Patent Publication Number: US-6702966-B1

Title: Method for manufacturing cement fiber sheets

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 of Japanese Patent Application No. 2000-037078, filed on Feb. 15, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a method for manufacturing cement fiber sheets, and more specifically to a technique for manufacturing cement fiber sheets, for example, used for exterior construction material (siding board, roofing tiles, etc.), exterior products (fences, gates, etc.), and interior construction material (floors, walls, ceiling, etc.). 
     2. Description of Related Art 
     Conventionally, in manufacturing these types of cement fiber sheets, there is known a construction method for manufacturing cement fiber sheets in which slurry including fiber and cement materials is discharged from a discharging port for controlling the thickness supplied onto permeable sheets, suctioned and dewatered. 
     However, accumulated foreign matter constantly enters the slurry from, for example, compounding equipment, mixing equipment, piping, pumps, etc., and falling matter also enters. If the foreign matter enters, the foreign matter may directly affect the product appearance and in particular, depending on the size of foreign matter, holes, cracking, or tears may result. In addition, when slurry containing foreign matter passes the discharging port for controlling thickness, fine foreign matter is caught by the discharging port, which results in degradation of product surface quality, and as result, the product does not meet the product thickness standard. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in view of the problems of the above-mentioned conventional examples, and it is an object of the present invention to provide a method for manufacturing cement fiber sheets which can eliminate foreign matter in the slurry, thereby the thickness can be positively controlled and the product surface quality is ensured. 
     In the present invention, to solve the problems mentioned above, a method for manufacturing cement fiber sheets is provided in which slurry primarily including fibers and cement as material components is supplied onto a permeable sheet, then suctioned and dewatered. The method also includes a foreign matter removing process for removing foreign matter contained in the slurry material before supplying the slurry to the permeable sheet, a thickness control process for controlling slurry to a specified thickness after the foreign matter removing process, and a leveling process for smoothing the slurry surface after the thickness control process. These processes eliminate detrimental effects of foreign matter on the product appearance and at the same time make it possible to prevent holes, cracking, or breakage in products beforehand by providing a foreign matter removing process, and consequently, the product surface quality is ensured and thickness control is positively implemented. 
     In addition, the slurry concentration is desirably between 35 and 65%, and in such event, the fluidity of slurry is proper and effects of ensuring the product surface quality, as well as effects of positively implementing thickness control and leveling can be expected, and at the same time, the problem of ease of spilling of slurry can be simultaneously solved. 
     In implementing the leveling process of the present invention, a leveling device equipped with a smooth-forming pressure plate is desirably used for pressing and smoothing the slurry surface and at the same time, an endless sheet is desirably positioned rotatably between the slurry surface and smooth-forming pressure plate. Thus, it is possible to prevent cracking caused by chafing between the slurry surface and the leveler and at the same time the problem of product surface quality being degraded by the leveler itself can also be eliminated. 
     In implementing the thickness control process, it is desirable to use a thickness controller provided with a discharging port for discharging slurry to a specified thickness and to use a leveler for imparting vibrating action to the discharging part, and in such event, when slurry is discharged from the discharging port, it is possible to simultaneously control slurry thickness by the discharging port and to smooth the slurry surface by the vibrating action. 
     According to an aspect of the present invention a method is provided for manufacturing cement fiber sheets in which slurry primarily including fibers and cement as material components is supplied onto a permeable sheet, and then suctioned and dewatered. The method includes removing foreign matter contained in the slurry material before supplying the slurry to the permeable sheets, controlling a thickness of the slurry supplied to the permeable sheet and smoothing the slurry surface after the thickness control process. 
     According to a further aspect of the present invention, in the method a slurry concentration of between 35 and 65% is used. 
     Further according to an aspect of the present invention, the leveling operation is carried out by a leveler equipped with a smooth-forming pressure plate for pressing the slurry surface for smoothing, and at the same time an endless sheet is rotatably intervened between the slurry surface and the smooth-forming pressure plate. 
     Furthermore, according to another aspect of the present invention, in the method, when the thickness control operation is carried out, a thickness controller equipped with a discharge port for discharging slurry to provide a specified thickness and a leveler for providing vibrating action to the discharging port are used. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of certain embodiments of the present invention, in which like numerals represent like elements throughout the several views of the drawings, and wherein: 
     FIG. 1 is a schematic block diagram depicting a first embodiment according to the present invention; 
     FIG. 2 is a top view of a vibrating screen of the embodiment of FIG. 1; 
     FIG.  3 (A) is a front view of a thickness controller; 
     FIG.  3 (B) is a side view of a thickness controller; 
     FIG. 4 is a side of a vibrating leveler; 
     FIG. 5 is a schematic block diagram showing a second embodiment of the present invention; 
     FIG.  6 (A) is a front view of a thickness controller of another embodiment of the present invention; and 
     FIG.  6 (B) is a side view of a thickness controller. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, the present invention will be described in detail hereinafter. 
     In a first embodiment of the present embodiment, when cement fiber sheets primarily including fibers and cement as main materials are manufactured, the material including fibers and cement is made into a slurry of a proper concentration, and in the slurry state A (as shown in FIG.  1 ), the material is supplied onto a permeable sheet  1  after passing through a foreign matter removing apparatus  3  and thickness control apparatus  4  shown in FIG. 1, successively. The supplied slurry A is subjected to a vacuum and dewatered by suction to a proper water content or press-dewatered as required after the leveling apparatus  5 , and is cured and hardened to products. Curing may be natural curing (wet heat curing) or high-pressure steam curing (autoclave curing). As a way to perform the suction and dewatering, a sheet-form product, after the leveling apparatus  5 , is passed on a pressure reducer (or a vacuum source) to adjust the slurry to a specified water content. The permeable sheet may be wrapped around a plurality of driving rollers  9 ,  10  endlessly, for example, felt or wire (plastic, metal, etc.) may be used, and from the viewpoint of durability, felt and wire may be used together. 
     The slurry A is formed, for example, by pulp and cement which are dispersed in water. However it is to be understood that the slurry A compounding materials are not intended to be limited to this example. For example, cement and other fibers except pulp, or cement and other powders except silica, etc. may be used. The concentration of slurry A is desirably between about 35 and about 65% (solid weight/total weight). Experiments by the inventor have indicated that although the proper concentration varies in accordance with the slurry composition, generally maintaining a slurry concentration between about 35 and 65% is proper for fluidity of the slurry A and particularly achieve remarkable leveling effects. That is, if the slurry A concentration becomes high so as to exceed 65%, the fluidity is insufficient and consequently, effects of ensuring the product surface quality and effects of positively carrying out thickness control are unable to be expected. If the slurry A concentration is lower than 35%, the slurry A is easy to spill from the discharge port  7   b , and tends to be put into disorder even during production. It is understood that when the present invention is applied at a low concentration, the thickness is stably controlled by forming a slurry pool by tilting the permeable sheet  1  in front of the discharging port  7   b  (see FIGS. 3A-3B and  6 A- 6 B). 
     Accordingly, effects of ensuring the product surface quality, as well as effects of positively implementing thickness control and leveling are obtained, because the slurry concentration is between about 35 and about 65%, the fluidity of slurry is proper and at the same time, it is able to simultaneously solve the problem of ease of spilling of slurry from the discharging port. 
     The foreign matter removing apparatus  3  removes foreign matter contained in slurry A in order to form slurry A′ without harmful effects due to the foreign matter before dewatering. Furthermore, in the present embodiment, large foreign matter which is unable to pass a clearance of the discharging port  7   b  in the thickness control apparatus  4  is removed in advance by a slit-form foreign matter remover  11 . FIG. 2 shows one example of this slit-form remover  11 . In this example, a vibrating screen  11   a  with a pair of vibrators  11   c  arranged at both ends of slit-form screen  11   b  is used as the foreign matter remover  11 . Thus, by applying vibrating action to the screen  11   b , foreign matter in slurry A can be sufficiently removed before it is supplied onto the permeable sheet  1 . In this case, the minimum opening interval P of screen  11   b  is set to be smaller than the clearance H 1  (FIG. 3) of the discharging port  7   b . By this configuration, even if the opening interval P of the screen  11   b  is small, by vibrating the screen  11   b , removal of foreign matter in slurry A′ is positively carried out, and it is possible to prevent in advance the product surface quality from degrading by the foreign matter caught at the discharging port  7   b  when slurry A′ passes through the discharging port  7   b . In this way, carrying out treatment on foreign matter in the material of cement fiber sheet before suction dewatering device  8  enables positive thickness control and leveling, with the product surface quality ensured. 
     Next, the thickness control apparatus  4  brings slurry A′ to a specified thickness after the foreign matter removing apparatus  3 . As shown in FIG.  3 (A), a thickness controller  7  having a slurry charging port  7   a  is open at the top, and an elongated discharging port  7   b  is open at the front surface of the lower section. Clearance adjusting plate  13  that can be elevated with adjusting screws  12  is mounted to the top edge of the discharging port  7   b , and by vertically adjusting the position of the clearance adjusting plate  13 , the vertical clearance H 1  of the discharging port  7   b  is able to be adjusted. With this device, the thickness dimensions of slurry A′ discharged from the discharging port  7   b  can be controlled to a specified thickness. By intentionally varying the opening height of the discharging port  7   b  (clearance H 1 ) with the clearance adjusting plate  13 , cement fiber sheets with varying thickness can be manufactured. In addition, by varying the opening width (lateral width H 2 ) of the discharging port  7   b , it is easy to manufacture cement fiber sheets with varying lateral dimensions. 
     The leveling apparatus  5  is provided for smoothing slurry A′ surface after the thickness control apparatus  4 , and with this process, slurry A′ before dewatering is able to be formed into a sheet with good accuracy free of bad effects of foreign matter. In the present embodiment, as shown in FIG. 4, a vibrating leveler  2   a  is used for a leveler  2 . The vibrating leveler  2   a  includes a smooth-forming pressure plate  2   b  for smoothing the surface of slurry A′ discharged from the discharging port  7   b  of the thickness controller  7 , and a vibrator  2   c  for vibrating the smooth-forming pressure plate  2   b . The use of this type of vibrating leveler  2   a  enables effective leveling by vibrating leveler  2   a , and the product surface is able to be further improved. 
     In the present example, as shown in FIG. 4, the smooth-forming pressure plate  2   b  is tiltable and inclines downwardly in the travel direction B of the permeable sheet  1 . The smooth-forming pressure plate  2   b  is set to have an incidence angle θ of slurry A′, for example, between about 5 and about 10 degrees, and preferably 7 degrees. If the incidence angle θ is smaller than about 5 degrees, in particular, smaller than about 2 degrees, bubbles generated from products tend to remain on the surface, and if the incidence angle θ is greater than about 10 degrees in particular, when it exceeds about 20 degrees, a tendency to strip off may occur. Further when it exceeds about 30 degrees, thickness frequently tends to be uneven, and the desirable range of the incidence angle θ is assumed to be between about 5 and 10 degrees. In the present embodiment, 7 degrees is shown as one example. However, since the proper value of incidence angle θ varies in accordance with the slurry A concentration, the shape of the vibrating leveler  2   a , the travel speed of permeable sheet  1 , etc., it is necessary to adjust the angle θ due to these various conditions. Furthermore, the number of vibrating levelers  2   a  need not be limited to one but a plurality of units may be provided along the travel direction B of the permeable sheet  1 . 
     FIG. 5 shows a case in which an endless sheet  6  is installed between slurry A′ and the vibrating leveler  2   a . The endless sheet  6  includes an endless processed product of plastic mesh so that it is not subject to air bubbles generated at the time of vibrating leveling  5 , and particularly, it is effective to introduce the endless sheet  6  when a high level of product surface quality is required. In the present embodiment, the endless sheet  6  is wrapped endlessly around a plurality of rollers  20  arranged to externally surround the vibrating leveler  2   a . By pressing the smooth-forming pressure plate  2   b  against the slurry A′ surface via the rotatable endless sheet  6 , chafing does not occur between the smooth-forming pressure plate  2   b  and the slurry A′ surface. As a result, breaking of products caused by chafing between the slurry A′ surface and the vibrating leveler  2   a  is positively prevented. There is a problem of degrading the product surface quality by the influence of the vibrating leveler  2   a  itself, but installing the endless sheet  6  between the slurry A′ surface and the vibrating leveler  2   a , the above-mentioned problem is able to be solved. 
     Consequently, the use of endless sheets  6  is effective where still higher levels of product surface quality are required. However, if the higher levels of surface quality are not particularly required, the endless sheet  6  may be omitted. 
     In place of the vibrating leveler  2   a , for example, vibrating functions may be provided to the discharging port  7   b  of the thickness controller  7 , and thickness control and leveling may thus be simultaneously carried out at the discharging port  7   b . FIG.  6 (A) shows one example. In this example, at the upper part of the discharging port  7   b  of the thickness controller, a vibrating plate  30  is mounted, and a vibrator  31  is mounted on vibrating plate  30 . The bottom surface of the vibrating plate  30  has a clearance adjusting function. The top surface of the vibrating plate  30  is supported by the cushion retainer  32  mounted on the thickness controller  7  via a rubber cushion  33  so that vibration is not transmitted to the thickness controller  7 . The vibrating plate  30  has the function to smooth out the slurry A′ surface discharged from the discharging port  7   b  by the vibrating action in addition to the function of controlling the thickness size of slurry A′ surface discharged from the discharging port  7   b . When configured in this way, there is no need to use the vibrating leveler  2   a  at the leveling apparatus  5 , and it is possible to achieve an advantage that the leveling process is able to be simplified. Needless to say, the configuration equipped with the discharging port  7   b  having vibrating function of FIGS. 6A and 6B may be combined with the vibrating leveler  2   a  of FIG. 4, and in such event, this becomes still more effective to improve the product quality. 
     Description will be now made of Examples 1 through 4 of the present invention and Comparisons 1 through 3. Table 1 shows the results of Examples 1 through 4, while Table 2 shows the results of Comparison 1 through 3. 
     EXAMPLE 1 
     In the material compounding process, 5% pulp, such as Needle-leaved bleached Kraft pulp (NBKP), 50% cement, such as ordinary portland cement (OPC), and 45% silica powders were dispersed in water to make 25% (solid weight/total weight) slurry. In the foreign matter removing apparatus  3 , a slit form vibrating screen  11   a  (FIG. 2) was used. In this event, slit aperture (or minimum opening) interval P was set to 7 mm, and two units of vibrator  2   c  (150 W, 60 Hz) were used. The slurry after it was allowed to pass through the vibrating screen  11   a , was charged into a thickness controller  7  (FIGS. 3A and 3B) with a 10 mm vertical clearance H 1  (horizontal opening width H 2 : about 1000 mm) of the discharging port  7   b , the slurry A′ discharged from the discharge port  7   b  is supplied onto the permeable sheet  1 , and thereafter, it underwent the leveling process  5  to form a sheet. In the leveling process  5 , a leveler  2   a  (vibrator  2   c : 150 W, 60 Hz; press-down pressure: 12 kg was used. In addition, a smooth forming pressure plate  2   b  that served as vibrating plate is tilted so that the incidence angle θ of slurry A′ is 7 degrees. The width of the smooth-forming pressure plate  2   b  was set to 1000 mm and the length (flow direction) to 350 mm. 
     Thereafter, the sheet-form product that passed the vibrating leveler  2   a  was allowed to pass the pressure reducing device or suction device  8  (FIG.  1 ), thereby adjusting to a specified water content. In this event, the travel speed B of the permeable sheet  1  was set to 20 m/min (meter/minute) and the pressure reducing device  8  to 5 m in total length, and 34 Kpa in pressure reduction degree was used. The water content after dewatering was 28% (water volume/total weight). 
     In the present example 1, after dewatering, the sheet product was further press-dewatered, and after wet-heat curing, autoclave curing was carried out. Press-dewatering was carried out at 9.8 Mpa pressure for 2 seconds. Wet heat curing was carried out at 60° C. in saturated steam for 48 hours. Autoclave curing was carried out at 180° C. for 6 hours. 
     EXAMPLE 2 
     In Example 1 above, the slurry concentration was set to 40% or 60%. 
     EXAMPLE 3 
     In Example 1, an endless sheet  6  was rotatably installed between slurry A′ and vibrating leveler  2   a  (FIG.  5 ). For the endless sheet  6 , a plastic mesh endless processed sheet was used to prevent influence of air bubbles generated at the time of vibration leveling apparatus  5 . For the endless sheet  6 , a sheet 1.1 mm in mesh thickness, plain woven and aperture intervals of 1.44 mm was used. 
     EXAMPLE 4 
     In Example 1 above, in place of the vibrating leveling  2   a  of FIG. 4, a vibrating plate  30  and a vibrator  31  are mounted on the discharging port  7   b  of the thickness controller  7  shown in FIGS. 6A and 6B to provide leveling functions by vibrating action to the discharging port  7   b . The example was constructed in such a manner to prevent vibration from being transmitted to the thickness controller  7  by rubber cushion  33 . The vibrator  31  of 75 W and 60 Hz was used. 
     Therefore, it is possible to develop the efficiency of the system and at the same time to simplify the leveling process because when slurry is discharged from the discharging port  7   b , slurry thickness control and slurry surface smoothing are accomplished by the discharging port  7   b  for controlling slurry thickness and a vibrating plate  30  and a vibrator  31  for making the vibrating action in implementing the thickness control process. 
     Comparison 1 
     In Example 1, the thickness controlling process was omitted. 
     Comparison 2 
     In Example 1, the leveling process was omitted. 
     Comparison 3 
     In Example 1, the slurry concentration was set to 70% or higher. 
     The results of Examples 1 through 4 and of Comparisons 1 through 3 are shown in Table(s) 1 and 2 below. In the following Tables 1 and 2, “⊙”, “∘”, “Δ” and “X” respectfully represent “very good”, “good”, “satisfied” and “not good.” 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 (Test conditions) Slurry 
                 25% 
                 40% 
                 60% 
                 25% 
                 25% 
               
               
                 Concentration 
               
               
                 Foreign matter removal 
                 performed 
                 performed 
                 performed 
                 performed 
                 performed 
               
               
                 Thickness Control 
                 performed 
                 performed 
                 performed 
                 performed 
                 performed 
               
               
                   
                   
                   
                   
                   
                 with 
               
               
                   
                   
                   
                   
                   
                 leveling 
               
               
                   
                   
                   
                   
                   
                 function 
               
               
                 Vibration leveling 
                 performed 
                 performed 
                 performed 
                 performed 
                 equipped 
               
               
                   
                   
                   
                   
                 equipped 
                 to 
               
               
                   
                   
                   
                   
                 with 
                 discharge 
               
               
                   
                   
                   
                   
                 endless 
                 port 
               
               
                   
                   
                   
                   
                 sheet 
               
               
                 (Process condition) Slurry 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 fluidity condition 
               
               
                 Product Surface quality 
                 ◯ 
                 ◯ 
                 ◯ 
                 ⊚ 
                 Δ 
               
               
                 Thickness control 
                 ◯ ± 
                 ◯ ± 
                 ◯ ± 
                 ◯ ± 
                 ◯ ± 
               
               
                 accuracy 
                 1.2% 
                 0.7% 
                 0.8% 
                 0.6% 
                 1.5% 
               
               
                 (Product quality) 
                 ◯ 
                 ◯ 
                 ◯ 
                 ⊚ 
                 Δ 
               
               
                 Appearance 
               
               
                 Flexural strength 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
                 18 Mpa 
                 19 Mpa 
                 19 Mpa 
                 18 Mpa 
                 18 Mpa 
               
               
                 Absolute dry 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 Specific Gravity 
                 1.58 
                 1.59 
                 1.62 
                 1.57 
                 1.58 
               
               
                 Overall rating 
                 ◯ 
                 ◯ 
                 ◯ 
                 ⊚ 
                 Δ 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Comparison 1 
                 Comparison 2 
                 Comparison 3 
               
               
                   
               
             
            
               
                 (Test conditions) 
                 25% 
                 25% 
                 70% 
               
               
                 Slurry concentration 
               
               
                 Foreign matter 
                 performed 
                 performed 
                 performed 
               
               
                 removal 
               
               
                 Thickness control 
                 Not performed 
                 performed 
                 performed 
               
               
                 Vibration leveling 
                 performed 
                 Not performed 
                 performed 
               
               
                 (Process condition) 
                 ◯ 
                 ◯ 
                 Δ 
               
               
                 Slurry fluidity 
                   
                   
                 (partly 
               
               
                 condition 
                   
                   
                 retained) 
               
               
                 Product surface quality 
                 ◯ 
                 X 
                 X 
               
               
                   
                   
                 (breakage) 
                 (crack) 
               
               
                 Thickness control 
                 ◯ ± 
                 Immeasurable 
                 Immeasurable 
               
               
                 accuracy 
                 14.3% 
               
               
                 (Product quality) 
                 ◯ 
                 X 
                 X 
               
               
                 Appearance 
               
               
                 Flexural strength 
                 X 
                 X 
                 X 
               
               
                   
                 12 Mpa 
                 13 Mpa 
                 15 Mpa 
               
               
                 Absolute dry specific 
                 X 
                 ◯ 
                 ◯ 
               
               
                 gravity 
                 1.39 
                 1.56 
                 1.58 
               
               
                 Overall rating 
                 X 
                 X 
                 X 
               
               
                   
               
            
           
         
       
     
     In Table 2, the comparison, in case that the foreign matter removing process  3  was omitted is not shown, but if the foreign matter removing process  3  is not installed, problems shown in conventional cases apparently occur, and if aperture of minimum opening intervals P (FIG. 2) of the vibrating screen  11   a  used in the foreign matter removing process  3  are coarse, it is needless to say that the problem of the discharging port  7   b  of the thickness controller  7  being clogged by foreign matter in the slurry A′ certainly occurs. 
     As described above, it is possible to eliminate detrimental effects of foreign matter on the product appearance and at the same time it is possible to prevent holes, cracking, of breakage in products beforehand by providing a foreign matter removing process, and consequently, the product surface quality is able to be ensured and thickness control is able to be positively implemented. 
     It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.