Low pressure dryer

A low pressure dryer for granular or powdery material includes a plurality of hoppers rotatable about a common vertical axis serially among material filling and heating, vacuum drying and material discharge positions; pneumatic piston-cylinder means for rotating the hoppers about said axis among said filling and heating, vacuum drying and discharge positions; means for heating contents of a hopper at said filling and heating positions; means for sealing a hopper at said vacuum and drying positions; means for drawing vacuum within a hopper at said vacuum drying position and means for selectably permitting downward flow of dried granular or powdery material out of a hopper at said discharge position where said hoppers move collectively and unitarily one with another.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to drying granular or powdery material, preferably 
granular resin material, prior to processing thereof into intermediate or 
finished products, preferably by extrusion or molding. 
2. Description of the Prior Art 
Plastic resins are initially granular materials and are produced in 
pellets. These pellets are processed by extrusion or other means in which 
the granular resin pellets are heated until the pellets melt and may then 
be molded or extruded into a desired shape. Typically granular resins melt 
at elevated temperatures, for example from 300-400.degree. F., which is 
well above the boiling point of water. 
Many granular resins have affinity for moisture. These hydroscopic resins 
absorb moisture and cannot be properly processed by molding or extrusion 
until dried. If processed before dry, moisture in the plastic boils at or 
approaching the high plastic molding or extrusion process temperatures, 
leaving bubbles and perhaps other imperfections in the finished product. 
Hence, hydroscopic granular resins must be dried prior to molding or 
extrusion. 
Some granular resin materials are extremely hydroscopic and become 
unprocessable by molding or extrusion in ten minutes or less after exiting 
a dryer, due to the rapid absorption of moisture by the granular resin 
material. 
It is known to dry granular resin material by placing the granular resin 
material pellets on large shallow trays to a depth of one or two inches, 
and putting those trays into ovens for several hours. With this approach 
to granular resin material drying, resin temperatures of 150-180.degree. 
F., but no higher, can be used since many granular resin materials begin 
to soften at 200-210.degree. F. 
During the drying process, the granular resin material cannot be permitted 
to soften, since it becomes unmanageable. Once granular resin material 
begins to soften, at temperatures above the boiling point of water, the 
granular resin material pellets stick together in lumps or even melt into 
useless masses of solid plastic, making it impossible to further process 
the resin material into a useful article. 
SUMMARY OF THE INVENTION 
In one of its aspects, this invention provides a low pressure granular or 
powdery granular material dryer. The dryer preferably includes a rotatable 
preferably vertical shaft, a plurality of preferably vertically-oriented, 
open-ended preferably cylindrical hoppers which are preferably 
equiangularly positioned and rotatable about a vertical axis, which is 
preferably defined by the shaft, serially among material filling and 
heating, vacuum drying and dispensing positions. 
The dryer preferably further includes a pin extending vertically and 
radially displaced from the axis, a preferably triangular preferably 
horizontal plate rotatably receiving the pin proximate the center of the 
plate, a preferably horizontal link pivotally connecting said shaft and 
the plate, and a plurality of preferably pneumatic piston-cylinder 
combinations equiangularly operatively connected to the plate for rotating 
the shaft by sequentially moving the plate relative to the shaft thereby 
to move the hoppers among the filling and heating, vacuum drying and 
dispensing positions. 
The dryer yet preferably includes preferably pneumatic piston-cylinder 
actuated means for sealing the cylindrical hoppers at the vacuum drying 
station. 
In another of its aspects, this invention provides a hopper for use in a 
low pressure granular resin material or powdery material dryer where the 
hopper includes a preferably vertically-oriented preferably cylindrical 
shell having open ends with the shell preferably adapted to be sealingly 
closed by selectably contacting top and bottom plates thereagainst, 
thereby enabling vacuum to be drawn within the shell when desired. The 
hopper further preferably includes a funnel within the cylindrical shell 
and located proximate the shell bottom. The hopper further preferably 
includes an internal material flow control plate in the form of a dump 
flap located within the shell beneath the funnel. The dump flap is 
preferably pivotally connected to the shell for movement about the 
connection point away from a downwardly opening discharge orifice of the 
funnel, thereby to selectably release granular resin material from the 
hopper. 
In yet a further aspect of the invention, top and bottom plates preferably 
selectably seal the cylindrical shell thereby allowing vacuum to be drawn 
therewithin. Pneumatic piston-cylinder means may be provided for urging 
the top and bottom plates into sealing contact with the shell. 
The shell is desirably adapted to selectably dispense granular or powdery 
material stored therewithin at a dispense position, when the shell is at 
that position. The dispense position is preferably removed from the vacuum 
drying position. 
The hopper is further preferably adapted to effectuate material dispensing 
upon contact by an upwardly moving rod of a pneumatic piston-cylinder 
combination, thereby permitting downward flow from the funnel of material 
with the material thereby flowing out of the cylindrical shell. 
In yet another of its aspects, this invention provides a method for 
continuously drying granular or powdery material preparatory to mixing, 
molding, extruding or other processing of that material. The method 
preferably includes supplying granular or powdery material to a 
vertically-oriented cylindrical shell at a fill and heat position and 
heating the material within the shell by introduction of heated air into 
the cylindrical shell while at the fill and heat position. 
The method yet further preferably includes moving the vertically-oriented 
cylindrical shell through an arc about a vertical axis outboard of the 
shell periphery to a vacuum drying position and sealing open ends of the 
shell at such position. 
The method still yet further preferably includes drawing a preselected 
level of vacuum within the sealed shell for a time sufficient to evaporate 
moisture from the heated material within the shell to a desired degree of 
dryness. 
The method even yet further preferably includes bringing the shell to a 
material discharge position at which the bottom of the shell is open and 
then discharging the dried material from the cylindrical shell 
responsively to action of a preferably pneumatic piston-cylinder 
combination inserting a rod into the shell interior from below to move a 
material discharge gate proximate the bottom of the shell. 
The method preferably still yet even further includes moving the shell 
through an arc about the vertical axis to the fill and heat position and 
sequentially repeating the steps of supplying material to the shell, 
heating the material within the shell, moving the shell to the vacuum 
drawing position, drawing a sufficient level of vacuum within the shell to 
evaporate moisture from the material within the shell and moving the shell 
to a discharge position, for so long as the material is to be continuously 
dried. 
In yet another of its aspects, this invention provides a method for 
continuously supplying dried granular resin material for processing from a 
supply of material which is excessively moist where the method preferably 
includes substantially simultaneously performing the steps of heating a 
portion of the moist granular resin material to a selected temperature at 
which the moisture evaporates from the granular resin material at a 
preselected level of vacuum, drawing and maintaining the preselected 
vacuum for a second portion of the granular resin material which has been 
heated to the selected temperature for time sufficient to cause the 
moisture to evaporate therefrom and result in the second portion of 
granular resin material being at the preselected dryness and supplying to 
granular resin material processing equipment a third portion of the 
granular resin material which was dried to the preselected dryness by 
evaporation in the preselected level of vacuum after having been heated to 
the selected temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENT AND BEST MODE KNOWN FOR PRACTICING 
THE INVENTION 
Referring to the drawings in general and to FIGS. 9, 10 and 11 in 
particular, a low pressure granular material dryer manifesting aspects of 
the invention is designated generally 10 and includes a plurality of 
cylindrical hoppers, preferably three, each of which has been designated 
generally 12. Each hopper 12 preferably includes a cylindrical shell 14 
and is preferably substantially vertically-oriented with the axis of the 
cylinder extending substantially vertically in order to be rotatable 
preferably unitarily with the other hoppers about a substantially vertical 
axis defined by a preferably vertical shaft 24. 
Dryer 10 includes a frame, designated generally 22, on and within which 
vertical shaft 24 is rotatably mounted for rotation relative to frame 22, 
the details of which are discussed below. Cylindrical hoppers 12 rotating 
unitarily with vertical shaft 24 preferably move serially among a material 
fill and heat position designated generally 100, a material vacuum drying 
position designated generally 102 and a material dispensing position 
designated generally 104. Hoppers 12 move when and as required among fill 
and heat position 100, vacuum drying position 102 and dispensing position 
104. The three hoppers 12 start and stop together as required; they do not 
move continuously in a merry-go-round fashion among positions 100, 102 and 
104. 
Referring principally to FIGS. 9 and 10, frame 22 is formed of a plurality 
of vertically and horizontally extending preferably angle iron members 
which collectively define what appears as the edges of a rectangular 
parallelepiped. As visible in FIG. 10, frame 22 includes preferably four 
substantially vertical members 160, only two of which are visible in FIG. 
10; the remaining two substantially vertical members 160 are hidden behind 
the two members 160 visible in FIG. 10. 
Frame 22 further includes four upper substantially horizontally extending 
members 162 which collectively define the outer periphery of a square in 
geometrical terms; the four upper substantially horizontally extending 
members 162 are visible in FIG. 9; not all of members 162 are visible in 
FIG. 10. 
Frame 22 further yet preferably includes four lower horizontally extending 
members 164, one of which is visible in FIG. 10. The remaining lower 
members 164 lie immediately under the corresponding upper horizontally 
extending members 162 illustrated in FIG. 9. The four lower horizontally 
extending members 164 define the base of frame 22 for contacting a floor 
or other weight supporting structure on which dryer 10 rests. 
At least one and preferably a plurality of suspension members 166 extend 
laterally across the upper end of dryer 10, between selected upper 
horizontal members 162. One of such suspension members 166 is illustrated 
in FIG. 10. A hopper top sealing piston-cylinder combination designated 
generally 44, serving to seal the top of a hopper 12 at the vacuum drying 
position, is supported by one of horizontally extending suspension members 
166 as illustrated in FIG. 10. Similarly, a hopper upper closure 
piston-cylinder combination 98 located at material fill and heat position 
100, which piston-cylinder combination is used to close an upper end of a 
cylindrical hopper 12 at the fill and heat position 100, is supported by 
one of horizontally extending suspension members 166 as also illustrated 
in FIG. 10. 
First, second and third driving rotation piston-cylinder combinations 34, 
36, 38 are preferably pivotally connected to selected ones of upper 
horizontal members 162 of frame 22 as illustrated in FIG. 10. In the case 
of first driving rotation piston-cylinder combination 34, a triangular or 
cantilever extension may be provided from the proximate upper horizontal 
member 162 where the triangular extension has been designated generally 
182 in FIG. 9. Connections of driving rotation piston-cylinder 
combinations 34, 36 and 38 to frame 22 are denoted as pivotal connections 
180 in the drawings. 
Connection of generally triangular plate 28 with vertically-oriented shaft 
24 is effectuated by means of a pin connector 168 which is 
vertically-oriented and resides rotatably slidably within an aperture 
formed at the center of horizontal central portion 30 of generally 
triangular plate 28. Pin connector 168 fits rotatably not only within 
triangular plate 28 but also fits rotatably within an aperture in one end 
of a plate-pin connection arm 116 best shown in FIG. 9. While plate-pin 
connection arm preferably lies under triangular plate 28 as is apparent 
from FIG. 10, plate-pin connection arm 116 has been illustrated in solid 
lines in FIG. 9 to facilitate understanding. 
Plate-pin connection arm 116 is fixedly connected to vertical shaft 24 at 
the upper end thereof. 
In this arrangement movement of triangular plate 28, as effectuated by any 
of first, second or third driving rotation piston-cylinder combinations 
34, 36 or 38, results in pin connector 168 translating such motion to 
plate-pin connection arm 116. Rotation of plate-pin connection arm 116, 
being fixedly connected to shaft 24, results in shaft 24 rotating. As 
shaft 24 rotates, it carries hoppers 16 among the fill and heat position 
100, vacuum drying position 102 and material dispense position 104. 
Hoppers 16 move this way unitarily with shaft 24 as a result of hoppers 16 
being fixedly connected to shaft 24 by cantilever connecting rods 110, 
illustrated in phantom lines in FIG. 10. 
Shaft 24 is journaled in suitable bearings mounted on upper and lower shaft 
suspension plates 112 to define upper and lower shaft bearing assemblies 
114 as indicated in FIG. 10. Upper shaft suspension plate 112 is connected 
to a horizontally extending suspension member 166 by suitable nut and bolt 
combinations which have not been numbered but are clearly visible in FIG. 
10; lower shaft suspension plate 112 is connected to a lower horizontal 
member 164 as indicated generally in FIG. 10, again by suitable nut and 
bolt combinations which have not been numbered in the drawings. 
Referring to FIGS. 1 through 3 illustrating the fill and heat position 100 
of lower pressure dryer 10, at fill and heat position 100 a moist material 
supply hopper 64 has a supply of moist granular or powdery material, which 
is to be dried resident therein. A butterfly valve at the bottom of hopper 
64 is within a conduit 144 and is operated by a piston-cylinder 
combination 146 as clearly visible in FIGS. 1 and 3. 
Conduit 144 includes a telescoping portion 148 for connecting moist 
material supply hopper 64 with a hopper top sealing plate 150 at fill and 
heat position 100. Positioned around the outer periphery of hopper top 
sealing plate 150 is an annular lip 152. An aperture 154 is within hopper 
top sealing plate 150 and facilitates communication between telescoping 
portion 148 of conduit 144 and the interior of a hopper 14 when at the 
fill and heat position. 
Still referring to FIGS. 1 and 3, a hopper 14 is illustrated in position as 
a result of having been rotated to that position by rotation of vertical 
shaft 24 in response to first, second and third driving rotation 
piston-cylinder combinations 34, 36 and 38. 
At material fill and heating position 100, a blower 76 facilitates 
recirculation of heated air through material 74 resident within hopper 14 
to heat material 74. Blower 76 has an intake aperture 78 and an exhaust 
aperture 80. Exhaust aperture 80 connects to conduit 156 within which 
there are a plurality of heater elements 82 to heat air exhausted from 
blower 76 prior to flow through material within hopper 12. Conduit 156 
includes a telescoping portion 158 connecting with and exhausting into a 
supply plenum designated generally 86 via a plenum inlet 90 which is 
visible in both FIGS. 1 and 2. 
Plenum 86 includes an outlet screen 88 mounted at the upper end thereof, as 
illustrated generally in FIG. 2. Outlet screen 92 has a plurality of 
apertures 184 formed therein with apertures 184 concentrated towards the 
central portion of outlet screen 92 as illustrated in FIG. 2. Apertures 
184 serve to concentrate upward flow of the heating air about the central 
portion or central axis of hopper 14 which is desirable since this is 
where the majority of the material is concentrated to the shape of 
dispensing funnels 94, 96. A preferably silicon annular gasket 88 on 
plenum 86 provides tight sealing between supply plenum 86 and the open 
bottom of hopper 12 at the material fill and heat position illustrated in 
FIGS. 1 and 3. 
A pneumatic piston-cylinder combination 106 is mounted on a suitable 
cross-member, not illustrated in the drawings but forming a part of frame 
22. When actuated, piston-cylinder combination 106 serves to close the 
bottom of hopper 12 in the fill and heat position by moving supply plenum 
86 vertically upwardly, from the position illustrated in FIG. 1 to the 
position illustrated in FIG. 3, thereby effectuating a tight seal between 
outlet plenum 86 and hopper 12 to facilitate passage of heated air through 
granular or powdery material in hopper 14. 
Heated air, having passed through granular or powdery material within 
hopper 14, exhausts from hopper 14 via telescoping portion 148 of conduit 
144. A butterfly valve 66 having closed conduit 144 so that heated air 
passing through telescoping portion 148 of conduit 144 cannot escape 
through supply hopper 64, causes the heated, moist air to flow into heated 
air recirculator 70 at heated recirculation intake 72. A thermocouple 68 
positioned at heated air recirculation intake 72 senses temperature of 
heated air leaving hopper 14. A second thermocouple 84 is positioned 
proximate the outlet of the heated air supplied by blower 76, after the 
heated air has passed along heating elements 82. When the temperature 
sensed by thermocouples 68 and 84 are substantially equal, this is 
indicative of the granular or powdery material within hopper 14 having 
reached the desired temperature, namely the selected temperature of the 
air entering into supply plenum 86 after having been heated by heating 
elements 82. 
During material heating at the fill and heat position, hopper top sealing 
plate 150 is lowered into position against the upper extremity of hopper 
14 by action of a pneumatic piston-cylinder combination 98 which is 
connected to a suitable cross-member extending across the top of frame 22. 
Referring to FIGS. 4 through 8 in particular, each preferably cylindrical 
hopper 12 preferably includes a cylindrical shell designated generally 14. 
Each cylindrical shell 14 is preferably defined by an inner cylindrical 
tube referred to as a vacuum tube and designated 52 in the drawings and a 
concentric outer cylindrical tube referred to as an insulation tube and 
designated 54 in the drawings. Annular space between tubes 52 and 54, 
which space is designated generally 55 in the drawings, is preferably 
filled with thermal insulation to minimize heat transfer and heat loss out 
of cylindrical shell 14. 
A pair of downwardly opening material dispensing funnels designated 94 and 
96 respectively are secured within each cylindrical shell 14 of 
cylindrical hopper 12 proximate the bottom of hopper 12. The higher of the 
two material dispensing funnels is referred to as an upper material 
dispensing funnel and is designated 94 in the drawings. The lower of the 
two material dispensing funnels is referred to as the lower material 
dispensing funnel and is designated generally 96 in the drawings. Material 
dispensing funnels 94 and 96 are preferably fixedly secured, by suitable 
sheet metal screws or other fastening means, to a lower portion of vacuum 
tube 52 at the positions generally indicated in the drawings. 
Material dispensing funnels 94 and 96 preferably share a common funnel 
angle such that the sloped sides of the respective funnels are essentially 
parallel one with another. The sloped surface or side of upper material 
dispensing funnel is designated generally 122 in the drawings while the 
sloped side of lower dispensing funnel 96 is designated generally 124 in 
the drawings. 
As further apparent from the drawings, particularly FIGS. 6 through 8, 
upper dispensing funnel 94 is configured as an extremely truncated cone 
such that the downwardly dispensing opening of upper material dispensing 
funnel 94, which is designated 126 in the drawings, is substantially 
larger than a corresponding downwardly dispensing opening 128 of lower 
material dispensing funnel 96. This results from lower dispensing funnel 
96 being less truncated in the vertical direction than upper dispensing 
funnel 94, as is illustrated in the drawings. 
Use of two dispensing funnels such as dispensing funnels 94, 96 facilitates 
circulation of heated drying air around material in hopper 14 at filling 
and heating position 100 and further facilitates drying of the material in 
hopper 14 when the hopper is at vacuum drying position 102. 
Each hopper 14 preferably further includes a dump flap designated generally 
20 located below downwardly dispensing opening 128 of lower funnel 96. 
Dump flap 20 is pivotally connected to vacuum tube 52 by suitable screw 
connections which are illustrated in the drawings, particularly in FIGS. 
4, 5 and 8, and are numbered 140 and 170 respectively. 
Dump flap 20 includes a central portion 172 which is generally planar in 
configuration as illustrated in the drawings, particularly FIGS. 6, 7 and 
8, and has a weight 130 located at one side thereof, offset from the point 
of pivotal connection between dump flap 20 and dump actuator 62, which 
point of pivotal connection is denoted 132 in the drawings, and also 
offset from the pivotal connection of dump flap 20 with vacuum tube 52 of 
hopper shell 14 as effectuated by screw-nut connection 170 and offset from 
pivotal connection 140 of pivoting arm 134 to the interior surface of 
vacuum tube 52. Weight 130 helps to cause dump flap 20 to return to the 
position illustrated in FIG. 6 in response to gravitational force after 
material dispensing piston-cylinder combination 108 has been deactuated. 
Dump actuator 62 engages a generally vertical air 134 forming a part of 
dump flap 20. Dump actuator 62 includes a vertically movable arm 136, also 
illustrated in FIG. 7. Vertically movable arm 136 is mounted for sliding, 
vertical movement along the interior surface of vacuum tube 52 of 
horizontal shell 14. The extent of vertical movement of vertically movable 
arm 136 is controlled by a pin 174 illustrated in FIG. 7, which is 
preferably mounted fixedly to and extending radially inwardly from the 
interior of vacuum tube 52. A vertical slot 176, similarly visible in FIG. 
7, in vertically movable arm 136 receives pin 174. Interference between 
pin 174 and the ends of slot 176 limits vertical travel of movable arm 
136. 
Movement of arm 136 upwardly in FIGS. 6, 7 and 8 results from actuation of 
material dispensing piston-cylinder combination 108, which is preferably a 
pneumatically powered piston-cylinder combination. When piston-cylinder 
combination 108 is actuated, a piston rod 178 extending from 
piston-cylinder combination 108 contacts a horizontal tabular extension 
portion of vertically movable arm 136. This horizontal tabular extension 
of vertically movable arm 136 is designated 138 and is shown in FIG. 8. 
There tabular extension 138 is illustrated in solid lines in the "at rest" 
or unactuated position and in dotted lines in the position assumed by 
tabular extension 138, and hence vertically movable arm 136, when material 
dispensing pneumatic piston-cylinder combination 108 has been actuated and 
the piston rod associated therewith extends therefrom. 
Actuation of material dispensing piston-cylinder combination 108 moves 
vertically movable arm 136 upwardly, to the position illustrated in solid 
lines in FIG. 8; the movement of arm 136 is from the position illustrated 
in FIG. 6 to the position illustrated in FIG. 7. 
Vertically movable arm 136 is pivotally connected to an arm 134 portion of 
dump flap 20. 
Arm 134 connects the horizontal part of dump flap 20 to the inside of 
vacuum tube 52 via a pivotal connection identified as 140 in FIGS. 6, 7 
and 8. Arm 134 is pivotally connected not only to the interior vacuum tube 
52 at connection 140 but is also pivotally connected to vertically movable 
arm 136 at a pivotal connection 132. As a result, upward movement of 
vertically movable arm 136 causes pivotal movement of pivoting arm 134 
about pivotal connection 140. Since pivotal connections 140 and 170 are 
horizontally aligned along a common axis, pivotal movement of arm 134 
about this axis moves the horizontal part of dump flap 20 away from the 
dispensing aperture of lower funnel 96 thereby permitting granular or 
powdery material contained within hopper 12 to float downwardly outwardly 
therefrom when dump flap 20 is in the position illustrated in FIG. 7. 
Once preferably pneumatic hopper dispensing piston-cylinder combination 108 
has been deactuated, gravitational force acting with weight 130 tends to 
rotate dump flap 20 back to the horizontal, hopper closed, position 
illustrated in FIGS. 6 and 8. This causes vertically movable arm 136 to 
drop downwardly, from the position illustrated in FIG. 7 to the position 
illustrated in FIG. 6. This further causes arm 134 to rotate 
counterclockwise from the position illustrated in FIG. 7 to the position 
illustrated in FIG. 6, about pivotal connection point 140. This returns 
dump flap 20 to the horizontal position illustrated in FIG. 6 where 
granular material in hopper 12 cannot flow outwardly downwardly therefrom 
through the open bottom of hopper 12. 
The horizontal portion 172 of dump flap 20 is positioned sufficiently close 
to and sufficiently overlaps downwardly dispensing opening 128 of lower 
funnel 96 about the periphery of dispensing opening 128 that the angle of 
repose of any granular or powdery material within hopper 12 is sufficient 
to prevent downward flow of material through the gap between horizontal 
portion 172 of dump flap 20 and dispensing opening 128 of lower funnel 96. 
Material dispensing piston-cylinder combination 108 is preferably mounted 
either on a portion of frame 22 below dryer 10 or on some other stable 
member such as the floor of an installation where dryer 10 may be used. In 
either case, material dispensing piston-cylinder combination 108 is 
stationary in the sense that piston-cylinder combination 108 does not 
rotate with hoppers 12 as they are moved among fill and heat position 100, 
vacuum drying position 102 and material dispense position 104; hopper 
dispensing piston-cylinder combination 108 remains at material dispense 
position 104. 
As apparent from FIG. 8, dump flap 20 includes two arms 134, 134A. Arm 134A 
which is located at the side of dump flap 20 remote from material 
dispensing piston-cylinder combination 108 is pivotally connected directly 
to vacuum tube 52, preferably by screw-nut combination 170 as illustrated 
in FIGS. 4 and 5, for pivotal movement as dump flap 20 is actuated. 
In FIGS. 4 and 5 one of hoppers 12 is illustrated at vacuum drying position 
102. FIG. 4 illustrates hopper 12 at vacuum drying position 102 prior to 
movement of hopper top and bottom vacuum sealing plates 40, 42 into 
position to seal cylindrical shell 14 so that a vacuum may be drawn 
therewithin. 
Hopper top and bottom vacuum sealing plates 40, 42 are preferably 
respectively connected to unnumbered piston rod extensions which are 
connected to and are parts of hopper top and bottom sealing 
piston-cylinder combinations 44, 46 respectively. Piston-cylinder 
combinations 44, 46 are preferably pneumatically actuated; the cylinder 
portions thereof are preferably fixedly connected to horizontally 
extending cross-members of frame 22 as indicated generally in FIGS. 4 and 
5. 
Hopper top and bottom vacuum sealing plates 40, 42 are most preferably of 
dome-like shape, as illustrated in FIG. 4, and have upper and lower vacuum 
sealing gaskets 58, 60 positioned running circumferentially around the 
unnumbered preferably circular lips of preferably dome-like hopper top and 
bottom vacuum sealing plates 40, 42 respectively. 
When a hopper 12 is located at vacuum drying position as illustrated in 
FIG. 4, pneumatic actuation of respective hopper top and bottom sealing 
piston-cylinder combinations 44, 46 respectively causes respective 
dome-like hopper top and bottom vacuum sealing plates 40, 42 to move 
vertically towards cylindrical hopper shell 14. Arrows A in FIG. 4 denote 
the vertical movement of hopper top and bottom vacuum sealing plates 40, 
42 respectively. 
When hopper cylindrical shell 14 is located at vacuum drying position 102, 
actuation of respective piston-cylinder combinations 44, 46 moves top and 
bottom sealing plates 40, 42 downwardly and upwardly respectively to 
effectuate an airtight, vacuum maintaining seal between the preferably 
circular periphery of top and bottom sealing plates 40, 42, where vacuum 
gaskets 58 and 60 are preferably located and the preferably circular 
circumferential top and bottom edges of vacuum tube 52. The hopper top and 
bottom vacuum sealing plates 40, 42 in this position, with gaskets 58, 60 
in sealing connection with the circumferential circular top and bottom 
edges of vacuum tube 52, as illustrated in FIG. 5. 
Top vacuum sealing plate 40 preferably includes a fitting, not numbered in 
the drawings, selectably connectingly receiving a preferably flexible 
vacuum line 50 which is preferably connected to a vacuum pump depicted 
schematically in FIG. 5 and designated 48. When hopper top and bottom 
vacuum sealing plates 40, 42 have been engaged with cylindrical shell 14 
as illustrated in FIG. 5 and vacuum pump 48 is actuated, vacuum is drawn 
within hopper 12 at this vacuum drying position. As pressure drops within 
hopper 12 at this vacuum drying position, moisture rapidly evaporates from 
granular resin material within hopper 12. 
Once moisture has been evaporated from resin material within hopper 12 when 
located at vacuum drying position 102 and the resin material has reached a 
desired degree of dryness, hopper top and bottom sealing piston-cylinder 
combinations 44, 46 are permitted to return to their default positions 
illustrated in FIG. 4. This retracts hopper top and bottom vacuum sealing 
plates 40, 42 away from and out of contact with cylindrical shell 14, 
thereby permitting air once again to enter cylindrical shell 14 and 
permitting cylindrical shell 14, having the now-dried granular resin 
material therewithin, to be moved to the material dispensing position. 
The time during which vacuum is drawn within hopper 12 while located at 
vacuum drying position 102 may be adjusted by microprocessor control means 
connected to and associated with the low pressure granular material dryer. 
Similarly, the level of vacuum drawn in hopper 12 at vacuum drying 
position 102 may be adjusted. Furthermore, air withdrawn from hopper 12 by 
vacuum pump 48 may be monitored for moisture content and vacuum pump 48 
may be halted once the desired low level of moisture of the material 
within hopper 12 has been attained. The microprocessor control means 
controls operation of the low pressure dryer, including operation of the 
pneumatic piston-cylinder combinations, the blower, the vacuum pump, etc. 
Referring to FIGS. 9, 10 and 11, plate-pin connection arm 116 is rotatably 
connected to a generally horizontal plate 28 by pin connector 168. Pin 
connector facilitates rotation of plate 28 respecting plate-pin connection 
arm 116 and hence respecting pin-like extension 26 and vertical shaft 24. 
Plate 28 includes a horizontal central portion 30 and downwardly projecting 
lips 32 extending from the periphery of plate 28. 
Three preferably pneumatically actuated piston-cylinder combinations 34, 36 
and 38 are designated respectively first, second and third piston-cylinder 
combinations and are pivotally connected to frame 22, specifically to 
upper horizontally extending member 162 of frame 22, as generally 
illustrated respecting second and third piston-cylinder combinations 36, 
38 in FIG. 9. The pivotal connections are designated 180 in FIG. 9. 
To facilitate rotation of plate 28 about an axis defined by vertical shaft 
24, first, second and third piston-cylinder combinations 34, 36, 38 are 
actuated as needed. Each piston-cylinder combination 34, 36, 38 has a 
piston rod extension which fits loosely within a respective aperture 
formed in a respective portion of a downwardly projecting lip 32, with the 
piston rods being retained in position within those apertures by nuts 
threaded on the piston rod extremities as illustrated generally in FIGS. 9 
and 11. 
With this arrangement, as piston-cylinder combinations 34, 36, 38 are 
actuated to move their associated piston rods, from extended positions in 
which the piston rods of piston-cylinder combinations 36, 38 are 
illustrated in FIG. 11 to the retracted position in which the piston rod 
extension of piston-cylinder combination 34 is illustrated in FIG. 11. As 
a result plate 28 and hence, vertical shaft 24 and cylindrical hoppers 12 
attached thereto rotate about the axis of vertical shaft 24, thereby 
moving hoppers 12 serially among the material fill and heat, vacuum drying 
and material dispense positions 100, 102, 104 respectively as illustrated 
in FIGS. 9 and 11. 
For example, referring to FIG. 9, upon actuation of first driving rotation 
piston-cylinder combination 34 to extend the piston shaft therefrom 
forwardly out of the retracted position illustrated in FIG. 9 and 
actuation of third driving rotation piston-cylinder combination 38 to 
cause the piston shaft associated therewith to retract to within 
piston-cylinder combination 38, plate 28 rotates counterclockwise as 
considering FIG. 9, in the direction indicated by arrow A, with such 
rotation of plate 28 being about pin connector 168 and as illustrated in 
FIG. 11 and indicated by arrow B. 
As plate 28 rotates about pin connector 168 in the direction indicated by 
arrow A, plate 28 together with pin connector 168 rotate with horizontally 
extending plate-pin connection arm 116 pivotally about the axis defined by 
vertical shaft 24 thereby rotating shaft 24. This rotation results from 
plate-pin connection arm 116 being fixedly connected to shaft 24. Hence, 
as first, second and third driving rotation piston-cylinder combinations 
34, 36 and 38 respectively are actuated in a sequential manner, plate 28 
rotates about pin connector 168 and plate 28, pin connector 168 and 
plate-pin connection arm 116 all rotate about the vertical axis defined by 
shaft 24 thereby to rotate shaft 24. 
The vertically-oriented cylindrical sides of hopper shells 14 defined by 
vacuum tubes 52 and insulation tubes 54 are connected to shaft 24 for 
rotation therewith by cantilever connecting rods 110 as best illustrated 
in FIG. 10. Each cylindrical shell 14 of a cylindrical hopper 12 may be 
removable from its associated cantilever connecting rods 110 if desired; 
preferably two cantilever connecting rods 110 are provided for each hopper 
12, with one rod 110 connecting hopper 12 to vertical shaft 24 at 
positions relatively close to but removed from the vertical extremities of 
hoppers 12, as illustrated in FIG. 10. 
FIG. 9 has been drawn without depiction of moist material supply hopper 64, 
exhaust plenum 142 and the structure associated therewith, to enhance 
drawing clarity. Similarly, hopper dispensing piston-cylinder 108 has been 
depicted in FIG. 9 even though it is to be understood that such 
piston-cylinder combination would not be visible in the view from above 
dryer 10 since when a hopper 12 is at material dispense position 104, 
piston-cylinder combination 108 is blocked from view from above. 
Arrow B in FIG. 11 depicts the preferred direction of rotation of vertical 
shaft 24 and hoppers 12 so as to move hoppers 12 serially from the 
material fill and heat position 100 to material vacuum drying position 
102, then to material dispense position 104 and then to material fill and 
heat position 100, where this cycle may repeat. 
At the material vacuum drying position, the heated material is preferably 
subjected to a vacuum of about 27.5 millimeters of mercury or greater. 
This lowers the evaporation point or boiling point of water to only 
120.degree. F., thereby causing the moisture within the heated material to 
evaporate and be drawn off through the vacuum pump drawing vacuum within 
hopper 12 at the vacuum drying position 102. Once the vacuum drying 
process is sufficiently complete, piston-cylinder combinations 44, 46 
retract hopper top and bottom sealing plates 40, 42 so that hopper 12 may 
move from the vacuum drying position to the material dispense position. 
Blower 70 is preferably a one horsepower blower. Preferably two heater 
elements 82 are utilized, as illustrated in the drawings. Air flow through 
supply plenum 86 is preferably restricted to 4.5 ounces of pressure. 
As depicted schematically in the drawings by line 74 indicating the angle 
of repose of within hopper 12, an air space is permitted to remain within 
hopper 12 to accommodate material spillage during movement of hoppers 12 
and cycling of the drying process. 
The material fill and heat and vacuum drying functions may each take 
approximately twenty minutes. Accordingly, in one hour, all three hoppers 
12 preferably cycle through material fill and heat position 100, material 
vacuum drying position 102 and material dispense position 104. If each 
hopper 12 is approximately 10 inches in diameter and 24 inches high, each 
hopper 12 will hold about one cubic foot of granular resin material, which 
is about thirty-five pounds of granular resin material. With such 
configuration, dryer 10 embodying the invention can provide about 100 
pounds per hour of dried granular resin material for subsequent processing 
by plastic injection molding or extrusion equipment. 
As is apparent from the drawings, hoppers 12 are preferably provided 
equally spaced around vertical shaft 24 with hoppers 12 120.degree. apart.