A method for realizing an archimedes screw spiral

Abstract: The method for realizing the screw spiral of the invention comprises the phases of: preparing a die (10) suitable for casting plastic materials, comprising a tubular core (11) provided with a central cavity (1) and having an internal surface (2) and exhibiting a channel (3) extending spirally and coaxially to the core (11), wherein the central cavity (1) and the channel (3) in combination give rise to a moulding cavity (4) of said die (10); insertion in the central cavity (1) of the core (11) of a metal stalk (6) twisted about itself in such a way as to obtain a spiral shape therefrom spiralling in a direction which is opposite to a direction of the spiral of the channel (3) and held in a coaxial position to said core (11); filling of the moulding cavity (4) with a molten plastic material in order to obtain after solidification thereof a screw (5) containing the stalk (6) embedded in a centre thereof; extraction of said screw (5) from said moulding cavity (4).

Description: In the field of Archimedes screw spiral manufacture, the prior art teaches the lengthwise deformation of a rectangular metal sheet so that it assumes a spiral shape, and thereafter a welding of a longitudinal edge of the resulting spiral to a cylindrical shaft. Generally the surface layer of the spiral is subsequently treated to improve its mechanical properties. This process is laborious and expensive; further, it is applicable only with deformable and weldable materials. GB-A-2 065 817, which discloses the features of the preamble of claim 1, relates to a screw and screwdriver combination in which the screw is formed of a plastic mouldable material about a rigid core member. The main aim of the present invention is to make available a method for realizing a spiral of an Archimedes screw which obviates the above-mentioned limits and drawbacks inherent in the prior art. Some advantages of the invention are represented. by the fact that it can be used to produce Archimedes screw spirals in plastic materials, preferable polyeurethane; it permits production of constant-step and variable-step spirals; it provides spirals having good mechanical properties, which are fluent and give a good seal; and it requires the use of simple and economical means for construction. These aims and advantages and others besides are all attained by the method of the invention, as it is characterized in the claims that follow. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows, of an embodiment of the invention, illustrated in the form of a non-limiting example in the accompanying drawings, in which: figure 1 is a partially-sectioned lateral view of a die used in a first embodiment of the method; figure 2 is a schematic representation of an operative phase of the first embodiment of the method; figure 3 is a schematic lateral view of a die which can be used in a second embodiment of the invention, with some parts removed better to evidence others; figure 4 shows an operative phase of a third embodiment of the method. With reference to the figures of the drawings 1 and 2, 10 denotes in its entirety a die for casting plastic materials, comprising a tubular core 11 which in the example is made in two parts, that is an external part 12 and an internal part 15, both tubular in shape, one being insertable into the other, wherein the internal surface 13 of the external part 12 is coupled with the external surface 14 of the internal part 15. 1 denotes a central cavity afforded in the internal surface 2 of the internal part 15 of the core 11. A through-channel 3 is realized on the walls of the internal part 15, which channel 3 extends spirally coaxially to the core 11. The channel 3 is spiral-shaped with constant step. The central cavity 1 and the channel 3 together give rise to a moulding cavity 4 of the die 10. 6 denotes a metal stalk 6, coaxial to the core 11 and preferably constituted by a flat twisted bar presenting a helical surface. The stalk 6 is arranged centrally of the central cavity 1 such that it presents its helical surface twisting in an opposite direction to that of the spiral of the channel 3. Further provided are means, of known type and not illustrated, for keeping the stalk 6 in position with respect to the core 11, immobilizing the stalk 6 in the position of figure 1, where it is distant from the internal surface 2 describing the central cavity 1. In figure 2, 5 denotes an Archimedes screw made using the method. The Archimedes screw 5 comprises a central support shaft 51 made of plastic, and a spiral surface 50 made in a single piece with the central support shaft 51, which spiral surface 50 winds about the central support shaft 51. The Archimedes screw 5 further comprises, enclosed in the material forming the central support shaft 51, the stalk 6, constituted by a flat twisted plate presenting a spiral surface with screw direction opposite to that of the spiral surface 50. In figure 2, 16 denotes the unscrewing direction of the Archimedes screw 5 by means of which said screw 5 is removed from the die 10. With reference to figure 3, 20 denotes a die, suitable for casting plastic materials, which comprises a tubular core 21 provided with an internal surface 2 describing a central cavity 1. The die of figure 3 differs from that of figures 1 and 2 in that the core 21 is made in a single piece and the spiral channel 3 is made blind on the internal surface 2 of the core 21. Apart from this, the elements relative to the die 20 are practically the same as those relating to the die 10. With reference to figure 4, 30 denotes a die for casting plastic materials, comprising a tubular core 31, which internal surface (not shown in figure 4) describes an internal cavity. This internal surface exhibits a helical channel, not illustrated, shaped and arranged as those of the previous embodiments. Differently to the previous embodiments, however, the core 31 of figure 4 is made in two pieces 32 and 33, coupled and separable along a median and longitudinal separation plane 34 by means of a reciprocal distancing movement. Also, the cast piece is constituted by a variable-step Archimedes screw 5. According to the invention, a method for realizing the spirals of Archimedes screws comprises the phases of: i) preparing one of the above-described dies 10, 20 or 30; ii) inserting the stalk 6 in the central cavity 1 of the relative core 11, 21, 31, and stablilizing same in a predetermined position; iii) filling the moulding cavity 4 with a molten plastic material, preferably polyeurethane, in order to obtain, after solidification, a piece in which the stalk 6 is embedded; iv) extracting the screw from the moulding cavity 4. The stalk 6 is anchored to the relative die so that it will not be displaced by effect of the hydrostatic thrust of the molten plastic during the casting of phase iii) above. In the examples of figures 2 and 3, where the helical step of the Archimedes screw (corresponding to the channel 3 step) is constant, the extraction of the cast screw is achieved by a reciprocal helical displacing between the screw and the die 1, 20; in other words, the screw is unscrewed in the direction indicated by arrow 16. In the embodiment of figure 4, where the channel 3 step is variable, the extraction of the cast screw is achieved by reciprocal distancing of the two parts 32, 33 of the die 30 in a normal direction to the separation plane 34. The presence of the stalk 6 guarantees a degree of rigidity of the Archimedes screw 5. Further, the special conformation and arrangement of the stalk 6, with the spiral of the metal plate winding in opposite direction to that of the spiral surface 50 of the helix, further improves the mechanical properties thereof, which also prevents the stalk 6 from disengaging from the body of the spiral.

Claims: A method for realizing a screw spiral, comprising the following phases: preparation of a die (10, 20) suitable for casting plastic materials, which die (10, 20) comprises a tubular core (11, 21) exhibiting a central cavity (1) and having an internal surface (2) describing said central cavity (1) and exhibiting a channel (3) extending spirally and coaxially to said core (11, 21), said channel (3) exhibiting a constant-step spiral shape, wherein said central cavity (1) and said channel (3) in combination give rise to a moulding cavity (4) of said die (10, 20); insertion in said central cavity (1) of said core (11, 21) of a metal stalk (6) held in a coaxial position to said core (11, 21); filling of said moulding cavity (4) with a molten plastic material in order to obtain after solidification thereof a screw spiral (5) containing embedded in a centre thereof said stalk (6); extraction of said screw spiral (5) from said moulding cavity (4); characterized in that: the screw spiral (5) is the spiral of an Archimedes screw; said phase of extraction of said screw spiral (5) is achieved by performing a reciprocal unscrewing of said screw spiral (5) and said die (10, 20). A method for realizing a screw spiral, comprising the following phases: preparation of a die (30) suitable for casting plastic materials, which die (30) comprises a tubular core (31) exhibiting a central cavity (1) and having an internal surface (2) describing said central cavity (1) and exhibiting a channel (3) extending spirally and coaxially to said core (31), wherein said central cavity (1) and said channel (3) in combination give rise to a moulding cavity (4) of said die (30); insertion in acid central cavity (1) of said core (31) of a metal stalk (6) held in a coaxial position to said core (31); filling of said moulding cavity (4) with a molten plastic material in order to obtain after solidification thereof a screw spiral (5) containing embedded in a centre thereof said stalk (6); extraction of said screw spiral (5) from said moulding cavity (4); characterized in that: the screw spiral (5) is the spiral of an Archimedes screw; the channel (3) step is variable; said die (30) is made in two parts (32, 33), reciprocally coupled and separable at a median and longitudinal separation plane (34), and in that said phase of extraction of said screw spiral (5) is achieved by reciprocally distancing said two parts (32, 33) of said die (30). A method for realizing a screw spiral, in particular as in claim 1, comprising the following phases: preparation of a die (10) suitable for casting plastic materials, which die (10) comprises a tubular core (11) exhibiting a central cavity (1) and having an internal surface (2) describing said central cavity (1) and exhibiting a channel (3) extending spirally and coaxially to said core (11), wherein said central cavity (1) and said channel (3) in combination give rise to a moulding cavity (4) of said die (10); insertion in said central cavity (1) of said core (11) of a metal stalk (6) held in a coaxial position to said core (11); filling of said moulding cavity (4) with a molten plastic material in order to obtain after solidification thereof a screw spiral (5) containing embedded in a centre thereof said stalk (6); extraction of said screw spiral (5) from said moulding cavity (4); characterized in that: the screw spiral (5) is the spiral of an Archimedes screw; constituted by an external part (12) and an internal part (15), both said external part (12) and said internal part (15) being tubular; said internal part (15) being insertable into said external part (12); said channel (3) being realized throughout on walls of said internal part (15). A spiral of a screw, comprising: a central support shaft (51), made of a plastic material; a spiral surface (50), made in a single piece with said central support shaft (51), which winds coaxially about said central support shaft (51); a stalk (6), embedded in a centre of said plastic material forming said central support shaft (51); characterized in that the screw spiral (5) is the spiral of an Archimedes screw and the stalk (6) presents a helical surface. A spiral as in claim 4, characterized in that the helical surface of the stalk (6) winds in a direction which is opposite to a winding direction of said spiral surface (50). A spiral as in claim 4 or 5, characterized in that said stalk (6) comprises a flat plate twisted about itself in such a way as to obtain a spiral shape thereof.

Inventors: VINCENZI LAMBERTO, VINCENZI, LAMBERTO
Applicants: IDR HOLDING S A, IDR HOLDING S.A.
Application year: 1996
Main classification: B29D1
IPC codes: B29D1, B29C70