NZ627442B2 - A pressing assembly and method for forming a depression within a moving, gypsum board - Google Patents
A pressing assembly and method for forming a depression within a moving, gypsum board Download PDFInfo
- Publication number
- NZ627442B2 NZ627442B2 NZ627442A NZ62744212A NZ627442B2 NZ 627442 B2 NZ627442 B2 NZ 627442B2 NZ 627442 A NZ627442 A NZ 627442A NZ 62744212 A NZ62744212 A NZ 62744212A NZ 627442 B2 NZ627442 B2 NZ 627442B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- board
- pressing
- assembly
- speed
- moving
- Prior art date
Links
- 229910052602 gypsum Inorganic materials 0.000 title claims abstract description 56
- 239000010440 gypsum Substances 0.000 title claims abstract description 56
- 230000036571 hydration Effects 0.000 claims description 12
- 238000006703 hydration reaction Methods 0.000 claims description 12
- 229920002545 silicone oil Polymers 0.000 description 12
- 238000005520 cutting process Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005755 formation reaction Methods 0.000 description 3
- 239000005871 repellent Substances 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 210000001503 Joints Anatomy 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000011505 plaster Substances 0.000 description 2
- 210000001138 Tears Anatomy 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- PASHVRUKOFIRIK-UHFFFAOYSA-L calcium sulfate dihydrate Chemical group O.O.[Ca+2].[O-]S([O-])(=O)=O PASHVRUKOFIRIK-UHFFFAOYSA-L 0.000 description 1
- ZOMBKNNSYQHRCA-UHFFFAOYSA-J calcium sulfate hemihydrate Chemical compound O.[Ca+2].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O ZOMBKNNSYQHRCA-UHFFFAOYSA-J 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000001351 cycling Effects 0.000 description 1
- 150000004683 dihydrates Chemical group 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 230000000737 periodic Effects 0.000 description 1
- 229920001296 polysiloxane Polymers 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000002940 repellent Effects 0.000 description 1
- 238000007665 sagging Methods 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
- B28B11/00—Apparatus or processes for treating or working the shaped or preshaped articles
- B28B11/08—Apparatus or processes for treating or working the shaped or preshaped articles for reshaping the surface, e.g. smoothing, roughening, corrugating, making screw-threads
- B28B11/0863—Apparatus or processes for treating or working the shaped or preshaped articles for reshaping the surface, e.g. smoothing, roughening, corrugating, making screw-threads for profiling, e.g. making grooves
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
- B28B11/00—Apparatus or processes for treating or working the shaped or preshaped articles
- B28B11/08—Apparatus or processes for treating or working the shaped or preshaped articles for reshaping the surface, e.g. smoothing, roughening, corrugating, making screw-threads
- B28B11/10—Apparatus or processes for treating or working the shaped or preshaped articles for reshaping the surface, e.g. smoothing, roughening, corrugating, making screw-threads by using presses
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
- B28B17/00—Details of, or accessories for, apparatus for shaping the material; Auxiliary measures taken in connection with such shaping
- B28B17/02—Conditioning the material prior to shaping
- B28B17/023—Conditioning gypsum
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
- B28B19/00—Machines or methods for applying the material to surfaces to form a permanent layer thereon
- B28B19/0092—Machines or methods for applying the material to surfaces to form a permanent layer thereon to webs, sheets or the like, e.g. of paper, cardboard
Abstract
pressing assembly (10) and a method for forming a depression within a moving, wet gypsum board is disclosed. The assembly comprises a pressing head comprising a pressing surface which is arranged to contact the board, and a support member, the pressing head being arranged to compress a portion of the board between the pressing surface and the support member (17) to form a depression within the board (10). The pressing surface comprises a first and second surface portion separated by a relief portion, which is arranged to press the board toward the support head (17) with less compressive force than the first and second surface portion. The assembly further comprises drive means (22) for moving the pressing head and the support member in a first direction which substantially corresponds with the direction of the moving board, and a second direction which is substantially perpendicular to a plane of the board, while the speed of the pressing assembly in the first direction substantially matches the speed of the board. the board between the pressing surface and the support member (17) to form a depression within the board (10). The pressing surface comprises a first and second surface portion separated by a relief portion, which is arranged to press the board toward the support head (17) with less compressive force than the first and second surface portion. The assembly further comprises drive means (22) for moving the pressing head and the support member in a first direction which substantially corresponds with the direction of the moving board, and a second direction which is substantially perpendicular to a plane of the board, while the speed of the pressing assembly in the first direction substantially matches the speed of the board.
Description
A Pressing Assembly and a Method for Forming a Depression within a Moving,
Wet Gypsum Board
The present invention relates to a pressing assembly and a method for forming a
depression within a board, and particularly, but not exclusively, to a pressing assembly and a
method for forming a depression within a moving, wet gypsum based board.
Any discussion of the prior art throughout the specification should in no way be
considered as an admission that such prior art is widely known or forms part of common general
knowledge in the field.
A gypsum plasterboard or wall board comprises an inner layer of gypsum (calcium
sulphate dihydrate form) sandwiched between two outer layers of lining paper. Gypsum board is
produced by feeding calcined gypsum (hemihydrate form), also known as stucco, into a
continuous mixer with water and additives. The slurry produced is then placed between
continuous layers of lining paper and passed through an extrusion system that compresses it to
the desired thickness. As this continuous wet plasterboard moves along the conveyor line the
calcium sulfate hemihydrate rehydrates to its original dihydrate form. The wet plasterboard is
initially soft but then board core quickly sets and therefore hardens. The paper becomes
chemically and mechanically bonded to the board core. Then the plasterboard is cut to length
and dried to drive off the excess water content to produce a rigid drywall.
Plasterboards are typically used to line walls and ceilings, and are secured to walls
and ceilings in a side-by-side relation. The joint between the boards is typically covered with a
mesh tape and a jointing compound is then applied to the arrangement of boards to cover the
joints therebetween and thus provide a smooth finish. This obviates the requirement to plaster
the entire board, or to have a large joint. However to reduce the finishing time and quantity of
finishing plaster used to obtain a smooth finish, plasterboards are also formed with a longitudinal
tapered edge such that the mesh tape is applied at the tapered region and the tapered region is
then filled to cover the joints.
In order to form this taper, it is necessary to compress the gypsum with a pressing
device, but this must be performed once the wet gypsum layer has partially set, to prevent the
lining from becoming detached from the gypsum and to ensure that the partially set gypsum can
retain the pressed shape. EP0482810 discloses that to avoid a lateral shift in the gypsum during
compression, the gypsum must be set to a minimum point before the pressure can be
successfully applied. The setting must reach the point where the core has attained a sufficient
degree of stiffness to allow compression without the gypsum mass moving laterally.
The reshaping of the gypsum layer to create the taper, is generally performed by
compressing the gypsum layer from the underside thereof, and this is typically performed at a
position along the production line which corresponds to a specified time in the hydration cycle of
the gypsum layer. Reshaping the layer early in the hydration cycle has the advantage of
lowering the force required to compress, namely densify the gypsum, however, the reduced
viscosity of the gypsum early in the hydration cycle and the formation of the taper depression in
the underside of the layer, reduces the ability of the compressed gypsum to retain the
compressed shape. In particular, the gypsum layer may tend to sag after the reshaping
operation, such that a depression is formed in the upper side of the gypsum layer (that is,
opposite the region of application of the compressive force). Conversely, reshaping the gypsum
layer later in the hydration cycle, increases the force required to compress, namely densify the
layer, but enables the compressed layer to retain the desired shape. EP0482810 discloses that
the reshaping is best performed later in the hydration cycle.
In accordance with the present invention as seen from a first aspect, there is provided
a pressing assembly for forming a depression within a moving, wet gypsum board, the assembly
comprising a pressing head comprising a pressing surface which is arranged to contact the
board, and a support member, the pressing head being arranged to compress a portion of the
board between the pressing surface and the support member to form a depression within the
board,
the assembly further comprising drive means for moving the pressing head and the
support member in a first direction which substantially corresponds with the direction of the
moving board, and a second direction which is substantially perpendicular to a plane of the
board, wherein,
the pressing surface comprises a first surface portion and a second surface portion,
the first and second surface portions being separated by a relief portion and being arranged to
press the board toward the support head with a compressive force that is greater than any
compressive force exerted on the board by the relief portion.
Preferably, the pressing surface is arranged so that the relief portion does not exert
any compressive force on the board. In general, the relief portion comprises a trough. Typically
the trough extends across the pressing surface.
Advantageously, the pressing assembly minimises any lateral shift in the lining
material relative to the gypsum core by compressing the board while moving with minimal
relative speed to the board. In addition, the movement of the pressing head substantially
perpendicular to the plane of the board, as opposed to along the board, further helps minimise
the development of ridges and raised portions around the depression.
The relief portion further provides for a less densified region of the board disposed
between the two more densified regions. The less densified region serves as a support for the
taper formed by the first and second surface portion either side thereof, and thus minimises the
recovery of the reshaped board to its original shape. In particular, the relief portion may help to
avoid sagging of the board after the reshaping operation. That is, it may help to prevent the later
formation of a depression in the surface of the board opposite the region at which the pressing
assembly contacts the board. Accordingly, the assembly of the present invention enables the
board to be compressed early during the hydration cycle and thus facilitates a reduction in the
required compressive force.
In addition, it is found that the less densified portion facilitates an easier cutting of the
board compared to the more densified regions, prolongs the life of the cutting blade and further
minimises any snagging of the blade during the cutting operation.
Preferably, the drive means is arranged to accelerate the pressing head and the
support member in the first direction to a speed which substantially matches a speed of the
moving board. The drive means is preferably arranged to move the pressing head toward the
support member to form a depression within the board, when the speed of the pressing head
and the support member in the first direction substantially matches the speed of the moving
board.
The pressing surface is preferably arranged to extend along a width of the board, such
that the depression is arranged to extend across the board.
Preferably, the relief portion has an elongate shape. Typically, the relief portion
extends from one region of the perimeter of the pressing surface to another region of the
perimeter of the pressing surface. Preferably, the pressing surface is arranged such that when
the pressing surface is pressed against the gypsum board, the orientation of the relief portion
corresponds to a lateral direction of the board.
Preferably, the first and second surface portions extend in an outward direction of the
pressing head as they each approach the relief portion. Effectively, therefore, the first and
second surface portions provide the pressing surface with a generally convex shape.
Preferably, the first and second surface portions each comprise a planar surface.
The pressing surface is preferably disposed upon a die, which may be detachably
coupled to the pressing head or formed integrally therewith. The relief portion is preferably
arranged to extend across the width of the board and preferably comprises an aperture disposed
in the die or a recess formed therein.
In accordance with the present invention as seen from a second aspect there is
provided a method for forming a depression within a moving, wet gypsum board, the method
comprising the use of a pressing assembly, the method comprising the steps of
providing a gypsum board;
moving the pressing assembly in the direction of travel of the board, such that the
speed of the pressing assembly in the direction of travel of the board substantially matches the
speed of the board, while simultaneously causing the pressing assembly to move towards the
board, to bring the pressing assembly into contact with a portion of the board; and
causing the pressing head to compress the board to substantially simultaneously form
a first depression and a second depression, the first and second depressions being located
either side of a comparatively uncompressed board portion.
The method typically further comprises the preliminary step of causing the pressing
assembly to accelerate to the speed of the board. .Typically the method further comprises the
step, after the step of causing the pressing head to compress the board, of decelerating the
pressing assembly.
Typically, the pressing assembly travels from an initial stationary position to a final
stationary position. In general, the pressing assembly is arranged to return to the initial
stationary position after reaching the final stationary position.
The method preferably further comprises comparing the speed of the pressing
assembly in the direction of travel of the board to the speed of the moving board and adjusting
the speed of the pressing assembly in dependence of the difference therebetween.
Typically, the speed of the pressing assembly in the direction of travel of the board is
matched to the speed of the board by means of a Hoekens linkage or by a hypotrochoid motion.
The step of causing the pressing head to contact and compress the board is typically
carried out when at least 10% of the gypsum hydration has occurred, preferably when at least
40% of the gypsum hydration has occurred, more preferably when at least 60% of the gypsum
hydration has occurred.
Typically the gypsum board comprises silicone oil. Preferably, the oil is present in an
amount greater than 100 g/m3, more preferably greater than 200 g/m3. Preferably, the oil is
present in an amount less than 6000 g/m3, more preferably less than 800 g/m3, most preferably
less than 400 g/m3.
For reference, the weight of the board as a whole is typically below 960 kg/m3, and
generally in the range between 480 and 720 kg/m3.
It has been observed that the presence of silicone oil may help to increase the depth
of first and second depressions produced through the method of the present invention.
Additionally, the presence of silicone oil may help to inhibit the formation of blisters between the
gypsum core and any liner provided on the surface of the gypsum board. It is thought that these
effects may be due to the increased deformability of the gypsum, arising from the presence of
the silicone oil.
Silicone oil is known for use as a water repellent in gypsum boards. Surprisingly,
however, it has been found that the effect of increasing the depth of the depressions and/or
reducing the incidence of blistering may be achieved using levels of silicone oil that are
significantly lower than those required to provide a water-repellent effect.
That is, in order to provide a water-repellent board, silicone must typically be present
in an amount greater than 1440 g/m3, more generally in the range of 2400 – 4800 g/m3. By
contrast, much lower amounts of silicone oil are required to increase the depth of depressions
and/or reduce blistering. For example, these effects may be achieved using silicone oil in
amounts of just 320 g/m3, or even lower.
Further preferred features of the method according to the second aspect, may
comprise one or more of the features of the pressing assembly of the first aspect.
Unless the context clearly requires otherwise, throughout the description and the
claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive
sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including,
but not limited to”.
The invention will now be described by way of example only with reference to the
accompanying Figures, in which:
Figure 1 is a side view of a pressing assembly according to an embodiment of the
present invention, disposed within a gypsum board production line;
Figure 2 is a plan view of the pressing assembly illustrated in figure 1;
Figure 3 is a front view of the pressing assembly illustrated in figure 1;
Figure 4 is a magnified view of the die disposed upon the pressing head;
Figure 5 is a perspective view of a continuous board;
Figure 6 is a magnified longitudinal sectional view taken along line A-A of figure 5,
across a depression created by the pressing assembly according to an embodiment of the
present invention;
Figure 7 is a perspective view of a board sheet; and
Figure 8 is a flow chart of the steps associated with a method of forming a depression
within a moving, wet gypsum board according to an embodiment of the present invention.
Figure 9 is a sectional view of the die disposed on the pressing head, according to a
second embodiment of the invention.
Referring to figures 1 to 4 of the drawings, there is illustrated a pressing assembly 10
according to an embodiment of the present invention for forming a depression 105 within a wet
gypsum board 100 as illustrated in figures 5 and 6 of the drawings, as the board 100 moves
along a production line. The continuous board 100 comprises a layer of wet gypsum 101
disposed between a first and second liner material 102, 103. The liners 102, 103 are folded over
each other along longitudinal side edges thereof to define longitudinal side edges 104a, 104b of
the board 100 and to prevent the gypsum 101 from passing out from between the liners 102,
103. The pressing assembly 10 is disposed within the production line and the board 100 is
supported upon a bed of rollers (not shown) disposed either side of the assembly 10. The board
100 is driven through the assembly 10 in a direction which is substantially parallel to the
longitudinal side edges 104a, 104b of the board 100, at a substantially constant speed by a
roller platform 11. The roller platform 11 comprises a substantially rectangular roller frame 12
having a plurality of rollers 13 which extend across the frame 12 between opposite longitudinal
roller frame members 12a, and which is held in a substantially horizontal configuration,
substantially level with the bed of rollers (not shown), by a plurality of frame legs 14.
The pressing assembly 10 is arranged to form a depression 105 within the board 100
at periodic intervals along the length thereof as the board 100 passes through the pressing
assembly 10. The depressions 105 are arranged to extend substantially across the board 100, in
a direction which is substantially transverse to the longitudinal side edges 104 of the board 100;
however, the skilled reader will recognise the depressions 105 may be formed across the board
at an alternative angle to the longitudinal side edges 104. The continuous board 100 is then cut
across the board 100 within the depressions 105 to form a board sheet 200 as illustrated in
figure 7 of the drawings. The longitudinal side edges of the board sheet 200 each have a first
portion 201a, 201b that is perpendicular to the faces of the board sheet, and a second portion
203a, 203b that is oriented at an oblique angle to the faces of the board sheet. Lateral side
edges extend substantially transverse to the longitudinal side edges 201, 201b, and similarly
have a first portion 202a, 202b that is perpendicular to the faces of the board sheet, and a
second portion 106, 107 that is oriented at an oblique angle to the faces of the board sheet.
Thus, the board sheet 200 has tapered edges extending around its entire perimeter.
Referring to figures 1 to 3 of the drawings, the assembly 10 comprises a support frame
for supporting a pressing head 16 and a support member 17. The support frame 15 is
substantially rectangular in shape and comprises opposite longitudinal 15a and lateral side
members 15b, the latter of which are arranged to extend substantially perpendicular to the roller
platform 11 and thus the plane of the board 100. In contrast, longitudinal side members 15a of
the support frame are arranged to extend in a plane substantially parallel to the roller platform, in
a direction which is substantially transverse to the longitudinal roller frame members 12a. The
pressing head 16 and support member 17 are arranged to extend across the width of the
support frame 15, between lateral side members 15b, and are orientated substantially parallel to
a plane of the board 100.
The pressing head 16 comprises a first drive unit 18 disposed at each longitudinal end
thereof, which are arranged to drive the head 16 along the lateral side members 15b within the
frame 15. The support member 17 comprises a second drive unit 19 disposed at each
longitudinal end thereof which are arranged to similarly drive the member 17 along the lateral
side members 15b within the frame 15. The first and second drive units 18, 19 thus enable the
separation of the pressing head 16 and the support member 17 and thus their separation from
the board 100, which is arranged to pass therebetween, to be varied.
The support frame 15 is itself held in a fixed orientation upon the roller platform 11 with
respect to the board, by a drive arrangement 20 which is arranged to drive the support frame 15
along the board 100 substantially parallel to the direction of travel of the board 100. The
arrangement 20 comprises two support poles 21, one of which extends through each lateral side
member 15b of the support frame 15, and are separately coupled at each end thereof to a pair
of frame legs 14. The arrangement 20 further comprises a third drive unit 22 disposed upon
each lateral side member 15b for driving the support frame 15 back and forth along the support
poles 21. In this respect, the support poles 21 enable the pressing head 16 and support member
17 to move in a first direction which is substantially along the board 100, substantially parallel to
the direction of travel of the board 100, whereas the lateral side members 15b enable the
pressing head 16 and support member 17 to move in a second direction which is substantially
perpendicular to the plane of the board 100.
The assembly 10 further comprises one or more sensors (not shown) associated
therewith for sensing the speed of travel of the board 100. The sensors are arranged to output a
signal which is input to the first, second and third drive units 18, 19, 22, to affect the speed at
which the pressing head 16 and support member 17 become driven along the support frame 15
and the support poles 21.
The pressing head 16 is illustrated in the drawings as being disposed substantially
below the board 100 and thus the support member 17, however, the skilled reader will recognise
that this arrangement may be reversed with the pressing head 16 disposed above the board 100
and thus the support member 17. Referring to figure 4 of the drawings, the side of the pressing
head 16 disposed adjacent the board 100 comprises a die 23 which may be detachably coupled
thereto or which may be formed integrally therewith. The die 23 extends between opposite
longitudinal ends of the pressing head 16, and is arranged to extend across the width of the
board 100.
The die 23 comprises a first and second longitudinal side edge 24a, 24b, which are
arranged to extend across the board, and from which extend a first and second substantially
planar pressing surface 25, 26, respectively. The first surface 25 is inclined with respect to the
direction of travel of the board 100 and the second surface 26 is declined with respect to the
direction of travel of the board 100, such that the first and second pressing surfaces 25, 26
converge in a direction which is away from the pressing head 16 and the respective longitudinal
side edges 24a, 24b of the die 23, toward a relief portion 27 disposed substantially centrally of
the die 23. In this respect, the first and second surface portions 25, 26 are arranged to create
opposed tapers 106, 107 within the gypsum board 100. The relief portion 27 is arranged to
extend along the length of the die 23 and may comprise an aperture (not shown) disposed
therein, or a recess 28, as illustrated in figure 4 of the drawings.
Referring to figure 8 of the drawings there is illustrated a method 300 according to an
embodiment of the present invention. During use, the board 100 is driven through the assembly
by the rollers 13 disposed upon the roller platform 11, between the pressing head 16 and the
support member 17, at constant speed. The support member 17 and pressing head 16 are
subsequently accelerated at step 310, from a first stationary position, along the first direction by
the third drive units 22, along the support poles 21, to a speed which substantially matches the
speed of the board 100 through the assembly 10. This speed is monitored by comparing the
relative speed between the board 100, and the pressing head 16 and support member 17, as
determined using the sensors (not shown). The pressing head 16 and support member 17 are
simultaneously driven at step 310 along the lateral side members 15b of the support frame 15,
by the first and second drive units 18, 19, to a position adjacent an upper and lower face of the
board 100, respectively.
When the speed of the pressing head 16 and support member 17 in the first direction
substantially matches the speed of the board 100, namely when relative speed is within
substantially ±0.1% of the board speed, the first and second drive units 18, 19 are arranged to
drive the support member 17 and the pressing head 16 toward each other at step 320, to
compress the board 100 along the width thereof and thus form a depression 105 within the wet
gypsum. The support member 17 is arranged to resist the upward force from the pressing head
16 and presents a sufficiently smooth and large surface compared with the face of the die 23, to
avoid forming a depression (not shown) on the upper surface of the board 100.
The first drive units 18 disposed on the pressing head 16 are arranged to control the
speed at which the pressing head 16 is driven in and out of the board 100 and permit a
controlled steady pressing in phase, a short constant press and a withdrawal. Moreover, the
compressing of the board 100 while maintaining minimal relative speed between the board 100
and the pressing head 16 minimises the accumulation of wet gypsum either side of the
depression 105, which would otherwise present an undesirable bulge or protuberance in the
dried board.
As the board 100 is compressed, the wet gypsum 101 disposed between the liners
102, 103 becomes compressed between the pressing surfaces of the die 23 and the support
member 17. The first and second pressing surfaces 25,26 are arranged so that the recess 28
does not exert any compressive force on the board. Thus, the resulting longitudinal sectional
shape of the board 100, as illustrated in figure 6 of the drawings comprises first and second
opposed taper regions 106, 107 which extend into the board 100, toward an uncompressed,
raised support step 108. The portion of gypsum disposed within the raised step 108 is therefore
less densified than the portion of the board 106a, 107a disposed either side thereof.
The depth to which the die 23 is arranged to press into the board 100 may be varied
by monitoring the force applied to the board 100 using a force sensor (not shown), for example,
or by monitoring a fixed position upon the pressing head 16 with respect to a reference position
upon the assembly 10, for example. Once the board 100 has been compressed to form the
opposed tapers 106, 107 either side of the support step 108, the separation of the pressing head
16 and the support member 17 is then increased and the pressing head 16 and support member
17 are decelerated in the first direction to a second stationary position at step 330. The pressing
head 16 and support member 17 are then driven in a second direction at step 340 back along
the support poles 21 from the second position to the first position for subsequent pressing of the
board 100. The cycling of the pressing head 16 and the support member 17 from the first
position to the second position and back to the first position is controlled to ensure that the
depressions 105 are formed at equally spaced positions on the board 100, namely within ±2mm.
This ensures that the resulting boards 200 which are formed by cutting along the central portion
of the depressions 105 comprise substantially the same length.
The boards 200 are formed by cutting the board 100 with a cutting blade (not shown)
along the less densified portion of the board within the depressions. The less densified portions
enable the continuous board 100 to be cut more easily than if the continuous board 100 was cut
along a densified portion, prolong the life of the cutting blade (not shown) and minimise an
snagging of the blade (not shown) on the board 100 which may otherwise tear the liners 102,
103 of the board 100.
Fig. 9 shows an alternative configuration of the die disposed on the pressing head,
according to a second embodiment of the invention. In contrast to Fig. 4, the first pressing
surface 25a,25b and the second pressing surface 26a,26b are each divided into two parts. The
outer parts 25b, 26b of the first and second pressing surfaces are co-planar, while the inner
parts 25a,26a are inclined relative to each other and relative to the outer parts 25b,26b, so that
the inner parts 25a,26a protrude from the pressing surface.
In addition, Fig. 9 shows a further optional feature of the die, namely that the base 30
of the recess is located inwardly of the plane defined by the outer parts 25b,26b of the first and
second pressing surfaces.
The following worked examples are presented by way of illustration only.
EXAMPLE 1
Two gypsum boards were provided in which Board A contained silicone oil in an
amount of 320 g/m3, while Board B contained no silicone oil.
Board A and Board B were pressed according to the method set out in Figure 8, and
were both subjected to the same load during the step 320 in which the pressing head 16 and the
support member 17 are driven towards each other.
The maximum taper depth achieved for Board A was 1.5mm, whereas the maximum
taper depth achieved for Board B was 1.0mm (the maximum taper depth was measured after
removal of the compressive force, and after drying of the board).
EXAMPLE 2
Two gypsum boards were provided in which Board C contained silicone oil in an
amount of 480 g/m3, while Board D contained no silicone oil.
The boards were pressed according to the method set out in Figure 8.
The Boards were visually examined to see if blistering had occurred between the liner
of the board and the underlying gypsum. The results are given in Table 1 below:
Board C Board D
Pressed region No blistering observed Blistering observed
Unpressed region No blistering observed No blistering observed
Claims (13)
1. A pressing assembly for forming a depression within a moving, wet gypsum board, the assembly comprising a pressing head comprising a pressing surface which is arranged to contact the board, and a support member, the pressing head being arranged to compress a portion of the board between the pressing surface and the support member to form a depression within the board, the assembly further comprising drive means for moving the pressing head and the support member in a first direction which substantially corresponds with the direction of the moving board, and a second direction which is substantially perpendicular to a plane of the board, wherein, the pressing surface comprises a first surface portion and a second surface portion, the first and second surface portions being separated by a relief portion and being arranged to press the board toward the support head with a compressive force that is greater than any compressive force exerted on the board by the relief portion.
2. An assembly according to claim 1, wherein the relief portion comprises a trough.
3. An assembly according to any one of the preceding claims, wherein the drive means is arranged to accelerate the pressing head and the support member in the first direction to a speed which substantially matches a speed of the moving board.
4. An assembly according to claim 3, wherein the drive means is arranged to move the pressing head toward the support member to form a depression within the board, while the speed of the pressing head and the support member in the first direction substantially matches the speed of the moving board.
5. An assembly according to any one of the preceding claims, wherein the first and second surfaces separately comprise a planar surface.
6. An assembly according to any one of the preceding claims, wherein the pressing surface is disposed upon a die, which may be detachably coupled to the pressing head or formed integrally therewith.
7. An assembly according to any preceding claim, wherein the relief portion is arranged to extend across the width of the board and preferably comprises an aperture or recess
8. A method for forming a depression within a moving, wet gypsum board, the method comprising the use of a pressing assembly, the method comprising the steps of providing a gypsum board; moving the pressing assembly in the direction of travel of the board, such that the speed of the pressing assembly in the direction of travel of the board substantially matches the speed of the board, while simultaneously causing the pressing assembly to move towards the board, to bring the pressing assembly into contact with a portion of the board, and causing the pressing assembly to compress the board to substantially simultaneously form a first depression and a second depresssion, the first and second depressions being located either side of a comparatively uncompressed board portion.
9. A method according to claim 8, further comprising comparing the speed of the pressing assembly in the direction of travel of the board to the speed of the moving board and adjusting the speed of the pressing assembly in dependence of the difference therebetween.
10. A method according to claim 9, wherein the speed of the pressing assembly in the direction of travel of the board is matched to the speed of the board by means of a Hoekens linkage.
11. A method according to claim 9, wherein the speed of the pressing assembly in the direction of travel of the board is matched to the speed of the board by means of a hypotrochoid motion.
12. A method according to any one of claims 8 to 11, wherein the step of causing the pressing assembly to contact and compress the board is carried out when at least 10% of the gypsum hydration has occurred.
13. A method according to any one of claims 8 to 11, wherein the step of causing the pressing assembly to contact and compress the board is carried out when at least 40% of the gypsum hydration has occurred, preferably when at least 60% of the gypsum hydration has occurred.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP11290582.3 | 2011-12-15 | ||
EP11290582.3A EP2604401A1 (en) | 2011-12-15 | 2011-12-15 | A pressing assembly and method for forming a depression within a moving, wet gypsum board |
EP12290248.9A EP2604402B1 (en) | 2011-12-15 | 2012-07-23 | A pressing assembly and method for forming a depression within a moving, wet gypsum board |
EP12290248.9 | 2012-07-23 | ||
PCT/EP2012/075380 WO2013087766A1 (en) | 2011-12-15 | 2012-12-13 | A pressing assembly and method for forming a depression within a moving, gypsum board |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ627442A NZ627442A (en) | 2016-01-29 |
NZ627442B2 true NZ627442B2 (en) | 2016-05-03 |
Family
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