Mixer and mixing method for gypsum slurry

Abstract

A mixer has a circular housing defining a mixing area for mixing and kneading of a gypsum slurry. A rotary disc is positioned in the housing and rotated in a predetermined rotational direction. A rotary driving shaft cointegrally connected with the rotary disc and a plurality of scrapers are positioned in the mixing area. A slurry discharge port is provided on an annular wall of the housing for feeding the gypsum slurry of the mixing area onto a sheet of paper for gypsum board liner. An opening of the slurry discharge port is divided into a plurality of narrow openings, so that fluid resistance on the gypsum slurry flowing out of the mixing area is increased. An annular basal part rotates integrally with the rotary disc and an inner end portion of the scraper is fixed to the annular basal part.

Claims

1. A mixer for preparation of gypsum slurry, which has a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft extending through an upper or lower plate of the housing to be integrally connected with the rotary disc, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line, comprising: a scraper which is positioned above said rotary disc in said mixing area formed between the disc and said upper plate, which is spaced apart from an upper surface of the disc, and which is spaced at a small distance from a lower surface of the upper plate for scraping off the slurry from the lower surface of the upper plate; and an annular basal part which is provided on said rotary disc in a center region of the disc so as to rotate integrally with the disc and which is formed to surround a rotational center axis of said rotary driving shaft, wherein an inner end portion of said scraper is fixed to the annular basal part, an outer end portion of the scraper is positioned in a peripheral zone of the disc, and said slurry discharge port is positioned on an annular wall of said housing; and wherein said slurry discharge port is provided with a fluid passage dividing member which divides an opening of the port into a plurality of narrow openings so as to increase fluid resistance on the gypsum slurry flowing out of said mixing area through said opening of the port.

2. The mixer as defined in claim 1, wherein said scraper is bent or curved backward in a rotational direction of the disc, between said inner and outer end portions.

3. The mixer as defined in claim 1, wherein said annular basal part is positioned in concentricity with said rotational center axis.

4. The mixer as defined in claim 3, wherein a diameter of said annular basal part is set to be three or more times as large as a diameter of said rotary driving shaft, and said inner end portion of the scraper is fixed onto an upper surface of the annular basal part.

5. The mixer as defined in claim 1, wherein a center axis of the inner end portion of said scraper horizontally extends in a direction at an angle ranging from 60 degrees to 120 degrees with respect to a line segment passing through a supporting center of the scraper and a center of rotation of said rotary disc.

6. The mixer as defined in claim 1, wherein said dividing member is defined by a plurality of guide members which divide said opening of the slurry discharge port into a plurality of slits, or a meshy or lattice member transversely and vertically dividing the opening of the port.

7. The mixer as defined in claim 1, wherein a pin for augmenting a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port is provided to stand on a periphery of said rotary disc.

8. The mixer as defined in claim 1, wherein a total area of said slurry discharge port is set to be in a range from 2% to 10% of a total area of an inner circumferential surface of said annular wall, and wherein an open area ratio of the slurry discharge port is set to be in a range from 50% to 80% of the total area of the slurry discharge port.

9. A mixer for preparation of gypsum slurry, which has a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft extending through an upper or lower plate of the housing to be integrally connected with the rotary disc, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line, comprising: a scraper which is positioned above said rotary disc in said mixing area formed between the disc and said upper plate, which is spaced apart from an upper surface of the disc, and which is spaced at a small distance from a lower surface of the upper plate for scraping off the slurry from the lower surface of the upper plate; and an annular basal part which is provided on said rotary disc in a center region of the disc so as to rotate integrally with the disc and which is formed to surround a rotational center axis of said rotary driving shaft, wherein an inner end portion of said scraper is fixed to the annular basal part, an outer end portion of the scraper is positioned in a peripheral zone of the disc, and the scraper is bent or curved backward in a rotational direction of the disc between said inner and outer end portions.

10. The mixer as defined in claim 9, wherein said rotary disc is provided with a gear tooth portion for augmenting a fluid flow of said slurry flowing out of said mixing area through said slurry discharge port.

11. The mixer as defined in claim 9 wherein said scraper has a single bending part which bends at an angle in a range of 4515 degrees, or wherein the scraper is bent at a plurality of the bending parts or generally curved, and a distal end portion of the scraper is directed in a direction of an angle in a range of 7515 degrees with respect to an radial direction of said mixing area.

12. The mixer as defined in claim 9, wherein said annular basal part is positioned in concentricity with said rotational center axis.

13. The mixer as defined in claim 12, wherein a diameter of said annular basal part is set to be three or more times as large as a diameter of said rotary driving shaft, and said inner end portion of the scraper is fixed onto an upper surface of the annular basal part.

14. The mixer as defined in claim 9, wherein a pin for augmenting a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port is provided to stand on a periphery of said rotary disc.

15. A mixer for preparation of gypsum slurry, which has a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft integrally connected with the rotary disc, a scraper positioned in the mixing area, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line: wherein said rotary driving shaft extends through an upper or lower plate of said housing to be connected with said rotary disc; wherein an inner end portion of said scraper is positioned in a center region of said rotary disc, an outer end portion of the scraper is positioned in a peripheral zone of the disc, and said slurry discharge port is positioned on an annular wall of said housing; wherein said slurry discharge port is provided with a fluid passage dividing member which divides an opening of the port into a plurality of narrow openings so as to increase fluid resistance on the gypsum slurry flowing out of said mixing area through said opening of the port; and wherein a pin for augmenting a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port is provided to stand on a periphery of said rotary disc and a distal end portion of said scraper is supported by said pin.

16. A mixing method for gypsum slurry with use of a mixer for preparation of the gypsum slurry, the mixer having a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft extending through an upper or lower plate of the housing to be integrally connected with the rotary disc, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line: wherein a scraper is positioned above said rotary disc in said mixing area formed between the disc and said upper plate, and the scraper is spaced apart from an upper surface of the disc and is spaced at a small distance from a lower surface of the upper plate for scraping off the slurry from the lower surface of the upper plate; wherein an annular basal part is provided on said rotary disc in a center region of the disc so as to rotate integrally with the disc and is formed to surround a rotational center axis of said rotary driving shaft; wherein said scraper is horizontally supported by fixing an inner end portion of the scraper to the annular basal part, an outer end portion of the scraper is positioned in a peripheral zone of said rotary disc, said slurry discharge port is positioned on an annular wall of said housing, and an opening of said slurry discharge port is divided into a plurality of narrow openings so as to increase fluid resistance on the gypsum slurry flowing out of said mixing area through said opening of the port; and wherein said rotary driving shaft rotates said rotary disc and said scraper about said rotational center axis so that said slurry is mixed and kneaded in said mixing area and the slurry is moved toward the periphery of the mixing area by centrifugal force acting on the slurry, whereby the slurry flows out of said mixing area through said slurry discharge port.

17. The mixing method as defined in claim 16, wherein said scraper is bent or curved backward in a rotational direction of said rotary disc, between said inner and outer end portions.

18. The mixing method as defined in claim 16, wherein said annular basal part is positioned in concentricity with said rotational center axis.

19. The mixing method as defined in claim 16, wherein a center axis of said inner end portion of the scraper is oriented in a direction at an angle ranging from 60 degrees to 120 degrees with respect to a line segment passing through a supporting center of the scraper and a center of rotation of said rotary disc.

20. The mixing method as defined in claim 16, wherein, as a device for dividing said opening into the narrow openings, a plurality of guide members dividing said opening into a plurality of slits are positioned in said slurry discharge port, or a meshy or lattice member transversely and vertically dividing said opening is positioned in the slurry discharge port.

21. The mixing method as defined in claim 16, wherein a pin is provided to stand on a periphery of said rotary disc, so as to augment a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port.

22. A mixing method for gypsum slurry with use of a mixer for preparation of the gypsum slurry, the mixer having a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft extending through an upper or lower plate of the housing to be integrally connected with the rotary disc, a scraper positioned in the mixing area, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line: wherein a scraper is positioned above said rotary disc in said mixing area formed between the disc and said upper plate, and the scraper is spaced apart from an upper surface of the disc and is spaced at a small distance from a lower surface of the upper plate for scraping off the slurry from the lower surface of the upper plate; wherein an annular basal part is provided on said rotary disc in a center region of the disc so as to rotate integrally with the disc and is formed to surround a rotational center axis of said rotary driving shaft; wherein said scraper is horizontally supported by fixing an inner end portion of the scraper to the annular basal part, and the scraper is bent or curved backward in a rotational direction of the disc, between said inner and outer end portions; and wherein said rotary driving shaft rotates said rotary disc and said scraper about said rotational center axis so that said slurry is mixed and kneaded in said mixing area.

23. The mixing method as defined in claim 22, wherein said rotary disc is formed with a gear tooth portion in a periphery of said rotary disc, thereby augmenting a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port.

24. The mixing method as defined in claim 22, wherein said annular basal part is positioned in concentricity with said rotational center axis.

25. The mixing method as defined in claim 22, wherein a pin is provided to stand on a periphery of said rotary disc, so as to augment a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port.

26. A mixing method for gypsum slurry with use of a mixer for preparation of the gypsum slurry, the mixer having a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft integrally connected with the rotary disc, a scraper positioned in the mixing area, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line: wherein an inner end portion of said scraper is positioned in a center region of said rotary disc, an outer end portion of the scraper is positioned in a peripheral zone of the disc, said slurry discharge port is positioned on an annular wall of said housing, and an opening of said slurry discharge port is divided into a plurality of narrow openings so as to increase fluid resistance on the gypsum slurry flowing out of said mixing area through said opening of the port; wherein said rotary driving shaft extends through an upper or lower plate of said housing, and the shaft rotates said rotary disc and said scraper about a rotational axis of the shaft so that said slurry is mixed and kneaded in said mixing area and the slurry is moved toward the periphery of the mixing area by centrifugal force acting on the slurry, whereby the slurry flows out of said mixing area through said slurry discharge port; and wherein a pin is provided to stand on a periphery of said rotary disc, so as to augment a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port, and a distal end portion of said scraper is supported by said pin.

27. A mixer for preparation of gypsum slurry, which has a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft integrally connected with the rotary disc, a scraper positioned in the mixing area, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line: wherein said rotary driving shaft extends through an upper or lower plate of said housing to be connected with said rotary disc; wherein an inner end portion of said scraper is positioned in a center region of said rotary disc, an outer end portion of the scraper is positioned in a peripheral zone of the disc, and the scraper is bent or curved backward in a rotational direction of the disc between said inner and outer end portions; and wherein a pin for augmenting a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port is provided to stand on a periphery of said rotary disc and a distal end portion of said scraper is supported by said pin.

28. A mixing method for gypsum slurry with use of a mixer for preparation of the gypsum slurry, the mixer having a circular housing defining a mixing area for mixing and kneading of the gypsum slurry, a rotary disc positioned in the housing and rotated in a predetermined rotational direction, a rotary driving shaft integrally connected with the rotary disc, a scraper positioned in the mixing area, and a slurry discharge port provided on the housing for feeding the gypsum slurry of the mixing area onto a production line: wherein an inner end portion of said scraper is positioned in a center region of said rotary disc, an outer end portion of the scraper is positioned in a peripheral zone of the disc, and the scraper is bent or curved backward in a rotational direction of the disc, between said inner and outer end portions; wherein said rotary driving shaft extends through an upper or lower plate of said housing, and the shaft rotates said rotary disc and said scraper about a rotational axis of the shaft so that said slurry is mixed and kneaded in said mixing area; and wherein a pin is provided to stand on a periphery of said rotary disc, so as to augment a fluid flow of said slurry flowing out of the mixing area through said slurry discharge port, and a distal end portion of said scraper is supported by said pin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an explanatory process diagram partially and schematically illustrating a production process of gypsum boards.

(2) FIG. 2 is a partial plan view of a gypsum board manufacturing apparatus in which an arrangement of a gypsum board production line is schematically illustrated.

(3) FIG. 3 is a plan view illustrating a whole arrangement of a mixer.

(4) FIG. 4 is a perspective view illustrating the whole arrangement of the mixer.

(5) FIG. 5 is a transverse cross-sectional view illustrating an internal structure of the mixer.

(6) FIG. 6 is a fragmentary sectional perspective view showing the internal structure of the mixer.

(7) FIG. 7 includes a transverse cross-sectional view and a partially enlarged cross-sectional view of the mixer, which show a positional relation among a rotary shaft, scrapers, and an annular basal part.

(8) FIG. 8 includes a vertical cross-sectional view and partially enlarged cross-sectional views of the mixer, which show the positional relation among the shaft, the scrapers, and the basal part.

(9) FIG. 9 includes cross-sectional views and a perspective view illustrating a configuration of the scraper.

(10) FIG. 10 includes perspective views and enlarged vertical cross-sectional views showing structures of the slurry discharge port.

(11) FIG. 11 includes transverse cross-sectional views of the mixers showing modifications of the positional relation among the rotary shaft, the scrapers, and the basal part.

(12) FIG. 12 includes transverse cross-sectional views of the mixers, each exemplifying the positional relation between the scraper and the pin.

(13) FIG. 13 is a partially enlarged cross-sectional view of the mixer showing a modification of the annular basal part.

(14) FIG. 14 includes a transverse cross-sectional view and a partially enlarged cross-sectional view of the mixer provided with the scrapers, each of the scrapers being bent at a single bending part, backward in the rotational direction.

(15) FIG. 15 includes a transverse cross-sectional view and a partially enlarged cross-sectional view of the mixer provided with the scrapers, each of the scrapers having a number of bending parts bent backward in the rotational direction.

(16) FIG. 16 is a transverse cross-sectional view of the mixer provided with the scrapers, each of the scrapers being generally curved backward in the rotational direction.

(17) FIG. 17 is a transverse cross-sectional view of the mixer provided with the scrapers, each of the scrapers being curved backward in the rotational direction, and which has a number of gear tooth portions formed in a peripheral zone of the rotary disc.

EMBODIMENT

(18) With reference to the attached drawings, preferred embodiments of the present invention are described hereinafter.

(19) FIG. 1 is an explanatory process diagram partially and schematically illustrating a production process of gypsum boards, and FIG. 2 is a partial plan view schematically illustrating an arrangement of a gypsum board production line.

(20) As shown in FIGS. 1 and 2, a lower sheet of paper 1, which is a sheet of paper for a gypsum board liner, is conveyed along a line of production. The mixer is defined by a scraper-type mixer 10, which is located in a predetermined position in relation to a conveyance line, for example, in a position above the conveyance line. Powder ingredients P (calcined gypsum, adhesive agent, set accelerator, additives, admixture, and so forth) and mixing water L are fed to the mixer 10. The mixer 10 mixes and kneads the powder ingredients P and the mixing water W and prepares slurry (calcined gypsum slurry) 3 to be fed onto the sheet 1 of the production line. The slurry 3 is delivered through a slurry delivery section 4 and a slurry outlet tube 7, and is poured onto a widthwise center area of the sheet 1 (a core area of the gypsum board) through a slurry outlet port 7a. A part of the slurry 3 is delivered to fractionation conduits 8 (8a, 8b) to be poured onto widthwise end portions of the sheet 1 (edge zones of the gypsum board) through slurry outlet ports 8c, 8d. Into the slurry 3 to be poured onto the widthwise center area, foaming agent or foam M for adjustment of its specific gravity is mixed. The foaming agent or foam M is introduced into the section 4. If desired, the foaming agent or foam M may be fed to the slurry in the fractionation conduits 8.

(21) The sheet 1 is conveyed together with the slurry 3 to reach a pair of forming rollers 18 (18a, 18b). An upper sheet of paper 2 travels partially around a periphery of the upper roller 18a to convert its direction toward a conveyance direction. The diverted sheet 2 is brought into contact with the slurry 3 on the lower sheet 1 and transferred in the conveyance direction substantially in parallel with the lower sheet 1. A continuous belt-like three-layered formation 5 constituted from the sheets 1,2, and the slurry 3 is formed on a downstream side of the rollers 18. This formation 5 runs continuously at a conveyance velocity V while a setting reaction of the slurry proceeds, and it reaches roughly cutting rollers 19 (19a, 19b). If desired, a variety of forming devices, such as the forming device depending on a passing-through action of an extruder or a gate with a rectangular opening, may be employed instead of the forming rollers 18.

(22) The cutting rollers 19 sever the continuous belt-like layered formation into boards of a predetermined length so as to make boards, each having a gypsum core covered with the sheets of paper, in other words, green boards. The green boards are conveyed through a dryer (not shown) that is located toward a direction shown by an arrow J (on a downstream side in the conveyance direction), whereby the green boards are subjected to forced drying in the dryer. Thereafter, they are trimmed to be boards, each having a predetermined product length, and thus, gypsum board products are produced.

(23) FIGS. 3 and 4 are plan and perspective views illustrating the whole arrangement of the mixer 10, and FIGS. 5 and 6 are a transverse cross-sectional view and a fragmentary sectional perspective view showing an internal structure of the mixer 10.

(24) As shown in FIGS. 3 and 4, the mixer 10 has a flattened cylindrical housing 20 (referred to as housing 20 hereinafter). The housing 20 has a horizontal disk-like upper plate or top cover 21 (referred to as upper plate 21 hereinafter), a horizontal disk-like lower plate or bottom cover 22 (referred to as lower plate 22 hereinafter), and an annular wall or outer circumferential wall 23 (referred to as annular wall 23 hereinafter) which is positioned in peripheral portions of the upper and lower plates 21, 22. The plates 21, 22 are vertically spaced apart at a predetermined distance, so that an internal mixing area 10a for mixing and kneading the powder materials P and the mixing water L is formed in the mixer 10.

(25) A circular opening 25 is formed at a center part of the upper plate 21. An enlarged lower end portion 31 of a vertical rotary shaft 30 extends through the opening 25. The shaft 30 is connected with a rotary driving device (not shown), such as an electric drive motor, and driven in rotation in a predetermined rotational direction (clockwise direction R as seen from its upper side in this embodiment). If desired, a variable speed device, such as a variable speed gear mechanism or a variable speed belt assembly, may be interposed between the shaft 30 and an output shaft of the rotary driving device.

(26) A powder supply conduit 15 is connected to the upper plate 21, for feeding the mixing area 10a with the powder ingredients P to be mixed. A water supply conduit 16 is also connected to the upper plate 21, for supplying a quantity of mixing water L to the area 10a. If desired, an internal pressure regulator and so forth (not shown) may be further connected to the upper plate 21, for limiting excessive increase in the internal pressure of the mixer 10.

(27) Fractionation ports 8e, 8f, each of which may be regarded as a kind of slurry discharge port, are provided on the annular wall 23, on the opposite side of the section 4. The fractionation conduits 8a, 8b are connected to the ports 8e, 8f, respectively. In this embodiment, the ports 8e, 8f are positioned, angularly spaced at a predetermined angle from each other.

(28) A slurry discharge port 40, which constitutes the slurry delivery section 4, is formed on the annular wall 23, angularly spaced at a predetermined angle from the fractionation port 8f in the rotational direction R (on the downstream side). The port 40 opens on an inner circumferential surface of the wall 23.

(29) As shown in FIGS. 5 and 6, an enlarged open end of a hollow connecter section 41 is connected to the slurry discharge port 40. The section 41 extends outward from the annular wall 23. A reduced open end of the section 41 is connected to an upper end portion of the slurry delivery tube 42. The tube 42 is a constituent of a mixer, which is usually called a vertical chute or canister. The tube 42 constitutes the slurry delivery section 4 together with the port 40 and the section 41.

(30) A foam-feeding conduit 45 for feeding the foam or foaming agent M to the slurry is connected to a hollow connector section 41. A foam feeding port 46 opens on an internal wall surface of the section 41. The foam or foaming agent M for adjusting the volume of the slurry is fed to the slurry in the section 41 by the conduit 45.

(31) The slurry and foam are introduced through the hollow connector section 41 into a vertical in-chute area (intratubular area) in the slurry delivery tube 42. The slurry and foam turn around the center axis of the tube 42, so that the slurry swirls in the in-chute area of the tube 42. The slurry and foam are subjected to a shearing force so as to be mixed with each other, whereby the foam is uniformly dispersed in the slurry. The slurry in the tube 42 gravitationally flows down in the in-chute area. Then, the slurry is delivered to the widthwise center area of the lower sheet 1 through the slurry outlet tube 7 (FIGS. 1 and 2). The tube 7 is a so-called boot.

(32) In the housing 20, a rotary disc 32 is rotatably positioned. A lower face of the end portion 31 of the shaft 30 is fixedly secured to a center part of the disc 32. An axis of rotation or a center axis of the disc 32 coincides with the center axis 10b of the shaft 30. The disc 32 is rotated with rotation of the shaft 30 in a direction as indicated by the arrow R (clockwise direction).

(33) As shown in FIGS. 5 and 6, a plurality of scrapers 50 are positioned in the housing 20 and angularly spaced at an angular interval of 120 degrees. An annular basal part 70 for supporting internal end portions of the scrapers 50 is formed outside of the lower end portion 31 of the shaft 30. The basal part 70 is integral with the disc 32 and the lower end portion 31, so as to rotate with the shaft 30. The basal part 70 has a horizontal flat upper surface 72. Timer end portions of the scrapers 50 are fixed onto the upper surface 72 of the basal part 70 by fixing tools or anchoring tools 71 such as bolts or screws. Each of the scrapers 50 is supported in a form of a cantilever by the basal part 70. Each of the scrapers 50 extends outward in the mixing area 10a to terminate at a position in close proximity to the inner circumferential wall surface of the annular wall 23.

(34) FIGS. 7 and 8 include a transverse cross-sectional view, a vertical cross-sectional view and partially enlarged cross-sectional views showing the positional relation among the shaft 30, the scrapers 50, and the basal part 70.

(35) As shown in FIGS. 7 and 8, the basal part 70 is formed around the lower end portion 31, coaxially about a center axis 10b of the disc 32. An external radius r3 of the basal part 70 is set to be two to three times as large as an external radius r1 of the lower end portion 31 (three to five times as large as a diameter of the shaft 30).

(36) As shown in FIG. 8(B), the height h2 of the basal part 70 is smaller than the height h1 of the mixing area 10a. An upper surface 72 of the basal part 70 defines a horizontal plane spaced apart from a lower surface of the upper plate 21. For instance, in a case where the mixer 10 has the mixing area 10a increased in its volume, the height h1, h2 is increased equally so that the dimension h3 between the upper plate 21 and the upper surface 72 is kept at a constant value. Therefore, the scraper 50 and the upper plate 21 keep their constant positional relation therebetween.

(37) The fixing or anchoring tools 71 for supporting the inner end portion of the scraper 50 are positioned in a pair. As shown in FIG. 7(B), a supporting center 75 of the scraper 50 is positioned between fulcrums defined by the left and right fixing or anchoring tools 71, respectively. A center axis 50a of the scraper 50 passes through the supporting center 75. The axis 50a extends in a tangential direction with respect to an imaginary perfect circle centered at the center axis 10b and having a radius r2. In FIG. 7(B), a normal line of the circle passes through the center axis 10b and the supporting center 75. An angle 1 between the center axis 50a and the normal line is 90 degrees. The angle 1 is not necessarily 90 degrees, but the angle 1 may be set to be, preferably, an angle in a range between 60 degrees and 120 degrees, more preferably, the angle in a range between 75 degrees and 115 degrees. The scraper 50 horizontally extends in a position in close proximity to a lower surface of the upper plate 21. The scraper 50 terminates at a position in close proximity to the inner circumferential wall surface of the annular wall 23.

(38) As shown in FIGS. 8(A) and 8(B), the scraper 50 is supported in the cantilever style by the basal part 7. However, the scraper 50 may be supported in a two-points or a both-ends supporting style by the basal part 7 and a pin 36, as shown in FIG. 8 (C), wherein a distal end portion (a distal end face 59) of the scraper 50 is positionally aligned and connected with the pin 36.

(39) FIG. 9(A) is a cross-sectional view of the scraper 50, FIG. 9(B) is a partial perspective view showing a configuration of the distal end portion of the scraper 50, and FIG. 9(C) is a cross-sectional view showing a modification of the scraper 50.

(40) The scraper 50 has a structure comprising a member 51 formed from a metal and an abrasion-resistant ceramic plate 52 embedded in an upper surface of the member 51. The scraper 50 has a cross-section of an isosceles trapezoid shape, which comprises horizontal upper and lower faces 53, 58, a vertical front and rear faces 54, 55, inclined front and rear faces 56, 57, and the distal end face 59. Inclination angles 2, 3 of the inclined faces 56, 57 with respect to the lower face 58 are substantially the same. The upper face 53 is spaced apart at a very small distance S from the lower surface of the upper plate 21. The distance S is set to be a value in a range from 1 to 5 mm. As shown in FIG. 7(A), the end face 59 is oriented approximately in the same direction as the tangential direction of the inner circumferential wall surface of the annular wall 23. The end face 59 is spaced apart at a distance approximately ranging between 5 and 10 mm, from the inner circumferential wall surface of the annular wall 23. If desired, the lower face 58 and the inclined faces 56, 57 of the scraper 50 may be formed as a curved surface 58 that has a generally semicircular or arcuate profile as shown in FIG. 9(C).

(41) As shown in FIG. 8, a scraper 60 is further provided on a lower surface of the disc 32. The scraper 60 is located in the same position as the position of the scraper 50, as seen in the plan view. A lower face of the scraper 60 is spaced apart from an upper surface of the lower plate 22, at a small distance in a range from 1 to 5 mm.

(42) As shown in FIGS. 5 and 6, a disc 32 has a peripheral edge with a perfect circle profile. Pins 36 are vertically fixed on a peripheral zone of the disc 32. The fluid mixture (slurry) of the powder ingredients P and the mixing water L moves outward on the disc 32 under the centrifugal force, and flows through the slurry discharge port 40 to the hollow connector section 41, as shown in the partially enlarged view of FIG. 5. The pin 36 pushes or energizes such a flow of slurry toward a rotational and outward direction. That is, the pin 36 augments the movement of the slurry flowing through the port 40 to the section 41. The port 40, through which the flow of slurry passes, is provided with a plurality of horizontal guide members 47 that divide an opening of the port 40.

(43) FIG. 10(A) is a perspective view showing a structure of the slurry discharge port 40, and FIG. 10(B) is an enlarged vertical cross-sectional view showing a slit configuration of the port 40. FIG. 10(C) and FIG. 10(D) are a perspective view and an enlarged vertical cross-sectional view showing a modification of the port 40.

(44) As shown in FIG. 10(A), the slurry discharge port 40 is provided with the horizontal guide members 47 vertically spaced apart from each other at a uniform interval. Each of the guide members 47 extends in a circumferential direction of the annular wall 23 over the whole width of the port 40. Both ends of each of the guide members 47 are fixed to portions of the wall 23 located on both sides of the port 40. The port 40 is divided into a plurality of narrow openings. The guide members 47 are strips made of metal or resin, each having a square cross-section as shown in FIG. 10(B). For example, each of the guide members 47 has a thickness in a range from 1 to 5 mm and a depth in a range from 5 to 50 mm, in its cross-section. Horizontal slits 48, each having a height in a range from 4 to 15 mm, are formed to be slurry fluid passages between the guide members 47. Such a slits-configuration of the port 40 acts as an orifice, which imposes the fluid resistance on the slurry flowing through the port 40 to the hollow connector section 41, whereby the slits-configuration functions to ensure a retention time of the slurry in the mixing area 10a. Such a slits-configuration of the guide members 47 and the slits 48 is also provided on each of the fractionation ports 8e, 8f which is a kind of the slurry discharge port.

(45) An open area ratio of the slurry discharge port 40 is set to be, preferably in a range from 50% to 80%, more preferably, in a range from 55% to 75%, wherein the open area ratio of the port 40 is defined by A2/A1, wherein A1 is the total area of the port 40 along the inner circumferential surface of the annular wall, in other words, WT, and wherein A2 is an effective open area of the slit 48, in other words, Wtthe number of slits. In the example as illustrated in the figure, the number of slits is five. Similarly, the open area ratio of the fractionation port 8e, 8f is set to be, preferably in a range from 50% to 80%, more preferably, in a range from 55% to 75%, wherein the open area ratio of the port 8e, 8f is defined by A4/A3, wherein A3 is the total area of the port 8e, 8f along the inner circumferential surface of the annular wall, and wherein A4 is an effective open area of the port 8e, 8f.

(46) Furthermore, the total area A1+A3 of the slurry discharge port 40 and the fractionation ports 8e, 8f is set to be in a range from 2% to 10%, preferably in a range from 3% to 8%, with respect to the total area of the whole circumferential surface of the annular wall 23 (the diameter of the circumferential wall surface3.14the height of the circumferential wall surface).

(47) Alternatively, the horizontal guide member 47 and the horizontal slit 48 may be modified to be a vertical guide member and a vertical slit, or the guide member may be inclined with respect to the fluid direction of the slurry. Furthermore, as shown in FIGS. 10(C) and 10(D), the slurry discharge port 40 and the fractionation ports 8e, 8f may be divided into a large number of narrow openings by guide members 49 arranged in the form of a lattice, whereby narrow fluid passages 48, each having a square cross-section, are formed therein. Also in such a configuration of the port 40, the open area ratio and so forth is preferably set to be as described above.

(48) FIG. 11 includes transverse cross-sectional views of the mixer 10 showing modifications of the positional relation among the rotary shaft 30, the scrapers 50 and the annular basal part 70.

(49) In the mixer 10 as shown in FIG. 11(A), the four scrapers 50 are oriented in directions angularly spaced apart at an angular interval of 90 degrees from each other. In the mixer 10 as shown in FIG. 11(B), the two scrapers are oriented in directions angularly spaced apart at an angular interval of 180 degrees from each other. If necessary, the five or more scrapers 10 may be provided in the mixing area 10a of the mixer 10. If desired, the scrapers 50 may not be spaced at a uniform angular interval, but it is possible to position the scrapers 50 so as to be angularly spaced at unequal angular intervals.

(50) FIG. 12 includes transverse cross-sectional views of the mixer 10, each showing the positional relation between the scrapers 50 and the pins 36.

(51) As shown in each of the figures included in FIG. 12, the scrapers 50 are positioned to be angularly spaced apart from each other, for example, at an angular interval of 120 degrees. The pins 36 are located in positions, preferably, in association with the positions of the scrapers 50. Preferably, the scrapers 50 and the pins 36 are located in rotational symmetry positions with respect to the center axis 10b of the rotary shaft 30, as seen in the plan view. For instance, in the layout of the pins 36 as shown in FIG. 12(A), the pins 36 are positioned in the periphery of the rotary disc 32 so as to be angularly spaced apart from each other at an angular interval a of 120 degrees, in accord with the positions of the scrapers 50. The angular phase of the scrapers 50 and the angular phase of the pins 36 differ from each other by 60 degrees (a/2). On the other hand, in the layouts of the pins 36 as shown in FIGS. 12(B) and 12(C), the pins 36 are positioned in the periphery of the rotary disc 32 so as to be spaced apart from each other at the angular interval b of 40 degrees, or the angular interval c of 30 degrees. The distal end portions of the scrapers 50, which positionally match the pins 36, are supported by the pin 36, as shown in FIG. 8(C). Such a rotational symmetry of the scrapers 50 and the pins 36 prevents pulsation or irregular flow of the slurry from being caused when the slurry flows through the ports 40, 8e, 8f. This is advantageous for stabilization of the discharge flow rate of the slurry.

(52) FIG. 13 is a partially enlarged cross-sectional view showing a modification of the annular basal part 70.

(53) The annular basal part 70 is not necessarily integral with the rotary shaft 30 and the enlarged lower end portion 31, but the part 70 may be formed with an inner circumferential surface 76 spaced apart from an outer circumferential surface of the portion 31. In FIG. 13, an annular gap 77 having a predetermined width (r4r1) is formed between the portion 31 with the external radius r1 and the basal part 70 with the internal radius r4.

(54) The operation of the mixer 10 is described hereinafter.

(55) In operation of the rotary driving device, the rotary disc 32 and the scrapers 50 are rotated in the direction R, and the powder ingredients P and the mixing water L to be mixed in the mixer 10 are fed into the mixer 10 through the powder supply conduit 15 and the water supply conduit 16. The powder ingredients P and the mixing water L, which flow into the mixing area 10a, are agitated and mixed, and are moved radially outward on the rotary disc 32 under the action of the centrifugal force, until reaching the peripheral zone of the disc 32. The scrapers 50, 60 scrape off or remove the slurry adhered to the lower surface of the upper plate 21 and the upper surface of the lower plate 22. The pins 36 scrape off or remove the slurry adhered to the inner circumferential surface of the annular wall 23.

(56) The slurry reaching the peripheral zone of the mixing area 10a is pushed outward and frontward in the rotational direction by the pins 36 and flows through the slurry discharge port 40 to the hollow connector section 41. The foam feeding port 46 of the foam-feeding conduit 45 feeds the slurry with a required quantity of foam or foaming agent M. The slurry including the foam or foaming agent M flows into the slurry delivery tube 42 through the section 41 and is subjected to the rotational power and the shearing force in the tube 42, whereby mixing of the slurry is further progresses. Thereafter, the slurry is delivered onto the widthwise center part of the lower sheet 1 through the slurry outlet tube 7.

(57) The slurry reaching the peripheral zone of the mixing area 10a also flows into the fractionation tubes 8a, 8b through the fractionation ports 8e, 8f. Such slurry is delivered to the edge zones of the lower sheet 1. For instance, the slurry in vicinity to the ports 8e, 8f is delivered to the tubes 8a, 8b without the foam or foaming agent fed to the slurry. Therefore, the slurry fed to the edge zones of the lower sheet 1 has a relatively high specific gravity.

(58) In such an operation of the mixer 10, the scrapers 50 energize the slurry of the mixing area 10a radially outward of the rotary disc 32, so as to cause the slurry to be discharged out of the mixing area through the ports 40, 8e, 8f, in cooperation with the aforementioned action of the pins 36. Since the fluid resistance on each of the ports 40, 8e, 8f is increased by provision of the aforementioned slits-configuration (or, the lattice configuration or the like), the retention time of the slurry in the mixing area 10a is extended. Therefore, the slurry is sufficiently mixed in the mixing area 10a.

(59) FIGS. 14-17 are transverse cross-sectional views generally showing the whole arrangements of the mixer 10, each being provided with the scrapers bent or curved backward in the rotational direction. In each of these figures, the constituents or components, which are substantially the same as those in the aforementioned embodiments, are indicated by the same reference numerals.

(60) The scraper 50 as shown in FIGS. 5-13 extends straight from the annular basal part 70, but the scraper 50 as shown in FIG. 14 has a bending part 80 bent backward in the rotational direction. That is, at the bending part 80, a center axis 50a of the scraper 50 is bent at an angle 4 backward in the rotational directions and extends outward therefrom. The scraper 50 terminates at a position in close proximity to the inner circumferential wall surface of the annular wall 23. The center axis 50a and a radial direction of the mixing area 10a intersect at an angle 5 on the distal end face 59 with each other. Each of the angles 4, 5 is set to be, preferably, an angle in a range of 4515 degrees, more preferably, the angle in a range of 4510 degrees.

(61) The powder supply port of the powder supply conduit 15, which is located on the upper plate 21, is shown as an opening 17 by a dotted line in FIG. 14. As shown in a partially enlarged view of FIG. 14, a center 17a of the opening 17 is spaced apart at a distance (a radius) r5 from the center axis 10b. The innermost end 17b of the opening 17 is spaced apart at a distance (a radius) r6 from the center axis 10b. The bending part 80 is spaced apart at a distance (a radius) r7 from the center axis 10b. Preferably, a position of the bending part 80 is set to be in a region meeting a condition of r5>r7>r6.

(62) The mixer 10 as shown in FIG. 15 has the scrapers 50 bent backward in the rotational direction, at a number of bending parts 80. The centerline 50a of the scraper 50 is bent backward in the rotational direction, at an angle 6 in each of the bending parts 80. The angle 6 is set to be, preferably, an angle in a range of 1510 degrees, more preferably, the angle in a range of 155 degrees. At the distal end portion of the scraper 50, the center axis 50a is directed toward a direction of the angle 5 with respect to the radial direction of the mixing area 10a, wherein the angle 5 is 7510 degrees.

(63) The mixer 10 as shown in FIG. 16 has the scrapers 50 generally curved backward in the rotational direction. Preferably, the centerline 50a is a curve that extends outward from an outer circumferential edge of the annular basal part 70, substantially in a form of involute curve. Also in the scraper 50 as shown in FIG. 15, the center axis 50a bent in a number of the bending parts 80 is, preferably, defined by line segments approximately along an involute curve.

(64) Furthermore, in the mixer 10 as shown in FIGS. 14-16, only one of the distal end portions of the scrapers 50 is positionally matching the pin 36. However, as shown in FIGS. 12(B) and 12(C), it is possible to positionally match all of the distal end portions of the scrapers 50 with the pins 36, thereby supporting all of the distal end portions of the scrapers 50 by the pins 36.

(65) FIG. 17 shows the mixer 10 provided with the rotary disc 32, which has a number of gear tooth portions 37 formed in the peripheral zone of the disc 32, instead of the pins 36. As set forth above, the slurry moving outward on the disc 32 under the centrifugal force flows through the slurry discharge port 40 to the hollow connector section 41, as shown by an arrow in FIG. 17. The gear tooth portions 37 pushes or energizes the flow of slurry toward a rotational and outward direction, in cooperation with the scrapers 50 bent or curved backward in the rotational direction. That is, the gear tooth portions 37 and the scrapers 50 augment the movement of the slurry flowing through the port 40 to the section 41, similarly to the aforementioned action of the pins 36. Therefore, an action similar to the action of the pins 36 augmenting the movement of the slurry can be obtained by such a combination of the gear tooth portions 37 and the scrapers 50.

(66) According to the experiments of the present inventors with respect to the mixer 10 having the aforementioned arrangement, the density distribution and the fluid velocity distribution of the slurry in the mixing area 10a are uniformized in a case where the scrapers 50 bent or curved backward in the rotational direction are used, whereby the slurry can be sufficiently mixed and kneaded in a relatively short period of time. The main reasons for this are considered to be as follows:

(67) (1) In a case of the scraper-type mixer, the dead water region or the slurry staying region is hardly generated in the mixing area 10a, in comparison with the pin-type mixer;

(68) (2) In a case of the bent or curved scraper 50, the dead water region or the slurry staying region is hardly generated behind the scraper 50 (on the side backward in the rotational direction); and

(69) (3) A relatively strong force or pressure directed radially outward of the mixing area 10a is given to the slurry by the scraper 50.

(70) Although the present invention has been described as to the preferred embodiments, the present invention is not limited thereto, but may be carried out in any of various modifications or variations without departing from the scope of the invention as defined in the accompanying claims.

(71) For instance, the annular basal part different from the rotary shaft is formed around its enlarged lower end portion in the aforementioned embodiments, but the annular basal part may be formed by additionally enlarging the diameter of the lower end portion of the rotary shaft.

(72) Furthermore, although the pins are arranged in a single-row along the periphery of the rotary disc in the aforementioned embodiments, the pins may be arranged, for example, in double-rows along the periphery of the rotary disc, wherein the pins are provided to stand in pairs, on the periphery of the rotary disc.

(73) Furthermore, the mixer of the present invention may be used for not only production of gypsum boards, but also production of gypsum based boards, such as glass mat boards, or gypsum based boards with glass fiber nonwoven fabric.

INDUSTRIAL APPLICABILITY

(74) The present invention is applicable to a scraper-type mixer and mixing method in which a plurality of scrapers are arranged in a mixing area. According to the mixer and mixing method of the present invention, the retention time of the gypsum slurry in the mixing area can be increased, whereby the slurry can be sufficiently mixed in the mixing area; or the density distribution and the velocity distribution of the slurry in the mixing area can be uniformized, whereby the slurry can be uniformly mixed and kneaded in the mixing area. Thus, the practically remarkable effects can be obtained from the present invention.

LIST OF REFERENCE NUMERALS

(75) 10 mixer 10a mixing area 10b center axis of rotary disc 15 powder supply conduit 16 water supply conduit 20 housing 21 upper plate 22 lower plate 23 annular wall 30 rotary shaft 31 enlarged lower end portion 32 rotary disc 36 pin 37 gear tooth portion 40 slurry discharge port 41 hollow connector section 47, 49 guide member 48 slit 48 narrow fluid passage 50 scraper 50a center axis of scraper 70 annular basal part 71 fixing tool or anchoring tool 72 upper surface of annular basal part 75 supporting center 80 bending part