Abstract:
In a conical twin-screw extruder in which two rotor shafts having flights on the outer peripheral surfaces thereof and being adjacent to each other in the lateral direction are accommodated in a barrel having a raw material supply port on one side and a raw material discharge port on the other side, and the distance between the rotor shafts and the outside diameters of the flights thereof are gradually reduced from the supply port side to the discharge port side, characteristically, the barrel is provided with a water-removing port for removing water contained in a raw material supplied through the raw material supply port, out of the barrel. The extruder can be applied to raw materials various shapes, sizes, and properties.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a conical twin-screw extruder and a dehydrator for use in dehydration of water-containing raw materials such as thermoplastic elastomers, rubbers, resins, and the like which contain water, respectively.  
         [0003]     2. Description of the Related Art  
         [0004]     There is known a dehydrator described in Japanese Unexamined Patent Application Publication No. 2001-353719 as a dehydrator useful for water-containing raw materials. In FIG. 2 of this Patent Document, a technique is disclosed by which a conical single-screw extruder is used as a dehydrator, and a parallel twin-screw extruder is arranged in tandem to be used as a dehydrator.  
         [0005]     Referring to the above-described known dehydrator, a water-containing raw material to be supplied should have specifications corresponding to a machine. Thus, there has been a problem in that the dehydrator can not be applied to various types of raw materials.  
         [0006]     In particular, in some cases, the hydrator can not constantly nip all of the materials ranging from a powdery raw material to a raw material in a large block shape having a diameter of more than 200 mm. Therefore, problems occur in that variations in processing amount are caused when the dehydrator is used. Moreover, there are some cases in which no production can be performed with raw materials supplied, depending on the shapes and sizes thereof.  
         [0007]     Moreover, dehydrators of known types can be applied to raw materials having a water content of about 10% to 40%. Problematically, the dehydrators can not process raw materials having a water content of about 80%, raw materials containing a large amount of water, e.g., those which are conveyed together with water, and so forth.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, an object of the present invention is to provide a dehydrator which can be applied to raw material having various shapes, sizes and properties.  
         [0009]     To achieve the above-described object, the following means are provided according to the present invention. That is, in a conical twin-screw extruder in which two rotor shafts having flights on the outer peripheral surfaces thereof and being adjacent to each other in the lateral direction are accommodated in a barrel having a raw material supply port on one side and a raw material discharge port on the other aide, and the distance between the shafts of the rotor shafts and the outside diameters of the flights thereof are gradually reduced from the supply port side to the discharge port side, characteristically, the barrel is provided with a water-removing port for removing water contained in a raw material supplied through the raw material supply port out of the barrel.  
         [0010]     A conical twin-screw extruder can be applied to raw materials with various shapes and sizes, since the nipping performance for a raw material supplied through a raw material supply port is superior, compared to that of a conical single-screw extruder or a parallel twin-screw extruder. The conical twin-screw extruder can compress a water-containing raw material at a high ratio. Thus, the dehydrating effect is high. Accordingly, the conical twin-screw extruder can be used as a dehydrator for a water-containing raw material by providing a water-removing port for the barrel.  
         [0011]     Preferably, the axial lines of the two rotor shafts form an angle of 10 to 40 degrees.  
         [0012]     If the angle defined by the rotor shafts is less than 10 degrees, the lengths of the rotor shafts must be increased to ensure the compression ratio. Thus, it becomes meaningless to change the distance between the shafts. If the angle exceeds 40 degrees, the lengths of the rotor shafts will be small. Thus, the lengths sufficient for dehydration of the rotor shafts can not be ensured. Moreover, it is unprofitable that the diameter of the shaft having a relatively large diameter will be excessively large.  
         [0013]     Preferably, the flights of one of the rotor shafts and the flights of the other of the rotor shafts are in the meshed state, and the two rotor shafts can be rotated in different directions.  
         [0014]     With the constitution employed as described above, the nipping performance for raw materials having various shapes is enhanced. Thus, raw materials having various shapes, that is, having a powdery shape, a crumb shape, or a veil shape, can be efficiently conveyed and compressed.  
         [0015]     Preferably, the barrel has a chamber peripheral wall surrounding the flights, the chamber peripheral wall is formed in such a manner that the cross-section has substantially a shape consisting of two circles which have the same diameter and overlap with each other, the size of the cross-section is gradually decreased from the raw material supply port to the raw material discharge port, and the chamber peripheral wall is provided with the water-removing port.  
         [0016]     With the constitution employed as described above, a raw material can be highly compressed without the conveying capacity being deteriorated. Therefore, the dehydration effect and the processing capability can be enhanced.  
         [0017]     The raw material supply port may be opened on the upper side, the discharge port may be opened in the axial direction of the rotor shafts, and the water-removing port may be opened in the radial direction of the rotor shafts.  
         [0018]     Preferably, a screen is provided for the water-removing port.  
         [0019]     Fine particles, which are contained in a raw material, or are generated in a process, are suppressed from leaking through the water-removing port, since the screen is provided for the water-removing port. Thus, water only can be separated and removed.  
         [0020]     Preferably, the screen is a wedge wire screen having a predetermined clearance, or a punching plate.  
         [0021]     Preferably, each of the flights is formed in such a manner that the maximum diameter is 1.5 to 5.0 times of the minimum diameter.  
         [0022]     A sufficient compression force can be ensured by setting the maximum diameter of the flight of the rotor shaft at least 1.5 times of the minimum diameter. Moreover, the raw material supply port of the barrel can be easily increased. If the maximum diameter is set more than 5 times of the minimum diameter, unsuitably, the angle defined by the rotor shafts becomes at least 40 degrees.  
         [0023]     Preferably, one of the rotor shafts is extended from the other rotor shaft in the axial direction on the discharge port side, and the extended portion functions as a single-shaft metering portion from which a raw material is extruded out at a constant rate.  
         [0024]     With the constitution employed as described above, variations in conveying amount per unit time are reduced. Thus, a raw material can be supplied at a constant amount-rate to the succeeding process.  
         [0025]     Preferably, a gear pump is connected on the raw material discharge port.  
         [0026]     The inner pressure of the barrel can be enhanced with the gear pump. Thus, the dehydrating efficiency can be enhanced. Moreover, the accuracy of the supply to the succeeding process can be enhanced by metering the raw material with the gear pump, even if no metering portion is provided. In the case in which the metering portion is provided, the accuracy of the supply to the succeeding process can be still more enhanced.  
         [0027]     Preferably, a throttling portion is connected to the raw material discharge port instead of the gear pump. The dehydrating efficiency can be enhanced by the back pressure, which is caused by the resistance at the discharge port given by the throttling portion.  
         [0028]     Both of the gear pump and the throttling portion may be provided.  
         [0029]     Also, there may be provided a dehydrating apparatus comprising a parallel twin-screw extruder connected to the above-described conical twin-screw extruder and positioned downstream of the conical twin-screw extruder, the parallel twin-shaft extruder containing a heater for heating the extruder barrel, a dehydrating screen and/or a vent for removing steam provided for the extruder barrel.  
         [0030]     Preferably, a pressure-reducing and deaerating device is connected to the vent.  
         [0031]     According to the above-described dehydrating apparatus, a raw material with a high water content can be continuously dehydrated and/or dried to be formed into pellets.  
         [0032]     According to the present invention, raw materials various shapes, sizes and properties can be processed with the same apparatus. 
     
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0033]      FIG. 1  is a cross-sectional plan view showing an embodiment of a conical twin-screw extruder of the present invention.  
         [0034]      FIG. 2  is a cross-sectional side view of the conical twin-screw extruder of  FIG. 1 .  
         [0035]      FIG. 3  is a cross-sectional view taken along line A-A in  FIG. 2 .  
         [0036]      FIG. 4  is a cross-sectional view taken along line B-B in  FIG. 3 .  
         [0037]      FIG. 5  is a cross-sectional plan view showing another embodiment of a conical twin-screw extruder of the present invention.  
         [0038]      FIG. 6  illustrates the structure of a dehydrating apparatus according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]     Embodiments of the present invention will be further described with reference to the drawings.  
         [0040]     Referring to  FIGS. 1 and 2 ,  FIG. 1  is a cross-sectional plan view of a conical twin-screw extruder  1  for compressing and dehydrating thermoplastic elastomers, rubbers, resins, or the like each containing water.  FIG. 2  is a cross-sectional side view of the conical twin-screw extruder  1 .  
         [0041]     The conical twin-screw extruder  1  contains an extruder-body barrel  2 . A raw material supply port  3  for supplying a water-containing raw material is provided on one side of the barrel  2 . A raw material discharge port  4  for discharging the raw material from which water has been removed is provided on the other side of the barrel  2 .  
         [0042]     Two rotor shafts  5  for conveying the water-containing raw material supplied through the supply port  3  and simultaneously compressing the raw material are disposed adjacently to each other in the horizontal direction, inside the barrel  2 . The raw material supply port  3  has an opening on the upper side, and the discharge port  4  has an opening in the axial direction of the rotor shafts  5 .  
         [0043]     The two rotor shafts  5  are arranged in such a manner that the distance between the rotor shafts  5  is gradually decreased from the supply port  5  side to the discharge port  4  side. A flight  6  is formed on the outer periphery of each of the rotor shafts  5 . The fight  6  is formed in a spiral vane shape. The rotor shaft  5  and the flight  6  are formed in such a manner that the outside diameters thereof gradually decrease from the supply port  3  side to the discharge port  4  side.  
         [0044]     The rotor shafts  5  are arranged so that the angle θ formed by the axial lines is in the range from 10 to 40 degrees. The two rotor shafts  5  are arranged in such a manner that the flights  6  thereof are in the meshed state. The reason for the above-described setting of the angle θ is as follows. That is, if the angle θ is excessively large, i.e., more than 40 degrees, the nipping performance will be inferior in the area of the compression zone to the metering zone. Moreover, a high load is applied in the compression zone, so that mechanical problems occur. If the angle θ is set smaller than 10 degrees, nipping performance will be inferior unless the diameters of the flights  6  are set large. However, in the case in which the diameters of the flights  6  are increased, the mechanical lengths become longer. Therefore, the above-described angle range is preferable.  
         [0045]     The flights  6  positioned under the supply port  3  have such a shape that the flights  6  can nip raw materials which range from a powder having a size of about 10 μm to large blocks having a diameter of about 200 mm.  
         [0046]     Each flight  6  is formed in such a manner that the maximum diameter D thereof is 1.5 to 5 times of the minimum diameter d thereof. When the maximum diameter D is 5.0 times of the minimum diameter d, the flight  6  can nip a raw material having a size of about 5 times of the minimum diameter d of the flight  6 . Moreover, the flights  6  positioned under the supply port  3  and having the above-described sizes can directly supply a raw material containing a large amount of water, i.e., having a water content of 10 to 90%. Moreover, when a raw material having a high water content is supplied, the discharge amount can be also increased.  
         [0047]     The diameter ratios D/d of the flights  6  have a relationship to the above-described angle θ. The volume of the supply port  3  can be sufficiently increased with respect to the discharge port  4 , by setting the ratio D/d in a range of 1.5 to 5.0. From the viewpoint of compression and dehydration, it is desirable to set the maximum diameter D large value with respect to the minimum diameter d. However, if the maximum diameter D is set large, the angle θ between the shafts become wide. Thus, the nipping in a raw material becomes deficient in the metering zone. Mechanical problems occur, due to the increased load in the compression zone.  
         [0048]     The two rotor shafts  5  on the larger diameter sides are cantilevered on the end walls of the barrel  2 . A driving device  7  is provided in this supporting portion.  
         [0049]     The driving device  7  causes the two rotor shafts  5  to rotate in the different directions. The rotational directions of the rotor shafts  5  are such that a raw material supplied through the supply port  3  is nipped between the two rotor shafts  5 .  
         [0050]     According to this embodiment, one of the rotor shafts  5  is driven by a motor  8 , and the other rotor shaft  5 , linked with and connected to a bevel gear  9 , is rotated in the different direction. However, the driving system is not restricted to the above-descried one.  
         [0051]     A water-removing port  10  is provided for the barrel  2 . Water contained in a raw material supplied through the raw material supply port  3  is discharged through the water-removing port  10  until the raw material is discharged from the discharge port  4 . The water-removing port  10  is opened in the radial direction of the rotor shafts  5 .  
         [0052]     The water-removing port  10  is provided downward of the raw material supply-port  3 .  
         [0053]     As shown in  FIGS. 2 and 3 , the barrel  2  contains a chamber peripheral wall  11  surrounding the flights  6 . The chamber peripheral wall  11  is formed in such a manner that the cross-section has substantially a spectacle-hole-shape (a shape consisting of two circles having the same diameter and overlapping with each other). The size of the cross-section is gradually decreased from the raw material supply port  3  to the discharge port  4 . A gap is formed between the chamber peripheral wall  11  and the upper side of the flights  6 . The gap is decreased toward the top-end side. The gap facilitates the nipping in a raw material. Moreover, a mechanical load, caused by the difference between the conveyed amounts of a raw material in the large diameter portions of the flights  6  and in the small diameter portions thereof, can be allowed for, due to the back-flow of the raw material.  
         [0054]     The water-removing port  10  is formed in the chamber peripheral wall  11 . The water-removing port  10  is formed ranging from the side-surface of the chamber peripheral wall  11  to the lower surface thereof.  
         [0055]     The water-removing port  10  has an opening of which the size is such that a raw material cannot pass through the opening but water can pass through the opening. In the case in which the water-removing port  10  has a large opening, a screen  12  may be provided for the opening, and thus, the water-removing port  10  is obtained.  
         [0056]     As shown in  FIG. 4 , as the screen  12 , preferably, a wedge wire screen which provides a gap substantially in parallel to the rotor shafts  5 . The screen  12  may be a punching plate which is a porous plate. However, the screen  12  is not restricted to the screen or plate.  
         [0057]     Preferably, that the voids or the pore size is large from the viewpoint of the removal of a large amount of water. However, it is desirable that the size of the voids or the pore size is in the range of 0.1 to 3.0 mm to prevent a raw material from leaking.  
         [0058]     The above-described structure of the conical twin-screw extruder according to the present invention is sufficient for the main structure thereof. Moreover, according to this embodiment, one of the rotor shafts  5  is more extended in the axial direction compared to the other rotor shaft  5 , on the discharge port  4  side. This extension portion  13  functions as a single-shaft metering portion  14  for determining the amount of a raw material and extruding the raw material therefrom. The rotor shaft  5  having the metering portion  14  is longer than the other rotor shaft  5 , that is, the length is 1.05 to 2.0 times of that of the other rotor shaft  5 .  
         [0059]     The metering portion  14  contains a spiral flight  15  and a cylindrical metering portion barrel  16 . The spiral flight  15  is formed in the extension portion  13  of the rotor shaft  5  and having a constant diameter and a constant pitch. The cylindrical metering portion barrel  16  surrounds the flight  15 . The metering portion barrel  16  is connected to the raw material discharge port  4  of the extruder-body barrel  2 .  
         [0060]     According to the conical twin-screw extruder having the above-described structure, a water-containing raw material is supplied through the raw material supply port  3 . The supplied raw material is nipped between the flights  6  in the meshed state, due to the rotation of the two rotor shafts  5  in the different directions, and is conveyed toward the discharge port  4  side. In the case of a raw material containing a large amount of water such as a raw material conveyed by use of water, the water is removed through the water-removing port  10  located near the raw material supply port  3 . The raw material containing water conveyed due the rotation of the rotor shafts  5  is strongly compressed because of the conical forms of the rotor shafts  5 , so that water is separated. The separated water is caused to flow in the backward direction and removed through the water-removing port  10 . The dehydrated raw material is supplied through the discharge port  4  into the metering portion  14 . The metering portion  14  is filled with the raw material, since the conveying capacity of the flight  15  is smaller than that of the flights  6 . Then, the raw material is supplied to the succeeding process at a constant amount-rate.  
         [0061]      FIG. 5  shows another embodiment of the present invention. A gear pump  17  is connected to the outlet of the metering portion  14 . A throttling portion  18  is provided at the outlet of the gear pump  17 . The throttling portion  18  is made up of an orifice plate, and so forth. The throttling portion  18  is required to render a resistance to the flow of a raw material. The throttling portion  18  has such a structure that the cross section of the tube thereof can be changed.  
         [0062]     The hydration efficiency can be enhanced by increasing the inner pressure in the vicinity of the discharge port  4  of the conical twin-screw extruder by means of the gear pump  17 . Moreover, the accuracy of the supply to the succeeding process can be enhanced by metering the raw material with the gear pump  17 .  
         [0063]     The hydration efficiency can be also enhanced due to a resistance rendered by the throttling portion  18 . The throttling portion  18  may be provided upstream of the gear pump  17 . The throttling portion  18  and the gear pump  17  may be independently provided. In the case of the conical twin-screw extruder not provided with the metering portion  14 , the throttling portion  18  and the gear pump  17  may be connected to the raw material discharge port  4 .  
         [0064]      FIG. 6  shows a tandem type dehydrator in which the conical twin-screw extruder is connected to a parallel twin-screw extruder  19  through a connecting piece (not shown).  
         [0065]     The parallel twin-screw extruder  19  contains a heater (not shown) for heating an extruder barrel  20 , a dehydrating screen  21  provided for the extruder barrel  20 , and a vent  22  for removing steam. A pressure-reducing and deaerating device  23  is connected to the vent  22 .  
         [0066]     Both of the dehydrating screen  21  and the steam removing vent  22  are not necessarily provided. That is, either one of them may be provided.  
         [0067]     With the dehydrating apparatus having the above-described constitution, a raw material with a high water content can be continuously dehydrated and deaerated to produce pellets as a product.  
         [0068]     The present invention is not limited to the above-described embodiments.  
         [0069]     The present invention can be used in apparatuses for manufacturing thermoplastic elastomers, rubbers, and resins.