CA1327687C

CA1327687C - Removing volatiles from plastic materials delivered to an extrusion or injection molding machine

Info

Publication number: CA1327687C
Application number: CA000398389A
Authority: CA
Inventors: Jaro Kopernicky
Original assignee: Mold Masters 2007 Ltd
Current assignee: 4437667 Canada Inc
Priority date: 1982-03-15
Filing date: 1982-03-15
Publication date: 1994-03-15
Anticipated expiration: 2011-03-15

Abstract

INVENTION: REMOVING VOLATILES FROM PLASTIC
MATERIALS DELIVERED TO AN EXTRUSION
OR INJECTION MOLDING MACHINE
INVENTOR: JARO KOPERNICKY

ABSTRACT OF THE DISCLOSURE

A device is described which eliminates the pre-drying of particulate plastic prior to processing by an extrusion or injection molding machine. A
tubular guide member directs particulate plastic under gravity into the feed inlet of the machine. During delivery, the temperature of the particulate plastic is raised with heated air flows to between about 150-200°F. Suction is applied to the feed inlet of the machine to remove volatiles (primarily water) released when the temperature of the particulate plastic is increased by contact with the heated barrel and screw-drive of a machine. Temperature and suction controls permit selection of operating temperature and suction levels that ensure removal of volatiles prior to any extensive plasticization and transfer along the barrel which would otherwise preclude proper removal of volatiles.

Description

" 1327687 `~FIELD OF THE INVENTION
~ . _ ~ The invention relates to the processing of '~ particulate plastics in extrusion or injection-molding machines and in particular to the elimination of i`
volatiles contained in such plastics. `

~;` BACKGROUND OF THE INVEN~ION
A major problem in the injection molding of plastic relates to the rémoval of volatiles (primarily moisture) commonly contained in particulate feed materials. Failure to adequately remove moisture tends to produce bubbles in the resultant product which seriously degrade the quality of the product.

In the prior art, it has been common to pre-dry particulate feed material in a reservoir through which heated air flows are directed. Several .
hours of drying are commonly re~uired with a considerable ~;
expenditure of energy. Warm damp air that has been exhausted from the reservoir is sometimes passed through a dessicant filter, re-heated and re-circulated through the reservoir to provide a very dry air flow.
The dessicant filters must periodically be purged of -~
water, and elaborate systems had been proposed for moving such filters between an operative position and purging apparatus without significantly interrupting the drying process.

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-` A method has been proposed to eliminate pre-drying. In U.S. patent No. 3,826,477 which issued on 2 July 30, 1974 to Xunogi et al there is described a method for venting the barrel of a m~lding machine to remove volatiles prior to injection. The method `i~ involves forming the barrel in sections of stepped internal diameter and adapting the associated screw-y drive to reduce the accumulation of plasticized material in a section of increased diameter. This section is subject to reduced internal pressure and a vent connected to a vacuum pump removes volatiles from this section without significant expulsion of plasticized material. Such a technique has apparently not been entirely successful, and in some instances a measure of pre-drying has been felt necessary to obtain a satisfactory molded product.
.'' Accordingly, it is an object of the present invention to provide a method that permits damp particulate plastic to be processed without pre-drying in an extruder or injection molder and to provide a device embodying the method which can eliminate the need for pre-drying without requiring modification of an existing extruder or injection molder or cons'ruction of a plastic processing machine with a -! 25 stepped barrel and complex screw-drive.

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`- 1 BRIEF SUM~RY OF THE `INVENTION
In a first aspect, the invention provides a process which permits damp particulate plastic to be ~`~ processed without pre-drying in an extruding or injection-molding machine. The process involves heating the damp particulate plastic externally of the barrel to a pre-selected temperature which can be empirically determined in a manner described more ~ully below without knowleage of the actual value. In typical applications, the temperature may be in the order ot 150-200F. The heated damp particulate material is delivered downwardly through generally vertically extending guide means to the material inlet of the machine wherein contact with the heated barrel and the screw-drive releases volatiles from the damp particulate plastic; and applying controlled suction to the guide means whereby heated air is drawn inwardly through the particulate plastic flowing downward t~rough the guide means, and substantially àll of the released volatiles are removed from the material inlet upwardly through the guide means. -~
In a second aspect the invention provides a device adapted to permit dàmp particulate plastic to ;~
be processed`without pre-drying in an extruding or ¦ injection-molding m~chine. Guide means are provided 1 25 for directing movem~nt of the particulate plas~ic to the material inlet of the machine, including an inlet .,,.7 , .

` 1327687 1 for receiving the particulate plastic and an outlet adapted to be placed in communication with the machine's material inlet. Means are provided for raising the temperature of the particulate plastic during movement between the inlet and outlet of the guide means, including temperature control means which permit selection of the temperature to which the particulate plastic is heated.
Means are provided ~or applying controlled suction to the guide means whereby air is drawn into the guide means through the particulate plastic flowing downward ~ through the guide means, and substantially all of the `~ volatiles released from the damp particulate plastic in the barrel of the machine are removed upwardly through the material inlet and the guide means, and heating means for raising the temperature of the air being drawn into the guide means~
The term "heating" as used in this disclosure and the appended claims should be distinguished ~rom ~pre-drying~. The latte~ term is intended to designàte substantial removal of volatiles (primarily water~ from d ~ particulatc plastlc prior to ~ ' - . :
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` - 6 - 1327687 introduction of the materials into an extruding or injection-molding machine, a prior art practice. The . principle of operation embodied in devices of the -~ present invention is to heat damp particulate plastic externally of the barrel to a temperature (typically between about 150-200F) sufficient to ensure that .
contact with the heated barrel and screw-drive of .
the plastic processina machine "adjacent" the material inlet of the n;achine, that is, prior to an extensive plasticization and transfer by the screw-drive, causes release of substantially all volatiles contained in .
the damp particulate plastic. In such circumstances, suction applied at the material inlet where feed material ;;
j is introduced into the interior of the barrel (which ¦ 15 suction obviously cannot be so great as to interfere with delivery and processing of the feed material) which obviously cannot be at a level which can ::`
suffice to remove substantially all the released volatiles.
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i BRIEF DE~CRIPTION OF THE DRAWINGS

: 20 The invention will be better understood with refer~nce to drawings which illustrate a preferred embodiment of a de~ice constructed according to the invention, in which:

~ 7 ~ 1327687 -~ Fig. 1 is a fragmented, elevational view -~ illustrating the device mounted on an injection molding machine;

Fig. 2 is a cross-sectional view of the device in a plane parallel to the plane of Fig. 1 and substantially through the centre of the device; and, ~ig. 3 is a fragmented, elevational view illustrating the device adapted for self-feeding from a reservoir of particulate plastic material.

DESCRIPTION OF THE PRE~ERRED EMBODIMENT

Reference is made to Fig. 1 which illustrates a device embodying the invention and generally indicated by the reference numeral 10. The device 10 is ceated about the material inlet 12 of an injection malding machine 14 having a heated barrel 16 and a screw-drive `
18 that serve to plastici~e particulate plastic.
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The device 10 includes means adapted to guide part~culate plastic under the influence of gravity to the material inlet 12 of the machine 14.
The guide means include a tubular guide member 20 constructed in four steel rings 22, 24, 26, 28 about 4 inches in diameter and 1/4 inch in thickness. The S rings are spaced vertically to provide apertures 30 "~

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`` 1327687 ~ - 8 -~. , ~` which are generally annular except for weld points which are not illustrated in the drawings. The apertures 30 are angled upwardly at about 45 to the ~- interior surface of the tubular guide member 20 to permit the passage of air but preclude the escape of particulate materials (because of the natural angle of repose of the materials). An annular heating band 32 is secured with a ~trap connector to the outer surface of each of the rings, and the heating bands 32 are coupled to a temperature controller 34 which ~ can be used to vary the power supplied to the heatinq ¦ bands 32. Together, the bands 32 have a maximum heat generating capacity of about 400 watts and serve to heat air flows drawn into the guide member through the apertures 30 as described more fully below.

The guide means also include a bell-shaped housing 36 which is snuggly fit about and bolted to the upper ring 22. An opening 38, circumscribed by an abuttment flange 40, serves as an inlet for the guide~means. A hopper 42 ~fragmented) is bolted to the abuttment flange 40 and serves as a reservoir for materials to be delivered by the device 10. A
second bell-shaped housing 44 is fitted in a similar manner about the lower ring 28, and has an opening 46 which serves as an outlet for the guide means. The opening 46 is circumscribed by an abuttment flange 48 .",~,.

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that is bolted to the machine 14 to place the opening 46 in communication with the material inlet 12.

~' Means are provided for generating a flow of -~ heated air through materials guided in the tubular guide member 20. These means include the heating bands 32 and temperature controller 34 described above.
A cylindrical sheet metal housing 50 defines a t~substantially closed compartment about the tubular `-guide member 20 and heating bands 32: leakage of -~
air from the housing is not particularly critical as the general object in providing the housing 50 is -to contain heat radiated by the bands 32. The housing 50 is constructed in two housing portions 52, 54 which can be located about the guide member 20 during assembly. The housing portions 52, 54 are formed with longitudinal flanges 56 lonly one pair illustrated) '. :
which can be secured to one another by means of bolts 58 (only one specifically indicated~. The housing 50 is dimensioned to fit snuggly between annular surfaces 60 of the~bell-shaped housings 36, 40 but, as mentioned above, strict sealing engagement is not necessary.
- Air can be drawn into the housing 50 through an inlet . : ~
pipe 62 $ormed with the housing portion 52 for heating ;~

by the bands 32. A damper 64 pivotally mounted within `-the inlet pipe 62 and rotatable by means of a control `
arm 66 external to the inlet pipe 62 permits regulation -- .

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- lo 1327687 of air intake. Air is drawn from the interior of the housing 50 into the guide member 20 by application of suction to a conduit 68 which is centrally located in the guide member 20. The conduit 68 includes a meshed body portion 70 with apertures that permit passage of air but preclude the entry of particulate plastic typically used in injection molding or extrusion.
~he conduit 68 include~ an elbow 72 which extends through a sidewall of the bell-shaped housing 36 and which is sealed to the housing 36 by welding.
Application of suction to the interior of the conduit - 68 causes air heated by the bands 32 to be drawn through the apertures 30 formed in the guide member 20.

j 15 The conduit 68 also serves to apply suction at the material inlet 12 of the injection molding machine 14. Thus, the conduit 68 is formed at a lower end with an extension conduit 74 that extends into the material inlet 12 to direct suction for removal 2~ of volatiles~ The extension conduit 74 is a telescoping member with an outer tube 76 slidably mounted over an inner tube 78. A simple lock assembly is provided i to prevent telescoping of the outer tube 76 into the screw-drive 18. The lock assembly consists of a rod 80 hingedly connected to the outer tube 76 and extending through an aperture provided in the bell-shaped housing . . .

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- ll - 1327687 ` 44. A knob 81 is secured to an end of the rod 80 to prevent telescoping of the tube 75 beyond a pre-determined position relative to the remainder of the -~ conduit 68. The length of the conduit 74 is selected to locate the point of application of suction just above the screw drive 18 as illustrated in fig. 1.

A heat gathering housing 82 (extensively fragmented in the view of fig. 1) is mounted about the barrel 16 of the machine 14 to gather heat radiated by the barrel 16 during operation. The housing 82 is ~t coupled by a flexible conduit 84 to the inlet pipe 62 of the housing 50. This arrangement permits pre-heating of air which is further heated by the bands 32. :.
~ In typical applications, the air may be pre-heated ¦ 15 to a temperature of about 120-130F thereby significantly reducing the power requirements imposed on the heater bands 32.

An exhaust pipe 86 of about 2 inch diameter is strapped to the elbow ?2 and carries a substantially radia~ly symmetric metal nozzle 88 to which pressurized air can be applied to produce suction in the 3 interior of the conduit 68. The nozzle 88 has a first :
annular portion 90 which contacts the interior :`
surface of the exhaust pipe 86 in substantially conforming engagement, a second annular portion 92 which is spaced from the interior surface of the -i exhaust pipe 86 to define an annular space 94, and ~
a third annular portion 96 with an annular outer , ~.-.
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surface 98 marginally spaced from the interior surface of the exhaust pipe 86 to define an annular nozzle :~ outlet. An air hose 80 secured to the exhaust pipe 86 places a regulator 102 in pressure communication with the annular space 94. The regulator 102 can be connected to any convenient source of compressed air (not illustrated) to apply air under pressure to the annular space 94 of the nozzle 88 to cause a stream of air to flow about the surface 98 into the exhaust pipe 86. In typical applications 3-5 pounds of pressure are applied to the hose 100 by the regulator 102 and generates sufficient suction in the interior of the conduit 68 both to draw heated air flows and to exhaust volatiles at the material inlet 12 of the machine 14, as well as permitting a material delivery function described more fully below~ A nozzle of simpler construction ~for example a right-angled tube) can be used, but the nozzle 88 is relatively simple t~o install and cannot be rotated by vibration or the . 20 like into a position in which air flows would be misdirectèd.

Operation of the device 10 in combination with the machine 14 is essentially as follows.
Particulate plastic 104 is gravity fed from the hopper 42 into the tubular guide member 20 and ultimately into the material inlet 12 of the machine 14. The :

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delivery rate is determined entirely by the take-up rate of the machine 14. During start-up, materials loaded into the tubular guide member 20 should be heate for about 5-10 minutes with heated air flows prior to starting operation of the machine 14. The machine 14 should then be purged with several shots. Resulting -~i sample products should be inspected visually for defects such as lines of bubbles characteristic of unvented volatiles. If a new plastic is being introduced ~; 10 into the machine 14, the heat delivered by the bands 32 should be increased until a satisfactory product is obtained substantially free of any deleterious ~ualities. In practice, the temperature to which particulate plastic materials are to be heated is not unduly critical: heating to temperatures in the - -range of 150-200F is satisfactory for most plastics, and exceeding some predetermined minimum temperature at which a satisfactory product can be obtained has not in testing adversely affected the resultant product. The setting of the pressure in the air hose - ;
100 is also not particularly critical as pressure `~`
must simply exceed some empirically determined minimum ;~;
value at which volatiles are sufficiently removed ;`
from the material ir~let 12 that a satisfactory product `
is obtained. The general object is to heat particulate plastic to a temperature sufficient to cause substantialy `
all volatiles to be liberated in the heated barrel 16 B
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~ prior to extensive plasticization and transfer along ~, the screw-drive 18. In such circumstances, substantially all volatiles can be removed through the material ~ inlet 14 by application of a properly selected amount -~ 5 of suction, a level which of course does not disrupt the processing or delivery of the particulate plastic.

~' In practice, a pressure setting satisfactory for one type of material will generally be satisfactory ~` for another; however, a case may arise where both temperature and pressure must be adjusted to obtain a satisfactory product when a new material is being plasticized. Typical feed rates which can be achieved using the device 10 are as follows: typical nylon materials at 100 pounds per hour, ABS products at 120 pounds per hour, and polycarbonates at 70 pounds per hour. Heat settings for the bands 32 may have to be varied if plastic materials are stored or plasticized in a particularly humid environment. Increased feed rates can be obtained by constructing the guide member 20 with additional aligned rings, or by an overall increase in the dimensions of the device 10 (the housing 50 being about 10 inches in diameter, and the distance between the inlet and outlet of the device 10 being about 28 inches).
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.` - lS - 1327687 .'' .~ Fig. 3 shows the device 10 adapted for self-regulating uptake of feed material. The bell-shaped housing 36 effectively defines in use a . substantially sealed compartment about the inlet . 5 opening 38 and about an apertured portion 106 of the conduit 68. Thus, when the level of particulate . plastic drops below the apertured conduit portion 106, the suction applied to the interior of the conduit 68 produces greater negative pressure at the inlet opening 38. This suction is applied to a supply conduit 108 which has an upper end portion 110 in : :.
substantially sealed pressure communication with the inlet opening 38 ~the hopper 42 having been removed) and a lower end portion 112 located in a mass of particu- :late plastic (pelletized) 114 contained in a reservoir 116 (shown in cross-section). A tube 118 connected :to a source of compressed air directs a flow of air upwardly in the material supply conduit 108, thereby producing a negative pressure in the conduit 108 that tends to draw the material 114 into the conduit 108.
The pressure applied to the tube 118 is regulated ! ~ `
so that material 114 is not drawn up the conduit 108 -~
until additional negative pressure is created within the bell-shaped hou;sing 36 by suction applied from :the conduit 68. Comse~uently, material 114 is dxawn into the device 10 only until the apertures of the .. ~ . . .

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` - 16 - 1327687 conduit portion 106 are covered with the material 114.
. The rate of take-up of material 114 through the conduit 108 is thus constrained to correspond to the rate ; at which material is consumed by the machine 14. A
vibrator 119 in pressure communication with the tube . 118 and operated by pressure in the tube 118 vibrates the cond~uit 108 thereby agitating the material 114 in ~i the reservoir 116 to prevent bare spots from forming I about the lower end portion 112 of the conduit 108.

¦ 10 A second reservoir 1~0 which is a cyclone type separator communicates with the exhaust pipe 86 via an inlet pipe 122 mounted about the exhaust pipe 86. An open upper end 124 of the reservoir 120 permits air exhausted from the tubular guide member 20 to escape. Particulate plastic materials entrained by the air f lows deposit at the bottom of the rleservoir 120, and are returned to the inlet opening 3B through a tube 126 which receives any suction applied ! in the interior of the bell-shaped housing 36.

! 20 It will be appreciated that a particular .
device has been described to exemplify the principles -.
of operation of the invention and its associated method, and that many modifi.cations may be made in the device described without departing from the spirit of the j 25 invention and the scope of the appended claims. It should ~ also be appreciated that the term "damp particulate ` B :`:

-plastic" as used in this specification refers to hygroscopic plastics which have not been subject to th . "pre-drying" normally required for processing in a .- conventional extruder or injection-molder, which has not been fitted with venting apparatus for removal of moistur~ and other volatiles present in the plastic.

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Claims

1. A process which permits damp particulate plastic to be processed without pre-drying in a plastic processing machine of the extrusion or injection molding type in which a heated barrel containing a screw-drive plasticizes the particulate plastic, said machine having a material inlet through which particulate plastic external to the barrel is introduced into the interior of the barrel for plasticizing, comprising:
delivering the damp particulate plastic downwardly through generally vertically extending guide means to the material inlet of the machine wherein contact with the heated barrel and the screw-drive releases volatiles from the damp particulate plastic; and applying controlled suction to the guide means whereby;
heated air is drawn inwardly through the particulate plastic flowing downward through the guide means, and substantially all of the released volatiles are removed from the material inlet upwardly through the guide means.

2. A process as claimed in claim 1 wherein the damp particulate plastic is heated in the guide means to a pre-selected temperature in the range of about 150° to 200°F.

3. A process as claimed in claim 1 wherein the damp particulate plastic flows downwardly through the guide means and into the machine inlet under the influence of gravity.

4. A process as claimed in claim 1 wherein the guide means has a sidewall with a multiplicity of apertures which the heated air is drawn inwardly therethrough.

5. A process as claimed in claim 4 wherein the incoming air is pre-heated to a predetermined temperature by electric heating means.

6. A process as claimed in claim 5 wherein the incoming air is collected adjacent the heated barrel of the plastic processing machine.

7. A device adapted to permit damp particulate plastic to be processed without pre-drying in a plastic processing machine of the extrusion or injection molding type in which a heated barrel containing a screw-drive plasticizes the particulate plastic, said machine having a Claim 7 continued...
material inlet through which particulate plastic external to the barrel is introduced into the interior of the barrel for plasticizing, comprising:
guide means for directing movement of the particulate plastic downward to the material inlet of the machine, wherein contact with the heated barrel and the screw-drive releases volatiles from the damp particulate plastic, the guide means including an inlet for receiving the particulate plastic and an outlet adapted to be placed in communication with the material inlet of the machine;
suction means for applying controlled suction to the guide means whereby;
air is drawn into the guide means through the particulate plastic flowing downward through the guide means, and substantially all of the volatiles released from the damp particulate plastic in the barrel of the machine are removed upwardly through the material inlet and the guide means; and heating means for raising the temperature of the air being drawn into the guide means.

8. A device as claimed in claim 7, further including temperature control means which permit selection of the temperature to which the particulate plastic is heated by Claim 8 continued...
the heated air being drawn into the guide means.

9. A device as claimed in claim 8, further including suction control means which permit the selection of the amount of suction applied to the guide means.

10. A device as claimed in claim 9 wherein the guide means comprises a generally tubular guide member having a circumferential sidewall with a multiplicity of apertures through which the heated air is drawn.

11. A device as claimed in claim 10 wherein the suction means comprise:
a conduit having a body portion and a first end portion and a second apertured end portion positioned generally at the outlet of the guide member, the body portion being located within the guide member and having a multiplicity of apertures therethrough;
a nozzle located at the first end portion of the conduit whereby an air flow provided by a source of compressed air generates a suction in the body portion of the conduit; and pressure regulating means adapted to control the flow of compressed air to the nozzle, whereby the amount of suction applied to the guide member can be selected.

12. A device as claimed in claim 11 wherein the air drawn inwardly to the body portion of the conduit through the apertures in the guide member and the apertures in the conduit is heated to a predetermined temperature by electric heating elements extending around the guide member.

13. A device as claimed in claim 12 further including;
a housing surrounding the guide member;
a heat gathering housing located about the barrel of the plastic processing machine to receive air heated by the barrel; and means in pressure communication with the heat gathering housing for drawing the heated air into the housing around the guide member;
whereby waste heat is recovered from the barrel of the machine to reduce the cost of heating the air being drawn into the guide member.

14. A device as claimed in claim 10 wherein the said second apertured end portion of the conduit is positioned centrally at the material inlet of the machine.

15. Apparatus for removing moisture from granules of plastic resin comprising an elongate bin which is vertically oriented in use, said bin having means for introducing granular resin into the upper region thereof, whereby such granular resin moves downwardly of said bin under the influence of gravity, means for discharging granular resin from the lower region of said bin, said bin periphery having a plurality of apertures therein, means extending lengthwise of and centrally of said bin to define a channel for permitting a flow of gases thereinto and therealong, means for effecting a flow of gas for drying granular resin through the apertures in said bin periphery, over granules of resin in said bin, and into and along said channel means, said channel means being adapted to exhaust such gases away from such granular resin and outwardly of said bin.

16. Apparatus of claim 15, wherein channel means comprises a tubular member having a plurality of apertures in its surface to permit gases which have flowed over and around such granules of resin to pass into said tubular member and therealong for exhausting exterior of said bin.

17. Apparatus of claim 15, wherein said means for effecting gas flow includes means for generating a lower gas pressure at the region where said channel means Claim 17 continued...
exhausts such gases out of said bin compared to the gas pressure at the bin periphery.

18. Apparatus of claim 15, wherein means is provided externally of said bin to heat gases in an enclosure about the bin prior to flowing through the apertures in the bin periphery, such heated gases flowing upwardly of said channel after flowing over such granular resin.

19. Apparatus of claim 18, wherein a housing surrounds said heating means to house said bin, said housing having an opening to permit gases in the form of air to be drawn into said housing.

20. Apparatus for conditioning granular plastic resin for use in a plastics molding or extrusion machine, said apparatus comprising a bin having a granular resin feed opening and granular resin discharge opening so arranged that when in use said bin is vertically oriented to provide for gravity feed of such resin downwardly of the bin, means associated with said bin for passing heated gases through said bin and over such granular resin to remove at least surface moisture from such resin and warm such resin, means extending lengthwise of said bin to define a primary channel for permitting gases flowing over such granular Claim 20 continued...
resin to pass upwardly of said channel means, said channel means being adapted to direct such gases out of said bin, and means forming an extension of said channel means to extend beyond said bin discharge opening and adapted to extend into an inlet for receiving conditioned granular resin of a plastics molding or extrusion machine when said bin is in use, said extension means forming a secondary channel into which pass water vapour given off by plasticizing such granular resin in a plasticizing screw of such plastics forming machine whereby the upward passage of such gases in said channel means draws such water vapour into said secondary channel and upwardly into said primary channel for discharge out of said bin.

21. Apparatus of claim 20, wherein said extension means is of sufficient length that when said apparatus is in use, said extension means is adjacent a screw of a plastics molding or extrusion machine.

22. Apparatus of claim 20, wherein means is provided for heating such gases prior to passage over such granular resin, such heated gases by virtue of their higher temperature flow upwardly of said channel means thereby withdrawing gases including water vapour from the lower portion of said secondary channel.

23. A method for conditioning granules of plastic resin prior to their use in a plastics forming machine comprises passing said granules of plastic resin downwardly through a bin having perforated sidewalls, passing drying air through the bin sidewalls and over said granular resin to remove at least surface moisture from and warm the resin, removing such drying air for discharge from the bin by passing such air upwardly through a channel formed by a perforated tubular arrangement located centrally of the bin, extending said tubular arrangement into the resin receiving part of said plastics forming machine to adjacent a region where such prewarmed resin becomes plasticized and gives off water vapour and withdrawing such water vapour through said tubular arrangement for discharge from the bin.

24. A method of claim 23, wherein said tubular arrangement a relative lower pressure is generated at an outlet for said tubular arrangement which outlet is external of said bin to discharge thereby such drying air with water vapour.

25. A method of claim 23 or 24, wherein said drying air is heated prior to passing through the perforated bin sidewall.

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