Abstrict The hot air dryer for plastic materials is disclosed. Three desiccant
cartridges are carried on a rotatable turret and each cartridge
is indexed successively from a process air station to a regeneration
station and then to a cool down station. At each station, the cartridges
are clamped between sets of upper and lower conduit fittings to
provide a closed air flow path. A clamp spring acts on a lower conduit
carrier to raise the cartridges against the set of upper conduit
fittings to a clamped or closed position. The clamping actuator
including a motor driven lead screw acts on the carrier to retract
it against the resistance of the clamp spring to lower the turret
and hence the cartridges away from the set of upper fittings to
a stop position and the carrier is further retracted to separate
the set of lower conduit fittings from the lower end of the cartridges
thereby opening the clamp and the air flow path through the cartridges.
A turret drive mechanism rotates the turret to the next index position
and the clamp actuator closes the clamp to place the dryer in readiness
for another cycle.
Claims What is claimed is:
1. A hot air dryer comprising:
a rotatable turret,
a set of desiccant cartridges supported on said turret, each of
said cartridges including inlet and outlet cartridge fittings at
opposite ends,
a first set of conduit fittings equally spaced from each other
and disposed at one end of said cartridges,
a second set of conduit fittings equally spaced from each other
and disposed at the other end of said cartridges, each conduit fitting
in said first set corresponding with one of said conduit fittings
in said second set to form a corresponding pair of conduit fittings,
said turret being rotatable about a turret axis to successive index
positions in which each of said cartridge fittings at one end of
said cartridges is aligned with one of said conduit fittings in
said first set to form a pair of mating fittings and each of said
cartridge fittings at the other end of said cartridges is aligned
with one of said conduit fittings in said second set to form a pair
of mating fittings,
said set of cartridges, said first set of conduit fittings and
said second set of conduit fittings being movable axially relative
to each other between open and closed positions in which the fittings
of each of said pairs of mating fittings are disengaged and engaged
with each other, respectively,
driving means for rotating said turret from one index position
to the next when said fittings are in said open position,
a process air flow path connected between a first corresponding
pair of conduit fittings,
a regeneration air flow path connected between a second pair of
corresponding conduit fittings,
a cooling air flow path connected between a third pair of corresponding
conduit fittings,
and actuating means for moving said cartridges and said conduit
fittings to said open position before said turret is rotated and
for moving said cartridges and conduits to said closed position
after said turret is stopped in said next index position.
2. The invention as defined in claim 1 wherein one of said sets
of conduit fittings is stationary and said actuating means comprises:
first force applying means for moving the other of said sets of
conduit fittings into engagement with one of said sets of cartridge
fittings and for moving said cartridges so that the other of said
sets of cartridge fittings are in engagement with the said one of
said sets of conduit fittings,
and second force applying means for moving said cartridges so that
the other of said sets of cartridge fittings is disengaged from
said one of said sets of conduit fittings and the other of said
sets of conduit fittings and other of said sets of conduit fittings
is disengaged from said one of said sets of cartridge fittings.
3. The invention as defined in claim 2 wherein said first force
applying means is a spring and the second force applying means is
a lead screw and a motor.
4. The invention as defined in claim 3 wherein:
said turret axis is vertical, said first and second sets of conduit
fittings are disposed at the lower and upper ends of said cartridges,
respectively.
5. The invention as defined in claim 1 wherein the number in each
of said sets is three.
6. The invention as defined in claim 1 wherein each of said conduit
fittings comprises an annular seal adapted to sealingly engage one
of said cartridge fittings.
7. The invention as defined in claim 1 wherein said process air
flow path extends between said first corresponding pair of conduit
fittings and includes a process air heater and a process air blower
and wherein said cooling air flow path extends between said third
corresponding pair of conduit fittings and includes said process
air heater and said process air blower.
8. The invention as defined in claim 7 wherein said regeneration
air flow path extends between said second corresponding pair of
conduit fittings and includes a regeneration air heater and a regeneration
air blower.
9. The invention as defined in claim 7 wherein said cooling air
flow path includes a flow restrictor.
Description FIELD OF THE INVENTION
This invention relates to drying apparatus; more particularly,
it relates to a hot air dryer with multiple desiccant cartridges
which are indexed to successive operating stations.
BACKGROUND OF THE INVENTION
Hot air dryers are conventionally used in processing engineering
thermoplastic material while it is in pellet form. Most engineering
plastics are hygroscopic and tend to adsorb moisture during storage
and processing. Nonhygroscopic plastics are susceptible to surface
contamination by moisture. In order to enhance the quality of the
finished product, the raw plastic should be dried before processing.
This is commonly achieved by flowing heated dry air through the
plastic material which is held in a drying hopper. In practice,
the heated dry air, commonly referred to as "process air",
is produced by passing it through a desiccant or molecular sieve
for dehumidification and then through a heater before it is delivered
to the plastic material. The dry process air is continuously recirculated
until the desiccant requires regeneration to remove the adsorbed
moisture. As a practical matter, plural desiccant beds in the form
of interchangeable cartridges, are used in the drying apparatus.
When the desiccant cartridge requires regeneration, it is replaced
by a regenerated cartridge and is itself regenerated by flowing
heated air therethrough. Following regeneration, it is common practice
to cool the desiccant cartridge by flowing cooler air therethrough
to reduce the desiccant temperature so that it will more effectively
adsorb moisture when it is placed on stream to dehumidify the process
air.
In the prior art, drying apparatus is known in which a desiccant
bed is automatically moved from the process station to a regeneration
station and replaced by a regenerated desiccant bed. This has been
accomplished by a continuously rotating desiccant bed with a process
air flow path through one sector and a regeneration air flow path
through another sector. This arrangement provides for continuous
regeneration and avoids the need for complex valves for switching
the air flow paths. This is described in advertising bulletin no.
20 dated January 1968 by Thoreson-McCosh, Inc. which describes "Des-i-dri"
hopper dryers. A two station indexing hot air dryer is described
in the Cooke U.S. Pat. No. 870546 granted Nov. 12 1907.
Hot air dryers are also known which utilize three or more cartridges
mounted on a turret or carrousel which is indexed automatically
to successive stations for process mode, regeneration mode, and
cool down mode operation. In this dryer, the cartridges are mounted
between two manifolds with rotary valves for gradually changing
the flow rate as the carrousel moves the cartridges from one station
to the next. This hot air dryer is described in a publication by
Con-Air, Inc. as form number 9300CL3-84. An air dryer of this type
is also disclosed in the Graff U.S. Pat. No. 3487608 granted Jan.
6 1970.
A general object of this invention is to provide an improved hot
air dryer which overcomes certain disadvantages of the prior art.
SUMMARY OF THE INVENTION
In accordance with this invention, a hot air dryer is provided
which utilizes a set of desiccant cartridges on an indexing turret
to provide successive process, regeneration and cool down modes
of operation without the need for complex rotary valve or manifolds.
This is provided by relative axial movement of the cartridges and
the corresponding dryer conduit fittings whereby they are clamped
together in the operating modes and are separated to permit indexing
between stations.
Further, according to this invention, a rotatable turret supports
a set of desiccant cartridges. Each of the cartridges is provided
with an inlet air fitting on one end and an outlet air fitting on
the other. A first set of conduit fittings and a second set of conduit
fittings corresponding thereto are disposed at opposite ends of
the cartridges to form corresponding pairs of conduit fittings.
The turret is rotatable to successive index positions in which the
cartridge fittings are aligned with corresponding pairs of conduit
fittings. The desiccant cartridges and the conduit fittings are
movable axially relative to each other between open and closed positions
in which the cartridge fittings and conduit fittings are disengaged
and engaged. The turret is rotated by driving means from one index
position to the next when the cartridges and the conduit fittings
are in the open position. The cartridges and conduit fittings are
moved axially by actuating means to the open position before the
turret is rotated and to the closed position after the turret is
stopped in the next index position. A process air flow path, a regeneration
air flow path and a cooling air flow path are connected respectively
with the corresponding pairs of fittings in the index positions.
A more complete understanding of this invention may be obtained
from the detailed description that follows taken with the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of the hot air dryer of this invention;
FIG. 2 is a front elevation view of the dryer with the front cover
panel removed;
FIG. 3 is a side elevation view of the dryer with the side cover
panel removed;
FIG. 4 is a view taken on lines 4--4 of FIG. 2;
FIG. 5 is a view taken on lines 5--5 of FIG. 2; and
FIG. 6 is a schematic diagram of the electrical control circuit.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to the drawings, there is shown an illustrative embodiment
of this invention in a hot air dryer with an indexing turret carrying
three desiccant cartridges and especially adapted for drying plastic
materials. It will be understood as the description proceeds, that
the invention is useful in other applications and may be practiced
in other embodiments.
The hot air dryer 10 of this invention will be described with reference
to FIGS. 1 through 6. As shown in FIG. 1 the dryer 10 is connected
with a drying hopper 12 in a typical application for dehumidifying
plastic pellets. The hopper 12 is suitably mounted on top of an
injection molding machine (not shown) or the like. The dryer 10
comprises, in general, a process station A, a regeneration station
B and a cooling station C. A carrousel or turret 14 is mounted for
rotation about a vertical axis and supports a set of desiccant beds
or cartridges 16 16' and 16" for rotation therewith. A turret
drive mechanism 18 rotatably drives the turret 14 about its axis
in an intermittent manner so that each of the desiccant cartridges
is indexed successively into the process station A, regeneration
station B and cooling station C. A process air flow path 22 is provided
at station A so that process air passes through the desiccant cartridge
16. A regeneration air flow path 24 is provided at station B so
that regeneration air is passed through desiccant cartridge 16'.
A cooling air flow path 26 is provided at station C to pass cooling
air through cartridge 16". A clamping actuator 28 is adapted
to connect the air flow paths 22 24 and 26 with the cartridges
16 16' and 16" when the turret 14 is stopped with the cartridges
in the respective stations and to disconnect the air flow paths
prior to indexing motion of the turrent to the successive position.
The dryer 10 will be described in greater detail below.
As depicted in FIG. 1 the process air flow path 22 regeneration
air flow path 24 and cooling air flow path 26 are open. In this
open condition, the desiccant cartridges 16 16' and 16" are
effectively removed from the air flow paths. In this condition,
the turret drive mechanism 18 is operated to advance the turret
by one station so that each cartridge is placed in the succeeding
station. With the turret thus indexed in alignment with the stations,
the clamping actuator 28 is operated to close the air flow paths
22 24 and 26 and thus connect the desiccant cartridges 16 16'
and 16" in circuit therewith, respectively. Before describing
the turret drive mechanism 18 and the clamping actuator 28 the
air flow paths of the dryer will be described.
The process air flow path 22 comprises an inlet conduit 32 which
extends from an outlet fitting on the drying hopper 12 to the inlet
of a filter 34. The filter 34 is adapted to remove particles, such
as fines from the plastic pellets in the hopper 12 from the air
flow. The outlet of the filter 34 is connected through a conduit
36 to the inlet of a blower 38. The outlet of the blower is connected
through a flexible conduit 41 to a rigid conduit 42 which terminates
in a lower conduit fitting 44. The lower conduit fitting is adapted
to sealingly engage a cartridge fitting 46 at the inlet of cartridge
16. The conduit fitting 44 and cartridge fitting 46 are shown in
detail in FIG. 5. The conduit fitting 44 comprises an annular flange
43 with an annular gasket or seal 45 mounted thereon. The cartridge
fitting 46 is a flat annular surface on the end plate of the cartridge
16 surrounding the air flow passage therein. The other conduit and
cartridge fittings are of the same construction. An upper conduit
fitting 52 is adapted to sealingly engage a cartridge fitting 48
at the outlet of the cartridge 16. The conduit fitting 52 is connected
through a conduit 54 with the inlet of a process air heater 56.
The outlet of the heater 56 is connected through an outlet conduit
58 which is connected with the inlet of the drying hopper 12.
The regeneration air flow path 24 comprises a blower 62 which has
an inlet open to the ambient air through a filter 64. The outlet
of blower 62 extends through a conduit 66 to the inlet of a regeneration
air heater 68. The outlet of the heater 68 extends through a conduit
72 to an upper conduit fitting 74. The fitting 74 is adapted to
sealingly engage a cartridge fitting 76 at the inlet of cartridge
16'. The cartridge 16' has an outlet fitting 78. A lower conduit
fitting 82 is adapted to sealingly engage the cartridge fitting
78. A rigid conduit 84 extends from the conduit fitting 82 to a
flexible conduit 85 which discharges the regeneration air to the
atmosphere.
The cooliing air flow path conveys a portion of the process air
from the outlet of blower 38 through the cartridge 16" at station
C. For this purpose, it comprises a horizontal rigid conduit 92
which branches from the conduit 42 and through a vertical rigid
conduit 94 which terminates in a lower conduit fitting 96. The fitting
96 is adapted to sealingly engage the cartridge fitting 98 at the
inlet end of the cartridge 16" instation C. An upper conduit
fitting 104 on a conduit 106 is adapted to sealingly engage the
cartridge fitting 102 at the outlet end of cartridge 16". The
conduit 94 is provided with an orifice plate 108 to restrict the
air flow through the cooling air flow path. Conduit 106 extends
to a second inlet of the process air heater 56. From the outlet
of the heater 56 the cooling air flow path coincides with the process
air flow path through the hopper 12 filter 34 and back to the blower
38.
The mechanical structure of the hot air dryer 10 will now be described
in greater detail, particularly with reference to FIGS. 1 2 and
3. A stationary platform 122 is supported on the frame of the cabinet
124 and by legs 126 which extend to the cabinet floor. A conduit
carrier 128 in the form of a channel is secured, as by welding,
to the rigid conduit 84 and the horizontal conduit 92. The carrier
128 is supported on the stationary plateform 122 by a compression
or clamp spring 132. A support plate 134 is mounted on the platform
122 by legs 136. The turret 14 is mounted on the support plate 134
in a manner which will be described presently.
The turret 14 comprises a turret shaft 142 having a vertical axis
of rotation and supported for rotation in a lower bearing 144 on
support plate 134. The upper end of the turret shaft 142 is supported
for rotation in an upper bearing 146 which is mounted on a stationary
platform 147. A collar 148 is secured to the lower end of the shaft
142 above the bearing 144. The turret shaft 142 is axially movable
in the bearings 144 and 146. The downward movement of the shaft
142 is limited by the collar 148 which engages the bearing 144 when
the shaft is in its lower position.
For the purpose of carrying the cartridges 16 16' and 16"
on the turret 14 a lower turret plate 152 is mounted on the shaft
by a collar 153. The cartridges 16 16' and 16" rest on the
lower turret plate 152 and an upper turret plate 154 secured to
the turret shaft 142 by a collar 155 is seated against the upper
ends of the cartridges. A set of index pins 156 are equally spaced
circumferentially and extend vertically through the lower turret
plate 152. Each index pin comprises a bolt and nut and the three
nuts on the upper surface of the turret plate serve as spacers or
locating lugs for positioning the three cartridges. The cartridges
are individually secured to the turret 14 by individual clamp bands
158. Each of the index pins 156 referred to above has a shank extending
beneath the turret plate 152 and is adapted to engage the actuator
of a microswitch 174 for turret indexing purposes, as will be described
subsequently.
The turret drive motor 162 is mounted by a bracket 164 on the platform
122. A driving sprocket 166 is mounted on the shaft of the motor
162 and is coupled through a drive chain 172 to a driven sprocket
168 on the turret shaft 142. Thus, when the motor is energized the
turret 14 is rotated; the motor 162 is controlled for intermittent
rotation in a manner to be described subsequently.
As described above, the conduit carrier 128 is supported on the
clamp spring 132. This spring exerts sufficient force to support
the conduit carrier and the turret 14 and to sealingly clamp the
conduit and cartridge fittings together so that the air flow paths
are in the closed position, as shown in FIGS. 2 and 3. In the closed
position of the air flow paths, the lower conduit fittings 44 82
and 96 are in sealing engagement with the lower cartridge fittings
46 78 and 98 respectively, and the upper cartridge fittings 48
76 and 102 are sealingly engaged with the upper conduit fittings
52 74 and 104 respectively. With the air flow paths in the closed
position, the dryer is operative to supply process air to the hopper
12 at station A and, at the same time, regenerate the cartridge
at station B and cool down the cartridge at station C. As described
above, the air flow paths must be opened in order to permit indexing
of the turret between stations. In the open position, the upper
conduit fittings 54 74 and 104 are vertically spaced from the upper
cartridge fittings 4876 and 102 and also the lower conduit fittings
44 82 and 96 are vertically spaced from the lower cartridge fittings
46 78 and 98 respectively. In this open condition of the air flow
path the blowers 38 and 62 continue to operate and the air flow
is discharged to the atmosphere at the conduit fittings during the
time interval required to index the turret from one station to the
next.
In order to open the air flow path to permit the indexing of the
turret, the clamping actuator 28 is provided. The actuator 28 comprises
an electric motor 182 a lead screw 184 and a travelling nut 186.
The motor 182 is mounted on a gear box 188 which in turn is secured
by a bracket 192 to the floor of the cabinet 124. The travelling
nut 186 is mounted on a U-shaped link 194 which, at its upper end,
is secured to the conduit carrier 128. The motor 182 is drivingly
connected with the lead screw 184 through a gear train (not shown).
When the lead screw 184 is driven in one direction, the travelling
nut 186 is retracted onto the lead screw and the conduit carrier
128 is pulled downwardly or retracted against the compression force
of the spring 132. This downward movement of the carrier 128 lowers
the conduit fittings 44 82 and 96 and the cartridges 16 16' and
16" and the turret 14 are lowered therewith. This causes the
cartridge fittings 48 76 and 102 to separate from the upper conduit
fittings 52 74 and 104 respectively. Downward movement of the
turret 14 and hence the cartridges, is arrested by the engagement
of the collar 148 on the turret shaft 142 with the bearing 144.
Continued rotation of the motor 182 further retracts the carrier
128 against the spring 132 and the lower conduit fittings 44 82
and 96 are separated from the lower cartridge fittings 46 78 and
98 respectively. When this open position is reached, the motor
182 is turned off by a limit switch, as will be described subsequently.
After the turret is indexed, with the air flow in the open position,
to the next station, the flow paths are closed by rotation of the
motor 182 in the opposite direction. This gradually releases the
compression of clamping spring 132 which raises the carrier 128
causing reversal of the sequence described above and restoring the
air flow paths to the closed position.
The control circuit for the opening and closing cycle of the air
flow paths will be described with reference to FIG. 6. The control
circuit for the actuator motor 182 and the drive motor 162 is connected
between lines L1 and L2 of a supply voltage source. The limit switch
174 which is actuated by the indexing pins 156 on the turret 14
has its movable contact connected with the line L1. A timer 212
is connected between the upper fixed contact of the limit switch
174 and line L2. Timer 212 actuates normally open switch contacts
214 which are connected in series with a control relay 216 between
the upper fixed contact of limit switch 174 and line L2. Control
relay 216 actuates normally closed switch contacts 218 and normally
open switch contacts 222. For controlling the energization of the
motors 182 and 162 switch contacts 218 are connected in series with
the upper limit switch 224 and the clamp actuating motor 182 between
the upper fixed contact of limit switch 174 and line L2. The switch
contacts 222 are connected between line L1 and the lower fixed contact
of limit switch 174. A lower limit switch 226 is connected in series
with the turret drive motor 162 between the lower fixed contact
of limit switch 174 and line L2.
In operation, repeated cycles of the drying apparatus are executed
under the control of the control circuit shown in FIG. 6. It will
be assumed that the cycle starts with the cartridge 16 in the process
station A with the clamping actuator closed ("clamp" closed)
so that process air is supplied to the hopper 12 and the cartridge
16' is being regenerated and the cartridge 16" is being cooled
down. In this condition, the limit switch 174 is closed against
the upper fixed contact as shown in FIG. 6. This energizes the timer
212 and, during the time-out interval which may be in the order
of seventy minutes, the motors 162 and 182 are deenergized. When
the timer 212 times out, it actuates the switch contacts 214 to
the closed position which energizes the control relay 216. This
control relay actuates the switch contacts 222 to the closed position
and the contacts 218 to the open position. With contacts 222 closed,
the clamp motor 182 is energized through the lower limti switch
226 which is closed when the clamp is closed. Thus, the clamp motor
182 is driven in the direction to open the clamp i.e. lower the
carrier 128. When the open position is reached, the lower limit
switch 226 is open and the upper limit switch 224 is closed. When
lower limit switch 226 is closed, the turret drive motor 162 is
energized, contacts 222 having been previously closed by control
relay 216. The turret is rotated until the limit switch 174 is actuated
by the succeeding index pin 156 which momentarily closes the movable
contact of the limit switch 174 against the lower fixed contact.
This resets the timer 212 and energizes the control relay 216 which
opens contacts 222 and closes contacts 218. With contacts 222 open,
turret motor 162 is deenergized and the turret stops in the next
index position. With contacts 218 closed and upper limit switch
224 closed, the clamp motor 182 is energized in the reverse direction
and the carrier 128 is raised to close the clamp. When the closed
condition is reached, the upper limit switch 224 is opened and the
lower limit switch 226 is closed thus placing the control circuit
in readiness for execution of the next cycle.
Although the description of this invention has been given with
reference to a particularly embodiment, it is not to be construed
in a limiting sense. Many variations and modifications will now
occur to those skilled in the art. For a definition of the invention
reference is made to the appended claims. |