CA1284290C - Method and apparatus for reclaiming gypsum from waste wallboard - Google Patents

Abstract

METHOD AND APPARATUS FOR RECLAIMING
GYPSUM FROM WASTE WALLBOARD

ABSTRACT

This invention pertains to a method and apparatus for reclaiming gypsum from waste gypsum wallboard. The invention is directed to an apparatus that is useful for separating paper laminate from gypsum wallboard comprising: a) a first roller means; b) a second means spatially disposed from the first roller means. The first and/or second means can be driven together or independently from the same or a separate power source.

Description

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METHOD AND APPARATUS FOR RECLAIMING
GYPS~M FROM WASTE WALLsoARD

FIELD OF THE INVENTION

This invention pertains to a method and appar-atus for reclaiming gypsum from waste gypsum wallboard.

BACKGROUND OF TE~E INVENTION

Gypsum wallboard, comprising a gypsum core and planar paper outer surfaces, is widely and extensively used by the western building construction industry in the construction of residential and commercial build-ings. The gypsum wallboard is typically supplied insheets measuring 4 feet by 8 feet. In many situations, only a portion of the wallboard panel can be used, the extraneous portions being cut away by the wallboard installer. As a consequence, in any building construc-tion or renovation project, there is generated a sub-stantial amount of waste gypsum wallboard. As much as 10 percent of the gypsum wallboard panels supplied to the construction site may end up as waste gypsum wall-board.

This waste wallboard has, in the past, created disposal problems in the Greater Vancouver Regional District in British Columbia, Canada, because when the waste wallboard is buried in a conventional waste landfill operation, obnoxious hydrogen sulfide gas and soil leachate are generated. The generated odour prob-lem has made it necessary to initiate a program of special sorting, stockpiling, storage, and material-shandling to faciliate ocean dumping. Currently, in the Greater Vancouver Regional District of British Columbia, 12~34290 approximately 20,000 tons per year of gypsum wallboard waste material is dumped in the Pacific ocean. This is an expensive waste disposal procedure. It may also lead ultimately to ocean pollution.

A serious problem with waste gypsum wallboard is that the paper outer layers remain bonded to the gypsum core. It is difficult to efficiently remove the paper outer layers from the core without leaving a substantial amount of paper residue on the gypsum. Gypsum wallboard manufacturers have to date been unable to recycle any more than about one percent of the total waste wallboard production, because paper contamination of the finished product must be minimized. Such manufacturers currently use a combination of hammer mills and screening plants which, under ideal conditions, is capable of removing about 65 percent of the paper. This process requires considerable energy consumption and creates unwanted airborne dust.

SUMMARY OF THE INVENTION
The invention is directed to an apparatus that is useful for separating paper laminate from gypsum wallboard comprising: (a) a first roller means; and (b) a second means spatially disposed from the first roller means. The first and/or second means can be driven together or independently from the same or independent power source(s).

The second means can be a roller. In the apparatus, the first and second roller means may be axially mounted parallel cylindrical rollers. The surface areas of the first and second rollers may be smooth.

In the apparatus, the first and second rollers may be mounted on steady bearings. In the apparatus the first and second rollers may be reinforced by back-up rollers. A second pair of rollers may be mounted in tandem with the first and second rollers.

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The invention is also directed to a process of removing paper laminate from paper laminate gypsum core wallboard comprising passing the wallboard through a pair of parallel axially mounted roller means, the aperture between the pair of roller means being sized to be slightly less than the cross-sectional dimension of the wallboard so that the roller means generates a wave form action in the wallboard, thereby inducing the two paper laminates to separate from each side of the gypsum core.

In the method, one of the roller means may be powered, while the other roller means may be unpowered and follows the powered roller means when wallboard is passed between the pair of roller means. Alternatively, both rollers may be powered with a limited slip device, or by separate power sources that can speed up, or slow down as resistance increases or decreases.

DRAWINGS
In drawings which illustrate specific embodiments of the invention but which should not be construed as restricting the spirit or scope of the invention in any way:

F gure 1 illustrates a side elevation view of a twin roller system used to separate the paper laminates from each side of a gypsum core:

Figure 2 illustrates a cross-sectional side view of a typical gypsum wallboard construction;

Figure 3 illustrates an end view of a conventional gypsum wallboard;

Figure 4 illustrates a side elevation view of gypsum wallboard apparatus comprising a pair of main rollers reinforced respectively by a pair of back-up rollers abutting the respective lZ~34;;:90 sides of the roller opposite the compression faces of the rollers; and Figure 5 illustrates a side elevation view of a gypsum wallboard separation apparatus comprising a first pair of rollers and a second pair of rollers mounted in tandem with the first pair of rollers.

DETAILED DESCRIPTION OF

SPECIFIC EMBODIMENTS OP THE INVENTION

Figure l of the drawings illustrates a side elevation view of the twin roller system as it is used to separate the paper laminates from each side of the gypsum core. The bottom roller as shown in Figure 1 of the drawings need not be a roller.
It can be a stationary surface such as a floor or the top of a table. When only one roller is used, the interface between the layer of paper abutting the roller and the gypsum core separ-ates. The gypsum-paper interface on the opposite side of the wallboard must be separated in a subsequent operation by passing the gypsum wallboard in inverted manner so that the roller abuts the exterior surface of the paper on the non-separated side of the gypsum wallboard. As depicted in Figure 1, the upper roller 2 is rotatably mounted on a shaft 4. The top roller 2 in one embodiment is non-driven. The lower roller 6 is also rotatably mounted on a shaft 8, which has a drive - 3a -,. . .

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gear 10 mounted thereon. The lower roller 6 is driven by a suitable drive means via gear 10 in a counterclock-wise direction, as indicated by the directional arrow.
AS can be seen in Figure l, the non-driven rcller 2 and the driven roller 6 are spaced apart so that they have an aperture between them which is slightly less than the thickness of the waste wallboard product 12. The rollers 2 and 6 compress the exterior regions of the wallboard product 12 slightly, and by means of a wave action as described herein, causes the two paper laminates 14 and 16 to separate from each side of the gypsum core 18.

A~ter separation, the respective paper laminates 14 and 16 may be easily separated from the gypsum core 18 with minimum gypsum residue on the paper.
The wave form action created in the wallboard by the pair of rollers 2 and 6, it has been found, does not crush the gypsum core 18, but generally leave the core in one piece for easy handling.

In an alternative embodiment, both rollers 2 and 6 may be driven, either independently from separate power sources, or from a common power source with a slip clutch between the two drive mechanisms. It is impor-tant that the two rollers can rotate at independent speeds to accommodate waves and imperfections in the wallboard 12. Independent drive motors can be used which can speed up or slow down as required.
Figure 2 of the drawings illustrates a cross-sectional side view of a typical gypsum wallboard con-struction. The upper paper sheet 14 and the lower paper sheet 16 encase the gypsum core 18. Typically, the paper laminate 14 is the back-face of the wallboard - ~Z84~90 while the paper laminate 16 is the front face of the wallboard. AS can be seen in Figure 2, which is exag-gerated for emphasis, a large number of discrete air bubbles 20 are entrapped in the core 18 during the formation of the gypsum wallboard. Since the gypsum wallboard is normally formed along a horizontal produc-tion line, a majority of the entrapped air bubbles migrate to the top of the core 18 and come to rest in the region adjacent the rear paper laminate 14. The bubbles 20, and the uneven distribution thereof, add a variability factor to the waste recovery process and thus demand that the opening (aperture) between the roller pair 2 and 6 cannot be uniform. Likewise, roller speeds must be independent to accommodate the imperfec-tions.

Figure 3 illustrates an end view of a conven-tional gypsum wallboard, and in particular illustrates the tapered edges 22 and 24. To maximize efficiency in waste paper removal from the waste gypsum wallboard, we have found that it is preferable to cut away the tapered edges 22 and 24 before feeding the waste gypsum wall-board into the rollers 2 and 6.

A difficulty we have discovered with narrower diameter rollers is that when such rollers extend over a distance of 4 feet or more, in order to accomodate the width of a standard wallboard, the interior regions of the roller may warp or bow slightly away from the wallboard, which means that less compression force is applied to the interior regions of the wallboard, compared to the outer regions of the rollers. In order to maintain a uniform compression force across the span of the rollers, it may be necessary to utilize steady bearing rollers, which are mounted on the sides of the rollers remote from the wallboard compressing side of the rollers. Such steady bearing rollers help minimize the bowing that may take place in narrow diameter long rollers.

Alternative systems for maintaining linear dimension stability of small diameter rollers can be designed. For example, it may be feasible to mount a narrow diameter roller against a pair of reinforcing rollers abutting the side of the roller opposite the compression face of the roller. The pair of reinforcing rollers serve to cradle the operational roller as it rotates during the wallboard separation process. Such an arrangement is illustrated in side elevation view in Figure 4 of the drawings.

In certain situations, it may be advantageous to utilize roller pairs in series with one another in order to maximize paper laminate separation action. TWo or more pairs of rollers may be utilized for this purpose. The aperture between the downstream pair of rollers may be varied relative to the aperture between the upstream rollers, in order to enhance paper laminate separation. Such an arrangement is illustrated in side elevation view in Figure 5.

ExamPle Research and development on the problem of completely removing the paper from waste gypsum wall-board was commenced using various techniques. Methods which were initially tried but later discarded were:
mass crushing and screening, localized impact crushing, hydraulic shearing, abrasive planing, burning, cold and hot water separation by agitation and water jet peeling.

We found that all of these processes had assorted dis-advantages in handling and sorting of material, dust control, energy consumption, and production of unmanage-able by-products.

After considerable experimentation and dis-appointments with other techniques, we discovered that a pair of smooth rolls of similar size diameters, with one roller being driven and the other following in the oppo-site direction, when set at an appropriate roller open-ing size compressed and removed the back and face paper sheets of waste and new gypsum wallboard efficiently and consistently with minimum gypsum residue on the sepa-rated paper.
We discovered that the rollers acted by frac-turing the crystalline particles of gypsum which bonded the paper to the core gypsum material. We also dis-covered that the paper separation process was induced by a "wave-like" motion which was generated by the rollers.
This motion compressed the bonding particles into the adjacent entrapped air pockets, thereby creating a total release of the paper.

We have also discovered several critical ~eatures and properties that the rollers must have:

1. The rollers must have an aperture set at a dimension slightly smaller than the wallboard thickness.
If the aperture is too small, the core will fracture along in the centre line of the core, thereby rendering the process useless because about half the gypsum core remains adhered to each paper sheet.

2. The roller aperture must be adjustable. The air content of the core material and the thickness of the wallboard varies from producer to producer and even from one day's production to the next. Thus no set aperture can be used.

3. The rollers must be constructed of suffi-ciently strong material, e.g. steel, to minimize flexing due to high compressive strength of the wallboard.

4. The span of the rollers can be increased by using "steady bearings", which prevent the rollers from bowing.

5. The roller surfaces should preferably be smooth to create a consistent wave-like paper separation motion in the wallboard.

6. Rollers with knurled surfaces are somewhat effective but are less efficient due to locational debonding between the paper and the core.

7. For best results, in certain situations, it may be discovered that both rollers should not be driven. In this situation, one should be driven and the other should follow in order to accomodate different wallboard surface characteristics and thicknesses. In typical wallboard, the air bubbles are more concentrated on the backside of the wallboard. Also, there is gener-ally damage caused to the wallboard surface duringinstallation and scrap removal. These differences are variable and cause the rollers to speed up and slow down together or separately in relationship to the wallboard area travelled over by the rollers. In other situa-tions, it may be found that both rollers can be driven lZ84Z9~

with a limited slip device, or friction clutch device,or by two separate motors.

8. For typical 1/2" or 5/8" wallboard, a pair of rollers of 1 1/2" diameter create the best wave motion for core-paper separation. we have experimented with 1/2" diameter to 12" diameter rollers but have found that roller sizes in the 1" to 4" diameter range are most successful.

9. The rollers can be used in tandem for treating running 5/8" and 1/2" wall board simultaneously, or can be used adjacent to one another for hand or machine sorting.

10. Using a hand-cranked prototype, roller rota-tion speeds in the range of 60 to 100 rpm have been found to be suitable. However, under production condi-tions, we do not foresee any problem in operating the rollers at about 1,000 rpm. The higher rotational speeds would increase production capacity. AS a general rule, both rollers should be independently driven for higher productions speeds.

Process operation Characteristics In preparing the waste wallboard for separa-tion, we have found that it is more efficient to remove the factory tapered edge (which is of less thickness than the interior) by cutting prior to separation.
Multiple sets of rolls with progressively smaller openings can be used to compress the board and its factory tapered edge.

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Removal of 100 percent of the front and back paper from the gypsum core material is possible using our process and apparatus. our process therefore should allow all of the 10 percent of construction wallboard waste to be recycled. The process and apparatus are energy efficient to operate. The system creates very little dust or noise pollution.

If both rollers are driven, we have determined that binding problems occur, gear and motor wear prob-lems ensue, and operation is not as trouble-free as is the case when only one of the rollers is driven unless each roller is driven independently or there is a slip clutch between the rollers so that they can deal with individual imperfections. Having one drive roller, and one follower roller, is best suited for accommodating the variations in consistency and thickness in various wallboards, at relatively low speeds. At higher speeds, two driven rollers are advantageous provided they can travel at independent speeds when necessary.

We have also discovered that it is incon-sequential whether the side of the wallboard with the concentration of air bubbles faces up or down, or faces the drive roller than the follower roller. Either orientation appears to work equally well. We have dis-covered, however, that if the aperture between the two rollers is set too wide, so that a suitable compression force on the wallboard is not obtained, complete separa-tion of the paper laminate on the concentrated bubble~ide of the core takes place, but there is not consis-tent separation of the paper laminate on the opposite side. On the other hand, if the aperture between the two rollers is set too narrow, undue bite occurs on the two faces of the wallboard and the gypsum core tends to 1;~8~

fracture approximately equidistant between the two paper laminates.

Smaller diameter rollers are preferred because a stronger, more useful paper-gypsum separating wave action is generated by small rollers. If larger rollers are used, it appears that insufficient concentrated bite between the rollers is obtained, and the necessary wave action for paper laminate separate does not occur, or is not optimum. Larger rollers also tend to leave too much gypsum residue on the paper laminates, even though there may be separation of the paper from the gypsum core.
Since the separated paper laminates are discarded, it is advantageous for efficiency and economy reasons that as little gypsum as possible remains on the paper. With smaller diameter rollers, we have found that less than 3 percent gypsum residue remains on the separated paper laminates.

We have also observed, during operation of the prototype, that the wave action that is created in the interior of the gypsum wallboard as the wallboard passes through the aperture between the two rollers, tends to cause the paper laminate to hop or skip in small visible increments. This action appears to promote a separation action between the paper laminates and the gypsum core.

It has also been determined that if too high a compression force is exerted by the rollers on the gyp-sum wallboard, the separated paper laminate tends tocurl backwardly. This can cause problems by the paper becoming caught up in the upstream side of the roller.
In such cases, it may be necessary to install blades or foils which prevent the paper from curling backwardly and being caught up in the rollers. The ideal operating situation occurs where proper compression forces are applied and the separated wallboard paper laminate tends to remain relatively linear, with the core an integral entity in itself. In this fashion, the generation of airborne gypsum dust is minimized and is retained between the linear paper laminates.

As will be apparent to those skilled in the art in light of the foregoing disclosure, many altera- ~
tions and modifications are possible in the practice of this invention without departing from the spirit or scope thereo. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

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Claims (14)

1. An apparatus for separating paper laminate from both sides of paper laminated gypsum wallboard comprising:
(a) a first roller means;
(b) a second roller means spatially disposed from the first roller means; and (c) power means for driving either one or both of the roller means.

2. An apparatus as defined in claim 1 wherein the first and second roller means are axially mounted parallel cylindrical rollers.

3. An apparatus as defined in claim 1 wherein the first roller means is driven by the power means.

4. An apparatus as defined in claim 1 wherein the first and second roller means are driven by the power means but each roller means can rotate at an independent speed.

5, An apparatus as defined in claim 4 wherein the first and second roller means are driven independently by separate power means.

6. An apparatus as defined in claim 2 wherein the surface areas of the first and second rollers are smooth.

7. An apparatus as defined in claim 2 wherein the surfaces of the first and second rollers are roughened.

8. An apparatus as defined in claim 2 wherein the first and second rollers are mounted on steady bearings.

9. An apparatus as defined in claim 2 wherein the first and second rollers are reinforced by back-up rollers.

10. An apparatus as defined in claim 2 wherein a second pair of rollers is mounted in tandem with the first and second rollers.

11. A process of removing paper laminate from paper laminate gypsum core wallboard comprising passing the wallboard through a pair of parallel axially mounted roller means, the aperture between the pair of roller means being sized to be slightly less than the cross-sectional dimension of the wallboard so that the roller means generates a wave form action in the wallboard, thereby inducing the paper laminate to separate from the gypsum core.

12. A method as defined in claim 11 wherein one of the roller means is powered, while the other roller means is unpowered and follows the powered roller means when wallboard is passed between the pair of roller means.

13. A method as defined in claim 11 wherein each roller means is independently powered so that each roller means can rotate at an independent speed.

14. An apparatus for separating paper laminate from paper laminated gypsum wallboard comprising:
(a) a first roller means;
(b) a second means spatially disposed from the first roller means and adapted to exert a force between the first roller means and gypsum wallboard when it is passed through the space between the first roller means and the second means; and (c) power means for rotating the first roller means against the wallboard when the wallboard is passed between the first roller means and the second means.