Gypsum board forming device with improved slurry spread

Disclosed is a gypsum board forming device which provides improved slurry spread. The device includes a forming table with an arcuate or angled profile that promotes a uniform slurry spread. An arcuate or angled hinge plate can also be included to further promote the uniform distribution of slurry prior to an extrusion plate. As a result of the improved slurry spread, gypsum board with increased strength and durability can be created.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system for improving slurry spread. More specifically, the present invention relates to a forming table with an arcuate or angled cross section that improves the distribution of slurry in the area immediately prior to the pinch point.

2. Description of the Background Art

The prior art contains several examples of gypsum board forming devices. These devices employ various mechanisms for ensuring the shape and quality of the resulting board. For example, U.S. Pat. No. 2,722,262 to Eaton discloses an apparatus for the continuous production of a paper encased gypsum plaster strip. The apparatus includes a table over which a continuous strip is passed. The apparatus further includes a block and side guide members for shaping the strip and associated gypsum.

Additionally, U.S. Pat. No. 3,373,065 to Gutzman discloses a gypsum board forming machine. Support guides on the bed of the machine raise the edge portions of the bottom cover sheet to form a trough. Due to the depth of the trough, the head of the slurry which accumulates at the entrance to a board forming passageway is laterally confined.

U.S. Pat. No. 1,751,953 to Spengler discloses a plaster board manufacturing apparatus. The apparatus includes a conveyor onto which a plastic material is deposited. Damming bars are provided to prevent the plastic material from flowing from the applied sheet or from banking too near the edge thereof.

Finally, U.S. Pat. No. 5,718,797 to Phillips et. al. discloses an apparatus for manufacturing gypsum board. The apparatus includes a conveyor and a duct for dispensing gypsum slurry. The slurry flows and spreads out across an underlying sheet. Folding shoes are included at the borders for folding the borders upwardly.

Although the above referenced inventions achieve their individual objectives, all suffer from common drawbacks. Namely, none of the referenced inventions is directed at promoting the uniform distribution of slurry adjacent a pinch point.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of this invention to provide a gypsum board forming device that promotes the uniform distribution of slurry adjacent a pinch point.

It is yet another objective of this invention to provide a gypsum board forming device the promotes the spread of slurry to the edges of an associated forming table.

It is another objective of this invention to provide a gypsum board forming device that produces boards without voids and that have an improved strength and durability.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a gypsum board forming device which provides improved slurry spread. The device includes a forming table with an arcuate or angled profile that promotes a uniform distribution of slurry. The shape can be used in conjunction with conventional agitators that are likewise used to promote slurry spread. An arcuate or angled hinge plate can also be included to further promote the uniform distribution of slurry prior to an extrusion plate. As a result of the improved slurry distribution, boards with increased strength and durability can be created. The various details of the present invention, and the manner in which they interrelate, will be described in greater detail hereinafter.

With reference now toFIG. 1, the gypsum board forming device20of the present invention is depicted. Device20preferably includes three forming tables (22,24and26) arranged in end to end fashion. Nonetheless, those skilled in the art will appreciate that any number of board forming tables can be employed in conjunction with the present invention. As is known, the tables can include vibrators or agitators50(noteFIG. 5) that promote the uniform distribution of slurry.

A gypsum slurry42is supplied to the forming tables from a continuous mixer28via one or more boots60. Mixer28accepts the raw materials used to produce gypsum (i.e. stucco, plaster, gypsum, water and other additives) and produces a slurry mixture suitable for use in making gypsum board. The specific mixer28depicted includes three outlets (30,32and34), although any number of outlets can be employed depending upon the nature of the boards being produced. Separate mixing chambers can be included within mixer28for the purpose of providing slurry with varying consistency at the respective outlets. For example, slurry42provided to the facing sheets of the board may be more dense than the slurry constituting the core of the board.

With continuing reference toFIG. 1, the lower supply roll36of the device20is illustrated. This lower supply roll36spools out a bottom facing sheet38to the upper surface of the first forming table22. As is known in the art, this bottom facing sheet38can take the form of a fiberglass mat or a paper sheet. The composition and size of the sheet can be varied and will depend upon the intended use of the boards being produced.

After the facing sheet38is laid out on the forming table22, slurry42from mixer28is dispensed over top of sheet38by way of the first slurry outlet30. Thereafter, a roll coater44is used to spread the gypsum slurry42over bottom facing sheet38. Roll coater44preferably supplies a sufficient amount of pressure to ensure that the slurry penetrates the fibers of the mat, or is otherwise coated to the paper, so as to create a permanent bond. The speed of the rollers and the applied pressure can be adjusted to achieve optimal distribution and penetration. As is known in the art, a tensioning roller can be positioned immediately below the roller coater44.

FIG. 1illustrates that additional slurry42is dispensed over the facing sheet38along a second forming table24and via the second slurry outlet32. This additional slurry42forms the core of the resulting gypsum board product. Thus, the amount of slurry supplied by the second slurry outlet32will depend upon the intended use of the gypsum board being created.

A top facing sheet46is thereafter supplied from an upper supply roll48. As noted inFIG. 1, additional slurry from outlet34can be supplied to the lower surface of this top facing sheet46. The slurry supplied to this facing sheet is preferably more dense than the slurry used to form the core. Sheet46can consist of the same construction used for the lower facing sheet38. In a manner known in the art, the upper sheet46is thereafter delivered overtop of the gypsum slurry42to form a composite board construction.

As illustrated inFIG. 1, this upper sheet46is preferably delivered to the process via an extruder assembly. The extruder assembly includes both a hinge plate52and an extruder plate54. These plates (52and54) are pivotally interconnected to one another along a hinge56and are generally oriented at a distance above the bottom plate of the extruder assembly.

Hinge56allows the two plates (52and54) to pivot with respect to each other. In normal operation, slurry accumulates in a head58adjacent to the hinge plate52. Slurry head58, in turn, causes the hinge plate52to pivot upwardly relative to the horizontal. By contrast, once slurry42reaches the extruder plate54it is generally smoothed out and has attained a thickness that generally matches the desired board thickness. Accordingly, as the hinge plate52forces the slurry head58into extruder plate54, a pinch point62is created.

Pinch point62may have the undesirable tendency of creating a non-uniform profile in the slurry42as it approaches the extruder plate54. This non-uniform profile64is illustrated inFIG. 6. One characteristic of this profile is that eddie currents66are formed in the areas adjacent the edges of the forming table26. The non-uniform slurry64distribution has many undesirable consequences. For instance, the resulting gypsum board often includes voids and density variations that yield boards of reduced strength.

In accordance with the present invention, a uniform distribution of slurry is promoted by providing an arcuate cross section68along the second and third forming tables (24and26). More specifically, as noted inFIG. 2a, table24includes a raised central area72and lower side regions74in the area immediately adjacent the second outlet32of mixer28. The profile transitions from the arcuate profile along the second forming table24(noteFIG. 2a), to a slightly less arcuate profile along the third forming table26(noteFIG. 3a), and finally to a planar profile78immediately adjacent the extruder plate54(noteFIG. 4). This continuous transition ensures an adequate distribution of slurry at the slurry head58, but at the same time ensures that a flat board is produced within extruder plate54.

Although the preferred embodiment is described in conjunction with arcuate profiles (noteFIGS. 2aand3a), the present invention can also be carried out with other shapes. For example, forming tables with an angled profile (noteFIGS. 2band3b) and likewise be used to promote slurry distribution. Namely, the tables would include a raised center portion88with downwardly sloped sides86. The preferred embodiment would likewise be tapered from the second to the third tables (24and26). In other words, the angle formed along the second table24(FIG. 2b) would be greater than angle along the third table26(FIG. 3b). This transition would be continuous with a planer cross section78being achieved immediately before the extruder plate54(FIG. 4).

Still yet further slurry distribution can be achieved via an arcuate or angled hinge plate52. Namely, the distal end52aof hinge plate52can be curved upwardly82with respect to the third forming table26(noteFIG. 3a). Namely, the curvature82of the distal end52aof plate52would be opposite the curvature68of the underlying table26. As noted inFIG. 3a, this has the tendency of forcing the slurry42between plate52and table26to the outer edges of the table, thereby promoting a more uniform distribution. This construction, in turn, eliminates the eddies66that would otherwise form between two planar profiles.

Although extruder plate52has been described with an arcuate cross section82, an angled cross section92can also be used at the distal end52aof hinge plate52(noteFIG. 3b). Again, the preferred angle is opposite the angle of the underlying table26. In other words, whereas the sides86of table26are angled downwardly, the sides90of the distal end52aof hinge plate52are upwardly angled. Consequently, slurry42is pushed outwardly in a manner akin to water passing over a ships bow.

Whatever shape is used for the distal end52aof hinge plate52, the proximal end52badjacent pinch point62is planar80(noteFIG. 4). Again, there is preferably a uniform transition between the distal and proximal ends (52aand52b). This planar cross section80of the proximal end52bis illustrated inFIG. 4an ensures that the top sheet46is evenly applied to the underlying slurry42.

In still yet further embodiments of the present invention, the shape of the distal end52aof hinge plate52can be changed. In one embodiment, this is achieve by forming hinge plate52from an expansible bladder than can be inflated or deflated as necessary to change the shape and/or curvature of the plate. In still yet another embodiment, the angled hinge plate92includes a hinge intermediate sides90which allows the angle formed to be adjusted as needed.