Screw conveyor to convey powdery material, in particular cement or the like

Abstract

A screw conveyor to convey powdery material, in particular cement. The screw conveyor comprises: a transfer screw; and a trough containing the transfer screw; the trough being provided with an inlet section and an outlet section of the powdery material. The screw conveyor is characterized in that the screw comprises: at least a first screw portion having a first law of continuous variation of the pitches of the screw, which can be graphically represented by means of a first function having in at least one stretch a first derivative other than zero; and at least a second screw portion having a second law of continuous variation of the pitches of the screw, which can be graphically represented by a second function having in at least one stretch a first derivative other than zero. The first law of continuous variation of the pitches is different from the second law of continuous variation of the pitches.

Claims

1. A screw conveyor (100) to convey a powdery material, in particular cement; said screw conveyor (100) comprising: a transfer screw (70); and a trough (80) containing said transfer screw (70); said trough (80) being provided with an inlet section (81) and an outlet section (82) for the powdery material; characterized in that said transfer screw (70) comprises: at least a first screw portion ((TSEC); (ASEC)) having a first law of continuous variation of the pitches (PTC) of the transfer screw (70), which can be graphically represented by means of a first function having in at least one stretch a first derivative other than zero; and at least a second screw portion ((LSEC); (ASEC)) having a second law of continuous variation of the pitches (PTC) of the transfer screw (70), which can be graphically represented by means of a second function having in at least one stretch a first derivative other than zero; said first law of continuous variation of the pitches (PTC) being different from said second law of continuous variation of the pitches (PTC); at least one transfer screw portion (TSEC) having a length (L2), which extends between an inlet section (81) and an intermediate section (83) of said trough (80); the transfer screw portion (TSEC) having a continuously increasing pitch, point by point; and at least one accelerating and launching screw portion (LSEC) having a length (L3), which extends from the intermediate section (83) to an outlet section (82) of said trough (80); the accelerating and launching screw portion (LSEC) having a continuously increasing pitch; the laws of variation of the pitches of the points belonging to the screw portions (TSEC) and (LSEC) being different from one another; characterized in that the law of variation of the pitch, point by point, of said at least one transfer screw portion (TSEC) can be represented by a first straight line having a first sloping angle (1), and in that the law of variation of the pitch, point by point, of said at least one accelerating and launching screw portion (LSEC) can be represented by a second straight line having a second sloping angle (2) different from said first sloping angle (1).

2. Screw conveyor (100), according to claim 1, characterized in that said first law of variation of the screw pitches (PTC) and said second law of variation of the screw pitches (PTC) are both different linear laws.

3. Screw conveyor (100), according to claim 1, characterized in that said first law of variation of the screw pitches (PTC) and said second law of variation of the screw pitches (PTC) are both different curved laws.

4. Screw conveyor (100), according to claim 1, characterized in that said first law of variation of the screw pitches (PTC) is a linear law and said second law of variation of the screw pitches (PTC) is a curved law.

5. Screw conveyor (100), according to claim 1, characterized in that (2)>(1).

6. Screw conveyor (100), according to claim 1, characterized in that at least one of the laws of variation of the pitch, point by point, of said at least one transfer screw portion (TSEC) or of said at least one accelerating and launching screw portion (LSEC) can be represented by a curve (CV).

7. Screw conveyor (100), according to claim 6, characterized in that the variation of the pitch, point by point, of said at least one transfer screw portion (TSEC) or of said at least one accelerating and launching screw portion (LSEC) increases with the square of the distance of the point of the screw from a starting point (P0).

8. Screw conveyor (100), according to claim 1, characterized in that two adjacent screw portions ((TSEC), (LSEC); (TSEC), (ASEC); (ASEC), (LSEC)) are continuously connected without cusps in the joining areas.

9. A screw conveyor (100) to convey a powdery material, in particular cement; said screw conveyor (100) comprising: a transfer screw (70); and a trough (80) containing said transfer screw (70); said trough (80) being provided with an inlet section (81) and an outlet section (82) for the powdery material; characterized in that said transfer screw (70) comprises: at least a first screw portion ((TSEC); (ASEC)) having a first law of continuous variation of the pitches (PTC) of the transfer screw (70), which can be graphically represented by means of a first function having in at least one stretch a first derivative other than zero; and at least a second screw portion ((LSEC); (ASEC)) having a second law of continuous variation of the pitches (PTC) of the transfer screw (70), which can be graphically represented by means of a second function having in at least one stretch a first derivative other than zero; said first law of continuous variation of the pitches (PTC) being different from said second law of continuous variation of the pitches (PTC); at least one transfer screw portion (TSEC) having a length (L2), which extends between an inlet section (81) and an intermediate section (83) of said trough (80); the transfer screw portion (TSEC) having a continuously increasing pitch, point by point; and at least one accelerating and launching screw portion (LSEC) having a length (L3), which extends from the intermediate section (83) to an outlet section (82) of said trough (80); the accelerating and launching screw portion (LSEC) having a continuously increasing pitch; the laws of variation of the pitches of the points belonging to the screw portions (TSEC) and (LSEC) being different from one another; characterized in that at least one anti-siphon screw portion (ASEC) having a length (L4) is provided between said at least one transfer screw portion (TSEC) and said at least one accelerating and launching screw portion (LSEC).

10. Screw conveyor (100), according to claim 9, characterized in that the law of variation of the pitch, point by point, of said at least one transfer screw portion (TSEC) can be represented by a first straight line having a first sloping angle (1), and in that the law of variation of the pitch, point by point, of said at least one accelerating and launching screw portion (LSEC) can be represented by a second straight line having a second sloping angle (2) different from said first sloping angle (1) and characterized in that the law of variation of the pitch, point by point, of said at least one anti-siphon screw portion (ASEC) can be represented by a third straight line having a third sloping angle (3) with an opposite direction relative to said two sloping angles (1) and (2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present invention, some embodiments will be now described, three of them referring to the prior art and the other two referring to the present invention, in which:

(2) FIG. 1 (with the relative graph of FIG. 1a) schematically shows a longitudinal section of a screw portion of a screw having a constant pitch (prior art);

(3) FIG. 2 (with the relative graph of FIG. 2a) schematically shows a longitudinal section of a screw portion having a pitch varying according to a step function (prior art);

(4) FIG. 3 (with the relative graph of FIG. 3a) schematically shows a longitudinal section of a screw portion having a pitch continually varying according to an sloping straight line or a curve (prior art);

(5) FIG. 4 (with the relative graph of FIG. 4a) schematically shows a longitudinal section of a first embodiment of a screw conveyor made according to the teaching of the present invention; and

(6) FIG. 5 (with the relative graph of FIG. 5a) schematically shows a longitudinal section of a second embodiment of a screw conveyor made according to the teaching of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

(7) Incidentally, the axial distance (along a longitudinal symmetry axis of the screw) separating any point of the crest from its homologue on the next crest will here be defined as the pitch of a point of the screw crest (PTC). Furthermore, a screw portion (SEC) indicates any portion of a screw possibly wound around a central tube with the same law of variation of the pitches of the points; said law of variation of the pitches of the points being representable by a function having at any point a first derivative other than zero.

(8) Moreover, in this context, the term stretch indicates a span within the aforementioned screw portion (SEC).

(9) Furthermore, as already known from the Fermat's theorem on stationary points, in any function, the first derivative is equal to zero when the tangent is horizontal; i.e. at maximum points, at minimum points or at inflection points with a horizontal tangent.

(10) In the first example referring to the prior art, shown in FIG. 1 and in the corresponding graph of FIG. 1a, any point (PNT1) of a screw 70 has a pitch (PTC1) equal to the pitch of another point (PNT2) close to it (where (L) is the generic distance of any point of the screw 70 from a starting point (P0) (point zero)).

(11) In more detail, the graph of FIG. 1a graphically shows the law of variation of the pitch (in this case constant) of the screw by taking the longitudinal symmetry axis (X) as the axis of the abscissas and by taking the axis of the values of the pitches as the axis of the ordinates.

(12) Therefore, in this case, the law of variation of the pitches of the points is represented by a straight line on the axis of the ordinates, parallel to the axis of the abscissas (i.e. the longitudinal symmetry axis (X) of the screw 70), the straight line indicating in the present case the constancy of the value of the pitch (PTC) at any point (PNT1) (PNT2) of the screw 70.

(13) If, on the other hand (FIG. 2 and relative graph of FIG. 2aprior art), there is a discrete passage from a first screw portion (SEC1) of the screw 70 to a second screw portion (SEC2) (always of the screw 70), this means that there is a passage from a pitch (PTC1) of all the points belonging to the first screw portion (SEC1) to a pitch (PTC2) of all the points belonging to the second screw portion (SEC2); and this is the situation actually described and shown in EP-A2-0 816 938 (MITA INDUSTRIAL CO. LTD).

(14) Thus, as shown in FIG. 2, always referring to a prior art case, there is a first law of variation of the pitches of the points represented by a first straight line, parallel to the axis of the abscissas (graph of FIG. 2a), indicating the constancy of the value of the pitch (PTC1) at any point (PNT1), (PNT2) of the first screw portion (SEC1) of the screw 70.

(15) Moreover, always in FIG. 2 (prior art), there is a second law of variation of the pitches of the points represented by a second straight line, parallel to the axis of the abscissas (graph of FIG. 2a), indicating the constancy of the value of the pitch (PTC2) at any point (PNT1), (PNT2) of the second screw portion (SEC2) of the screw 70.

(16) Incidentally, also the graph of FIG. 2a graphically represents the law of variation of the screw pitches by taking the longitudinal symmetry axis (X) of the screw as the axis of the abscissas and the axis of the values of the pitches as the axis of the ordinates.

(17) FIG. 3 and the corresponding graph of FIG. 3a, referring to a third case always belonging to the prior art, show a situation in which a screw portion (SEC3) has a same law of variation of the pitches (PTC) of the single points (PNTs) forming the screw 70.

(18) Also the graph of FIG. 3a graphically represents the law of variation of the screw pitches by taking the longitudinal symmetry axis (X) as the axis of the abscissas and the axis of the values of the pitches as the axis of the ordinates.

(19) As already known, speed variation (acceleration) can be proportional to time (uniformly accelerated motion) or can be bound to the square of time (see below) or to other types of functions.

(20) If therefore, as shown in FIG. 3 and in the graph of FIG. 3a, the central tube 50 is subjected to an acceleration along the direction of advancement, any first point (PNT1) of the screw portion (SEC3) will have a pitch (PTC1) other (in this case smaller) than the pitch (PTC2) of a second point (PNT2) (adjacent to the first point (PNT1)) belonging to the same screw portion (SEC3).

(21) In other words, the two points (PNT1) and (PNT2) belonging to the same screw portion (SEC3) only share the law of speed variation (acceleration) of the central tube 50 when the screw 70 winds around it in the building phase. This results in a pitch difference, point by point, in the same screw portion (SEC3).

(22) Obviously, when normally using the screw for conveying powdery material or grains, all points belonging to the crest of a given screw portion have the same angular speed and the same tangential speed since they have the same distance from the axis (X).

(23) Therefore, a so-called structural aspect of the screw, as described above, must be distinguished from a functional aspect of the screw when it is actually mounted in a screw conveyor.

(24) In short, FIG. 3a shows a straight line (LN) when the variation of the pitch for each point belonging to the same screw portion (SEC3) is constant, or a curved line (CV) when the variation of the pitch for each point belonging to the same screw portion (SEC3) increases (or decreases), e.g. with the square of the distance between the screw point and a starting point (P0) (point zero).

(25) FIG. 4 indicates with the reference number 100 as a whole a first embodiment of a screw conveyor to convey a powdery material made according to the teaching of the present invention.

(26) The screw conveyor 100 comprises a spiral blade 90 of a screw 70 wound around the central tube 50 and contained in an outer trough 80 provided with an inlet section 81 and an outlet section 82 of the fluidised powdery material; these sections are known with respect to the state of the art.

(27) Incidentally, exactly at a loading mouth (HP) of the screw conveyor 100, there is a screw portion (ESEC) for the extraction of the powdery material, but it will not be analysed in detail in the present description because it is of a known type.

(28) In use, the present screw conveyor 100 creates a suction depression.

(29) The inlet section 81 is therefore the first cross section immediately after the hopper unloading mouth (HP).

(30) The screw 70 is rotated by an electric motor (MT).

(31) Constructively, the screw 70 made according to the teaching of the present invention is obtained by means of a rototranslating motion of a central tube 50 (around and/or along the longitudinal symmetry axis (X) of the screw 70) and winding around it a spiral blade 90.

(32) In this case, the longitudinal symmetry axis (X) of the screw 70 is the same as the longitudinal symmetry axis of the central tube 50.

(33) Moreover, in the present invention, the central tube 50 has a certain law of acceleration along the axis (X).

(34) In the present invention, the laws of acceleration of the central tube 50 vary by passing from a screw portion (SEC) to the other, while always and in any case using a same spiral blade 90 for the same screw 70.

(35) The first embodiment shown in FIGS. 4 and 4a, having a total length of the screw conveyor (L1) (from the inlet section 81 to the outlet section 82), shows the following two different screw portions 70 (other than the aforementioned extraction screw portion (ESEC), whose width substantially coincides with the width of the loading mouth (HP)):

(36) a first transfer screw portion (TSEC) having a length (L2) and extending between the inlet section 81 and an intermediate section 83; the first transfer screw portion (TSEC) having, in a preferred embodiment, a continuously increasing pitch (according to a first law of variation), thus having a first derivative other than zero; and

(37) a second accelerating and launching screw portion (LSEC) having a length (L3) and extending, in turn, from the intermediate section 83 to the outlet section 82; the second accelerating and launching screw portion (LSEC) having, in a preferred embodiment, a continuously varying pitch (according to a first law of variation), thus having a first derivative other than zero.

(38) Generally, the laws of variations of the pitches of the points belonging to the portions (TSEC) and (LSEC) are different.

(39) Moreover, the two portions (TSEC) and (LSEC) of the same screw 70 are advantageously made by using the same preferably metal spiral blade 90 wound around the same central tube 50.

(40) However, the screw 70 according to the invention can be also manufactured through a moulding process or the like. In fact, as shown in FIG. 4a, the progress of the pitches based on the distance of the point of the screw crest with respect to a starting point (P0) (point zero) can be represented by a broken line with two sloping segments (RT1) and (RT2); in which the sloping segment (RT1) corresponds to the respective screw portion (TSEC), whereas the sloping segment (RT2) corresponds to the respective screw portion (LSEC), the one being the continuation of the other.

(41) Also the graph of FIG. 4a graphically shows the law of variation of the screw pitches by taking the longitudinal symmetry axis (X) as the axis of the abscissas and the axis of the values of the pitches as the axis of the ordinates.

(42) The slope (2) of the sloping segment (RT2) is different from the slope (1) of the sloping segment (RT1).

(43) In this case, the slopes (1), (2) of the segment (RT1) and respectively of the segment (RT2) represent the so-called first derivatives of the two segments (RT1), (RT2) and such slopes (1), (2) are both other than zero.

(44) In particular, advantageously but not necessarily, the slope (2) of the sloping segment (RT2) is greater than the slope (1) of the sloping segment (RT1) (FIG. 4a).

(45) A second embodiment of the present invention shown in FIGS. 5, 5a, wherein the corresponding elements are indicated by the same numbers and symbols of FIGS. 4, 4a, shows the following different three screw portions 70 (other than the aforesaid extraction screw portion (ESEC), whose width substantially coincides with the width of the loading mouth (HP)):

(46) a first portion of a transfer screw (TSEC) having a length (L2), substantially equal to the analogous first portion of FIGS. 4 and 4a;

(47) a second accelerating and launching screw portion (LSEC), having a length (L3), substantially equal to the analogous second portion of FIGS. 4 and 4a; and

(48) a third anti-siphon screw portion (ASEC) having a length (L4); the third anti-siphon screw portion (ASEC) being comprised between the first transfer screw portion (TSEC) and the second accelerating and launching screw portion (LSEC); the third anti-siphon screw portion (ASEC) having a continuously decreasing pitch, point by point, and a decreasingly sloping angle (with a first derivative other than zero).

(49) Also the graph of FIG. 5a graphically shows the law of variation of the screw pitches by taking the longitudinal symmetry axis (X) as the axis of the abscissas and the axis of the values of the pitches as the axis of the ordinates. Moreover, the three portions (TSEC), (LSEC) and (ASEC) of the same screw 70 are made using the same preferably metal spiral blade 90 wound around the same central tube 50.

(50) Thus, in the second embodiment (FIGS. 5, 5a), also providing the anti-siphon screw portion (ASEC) (defined by the intermediate sections 83 and 84) between the first sloping segment (RT1) having a sloping angle (1) (with a first derivative other than zero) and the second sloping segment (RT2) having a sloping angle (2) (with a first derivative other than zero), there is a third sloping segment (RT3) with a third sloping angle (3) (with a first derivative other than zero) and having an opposite direction with respect to the sloping angles (1) and (2). In this case, the slopes (1), (2), (3) of the three segments (RT1), (RT2), (RT3) represent the so-called first derivatives of the three segments (RT1), (RT2) and (RT3) and said slopes (1), (2) and (3) are all other than zero.

(51) In a further non-shown embodiment, the first law of variation of the screw pitches (PTC) is a linear law (corresponding to a function, which can be graphically represented by a sloping segment) whereas the second law of variation of the screw pitches (PTC) is a curved law (corresponding to a function which can be graphically represented by a curve).

(52) Two adjacent portions (TSEC), (ASEC), (LSEC) can be continuously connected without cusps in the joining areas.

(53) This technical solution allows a further improvement of the efficiency of the device also avoiding the turbulence generated by sudden pitch jumps between different screw portions.

(54) The main advantage of the screw conveyor object of the present invention is the fact that, at the same flow rate of powdery material, there is less power consumption (e.g. electric power consumed by the motor (MT)) to rotate the transfer screw.

(55) An additional advantage of the present screw conveyor is the fact that it works more efficiently even when it has a certain slope with respect to the ground. For example, these screw conveyors maintain high yields even with sloping angles relative to the ground greater than 35.