Note: Descriptions are shown in the official language in which they were submitted.
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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,
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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
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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
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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
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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
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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
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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
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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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