DE3320978A1 - PLASTIC MATERIAL DRYING PROCESS - Google Patents

Description

1 . ί '

Ι]]:. :: '] 332Ü978

Plastic material drying process

In the plastics processing industry it is generally used; j known that a precise method for preconditioning the processing to j plastic material is required with respect to ι the moisture content and temperature, and then ^{anschlies-> [send} satisfactory production results in the Erzeuouna of,

To be able to guarantee Kunststoffartikelη. A generally be j known preconditioning method, which is also known as a j | Duty cycle is a closed air cycle> ' with a process air blower for the delivery of pressurized Process air sequentially through a drying device for the purpose of | Influencing and controlling the moisture content of the process air, with an air heater to heat the process air, heating

i heating a supply of plastic material in a drying container by means of the dry to a predetermined temperature Temperature range heated process air in such a way that the heated material has such a temperature and such a moisture content that this material is then converted into end products
can be processed, which affects the quality and appearance,
as it is desired by the customer base. To
the process,
air in turn to the inlet side of the blower in order to enrögl i chen that this process air is released from the drying container
can be recirculated. This is how the
Process air in an essentially closed circuit which is "no" closed by the ambient air. As is known, the supply of plastic material can consist of one of numerous,
fruit! r-non-permeable pellets and from re-crushed

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! Waste material exist, which mixture is common in the plastics processing industry is used. Fine wei tproeh'cndo Mc-

. This well-known drying cycle is written for

the average skilled person is not required, especially in

! With regard to existing prior publications of such drying

engineering cycles, such as the "Engineering Data No. 93oo and 93o3"

j Bulletins published by Conair, Inc., their

j address is Conair Building, Franklin, Pennsylvania 16323, and '■

. also from US Pat. No. 3,487,608.

As is also known, some plastic materials require heating to temperatures above those normally used for drying plastics, and for this purpose so-called "high" performance dryers with the operating cycle described above are used . such "high" drier include a heat exchanger, for example a water-cooled heat exchanger in the path of the process air between the drying container and between the inside of the blower, the temperature of the process air to minimize the back flow from the Trocknunpsbe- _i containers to provide an effective moisture removal In this case, too, a further description of this working cycle does not appear to be necessary in view of the relevant prior publications, such as the Conair Bulletin "Engineering Data No. 93o9 ^{! L} and the US patent referenced above. All of these publications as well as the US patent are cited here in order to make it easier to understand the working cycle according to the invention.

The object of the invention is to create a new, improved plastic material drying process in which the process air runs through a closed cycle in which there is a fan, but this is the volume of the process air is changed by optionally passing parts of the Process air around the fan (Hei paß.führung). That should

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j Volume of the process air that is fed to the drying container:

will be changed in accordance with predetermined temperatures!

J the process air exiting the drying vessel. A j

I- I

A more specific object of the invention is to create a new, improved Kuns tstof fmateri al drying process in which the process air flows in a closed circuit, the volume of the process air being reduced in accordance with the temperature of the process air exiting a drying container, upon reaching or exceeding a predetermined \ temperature, whereas the VoT 'is increased in accordance with the men! Temperature of the process air that exits the drying housing when a lower temperature is reached or ■ is not reached.

To solve this problem, the invention consists in an improved drying process in which a controlled volume of process air from the outlet side to the inlet side of the fan is matched (passed by) according to predetermined temperatures of the process air emerging from the drying housing. All of the process air passed by is added to the process air before it enters the cooling device and into the air heater, so that the energy to be supplied to the air heater can be reduced. As is known, the air heater is supplied with heating energy after the inlet temperature of the drying case is negated. Normally, the inlet temperature of the process air that is supplied to the drying enclosure is maintained within a predetermined temperature range, wherein oer Energi g e out-ang of the heater is changed in accordance with the Veränderunger the inlet temperature to your drying enclosure. In the invention, the temperature properties of the process air exiting the drying housing are scanned in order to control the bypass flow of the process air in such a way that when the air emerging from the drying housing reaches or exceeds a certain temperature value, the volume of the drying housing to qfil fed process air is reduced-through opening

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: a volume-adjustable flow valve in the Reipass

^: leitunq, whereas if the temperature of the

; nungsgehduse exiting process air to a predetermined

The temperature drops or falls below this, the flow of Process is reduced or else by this control valve is completely interrupted, which then increases the volume of the process air supplied to the drying container.

ι The speed at which this

ι outlet temperature increased to control the flow of the process i

uses air. · "I

Further objects and features of the invention emerge from the ί following description and from the graphic representation; a preferred embodiment at the time of registration game of invention. j

Fig. Γ is a schematic representation of the elements of a Drying process (drying cycle) that is carried out according to the Invention principles is trained.

Fic. 2 is the schematic part 1 of what is shown in fin Drying method using a heat exchanger.

The closed plastic material drying cycle ₃ modified by the invention is generally known. It consists of a: process air blower 2, the high pressure outlet line 4 of which is connected to the inlet of a suitable drying device; 6, then an off! aßl ei tune 9, which from the drying pin 6 to the inlet side of a suitable air heater Io;

leads, further i ^: via an outlet line 12 from det .; Air heater ι ο ■; ' to the first 3? sfii te one. Drying container 1Ί, and a / "■ v ^c . 1 p" -leitunn 16 from Ow. Drying container H again; ii deiii Prozni ¹ ! uf tj blower 2. · In such a well-known drying process (Tröcknunnszykl us) pine pre-ordered M

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of plastic material 18 in the drying container 14, and after the heating and drying that takes place therein are parts of this material removed one after the other from the drying container 14, The amount of these individual withdrawals depends on 'the material requirements for a subsequent material' Processing operation, for example on the material requirements a molding machine 2o, which via a line 2o for Ent-; take it out of the drying container; 14 taken --- material s

is connected to this. The drying container 14 is also gradually refilled with unheated plastic material according to the space available in the drying container, namely via a supply device 24 and a supply line 26, in conjunction with a supply 28 of unheated plastic material The drying container 14 is designed so that a predetermined amount of heated or dried material can be received per unit of time, which is required for continuous operation of the subsequent processing machine, measured for example in kilograms per hour Incoming process air must have sufficient heat content or sufficient drying capacity to heat and dry the required weight of plastic material to produce the desired amount of dried plastic material on a continuous basis for the subsequent to be able to hand over the processing. As is known, the maximum or a continuous supply of dried plastic material is not always necessary, and accordingly the heat content of the process air supplied to the drying container 14 can be reduced if the material requirement is lower. .If previously supplied to the temperature of the .dom drying vessel 14 by means of electrical resistance Heheizunqsvorrichtüng 3o, heated air within a ·· -vorbestimmten egg η 1 aßtemperaturberei held chs. For this purpose, in the line 12 is immediately before the drying container. 14 a temperature sensor 32 provided, desse

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Ausgan gss gnal i is directly proportional to temperature uer dor in egg on j Trocknungsbehdlter 14 incoming process air. The output signal of the temperature sensor 32 actuates a control unit tunn 34 j which is switched on in the feed line 36 for the electrical resistance heating device 3o and is used to control the supply of electrical energy to the heating device 3o. By changing the switch-on and switch-off times of the heating device 3o, the heat content of the drying. nungsbehäl ter 14 supplied process air can be changed.

Heated process air enters the drying vessel 14 and flows through the amount of plastic material IR, penetrating it, through with heat exchange with this material, so that this to one lying within a preselected temperature range Temperature is heated that is correct for the subsequent Processing. By choosing a drying container 14 The right size for the material being dried, the condition of the material being dried and the quantity requirements on dried material, this is done in the drying process' material located in the drying container 14 in this held for a sufficient period of time, commonly referred to as "dwell time", to be able to and way of ensuring the desired drying of this material. When the process air flows through the drying container 14, the material 18 contained therein is heated, and at the same time the material 18 emerging from this material is discharged Absorbs moisture. This heat exchange has the consequence that the temperature of the process air in the drying container 14, compared to the inlet temperature of the process air in this drying container 1.4, is reduced: '' The cooled, Γ-dich ti'-koi t ^ n thnl tende process air is from the drying container 1-i over ei ^ off! a! 31 ei tunn 16 of the same to the inlet " side of the process! air blower 2 released. This blower ^ •• ■ causes an increase in the pressure of the process air, in which case this in turn under i; jerked process air via the -Hoch el back- - '.

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Outlet line 4 flows to drying device 6, in which j the moisture content of the process air to a suitable:

The value is reduced so that the process air then turns again 14 can absorb moisture in the drying container. j The process air flows from the drying device 6 via its Ausl'aßlei device 3 to the air heater lo, in which the process air, as j already described above, is heated. In this cycle of operation, the total volume of the drying vessel becomes 14 released process air in the drying device 6 is dehumidified and heated in the air heater Io. In this context becomes during those periods of time during which plastic material 18 discharged from the drying container 14 and during which material to be heated into the drying container 14 is introduced, ambient air into the drying vessel 14 enter. Since the duty cycle and the associated Components, elements, etc., as described above, are well known, a more detailed description thereof is for an average skilled person is not required.

In the new and improved drying cycle according to the invention is a process air tuning valve 4o via a line 42 to the j

Lines 4 and 16 connected to optionally pass process air around the process air blower 2 in the bypass before the process air is dehumidified in the manner described above and is heated. Since the inlet of the valve 4o is in flow connection with the high pressure side of the fan 2, Process air flows from line 4 to line 17 through valve 4o only during the drying cycle process, i.e. therefore when the fan 2 is working. A temperature sensor 44 is switched on at a suitable point in the outlet line 16, which measures the temperature of the process air at its outlet from the drying container 14. The output signal of this temperature sensor 44 is directly proportional to this outlet temperature. In the basic cycle according to the invention is the temperature sensor 41 connected to a npr control device 46, the control device

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the electrical energy supply of a Botäti supply vorri chi ιιηπ 48 is used in such a way that the valve 1 element of the valve Io in Richtunn <

on its open position, or in its fully open position bc-! is turned away when the temperature of the process air from the j Drying container 14 a predetermined upper temperature limit { reaches or exceeds, and that the Venti 1 element of the valve 14 in the direction of its closed position, or up to this Closed position inside, is moved when the outlet temperature of the Process air from the drying container 14 a predetermined lower temperature limit reached or below.

So if in cases where the valve 4o is closed and { the outlet temperature of the process air from the drying vessel; 14 in the line 16 reaches this upper temperature value or exceeds j, so wi rd the valve 4o opened by the operation of the ι temperature sensor 44, the control device 46 and the actuating device 48, so that then a part of the process air around the fan 2 around the Line 42 and the valve 4o is fitted. When opening the valve 4o, the non-matching part of the process air flows through the drying device 6, the air heater Io and the drying container "14 I with a reduced volume compared to the process air volume that flows through these units when the j valve is closed 4o. at the reduced process! uftvolurne η I ι caused by the air heater Io the heat output of Beheizungs- ¹ device! 3o an increase in the temperature of the lowered J volume of process air in the air heater lo, more rapidly, ι as this is the case when all of the process air flows through the air heater Io. The temperature sensor 32 senses whether the heated, reduced volume of the process air reaches or exceeds a predetermined upper temperature limit, and uses the Control device 34 switches off the electrical resistance heating device 3o g 3o only enough heat to transfer to the reduced volume of process air to this

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reduced process air volume, which is fed to the drying container to keep at a temperature. which is controlled by the temperature sensor 32. The temperature sensor 32 scans _: when the heated, reduced volume process air reaches the lower temperature limit, or falls below this, after which the heating device is then switched on again via the control device 34.

As long as the temperature of the process air in line-16 is below the preselected upper temperature limit at which the Temperature sensor 44 actuates the control device 46, controls the temperature sensor 32 via the control device 34 the activation the heating device 3o, so that the Drying container 14 incoming process air within the desired Temperature range is maintained. When the process air temperature in line 16 again reaches the predetermined temperature reaches or exceeds at which the temperature sensor 44 actuates the control device 46, causes the output channel of the temperature sensor 44 via the control device 46 an actuation of the actuating device 48 in the sense of a further ap opening of the valve 4o and thus an increase in the size of the fan 2 process air fitted over. Since the flow of the process air supplied increases the flow of process air in the bypass, the flow of process air decreases through the drying cycle to the point at which the valve 4o in its full opening position: The valve 4o is dimensioned in such a way that it allows the flow of such a bypass amount of process air allows, as would be required in a drying cycle in which the valve 4o is to be used. The control device 46 is provided with a (not shown) Provide control to set off an alarm. If valve -1o is in its fully open position and the process air temperature in the line 16 nevertheless that temperature range exceeds, within which the temperature sensor 44 The actuating device 48 via the control device 46 controls. "..

When the trial! uf t-temperature in the line 16 dip unt.ore Limit of the desired temperature range in the Lei tuna 16 reached or falls below, causes the equilibrium sense of the Temperature sensor 44, depending on the temperature in the Lei bunq 16, a movement of the valve via the control device 46 in the direction of its closed position, or in this Schliep.iaqo in to reduce the bypass air flow and reduce the amount of the process air flowing through the drying cycle great. By increasing the amount of the dry ' The temperature sensor causes the process air flowing through the cycle

32, via its associated control device 34, the activation d-er heating device 3o to the temperature of the drying container 14 incoming process air within the desired

! th area. When the valve 4o is partially closed

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ι has and the temperature in line 16 below the lower

Limit of the temperature range desired in line 16 remains, then causes the output signal of the temperature sensor 44 via the control device 46 a movement of this valve into a more closed position, thereby reducing the bypass air flow is further reduced. In this way, the drying cycle According to the invention, the temperature of the process air j in the line 16 is continuously monitored in order to achieve a thermal equilibrium j between the one for the material flow through the drying area

J

{container 14 through and that of the heating device 3o to maintain the generated heat. During periods one

-. low heat requirement for drying the material 18 in ^

ί drying container 14 is the consumption of electrical Energy in the electrical resistance heater 3o reduced. Since every suitable type and construction for the '

J Process air adjustment valve 1 4o and for the actuation device 48 find use in connection with the invention,

[is for the average i ttsf achmann no more, more ins! A detailed description of these units is required ". j The same applies analogously to the various teir-peratun ! sensors and control devices as described above

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because they can be of any suitable type, ■ to cause the opening and closing of the valve 4o in the manner described and W-M se.

With the improved working method, as described above I

as can be seen, a thermal equilibrium i are produced, in which the variable heat requirements I

i ments due to the material 18 are compensated by the different, different heat content of a variable volume of process! air. Within the limits set by the predetermined actuation temperature signals to the control device 46, the volume of the process air is reduced for low (relatively seen) heat demand periods and increased for (again, relatively seen) higher heat demand periods. Various factors, such as the temperature of the incoming material, the moisture content of that material, the type of material being dried, and the throughput requirements for the material cause changes in the amount of heat required to dry the material; as a result, the temperature selected for opening and closing the valve 4o changes, and therefore no specific working temperatures have been suggested. The control device 46 is preferably provided with logically operating means for the purpose of determining a & r speed with which the outlet temperature of the process air increases so that the valve member of the valve 4o can be opened for the purpose of passing a predetermined volume of process air before the temperature of the drying container 14 ahgeqeben Process air actually reaches that temperature which is necessary to actuate the actuating device 48 in the manner described above. It should also be pointed out that the control device 46 is designed in such a way that the movement of the valve 40 is maintained as far as possible in the event of intermittent temperature peaks in the line 16. Since any suitable control Can be used to operate the actuator run es vbrri chtuna 48 as described

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there is no need to refer to a wei lcrqehonde Ueschrei Iujm'i i! ii "; nr s ι ι · ι.« · ι · ιπι . < , because they are not required for an understanding of the invention

is. !

Fig. 2 shows a modification of the drying method described above. Here, a heat exchanger 55, as is known, is switched into the line 16 before the connection of the line 42 to the line 16. Such a heat exchanger 55 is required in certain high-temperature drying processes in which the outlet temperature of the process air from the drying container 14 is higher than in the case of the method described above. travel. With the exception desssen that a Steuervorri ^chtunq: 46 is provided, operating under higher temperature conditions, the operation is in the method rri 55 t of the heat exchanger, the same as in the already described further above.

There have been preferred embodiments of the invention, accordingly the existing regulations, and some possible modifications have been presented, however the average specialist must be aware that; even Still other modifications can be made without departing from the spirit and scope of the invention will. Therefore, the claims are drawn up so that they are modifications of the construction described, ~ the possible for the average person skilled in the art without an inventive step are include.

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List of reference numbers used:

2 process air blower

4 high pressure outlet line:

6 drying device '

8 outlet line from 6 to Io j

Io air heater

12 outlet pipe from Io to 14 j

14 drying container!

16 outlet line from 14 to 2!

18 amount of plastic material in 14!

2o molding machine

22 line to 2o

24 feeding device for 14

26 feed line from 24 to 14

28 plastic supply

3o electrical resistance heating device

32 temperature sensors

34 control device

36 feed line for 3o

4o process air adjustment valve

42 Bypass line for 4o

44 temperature sensors

46 control device

48 actuating device

55 heat exchangers

Claims (1)

K '' ί.) I: ■ L INO. ! . Λ ί ,: i ι '; ν ..,. 2 7 κ * m Conair, Inc. Conair Building Franklin, Pennsylvania 16323 / USA Claims 1.JKunststoffstoff-Trocknunqsverfahren in which a blower the process air moves through a closed flow path, in which at least one process air heater and one after the other a drying container, both on the outlet side of the fan, are arranged, the process air emerging from the drying vessel being returned to the inlet side of the fan is, characterized in that the volume of the Air heater (lo) and flowing through the drying container (14) Process air is changed without the direct discharge of process air from its closed flow path. 2. Plastic material drying method according to claim 1, characterized characterized in that the change in volume is controlled is determined by the temperature of the drying container (14) escaping process air. 3. Kunststof fmateri al drying process according to claim 1 or ?., "Characterized in that the change in volume by optional addition of process air directly to the process air Ge .. bubble (2) is done around. COPY ι · | 4. A plastic material drying method according to claim 3, characterized in that; characterized in that the volume change is by passing
a variable volume of the process air takes place. ! i 15. Plastic material drying process according to one or more of claims 1 to 4, characterized in that the Moist
keitshalt the process air before passing through the
Air heater (lo) is reduced (drying device 6). Plastic material drying process according to one or more | of claims 1 to 5, characterized by an adjustable | Process air tuning valve 1 (4o) to control the flow rate 1
of process air through this valve, devices for connecting this valve (4o) with the outlet side (line 4) and ■ the inlet side (line 16) of the process air blower (2) to generate a bypass flow path for the process air the
Fan (2) around, a temperature sensor (44) for the out of the
Drying container (14) exiting process air to generate
of output signals at predetermined temperatures of this exiting process air, and by a control device (46) and. an actuating device (48) which respond to these output signals in the sense of opening or closing the process air tuning valve (4o). 7. Plastic material drying method according to claim 6, characterized ι characterized in that the control device (46) on the gear - speed of change in the. j : ',. Kunststoffmateri al-drying method according to claim 6, characterized in ¹ ,, is that the process air before it flows through the fan · superheater (lo), Ge j passes through pine drying device (6). i 9. plastic material drying method according to claim 6, characterized in
characterized in that a control device (34) for control BAD ORIGINAL / 3 ORiGiWAL INSPECTED COPY the heat output of the air heater (lo) is provided. jlo.Kunststoffmateri al drying method according to claim 6, characterized j characterized that by the Steuervorrichtunq (34) for the Process air air heater (lo) - the heat generated by this air heater (lo) is decreased when the process air t-Abs tinimventil (4o) is at least partially open. COPY