Patent Description:
A gypsum board is known in the art as a board having a gypsum core covered with sheets of paper for gypsum board liner, and is widely used in various kinds of buildings as an architectural interior finish material, because of its advantageous fire-resisting or fire-protecting ability, sound insulation performance, workability, cost performance and so on. In general, the gypsum board is produced by a continuous slurry pouring and casting process. This process comprises a mixing step for admixing calcined gypsum, adhesive auxiliary agent, set accelerator, foam (or foaming agent), and other additives, admixtures and so forth, with mixing water in a mixer; a forming step for pouring a calcined gypsum slurry prepared in the mixer (referred to as "gypsum slurry" or "slurry" hereinafter) into a space between sheets of paper for gypsum board liner and forming them to be a continuous belt-like formation having a plate-like configuration; and a drying and cutting step for roughly cutting the solidified continuous belt-like layered formation, drying it forcibly and thereafter, trimming it to have a product size.

A thin type of circular centrifugal mixer is known in the art as the mixer for preparing the gypsum slurry by mixing the calcined gypsum, water and so forth. This type of mixer comprises a flattened circular casing and a rotary disc rotatably positioned in the casing. A plurality of material feeding ports for feeding the above constituent materials into the mixer are disposed in a center region of a top cover or an upper plate of the casing, and a slurry outlet port for delivering a mixture (a slurry) out of the mixer is provided on the periphery of the casing or on a lower plate (bottom cover) thereof. The ingredients to be mixed are supplied onto the rotary disc through the respective feeding ports, and they are mixed while being moved radially outward on the disc under an action of centrifugal force, and then, delivered out of the mixer through the slurry outlet port, which are positioned on the periphery or the lower plate (bottom plate). The mixer with this arrangement is disclosed in, e.g., International Publication of <CIT> (Patent Literature <NUM>).

As regards a method for delivering the slurry prepared in the mixer to the outside of the mixer, the following three kinds of methods are mainly known in the art:.

In general, a quantity of foam or foaming agent is fed to the slurry in the mixer, in order to regulate or adjust the specific gravity of the gypsum board. Proper mixing of the foam or foaming agent with the slurry is considered to be essential for reduction in the weight of the gypsum board. Therefore, in the method for producing gypsum boards in recent years, a technique for properly mixing an appropriate quantity of foam or foaming agent with the slurry is considered to be especially important. As regards reduction in a supply amount of foam or foaming agent and uniform mixing of the slurry and the foam, it is considered that a relation is very important between a method for feeding the foam or foaming agent to the slurry and a method for delivering the slurry (Patent Literatures <NUM> and <NUM>).

For instance, each of International Publications of <CIT> and <CIT> (Patent Literatures <NUM> and <NUM>) discloses a technique intended to attain homogeneous dispersion and distribution of the foam or foaming agent in the slurry with use of a slurry swirling flow in a vertical chute.

The slurry delivered from the mixer in such a method for delivering the slurry is discharged onto an upper surface of the sheet of paper for gypsum board liner through a slurry discharge port of a slurry delivery conduit. The conduit configures, in general, a curved or L-shaped fluid passage. This kind of fluid passage is, in general, called as a "boot(s)", a "discharge boot(s)", or the like. The sheet of paper for gypsum board liner is a continuous belt-like material with a width of about <NUM>, which is continuously conveyed on a production line of a gypsum board production apparatus in a relatively high speed. A bifurcation type or distribution type of boot is known in the art, which has a plurality of slurry discharge ports spaced apart from each other in a widthwise direction of the sheet, in order to pour and spread the slurry uniformly on the sheet throughout the overall width of the sheet. For instance, a "multi-leg discharge boot", which is disclosed in International Publications of <CIT> (<CIT>) (Patent Literature <NUM>), is such a bifurcation type or distribution type of boot having a pair of left and right slurry discharge ports for discharging the slurry prepared by the mixer onto the sheet.

<FIG> includes a plan view and a side elevational view showing a structure of the conventional slurry delivery conduit. <FIG> includes a perspective view and a cross-sectional view taken along line V-V, which show a structure of the slurry delivery conduit as disclosed in Patent Literature <NUM>.

A boot <NUM> as shown in <FIG> has a vertical tube <NUM> generally in a cylindrical form and a pair of left and right slurry delivery tubes <NUM>. A center axis Z-Z of the tube <NUM> is oriented in a vertical direction. The tubes <NUM> are connected to the tube <NUM> at a lower part <NUM> reduced in its diameter. An opening at a terminal end of each of the tubes <NUM> defines a slurry discharge port <NUM> which discharges the slurry as shown by an arrow α. The ports <NUM> discharges the slurry onto an upper surface of the sheet of paper for gypsum board liner <NUM> (illustrated by one dotted chain lines), which runs in a direction of an arrow J. The conveying direction J of the sheet <NUM> is in parallel with the center axis X-X of the production line of the gypsum board production apparatus. Each of the tubes <NUM> is a rectilinear tube, which extends straightly in a direction at an angle θa/<NUM> with respect to the center axis X-X of the production line of the apparatus as seen in the plan view (<FIG>), and which extends straightly and obliquely downward from the lower portion <NUM> as seen in the side elevational view (<FIG>). A divergent angle θa of the tubes <NUM> is set to be, e.g., an angle approximately ranging from <NUM> degrees to <NUM> degrees, and an inclination angle θb of the tubes <NUM> is set to be, e.g., an angle approximately ranging from <NUM> degrees to <NUM> degrees. As shown by the arrows α, the slurry discharge ports <NUM> discharge the slurry bilaterally symmetrically as seen in the plan view, in the directions of the angles θa, θb.

A boot <NUM> as shown in <FIG> has a vertical tube <NUM>, a heel portion <NUM>, a bifurcation part <NUM> and a pair of left and right slurry delivery tubes <NUM>. The center axis Z-Z of the tube <NUM> generally in a cylindrical form is oriented in a vertical direction. The heel portion <NUM> curvedly extends from a lower end portion of the tube <NUM>. The bifurcation part <NUM> is connected to a downstream end of the heel portion <NUM>. The tubes <NUM> are connected to the bifurcation part <NUM>. The bifurcation part <NUM> includes a bifurcating portion <NUM> which splits a slurry current Sa entering into the bifurcation part <NUM> from the heel portion <NUM>. As shown in <FIG>, which is the cross-sectional view taken along line V-V of <FIG>, a wall surface region <NUM> is formed inside of the bifurcating portion <NUM> (inside of a fluid passage). The wall surface region <NUM> is substantially perpendicular to the slurry current Sa. The tube <NUM> is a rectilinear tube, which extends straightly in a direction substantially parallel with the center axis X-X of the production line of the gypsum board production apparatus, as seen in its plan view, and which extends somewhat obliquely downward from the bifurcation part <NUM>, as seen in its side elevational view. As shown by the arrow α, each of the slurry discharge ports <NUM>, which is an opening at a terminal end of each of the tubes <NUM>, discharges the slurry in the direction substantially parallel with the conveying direction J of the sheet <NUM>, as seen in the plan view. Patent Literature <NUM> describes injection into moulds at elevated injection pressure of a mixture containing <NUM> to <NUM> parts by weight of water to <NUM> parts by weight of gypsum anhydrite is filled into moulds. A continuously operating mortar mixing machine is connected at its outlet side to a pressure pump and the pressure pump is connected to a filling nozzle. Patent Literature <NUM> describes an apparatus configured for connection to a mixer for receiving a slurry and altering the flow characteristics of the slurry, wherein the apparatus includes a conduit having a main inlet in slurry receiving communication with the mixer outlet and extending to a spout for discharging the slurry, at least one conduit restrictor associated with the conduit for creating back-pressure between the conduit restrictor and the mixer outlet for keeping the mixer full, and at least one pressure reducer associated with the discharge spout and configured for reducing the pressure of the slurry dispensed from the discharge spout. It discloses also a slurry delivery conduit according to the preamble of claim <NUM>. Patent Literature <NUM> describes a method and apparatus at the point of insertion of aqueous foam into calcined gypsum slurry. An inlet for foam is located closer to the discharge outlet of a slurry mixing chamber than the location of the inlet for calcined gypsum, or the inlet for foam is located in a discharge conduit connected to the discharge outlet of the slurry mixing chamber.

The bifurcation type or distribution type of boot, which discharges the slurry from the left and right slurry discharge ports in a pair, is advantageous for pouring and spreading the slurry on the sheet of paper for gypsum board liner, uniformly over the entire width of the sheet. However, a difference in a flow rate may occur between the slurries discharged through the respective ports, or a difference in the specific gravity may be caused between the slurries discharged through the respective ports. This is considered to be a phenomenon that derives from a directivity of the rotational movement of the slurry in the mixer, a directivity of the slurry outlet port of the mixer, a directivity or behavior of the slurry swirling flow in the chute, and so forth.

If the difference in the specific gravity is caused between the left and right discharge ports, a deviation of distribution, maldistribution or uneven distribution is apt to occur in the widthwise direction of the sheet of paper for gypsum board liner, with respect to the distribution of the specific gravity of the slurry fed on the sheet. This is undesirable for improvement of the product quality of the gypsum board product. Further, if the difference in the flow rate is caused between the discharge ports, a stagnation of the slurry, which results in a partial solidification of the slurry, is apt to occur in one of the delivery tubes with the flow rate being relatively low. This may result in production and adhesion of a gypsum lump, its hardened matter, its solidified matter, or the like in or to the tube. In a case where such a hardened gypsum lump is enlarged and is released onto the sheet, there is a possibility of an interruption of the operation of the production line, owing to paper breakage of the sheet, or a possibility of quality degradation of the gypsum board product or the like. In order to prevent such a problem from being caused, it is desirable to make a countermeasure for eliminating the difference in the flow rate between the ports.

Further, in the conventional structure of the slurry delivery conduit as shown in <FIG>, the slurry flow delivered through each of the slurry discharge ports is directed obliquely outward of the sheet as seen in the plan view, and therefore, a part of the slurry may scatter or spread to the outside of the sheet, owing to the strength of the slurry flow, and such a slurry may be hardened outside of the sheet. This results in necessity of cleaning operation and so forth for removing the hardened gypsum lump adhered to a conveying table, a machine frame and so forth.

Such a phenomenon that the slurry scatters or spreads to the outside of the sheet might be able to be overcome by orienting the delivery tube toward a direction parallel with the center axis of the production line and directing the discharged slurry toward a direction substantially parallel with the conveying direction of the sheet, as in the structure of the slurry delivery conduit shown in <FIG>. In the structure of the slurry delivery conduit shown in <FIG>, however, a wall surface region (indicated by the reference numeral <NUM> in <FIG>) substantially perpendicular to the slurry current is configured inside of the bifurcating portion (in the fluid passage). Since a stagnation of the slurry occurs in the vicinity of this wall surface region, the gypsum lump, its hardened matter, its solidified matter, or the like is apt to be produced in the vicinity of the wall surface region and to be adhered to the wall surface region. As set forth above, if such a hardened gypsum lump is enlarged therein and is released onto the sheet, there is a possibility that the operation of the production line is interrupted owing to the paper breakage of the sheet, or a possibility that quality degradation of the gypsum board product or the like is caused. Therefore, provision of the wall surface region inducing the stagnation of the slurry is undesirable for improvement of productivity and quality of the gypsum board product. Further, the orientation of the slurry delivery tube in the direction parallel with the center axis of the production line results in a reduction of the distance between the left and right slurry discharge ports, and therefore, it becomes difficult to pour and spread the slurry uniformly throughout the width of the sheet. This impairs the advantages of the bifurcation type or distribution type of slurry delivery conduit.

An object of the present invention is to provide a slurry delivery conduit of a mixer and a slurry delivery method arranged to divide a current of a gypsum slurry prepared by the mixer and to discharge the slurry streams through a plurality of slurry discharge ports onto a sheet of paper for gypsum board liner, which can prevent the differences in the flow rate and the specific gravity of the slurry from occurring between the discharge ports, which can smoothly divide the slurry current without provision of an intratubular vertical wall surface region and so forth inducing a stagnation of the slurry in a branch part of the conduit, and also, which can ensure a sufficient distance between the discharge ports.

Another object of the present invention is to reduce a frequency of occurrence of scattering or spreading of the gypsum slurry to the outside of the sheet, or to prevent such a phenomenon from occurring.

The present invention provides a slurry delivery conduit for a mixer of a gypsum board production apparatus, wherein the mixer has a mixing area for mixing of a gypsum slurry to be fed onto a continuously conveyed sheet of paper for gypsum board liner and wherein the slurry delivery conduit configures a curved or L-shaped fluid passage, which is arranged to discharge the slurry introduced from a mixing area of the mixer, onto said sheet through slurry discharge ports of the slurry delivery conduit, comprising:.

The present invention also provides a slurry delivery method in which a gypsum slurry is introduced into the slurry delivery conduit from a mixing area of a mixer for mixing of the gypsum slurry, the slurry delivery conduit configuring a curved or L-shaped fluid passage, and the gypsum slurry is discharged through slurry discharge ports of the slurry delivery conduit onto a continuously conveyed sheet of paper for gypsum board liner, so that the slurry is continuously poured and spread on the sheet, comprising:.

According to the arrangement of the present invention as set forth above, the slurry is introduced from the mixing area into the rectilinear tube segment for providing an axial or rectilinear current of the slurry, whereby the slurry flow is rectified therein. The branch part splits the axial or rectilinear current smoothly by a fluid passage in a form of V-letter. This fluid passage is configured by the tube wall portions of the adjacent branch tube segments, which join with each other to configure a transverse or horizontal cross-section in the form of V-letter. The resultant branched streams of the slurry, which move in directions divergent on the downstream side in the conveying direction of the sheet, are discharged from the slurry discharge ports of the branch tube segments, respectively. The distance between the slurry discharge ports can be desirably ensured by an appropriate setting of the joining angle of the branch tube segments. The branch part, which splits the axial or rectilinear current by the fluid passage in the form of V-letter, is not provided with a vertical wall surface region and so forth which may induce the stagnation of the slurry, and therefore, the production or adhesion of the gypsum lump, its hardened matter, its solidified matter, or the like, is surely avoidable.

Further, the slurry delivery conduit with the aforementioned arrangement is adapted to divide the slurry current at the branch part, after the slurry flow introduced from the mixing area is rectified in the rectilinear fluid passage of the rectilinear tube segment so as to be the axial or rectilinear current. The rectilinear tube segment, which rectifies the slurry flow in such a manner, acts as a buffer zone or buffer area, which at least partially eliminates or cancels a downstream sustainable or continuable effect of the rotational motion or behavior of the slurry generated on the upstream side of the slurry delivery conduit, or which prevents such an effect on the upstream fluid passage from being regenerated in the slurry delivery conduit. Thus, according to the structure of the slurry delivery conduit and the delivery method as set forth above, the differences in the flow rate and the specific gravity of the slurry can be prevented from occurring between the slurry discharge ports.

Preferably, the rectilinear tube segment has a fluid passage length in a range from <NUM> to <NUM>, and a tube-wall joint portion of the branch tube segments in the form of V-letter configures a counter-flow splitting or dividing element in an intratubular area of the branch part. A tapering point of the splitting or dividing element is directed against the axial or rectilinear current in the rectilinear tube segment so as to be oppositely faced against the current. If the fluid passage length of the rectilinear tube segment is set to be equal to or smaller than <NUM>, it is difficult to ensure a sufficient effect of the rectilinear tube segment which prevents the flow rate and the specific gravity of the slurry from differing between the slurry discharge ports. Therefore, it is preferable to increase the fluid passage length so as to avoid occurrence of the differences in the flow rate and the specific gravity between the ports. On the other hand, if the length of fluid passage is set to be excessively increased, the gypsum lump, its hardened matter, its solidified matter, or the like is apt to be adhered to the inside surface of the rectilinear tube segment, and also, it becomes difficult to preferably ensure the structural stability of support for the delivery conduit. Therefore, it is preferable that the fluid passage length of the rectilinear tube segment is set to be equal to or smaller than <NUM>, as set forth above.

More preferably, centers of the slurry discharge ports adjacent to each other are spaced apart from each other, at a distance of at least <NUM> in a widthwise direction of the sheet. In general, the width of the sheet is about <NUM>, and such spacing of the ports allows the slurry to be poured and spread on the sheet, substantially uniformly.

In a preferred embodiment of the present invention, the center axis of the rectilinear tube segment is oriented in a direction substantially parallel with the conveying direction as seen in the plan view, and the branch tube segments are positioned bilaterally symmetrically with respect to the center axis. The term reading "substantially parallel" means that the direction may not be necessarily parallel strictly, but an error of plus or minus <NUM> degrees or so, or an error of plus or minus <NUM> degrees or so is permissible. Each of the branch tube segments has a discharge tube portion at its terminal end part, wherein the discharge tube portion extends, while bending widthwise inward of the sheet. Each of the discharge tube portions has the slurry discharge port, which is directed to deliver the slurry in a direction substantially parallel with the conveying direction as seen in the plan view. According to such an arrangement, the slurry can be discharged from the slurry discharge port onto the sheet in a direction substantially parallel with the conveying direction of the sheet as seen in the plan view, and therefore, the frequency of occurrence of scattering or spreading of the slurry to the outside of the sheet can be reduced, or such a phenomenon can be prevented from occurring.

Preferably, the slurry delivery conduit is provided with a supporting mechanism for supporting the branch tube segment or the discharge tube portion. This supporting mechanism comprises an annular member entirely enclosing an outer circumferential surface of the discharge tube portion or the branch tube segment, a suspending device for suspending the annular member, and a supporting device which is positioned in an area above the discharge tube portion or the branch tube segment and which supports an upper part of the suspending device. The suspending device is integral with the annular member, so that an angular position of the annular member is changed, depending on a rotational position of the suspending device. The supporting device rotatably supports the suspending device. As a slurry discharge direction of the slurry discharge port is changed in accordance with the angular position of the annular member in relation to the rotation of the suspending device, the slurry discharge direction of the port can be changed or adjusted by changing the angular position of the annular member.

More preferably, a vibration transmission member is integrally connected to the annular member, and a vibration element of a vibrator is connected to the vibration transmission member. A vibration of the vibration element transmits to the discharge tube portion through the vibration transmission member and the annular member.

Preferably, the slurry delivery conduit is provided with a tube-wall pushing mechanism or member which presses a tube wall of the vertical tube or the rectilinear tube segment so as to locally deform an intratubular fluid passage of the vertical tube or the rectilinear tube segment. The tube-wall pushing mechanism or member locally presses the tube wall of the intratubular fluid passage of the vertical tube or the rectilinear tube segment, so as to locally change a cross-section of the fluid passage of the vertical tube or the rectilinear tube segment. Since the deformation of the tube wall causes the cross-section of the fluid passage to be locally reduced, a velocity distribution of the slurry varies, or a stagnation zone, which may be locally caused in the slurry delivery conduit, disappears due to the change of the cross-section of the fluid passage. Therefore, according to the slurry delivery conduit with such a tube-wall pushing mechanism or member, the fluid flow characteristics or the velocity distribution of the slurry in the slurry delivery conduit can be improved for effective mixing of the slurry, or the stagnation zone of the slurry can be prevented from occurring, owing to the local deformation or transformation of the cross-section of the fluid passage. Thus, the lump of the gypsum slurry, its hardened matter, its solidified matter, or the like can be prevented from being generated or adhered in or to the slurry delivery conduit.

In a preferred embodiment of the present invention, the slurry delivery conduit is a piping element with a bifurcate or Y-letter form, which has a configuration and structure bilaterally symmetric with respect to a center axis of the gypsum board production apparatus, and the left and right slurry discharge ports in a pair are disposed in positions bilaterally symmetric with respect to the center axis of the gypsum board production apparatus, wherein the flow rates of the ports are set to be equal to each other. If desired, the diameters of the left and right branch tube segments may be varied to differ from each other so that the flow rates of the respective discharge ports are set to be the flow rates different from each other. Further, in spite of an initial setting such that the flow rates of the ports are equal to each other, there may be caused a phenomenon in that the flow rates of the left and right ports differ from each other, owing to an influence of the rotational motion of the slurry on the upstream side of the conduit and so forth. In such a case, the diameters of the left and right branch tube segments may be set to be different from each other, for adjusting the flow rates of the ports to be equal to each other.

From another aspect of the invention, the present invention provides a gypsum board production apparatus comprising the slurry delivery conduit with the arrangement as set forth above.

From yet another aspect of the invention, the present invention provides a method for producing a gypsum board with use of the slurry delivery method arranged as set forth above.

According to the present invention, a slurry delivery conduit of a mixer and a slurry delivery method can be provided, which are arranged to divide a current of a gypsum slurry prepared by the mixer and to discharge the slurry through a plurality of slurry discharge ports onto a sheet of paper for gypsum board liner, wherein the differences in the flow rate and the specific gravity of the slurry can be prevented from occurring between the discharge ports, the slurry current can be smoothly divided without provision of a vertical wall surface region and so forth inducing a stagnation of the slurry inside of the bifurcation part of the conduit, and also, a sufficient distance can be ensured between the discharge ports.

Further, according to the present invention with the arrangement, which allows the gypsum slurry to be discharged through the slurry discharge ports in a direction substantially parallel with the conveying direction of the sheet of paper for gypsum board liner as seen in the plan view, the frequency of occurrence of scattering or spreading of the gypsum slurry to the outside of the sheet can be reduced, or such a phenomenon can be prevented from occurring.

With reference to the attached drawings, preferred embodiments of the present invention are described in detail hereinafter.

<FIG> is an explanatory process diagram partially and schematically illustrating a forming process of a gypsum board. <FIG> is a partial plan view schematically illustrating an arrangement of a gypsum board production apparatus, and <FIG> are a plan view and a transverse cross-sectional view, each illustrating a structure of a mixer. <FIG> is a fragmentary sectional perspective view showing an internal structure of the mixer and a structure of a slurry delivery conduit. In <FIG>, the structure of the slurry delivery conduit is depicted, which discharges a slurry to a widthwise center area (a core zone) of a lower sheet of paper. Depictions of fractionation conduits and their slurry discharge ports, which discharge the slurry to widthwise end portions (edge zones) of the lower sheet, are omitted from <FIG>.

As shown in <FIG> and <FIG>, a gypsum board production apparatus is provided with a conveyor device, which conveys a lower sheet of paper <NUM> in a direction of an arrow J. The lower sheet <NUM> is a sheet of paper for gypsum board liner. The lower sheet <NUM> is conveyed along a manufacturing line. A mixer <NUM> is located in a predetermined position in relation to a conveying line. In this embodiment, the mixer <NUM> is positioned in an area immediately above a conveying table T, in line with a center axis X-X of the gypsum board production apparatus. Liquid (water) W and powder ingredients P, such as calcined gypsum, adhesive agent, set accelerator, additives, admixtures, and so forth, are fed to the mixer <NUM>. The mixer <NUM> mixes these constituent materials. The mixer <NUM> feeds the resultant slurry (a calcined gypsum slurry) <NUM> (3a) onto the lower sheet <NUM> through a slurry delivery section <NUM> and a slurry delivery conduit <NUM>, and feeds the slurry <NUM> (3b) onto the lower sheet <NUM> through fractionation conduits <NUM> (7a, 7a). The slurry delivery section <NUM> is so arranged that the slurry effluent from a peripheral zone of the mixer <NUM> is introduced into the slurry delivery conduit <NUM>. The slurry delivery conduit <NUM> is so positioned as to deliver the slurry <NUM> (3a) from the section <NUM> to the widthwise center zone (the core zone) of the lower sheet <NUM> through each of slurry discharge ports <NUM> (referred to as "discharge ports <NUM>" hereinafter). Piping of the fractionation conduits 7a, 7b is so arranged that the slurry <NUM> (3b) effluent from the peripheral zone of the mixer <NUM> is delivered to the widthwise end portions (the edge zones) of the lower sheet <NUM> through left and right slurry discharge ports <NUM>.

The lower sheet <NUM> is conveyed together with the slurry <NUM> (3a, 3b) to reach forming rollers <NUM> (8a, 8b). An upper sheet of paper <NUM> travels partially around a periphery of the upper roller 8a to be redirected toward a conveying direction. The redirected upper sheet <NUM> is brought into contact with the slurry <NUM> on the lower sheet <NUM> and transferred in the conveying direction substantially in parallel with the lower sheet <NUM>. A continuous belt-like three-layered formation <NUM> constituted from the sheets <NUM>,<NUM> and the slurry <NUM> is configured on a downstream side of the rollers <NUM>. The continuous belt-like formation <NUM> runs continuously at a conveyance velocity V while a setting reaction of the slurry proceeds, until it reaches roughly cutting rollers <NUM> (9a, 9b). If desired, a variety of forming methods, such as a forming method with use of an extruder or a forming gate with a rectangular opening for a path of materials, may be employed, instead of the forming method with use of the forming rollers <NUM>.

The cutting rollers <NUM> cut the continuous belt-like layered formation into boards, each having a predetermined length, whereby plates, each having a gypsum core covered with the sheets of paper for gypsum board liner, i.e., green boards for gypsum boards are produced. The green boards are conveyed toward the direction as shown by the arrow J, and are passed through a dryer (not shown) to be subjected to a forced drying process in the dryer, and thereafter, they are trimmed to be board products, each having a predetermined product length, and thus, gypsum board products are produced.

As shown in <FIG> and <FIG>, the mixer <NUM> in this embodiment is a pin-type mixer which has a flattened cylindrical housing or casing <NUM> (referred to as "casing <NUM>" hereinafter). An internal mixing area <NUM> for mixing the powder ingredients P and the liquid (water) W is defined in the casing <NUM>. A lower end portion of a vertical rotary shaft <NUM> extends through a center part of an upper plate of the casing <NUM>. An upper end portion (not shown) of the shaft <NUM> is connected with a rotary driving device, such as an electric motor (not shown), and is rotated in a predetermined rotational direction (a clockwise direction γ as seen in its plan view, in this embodiment).

A powder supply conduit PP for supply of the powder ingredients P to be mixed is connected to an upper plate of the casing, and a water supply conduit WP for supply of the mixing water W is also connected to the upper plate of the casing. On an opposite side of the slurry delivery section <NUM>, fractionation ports <NUM> (7c, 7d) are provided on an annular wall <NUM> of the casing <NUM>. The fractionation conduits 7a, 7b are connected to the ports 7c, 7d on the wall <NUM>, respectively.

As shown in <FIG>, a slurry outlet port <NUM> of the slurry delivery section <NUM> is positioned on the annular wall <NUM>. A foam feeding conduit <NUM>, which feeds a foam M to the slurry for adjustment of the specific gravity of the slurry, is connected to a hollow connector segment <NUM> of the section <NUM>. A foam feeding port of the conduit <NUM> opens on an internal wall surface of the connector segment <NUM>.

As shown in <FIG>, a rotary disc <NUM> is rotatably positioned in the casing <NUM>. A center part of the disc <NUM> is fixedly secured to an enlarged lower end portion of the shaft <NUM>, and is rotated with rotation of the shaft <NUM> in a direction as indicated by the arrow γ (the clockwise direction). A number of gear tooth portions <NUM> are formed in a peripheral zone of the disc <NUM>. A number of lower pins (movable pins) <NUM> are arranged on upper surfaces of the disc <NUM> and the gear tooth portions <NUM>. A number of upper pins (stationary pins) <NUM> are fixed to an upper plate of the casing to depend therefrom in the internal mixing area <NUM>. The upper and lower pins <NUM>, <NUM> are alternately arranged in a radial direction of the disc <NUM>, and during a rotational operation of the disc, the pins <NUM>, <NUM> make relative motions so as to mix the raw materials fed into the casing <NUM> for production of the gypsum boards. Each of the gear tooth portions <NUM> presses or energizes the mixed fluid (i.e., the slurry) in a rotational and radially outward direction of the disc <NUM>.

When the gypsum boards are to be produced, the rotary driving device (not shown) of the mixer <NUM> is operated to rotate the disc <NUM> in the direction of the arrow γ, and the ingredients (powder materials) P and the mixing water W to be mixed in the mixer <NUM> are fed into the mixer <NUM> through the conduits PP, WP. The powder ingredients P and the mixing water W are mixed in the mixing area <NUM> of the mixer <NUM>, while moving radially outward on the disc <NUM> under an action of centrifugal force and moving in a circumferential direction in the peripheral zone.

A part of the slurry produced in the mixing area <NUM> is discharged through the conduits 7a, 7b onto the edge zones of the lower sheet <NUM>, but most of the slurry produced in the mixing area <NUM> flows out through the slurry outlet port <NUM> to the hollow connector segment <NUM>. A predetermined quantity of foam is fed to the slurry by the foam feeding port of the foam feeding conduit <NUM>, and the slurry fed with the foam flows into a vertical cylindrical chute <NUM> of the slurry delivery section <NUM>.

The slurry and the foam entering the chute <NUM> turn around a center axis of the chute <NUM>, so that the slurry swirls along an inside circumferential wall surface of the chute <NUM>. Owing to the turning or swirling motion of the slurry in the chute <NUM>, the slurry and the foam are subjected to a shearing force, whereby they are mixed with each other, so that the foam is uniformly dispersed in the slurry. The slurry mixed with the foam in the chute <NUM> is discharged onto the lower sheet <NUM> through the slurry delivery conduit <NUM> (referred as "delivery conduit <NUM>" hereinafter) connected to a lower end of the chute <NUM>. As regards the structure of the chute <NUM>, it is described in detail in <CIT> (Patent Literature <NUM>) which is an international publication of a PCT application filed by the same applicant, and therefore, a further detailed explanation thereof is omitted by referring to this PCT pamphlet.

As shown in <FIG>, a vertical tube <NUM> of the delivery conduit <NUM> is concentrically and integrally connected to a lower side of the chute <NUM>. A rectilinear tube segment <NUM> of a Y-tube <NUM> is integrally connected to an outer circumferential surface of a lower end portion of the vertical tube <NUM>. As a whole, the Y-tube <NUM> has a bifurcate form or Y-letter configuration. The rectilinear tube segment <NUM> extends along the center axis X-X and bifurcates into a pair of left and right branch tube segments <NUM> branched by a bifurcation part <NUM>. A set of the tube segments <NUM> extends in the direction of the arrow J, while diverging as a whole. Each of the tube segments <NUM> includes a discharge tube portion <NUM> at its terminal end part. Each of the discharge tube portions <NUM> is bent toward a direction substantially parallel with the center axis X-X, and is provided with the discharge port <NUM>. In general, the delivery conduit <NUM> is a component of the gypsum board production apparatus, which can be called as a "boot", "discharge boot", "multi-leg boot", "bifurcate boot", and so forth. The delivery conduit <NUM> can be also expressed as a "chute" simply, since it may be deemed as a part of the vertical chute <NUM>.

<FIG> is a perspective view illustrating a structure of the delivery conduit <NUM>. <FIG> and <FIG> include a plan view, a side elevational view and cross-sectional views taken along lines I-I, II-II, III-III and IV-IV respectively, which illustrate a structure of the vertical tube <NUM> and a structure of the Y-tube <NUM>. <FIG> includes vertical and horizontal cross-sectional views showing a structure for supporting the Y-tube <NUM>. With reference to <FIG>, the arrangement of the delivery conduit <NUM> is further explained hereinafter. Depictions of the fractionation conduits 7a, 7b and the slurry discharge ports <NUM> for discharging the slurry to the widthwise end portions (the edge zones) of the lower sheet <NUM> are omitted from <FIG>.

As shown in <FIG>, the vertical tube <NUM> is a piping element which is closed at its lower end portion by a horizontal bottom plate 12a and which has a cross-section in a form of a perfect circle. The tube <NUM> configures a vertical fluid passage having an equal or equivalent diameter (inner diameter) D1 as a whole. A vertically extending center axis Z-Z of the tube <NUM> is identical with a center axis of the vertical chute <NUM>. The diameter D1 is set to be, for instance, a dimension in a range from <NUM> to <NUM>. The intratubular fluid passage of the tube <NUM> is in fluid communication with an intratubular area of the chute <NUM>. The tube <NUM>, as well as the chute <NUM>, may have the center axis Z-Z somewhat inclined with respect to the vertical direction.

As shown in <FIG>, an upstream end of the rectilinear tube segment <NUM> of the Y-tube <NUM> is connected to an outer circumferential surface of a lower end portion of the vertical tube <NUM>. An intratubular fluid passage of the Y-tube <NUM> is in fluid communication with the intratubular fluid passage of the vertical tube <NUM>. The Y-tube <NUM> is inclined downward at an angle θ1 as a whole, wherein the angle θ1 is set to be, for instance, an angle ranging from <NUM> degrees to <NUM> degrees. The rectilinear tube segment <NUM> is a piping element having a fluid passage with a uniform cross-section in a form of a perfect circle. A diameter (inner diameter) D2 of the intratubular fluid passage of the rectilinear tube segment <NUM> is set to be a dimension in a range from <NUM> to <NUM>. The fluid passage length or tube length L1 of the tube segment <NUM> is set to be a dimension in a range from <NUM> to <NUM>.

The rectilinear tube segment <NUM> is bifurcated into the left and right branch tube segments <NUM> in a pair, by the bifurcation part <NUM>. The bifurcation part <NUM> bifurcates the fluid passage bilaterally symmetrically with respect to the center axis X-X. The branch angle θ2 of the branch tube segments <NUM> at the bifurcation part <NUM> is set to be an angle in a range from <NUM> degrees to <NUM> degrees, preferably in a range from <NUM> degrees to <NUM> degrees. The discharge tube portion <NUM> is in continuation with the branch tube segment <NUM> by a bending portion <NUM>, which is bent substantially toward a direction of the center axis X-X. Circular openings at terminal ends of the discharge tube portions <NUM> open toward the conveying direction of the lower sheet <NUM> (the direction of the arrow J), in a position slightly spaced upward from the lower sheet <NUM>, thereby forming the left and right discharge ports <NUM> in a pair. A distance L4 between the ports <NUM> is set to be a dimension in a range from <NUM> to <NUM>.

A diameter (internal diameter) D3 of the intratubular fluid passage in each of the branch tube segments <NUM> and the discharge tube portion <NUM> is set to be a dimension in a range from <NUM> to <NUM>. The internal diameter of each of the discharge ports <NUM> is the same as the diameter D3. A length L2 of the fluid passage of the branch tube segment <NUM> is set to be a dimension in a range from <NUM> to <NUM>, and a length L3 of the fluid passage of the discharge tube portion <NUM> is set to be a dimension in a range from <NUM> to <NUM>.

Each of the vertical tube <NUM> and the Y-tube <NUM> has integrally assembled structure of piping elements, or an integrally assembled structure of piping elements, plates and so forth, wherein the piping elements, plates and so forth made of a flexible material, such as rubber, elastomer or synthetic resin, have been appropriately cut and fabricated, and then, integrally combined by a jointing method, such as adhesive bonding, fusion bonding or welding. Each of the angles θ1, θ2 has been preset by combining the piping elements with each other in a suitable relative angle, and a difference (D2-D3) between the diameters of the tubes <NUM>, <NUM> has been compensated with the structure and configuration of the bifurcation part <NUM>.

As shown in <FIG>, the left and right branch tube segments <NUM> extend from the bifurcation part <NUM> on the downstream side in the conveying direction of the lower sheet, in such a manner that the branch tube segments <NUM> diverge in a form of V-letter. Tube walls 16a of the branch tube segments <NUM> join with each other at a joint portion <NUM> and join with the bifurcation part <NUM> along joint lines <NUM>. As shown in <FIG>, the left and right tube walls 16a joining at the angle θ2 in the joint portion <NUM> configure a bifurcating fluid passage having a cross-section in a form of V-letter, in an intratubular area of the bifurcation part <NUM>. The tube walls 16a also form a counter-current splitting or dividing element <NUM> (referred to as "splitting element <NUM>" hereinafter) on the intratubular side of the joint portion <NUM>. The splitting element <NUM> has a horizontal or transverse cross-section in a form of V-letter. A tapering point of the splitting element <NUM> positioned on the center axis X-X is directed to be oppositely faced against a slurry main axial current or a slurry rectilinear current S (referred to as "slurry main axial current S" hereinafter) in the rectilinear tube segment <NUM>. The slurry main axial current S is spit or divided into bilaterally symmetrically branched slurry streams S1, S2 by the splitting element <NUM>. Each of the slurry streams S1, S2 is discharged onto the lower sheet <NUM> through each of the left and right discharge ports <NUM>, as set forth above.

The splitting element <NUM> is not provided with a vertical wall surface or the like, which might, otherwise, result in occurrence of a stagnation of the gypsum slurry, and therefore, a lump of the gypsum slurry, its hardened matter, its solidified matter, or the like can be surely prevented from being produced therein. Furthermore, the gypsum slurry introduced from the vertical chute <NUM> into the vertical tube <NUM> is rectified so as to be an axial current or a rectilinear current, in a rectilinear fluid passage of the rectilinear tube segment <NUM>, and thereafter, the current is divided into streams at the bifurcation part. An effect of a rotational motion of the gypsum slurry and so forth, which occurs in the mixing area <NUM>, the vertical chute <NUM> and so forth, is substantially eliminated or cancelled in the rectilinear fluid passage of the rectilinear tube segment <NUM>. Therefore, a substantial difference in the flow rate between the slurry streams S1, S2 can be prevented from occurring significantly. Also, the specific gravities of the gypsum slurries discharged from the slurry discharge ports <NUM> onto the lower sheet <NUM> can be prevented from being substantially different from each other between these ports <NUM>.

Furthermore, each of the branch tube segments <NUM> is arranged in continuation to the discharge tube portion <NUM> through the bending portion <NUM> (<FIG>) , and a terminal end opening of the tube segment <NUM>, i.e., the discharge port <NUM> opens toward the conveying direction of the lower sheet <NUM> (the direction of the arrow J). Therefore, a phenomenon that results in scattering or spreading of the gypsum slurry out of the lower sheet <NUM> is hardly caused.

As an experiment for testing an effect of the present invention, the present inventors, et al. carried out a test for researching a relationship between the flow passage length L1 of the rectilinear tube segment <NUM> and the difference in the specific gravity, wherein the latter is the difference in the specific gravity which occurs between the slurries discharged from the respective discharge ports <NUM>. The relationship between the length L1 and the difference in the specific gravity obtained from the test is shown in the table below, wherein "<NUM>" means that the difference in the specific gravity was undetectable.

In general, it is preferable that the difference in the specific gravity is equal to or smaller than <NUM>, and therefore, the length of fluid passage L1 is preferably set to be equal to or greater than <NUM>.

As regards the phenomenon that results in scattering or spreading of the gypsum slurry to an outside area of the lower sheet <NUM>, the present inventors, et al. also carried out a test for comparing the Y-tube <NUM> according to the present embodiment and a comparative example of the Y-tube. In the test, the prepared Y-tube <NUM> of the present embodiment is provided with the discharge tube portions <NUM> which is formed by bending terminal end parts of the branch tube segments <NUM> at the bending portions <NUM>, whereas the prepared Y-tube of the comparative example has terminal end parts of the branch tube segments <NUM> straightly extending in continuation to the discharge tube portions <NUM> without bending the terminal end parts by such bending portions.

In a case where the gypsum board production machine is installed with the Y-tube <NUM> according to the present embodiment, the frequency of cleaning operations for removing the scattering or spreading gypsum slurry on the conveying table T and so forth was two times per eight hours. On the other hand, in a case where the gypsum board production machine is installed with the Y-tube of the comparative example, the frequency of cleaning operations for removing the scattering or spreading gypsum slurry on the conveying table T and so forth was twelve times per eight hours. Thus, it has been confirmed that the arrangement, in which the terminal end parts of the branch tube segments <NUM> are bent by the bending portions <NUM> so as to redirect each of the slurry discharge ports <NUM> toward a direction parallel with the conveying direction J, is an effective countermeasure for reducing the frequency of the phenomenon that results in scattering or spreading of the gypsum slurry to the outside area of the lower sheet <NUM>, or preventing such a phenomenon from occurring.

As shown in <FIG>, a bracket assembly <NUM> and a set of support assemblies <NUM> for positioning and supporting the Y-tube <NUM> in a preset position is provided in an area above the Y-tube <NUM>. The bracket assembly <NUM> comprises a base part <NUM> fixed to the vertical chute <NUM>, an L-shaped supporting element <NUM> supported by the base part <NUM>, and a supporting plate <NUM> horizontally protruding from the element <NUM> in a direction of the arrow J. The base part <NUM> may be fixed to the casing <NUM> or a frame (not shown) of the gypsum board production apparatus for supporting the casing <NUM>. The left and right support assemblies <NUM> in a pair are fixed to the plate <NUM> at their proximal ends, respectively. The part <NUM>, the element <NUM> and the plate <NUM> are metal components, such as components made of stainless steel.

The support assemblies <NUM> are provided with a pair of left and right supporting elements <NUM>, each being in a form of a rail; fully-threaded bolts <NUM>; tube support elements <NUM>, each being in an annular form; and vibration transmission plates <NUM>. The assemblies <NUM> constitute a supporting mechanism for the discharge tube portions <NUM>. Each of the supporting elements <NUM> is fixed to the supporting plate <NUM> by a nut and bolt assembly <NUM>. The fully-threaded bolt <NUM> is suspended by the supporting element <NUM>. Each of the tube support elements <NUM> is positioned at a lower end portion of each of the fully-threaded bolts <NUM>. Each of the vibration transmission plates <NUM> is integral with each of the tube support elements <NUM>. The discharge tube portion <NUM> extends through the tube support element <NUM>. A tube wall of the discharge tube portion <NUM> fits in the element <NUM> with a buffer material (not shown) being provided on an inside circumferential wall of the element <NUM>. A vibrator <NUM> is attached to each of the left and right plates <NUM>. A compressed air supply conduit <NUM> is connected to each of the vibrators <NUM>. A compressed air discharge conduit <NUM> for discharging the compressed air is also connected to each of the vibrators <NUM>. The conduit <NUM> is connected to a compressed air supply source, such as an air compressor (not shown).

The supporting element <NUM> has a slit, slot or elongated opening 41a (referred to as "slit 41a" hereinafter), which is positioned immediately above a center line of the tube segment of the Y-tube <NUM>. As shown in <FIG>, an upper end portion of the fully-threaded bolt <NUM> (referred to as "bolt <NUM>" hereinafter) extends through the slit 41a. Nuts 49a, 49b are screwed on the bolt <NUM> on upper and lower sides of the supporting element <NUM> respectively. The nuts 49a, 49b can be tightened to upper and lower surfaces of the supporting element <NUM>, with each of washers 49c, 49d being interposed between the upper or lower surface and the nut, whereby the upper end portion of the bolt <NUM> can be fixedly secured to the supporting element <NUM>.

The bolt <NUM> depends from the supporting element <NUM> to be integrally connected to a long nut 45a of the vibration transmission plate <NUM>. A body 45b of the plate <NUM> is integral with the tube support element <NUM>. A vibration is transmitted from a vibration element of the vibrator <NUM> (illustrated by one dotted chain lines) to the element <NUM> by the plate <NUM>, and then, the vibration is transmitted from the element <NUM> to the slurry in the intratubular fluid passage through the discharge tube portion <NUM>.

When the nuts 49a, 49b are loosened and the bolt <NUM> is turned as shown by the arrow η in <FIG>, the direction of the discharge port <NUM> is changed laterally of the lower sheet <NUM> as shown by the arrow λ in <FIG>. Therefore, the nuts 49a, 49b are slightly loosened and the bolt <NUM> is turned in a desired direction, and then, the nuts 49a, 49b are tightened again, whereby a direction α of the slurry discharged from the discharge port <NUM> can be finely adjusted laterally of the lower sheet <NUM>.

<FIG> includes side elevational views of the slurry delivery conduits, each showing a modification of the delivery conduit <NUM>.

The delivery conduit <NUM> as shown in <FIG> has the vertical tube <NUM> with a lower part 12b reduced in its diameter, and the rectilinear tube segment <NUM> of the Y-tube <NUM> is connected to the part 12b. The vertical tube <NUM> of the delivery conduit <NUM> as shown in <FIG> has the vertical conduit <NUM> with a gently curved lower part 12c. The part 12c is gradually reduced in its diameter and is in continuation with the rectilinear tube segment <NUM> of the Y-tube <NUM>. The vertical tube <NUM> of the delivery conduit <NUM> as shown in <FIG> has a lower part 12d reduced in its diameter, similarly to the vertical tube <NUM> as shown in <FIG>, but the part 12d further includes inclined portions 12e, 12f which are so inclined as to deflect the gypsum slurry flowing down in the tube <NUM>, toward the side of the rectilinear tube segment <NUM>.

<FIG> is a side elevational view partially showing the delivery conduit <NUM>, wherein the delivery conduit <NUM> is provided with a mechanism or member for pushing the tube wall (referred to as "tube-wall pushing device" hereinafter), which locally deforms the tube wall of the vertical tube <NUM> or the Y-tube <NUM>.

The delivery conduit <NUM> as shown in <FIG> is provided with the tube-wall pushing device <NUM> which presses the tube wall of the vertical tube <NUM> inward of its fluid passage. A part of the tube wall of the tube <NUM> located on the side opposite to the rectilinear tube segment <NUM> is pressed in a direction of an arrow F by a pressing part 81a of the device <NUM>, so that the intratubular fluid passage of the tube <NUM> is deformed. The pressing part 81a is connected to an actuator 81b of a driving device which applies an external force to the pressing part 81a. As shown in <FIG>, the delivery conduit <NUM> may be provided with a tube-wall pushing device <NUM> which pushes the tube wall of the rectilinear tube segment <NUM> inward of the fluid passage (in a direction of the arrow F). In a state depicted in <FIG>, an underside of the delivery conduit <NUM> is pushed upwardly by the device <NUM>. However, a lateral or upper side of the delivery conduit <NUM> may be pushed laterally or downwardly by the device <NUM>.

The delivery conduit <NUM> as shown in each of <FIG> is provided with an inclined-plate-type of tube-wall pushing device <NUM>, <NUM>, which presses the horizontal bottom wall 12a, the reduced lower part 12b or the curved lower part 12c in an obliquely upward direction (a direction shown by the arrow F). Each of the devices <NUM>, <NUM> locally deforms the horizontal bottom wall 12a and the reduced lower part 12b, or the curved lower part 12c, as shown by broken lines.

<FIG> are conceptual diagrams, each showing such a deformation of the tube wall. In <FIG>, there are shown an intratubular slurry flow Sb moving along a tube wall Tw, and a stagnation zone Sc generated in proximity to the tube wall Tw. The tube wall Tw as shown in <FIG> (D ) and <FIG> is, e.g., the tube wall of the rectilinear tube segment <NUM> as shown in <FIG>. The zone Sc occurs, owing to, e.g., a significant reduction in the velocity of the slurry flow Sb, a locally generated vortex flow, or the like. As shown by the arrow F in <FIG>, when pressing elements Pe of the tube-wall pushing devices <NUM>-<NUM>, e.g., the element Pe of the device <NUM> is pressed against a part of the tube wall Tw in the vicinity of the zone Sc, the tube wall Tw is deformed inward of the tube as shown in <FIG>. As a result, the velocity of the slurry flow in the vicinity of the zone Sc increases locally, and the zone Sc disappears.

In <FIG>, there is shown the stagnation zone Sc generated in proximity to a joint of the tube walls Tw', Tw", owing to a redirection of the slurry flow Sb. For instance, the tube walls Tw', Tw" are the horizontal bottom wall 12a and the tube wall of the reduced lower part 12b as shown in <FIG>, respectively. When the pressing element Pe' of the device <NUM> is pressed against a part of the tube wall Tw', Tw" in the vicinity of the zone Sc, the tube wall Tw', Tw" is deformed inward of the tube as shown in <FIG>. As a result, a velocity distribution of the slurry flow changes in the zone Sc and in the vicinity of the zone Sc, and the zone Sc disappears.

Thus, as the result of the deformation of the tube wall Tw, Tw', Tw" caused by the action of the device <NUM>-<NUM>, the cross-section of the fluid passage of the delivery conduit <NUM> is locally reduced, whereby the velocity distribution of the gypsum slurry flow varies, or the stagnation zone, which is generated locally in the Y-tube, disappears. Therefore, according to the delivery conduit <NUM> with the tube-wall pushing device <NUM>-<NUM>, the characteristics or the velocity distribution of the flow of the gypsum slurry can be improved for efficient mixing of the slurry, or the stagnation zone of the gypsum slurry can be prevented from occurring in the delivery conduit, due to the local deformation or transformation of the cross-section of the delivery conduit. As a result, the lump of the gypsum slurry, its hardened matter, its solidified matter, or the like can be prevented from generating in the fluid passage of the delivery conduit <NUM> or clinging onto the tube wall of the delivery conduit <NUM> and so forth.

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

For instance, the arrangement of the mixer according to the present invention can be equally applied to a mixer other than the pin-type mixer, such as a scraper-type mixer, or a pinless mixer (a vane-type mixer or the like).

In the embodiments as set forth above, the center axis of the vertical tube is oriented vertically, but the center axis of the chute may be oriented vertically or inclined.

In the embodiments as set forth above, the vertical tube and the Y-tube are piping elements made of a flexible material, such as rubber, elastomer or synthetic resin. However, the vertical tube and the slurry delivery conduit may be produced by integrally assembling metal pipes or metallic materials, such as stainless steel pipes and stainless steel plates, with use of a jointing method, such as a welding method for metal pipes.

In the embodiments as set forth above, the mixer is equipped with the vertical chute, which is attached to the slurry outlet port on the annular wall of the casing of the mixer. However, the present invention can be similarly applicable to a mixer with a different arrangement, such as a mixer having a tubular passage for transporting the slurry, which is transversely connected to the slurry outlet port provided on the annular wall of the casing, or a mixer having a slurry delivery tubular passage vertically connected to the slurry outlet port on the lower plate of the casing.

The present invention can be applied to a slurry delivery conduit and a slurry delivery method for a mixer which are so arranged that a current of a gypsum slurry prepared by the mixer is divided into streams and is discharged through a plurality of slurry discharge ports onto a sheet of paper for gypsum board liner. According to the present invention, a flow of the slurry can be suitably straighten or rectified, whereby the flow rate and the specific gravity of the slurry can be prevented from differing between the discharge ports; the slurry current can be divided smoothly without a factor of stagnation of the gypsum slurry being provided at a branch part of the delivery conduit; and the sufficient distance can be ensured between the discharge ports. Furthermore, according to the present invention, a discharge direction of the slurry can be suitably preset or adjusted, so that a frequency of occurrence of scattering or spreading of the gypsum slurry to the outside of the sheet of paper can be reduced, or such a phenomenon can be prevented from occurring. Therefore, the practical advantage of the present invention is remarkable.

Claim 1:
A slurry delivery conduit (<NUM>) for a mixer (<NUM>) of a gypsum board production apparatus, wherein the mixer has a mixing area (<NUM>) for mixing of a gypsum slurry (<NUM>) to be fed onto a continuously conveyed sheet of paper for gypsum board liner (<NUM>) and wherein the slurry delivery conduit (<NUM>) configures a curved or L-shaped fluid passage, which is arranged to discharge the slurry introduced from the mixing area (<NUM>) of the mixer, onto said sheet through slurry discharge ports (<NUM>) of the slurry delivery conduit (<NUM>), wherein the slurry delivery conduit (<NUM>) comprises:
a rectilinear tube segment (<NUM>), a branch part (<NUM>) for branching the rectilinear tube segment, and a plurality of branch tube segments (<NUM>) connected to the rectilinear tube segment through the branch part,
wherein said rectilinear tube segment extends straightly on a downstream side in a conveying direction (J) of said sheet to configure a rectilinear fluid passage for said slurry;
wherein adjacent tube wall portions of said branch tube segments join together at said branch part to configure a transverse or horizontal cross-section in a form of V-letter, and the adjacent branch tube segments extend from the branch part on the downstream side in the conveying direction, while diverging toward the downstream side at an angle (θ2) in a range from <NUM> degrees to <NUM> degrees as seen in a plan view; and
wherein said branch part splits an axial or rectilinear current (S) of said slurry (3a) flowing out through said rectilinear tube segment and introduces branched streams (S1, S2) of the slurry into said branch tube segments respectively, and each of the branch tube segments is provided with said slurry discharge port (<NUM>) at a terminal end part of the branch tube segment on the downstream side, so as to discharge the branched stream through the port onto said sheet,
characterized in that the slurry delivery conduit further comprises a vertical tube (<NUM>) into which the slurry is introduced from said mixing area (<NUM>), the rectilinear tube segment (<NUM>) being connected to an outer circumferential surface of a lower end portion of the vertical tube (<NUM>) through which the slurry is introduced into the rectilinear tube segment (<NUM>).