mechanism, including compressed fluids, or granular material and may be composed of different layers of material such as rubber and steel. The inserts 164 may be of uniform profile or may be tapered or segmental to

accommodate the variation in the resisting forces and in displacement distance over the length of the jaws.

[0048] Likewise the jaws themselves may vary in profile to suit requirements and may themselves have inserts or cappings of various profiles and materials to best suit the

requirements of the product being formed. Such inserts may take the form of rollers in the face or nose of the jaws to facilitate the sliding of the product on the jaws during forming. Again, such cappings or inserts on or in the jaws may be segmental and variable as to profile and materials used.

[0049] In operation of a prototype apparatus in accordance with the first aspect of the invention the maximum recorded force (F) required to pull a 400 mm diameter x 10 mm thick flat blank with a 125 mm diameter central hole to be deformed into a screw flight with a 140 mm pitch was 9.3 kg and the mechanical advantage of the proto type machine was: 1 to 1329. Thus the actual force applied was calculated to be: F = 9.3 kg x 1329 = 12.35 tonnes. A typical hydraulic press with matching mating helical dies for forming similar helical flights in accordance with the prior art would typically exert a force of approximately 20 tonnes to form a similar flight.

[0050] The invention is not restricted to the details of any forgoing embodiments. Variations in details of construction of the apparatus will be apparent to those skilled in the art and any suitable variations may be made within the scope of the appended claims. It should also be understood that so far as is feasible features, such as the form of the drive means, the manner of mounting of the respective movable plates/carriages, the form of the supporting machine frame etc of any one embodiment may be interchanged with features of any other embodiment within the scope of the invention. It should also be understood that in so far as the terms "upright", "below" and "above" have been used in describing specific embodiments, this is only for ease of understanding the illustrated versions and the orientation of the apparatus may vary in the way it is installed and used within the scope of the invention as defined by the appended claims.