Gypsum board manufacturing method and manufacturing device

As a lower forming plate 8, a forming plate having: a lower plate main body 10 constituted from an electrically conductive material; and a lower embedded electrode 12 embedded in the lower plate main body 10, the lower embedded electrode 12 being electrically insulated from the lower plate main body 10 by an insulator 14 and being embedded so as for a portion thereof to be exposed on the surface of the lower plate main body 10 making contact with a lower lining paper sheet 16 is used.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for producing a gypsum board.

BACKGROUND ART

A gypsum board is a sheet-like body having a structure in which an upper face, a lower face, and left and right side faces of a gypsum slab are covered by lining paper sheets, and is widely used as building materials such as ceiling materials, wall materials, and flooring materials.

As a method for producing a gypsum board, the following production method for example is known. First of all, a laminated material in which a gypsum slurry is continuously injected into a gap between a pair of lining paper sheets are formed while continuously supplying the pair of lining paper sheets. In forming the laminated material, the lower lining paper sheet is hold upward along a marked line formed in the edge portions of both sides thereof. Thereby, the upper face of the gypsum slurry is covered by the upper lining paper sheet, and the lower side face and left and right side faces of the gypsum slurry are covered by the lower lining paper sheet. The laminated material formed in this way is allowed to pass between a pair of upper and lower forming plates, thereby obtaining a molded body having a thickness depending on a space between plates. A gypsum board is obtained as a final product by drying the molded body.

However, in such a production method, there has been a problem that when, for example, the gypsum slurry is contaminated by foreign bodies (such as a lump of gypsum), the foreign bodies are caught between a pair of upper and lower forming plates and the lining paper sheet is cut by the foreign bodies. The problem is brought about because the foreign bodies larger than the space between a pair of upper and lower forming plates are caught between the pair of upper and lower forming plates when the gypsum slurry containing the foreign bodies enters there, and therefore the progress of the lining paper sheet is inhibited at the portion where the foreign bodies are caught while the progress of the lining paper sheet continues to progress at the other portions. When the production is continued with the situation where the foreign bodies are caught left unchanged, the lining paper sheet continuously supplied is continued to be cut, resulting in continuous production of defective gypsum board products. Moreover, when such a situation is continued, the lining paper sheet is finally torn completely, and therefore not only supply of the lining paper sheet but also production of the gypsum board cannot be continued. In such a case, complicated operation in which the foreign bodies are immediately removed, then the lining paper sheets are supplied again between the pair of upper and lower forming plates, and the gypsum slurry is injected into the gap of the pair of upper and lower lining paper sheets to restart the production has had to be conducted.

In order to solve the problems as described previously, the present applicant has proposed an apparatus for producing a gypsum board constituted so that a space between a pair of upper and lower forming plates is expanded when the cut of the lining paper sheet is detected (Patent Literature 1). The apparatus includes, for example, as shown in an apparatus100for producing a gypsum board as illustrated inFIG. 4, a roll136, an upper side forming plate124, a lower side forming plate108, an electrode (lower side external electrode138) arranged on the downstream side of the lower side forming plate108apart from the lower side forming plate108, an electric current detector120, and an air cylinder122. And a circuit140is constituted by electrically connecting the lower side external electrode138and the lower side forming plate108, and the electric current detector120and a power source D are electrically connected to the circuit140.

The apparatus100for producing a gypsum board makes it possible to detect the cut of the lining paper sheet by making use of the fact that the lining paper sheet is an insulator and the gypsum slurry is a good conductor of electricity. That is to say, in the apparatus100for producing a gypsum board, when the lower lining paper sheet116that is an insulator is cut, the gypsum slurry that is a good conductor makes contact with the lower side forming plate108and the lower side external electrode138and an electric current flows in the circuit140, and therefore the cut of the lower lining paper sheet116can be detected by the electric current detector120. Next, the air cylinder122lifts the upper side forming plate124depending on a signal from the electric current detector120, thereby expanding the space between the upper side forming plate124and the lower side forming plate108. Thereby, foreign bodies caught between the upper side forming plate124and the lower side forming plate108pass between the pair of forming plates. Thereafter, when the position of the upper side forming plate124is restored to the original position, production can be restarted. According to the production apparatus, the gypsum board can be produced continuously without stopping production and continuous production of a large amount of detective products can be avoided. Moreover, in addition to the detection of the cut of the lining paper sheet attributable to contamination of foreign bodies, the existence of defects can be detected because the gypsum slurry leaks out also in the case where defects (holes) are originally open in the lining paper sheet which makes an electric current to flow in the circuit140.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, the cases where the lining paper sheet is torn immediately after the foreign bodies in the gypsum slurry are caught between the forming plates and the production of a gypsum board is stopped have been increasing attributable to the following reasons: (1) the production speed of gypsum boards is becoming higher due to the technological innovation of gypsum board production technology in recent years, and therefore the tension applied on the lining paper sheet is increased; (2) reducing the weight and thickness of the lining paper sheets is facilitated from pressure to reduce costs, and therefore the lining paper sheets are becoming easier to cut; and so on.

Accordingly, a production method has earnestly been desired that makes it possible to continuously produce a gypsum board, the method being applicable to: high speed production of gypsum boards; production in which tension applied on the lining paper sheets is increasing; and production with a lining paper sheet having reduced weight and thickness, without stopping the production.

The present invention has been completed for solving the problems of the conventional technologies, and provides a method and an apparatus for producing a gypsum board making it possible to continuously produce a gypsum board, the method and apparatus being applicable to: high speed production of gypsum boards; production in which tension applied on the lining paper sheets is increasing; and production with a lining paper sheet having reduced weight and thickness, without stopping the production.

Solution to Problem

The present inventors have conducted diligent studies on the above-described problems to find that the problems of the conventional technologies can be solved by embedding inside the forming plate an electrode for detecting paper cut which have conventionally been arranged on the downstream side of the end of the forming plate, and have completed the present invention.

That is to say, according to the present invention, there is provided a method for producing a gypsum board, the method comprising a step of continuously injecting a gypsum slurry into a gap between a pair of upper and lower lining paper sheets while continuously supplying the pair of upper and lower lining paper sheets to form a laminated material and allowing the laminated material to pass between a pair of upper and lower forming plates to obtain a molded body having a thickness depending on a space between the plates, wherein a forming plate comprising: a plate main body constituted from an electrically conductive material; and an embedded electrode embedded in the plate main body, the embedded electrode being electrically insulated from the plate main body by an insulator and being embedded so as for a portion thereof to be exposed on a surface of the plate main body making contact with the lining paper sheet is used as at least one of the pair of upper and lower forming plates, a circuit is constituted by electrically connecting the plate main body and the embedded electrode embedded in the plate main body, and voltage is applied to the circuit, and when the lining paper sheet is cut to bring the plate main body and the embedded electrode into contact with the gypsum slurry and an electric current flows in the circuit, the space between the pair of upper and lower forming plates is expanded to remove a cause of conduction, and thereafter the space between the pair of upper and lower forming plates is restored to the original space.

In the production method of the present invention, it is preferable that the embedded electrode is embedded at a portion on the downstream side of the following starting position of forming in the plate main body.

[Starting Position of Forming]

A position on the most downstream side of the following (1) and the following (2):

(1) a position of an upstream end of either one of the pair of upper and lower forming plates; and

(2) a position of a downstream end of a taper portion in an embodiment wherein the taper portion whose plate thickness at a position in the taper portion becomes thinner as the position approaches upstream ends of the forming plates is formed in at least one of the pair of upper and lower forming plates, and a space between the pair of the forming plates at a position in the taper portion becomes larger, due to the taper portion, as the position approaches the upstream ends of the forming plates.

Moreover, in the production method of the present invention, it is preferable that: the embedded electrode is embedded, in the plate main body, at a portion within a range from the starting position of forming to a position on a downstream side of the starting position of forming by 50 mm; at least one material selected from the group consisting of phenol resin laminated plates with a cloth base material, phenol resin laminated plates with a paper base material, epoxy resin-impregnated glass fiber cloth, and epoxy resin-impregnated paper is used as the insulator; and at least one material selected from the group consisting of iron materials, stainless steel materials, and aluminum materials, or a material obtained by applying hard chromium plating thereon is used as the electrically conductive material.

Furthermore, according to the present invention, there is provided an apparatus for producing a gypsum board comprising a pair of upper and lower forming plates for forming a laminated material obtained by injecting a gypsum slurry into a gap between a pair of upper and lower lining paper sheets, the laminated material having a thickness depending on a space between the plates, wherein at least one of the pair of upper and lower forming plates comprises: a plate main body constituted from an electrically conductive material; and an embedded electrode embedded in the plate main body, the embedded electrode being electrically insulated from the plate main body by an insulator and being embedded so as for a portion thereof to be exposed on a surface of the plate main body making contact with the lining paper sheet, a circuit is constituted by electrically connecting the plate main body and the embedded electrode embedded in the plate main body, and the apparatus further comprises: an electric current detector electrically connected to the circuit; and an actuator moving at least one of the forming plates up and down in response to an electric signal from the electric current detector.

In the production apparatus of the present invention, it is preferable that the embedded electrode is embedded at a portion on a downstream side of the following starting position of forming in the plate main body.

[Starting Position of Forming]

A position on the most downstream side of the following (1) and the following (2):

(1) a position of an upstream end of either one of the pair of upper and lower forming plates; and

(2) a position of a downstream end of a taper portion in an embodiment wherein the taper portion whose plate thickness at a position in the taper portion becomes thinner as the position approaches upstream ends of the forming plates is formed in at least one of the pair of upper and lower forming plates, and a space between the pair of the forming plates at a position in the taper portion becomes larger, due to the taper portion, as the position approaches the upstream ends of the forming plates.

Further, in the production apparatus of the present invention, it is preferable that: the embedded electrode is embedded, in the plate main body, at a portion within a range from the starting position of forming to a position on a downstream side of the starting position of forming by 50 mm; the insulator is constituted from at least one material selected from the group consisting of phenol resin laminated plates with a cloth base material, phenol resin laminated plates with a paper base material, epoxy resin-impregnated glass fiber cloth, and epoxy resin-impregnated paper; and the electrically conductive material is at least one material selected from the group consisting of iron materials, stainless steel materials, and aluminum materials, or a material obtained by applying hard chromium plating thereon.

Advantageous Effects of Invention

According to the method or apparatus for producing a gypsum board, it becomes possible to continuously produce a gypsum board by the method and apparatus being applicable to high speed production of gypsum boards, production in which tension applied on the lining paper sheets is increasing, and production with a lining paper sheet having reduced weight and thickness, without stopping the production.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be explained in detail. However, the present invention is not limited to the following embodiments and includes all the objects containing matters used to specify the present invention.

[1] Method for Producing Gypsum Board:

The method for producing a gypsum board relates to a method for producing a gypsum board, the method comprising a step of continuously injecting a gypsum slurry into a gap between a pair of upper and lower lining paper sheets while continuously supplying the pair of upper and lower lining paper sheets to form a laminated material and allowing the laminated material to pass between a pair of upper and lower forming plates to obtain a molded body having a thickness depending on a space between the plates.

For example, any of a production apparatus1as illustrated inFIG. 1, a production apparatus1A as illustrated inFIG. 2, a production apparatus1B as illustrated inFIG. 3, and a production apparatus1C as illustrated inFIG. 5is a production apparatus capable of conducting the production method of the present invention, and with the production apparatuses, the step of continuously injecting the gypsum slurry4into the gap between a pair of upper and lower lining paper sheets2while continuously supplying the pair of upper and lower lining paper sheets2to form a laminated material and allowing the laminated material to pass between the pair of upper and lower forming plates6to obtain a molded body having a thickness depending on the space between the plates.

The gypsum slurry is a slurry containing calcined gypsum (β-type hemihydrate gypsum and α-type hemihydrate gypsum) and water as main components. In the present invention, the gypsum slurry includes a slurry using type III anhydrous gypsum in place of part or the whole of the calcined gypsum. The gypsum slurry may contain an additive such as an adhesion improver, a curing accelerator, or an admixture ingredient in addition to calcined gypsum and water.

The lining paper sheet is a lining paper sheet for producing a gypsum board. In the present invention, the lining paper sheet includes a glass fiber mat for producing a gypsum board. A sizing agent is mixed in the lining paper sheet for the purpose of suppressing water absorption and securing insulation properties during forming. Accordingly, water in the gypsum slurry does not penetrate into a surface layer of the lining paper sheet (a layer on the side not making contact with the gypsum slurry) immediately after the lining paper sheet makes contact with the gypsum slurry, and the lining paper sheet functions as an insulator. The thickness of the lining paper sheet is not particularly limited, however lining paper sheets having a thickness of 0.2 to 1.0 mm are usually used.

The production method of the present invention can suitably be used when gypsum boards are produced at a high speed. Specifically, the production method of the present invention can suitably be used when gypsum boards are produced at a production speed of 60 m/min or more.

In the production method of the present invention, a forming plate having: a plate main body constituted from an electrically conductive material; and an embedded electrode embedded in the plate main body, the embedded electrode being electrically insulated from the plate main body by an insulator and being embedded so as for a portion thereof to be exposed on a surface of the plate main body making contact with the lining paper sheet is used as at least one of the pair of upper and lower forming plates. By embedding the electrode for detecting the cut of the lining paper sheet in the plate main body, it becomes possible to detect the cut of the lining paper sheet earlier than in the case where the electrode is arranged on the downstream side of the end of the plate main body.

For example, when it is necessary to detect the cut of the lower lining paper sheet, a forming plate having: the lower plate main body10constituted from an electrically conductive material; and the lower embedded electrode12embedded in the lower plate main body10, the lower embedded electrode12being electrically insulated from the lower plate main body10by the insulator14and being embedded so as for a portion thereof to be exposed on the surface of the lower plate main body10making contact with the lower lining paper sheet16is used as the lower forming plate8, as shown in the production apparatus1as illustrated inFIG. 1.

Based on the similar idea, when it is necessary to detect the cut of the upper lining paper sheet, a forming plate having: the upper plate main body26constituted from an electrically conductive material; and the upper embedded electrode28embedded in the upper plate main body26, the upper embedded electrode28being electrically insulated from the upper plate main body26by the insulator30and being embedded so as for a portion thereof to be exposed on the surface of the upper plate main body26making contact with the upper lining paper sheet32may be used as the upper forming plate24, as shown in the production apparatus1A as illustrated inFIG. 2.

Further, when it is necessary to detect the cut of both the lower lining paper sheet and the upper lining paper sheet, the lower forming plate8as illustrated inFIG. 1and the upper forming plate24as illustrated inFIG. 2can be used together. That is to say, a forming plate having the lower embedded electrode12and the forming plate having an upper embedded electrode28are used as the lower forming plate8and the upper forming plate24respectively as illustrated in the production apparatus1B inFIG. 3.

Furthermore, an external electrode for detecting the cut of paper can be installed outside of the forming plate in addition to the embedded electrode for the purpose of backing up the embedded electrode. In the production apparatus1C as illustrated inFIG. 5for example, a forming plate having the embedded electrode12is used as the lower forming plate8, and a lower external electrode38for detecting the cut of paper is further installed outside of the lower forming plate8. The lower external electrode38is arranged on the downstream side of the lower forming plate8apart from the lower forming plate8. Moreover, the lower external electrode38is arranged so as to make contact with the lower lining paper sheet16. In such constitution, a circuit40that includes the lower external electrode38, the lower plate main body10, and a power source D3backs up a circuit18, thereby making it possible to detect the cut of paper in case the cut of paper cannot be detected by the circuit18including the embedded electrode12, the lower plate main body10, and the power source D1.

In addition, the lower external electrode38as illustrated inFIG. 5can also be installed in the production apparatus1A as illustrated inFIG. 2or the production apparatus1B as illustrated inFIG. 3. In such cases, the effect of backing up a circuit including an embedded electrode (lower embedded electrode12or upper embedded electrode28) such as the circuit34illustrated inFIG. 2, and the circuits18and34illustrated inFIG. 3can also be obtained by the circuit40including the lower external electrode38, the lower plate main body10, and the power source D3.

An upper external electrode (not illustrated in figures) can also be used as the external electrode for backup. The upper external electrode is an electrode that is arranged on the downstream side of the upper forming plate apart from the upper forming plate, and is arranged so as to make contact with the upper lining paper sheet. The circuit for backup that consists of the upper external electrode, the upper plate main body, and the power source can detect the cut of paper in the same manner as in the circuit40including the lower external electrode38as illustrated inFIG. 5, thereby making it possible to obtain the effect of backing up the circuit including the embedded electrode. Accordingly, the circuit including the upper external electrode can be used in place of or together with the circuit40including the lower external electrode38.

In the method for producing a gypsum board of the present invention, the constitution of the lower forming plate and upper forming plate is particularly important.

Specifically, the position where the upper embedded electrode or lower embedded electrode is arranged, the material quality of the insulator, the material quality of the electrically conductive material that constitutes the upper plate main body or lower plate main body, and so on become important. These will be explained specifically in the section of Apparatus for Producing Gypsum Board.

In the production method of the present invention, the circuit is constituted by electrically connecting the plate main body and the embedded electrode embedded in the plate main body, and voltage is applied to the circuit. Thereby, it becomes possible to detect the cut of the lining paper sheet when the plate main body and the embedded electrode make contact with the gypsum slurry and an electric current flows.

For example, when it is necessary to detect the cut of the lower lining paper sheet, the circuit18may be constituted by electrically connecting the lower embedded electrode12and the lower plate main body10to apply voltage to the circuit18as illustrated inFIG. 1. On the other hand, when it is necessary to detect the cut of the upper lining paper sheet, the circuit34may be constituted by electrically connecting the upper embedded electrode28and the upper plate main body26to apply voltage to the circuit34as illustrated inFIG. 2. Further, when it is necessary to detect the cut of both the lower lining paper sheet and the upper lining paper sheet, the circuit18may be constituted by electrically connecting the lower embedded electrode12and the lower plate main body10and the circuit34may also be constituted by electrically connecting the upper embedded electrode28and the upper plate main body26to apply voltage to both the circuit18and the circuit34as illustrated inFIG. 3.

The voltage applied to the circuit may be an alternating current or a direct current, and it is preferable that the voltage is a low voltage that is not dangerous to an operator when the operator makes contact with the circuit. It is preferable that the voltage is set to, for example, about AC 8V. Further, it is preferable that the lower plate main body10and/or the upper plate main body26are connected to a ground C as illustrated inFIG. 1toFIG. 3. Even a small electric potential difference can be detected by connecting these plate main bodies to the ground.

[1-3] Expansion of Space Between Plates:

In the production method of the present invention, the space between a pair of forming plates is expanded when an electric current flows in the circuit (namely, the cut of the lining paper sheet or the like is detected). Thereby, the foreign bodies that have been caught between the pair of upper and lower forming plates easily pass between the forming plates. Accordingly, the lining paper sheet does not continue to be cut due to the foreign bodies, and it never occurs that the lining paper sheet is completely torn and the production is stopped.

In the case where the production apparatus1as illustrated inFIG. 1is used for example, the space between a pair of the forming plates6can be expanded when an electric current flows in the circuit18(namely, when the cut of the lower lining paper sheet16, or the like is detected). On the other hand, in the case where the production apparatus1A as illustrated inFIG. 2is used, the space between a pair of the forming plates6can be expanded when an electric current flows in the circuit34(namely, when the cut of the upper lining paper sheet32, or the like is detected). Further, in the case where the production apparatus1B as illustrated inFIG. 3is used, the space between a pair of forming plates6can be expanded when an electric current flows in either the circuit18or the circuit34(namely, when the cut of either the lower lining paper sheet16or the upper lining paper sheet32is detected).

Examples of the method for expanding the space between forming plates include: (i) a method in which the upper forming plate is lifted while maintaining a state where the lower forming plate is fixed; (ii) a method in which the lower forming plate is brought down while maintaining a state where the upper forming plate is fixed; and (iii) a method in which the upper forming plate is lifted and the lower forming plate is brought down, and so on. The method (i) in which the upper forming plate24is lifted while maintaining a state where the lower forming plate8is fixed is adopted in any of the production apparatus1as illustrated inFIG. 1, the production apparatus1A as illustrated inFIG. 2, and the production apparatus1B as illustrated inFIG. 3. That is to say, the upper forming plate24is lifted to a position shown by broken lines inFIG. 1toFIG. 3. Such method is more preferable than the method (ii) and the method (iii) in terms of easiness of flow of the lower lining paper sheet when the space between the forming plates6is expanded. However, the method (ii) or the method (iii) may be adopted for the purpose of making the cleaning of an apparatus easy, or other purposes.

The space between the forming plates may be expanded to such an extent that the foreign bodies pass between a pair of forming plates. The specific space is not particularly limited, however it is preferable to expand the space by 2 to 4 cm wider than the original space from the reason that the time for expanding the space is made short to allow the foreign bodies to pass, and it is further preferably to expand the space by 2 cm wider. Moreover, it is more preferable that the speed of expanding the space between the forming plates is faster because the cut of the lining paper sheet is reduced more.

The means for expanding and restoring the space between the forming plates is not particularly limited. For example, an actuator can be used that moves up and down at least one of a pair of upper and lower forming plates in response to an electric signal when an electric current is detected. The actuator will be explained specifically in the section of Apparatus for Producing Gypsum Board.

[1-4] Restoration of Space Between Plates:

In the production method of the present invention, the space between a pair of the forming plates is restored to the original space after the cause of conduction is removed. The expression “after the cause of conduction is removed” means “after the foreign bodies that arise the cause of conduction (namely, the cut of the lining paper sheet, or the like) pass between the forming plates”. The situation where the foreign bodies are caught between the forming plates again and the lining paper sheet is cut can be prevented by restoring the space between the forming plates to the original space after the foreign bodies pass between the forming plates. And, the production of the gypsum board (the step of obtaining a molded body depending on the space between the forming plates) is restarted. When such a method is adopted, it never occurs that the lining paper sheet is completely torn and the production is stopped. That is to say, it is not necessary to conduct complicated operation in which the foreign bodies are removed, then the lining paper sheet is supplied again between a pair of upper and lower forming plates, and the gypsum slurry is injected into the gap of the pair of upper and lower lining paper sheets to restart the production.

Whether the cause of conduction is removed or not is evaluated by both the fact that the electric current has stopped flowing and the fact that the foreign bodies have passed between the forming plates. The fact that the electric current has stopped flowing can be detected by the electric current detector or the like which is electrically connected to the circuit. Examples of the method for restoring the space between the plates to the original space after the foreign bodies pass between the plates include a method in which the passing time required for the foreign objects to pass between the plates is determined from the feeding speed of the laminated body consisting of lining paper sheets and a gypsum slurry and the length of the forming plates, and the space between the plates is restored to the original space after the elapse of the passing time. Further, the examples also include a method in which the number of revolutions of the roll of a belt conveyor for feeding the laminated body is counted by a measuring roll, then the number of revolutions of the roll that corresponds to the time required for the foreign bodies to pass between the plates is determined from the relation between the number of revolutions of the roll and the feeding distance of the belt conveyor, and the space between plates is restored to the original space after the number of revolutions of the roll thus determined is counted.

The speed of restoring the space between the forming plates is not specifically limited. However, it is preferable to set the speed so that there is not a risk that the upper or lower lining paper sheet is not cut or the gypsum slurry on the lower lining paper sheet overflows and leaks outside.

[2] Apparatus for Producing Gypsum Board:

The method for producing a gypsum board of the present invention can be conducted, for example, with the apparatus for producing a gypsum board of the present invention explained below. The apparatus for producing a gypsum board of the present invention includes: a pair of upper and lower forming plates; an electric current detector; and an actuator as constituent members. Hereinafter, explanation will be made for each constituent member separately.

The production apparatus of the present invention includes a pair of upper and lower forming plates for forming a laminated material obtained by injecting a gypsum slurry into a gap between a pair of upper and lower lining paper sheets so that the laminated material has a thickness depending on the space between the plates. For example, any of the production apparatus1as illustrated inFIG. 1, the production apparatus1A as illustrated inFIG. 2, and the production apparatus1B as illustrated inFIG. 3includes a pair of upper and lower forming plates6(lower forming plate8and upper forming plate24) for forming a laminated material obtained by injecting the gypsum slurry4into the gap between a pair of upper and lower lining paper sheets2so that the laminated material has a thickness depending on the space between the plates.

At least one of a pair of upper and lower forming plates in the production apparatus of the present invention has: a plate main body constituted from an electrically conductive material; and an embedded electrode embedded in the plate main body. With the embedded electrode, it becomes possible to detect the cut of the lining paper sheet early.

For example, in the production apparatus1as illustrated inFIG. 1, the lower forming plate8has: the lower plate main body10; and the lower embedded electrode12embedded in the lower plate main body10for the purpose of detecting the cut of the lower lining paper sheet16. On the other hand, in the production apparatus1A as illustrated inFIG. 2, the upper forming plate24has: the upper plate main body26; and the upper embedded electrode28embedded in the upper plate main body26for the purpose of detecting the cut of the upper lining paper sheet32. In order to detect the cut of both the lower lining paper sheet and the upper lining paper sheet, a structure may be made in which the lower forming plate8has: the lower plate main body10; and the lower embedded electrode12embedded in in the lower plate main body10and the upper forming plate24has: the upper plate main body26; and the upper embedded electrode28embedded in the upper plate main body26, as shown in the production apparatus1B as illustrated inFIG. 3.

The plate main body is a member that constitutes a circuit by being electrically connected to the embedded electrode, and therefore it is necessary that the plate main body be constituted from an electrically conductive material. The kind of the electrically conductive material is not particularly limited. However, since the plate main body is an important member that determines the thickness of a molded body, it is necessary to avoid a change in shape attributable to wear as much as possible. Accordingly, it is preferable that the electrically conductive material that constitutes the plate main body is at least one material selected from the group consisting of iron materials, stainless steel materials, and aluminum materials, or a material obtained by applying hard chromium plating thereon. These materials are preferable in that these materials have a high rigidity and excellent wear resistance and size accuracy in addition to electric conductivity.

It is preferable that a material that constitutes the embedded electrode is also at least one material selected from the group consisting of iron materials, stainless steel materials, and aluminum materials, or a material obtained by applying hard chromium plating thereon from the similar reason to that in the plate main body. The shape of the embedded electrode is not particularly limited and may be used as long as the shape has a width to cover the entire width of a gypsum board to be produced. The embedded electrodes having various kinds of shapes such as, for example, round rod-like, square rod-like, and sheet-like shapes can be used.

The embedded electrode is electrically insulated by an insulator from the plate main body in which the embedded electrode is embedded. Thereby, it is possible to prevent a short circuit between the embedded electrode and the plain main body, and it is also possible to surely detect an electric current that flows between the embedded electrode and the plate main body.

For example, in the production apparatus as illustrated inFIG. 1, the lower embedded electrode12and the lower plate main body10are electrically insulated by the insulator14. On the other hand, in the production apparatus1A as illustrated inFIG. 2, the upper embedded electrode28and the upper plate main body26are electrically insulated by the insulator30. Further, in the production apparatus1B as illustrated inFIG. 3, the lower embedded electrode12and the lower plate main body10are insulated by the insulator14and the upper embedded electrode28and the upper plate main body26are also insulated by the insulator30.

In the production apparatus of the present invention, not only the embedded electrode but also the insulator is embedded in the plate main body. Since the plate main body is an important member that determines the thickness of a molded body, it is necessary to avoid a change in shape attributable to wear also in the insulator that forms part of the plate main body as much as possible. Moreover, it is not preferable that the exchanging work of members becomes complicated as a result that the wear resistance between the insulator and the plate main body or the like is different to bring about, for example, a different exchange period for each member. Accordingly, a favorable wear resistance in addition to the insulation performance is required for the insulator. Moreover, since the insulator is a member that is embedded in the plate main body, it is preferable, for the purpose of preventing voids or level difference between the insulator and the plate main body or embedded electrode from occurring, that: (1) the insulator is constituted from a material which has a good processability and which can be processed with a high size accuracy; and (2) the insulator is constituted from a material with which the void or level difference is hard to occur due to a change in size over time.

Conventionally, since it has been difficult to design an insulating material that satisfies the above-described requirements, it has been common general technical knowledge that a molded plate is constituted from a single material, and an idea of embedding an detection electrode inside the molded plate has not existed. For this reason, it is considered that a lower external electrode138for detecting the cut of paper has been arranged on a further downstream side of the downstream end of the forming plate (lower forming plate108) as shown in the production apparatus100as illustrated inFIG. 4. In order to solve the above-described problem of the insulating material, it is preferable that the insulator is constituted from at least one material selected from the group consisting of phenol resin laminated plates with a cloth base material (also referred to as “cloth-containing bakelite”), phenol resin laminated plates with a paper base material (also referred to as “paper-containing bakelite”), epoxy resin-impregnated glass fiber cloth (also referred to as “glass-epoxy resins”), and epoxy resin-impregnated paper (also referred to as “paper-epoxy resins”). These materials can suitably be used because of favorable wear resistance, processability, and size accuracy in addition to insulation performance. It is particularly preferable to use the phenol resin laminated plate with a cloth base material that is excellent in wear resistance, processability, and size accuracy among the above-described materials.

In the production apparatus of the present invention, the embedded electrode is embedded so as for a portion thereof to be exposed on the surface of the plate main body making contact with the lining paper sheet. In this case, it is preferable that the embedded electrode is arranged so that there is no level difference between the surface of the plate main body making contact with the lining paper sheet and the surface of the embedded electrode, and is arranged so that there is no gap between the embedded electrode and the insulator that will be mentioned later.

For example, in the production apparatus1as illustrated inFIG. 1, the rod-like lower embedded electrode12is filled in the groove portion of the insulator14having an approximately U-shaped section, and is embedded so as for a portion thereof (upper face) to be exposed on the surface of the lower plate main body10. On the other hand, in the production apparatus1A as illustrated inFIG. 2, the rod-like upper embedded electrode28is filled in the groove portion of the insulator30having an approximately U-shaped section, and is embedded so as for a portion thereof (bottom face) to be exposed on the surface of the upper plate main body26. Further, in the production apparatus1B as illustrated inFIG. 3, the rod-like lower embedded electrode12is filled in the groove portion of the insulator14having an approximately U-shaped section, and is embedded so as for a portion thereof (upper face) to be exposed on the surface of the lower plate main body10. Furthermore, the rod-like upper embedded electrode28is filled in the groove portion of the insulator30having an approximately U-shaped section, and is embedded so as for a portion thereof (bottom face) to be exposed on the surface of the upper plate main body26.

It is preferable that the forming plates have an embodiment in which a taper portion whose plate thickness at a position in the taper portion becomes thinner as the position approaches upstream ends of the forming plates is formed in at least one of the pair of upper and lower forming plates, and a space between the pair of the forming plates at a position in the taper portion becomes larger, due to the taper portion, as the position approaches the upstream ends of the forming plates. When such an embodiment is made, the holdup of the gypsum slurry is prepared immediately before the starting position of forming, thereby making it possible to keep the holdup volume of the gypsum slurry always constant. Accordingly, the gypsum slurry is molded while keeping a state in which the air is trapped therein, making it possible to effectively prevent a situation where gypsum boards in which internal voids are formed are produced. Thereby, it is possible to solve the problems of gypsum boards, such as bulging and denting, lowering of the smoothness, and dropping out of nails and screws (fixing failure of boards) when the gypsum boards are fixed, attributable to the above-described internal voids.

For example, in the production apparatus1as illustrated inFIG. 1, the production apparatus1A as illustrated inFIG. 2, the production apparatus1B as illustrated inFIG. 3, and the production apparatus1C as illustrated inFIG. 5, the embodiment is the one in which a taper portion whose plate thickness at a position in the taper portion becomes thinner as the position approaches the upstream end (edge on the upstream side of the plate) of the lower forming plate8is formed in the lower forming plate8, and a space between the pair of the forming plates6at a position in the taper portion becomes larger, due to the taper portion, as the position approaches the upstream end. However, a taper portion whose plate thickness at a position in the taper portion becomes thinner as the position approaches upstream end of a forming plate may be formed in the upper forming plate, or the taper portions may be formed in both the lower forming plate and the upper forming plate (not shown in the figures).

In the production apparatus of the present invention, it is preferable that the embedded electrode is embedded at a portion on a downstream side of the starting position of forming in the plate main body, and it is further preferable that the embedded electrode is embedded, in the plate main body, at a portion within a range from the starting position of forming to a position on the downstream side of the starting position of forming by 50 mm. The space between plates at the starting position of forming is narrower than the space between plates on the upstream side of the starting position of forming for the purpose of forming a laminated material obtained by injecting a gypsum slurry into a gap between a pair of upper and lower lining paper sheets so as to form the thickness of the laminated material depending on the space between plates. Therefore, the starting position of forming is a region where foreign bodies are liable to be caught and where there is a high possibility that the cut of the lining paper sheet is liable to occur. Accordingly, in order to detect the cut of the lining paper sheet early, it can be said that it is preferable to arrange the embedded electrode at a position near the starting position of forming. Specifically, it is particularly preferable that the embedded electrode is embedded at a portion within a range from the starting position of forming to a position on the downstream side of the starting position of forming by 25 mm.

On the other hand, there is a time lag from the time when the lining paper sheet is cut to the time when the gypsum slurry begins to leak out. Accordingly, it is more preferable that the embedded electrode is embedded at a position somewhat downstream side of the starting position of forming in the plate main body than that the embedded electrode is embedded at the starting position of forming in the plate main body. Moreover, when the production speed of the gypsum board becomes high, the position where the leak out of the gypsum slurry can be detected after the lining paper sheet is cut recedes from the starting position of forming. Accordingly, in the case where high speed production is conducted, it is preferable that the embedding electrode is embedded at a portion on further downstream side in the plate main body than in the case where low speed production is conducted. Specifically, it is preferable that the embedded electrode is embedded, in the plate main body, at a portion on further downstream side of a position on the downstream side of the starting position of forming by 15 mm.

As described above, it is necessary that an appropriate embedding position of the embedded electrode be determined, in the plate main body, within a portion on the downstream side of the starting position of forming (particularly, a portion within a range from the starting position of forming to a position on the downstream side of the starting position of forming by 50 mm) considering the production speed.

In addition, the “starting position of forming” means a position where forming of the laminated material obtained by injecting a gypsum slurry into a gap between a pair of lining paper sheets is started, and specifically means a position on the most downstream side of the following (1) and the following (2). Hereinafter, explanation will be made on the starting position of forming with reference toFIG. 6AtoFIG. 6E. In addition, the embedded electrode, the insulator, and so on are omitted, and only the shape of the forming plates are illustrated inFIG. 6AtoFIG. 6Efor the convenience of drawing. Moreover, the thick arrow inFIG. 6AtoFIG. 6Eshows a transportation direction (namely, downstream direction) of the laminated material.

(1) a position of an upstream end of either one of the pair of upper and lower forming plates; and

(2) a position of a downstream end of a taper portion in an embodiment wherein the taper portion whose plate thickness at a position in the taper portion becomes thinner as the position approaches upstream ends of the forming plates is formed in at least one of the pair of upper and lower forming plates, and a space between the pair of the forming plates at a position in the taper portion becomes larger, due to the taper portion, as the position approaches the upstream ends of the forming plates.

The production apparatus of the present invention is a production apparatus for obtaining a molded body having a thickness depending on the space between plates by allowing the laminated material to pass between a pair of upper and lower forming plates. Accordingly, in forming the laminated body, a pair of upper and lower forming plates are arranged so as to face each other, and forming is started at a position where the space of the plates is sufficiently narrowed to such an extent that forming is possible. In the case of an embodiment where the taper portion is not formed on the upstream side of any of the pair of upper and lower forming plates (upper forming plate and lower forming plate), a position of the upstream end of any one of the pair of upper and lower forming plates becomes the starting position of forming.

In the example as illustrated inFIG. 6Afor example, the position of the upstream end24aof the upper forming plate24and the position of the upstream end8aof the lower forming plate8are located on one straight line. That is to say, on the downstream side of the upstream ends24aand8a, a pair of upper and lower forming plates6are arranged so as to face each other, and the space between plates are sufficiently narrowed to such an extent that forming is possible. Accordingly, the position of the upstream end24aof the upper forming plate24(or the position of the upstream end8aof the lower forming plate8) becomes the starting position of forming P.

Moreover, in the example as illustrated inFIG. 6B, the pair of upper and lower forming plates are arranged so that the upstream end8aof the lower forming plate8protrudes on the upstream side of the upstream end24aof the upper forming plate24. In the case of such an embodiment, the pair of upper and lower forming plates6are arranged so as to face each other on the downstream side of the upstream end24aof the upper forming plate24, and the space between the plates is sufficiently narrowed to such an extent that forming is possible. Accordingly, the position of the upstream end24aof the upper forming plate24becomes the starting position of forming P.

In the case of an embodiment in which a taper portion whose plate thickness at a position in the taper portion becomes thinner as the position approaches upstream ends of the forming plates is formed in at least one of the pair of upper and lower forming plates, and a space between the pair of the forming plates at a position in the taper portion becomes larger, due to the taper portion, as the position approaches the upstream ends of the forming plates, the position of the downstream end of the taper portion can also become the starting position of forming in addition to the position of the upstream ends of the pair of upper and lower forming plates. Here, “the space between the pair of upper and lower forming plates at a position in the taper portion becomes larger, due to the taper portion, as the position approaches the upstream end” means, in other words, that the slope face of the taper portion is formed on the side of a face that makes contact with the lining paper sheet in the forming plate.

In the example as illustrated inFIG. 6Cfor example, the position of the upstream end24aof the upper forming plate24and the position of the upstream end8aof the lower forming plate8are located on one straight line. That is to say, a pair of upper and lower forming plates6are arranged so as to face each other on the downstream side of the upstream ends24aand8a. However, the space between the pair of upper and lower forming plates6becomes larger at the position of the upstream end8aof the lower forming plate8due to the taper portion8b, and the space is not sufficiently narrowed to such an extent that forming is possible. Accordingly, the position of the downstream end8cof the taper portion8bwhere space between the pair of upper and lower forming plates6is sufficiently narrowed becomes the starting position of forming P.

Moreover, also in the example as illustrated inFIG. 6D, the position of the upstream end24aof the upper forming plate24and the position of the upstream end8aof the lower forming plate8are located on one straight line, and a pair of upper and lower forming plates6are arranged so as to face each other on the downstream side of the upstream ends24aand8a. However, the space between the pair of upper and lower forming plates6becomes larger at the position of the upstream end24aof the upper forming plate24due to the taper portion24b, and the space is not sufficiently narrowed to such an extent that forming is possible. Accordingly, the position of the downstream end24cof the taper portion24bwhere space between the pair of upper and lower forming plates6is sufficiently narrowed becomes the starting position of forming P.

Further in the example as shown inFIG. 6E, it can be said that the upper and lower forming plates are arranged so that the upstream end8aof the lower forming plate8protrudes on the upstream side of the upstream end24aof the upper forming plate24and a pair of upper and lower forming plates6are arranged so as to face each other on the downstream side of the upstream end24aof the upper forming plate24. However, the space between the pair of forming plates6becomes larger due to the taper portion24bof the upper forming plate24and the taper portion8bof the lower forming plate8at the position of the upstream end24aof the upper forming plate24, and the space is not sufficiently narrowed to such an extent that forming is possible. Accordingly, the position of the downstream end24cof the taper portion24bwhere the space between the pair of upper and lower forming plates6is sufficiently narrowed becomes the starting point of forming P.

In the apparatus for producing a gypsum board of the present invention, a circuit is constituted by electrically connecting the embedded electrode and the plate main body in which the embedded electrode is embedded.

For example, the production apparatus1as illustrated inFIG. 1is an example in which the circuit18is constituted by electrically connecting the lower embedded electrode12, the lower plate main body10, and the pour source D1. On the other hand, the production apparatus1A as illustrated inFIG. 2is an example in which the circuit34is constituted by electrically connecting the upper embedded electrode28and the upper plate main body26. Further, as in the production apparatus1B as illustrated inFIG. 3, the circuit34may be constituted by electrically connecting the upper embedded electrode28and the upper plate main body26in addition to the circuit18constituted by electrically connecting the lower embedded electrode12and the lower plate main body10.

Furthermore, as illustrated inFIG. 5, the circuit40including the lower external electrode38, the lower plate main body10, and the power source D3may be constituted in addition to the circuit18. In addition, the circuit40including the lower external electrode38may be formed together with the circuit34including the upper embedded electrode28as illustrated inFIG. 2(not shown in the figure). Moreover, the circuit40may be formed together with the circuit18including the lower embedded electrode12as illustrated inFIG. 3and the circuit34including the upper embedded electrode28(not shown in the figure).

The apparatus for producing a gypsum board of the present invention includes an electric current detector electrically connected to the circuit that connects the embedded electrode and the plate main body. With the electric current detector, the cut of the lining paper sheet, or the like can be detected.

For example, the production apparatus1as illustrated inFIG. 1includes an electric current detector20that is electrically connected to the circuit18, and makes it possible to detect a current that flows between the lower embedded electrode12and the lower plate main body10. On the other hand, the production apparatus1A as illustrated inFIG. 2includes an electric current detector20that is electrically connected to the circuit34, and makes it possible to detect a current that flows between the upper embedded electrode28and the upper plate main body26. Further, the production apparatus1B as illustrated inFIG. 3includes an electric current detector20that is electrically connected to both the circuit18and the circuit34. Thereby, it becomes possible to detect both the current that flows between the lower embedded electrode12and the lower plate main body10and the current that flows between the upper embedded electrode28and the upper plate main body26. In the case where a plurality of circuits exist, a plurality of circuits18and34may share the electric current detector20as illustrated inFIG. 3.

The apparatus for producing a gypsum board of the present invention includes an actuator that moves at least one of forming plates up and down in response to an electric signal from the electric current detector.

For example, the production apparatus1as illustrated inFIG. 1, the production apparatus1A as illustrated inFIG. 2, the production apparatus1B as illustrated inFIG. 3, and the production apparatus1C as illustrated inFIG. 5include an actuator22that moves the upper forming plate24up and down in response to an electric signal from the electric current detector20. However, the production apparatus of the present invention may be a production apparatus including an actuator that moves the lower forming plate up and down, or may be a production apparatus including an actuator that moves both the upper forming plate and the lower forming plate up and down (not shown in the figure).

The actuator may be a device that drives the forming plate up and down depending on the electric current detector. Specific examples of the kind of the device include, but not particularly limited to, an air cylinder, an oil cylinder, a servomotor, and so on.

EXAMPLES

Hereinafter, the present invention will be explained in more specifically by Examples and Comparative Examples. However, the present invention is not limited to only the constitution of the following Examples.

As a production apparatus of Example 1, the production apparatus1as illustrated inFIG. 1was manufactured. A gypsum board to be produced was determined to be a gypsum board having a width of 910 mm and a thickness of 9.5 mm. In the production apparatus1, the lining paper sheet2(upper lining paper sheet32and lower lining paper sheet16) is transferred from the right-hand side to the left-hand side in the figure. The production apparatus is constituted so that the gypsum slurry4is continuously supplied on the lower lining paper sheet16. The roll36is a roll for changing the supplying direction of the upper lining paper sheet32.

The production apparatus including a pair of upper and lower forming plates6(the lower forming plate8and upper forming plate24) was used. The lower forming plate8having: the lower plate main body10; and the lower embedded electrode embedded in the lower plate main body10was used. The upper plate main body26and the lower plate main body10were constituted from a material obtained by applying hard chromium plating on an iron material. The lower embedded electrode12was made of a stainless material, and had a square section of 6 mm×6 mm and a square rod-like shape having a length of 1200 mm.

The lower embedded electrode12and the lower plate main body10were electrically insulated by the insulator14. The insulator14was constituted from a phenol resin laminated plate with a cloth base material. The insulator had an approximately U-shaped section and an approximately square rod-like shape in which a groove portion was formed. The lower embedded electrode12was filled in the groove portion of the insulator14and was embedded so that a portion thereof (upper face) was exposed on the surface of the lower plate main body10. The insulator14was arranged on the front and behind sides of the lower embedded electrode12with a width of 5 mm to electrically insulate the lower embedded electrode12. The lower embedded electrode12was embedded at a portion ranging from a position on the downstream side of the starting position of forming by 15 mm to a position on the downstream side of the starting position of forming by 21 mm in the lower plate main body10. That is to say, the lower embedded electrode12was exposed on the surface of the lower plate main body10over a width of 6 mm.

The taper portion was formed on the upstream end side of the lower forming plate8. The length of the taper portion was determined to be 50 mm, and the height of the taper portion was determined to be 4 mm. On the downstream side of the taper portion, the lower forming plate8and the upper forming plate24are arranged so as to face each other, and the forming space is formed so that the space between plates is sufficiently narrowed to such an extent that forming is possible. The forming space is formed from the starting position of forming to a position on the downstream side of the starting position of forming by 300 mm.

The lower embedded electrode12, the lower plate main body10, and the power source D1were electrically connected to constitute the circuit18.

The electric current detector20was electrically connected to the circuit18.

The actuator22moving the upper forming plate24up and down in response to an electric signal from the electric current detector20was installed. An air cylinder was used as the actuator.

[1-5] Production of Gypsum Boards:

Gypsum boards were produced using the above-described production apparatus. The production speed of the gypsum board was determined to be 150 m/min. The production apparatus was operated for 20 days under the condition of continuously operating the production apparatus for 24 hours per day to find that the number of the cases where the lining paper sheet was completely torn to stop continuous production was only one.

As a production apparatus of Example 2, the production apparatus1A as illustrated inFIG. 2was manufactured. The production apparatus was manufactured in the same manner as in the production apparatus of Example 1 except the matters described below.

The production apparatus including a pair of upper and lower forming plates6(lower forming plate8and upper forming plate24) was used. The upper plate main body26and the lower plate main body10were constituted from a material obtained by applying hard chromium plating on an iron material. The lower embedded electrode was not arranged in the lower forming plate8, and the upper embedded electrode28was arranged in the upper forming plate24. The upper embedded electrode28was made of a stainless material, and had a square section of 6 mm×6 mm and a square rod-like shape having a length of 1200 mm.

The upper embedded electrode28and the upper plate main body26were electrically insulated by the insulator30. The insulator30was constituted from a phenol resin laminated plate with a cloth base material. The insulator had an approximately U-shaped section and an approximately square rod-like shape in which a groove portion was formed. The upper embedded electrode28was filled in the groove portion of the insulator30, and was embedded so that a portion (bottom face) thereof was exposed on the surface of the upper plate main body26. The insulator30was arranged on the front and behind sides of the upper embedded electrode28with a width of 5 mm to electrically insulate the upper embedded electrode28. The upper embedded electrode28was embedded at a portion ranging from a position on the downstream side of the forming by 15 mm to a position on the downstream side of the starting position of forming by 21 mm in the upper plate main body26. That is to say, the upper embedded electrode28was exposed on the surface of the upper plate main body26over a width of 6 mm.

The upper embedded electrode28, the upper plate main body26, and the power source D2were electrically connected to constitute the circuit34.

The electric current detector20was connected to the circuit34.

[2-4] Production of Gypsum Boards:

Gypsum boards were produced using the above-described production apparatus. The production speed of the gypsum board was determined to be 150 m/min. The production apparatus was operated for 20 days under the condition of continuously operating the production apparatus for 24 hours per day to find that the number of the cases where the lining paper sheet was completely torn to stop continuous production was only two.

As a production apparatus of Example 3, the production apparatus1B as illustrated inFIG. 3was manufactured. The production apparatus was manufactured in the same manner as in the production apparatus of Example 1 except the matters described below.

The lower forming plate8was constituted in the same manner as in the production apparatus of Example 1. The lower embedded electrode12was embedded at a portion ranging from a position on the downstream side of the starting position of forming by 15 mm to a position on the downstream side of the starting position of forming by 21 mm in the lower plate main body10. The upper forming plate24was constituted in the same manner as in the production apparatus of Example 2.

The lower embedded electrode12, the lower plate main body10, and the power source D1were electrically connected to constitute the circuit18, and the upper embedded electrode28, the upper plate main body26, and the power source D2were electrically connected to constitute the circuit34.

The electric current detector20was electrically connected to the circuit18and the circuit34.

[3-4] Production of Gypsum Boards:

Gypsum boards were produced using the above-described production apparatus. The production speed of the gypsum board was determined to be 150 m/min. The production apparatus was operated for 20 days under the condition of continuously operating the production apparatus for 24 hours per day to find that the number of the cases where the lining paper sheet was completely torn to stop continuous production was only one.

As a production apparatus of Example 4, the production apparatus1B as illustrated inFIG. 3was manufactured. The production apparatus was manufactured in the same manner as in the production apparatus of Example 1 except the matters described below.

The lower forming plate8was constituted in the same manner as in the production apparatus of Example 1 except the position of the lower embedded electrode12. The lower embedded electrode12was embedded at a portion ranging from a position on the downstream side of the starting position of forming by 25 mm to a position on the downstream side of the starting position of forming by 31 mm in the lower main plate main body10. The upper forming plate24was constituted in the same manner as in the production apparatus of Example 2.

The lower embedded electrode12, the lower plate main body10, and the power source D1were electrically connected to constitute the circuit18, and the upper embedded electrode28, the upper plate main body26, and the power source D2were electrically connected to constitute the circuit34.

The electric current detector20was electrically connected to the circuit18and the circuit24.

[4-4] Production of Gypsum Boards:

Gypsum boards were produced using the above-described production apparatus. The production speed of the gypsum board was determined to be 150 m/min. The production apparatus was operated for 20 days under the condition of continuously operating the production apparatus for 24 hours per day to find that there were no cases where the lining paper sheet was completely torn and there were also no cases where the continuous production was stopped.

Comparative Example 1

As a production apparatus of Comparative Example 1, the production apparatus100as illustrated inFIG. 4was manufactured. The production apparatus was manufactured in the same manner as in the production apparatus of Example 1 except the matters described below.

The lower embedded electrode was not arranged in the lower forming plate108. Instead, the lower external electrode138was arranged at a position apart from the end (downstream end) of the lower forming plate108by 10 mm on the downstream side. The lower external electrode138was arranged in a state where the lower external electrode was electrically isolated from the surroundings. The lower external electrode138was made of an iron material obtained by applying hard chromium plating thereon, and had a square section of 24 mm×24 mm and a square rod-like shape having a length of 1200 mm. The upper forming plate124was constituted in the same manner as in the upper forming plate24of the production apparatus of Example 1.

The lower external electrode138, the lower forming plate108, and the power source D3were electrically connected to constitute the circuit140.

The electric current detector120was electrically connected to the circuit140.

[5-4] Production of Gypsum Boards:

Gypsum boards were produced using the above-described production apparatus. The production speed of the gypsum board was determined to be 150 m/min. The production apparatus was operated for 20 days under the condition of continuously operating the production apparatus for 24 hours per day to find that the number of the cases where the lining paper sheet was completely torn to stop continuous production reached 10.

INDUSTRIAL APPLICABILITY

The method and apparatus for producing a gypsum board of the present invention can suitably be used for producing gypsum boards useful as building materials such as ceiling materials, wall materials, flooring materials.

REFERENCE SIGNS LIST