Wallboard slurry mixer configured for reducing water:stucco ratio

Abstract

An agitator for a gypsum wallboard mixer is provided and includes a circular disc with an upper surface, a drive shaft extending vertically from the upper surface, a lump ring secured to the upper surface, the lump ring being provided in a plurality of spaced, adjacent arcuate segments.

Claims

1. An agitator for a gypsum wallboard mixer, the mixer including an annular lid ring having a diameter and connected to and depending from an inner surface of an upper wall, said agitator comprising: a circular disc with an upper surface; a drive shaft extending vertically from said upper surface; a lump ring secured to said upper surface, said lump ring having a diameter just smaller than said annular lid ring and being provided in three spaced, adjacent arcuate segments, each said segment extending approximately 120 of a circle defined by said lump ring; and wherein gaps are formed between ends of said adjacent segments.

2. The agitator of claim 1, wherein said circular disc has a vertical axis, and said drive shaft is mounted to said circular disc at said vertical axis.

3. The agitator of claim 1, wherein said three segments are of equal length.

4. The agitator of claim 1, wherein said gaps range from to 2 inches.

5. The agitator of claim 1, wherein said lump ring is inch tall.

6. The agitator of claim 1, further including at least one pin projecting from said upper surface of said circular disc.

7. The agitator of claim 1, wherein an upper edge of said lump ring overlaps a lower edge of the lid ring to create a serpentine path for the slurry as the slurry migrates radially outwardly due to centrifugal force.

8. A slurry mixer, comprising: an upper wall and a lower wall, with an annular peripheral wall attached to and vertically separating said upper and said lower walls, said upper, lower and annular peripheral walls defining a chamber, an annular lid ring having a diameter and connected to and depending from an inner surface of said upper wall; at least one inlet in at least one of said upper wall and said lower wall; a circular disc with an upper surface disposed in said chamber; a drive shaft extending vertically from said upper surface and projecting from said upper wall; a lump ring secured to said upper surface, said lump ring having a diameter just smaller than said lid ring and being provided in three spaced, adjacent arcuate segments each extending approximately 120 of a circle defined by said lump ring; and wherein gaps are formed between ends of said adjacent segments and wherein an upper edge of said lump ring overlaps a lower edge of the lid ring to create a serpentine path for the slurry as the slurry migrates radially outwardly due to centrifugal force.

9. The mixer of claim 8, wherein said lump ring is provided in three equal length segments.

10. The mixer of claim 8, wherein said gaps range from to 2 inches.

11. The mixer of claim 8, wherein said lump ring is inch tall.

12. The mixer of claim 8, further including at least one agitating formation projecting from said upper surface of said circular disc.

13. The mixer of claim 12, wherein said at least one agitating formation is a pin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an overhead plan view of a conventional gypsum slurry mixer;

(2) FIG. 2 is a cross-section taken along the line 2-2 of FIG. 1 and in the direction generally indicated;

(3) FIG. 3 is a fragmentary overhead plan view of a conventional gypsum slurry mixer;

(4) FIG. 4 is a fragmentary side perspective view of the conventional slurry mixer of FIG. 3;

(5) FIG. 5 is a fragmentary top perspective view of the present gypsum slurry mixer;

(6) FIG. 6 is a fragmentary overhead plan view of the present gypsum slurry mixer; and

(7) FIG. 7 is a fragmentary side perspective view of the present gypsum slurry mixer.

DETAILED DESCRIPTION

(8) Referring now to FIGS. 1 and 2, a prior art gypsum wallboard slurry mixer is generally designated 10, having a generally cylindrical shape, with a generally vertical axis 12, and upper wall 14, a lower wall 16 and an annular peripheral wall 18 secured to and vertically spacing the upper and lower walls. An inlet 20 for calcined gypsum and an inlet 22 for water are both preferably positioned in the upper wall 14, preferably proximate the vertical axis 12. It is contemplated that the location of the inlets 20, 22 may vary to suit the application, and may be provided in the lower wall 16 depending on the application. Also, the inlets 20, 22 are connected to corresponding supplies of calcined gypsum and water that deliver constituents to the mixer 10 by gravity feed. Also, as is well known in the art, other materials in addition to gypsum and water are added to the slurry to prepare gypsum products, such materials, collectively referred to as additives, including but are not limited to accelerators, retarders, fillers, binders and the like. The additives are supplied through the inlets 20, 22 or through supplemental designated inlets (not shown).

(9) Referring now to FIG. 2 an agitator 24 includes a circular disc 26 connected to a drive shaft 28 that is preferably located at the vertical axis 12. Preferably, the drive shaft 28 projects along the vertical axis from the upper wall 14. A motor (not shown) is connected to the drive shaft 28 and axially rotates the shaft and the disc 26. An upper surface 30 of the disc 26 preferably is provided with at least one vertically projecting agitating formation 32 such as a pin or a paddle to enhance agitation of the slurry. In addition, the mixer 10 includes an annular ring 34 connected to and depending from an inner surface 36 of the upper wall 14. The ring 34 is often referred to as a lid ring, and enhances mixing action in the mixer 10 by preventing larger agglomerations or lumps of calcined gypsum from exiting an interior chamber 38 of the mixer before becoming more finely divided and dispersed in the slurry. As is known in the art, the agitator 24 is located within the chamber 38.

(10) Referring now to FIGS. 3 and 4, it is also known to provide gypsum slurry mixers 10 with a so-called annular lump ring 40 attached to the upper surface 30 of the agitator disc 26. Preferably, the lump ring 40 has a diameter that is just smaller than the lid ring 34 and projects vertically upward, or opposite from the lid ring so that an upper edge 42 of the lump ring overlaps (while slightly radially displaced) a lower edge 44 of the lid ring to create a serpentine or labyrinth path (FIG. 4) for the slurry as it migrates from the vertical axis radially outwardly due to centrifugal force. A preferred height of the lump ring 40 is inch (0.9525 cm).

(11) It has been found that conventional mixers with the overlapping lid ring 34 and the lump ring 40 tend to increase the residence time of the slurry in the mixing chamber 38. A problem with longer slurry residence time in the mixing chamber 38 is that water needs to be added to maintain the desired viscosity of the slurry. In general, in wallboard panel production, it is undesirable to add water to the slurry because of the additional energy in the form of heat that is needed to dry the panel after forming. This heat is typically applied downstream of the mixer 10, after the wallboard panels have been formed.

(12) Referring now to FIGS. 5-7, the present wallboard slurry mixer is generally designated 50 and components shared with the mixer 10 are designated with identical reference numbers. A main feature of the mixer 50 is that the lump ring 40 is separated into three arcuate segments designated 40a, 40b, 40c. Each pair of the segments 40a, 40b, 40c is separated by a gap 52 which preferably extends vertically a height H of the lump ring 40 and ends at the upper surface 30 of the disc 26. While it is contemplated that the gap 52 varies between inch to 3 inches, a preferred gap is 2 inches (6.6675 cm). To maintain balance of the rotating disc 26, which has a rotational speed of approximately 300 RPM, three gaps 52 are provided in the lump ring 40, and the segments 40a, 40b and 40c are equal in arcuate length. In the preferred embodiment, each of the segments 40a, 40b, 40c extend approximately 120 of a circle defined by the lump ring 40. It is contemplated that other segment lengths are contemplated depending on the particular application.

(13) An advantage of providing the gaps 52 in the lump ring 40 is that the residence time of the slurry in the chamber 38 of the mixer 50 is reduced. By reducing the slurry residence time, the amount of water added to the slurry during mixing is also reduced, which consequently reduces the amount of energy needed to dry the wallboard panels once formed on the production line downstream of the mixer 50. A common measure of the amount of water in the gypsum wallboard slurry in the mixer 50 is the water:stucco ratio. This value represents the Total Water Weight divided by the Stucco Weight100%. A typical water:stucco ratio is 80%. In other words, for 1,000 pounds of stucco, 800 pounds of water is used. Using the water:stucco ratio, a value of Total Calculated Water is achieved using the equation:
Total Water=StuccoWater:Stucco Ratio.

(14) It has been found that the use of the gaps 52 has reduced the water:stucco ratio in the mixer 50 2% compared to the similar performance of the conventional mixer 10. With the prior art lump ring without the gaps 52, the mixer 10 had a water:stucco ratio of 85.5%. Using the present lump ring 40 with the gaps 52 resulted in a water:stucco ratio of 83.5%. In the mixer 10 with the prior lump ring, using the above formula: 0.855 (water:stucco ratio)9211b/MSF (stucco)=787.45 lb/MSF total water. In contrast, with the present mixer 50 having the gaps 52: 0.835921 lb/MSF=769 lb/MSF total water. The resulting 18 lb/MSF of total water reduction translates to a reduction of 10 degrees of heat in the kiln used to dry the resulting wallboard panels, and an increase of 5 ft/min of board speed.

(15) It has been found that the presence of the gaps 52 does not impair the function of the lump ring 40 in regulating the size of calcinated gypsum lumps which are allowed to pass out of the mixer 50.

(16) While a particular embodiment of the present wallboard slurry mixer configured for reducing water:stucco ratio has been described herein, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.