Note: Descriptions are shown in the official language in which they were submitted.
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Method and apparatus for sealing capsules and capsules
suitable for use in said method and apparatus
The present invention relates to a method and to an
apparatus for sealing telescopically joined capsules with
coaxial partly overlapping body parts, through subsequent
application of a solvent and thermal energy. The present
invention further relates to a capsule design particular
suitable for such process and apparatus.
The capsules to be sealed by utilizing the present
invention are preferably hard shell gelatin capsules or other
capsules made from materials or their compositions which are
pharmaceutically acceptable with respect to their chemical
and physical properties.
The problem to be solved with respect to such capsules
as compared to other dosage forms is the fact that the
coaxial body parts must be well sealed in order to avoid
leaking of any content to the outside or contamination
thereof. Further, tampering with the content of the capsule
or the capsule as such should be evident and externally
visible for safety purposes and any technique of sealing the
capsules must be suitable for large scale bulk production to
reduce manufacturing time and costs and to reduce waste due
to imperfections of the product.
EP 0 116 743 Al and EP 0 116 744 Al respectively
disclose similar methods and devices for sealing such
capsules having hard shell coaxial cap and body parts which
overlap when telescopically joined. The process employed
comprises the steps of dipping batches of the capsules
randomly oriented in mesh baskets or oriented with their cap
parts upright into a sealing fluid making capillary action
within the overlap of the cap and body parts or spraying the
sealing fluid or steam thereof onto the seam of the overlap,
removing the sealing fluid from the surface of the capsules
by an air blower, and applying thermal energy to the capsules
while conveying the baskets through a dryer. Both documents
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disclose the use of a wide range of sealing fluids and
specific temperatures and modes for the application of
thermal energy.
EP-0 180 543 Al also discloses a method for
sealing telescopically joined capsules with coaxial body
parts, through subsequent application of a sealing liquid to
the overlapping region at the joint between a cap and a
body, the removal of excess sealing liquid, and the
application of thermal energy for drying purposes. This
document particularly describes various designs of capsules
suitable to be used for such process which have a ridge type
structure in the cap and/or in the body for exactly
coaxially positioning the cap and the body.
The prior systems for sealing the telescopically
joined capsules with coaxial body parts, through subsequent
application of a solvent and thermal energy are partly
imperfect as regards the quality of the seal and the
controllability of the process parameters influencing the
quality of the seal.
The present invention aims at providing an
improved method and apparatus for sealing telescopically
joined capsules with coaxial partly overlapping body parts,
through subsequent application of a solvent and thermal
energy and an improved capsule design particularly suitable
for such process and apparatus.
According to aspects of the present invention,
there is provided a method and an apparatus for sealing
telescopically joined capsules with coaxial partly
overlapping body parts and a capsule design as defined in
the appended claims.
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2a
According to one embodiment, there is provided a
method of sealing a hardshell capsule having coaxial body
parts which overlap when telescopically joined with each
other, thereby forming a gap around a circumference of the
capsule, comprising the steps of: individually applying a
sealing liquid including a solvent uniformly to the external
edge of the gap of a capsule to be sealed to form a liquid
ring around the circumference of the capsule, removing
excess sealing liquid from the exterior of the capsule,
drying the capsule by applying thermal energy from outside
while gently tumbling and conveying the capsule on a
horizontal spiral path in a drying basket device.
According to another embodiment, there is provided
an apparatus for sealing a hardshell capsule having coaxial
body parts which overlap when telescopically joined with
each other, thereby forming a gap around a circumference of
the capsule, comprising: means for individually applying a
sealing liquid including a solvent uniformly to the external
edge of the gap of a capsule to be sealed to form a liquid
ring around the circumference of the capsule, means for
removing excess sealing liquid from the exterior of the
capsule, means for drying the capsule by applying thermal
energy from outside while gently tumbling and conveying the
capsule on a horizontal spiral path in a drying basket
device.
The present invention will now be described in
more detail, by way of example, with reference to the
accompanying drawings in which:
Fig. 1 shows an enlarged detail of an overlapping
sealing portion of a capsule according to the present
invention, and
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Fig. 2 shows a schematic structure of a drying basket
used in the method and apparatus of the present invention and
a path of the capsules during operation thereof.
First, general enumerative description will be made on
the system comprising the method and apparatus and capsule of
the present invention to highlight the key features and
aspects thereof. The below list is not ordered or
comprehensive but does cover in brief the aspects which will
differentiate the system of the invention from prior methods.
The present invention provides the following aspects:
It does not need orientated capsules which simplifies
operation and increases reliability of the process.
The sealing fluid application is spatially controlled to
optimize the wetted areas for good sealing, with minimum
tackiness and fastest drying.
The temperature of the sealing fluid can be controlled
to achieve efficient wicking and optimum dissolution rate.
This implies the use of both heating and cooling systems as,
for example, systems utilizing gelatin capsules require
temperatures above ambient, whereas HPMC (hydroxypropylmethyl
cellulose) systems work best with hot solvents and ambient
temperature drying.
The volume of sealing fluid applied on the space around
the gap between the body parts of the capsule, i.e. the cap
and the body, is adjustable to prevent excess wetting.
The sealing fluid is applied uniformly around the
capsule to get the full area seal required.
Excess sealing fluid is removed by a combination of
airjets and/or aspiration.
The system is designed so that capsule size change
requires a minimum change of components.
The system is designed to work with a range of sealing
fluids including, but not restricted to alcohol/water
mixtures in case of gelatin capsules as described in EP 0 116
743 Al and EP 0 116 744 Al. For capsules made out of
other materials, e.g. starch, HPMC,
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etc., alternative solvent systems are required. The present
invention provides a wide range of control for the critical
sealing and drying parameters, such as temperature, solvent
formulations, time, airflow, so as to enable optimum
processes to be used and well controlled.
The transportation of the capsules after sealing is
achieved in a fashion which minimizes contact with surfaces
of the apparatus and each other to reduce the risk of
sticking or cosmetic damage.
The rate of drying of the capsules is carefully
controlled to ensure that the inner overlapping surfaces bond
securely to each other as the solvent evaporates but the
fluid does not have time to diffuse into the bulk of the
capsule material.
Reliable bonding at the cap to body requires the
overlapping surfaces to be in contact at conditions where the
surface will weld into joint with a strength comparable to
the minimum time required for the gelatin long chain
molecules to intertwine. This sets the drying rate to which
the system is to be adjusted.
The contact pressure between the surface to be bonded is
maintained by a combination of the interference forces
resulting from the precise manufacturing control of the
capsules and expansion of the gelatin due to fluid
absorption.
Drying of all surfaces at uniform rate is necessary to
avoid distortion or poor sealing and is achieved by the air
blown, capsule tumbling mechanism of the drying basket device
of the present invention.
The implementation of the drying process uses an air
flow with control of temperature, flow rate and humidity
chosen to achieve the temperature, time, moisture profile
necessary to achieve a strong bond of the capsules.
The capsules are dried in the drying basket device which
provides control of transport rate whilst gently tumbling the
capsules to ensure all surfaces are uniformly dried and the
capsules do not stick together
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The surface, material and form of the helical screw in
the drying basket device is designed to ensure capsules are
not retained and are minimally damaged by the contact
therewith during operation.
5 The porosity of the structure forming the drying basket
device is designed to ensure low air resistance and uniform
airflow over the capsules.
Two or mare parallel high air jets adjustable in width
and location are directed up along the line of the lowest
point of the drying basket device with a speed sufficient to
lift any capsules tending to adhere to the surface.
The control of the rotational speed of the drying basket
device allows control of the time of drying as the axial
translation speed is a function of rotational speed.
Control of drying air parameters is achieved using servo
control systems to maintain uniform conditions even in the
event of external changes.
Implementation of the total sealing system is in a self
contained unit of small footprint making it compatible with
installation in the environment of a capsule filling line.
The system of the present invention thus enables sealing
of liquid filled capsules immediately after filling at a rate
compatible with conventional capsule filling lines.
As the apparatus of the present invention can be fed
from a standard hopper there is no requirement for closely
coupling the outfeed of the filler to the infeed of the
sealing apparatus of the invention. This allows buffer
volumes to be used to smooth production flow for short
stoppages of either the filler or the sealing apparatus.
The basic improvement of the method and apparatus of the
present invention over the prior art sealing systems reside
in the control of the gap geometry of the body parts of the
capsules to ensure full uniform wicking along the whole
overlapping length and the design of the drying process or of
the suitable devices for this step which removes the solvent
in a way that causes the gap to close completely and the body
parts to stick together perfectly.
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CAPSULE DESIGN
The capsule design most suited for use in the sealing
system of the present invention consists of two halves which
are concentrically overlapped partly when telescopingly
joined together. The fundamental method by which the seal is
made between the two halves is for a solvent or sealing
liquid to be introduced into the gap between the two halves
at the overlapping region such that as the solvent evaporates
the inner surfaces are drawn into contact whilst soft and
fused together.
To achieve a good seal with this method it is necessary
that a sealing liquid, i.e. a solvent must fill all of the
gap between the surfaces that are to bond together. For
capsules this is the full length of the overlapping region
between cap and body. The two surfaces to be bonded together
have to react to the solvent such that the inner surfaces are
soft and tacky at the time they are brought together to form
the bond. This may be achieved by controlling the
temperature and time that the solvent is in the gap before it
evaporates to bring the surfaces into contact. Finally, the
action of removing the solvent needs to apply a force to the
two surfaces to be bonded to hold them together as the bond
f orms .
The present invention addresses these issues in the
design of the capsule, the application of the solvent and the
mechanism of drying.
To support the uniform filling of solvent into the gap
the capsule is designed to have features which uniformly
separate both the surfaces to a predetermined distance whilst
the solvent is introduced into the gap. If the gap is wide in
some places and non existent in others then the distribution
of the solvent across the area will vary leading to poor
sealing at some points around the capsule. The gap is allowed
to close completely as the solvent is removed and the bond
forms. The closing forces are of limited strength so that
any resistance to the surfaces being pulled together may
reduce the bond strength. Also, as the product inside the
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capsule is not a solvent for the capsule material and if it
penetrates into the gap then it will block the action of the
sealing solvent, the capsule design is preferably such that
contamination of the gap by the products inside the capsule
is prevented.
An important aspect of the invention is the precision
with which all these requirements are achieved by the
tolerances of the capsule manufacture and the control of the
parameters such as temperature, time, solvent volumes,
solvent location, drying conditions with the sealing system.
There are various designs of the capsule in order to
achieve the required gap control whilst maintaining all the
other requirements of capsules such as, appearance,
manufacturability, ease of swallowing, etc.. A number of
suitable designs have been incorporated by reference to the
disclosure of EP-0 180 543 Al. One preferred implementation
uses a symmetric arrangement of at least 3 bumps in the body
which can optionally interlock into dimples or a groove in
the cap. These features provide axial positioning and hold
the cap concentric to the body so providing the uniform gap.
The exact implementation could include one or more variations
such as axial raised rings and matching grooves, a uniformly
roughened surface on one or more of the faces, a multiplicity
of bumps and dimples, a plurality of circumferential grooves
and dimples, and a spiral ridge and dimples.
The gap size is chosen so that volume of solvent wicked-
in is sufficient to perfuse the inner surface of the gap
sufficiently to modify the surface to become soft and tacky
to allow them to bond when pressed together. This volume will
be dependent upon the material, the temperature and the force
applied to bond the surfaces. Typically the gap is within the
range 0.05 mm to 0.5 mm. Typically the volume of solvent that
is required to initially fill the gap is between 5 l and 20
l.
In order to allow the gap to close as the solvent is
removed some allowance must be made for the movement. This
may be achieved by a number of designs the common feature
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being that the designs have no features extending into the
gap which remain rigid enough to prevent the gap from
closing. Where spacing features are employed then a design of
spacing features which, as it softens with the action of the
solvent, distorts to permit the required motion is
particularly advantageous. An example of such a feature is
shown in figure 1.
The geometry of the spacing feature shown in this figure
is such that there is surrounding space for the material of
the bump to flow into as the gap closes. Corresponding
designs for the other implementations are possible provided
the principle of allowing the deformation of the shapes to be
accommodated for minimum flow is followed.
Preventing the product infusing into the gap region
whilst the solvent is present requires providing a seal at
the end of the gap exposed to the interior region of the
capsule, providing a positive pressure from outside of the
capsules to inside to prevent flow of product into the gap,
and/or immobilizing the product to prevent it flowing into
the narrow gap.
The preferred embodiment of a capsule to be used in the
method and apparatus of the invention is to seal the top of
the gap by appropriate design of the locking features.
SOLVENT APPLICATION
The second requirement of sealing is to modify the _
interior surfaces of the gap between cap and body so that
they are soft and tacky as they are drawn together. As
described previously this requires control of the type and
amount of sealing liquid or solvent and the temperature
thereof. The present invention provides a mechanism for
implementing the concept with a wide range of solvents, of
the type described in previous patent applications related to
this field. The use of a capsule which has a well controlled
gap sealed off from the contents facilitates the
impregnation of the inner surfaces with the required volume
of solvent.
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In the preferred embodiment of the invention the solvent
is presented to the external edge of the gap uniformly around
the circumference. The surface tension effects draw the
solvent from the outside uniformly up into the gap provided
that the gap spacing is uniform. To prevent softening of the
external surfaces any excess solvent is removed as quickly as
possible.
There are various techniques for applying the solvent to
the gap including a spray emanating from several points
around the capsule directed towards the external edge of the
gap and lasting for. a period designed to deliver the
appropriate volume of solvent on the capsule, an
implementation as above, where the spray is replaced by an
array of piezo or thermal ink-jet heads dispensing the
appropriate solvent, an arrangement of sponges, brushes,
wicks, etc. which transfer solvent by contact to the required
position, and jets of solvent vapor directed to the open end
of the gap to condense the vapor directly on to the capsule.
In addition to dispensing the required volume uniformly
around the gap entrance, the system must remove any excess
liquid solvent on the surface of the capsule before it
softens the material. This can be achieved by various means,
including aspiration to suck away liquid, air jets to blow
liquid off the surface, wicking to absorb liquid on contact,
centrifuged force to spin off excess liquid, shaking to throw
off excess liquid or combinations of these measures.
The preferred embodiment of sealing apparatus of the
invention makes use of 3 spray nozzles spaced 1200 around the
circumference directed at the external opening of the overlap
gap with excess liquid being removed by a combination of
airjets and aspiration. In addition to the precise control of
the volume and location to which the solvent is applied, the
temperature of the capsule, solvent and the atmosphere need
to be held within defined limits. The level of control
required depends upon the materials and variability of the
environment. The apparatus is provided with a suitable
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temperature control system to provide the appropriate
conditions for operation in a wide range of environments.
SOLVENT REMOVAL
The third requirement is to remove the solvent in the
5 gap in a manner which generates a force to hold the surfaces
together as they dry. The ultimate method of solvent removal
is as a vapor, its transport being achieved by entrapment in
an airstream at the appropriate temperature. Transport of
the solvent from the gap to the air takes place by several
10 mechanisms like flow along the gap to support evaporation
from the exposed liquid surface, diffusion through the
capsule cap material to evaporate from the outer surface,
diffusion through the capsule body material and mixing with
or absorption into the contents fluid, and diffusion into and
binding to the capsule material of both cap and body.
All of these methods can participate in the drying
process in a way which removes the solvent without
introducing air. As this happens the atmospheric pressure
forces the cap and body surfaces together with a pressure up
to 100,000 Newton per square meter.
All of these transport mechanisms speed up if the
temperature is increased. However, excessive temperature can
lead to situations which prevent a good bond forming, for
example vapor bubbles forming and distorting the surface,
excess flow rates in the liquid allowing air entrapment,
internal pressure rise displacing air from inside the capsule
through the gap, thermal stresses distorting the capsule, or
excessive drying of the outer surfaces increasing the
stiffness to prevent closure.
The present invention optimizes the temperature and
airflow to achieve capsule drying at a commercially
acceptable rate without degrading the quality of the seal by
any of the mechanisms described above.
In the following a preferred embodiment of the apparatus
for sealing the capsules will be described in detail.
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In one preferred embodiment all of the requirements and
devices for effective sealing are implemented in a self
contained machine.
This embodiment has an input hopper which can receive
capsules from any source at any rate. Typically capsules
would be fed using a conveyor or an air transport system.
The capsules at this stage are mechanically held closed
by the features in the capsule caps and bodies and for a
partial seal sufficient to prevent the content of the
capsules from leaking out during mechanical transportation
with the sealing system.
The hopper is designed to feed capsules in a number of
entry tubes which will transport the capsules into the
sealing apparatus. Capsules are gravity fed from the hopper
into the tubes with the movement being assisted by a
reciprocating vertical motion of the input tubes over a
distance of between 0.5 cm and 5.0 cm and at a rate designed
to ensure smooth, blockage free motion.
An optional capsule orientation station can be inserted
between the hopper and the feed tubes to ensure that the
capsules enter the tubes with a predetermined orientation.
This function is not necessary for efficient sealing, but may
be used in combination with a reduced spray pattern head
designed to minimize the volume of solvent utilized or to
limit the softening of the capsule outer surfaces.
In one embodiment six input tubes are used and this
number will be taken as the example for subsequent
descriptions, however implementations with any number of
parallel paths may be used to meet the required throughput.
The capsules in the input tubes are prevented from
moving by mechanical latches whose opening cycles are
controlled by the system controller. In order to implement
the sealing function a large number of actions must be
undertaken with precision timing and relationships. In the
preferred embodiment all of these actions are controlled
using a Programmable Logic Controller (PLC) so that the
sequences and timings can be adjusted to meet the
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requirements of a range of solvent systems to suit different
capsule designs and materials. It is a feature of the present
invention that the PLC enables a single machine to be able to
work with different processes, materials and capsule sizes.
The actions demanded by the controller may be achieved
using combinations of a range of actuators, including, but
not limited to solenoids, pneumatic valves and cylinders,
motors, and cams.
At the start of the sealing cycle the PLC releases the
latch restraining the capsules and allows the leading capsule
in each tube to fall into the location at which the sealing
will take place. This point is known as the spray bar. The
spray bar has a mechanism to hold the capsules in place
whilst solvent is sprayed onto the middle section of the
capsules so that it is in uniform contact all around the end
of the overlap of the cap over the body. This is achieved by
surrounding each capsule with an annular manifold in which
are located a number of small holes. These holes are
positioned and angled such that liquid emanating from them
will reach the capsules at the desired location. Where the
capsules are not orientated then the area on the capsule
encountered by the solvent must be such that whatever
orientation the capsule is in the end of the gap is covered
in solvent. Where capsules are orientated, the area covered
by the solvent can be reduced to just that area around the
end of the gap. In order to achieve the desired coverage the
holes are angled, typically at 450 and uniformly spaced
around the capsule.
Each spray bar has holes for each of the capsule feed
tubes, typically 6, and liquid is fed to the spray nozzles by
a manifold within the spray bar. The liquid is forced from
the nozzles onto the capsules by pressurizing it by
connecting it to a permanently pressurized supply via a
control valve. The form and volume of solvent delivered to
the capsule is controlled by the EFD valve controller by
adjusting the time the valve is open and the pressure of the
supply. To prevent solvent delivery when not required,
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additional interlock valves may be included in the delivery
line.
The system typically delivers liquid volumes in the
range 20 l to 200 pl to each capsule, suing pressure in the
range 1 bar gauge to 5 bar gauge and spray times between 0.1
seconds and 1.0 seconds, depending upon the capsule size and
material.
The velocity and volume of the flow of solvent into the
annular space around the capsule can be adjusted to achieve
the desired form to ensure uniform penetration of the solvent
into the gap between cap and body. This includes conditions
like high velocity to form an aerosol mist, medium velocity
to form a liquid jet on to the surface, and low velocity to
form an liquid ring which expands to just touch the capsule.
The system supplies more solvent to the capsule than can
be taken up into the gap in order to ensure that all of the
area is well supplied by the solvent. The excess solution is
removed from around the capsule by vacuum suction and/or air
jets. This action is also controlled by the PLC and the
air/solvent is removed from the area around each capsule via
an additional array of holes located adjacent to the spray
nozzles. These holes are interconnected by a second manifold
in the spray bar and hence connected to a vacuum pump and
collection vessel in which the solvent vapor may condense and
liquid trap.
At the completion of the solvent spray and excess
removal, the capsules have the solvent in place in the gap
but are still tacky from the action of the solvent on the
exterior surfaces. The capsules must then be dried under
carefully controlled conditions so that the seal is correctly
formed and capsules do not stick together or become
cosmetically damaged by sticking to other surfaces.
The method by which this is achieved in the preferred
embodiment is to rotate the spray bar away from the feed
tubes to align the capsules with entry ports into a drying
basket. This is achieved by mounting the spray bars within a
cylinder which can rotate. To remove the capsules from the
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spray bar the cylinder is rotated 1200 and the capsules are
ejected by a combination of push rods and air jets. The
capsules fall down individual feed tubes angled at 600 to the
vertical into one end of a drying basket.
To maintain a high throughput the cylinder on which the
spray bars are mounted has fixings for 3 spray bars at 1200-
intervals. This rotation to eject brings a new spring bar
under the feed tubes ready for the start of the next cycle.
An additional feature permits the spray bar cylinder to
rotate in the opposite direction, when directed by the PLC
and for the capsules to be ejected into a separate shute
which does not feed into the cylinder but into a separate
outlet. This enables capsules to be removed from the machine
after sealing, but before drying in order for diagnostic or
process measurements to be undertaken.
In order for the machine to operate with capsules of
different sizes but to maintain precise control of both the
capsule feeding and the sealing operation some hardware
changes need to be undertaken to accommodate a change in
capsule size. The preferred embodiment limits these changes
to a small number of easy to access items, such as the feed
tube assembly, the spray bars, and the output sieve.
In addition, to ensure that the machine is operating
correctly a number of sensors may be employed to ensure that
capsules and fluids are available and have been transported
correctly. These include an optical sensor at the input
hopper to determine that capsules are available, fiber optic
sensors in the tubes between the spray bars and the drying
cylinder, pressure and vacuum sensors at the appropriate
locations, and flow sensors.
The basket into which the capsules are ejected after
filling comprises a tubular open mesh arrangement with
internal spiral guides. The cylinder is rotated slowly such
that the internal spiral causes capsules which fall onto it
from the sides, as they are lifted up by the rotation, to
move along the axis of the cylinder. In this fashion the
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capsules gently tumble around the cylinder following a spiral
path of the internal spiral guide(s).
DRYING BASKET FUNCTIONS
The conditions under which capsules are dried after
5 solvent has been introduced into the gap is critical to the
achievement of a good seal. The key functions that need to be
achieved in drying are:
- capsules are transported through the drying zone into
a bulk storage container;
10 - the time capsules are in the drying zone is controlled
to ensure that the capsules are sufficiently dry when
entering the bulk storage that they will not stick together;
- air flows all over the capsules to achieve fast
uniform drying;
15 - capsule to capsule contact is minimized to prevent
them sticking together;
- capsule to basket contact is minimized to prevent
sticking to the walls; and
- mechanical impact of the capsules is minimized to
prevent damage.
The drying basket device preferably has a design which
comprises a cylindrical structure predominantly fabricated
from a stainless steel mesh. The material inside which is
preferably a double spiral guide also is of stainless steel
material.
The dimensions of the cylinder are preferably a length
between 600 and 1,000 mm and a diameter between 100 mm and
200 mm with a length of 800 mm and a diameter of 160 mm being
a preferred embodiment. The ratio of diameter to length is
chosen to control the mechanical performance aspects, the
length is a function of the duration required in the drying
zone and the diameter is a function of the quantity of
capsules to be handled.
In this implementation with the dimensions stated
above the length is chosen to produce a capsule residence
time in the drying basket of between 10 seconds and 100
seconds.
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The cylindrical drying basket is orientated with its
axis horizontal. In the preferred embodiment, the basket is
constrained by rollers to allow it to rotate freely about the
horizontal axis. The rollers may be fabricated to provide
sufficient function to enable one of the rollers to be driven
to cause the drying basket to rotate or the basket may be
driven directly by a coupling at one end. The method of
support and rotational drive must provide free airflow
throughout the basket and be compatible with the requirements
for cleaning and maintaining cleanliness.
In one embodiment the internal double spiral has the
function of causing the capsule to tumble in one axial
direction as the basket is rotated. The pitch and form of the
spiral are critical to ensuring that all capsules are
transported axially at the same rate. In this embodiment the
spiral is fabricated from vanes spanning from a central shaft
to the mesh of the cylinder. Each vane consists of two arms
diametrically opposed spanning from the central shaft to the
wire mesh of the cylinder. Each vane is mounted onto the
shaft rotated with respect to its neighbors by a fixed angle.
This angle is typically 12 degrees. The vanes are stamped
from stainless steel sheet of typically 0.75 mm thickness and
may optionally be PTFE coated to ensure low surface energy.
The attachment of the vanes to the shaft and cylinder is
accomplished by mechanical fixtures incorporated in their
design. To facilitate this the shaft has circular grooves to
accommodate the vanes at a spacing chosen to provide the
desired spiral pitch. This pitch typically is 5.993 mm with
118 vanes producing a twin spiral structure with a spiral
pitch of 179.8 mm. The shaft has diametrically opposing flats
and the vanes have a corresponding profile to their central
hole so that the vanes can be slid onto the shaft and locked
onto the shaft at the desired groove by rotation. The
attachment of the vanes to the cylinder is accomplished by
grooves on the outer profile of the vanes that match to axial
wires attached to the inside of the cylindrical mesh. In a
typical embodiment 30 wires are used at 12 degree separation
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to match the vane arrangement. The assembly of the vanes into
the basket is accomplished by sliding the vanes onto the
shaft and rotating until they lock into place. The mesh of
the outer cylinder is constructed to combine the functions of
containing the capsules and providing the attachment fixtures
for the vanes whilst maximising the open area to permit good
air flow. To achieve this 134 separate rings of 0.16 mm
diameter stainless steel wire are welded around 30
longitudinal wires of 0.2 mm diameter of stainless steel
arranged at 121 increments around the circle. The
longitudinal wires are inside the circumferential wires so
that they act as attachment features for the vanes.
An alternative embodiment utilizes separate baskets
constructed out of separate sections to allow for ease of
removal. In this embodiment a 3 cm spiral construction is
employed such that each spiral has a pitch of 240 mm and the
basket has an internal diameter of 185 mm. The basket outer
and spiral arms are fabricated from flat stampings each with
the three arms formed in them and with a castellated rim such
that when stacked together with a 60 offset, around a central
shaft, the layers are spaced approximately 4 mm apart by the
castellations and form an internal spiral with the required
pitch. Known features interlock the sections together to
enable the drive from one end to rotate all sections.
The construction of the drying basket in the embodiments
described previously are examples of means of achieving the
required transport conditions as capsules pass through the
drying zones. The concept can also be achieved using a
variety of designs and construction techniques. This
includes, but are not limited to rectangular section baskets
with flat angled baffles arranged so that as the basket
rotates the capsules travel up the basket in one direction as
shown in Figure 2.
The rectangular section can reduce the manufacturing
cost significantly.
Further alternatives are a conveyor belt system where
the conveyor belt has an open mesh structure to permit air to
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18
circulate around the capsules, wherein vibration or air jet
can be optionally used to keep the capsules from sticking
together or to the belt, or a contra flow drop tube in which
warm air is fed into the bottom of a vertical tube at a
velocity adjusted so that the weight of the capsules was just
larger than the aerodynamic drag of the upward airstream. The
downward velocity of the capsules can therefore be adjusted
by adjusting the air velocity resulting in a transit time
sufficient to dry off the excess fluid.
In a further preferred embodiment of the cylindrical
drying basket device the central feature has 3 arms forming 3
interwoven spirals angled such that the spiral makes between
2 and 4 turns along the length of the drying basket.
The open mesh nature of both the outer cylinder and
spiral arms allows air flowing through the drying basket to
mix freely with the capsules.
To contain the basket it is housed in a surrounding
solid walled container with vents for air to come in and
leave. Air enters by way of two or more axial slits at the
base of the basket. The slits are sized to ensure that
entering air has a high velocity such that it is sufficient
to lift the capsules away from the inner surface of the
basket to enhance the tumbling action in ensuring that
capsules neither stick to the walls nor each other. Air
leaves the chamber via ports located at the opposite end from
the capsule feed.
The air fed to the drying basket comes from a compressor
unit capable of supplying large volumes of air at high
velocity. To condition the air to the desired temperature
heating or cooling heat exchangers are mounted between the
compressor and the slit entry point. Air entering the
compressor from the room is raised in temperature by the
compression and so without additional conditioning will enter
the dryer at between ambient and 300 C above ambient. By
heating or cooling the range can be controlled to within the
range 5OC to 80OC. The cooling heat exchanger is preferably
an air-water system of similar form to that used on cars. The
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19
exhaust from the drying basket is taken by an additional high
volume air pump which directs the air and solvent vapor along
duct work away from the machine.
The waste air can then be vented either into the room,
into the external air via ducts and chimney, or into a
condenser/scrubber to remove the solvent and condition the
waste air for release.
The choice of extract system depends upon the site of
operation and the solvent employed.
The use of bulk supply and extract air pumps enables the
pressure in the basket to be adjusted. Where solvent release
into the surrounding air is to be avoided, it is important
that at all locations within the dryer the pressure is less
than the room pressure. The PLC can control the motors
driving both pumps and hence can adjust both the pressure and
flow independently.
The action of the spiral in the drying basket means that
the residence time for a capsule in the drying basket is
controlled simply by the rotation speed. As a capsules reach
the end of the basket they fall into a sieve and drop into a
storage Container or onto a transport mechanism.
Where the solvent being used should not be released into
the room air additional features may be included with the
system to ensure all of the solvent is removed by the purging
air. These include guard shields around the spray bar
cylinder assembly which form a substantially closed volume
connected to the exhaust air pump to ensure any vapor
released in the area is removed, a transparent guard shield
to fit in place of the feed tube assembly to enable the
operator to view the spray bars having solvent dumped to
them, before commencing a sealing run, as a visual check to
their functioning, pressure balancing the airflows to ensure
that all of the volumes containing solvent are held below
atmospheric pressure, an airflow arrangement on the outlet to
enable capsules to exit without loss of solvent vapor, in
extreme cases the capsules leaving the dryer may be housed in
a sealed container through which air is blown to waste to
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remove any residual solvent vapor, control interlocks to
prevent access to the liquid fed parts o the machine for a
period after spraying which allows the airflow to remove an
residual solvent vapor, and/or selection of all materials in
5 contact with the liquid or vapor of the solvent to ensure
that there is no long term degradation.
