A process and machine for continuous formation of conveyor screws for archimedes-type screws

Abstract: In the process and machine of the invention, a band (2) is fed continuously between a pair of rollers (3a, 3b) which turn the band (2) into a spiral (4), into a central space of which a succession of support shafts (A, B) is advanced in order that the spiral forming is achieved about the continuously advancing support shafts. A welder (8) fixes the spiral (4) to each support shaft, and a cutting device (9) cuts the spiral into lengths, each of which lengths of spiral is fixed to a single shaft. Variably-stepped spirals can also be produced using the invention, with very good precision and relatively simply.

Description: The invention relates to a process and a machine for continuous formation of conveyor screws for archimedes type screws. Reference is specifically made to conveyor screws which each comprise an internal support shaft, about which a band is coaxially and spirally wound. The prior art teaches conveyor screws of this type, made by a process wherein the flat, continuous metal band is wound to form a spiral which is cut into lengths, each of which subsequently is welded to a support shaft. This known process exhibits various drawbacks. Firstly, it is long and laborious to make, and therefore expensive. Secondly, considerable accuracy and precision is needed, especially for the welding stage where the spiral is welded on to the shaft; considerably skilled and expert personnel is needed for this operation. Further, good-quality conveyor screws which obey the predetermined geometrical and dimensionsional tolerances are difficult to obtain. The difficulties are particularly relevant when variable-step screws are being made, where two spiral lengths having different steps are used consecutively. A still further drawback is the need for transport and storage of the lengths of spiral destined to be fixed on to the support shafts. FR-A-814 323 discloses a process for formation of conveyor screws for Archimedes screw systems, as in the preamble of claim 1, wherein each conveyor screw comprises an internal support shaft at a periphery of which a spiral is wound; the process, which comprises the step of infeeding a band continuously into a spiral forming zone in which the band is made to wind into a spiral shape, has the disadvantage of stopping production to use a new shaft. A machine according to the preamble of claim 6 is known from FR-A-814 323 as well. The main aim of the present invention is to provide a process for obviating the above-mentioned limitations and drawbacks in the prior art. An advantage of the invention is that it makes available a process which is relatively rapid and thus leads to increases in productivity. A further advantage is that variable-step conveyor screws can be produced with good geometrical precision and relatively simply. A further aim is to provide a constructionally simple and economical machine for realising the above-described process. An advantage of the machine is that it is relatively small. According to the invention, these aims and advantages and others besides are all attained by a process according to claim 1 and a machine according to claim 6. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of a preferred but non-exclusive embodiment of the invention, illustrated purely by way of nonlimiting example in the accompanying figures of the drawings, in which: figure 1 shows a schematic lateral view of a machine according to the invention; figure 2 is a plan view from above of figure 1. With reference to the above-mentioned figures of the drawings, 1 denotes in its entirety a machine for continuous forming of conveyor screws for archimedes-type screw conveyors. Each screw comprises an internal support shaft to which a spiral-fashioned metal band is externally fixed. The machine 1 comprises means for continuously feeding a uniform-width band 2 into a device 3 for spiral-forming. The means for continuously feeding, of known type, comprise a spool 5, from which the band 2 is continuously dispensed, and a guide 6, for example a roller-guide, for orienting and conveying the band 2 in an advancement direction. The guide 6, of known type, is provided with means for regulating the orientation of the band 2; the means for regulating continuously control and can vary the advancement direction of the band 2. The spiral-forming device 3, also of known type, receives the continuously-advancing belt 2 and by cold-forming causes it to wind into a spiral, developing along a horizontal axis x-x. In the present case the cold-forming is done by two rollers 3a and 3b, having their active surfaces inclined with respect to the band fed in between them. The internal edge of the spiral 4 of band is shaped and arranged as a cylindrical spiral of a predetermined diameter. The machine 1 comprises a first shaft movement device 7 for moving the support shafts A and B located upstream of the spiral-forming device 3. In the illustrated embodiment the first shaft movement device 7 comprises a truck 7a which can be commanded to move in both senses in direction F parallel to the horizontal axis x-x of the spiral 4. The truck 7a bears a chuck 7b for gripping and rotating a shaft A about an axis thereof and coaxially to the spiral. The chuck 7b is in effect a device for controlling rotation of a shaft, mounted on a mobile horizontal support, constituted by the truck 7a. The machine comprises a further support 7c predisposed at a certain distance from the truck 7a and supporting the rotating shaft A. The support 7c is horizontally mobile on command in both senses of direction F, preferably in synchrony with the truck 7a. The truck 7a is predisposed to introduce the support shaft into the centre of the spiral 4 of the band, in an advancement direction G, coaxially to the spiral. The external diameter of the shaft is about the same as the diameter of the internal edge of the spiral 4 destined to be fixed to the shaft. During formation the spiral is not only wound, but is also narrowed about the internal shaft: in other words, during the coupling of the spiral 4 with the shaft, the spiral 4 is not only wound about the shaft but is also deformed, in effect stretched, by effect of the contact with the shaft A. The machine is equipped with means 8 for fixing the spiral 4 to an internal support shaft A introduced through the centre of the spiral 4. The means for fixing are in the example constituted by an automatic welder 8a arranged on a group 8b which is mobile on command in a parallel direction to the axis x-x of the spiral in both senses. The welder 8a welds (e.g. spot-welds) the internal edge of the spiral 4 onto the circumference of the support shaft. A cutting device 9 is predisposed between the welder 8a and the rollers 3a, 3b, which cut the spiral 4 into lengths. Before cutting, each length will have been previously fixed to a support shaft, as will be better explained herein below. The cutting device 9, like the welder 8a, is mobile on command in the direction of the axis x-x of the spiral formation. Downstream of the spiral-forming device 3 (downstream being in reference to the direction G of advancement of the support shafts), the machine comprises a second movement device 10, similar to the first and opposite thereto. The second device 10 comprises a second truck 10a situated, with respect to the spiral-forming zone, on the opposite side of the first truck 7a. The second truck also bears means for gripping and rotating the support shaft, which means comprise a chuck 10b, opposite to the chuck 7b, for gripping and rotating a shaft arranged coaxially to the spiral. The two movement devices 7 and 10 operate in synchrony; in particular, the second movement device 10 receives a support shaft from the first movement device 7 and distances the shaft axially from the spiral-forming zone (i.e. the rollers 3a and 3b) after the spiral has been cut to a desired length. The two trucks 7a and 10a translate at speeds above the normal axially-directed advancement speed of the spiral being formed. Each support shaft A, B comprises at opposite ends thereof two internally-grooved collars A' and B'. Each end collar can be connected with a grooved coupling to an end collar of another shaft by means of a joint constituted by a short shaft 11, externally grooved so as to be couplable to either end collar. These grooved couplings enable the two shafts A and B to be joined coaxially to each other, so as to render the two shafts solid in rotation but disengageable from each other by simple reciprocal pulling in an axial direction. Other types of couplings could be used to join the two shafts A and B. Machine operation will now be described. Initially the opposite ends of a support shaft are gripped in the two chucks 7b and 10b. The front end of the shaft is located slightly downstream of the spiral-forming zone of the metal band. Starting from this configuration, the band 2 is fed continuously into the spiral-forming device 3, and the spiral 4 is therefore also continuously-formed at a controlled speed. At the same time the internal shaft is commanded, by the movement devices 7 and 10, to translate in direction G and to rotate about its own axis, at controlled translation and rotation speeds and in relation to the spiral-forming speed. The rotating-translating movement of the internal shaft and the formation of the external spiral are contemporaneous, so that the spiral will form about the moving shaft. The truck 7a and the chuck 7b cause the shaft to rotate and translate in synchrony with the movement of the spiral formation operation. The spiral formation operation is so regulated that the spiral exerts a certain squeezing pressure on the shaft. As soon as it is formed and wound on the shaft, the spiral, though not welded on the shaft, is however tightly held thereon. The spiral formation, starting from the flat straight band, is essentially realised by the action of the means for plastically deforming, i.e. the rollers 3a and 3b, in collaboration with the shaft. The presence of the shaft at the centre of the spiral while the latter is being formed contributes to the formation of a regular spiral and facilitates the subsequent welding operation. When the band spiral, moving rightwards (with reference to figures 1 and 2) in direction G, passes before the welder 8a, the welder 8a welds at least one point of the internal edge of the spiral to the outside of the internal shaft. This fixture is achieved without stopping the movement of the shaft and the formation of the spiral, thanks to the controlled movability of the means for fixing 8. When the welding is done, the spiral is solidly constrained to the shaft both in rotation and in translation, and the shaft draws the spiral with it when rotating and translating. This enables spirals to be produced with considerable precision and accuracy, in full respect of dimensional and geometrical tolerances and specifications, especially with regard to the screw spiral step. As the shaft advances rightwards in direction G, the welder 8a fixes the spiral to the shaft by a plurality of spots, or with a continuous seam if so desired. Before the whole shaft (moving in direction G) has passed in front of the rollers 3a, 3b, i.e. before the left end of the shaft has crossed the spiral formation zone, a second shaft is coupled coaxially behind the shaft, on which in the meantime the spiral continues to be formed. The second shaft is coupled to the back end of the first shaft, upstream of the spiral formation zone, while a tract of the first shaft is still passing through the zone. The second shaft is destined to pass through the above-mentioned zone immediately after the first shaft, practically continuously and without interrupting the movement of the shafts and the formation of the spiral. It is possible, if so preferred, to stop the movement during the passage from the first to the second shaft. The second shaft is coupled in the following way. The chuck 7b of the first truck 7a (upstream of the spiral forming zone) is disengaged from the first shaft. The left end of the first shaft is therefore free as it is no longer engaged in the first chuck 7b. The first shaft is however supported during this phase by the second movement means 10 and possibly by other supports (in this case the mobile support 7c). The truck 7a is subsequently commanded to retreat quickly, distancing from the rollers 3a, 3b in order to reach a retracted position in which a second shaft can be fixed to the chuck 7b. Before leaving the spiral forming zone, the truck 7a is quickly advanced in order that the free right end of the second shaft in can be inserted in the free left end of the first shaft, after insertion of a joint constituted by the short grooved shaft 11 into the end collars A' and B'. Thus a continuity is created between the two shafts, so that when the first shaft leaves the spiral forming zone, a second shaft, commanded to rotate and translate, immediately enters the empty central zone of the spiral. The result is that there is at all times a longitudinal element in the spiral formation zone, and precisely in the internal space created by the spiral, which advances and rotates continuously and in synchrony with the formation of the spiral, guaranteeing process continuity. Very soon after the left end of the first shaft has cleared the cutting device 9, the cutting device 9 is commanded to cut the spiral transversally. The spiral is cut at a tract of the second shaft which is close to the joining zone between the two shafts. The cut is made without involving the abovementioned tract of the second shaft, as it interests only the spiral 4, which it cuts to length with respect to the first shaft. After the cut, the second truck 10a, bearing the chuck 10b gripping the first shaft, is moved swiftly rightwards, distancing the first shaft from the second shaft and also removing it from the spiral forming zone. The first shaft, about which a length of spiral is wound and fixed, is thus drawn by the truck 10a and the chuck 10b into a position which facilitates the detachment of the shaft from the chuck 10b and the subsequent distancing of the machine. The separation and axial distancing of the first shaft from the second can be obtained thanks to the fact that the length of spiral which is solid to the first shaft has been detached, by means of the previous cut, from the remaining tract of spiral, which continues to develop about the second shaft. Firstly the above-mentioned separation between the two shafts is made possible by the fact that the grooved coupling between the shafts permits axial uncoupling. During the phase of separation and distancing of the two shafts, as in every other operation stage, the formation of the spiral can proceed with no interruption and at a more-or-less constant speed, though it can also be performed intermittently. The products manufactured using the above-described machine, i.e. a series of support shafts each externally bearing a tract of spiral, are to be considered finished products (or very nearly so), ready for use as conveyor screws in archimedes screw systems. In the next operative stage, after the shaft has been detached from the chuck 10b, the truck 10a is translated leftwards, opposite to direction G, nearing the spiral formation zone, in order that the chuck 10b can engage the right end of the second shaft, i.e. the shaft passing through the spiral forming zone and undergoing the spiral-forming operation. When the right end of the workpiece shaft has been gripped by the chuck 10b downstream of the spiral forming device 3, the other chuck 7b, situated upstream, is commanded to disengage from the left end of the shaft; the truck 7a is retreated to allow the chuck 7b to grip a third shaft; the other, free end of the third shaft is connected up, by means of the grooved coupling, to the free left end of the second shaft, which in the meantime continues to advance into the spiral forming zone. The connection between the two shafts is obtained as previously described. The operation process described up to this point is repeated cyclically for a desired number of shafts, resulting in a continuous process for manufacturing conveyor screws, with continuous and uninterrupted infeeding of the band used for making the spiral. The process is quick to evolve and requires a relatively small space in the direction in which the band is actually turned to make the spiral. In the described process, insertion of the shafts into the spiral forming zone, coaxially one after another, is preferably done with no interruptions and harmoniously with the creation of the spirals. This prevents any subsequent laborious spiral winding operations on the shaft. In the above-described preferred example, the spiral forming device is fixed and the support shafts are mobile with respect thereto. It would be possible, however, to set up other systems, for example systems having a mobile spiral forming device, which would obtain a relative axial movement between the shafts and the spiral under formation. The welding and cutting of the spiral can be automatically done, as in the illustrated example, or can be done manually or semi-automatically. The spiral forming device 3 can be advantageously provided with a plastic deformation parameter regulation system, and in particular could be equipped with one or more of the following devices: a forming roller pressure regulator, also for regulating the inclination of the rollers themselves; a flat band infeed angle variator situated internally of the rollers; and an infeed speed regulation device of the belt into the spiral forming device. Preferably also included is an advancement speed regulation device in the direction of arrow G, to regulate the speed of the shafts as they are moved into the spiral forming zone. A shaft rotation speed regulator is also advisable. By regulating all of the above-mentioned parameters, spirals having variable steps can be extremely precisely manufactured. Furthermore, the regulation of the working parameters guarantees (even before beginning the welding operation of the spiral to the shaft) a perfect coupling of the internal edge of the spiral with the peripheral surface of the shaft. The spiral can in fact be squeezed on to the shaft so tightly that the two elements can be considered solidly reciprocally constrained even before welding. In the above-described conveyor spiral manufacturing process, the first shaft inserted into the spiral forming zone could be a decoy, only used to facilitate the setting up of the spiral forming operation and subsequent infeeding of the actual workpiece shafts.

Claims: A process for continuous formation of conveyor screws for archimedes screw systems, wherein each conveyor screw comprises an internal support shaft at a periphery of which a spiral is wound, comprising infeeding a band (2) continuously into a spiral forming zone in which the band (2) is made to wind into a spiral shape; characterised in that it comprises: infeeding in succession a plurality of support shafts (A, B) to the spiral forming zone, in an advancement direction which coincides with an axis of a formed spiral, so that formation of the spiral occurs about an advancing shaft of the continuously advancing plurality of support shafts (A, B), which advancing shaft is positioned coaxially to the axis of the spiral; fixing the spiral on each of said plurality of support shafts, and cutting the spiral to form a length of spiral which is fixed on the shaft of the plurality of support shafts; whereby each support shaft, while advancing centrally of the spiral and coaxially thereto, is made to rotate about its own axis and is commanded to advance and rotate in synchrony with the spiral forming operation; the process comprising an operative cycle as follows in sequence: feeding two support shafts (A, B), one behind another, into the spiral forming zone, while the spiral (4) is being formed about a preceding of the two shafts (A, B); a front end of the preceding shaft (B) and a back end of a following shaft (A) being constrained respectively to a second movement device (10) and to a first movement device (7); fixing the spiral to the preceding shaft (B); cutting the spiral, during advancement of the shaft, after the front end of the following shaft (A) has entered the spiral forming zone, in order to form a length of spiral associated to the preceding shaft (B); rapidly distancing the preceding shaft (B) from the following shaft (A) in an axial direction by means of the second movement device (10); freeing the preceding shaft (B) bearing a length of spiral from the second movement device (10), while the following shaft (A) continues to advance into the spiral forming zone; rapidly nearing the second movement device (10) into the spiral forming zone and constraining the front end of the following shaft (A) thereto; releasing the back end of the following shaft (A) from the first movement device (7) and rapidly distancing the first movement device (7) in an axial direction away from the back end; constraining a back end of a further shaft to the first movement device (7) and rapidly connecting a free front end of the further shaft to the posterior end of the shaft which is at that time continuously advancing through the spiral forming zone. The process of claim 1, characterised in that a back end of the support shaft of the plurality of support shafts, while said support shaft is advancing along a centre of the spiral being formed, is constrained to a front end of an immediately following support shaft in such a way as to make the support shafts solid in rotation, said constraint being disconnectable by means of a simple distancing of the back and of one shaft from the front end of the other shaft. The process of claim 1 or 2, characterised in that the support shafts (A, B) are joined coaxially to each other by means of a joint (11) couplable to two ends of the support shafts (A, B), so as to render the shafts solid in rotation but disengageable from each other by simple reciprocal pulling in an axial direction. The process of claim 3, characterised in that each support shaft (A, B) comprises at opposite ends thereof two collars (A', B'); each end collar is connected to an end collar of another shaft by inserting said joint (11) into the end collars (A', B'). The process of claim 4, characterised in that the joint (11) is an externally grooved short shaft. A machine for continuous formation of conveyor screws for archimedes screw systems, wherein each conveyor screw comprises an internal support shaft at a periphery of which a spiral is wound, comprising means (5,6) for continuously feeding a band to a device (3) for spiral forming; characterised in that it comprises: a first movement device (7) for introducing a support shaft into a central space of a spiral formed from the band by the device (3) for spiral forming, with a shaft advancement direction which is coaxial to the spiral, said first movement device (3) being able to rotate the shaft about an axis thereof; means (8) for fixing the spiral to a support shaft introduced into the central space of the spiral; a cutting device (9) predisposed to cut the spiral into lengths, each of which lengths has been previously fixed to a support shaft; a second movement device (10), situated, with respect to the device (3) for spiral forming, on an opposite side to the first movement device (7); the second movement device (10) being able to receive from the first movement device (7) a support shaft, which it can axially distance from the spiral forming device (3) after a suitable length of spiral has been cut; the second movement device (10) comprising means for rotating the support shaft. The machine of claim 6, characterised in that the first movement device (7) and the second movement device (10) each comprise an axially-mobile support (7a, 10a) on which a gripping organ is predisposed for gripping and rotating a shaft.

Inventors: MARCHESINI VAINER, MARCHESINI, VAINER
Applicants: WAM SPA, WAM S.P.A.
Application year: 2000
Main classification: B21D11
IPC codes: B21C37