Title of Invention	CEMENTITIOUS BOARD MANUFACTURE
Abstract	According to the invention there is provided a method of accelerating the setting reaction of calcium sulphate hemihydrate and water comprising the steps of mixing water and calcium sulphate hemihydrate to produce a slurry (24), adding an accelerator to said mixture,applying ultrasonic energy to said mixture, the ultrasonic energy source having a power output greater than or equal to 1 kW. The present invention also relate to an apparatus for manufacturing gypsum wall board comprising:a mixer (18) for combining calcium sulphate hemihydrate and water,a mixer outlet(20) for depositing the gypsum slurry onto paper (12) mounted onto a conveyor (16), wherein said mixer comprises means (42,43,53) for supplying ultrasonic energy to the slurry.

Title of Invention

CEMENTITIOUS BOARD MANUFACTURE

Abstract

According to the invention there is provided a method of accelerating the setting reaction of calcium sulphate hemihydrate and water comprising the steps of mixing water and calcium sulphate hemihydrate to produce a slurry (24), adding an accelerator to said mixture,applying ultrasonic energy to said mixture, the ultrasonic energy source having a power output greater than or equal to 1 kW. The present invention also relate to an apparatus for manufacturing gypsum wall board comprising:a mixer (18) for combining calcium sulphate hemihydrate and water,a mixer outlet(20) for depositing the gypsum slurry onto paper (12) mounted onto a conveyor (16), wherein said mixer comprises means (42,43,53) for supplying ultrasonic energy to the slurry.

Full Text	Cementitious Board Manufacture This invention relates to the manufacture of cementitious board in which a slurry of cementitious material, commonly gypsum plaster, is deposited between two facing lining sheets and formed to a desired width and thickness prior to setting and drying. The process is normally carried out continuously and at high linear speed. To manufacture gypsum board an aqueous slurry of calcined gypsum (calcium sulphate hemihydrate) is continuously spread between upper and lower paper sheets. The product formed is then continuously conveyed on a moving belt until the slurry has set. The strip or sheet is then dried until the excess water in the gypsum board has evaporated. In the production of gypsum wallboard it is known to add various substances to the slurry to enhance the production process or the board itself. For example it is usual to lighten the weight of the slurry by incorporating foaming agents to provide a degree of aeration which lowers the density of the final wallboard. It is also known to decrease the setting time of the calcined gypsum slurry by incorporating gypsum set accelerators. Freshly ground gypsum (also known as a gypsum set accelerator) has a relatively short shelf life. The loss of acceleration efficiency of conventional accelerator materials is also exacerbated when the accelerator is exposed to heat and/or moisture. To combat this loss of efficiency it is known to coat the accelerator particles with, for example, sugar or a surfactant.. Accordingly, there is a need for a gypsum set accelerator or method of accelerating the set time of the gypsum slurry which alleviates the aforementioned problems. According to the present invention there is provided a method for accelerating the setting reaction of calcium sulphate hemihydrateand water comprising mixing water and calcium sulphate hemihydrateto produce a slurry, adding an accelerator to said mixture and applying ultrasonic energy to said mixture. The ultrasonic energy may be applied for a time of less than 10 seconds. The accelerator may be hydrated calcium sulphate. The accelerator may be a chemical accelerator. The chemical accelerator may be potassium sulphate (K2SO4). The slurry may be formed within a mixer and deposited via a mixer outlet onto paper so as to form gypsum plasterboard, said paper being located on a conveyor. The ultrasonic energy may be applied to the slurry when the slurry is located in the mixer outlet. The ultrasonic energy may be applied to the slurry once it is deposited on the paper conveyor. The ultrasonic energy may be applied using a radial shaped ultrasonic horn positioned at the exit mouth of the mixer outlet. The ultrasonic energy may be applied directly to the slurry in the mixer. The ultrasonic energy may be applied directly to the slurry in the mixer via probes inserted into the slurry contained within the mixer. The ultrasonic energy may also be applied via the rotor in the mixer. Also according to the present invention there is provided apparatus for manufacturing gypsum wall board comprising a mixer for combining calcium sulphate hemihydrate and water, a mixer outlet for depositing the gypsum slurry onto paper mounted onto a conveyor, wherein said mixer outlet comprises means for supplying ultrasonic energy to the slurry as it passes through said mixer outlet. Said mixer outlet may comprise a tubular shaped ultrasonic horn. Advantageously the application of ultrasonic energy together with a known accelerator provided a decreased setting time and therefore a more efficient plasterboard manufacturing process. The application of ultrasonic accelerator in to the mixer has also surprisingly alleviated material build up in the mixer. This is caused by the vibration produced by the application of ultrasonic energy to the mixer. In particular the combination of the use of ultrasonic energy in combination with a known gypsum accelerator has provided surprisingly goods results with the amount of particulate or chemical accelerators needed being reduced. Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a fragmentary diagrammatical view of a longitudinal section of a gypsum board manufacturing line. Figure 2 is an example of a shape of a mixer outlet according to an embodiment of the present invention. Figure 3 is a diagrammatic view of a mixer outlet in the shape of a radial horn according to a further embodiment of the present invention. Figure 4 is a diagrammatical section of a mixer with ultrasonic probes Figure 5 is a diagrammatical section of a mixer with an ultrasonic rotor according to a further embodiment of the invention Referring to figure 1 a first layer of paper 12 is fed from a roll 14 onto a conveyor or belt 16. A storage mixer 18 contains slurry of calcium sulphate hemi hydrate and water. This storage mixer 18 is provided with an outlet 20 connected to a conduit 22. A meter is connected to said conduit 22 for measuring and controlling the amount of stucco fed through the conduit 22. Additives are added to the storage mixer 18. Such additives may comprise retarders (e.g. proteins, organic acids), viscosity modifying agents (e.g. superplasticisers), anti-burning agents, boric acid, water-resisting chemicals (e.g. polysiloxanes, wax emulsions), glass fibres, fire-resistance enhancers (e.g. vermiculite, clays and/or fumed silica), polymeric compounds (e.g. PVA, PVOH) and other conventional additives imparted in known quantities to facilitate manufacturing such as starch. The storage mixer 18 is provided with an outlet 20 to deliver its combined contents in the form of slurry onto the paper 12. This slurry mixture is then delivered through an outlet pipe 22 onto the paper 12 provided on the moving belt 16. An additive such as starch is added to the slurry stream 24 in the mixer and a further layer of paper 26 is provided over its upper surface from a roll 28. The slurry if therefore sandwiched between two sheets of paper or cardboard 12 and 26. These two sheets become the facing of the resultant gypsum board. The thickness of the resultant board is controlled by a forming station 30 and the board is subsequently prepared by employing appropriate mechanical devices to cut or score fold and glue the overlapping edges of the paper cover sheets 12, 26. Additional guides maintain board thickness and width as the setting slurry travels on the moving conveyor belt. The board panels are cut and delivered to dryers to dry the plasterboard. In the current embodiment of this invention, the conduit 22 may be replaced by a ring shaped radial horn through which the slurry may be fed to the slurry stream 24 during transit through the conduit the ultrasonic energy may be delivered. Referring to figure 2, the conduit 22 may be constructed in the form of a metallic ultrasonic radial horn with outer metallic tubing 40 and inner bore 42. The slurry 24 passes through the conduit 22 where ultrasonic energy is imparted as it forms the slurry stream on the paper 12. Advantageously the use of ultrasonic energy applied to the gypsum slurry accelerates the setting time of the gypsum by causing accelerated crystallisation. It is understood that when the amount of ultrasonic energy applied to the gypsum slurry exceeds the natural forces holding together the molecules, cavitation occurs. The implosion of the cavitation bubbles produces short lived hot spots within the slurry. The collapse of some of the bubbles within the slurry enable nucleation sites to occur thus allowing accelerated crystallisation. This has the added advantage of making the slurry outlet nozzle a self cleaning delivery unit due the vibration produced by the ultrasonic energy. The vibrations at the mixer outlet also allow the slurry to be spread evenly across the moving conveyor. In one embodiment of this invention, the conduit 22 may be replaced by a wide mouthed tubular ultrasonic horn through which the slurry may be fed to the slurry stream 24 and during transit through the conduit the ultrasonic energy may be delivered. Referring to figure 3, the conduit 22 may be constructed in the form of a metallic ultrasonic radial horn with tubular outer metallic tubing 50 connected by some means to a conical section 52 thereby forming a wide mouthed slurry output bore 54. The slurry 24 passes through the conduit 22 where ultrasonic energy is imparted as it forms the slurry stream on the paper 12. Also advantageously by using a wide mouthed design of ultrasonic horn as the mixer outlet the slurry stream on the paper 12 may be more uniformly distributed and less reliant on the use of additional mechanical vibration apparatus. Referring now to figure 4 a pair of ultrasonic probes 52, 54 could alternatively be inserted into the mixer chamber 18 itself. The probes 52 and 54 advantageously act as a method for preventing mixer blockage by providing vibration to the slurry mixture. Referring to figure 5 the rotor 53 of the mixer is itself provided with ultrasonic energy via a generator 57. The rotor is essentially a conventional rotor but additionally provided with ultrasonic energy which it can impart to the gypsum slurry mixture fed into the mixer chamber 18. The following example results further illustrate the present invention but should not be construed as limiting its scope. With reference to the examples: • The slurry was made using stucco of different water gauges including 70, 80 and 90 wt % of stucco (no additives) to obtain different viscosities. • The different slurries with the different water gauges were insonated with an ultrasonic probe (at a fixed frequency of 20kHz) for different intervals, including 2, 3, 5, 10,15 and 20 seconds. • The set time for each insonation was measured using a Vicat set test. • To determine the effect of foam on the insonation, different slurries with different addition levels of foam was tested in the same manner as explained above for the unfoamed slurries. In this case the water gauges were kept constant and the foam addition level altered. • Both sets of examples (using unfoamed and foamed slurries) were repeated using different ultrasonic probes with different power outputs, (1kWand1.5kW). • The examples were repeated with the use of ultrasound in combination with particulate accelerator, Ground Mineral Nansa (GMN) and a chemical accelerator, potassium sulphate. Example 1 Prisms were made using 1000g of stucco at three different water gauges of 70, 80 and 90 wt% of stucco. Ultrasonic energy was applied to the slurry for 3, 5 and 10 seconds using an ultrasonic probe with a power output of 1kW. A large high- speed blender was used to mix the stucco and water for a dispersion time of 5 seconds. The water used remained at a constant temperature of 40QC. No foam was added to the slurry in this case. Example 2 Tests were carried out to determine the effect of ultrasonic acceleration on foamed slurries. Prisms were made using 1000g of stucco with a water gauge of 90 wt% of stucco. A foam generator was used to produce the foam to be added to the stucco blend. The foam generator was set to have an airflow rate of 2.5 l/min, foam flow rate of 0.25 l/min and a foam concentration of 0.3%. To produce the slurry mix, a large blender was used on low speed for a total dispersion time of 10 seconds. The 1kW ultrasonic probe was used at insonation times of 3, 5 and 10 seconds to accelerate the set of the gypsum slurry. The stucco and water was mixed in a large batch mixer for 3 seconds before the foam was added to the blend and mixed for a further 7 seconds to produce samples 1 and 2. In the case of samples 3 and 4, stucco was mixed with water for 3 seconds before the foam was added and mixed for a further 4 seconds. Result Table 2 Example 3 To compare the set times obtained with particulate accelerator as opposed to solely ultrasonic energy, prisms were made to test the effect of ultrasound on particulate accelerator (GMN). In this case, no foam was added and a water gauge of 90wt% of stucco with a water temperature 40SC was used. A large high-speed blender was used to mix the stucco and the GMN with water for a 5 second dispersion time. GMN was hand mixed into dry stucco powder for 30 seconds before making the slurry in the blender. Example 4 Non-foamed slurry was insonated using a higher power probe that could draw 1.5KW compared with 1kW power (that the previous probe was capable of). 10OOg of stucco with a water gauge of 90wt% (water temperature of 40QC) was again mixed in a high-speed blender for 5 seconds to produce the samples. Example 5 Non-foamed samples with two addition levels (0.06 and 0.1 wt%) of potassium sulphate (chemical accelerator) were insonated using a higher powered probe (1.5kW) for different intervals to determine whether ultrasonic cavitation could be used in conjunction with potassium sulphate to further accelerate the set time of gypsum slurry. As seen in table 5, the application of ultrasound energy in combination with a chemical accelerator (potassium sulphate) produces a substantial increase in set time. This particular combination of ultrasound energy and chemical accelerator has been found to be more effective in reducing the setting time of the gypsum slurry than either method on its own. Table 6 is a list of results obtained from 'on plant' trials using ultrasound according to the present invention to accelerate the setting of gypsum. The plots below emphasise the density reduction properties of using ultrasound. Comparing all the controls with the ultrasonically treated samples shows that all of them have a lower density than the controls. The treated samples had a corresponding strength with regard to density. The ultrasound did not have a detrimental effect on strength but simply reduced the density. The treated samples present the same proportional change in strength with density as seen from the control samples. The density reducing property of ultrasound is another beneficial effect. Ultrasound could therefore also be used to aerate the slurry, allowing a reduction in water gauge or foam usage. The reduction in water gauge is of greater economic benefit, since it would mean a reduction on the energy usage. The use of ultrasound would mean the benefit of mechanically aerating the slurry and achieving the same product densities with reduced quantity of water or foam. WE CLAIM: 1. A method of accelerating the setting reaction of calcium sulphate hemihydrate and water comprising the steps of: a. mixing water and calcium sulphate hemihydrate to produce a slurry b. adding an accelerator to said mixture c. applying ultrasonic energy to said mixture, the ultrasonic energy source having a power output greater than or equal to 1 kW. 2. A method as claimed in claim 1, wherein the slurry is formed within a mixer and deposited via a mixer outlet onto paper so as to form gypsum plasterboard, said paper being located on a conveyor. 3. A method as claimed in claims 1 and 2, wherein the accelerator is a particulate accelerator. 4. A method as claimed in claims 1 and 2, wherein the accelerator is a chemical accelerator. 5. 5. A method as claimed in claim 4, wherein the chemical accelerator is potassium sulphate. 6. A method as claimed in any of the preceding claims, wherein the ultrasonic energy is applied to the slurry when the slurry is located in the mixer outlet. 7. A method as claimed in claims 1 to 5, wherein the ultrasonic energy is applied to the slurry once it is deposited on the paper conveyor. 8. A method as claimed in claim 7, wherein the ultrasonic energy is applied using a radial shaped ultrasonic horn positioned at the exit mouth of the mixer outlet. 9. A method as claimed in claim 1, wherein the ultrasonic energy is applied directly to the slurry in the mixer. 10. A method as claimed in claim 9, wherein the ultrasonic energy is applied directly to the slurry in the mixer via probes inserted into the slurry contained within the mixer. 11. A method as claimed in any of the preceding claims, wherein the ultrasonic energy is applied for a time of less than 10 seconds. 12. A method as claimed in claim 9, wherein the ultrasonic energy is imparted to the mixer via the rotor. 13. An apparatus for manufacturing gypsum wall board comprising: a mixer for combining calcium sulphate hemihydrate and water a mixer outlet for depositing the gypsum slurry onto paper mounted onto a conveyor, wherein said mixer comprises means for supplying ultrasonic energy to the slurry, wherein said mixer outlet comprise a tubular shaped ultrasonic horn. 14. An Apparatus for manufacturing gypsum wall board comprising: a mixer for combining calcium sulphate hemihydrate and water a mixer outlet for depositing the gypsum slurry onto paper mounted onto a conveyor, wherein said mixer comprises means for supplying ultrasonic energy to the slurry , wherein the ultrasonic energy is imparted to the slurry via the mixer rotor. 15. Apparatus for manufacturing gypsum wall board as claimed in claim 14, wherein the mixer rotor is an ultrasonic horn. ABSTRACT CEMENTITIOUS BOARD MANUFACTURE According to the invention there is provided a method of accelerating the setting reaction of calcium sulphate hemihydrate and water comprising the steps of mixing water and calcium sulphate hemihydrate to produce a slurry (24), adding an accelerator to said mixture,applying ultrasonic energy to said mixture, the ultrasonic energy source having a power output greater than or equal to 1 kW. The present invention also relate to an apparatus for manufacturing gypsum wall board comprising:a mixer (18) for combining calcium sulphate hemihydrate and water,a mixer outlet(20) for depositing the gypsum slurry onto paper (12) mounted onto a conveyor (16), wherein said mixer comprises means (42,43,53) for supplying ultrasonic energy to the slurry.

Full Text

Cementitious Board Manufacture
This invention relates to the manufacture of cementitious board in which a slurry
of cementitious material, commonly gypsum plaster, is deposited between two
facing lining sheets and formed to a desired width and thickness prior to setting
and drying. The process is normally carried out continuously and at high linear
speed.
To manufacture gypsum board an aqueous slurry of calcined gypsum (calcium
sulphate hemihydrate) is continuously spread between upper and lower paper
sheets. The product formed is then continuously conveyed on a moving belt until
the slurry has set. The strip or sheet is then dried until the excess water in the
gypsum board has evaporated. In the production of gypsum wallboard it is
known to add various substances to the slurry to enhance the production process
or the board itself. For example it is usual to lighten the weight of the slurry by
incorporating foaming agents to provide a degree of aeration which lowers the
density of the final wallboard.
It is also known to decrease the setting time of the calcined gypsum slurry by
incorporating gypsum set accelerators. Freshly ground gypsum (also known as a
gypsum set accelerator) has a relatively short shelf life. The loss of acceleration
efficiency of conventional accelerator materials is also exacerbated when the
accelerator is exposed to heat and/or moisture.

To combat this loss of efficiency it is known to coat the accelerator particles with,
for example, sugar or a surfactant..
Accordingly, there is a need for a gypsum set accelerator or method of
accelerating the set time of the gypsum slurry which alleviates the
aforementioned problems.
According to the present invention there is provided a method for accelerating
the setting reaction of calcium sulphate hemihydrateand water comprising mixing
water and calcium sulphate hemihydrateto produce a slurry, adding an
accelerator to said mixture and applying ultrasonic energy to said mixture.
The ultrasonic energy may be applied for a time of less than 10 seconds.
The accelerator may be hydrated calcium sulphate.
The accelerator may be a chemical accelerator.
The chemical accelerator may be potassium sulphate (K2SO4).
The slurry may be formed within a mixer and deposited via a mixer outlet onto
paper so as to form gypsum plasterboard, said paper being located on a
conveyor.

The ultrasonic energy may be applied to the slurry when the slurry is located in
the mixer outlet.
The ultrasonic energy may be applied to the slurry once it is deposited on the
paper conveyor.
The ultrasonic energy may be applied using a radial shaped ultrasonic horn
positioned at the exit mouth of the mixer outlet.
The ultrasonic energy may be applied directly to the slurry in the mixer.
The ultrasonic energy may be applied directly to the slurry in the mixer via probes
inserted into the slurry contained within the mixer.
The ultrasonic energy may also be applied via the rotor in the mixer.
Also according to the present invention there is provided apparatus for
manufacturing gypsum wall board comprising a mixer for combining calcium
sulphate hemihydrate and water, a mixer outlet for depositing the gypsum slurry
onto paper mounted onto a conveyor, wherein said mixer outlet comprises
means for supplying ultrasonic energy to the slurry as it passes through said
mixer outlet.
Said mixer outlet may comprise a tubular shaped ultrasonic horn.

Advantageously the application of ultrasonic energy together with a known
accelerator provided a decreased setting time and therefore a more efficient
plasterboard manufacturing process. The application of ultrasonic accelerator in
to the mixer has also surprisingly alleviated material build up in the mixer. This is
caused by the vibration produced by the application of ultrasonic energy to the
mixer. In particular the combination of the use of ultrasonic energy in
combination with a known gypsum accelerator has provided surprisingly goods
results with the amount of particulate or chemical accelerators needed being
reduced.
Embodiments of the invention will now be described with reference to the
accompanying drawings in which:
Figure 1 is a fragmentary diagrammatical view of a longitudinal section of a
gypsum board manufacturing line.
Figure 2 is an example of a shape of a mixer outlet according to an embodiment
of the present invention.
Figure 3 is a diagrammatic view of a mixer outlet in the shape of a radial horn
according to a further embodiment of the present invention.
Figure 4 is a diagrammatical section of a mixer with ultrasonic probes

Figure 5 is a diagrammatical section of a mixer with an ultrasonic rotor according
to a further embodiment of the invention
Referring to figure 1 a first layer of paper 12 is fed from a roll 14 onto a conveyor
or belt 16. A storage mixer 18 contains slurry of calcium sulphate hemi hydrate
and water. This storage mixer 18 is provided with an outlet 20 connected to a
conduit 22. A meter is connected to said conduit 22 for measuring and
controlling the amount of stucco fed through the conduit 22.
Additives are added to the storage mixer 18. Such additives may comprise
retarders (e.g. proteins, organic acids), viscosity modifying agents (e.g.
superplasticisers), anti-burning agents, boric acid, water-resisting chemicals
(e.g. polysiloxanes, wax emulsions), glass fibres, fire-resistance enhancers (e.g.
vermiculite, clays and/or fumed silica), polymeric compounds (e.g. PVA, PVOH)
and other conventional additives imparted in known quantities to facilitate
manufacturing such as starch.
The storage mixer 18 is provided with an outlet 20 to deliver its combined
contents in the form of slurry onto the paper 12.
This slurry mixture is then delivered through an outlet pipe 22 onto the paper 12
provided on the moving belt 16.

An additive such as starch is added to the slurry stream 24 in the mixer and a
further layer of paper 26 is provided over its upper surface from a roll 28. The
slurry if therefore sandwiched between two sheets of paper or cardboard 12 and
26. These two sheets become the facing of the resultant gypsum board.
The thickness of the resultant board is controlled by a forming station 30 and the
board is subsequently prepared by employing appropriate mechanical devices to
cut or score fold and glue the overlapping edges of the paper cover sheets 12,
26. Additional guides maintain board thickness and width as the setting slurry
travels on the moving conveyor belt. The board panels are cut and delivered to
dryers to dry the plasterboard.
In the current embodiment of this invention, the conduit 22 may be replaced by a
ring shaped radial horn through which the slurry may be fed to the slurry stream
24 during transit through the conduit the ultrasonic energy may be delivered.
Referring to figure 2, the conduit 22 may be constructed in the form of a metallic
ultrasonic radial horn with outer metallic tubing 40 and inner bore 42. The slurry
24 passes through the conduit 22 where ultrasonic energy is imparted as it forms
the slurry stream on the paper 12.
Advantageously the use of ultrasonic energy applied to the gypsum slurry
accelerates the setting time of the gypsum by causing accelerated crystallisation.

It is understood that when the amount of ultrasonic energy applied to the gypsum
slurry exceeds the natural forces holding together the molecules, cavitation
occurs.
The implosion of the cavitation bubbles produces short lived hot spots within the
slurry. The collapse of some of the bubbles within the slurry enable nucleation
sites to occur thus allowing accelerated crystallisation.
This has the added advantage of making the slurry outlet nozzle a self cleaning
delivery unit due the vibration produced by the ultrasonic energy. The vibrations
at the mixer outlet also allow the slurry to be spread evenly across the moving
conveyor.
In one embodiment of this invention, the conduit 22 may be replaced by a wide
mouthed tubular ultrasonic horn through which the slurry may be fed to the slurry
stream 24 and during transit through the conduit the ultrasonic energy may be
delivered.
Referring to figure 3, the conduit 22 may be constructed in the form of a metallic
ultrasonic radial horn with tubular outer metallic tubing 50 connected by some
means to a conical section 52 thereby forming a wide mouthed slurry output bore
54. The slurry 24 passes through the conduit 22 where ultrasonic energy is
imparted as it forms the slurry stream on the paper 12. Also advantageously by

using a wide mouthed design of ultrasonic horn as the mixer outlet the slurry
stream on the paper 12 may be more uniformly distributed and less reliant on the
use of additional mechanical vibration apparatus.
Referring now to figure 4 a pair of ultrasonic probes 52, 54 could alternatively be
inserted into the mixer chamber 18 itself. The probes 52 and 54 advantageously
act as a method for preventing mixer blockage by providing vibration to the slurry
mixture.
Referring to figure 5 the rotor 53 of the mixer is itself provided with ultrasonic
energy via a generator 57. The rotor is essentially a conventional rotor but
additionally provided with ultrasonic energy which it can impart to the gypsum
slurry mixture fed into the mixer chamber 18.
The following example results further illustrate the present invention but should
not be construed as limiting its scope.
With reference to the examples:
• The slurry was made using stucco of different water gauges including 70,
80 and 90 wt % of stucco (no additives) to obtain different viscosities.
• The different slurries with the different water gauges were insonated with
an ultrasonic probe (at a fixed frequency of 20kHz) for different intervals,
including 2, 3, 5, 10,15 and 20 seconds.
• The set time for each insonation was measured using a Vicat set test.

• To determine the effect of foam on the insonation, different slurries with
different addition levels of foam was tested in the same manner as
explained above for the unfoamed slurries. In this case the water gauges
were kept constant and the foam addition level altered.
• Both sets of examples (using unfoamed and foamed slurries) were
repeated using different ultrasonic probes with different power outputs,
(1kWand1.5kW).
• The examples were repeated with the use of ultrasound in combination
with particulate accelerator, Ground Mineral Nansa (GMN) and a chemical
accelerator, potassium sulphate.
Example 1
Prisms were made using 1000g of stucco at three different water gauges of 70,
80 and 90 wt% of stucco. Ultrasonic energy was applied to the slurry for 3, 5 and
10 seconds using an ultrasonic probe with a power output of 1kW. A large high-
speed blender was used to mix the stucco and water for a dispersion time of 5
seconds. The water used remained at a constant temperature of 40QC. No foam
was added to the slurry in this case.

Example 2
Tests were carried out to determine the effect of ultrasonic acceleration on
foamed slurries. Prisms were made using 1000g of stucco with a water gauge of
90 wt% of stucco. A foam generator was used to produce the foam to be added
to the stucco blend. The foam generator was set to have an airflow rate of 2.5
l/min, foam flow rate of 0.25 l/min and a foam concentration of 0.3%. To produce
the slurry mix, a large blender was used on low speed for a total dispersion time
of 10 seconds. The 1kW ultrasonic probe was used at insonation times of 3, 5
and 10 seconds to accelerate the set of the gypsum slurry.
The stucco and water was mixed in a large batch mixer for 3 seconds before the
foam was added to the blend and mixed for a further 7 seconds to produce
samples 1 and 2. In the case of samples 3 and 4, stucco was mixed with water
for 3 seconds before the foam was added and mixed for a further 4 seconds.
Result Table 2

Example 3
To compare the set times obtained with particulate accelerator as opposed to
solely ultrasonic energy, prisms were made to test the effect of ultrasound on
particulate accelerator (GMN). In this case, no foam was added and a water
gauge of 90wt% of stucco with a water temperature 40SC was used. A large
high-speed blender was used to mix the stucco and the GMN with water for a 5
second dispersion time. GMN was hand mixed into dry stucco powder for 30
seconds before making the slurry in the blender.

Example 4
Non-foamed slurry was insonated using a higher power probe that could draw
1.5KW compared with 1kW power (that the previous probe was capable of).
10OOg of stucco with a water gauge of 90wt% (water temperature of 40QC) was
again mixed in a high-speed blender for 5 seconds to produce the samples.

Example 5
Non-foamed samples with two addition levels (0.06 and 0.1 wt%) of potassium
sulphate (chemical accelerator) were insonated using a higher powered probe
(1.5kW) for different intervals to determine whether ultrasonic cavitation could be
used in conjunction with potassium sulphate to further accelerate the set time of
gypsum slurry.

As seen in table 5, the application of ultrasound energy in combination with a
chemical accelerator (potassium sulphate) produces a substantial increase in set
time. This particular combination of ultrasound energy and chemical accelerator
has been found to be more effective in reducing the setting time of the gypsum
slurry than either method on its own.
Table 6 is a list of results obtained from 'on plant' trials using ultrasound
according to the present invention to accelerate the setting of gypsum.

The plots below emphasise the density reduction properties of using ultrasound.
Comparing all the controls with the ultrasonically treated samples shows that all
of them have a lower density than the controls. The treated samples had a
corresponding strength with regard to density. The ultrasound did not have a
detrimental effect on strength but simply reduced the density. The treated
samples present the same proportional change in strength with density as seen
from the control samples.
The density reducing property of ultrasound is another beneficial effect.
Ultrasound could therefore also be used to aerate the slurry, allowing a reduction

in water gauge or foam usage. The reduction in water gauge is of greater
economic benefit, since it would mean a reduction on the energy usage. The use
of ultrasound would mean the benefit of mechanically aerating the slurry and
achieving the same product densities with reduced quantity of water or foam.

WE CLAIM:
1. A method of accelerating the setting reaction of calcium sulphate hemihydrate and
water comprising the steps of:
a. mixing water and calcium sulphate hemihydrate to produce a slurry
b. adding an accelerator to said mixture
c. applying ultrasonic energy to said mixture, the ultrasonic energy source
having a power output greater than or equal to 1 kW.
2. A method as claimed in claim 1, wherein the slurry is formed within a mixer and
deposited via a mixer outlet onto paper so as to form gypsum plasterboard, said paper
being located on a conveyor.
3. A method as claimed in claims 1 and 2, wherein the accelerator is a particulate
accelerator.
4. A method as claimed in claims 1 and 2, wherein the accelerator is a chemical
accelerator.
5. 5. A method as claimed in claim 4, wherein the chemical accelerator is potassium
sulphate.
6. A method as claimed in any of the preceding claims, wherein the ultrasonic
energy is applied to the slurry when the slurry is located in the mixer outlet.

7. A method as claimed in claims 1 to 5, wherein the ultrasonic energy is applied to
the slurry once it is deposited on the paper conveyor.
8. A method as claimed in claim 7, wherein the ultrasonic energy is applied using a
radial shaped ultrasonic horn positioned at the exit mouth of the mixer outlet.
9. A method as claimed in claim 1, wherein the ultrasonic energy is applied directly
to the slurry in the mixer.
10. A method as claimed in claim 9, wherein the ultrasonic energy is applied directly
to the slurry in the mixer via probes inserted into the slurry contained within the mixer.
11. A method as claimed in any of the preceding claims, wherein the ultrasonic
energy is applied for a time of less than 10 seconds.
12. A method as claimed in claim 9, wherein the ultrasonic energy is imparted to the
mixer via the rotor.
13. An apparatus for manufacturing gypsum wall board comprising:
a mixer for combining calcium sulphate hemihydrate and water
a mixer outlet for depositing the gypsum slurry onto paper mounted onto a
conveyor, wherein said mixer comprises means for supplying ultrasonic energy to
the slurry, wherein said mixer outlet comprise a tubular shaped ultrasonic horn.
14. An Apparatus for manufacturing gypsum wall board comprising:
a mixer for combining calcium sulphate hemihydrate and water

a mixer outlet for depositing the gypsum slurry onto paper mounted onto a
conveyor, wherein said mixer comprises means for supplying ultrasonic energy to
the slurry , wherein the ultrasonic energy is imparted to the slurry via the mixer
rotor.
15. Apparatus for manufacturing gypsum wall board as claimed in claim 14, wherein
the mixer rotor is an ultrasonic horn.

ABSTRACT

CEMENTITIOUS BOARD MANUFACTURE
According to the invention there is provided a method of accelerating the setting
reaction of calcium sulphate hemihydrate and water comprising the steps of mixing water
and calcium sulphate hemihydrate to produce a slurry (24), adding an accelerator to said
mixture,applying ultrasonic energy to said mixture, the ultrasonic energy source having a
power output greater than or equal to 1 kW.
The present invention also relate to an apparatus for manufacturing gypsum wall
board comprising:a mixer (18) for combining calcium sulphate hemihydrate and water,a
mixer outlet(20) for depositing the gypsum slurry onto paper (12) mounted onto a
conveyor (16), wherein said mixer comprises means (42,43,53) for supplying ultrasonic
energy to the slurry.

CEMENTITIOUS BOARD MANUFACTURE

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