SCREW CONVEYOR TYPE DRYING APPARATUS

Abstract: A screw conveyor type drying apparatus comprises a plurality of hollow drive shafts (9a, 9b) each having a plurality of feed vanes (16) provided thereon along an imaginary helix positioned on the outer peripheral surface of the drive shaft, a driving device (11-15) for driving the drive shafts so that adjacent drive shafts are rotated in mutually opposite directions, the plurality of drive shafts being rotated in mutually opposite directions whereby a material to be dried is conveyed, and a device for feeding heating fluid into the hollow portions of the feed vanes through the hollow portions of the drive shafts, whereby the material coming in contact with the feed vanes during conveyance is heated and dried.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a screw conveyor type drying apparatus used for drying dehydrated sludge discharged, e.g., from sewage or excrement treatment plants or for drying feed or food which is high in water content. Description of the Prior Art Japanese Patent Application Laying-Open No. 131976/1982 discloses an example of a screw conveyor type drying apparatus having the aforesaid use. Therein, as shown in Fig. 16, a casing 100 is provided at one end thereof with a charge port 101 for material to be dried and a discharge port 102 for dried material. Disposed within the casing 100 is a hollow drive shaft 103 rotatably supported by the opposite ends of the casing 100. The drive shaft 103 is formed therearound with a plurality of feed vanes 104 of hollow construction which continuously extended along an imaginary helix positioned on the outer peripheral surface of the drive shaft 103. Further, to dry material, there is provided a mechanism whereby heating fluid 105 is fed into the hollow areas of the feed vanes 104 via the drive shaft 103 and then discharged therefrom. In the drying apparatus described above, a material to be dried which is charged into the casing through the charge port 101 is conveyed to the discharge port 102 as the feed vanes 104 are rotated along with the drive shaft 103, and at the same time the material is heated and dried by the heating fluid 105 fed into the feed vanes. According to the aforesaid drying apparatus, however, since the feed vanes 104 are formed continuously around the periphery of the drive shaft 103, i.e. continuously along the imaginary helix positioned on the outer peripheral surface of the drive shaft 103, there has been a problem that the rate of travel of the material is so high that the material is discharged through the discharge port 102 before it is fully dried. If the rate of travel of the material is reduced, the material cannot be stirred sufficiently. Furthermore, since the material is rotated along with the feed vanes 104, structurally, the stirring efficiency is inherently low; therefore, the material cannot be dried uniformly and the drying efficiency is not sufficiently high. On the other hand, Japanese Patent Application Laying-Open No. 131976/1982 discloses a conveyor type drying apparatus shown in Fig. 17. Therein, a hollow drive shaft 113 is rotatably installed in a casing 110, with a plurality of hollow vanes 114 attached to the outer periphery of the drive shaft 113. As for the positional arrangements of the feed vanes 114, however, sets of four feed vanes 114 are spaced along the length of the drive shaft 113, the four vanes in each set being spaced around the same circumference. Thus, despise the fact that the feed vanes 114 cross the axis of the drive shaft 113, a material to be dried cannot be dried efficiently. Further, since the four feed vanes 114 in each set are spaced around the same circumference, there has been a problem that the stirring efficiency is not high. As a result, there has been a drawback that conveying and drying a material requires a relatively large amount of energy. As a further example, Japanese Utility Model Application No. 193994/1984, as shown in Figs. 18 and 19, discloses a conveyor type drying apparatus using paddles 124 which are sector-shaped in plan view. More particularly, a plurality of pairs of paddles 124 are spaced along the length of a drive shaft 123, the two paddles 124 in each pair being spaced around the same circumference. In this drying apparatus, heating fluid is fed into the paddles 124, whereby a material to be dried which comes in contact with the paddles 124 is dried. As is clear from Fig. 18, the paddles 124 are disposed at right angles to the drive shaft 123. Thus, the paddles 124 themselves do not serve to convey the material; therefore, the material cannot be conveyed efficiently. Thus, there has been a drawback that in conveyance, the casing 130 must be inclined or a relatively large amount of energy must be supplied. SUMMARY OF THE INVENTION Accordingly, an object of the invention is to provide a conveyor type drying apparatus having such a construction that a material to be dried can be dried which being fully stirred without requiring a large amount of energy for conveyance. A conveyor type drying apparatus according to this invention includes a casing having a material charging port and a material discharging port which are spaced a predetermined distance in the direction of the conveyance. Disposed in the casing are a plurality of hollow drive shafts extending in the direction of conveyance. Drive means is provided for driving the plurality of drive shafts so that adjacent drive shafts are rotated in mutually opposite directions. The outer peripheral surface of each drive shaft is provided with feed vanes of hollow construction spaced a predetermined distance from each other and extending along an imaginary helix positioned on the outer peripheral surface. Each feed vane is shaped so that it spreads as it extends from the region where it is provided on the outer peripheral surface of the drive shaft to its front end. Further, means is provided for feeding heating fluid into the hollow portions of the feed vanes through the hollow portions of the aforesaid hollow drive shafts. In this invention, as the hollow drive shafts are rotated, a material to be dried is conveyed by the plurality of feed vanes extending along the imaginary helix positioned on the outer peripheral surface of each drive shaft. Therefore, since, in each space defined by adjacent feed vanes, the material is not conveyed by the feed vanes, the rate of travel of the material, as a whole, is reduced, making it possible for the material to stay longer in the casing, with the result that the material can be fully dried. Further, since adjacent drive shafts are rotated in mutually opposite directions, the feed vanes attached to adjacent drive shafts will convey the material while stirring it. The stirring of the material can be effected to the fullest extent and can be uniformally heated. If each feed vane is constructed to have a predetermined thickness, there is produced the effect of stirring the material by the front lateral end edge of the feed vane, i.e., its lateral end edge positioned forward as viewed in the direction of rotation. Thus, the material can be heated more uniformally. Further, by making gentler the angel at which the feed vanes are attached to the drive shafts, i.e., by reducing the angle which a tangent to the imaginary helix positioned on the outer peripheral surface of each drive shaft forms with respect to the cross-section of the drive shaft, it is possible to reduce the rate of travel of the material and hence to dry the material more fully. Further, by suitably selecting the spacing with which the feed vanes are attached, it is possible to feed back part of the material in the direction opposite to the direction of conveyance and hence to stir the material more fully and reduce the rate of travel of the material. These objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view, partly in section, of a screw conveyor type drying apparatus according to this invention; Fig. 1A is a front view, partly in section, of a modification of the screw conveyor type drying apparatus sown in Fig. 1; Fig. 2 is a plan view, partly in section, of the screw conveyor type drying apparatus shown in Fig. 1; Fig. 3 is a side view, partly in section, of the screw conveyor type drying apparatus; Fig. 4 is a plan view showing a plurality of drive shafts in the Fig. 1 embodiment and feed vanes provided on the drive shafts; Fig. 5 is a perspective view showing a plurality of feed vanes provided longitudinally of a drive shaft; Fig. 6A, 6B and 7 are views for explaining the relationship between the feed vanes provided on adjacent drive shafts, Fig. 6A is a sectional view, taken in the direction of the drive shaft, looking at feed vanes provided on one drive shaft, Fig. 6B is a sectional view, taken in the direction of the drive shaft, looking at feed vanes provided on the other drive shaft, and Fig. 7 is a schematic view showing the relationship between feed vanes provided on adjacent drive shafts; Fig. 8 is a fragmentary side view for explaining the pitch of feed vanes provided on a drive shaft; Fig. 9 is a perspective view showing the relationship between feed vanes provided on adjacent drive shafts; Figs. 10 and 11 are sectional views, taken in the direction of the drive shaft, illustrating the action of feed vanes provided on adjacent drive shafts; Fig. 12 is a perspective view of a modification of a feed vane, wherein the feed vane is constructed so that the lateral end surface is formed as an inclined surface which opens toward the discharge side; Fig. 13 is a sectional view, taken in the direction of the drive shaft, for explaining drain pipes projecting from feed vanes into the hollow portion of the drive shaft; Fig. 14 is a sectional view taken along the line XIV-XIV in Fig. 13; Fig. 15 is a plan view, partly broken away, showing another example of a mechanism for driving a plurality of drive shafts; Fig. 16 is a sectional view of an example of a conventional screw conveyor type drying apparatus; Fig. 17 is a sectional view of another example of a conventional screw conveyor type drying apparatus; and Figs. 18 and 19 are a front sectional view of still another embodiment and a sectional view taken along the line XIX-XIX in Fig. 18, respectively. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figs. 1 through 3 are views which outline a screw conveyor type drying apparatus according to an embodiment of the invention. A casing 2 is mounted on a base 1. The casing 2 is formed on the upper side thereof with a charge port 3 for material to be dried which is disposed adjacent one end of the casing 2 and on the lower side thereof with a discharge port 4 for dried material which is disposed adjacent the other end. The casing 2 is also formed with an air supply port 5 disposed above the discharge port 4 and an exhaust port 6 disposed adjacent the charge port 3. Hot air at 80-100°C is fed into the casing 2 through the air supply port 5 and discharged through the exhaust port 6. A plurality of inspection ports 7 are disposed in the upper region of the casing 2 and spaced along the length thereof. Further, a plurality of peep windows 8 are provided in the upper surface of the casing 2 for inspecting the interior of the casing 2. Further, inside the casing 2, a plurality of baffle plates 2a (shown in phantom lines) suspended from above are spaced in the direction of conveyance, thereby the upper region of the interior of the casing is divided into a plurality of spaces. A heating jacket 2c surrounds the casing 2. Heating fluid 17 to be later described is circulated in the jacket 2c, so that a material to be dried which is charged into the apparatus can be dried by coming in contact with the inner wall of the jacket 2 as well as with feed vanes to be later described. A plurality of, i.e., three, hollow drive shafts 9a, 9b and 9c are disposed parallel inside the casing 2. The opposite ends of each of the drive shafts project beyond the casing 2 and rotatably supported in bearings 10. The drive shafts 9a, 9b and 9c have transmission gears 11, 12 and 13 of the same size coaxially fixed thereto at one of their respective ends. The transmission gears 11 and 13 mesh with the centrally disposed transmission gear 12, whereby the drive shafts 9a and 9c disposed at opposite sides are rotated in the same direction and the central drive shaft 9b is rotated in the direction opposite to that for the other drive shafts 9a and 9c, the three drive shafts being rotated at the same speed. The drive shaft 9a is connected to a driving device 14 serving as a rotative drive source through a chain transmission mechanism 15 serving as a transmission mechanism, whereby the power from the driving device 14 is transmitted to the drive shaft 9a through the chain drive mechanism 15. Thus, the drive shaft 9a is driven for rotation by the driving device 14 and the drive shafts 9b and 9c are rotated by the transmission gears 11, 12 and 13 at the same speed as the drive shaft 9a. In the casing 2, a weir 2b is disposed immediately upstream of the discharge port 4, so that the material must go over the weir 2b before it can be discharged through the discharge port 4. Thus, the material can be fully dried and then discharged through the discharge port 4. The weir 2b may be arranged so that its height can be adjusted. In that case the staying time for the material can be adjusted and hence the degree of drying of the material can be adjusted. As shown in Fig. 4, around each of the drive shafts 9a, 9b and 9c, a number of sectorial feed vanes 16 are spaced a predetermined distance along an imaginary helix positioned on the outer peripheral surface of each of the drive shafts 9a, 9b and 9c. The construction of the plurality of feed vanes fixed on the outer peripheral surface of each of the drive shafts 9a, 9b and 9c will now be described in detail. As shown in Fig. 5, the feed vanes 16 are attached to the periphery of the drive shaft 9a in such a manner that the imaginary helix which is the path described by the attaching portions of the feed vanes 16 is right-handed. Similarly, the imaginary helix which is the path described by the attaching portions of the feed vanes 16 attached to the drive shaft 9c is right-handed. On the other hand, the imaginary helix which is the path described by the attached portions of the feed vanes 16 attached to the outer peripheral surface of the central drive shaft 9b is left-handed. Since the drive shaft 9a and 9c are rotated in the direction opposite to that for the drive shaft 9b, that is, since the drive shafts 9a and 9c are rotated counterclockwise as viewed from the charge side in the direction of the drive shaft while the other drive shaft 9b is rotated clockwise, the attachment of the feed vanes in the manner described above makes it possible to move the material in the direction of forward travel. Thus, if the drive shafts 9a through 9c are rotated in directions opposite to those described above, the feed vanes 16 will be attached so that the imaginary helixes are reversed in winding direction. The feed vanes 16 are attached to each of the drive shafts 9a, 9b and 9c in such a manner that they are paired and the pairs are spaced a predetermined distance from each other along the imaginary helix on the outer peripheral surface of the drive shaft 16. That is, as shown in Fig. 5, on the outer peripheral surface of the drive shaft 5, a pair comprises feed vanes 16′ and 16″ and the tailing end edge of another pair of feed vanes 16‴ and 16″″ at the stage next to the first pair, i.e., the rear end surface 160 of the rear feed vane 16‴ is spaced 3 pitches plus 30° from the leading edge of the preceding pair of feed vanes 16′ and 16″, i.e., the front end surface 161 of the front feed vane 16″. Herein, 1 pitch means the distance traveled the helix as it is rotated through 360° around the outer peripheral surface of the drive shaft 9a. The feed vanes 16′ and 16″ in the pair are each constructed to have a spread with a central angle of about 115° and are attached in position as they are shifted by sectorial spaces 16x and 16y each having a central angle of 65° within 1 pitch. This relationship will now be described with reference to Figs. 6A and 7. Fig. 6A is a sectional view, taken in the direction of the drive shaft, looking at the pair of feed vanes 16′ and 16″, and a curve 9A in Fig. 7 indicates the imaginary helix positioned on the outer peripheral surface of the drive shaft 9a to which the feed vanes 16′ and 16″ are attached; the portions of the curve to which the feed vanes 16′ and 16″ are attached are shown in thick lines. The characters ª, b and c in Fig. 7 correspond to ª, b and c in Fig. 6A and the character d represents the distance a set of feed vanes and the next set of feed vanes. As is clear from Fig. 6A and the curve 9A in Fig. 7, the pair of feed vanes 16′ and 16″ are mounted on the drive shaft 9a as they are shifted by spacings c , c of 65° (corresponding to the spaces 16x and 16y in Fig. 5) within 1 pitch, i.e., within 360°. The next pair of feed vanes which comes after the pair of feed vanes 16′ and 16″ is attached in position as it is shifted by 360° x 3 (3 pitches) + 30°. The spacing between adjacent feed vanes is selected on the following basis. That is, when the central angle of lack of feed vanes is represented by α, the pair of feed vanes, if uniformally arranged, are, of course, disposed with an angular spacing of β = (360° - 2α) / 2. In this case the next pair of feed vanes subsequent to said pair of feed vanes is disposed with a spacing of 3 pitches + about β / 2 from the preceding pair of feed vanes. The reason why adjacent pairs of feed vanes are disposed with such a relatively large spacing is that it is necessary to provide a space therebetween for receiving feed vanes attached to the outer peripheral surface of the adjacent drive shaft. The reasons for providing a shift amounting to a spacing of about β / 2 is as follows. That is, as shown in Fig. 5, when the next pair of feed vanes 16‴ and 16″″ are viewed in the coaxially direction, it is desired that they overlap each other over regions of about 1/2 of the respective spaces 16x and 16y between the feed vanes 16′ and 16″ in the preceding pair, whereby, as is clear from Fig. 5, continuous pairs of feed vanes successively cut into the material to be dried, effectively saving the driving power. Further, in serial pairs of feed vanes, by axially shifting spaces between feed vanes, e.g., spaces indicated by 16x and 16y, part of the material is fed back in the direction opposite to the direction of conveyance as indicated by arrow p in Fig. 5, thereby making it possible to obtain sufficient drying time. The presence of these spaces ensures a smooth action of feed vanes cutting into the material. In the embodiment described above, when the central angle of lack of feed vanes is set at 115° on the basis of the aforesaid reasons for selection, the β is 65°; thus, pairs of feed vanes on the respective drive shafts are shifted from each other by a spacing of 3 pitches + about β, i.e., 3 pitches + about 30°. In addition, as shown in Fig. 8, the feed vanes 16 attached to the drive shaft 9a form a relatively small angle with the direction which is at right angles to the axis of the drive shaft. That is, each feed vane 16 is attached so that the angle which a tangent to the aforesaid imaginary helix forms with a cross-section of the drive shaft is small, thereby making it possible to reduce the rate of conveyance of material to be dried and hence to provide sufficient drying time. Further, in this embodiment, the thickness of the feed vanes 16 is approximately equal to the amount e traveled per revolution of the aforesaid helix. However, the thickness of the feed vanes may differ from e . The relationship between feed vanes attached to the drive shafts 9a...9c will now be described. As shown in FIg. 9, between adjacent ones of the drive shafts 9a...9c, feed vanes attached to their respective drive shafts are at symmetrical positions when viewed in the direction of the drive shaft from the middle between adjacent drive shafts. Further, the central drive shaft 9b is supported at a position which is somewhat deviated from the drive shafts 9a and 9c on opposite sides toward the discharge port 4 of the casing 2, so that the feed vanes 16 in the pairs on the drive shaft 9a are fitted, in staggered relationship, between the feed vanes 16 in pairs on the drive shafts 9a and 9c, with overlap portions B (see also Fig. 4) being formed between the feed vanes 16 on the central drive shaft 9b and the feed vanes on the drive shafts 9a and 9b on opposite sides. By comparing Fig. 6B showing feed vanes 16′ and 16″ attached to the drive shaft 9b in the same manner as in Fig. 6A and the curve 9B (Fig. 7) showing the imaginary helix on the drive shaft 9b with the curve 9A showing the imaginary helix on the drive shaft 9a, the relationship between feed vanes on adjacent drive shafts can be better understood. That is, fitted between feed vanes in each pair attached along the imaginary helix 9A on the drive shaft 9a are feed vanes in each pair on the adjacent drive shaft 9b. Heating fluid 17, such as steam, is fed into the drive shafts 9a, 9b and 9c at one of their respective ends adjacent the charge port 3. As shown in Figs. 13 and 14, drain pipes 21 project from the hollow portions of the feed vanes into the interior of the drive shaft 9a. Thus, heating fluid 17 is fed into the feed vanes 16 and is condensed in said feed vanes 16, while the condensate is discharged into the interior of the drive shaft 9a through the drain pipes 21. The purpose of use of the projecting drain pipes 21 is to prevent heating fluid 17 which has condensed in feed vanes 16 and comes back to the drive shaft 9a from entering feed vanes 16 again when the feed vanes 16 are brought to the lower position. Thus, in this embodiment, since the heating fluid 17 which has condenses hardly enters the feed vanes 16, the feed vanes 16 can be maintained at high temperature all the time and hence the material which comes into contact with the feed vanes 16 can be efficiently dried. Further, as is clear from Figs. 8 and 9, each feed vane 16 has a predetermined thickness and also has lateral end surfaces 16p extending from opposite ends of the attaching portions which is along the imaginary helix to the front end of the feed vane 16. Therefore, the material disposed forward in the direction of rotation can be stirred by the lateral end surface 16p. Preferably, the lateral end surface 16p disposed forward in the direction of the rotation is an inclined surface which opens towards the discharged port 4 of the conveying device, as shown in Fig. 12, so that said lateral end surface 16p itself has the function of conveying material to be dried, thereby making it possible to increase the rate of conveyance of said material. Reversely, as shown in broken lines p , if the lateral end surface 16p is an inclined surface which is closed with respect to the discharge port 4 of the casing 2, the lateral end surface 16p will serve to move the material in the direction opposite to the direction of conveyance. When it is desired to reduce the rate of conveyance to thereby provide sufficient drying time, this can be attained by forming the lateral end surface 16p in the manner shown in broken lines p . In addition, the height of the feed vane 16 is selected in such a manner they are close to the outer peripheral surfaces of the adjacent drive shaft. With this arrangement, the material adhering to the outer peripheral surfaces of the adjacent drive shafts can be scraped off by the front ends of the feed vanes 16, so that the stirring and drying of the material can be made more efficient. In order to attain such a merit, however, it is necessary to take into account not only the height of the feed vanes 16 but also the outer diameter of the drive shafts. Thus, preferably the distance between adjacent drive shafts and the height of the feed vanes are selected in such a manner that the material adhering to the outer peripheral surface of a drive shaft is removed by the feed vanes attached to the adjacent drive shaft. A description will now be given of the operation of the screw conveyor type drying apparatus in the embodiment described above. A material to be dried is charged into the casing 2 through the charge port 3, and the material thus charged is gradually conveyed from the side associated with the charge port 3 toward the discharge port 4 by the feed vanes 16 provided on the drive shafts 9a, 9b and 9c. During travel in the casing 2, the material comes in contact with the outer surfaces of the feed vanes 16 and drive shafts 9a, 9b and 9c heated by the heating fluid 17 and is thereby dried, and the dried material goes over the weir 2b, whereupon it is discharged through the discharge port 4 into the outside of the apparatus. Since the feed vanes 16 described above are provided not continuously along the imaginary helix on each of the drive shafts 9a, 9b and 9c but with a predetermined spacing between adjacent feed vanes 16, the feeding of the material does not take place in the spaces between adjacent feed vanes 16. As a result, the material is fed very slowly in the casing 2; thus, it stays long in the casing 2 to have sufficient drying time. Further, since the sectorial feed vanes 16 are provided on the drive shafts 9a, 9b and 9c with a predetermined spacing between adjacent feed vanes, the material is moved while being raised and depressed by the end surfaces of the feed vanes 16 as the drive shafts 9a, 9b and 9c are rotated. Thereby the material is efficiently stirred. Further, between the feed vanes 16 on the central drive shaft 9b and the feed vanes 16 on the drive shafts 9a and 9c on opposite sides, there are defined overlap portions B (Fig. 4) which are fitted together in staggered relationship to each other. Thereby, as shown in Fig. 10, when the adjacent drive shafts 9a and 9b are rotated in mutually opposite directions until the space between adjacent feed vanes 16 is directed upward, there is defined a large space above the overlap portions B , from which space the material falls to the overlap portions B and, as the feed vanes 16 at the overlap portions B are rotated as shown in Fig. 11, the material entering the overlap portions B is nipped by the feed vanes 16 at the overlap portions B and is thereby loosened; thus, lumps of material are broken small. This breaking action of the overlap portions B on lumps of material prevents the material from adhering to the surfaces of the feed vanes 16. Further, since axially spaced front and rear feed vanes disposed on the drive shafts 9a, 9b and 9c are shifted in increments of 30° in planes at right angles to the axial direction, the feed vanes 16 do not simultaneously cut into the material but do so axially in turns. Thereby, the power for the drive shafts 9a, 9b and 9c is saved and the cutting of the feed vanes 16 into the material is facilitated. Further, in the case where the central angle of the feed vanes 16 is 115°C as described above, three plates for making feed vanes 16 can be produced from a single disk, a fact which means a reduction in manufacturing cost. In addition, if the drive shafts 9a, 9b and 9c are reversed in direction of rotation, i.e., if the drive shafts 9a nd 9c are rotated clockwise as viewed from the side associated with the charge port and the central drive shaft 9b counterclockwise, the material will be fed from the side associated with the discharge port 4 toward the side associated with the charge port 3; thus, by adapting the apparatus so that the drive shafts 9a, 9b and 9c can be driven for rotation both forward and backward, the staying time for the material can be adjusted and the stirring action on the material enhanced. Further, since the feed vanes 16 provided on each drive shaft, when viewed in the axial direction, are shifted in increments of 30°, the spaces between feed vanes in successive pairs on each of the drive shaft 9a, 9b and 9c are serially connected together (see Fig. 5); thus, part of the material is sent back in the direction opposite to the direction of conveyance and hence the material can be dried to a fuller degree. Further, since the front ends of the feed vanes provided on adjacent drive shafts are extended close to the outer peripheral surfaces of the drive shafts, the material adhering to the outer peripheral surfaces of the drive shafts can be scraped off by the front ends of the feed vanes; thus, the drying and stirring of the material can be effected more efficiently. In the screw conveyor type drying apparatus described above, three hollow drive shafts have been provided; however, four or more hollow drive shafts may be arranged to form a screw conveyor type drying apparatus. While the feed vanes 16 attached to the drive shafts 9a...9c have been shown having a sectorial form, they are not limited there to but may take any other form provided that they spread toward their front ends. Further, while the feed vanes have been attached in position along an imaginary helix so as to feed a material to be dried, they may be provided on the outer peripheral surfaces of some of the hollow drive shafts along the imaginary helix having such a direction that the material is moved in the direction opposite to the direction of conveyance. Further, as shown in Fig. 1A, of the feed vanes 56 provided on the outer peripheral surface of the drive shaft 9b, some, sown at 56A, may be disposed along such a helix as will move part of the material in the direction opposite to the direction of conveyance. In this case, the corresponding portions of the adjacent drive shafts will be provided with feed vanes similar thereto. This arrangement also makes it possible to increase the staying time for the material and to stir the material to a fuller degree. Further, in the apparatus shown in Figs. 1 and 2, the hollow drive shaft 9a has been connected to the driving device 14 through the chain transmission mechanism 15; however, as shown in Fig. 15, a relay idle shaft 31 may be provided between the driving device 14 and the transmission gear 11 coaxially provided on the front end of the hollow drive shaft 9a. In this case, the relay idle shaft 31 is coaxially provided with a sprocket 32 and a transmission gear 33, the sprocket 32 being connected to the driving device by a chain transmission mechanism 34, the transmission gear 33 meshing with the transmission gear 11 coaxially provided on the hollow drive shaft 9a. Thus, the tension from the chain transmission mechanism 34 is applied only to the relay idle shaft 31. Since the tension is not transmitted to the hollow drive shaft 9a, the latter can be rotated more stably than in the case of the apparatus shown in Fig.s. 1 and 2. However, for transmission of the rotative power of the driving device 14 to the drive shafts 9a...9c, it is not absolutely necessary to use the aforesaid chain transmission mechanisms 15 and 34; other transmission means such as a desired number of transmission gears may be used. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims: 1. A conveyor type drying apparatus comprising: a casing having a material charging port and a material discharging port which are spaced a predetermined distance in the direction of the conveyance, a plurality of hollow drive shafts which are disposed in said casing and whose longitudinal direction extends in the direction of conveyance, drive means for driving said plurality of hollow drive shafts so that adjacent drive shafts are rotated in mutually opposite directions, a plurality of feed vanes of hollow construction spaced a predetermined distance from each other and extending along an imaginary helix positioned on the outer peripheral surface of each of said drive shafts, each feed vane being shaped so that it spreads as it extends from the region where it is provided on the outer peripheral surface of the drive shaft to its front end, an means for feeding heating fluid into the hollow portions of the feed vanes through said hollow drive shafts. 2. A screw conveyor type drying apparatus as set forth in claim 1, wherein said feed vanes are provided along an imaginary helix disposed on the outer peripheral surface of a drive shaft and wound in the same direction as the direction of conveyance so that said feed vanes move to material to be dried in the direction of conveyance as the drive shaft on which said feed vanes are provided is rotated. 3. A screw conveyor type drying apparatus as set forth in claim 1, wherein part of said feed vanes are provided along an imaginary helix disposed on the outer peripheral surface of a drive shaft and wound in the direction opposite to the direction of conveyance so that the part of said feed vanes move a material to be dried in the direction opposite to the direction of conveyance as the drive shaft on which said feed vanes are provided is rotated. 4. A screw conveyor type drying apparatus as set forth in claim 1, wherein each said feed vane has a substantially sectorial shape. 5. A screw conveyor type drying apparatus as set forth in claim 1, wherein the outer peripheral surface of said hollow drive shaft is provided with a plurality of pairs of feed vanes disposed in one pitch of the imaginary helix. 6. A screw conveyor type drying apparatus as set forth in claim 5, wherein: the feed vanes in each pair are spaced from each other by an angular spacing β = (360° - 2α) / 2 when seen in the direction of the drive shaft and when the central angular of each feed vane being α, and the pair of feed vanes following said first pair are arranged so that each pair is shifted from the preceding pair by 3 pitches + about β / 2. 7. A screw conveyor type drying apparatus as set forth in claim 6, wherein said α is 115° and said β is 65°, and when seen in the direction of the drive shaft, a pair of feed vanes is shifted by about 30° from the preceding pair of feed vanes. 8. A screw conveyor type drying apparatus as set forth in claim 1, wherein the feed vanes on adjacent feed vanes are symmetrical with respect to a line when seen in the axial direction at the middle between two drive shafts. 9. A screw conveyor type drying apparatus as set forth in claim 1, wherein said feed vanes have a predetermined thickness so that the lateral end surfaces extending from opposite ends of the region where the feed vane is attached to the drive shaft have some area. 10. A screw conveyor type drying apparatus as set forth in claim 9, wherein of said lateral end surfaces, the one disposed forward in the direction of rotation is an inclined surface which opens toward the discharge port side so that a material to be dried which comes into contact with said lateral end surface is moved by said lateral end surface in the direction of conveyance as the drive shafts are rotated. 11. A screw conveyor type drying apparatus as set forth in claim 9, wherein of said lateral end surfaces, the one disposed forward in the direction of rotation is an inclined surface which is closed toward the discharge port side so that a material to be dried which comes in contact with said lateral end surface is moved by said lateral end surface in the direction opposite to the direction of conveyance as the drive shafts are rotated. 12. A screw conveyor type drying apparatus as set forth in claim 1, wherein the distance between said drive shafts and the height of said feed vanes are selected so that feed vanes on adjacent drive shafts, when seen in the axial direction, overlap each other over their greater portions. 13. A screw conveyor type drying apparatus as set forth in claim 12, wherein the height of said feed vanes is selected so that the font ends of the feed vanes come close to the portions of those outer peripheral surfaces of adjacent drive shafts which are closest to the feed vanes. 14. A screw conveyor type drying apparatus as set forth in claim 1, wherein the hollow portion of each feed vane communicates with the hollow portion of the drive shaft through drain pipes which project from the base of the feed vane into the hollow portion of the drive shaft. 15. A a screw conveyor type drying apparatus as set forth in claim 1, wherein at a position closer to said discharge port than are the feed vanes, said casing is provided with a weir at a stage prior to said dried material discharging port. 16. A screw conveyor type drying apparatus as set forth in claim 1, wherein said rotary drive mechanism comprises a rotary drive source, and a transmission mechanism for transmitting drive power from said rotary drive source to the hollow drive shafts. 17. A screw conveyor type drying apparatus as set forth in claim 1, wherein said transmission mechanism comprises endless transmission means connected to the rotary drive source, a relay shaft connected to said endless transmission means and having a first gear coaxially mounted thereon, and a second gear meshing with said first gear and coaxially attached to one of said hollow drive shafts. 18. A screw conveyor type drying apparatus as set forth in claim 1, wherein said casing, a baffle plate is provided so that it crosses the direction of conveyance. 19. A screw conveyor type driving apparatus as set forth in claim 18, wherein there are plurality of said baffle plates which are distributed along the direction of conveyance. 20. A drying apparatus comprising: a casing having material charging and discharging parts; means within the casing for conveying the material from the charging port to the discharging port, the conveying means comprising at least a first drive shaft and a second drive shaft arranged to be rotated in opposite directions, and a plurality of spaced vanes on each shaft, the vanes extending along an imaginary helical path on the outer surface of the shaft, the length of the outer periphery of each vane being greater than the length of the vane at the said outer surface of the shaft; and ducts within the shafts and vanes for supplying heating fluid thereto.

Inventors: OHATA, KENJI, TAZAKI, MITSUO
Applicants: KUBOTA LIMITED
Application year: 1986
Main classification: F26B17
IPC codes: F26B25, B65G33, B01F15, F26B7, F26B17, F26B23, F26B3