CH658425A5 - METHOD FOR THE PRODUCTION OF BLOW TUBE FILMS AND DEVICE FOR IMPLEMENTING THE METHOD. - Google Patents

Description

The invention relates to a method and a device for the production of blown tubular films by extruding thermoplastic material, such as polyolefin or polyvinyl polymer materials with or without additives, and pigments, from an annular slot die of an extrusion press and expanding it generally vertically and vor5

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preferably upwardly extruded tube with the help of a dynamic air volume which is practically enclosed by the tube and cools it on its inner surface. As a dynamic Lulivohimen ("dynamic" or "standing" bladder) an air mass is referred to that at a practically constant volume and pressure to a considerable extent, e.g. B. with flow rates of 100-500 m3 / h. or more is continuously exchanged to remove heat and contaminant vapor from the inside of the hose.

Methods of this type and devices for carrying them out have long been known and are described, for example, in US Pat. No. 2,668,323 (1954). In general, the outer surface of the extruded tube is also cooled, at least by the ambient air, but mostly by means of special ring-shaped cooling air nozzles near the ring slot nozzle to act on the outer surface, in particular during the solidification of the extrudate.

The rate of take-off or production of a given device for producing blown tubular films generally depends on the cooling rate, i. H. the amount of heat that can be dissipated per unit of time from the extrudate tube exiting the ring slot die with an extrusion temperature of typically 180-250 ° C on its way to a pair of nip rollers, which flats the tube and defines the upper end of the dynamic bubble or the one that is remote from the ring slot die .

Numerous proposals are known for increasing the cooling rates on the outer and / or inner surface, which are based on the replacement of cooling air by cooling liquid, such as water; However, it has been found that practically only air as the cooling medium enables an optimal balance of process management, process effort and product quality.

If air is specified as the cooling medium, the cooling rate can practically only be increased by increasing the cooling air flow and / or the temperature difference between cooling air and extrudate (i.e. cooling the air); Since the air cooling required here usually requires powerful cooling units and heat exchangers, increasing the cooling air flow is generally the more economical alternative.

There is probably no critical upper limit for the specific volume (ratio of cooling air volume to the amount of extrudate, e.g. in cubic meters of air per kilogram of extrudate) of the cooling air on the outer surface of the hose (hereinafter simply referred to as "outside air flow"); however, the cooling air flow can be , which cools the inner surface of the hose and maintains the dynamic bubble (hereinafter referred to as "indoor air flow"), cannot be enlarged for various reasons. A main reason for such a limitation is the fact that the overpressure of the dynamic bubble must be kept practically constant and very low, e.g. B. depending on the melt viscosity of the extruded polymer mass between 2 and 50 mm water column, typically 5-10 mm Ws, because the extrudate emerging at the ring slot die is viscous up to the so-called "frost line" (film solidification line) and could not withstand higher internal pressures or was very sensitive reacts to pressure fluctuations.

In practice, it has been shown that an internal air flow that can remove approximately half the amount of heat that can be dissipated with the external air flow from the dynamic bladder requires mechanical hose calibration in order to have the effect of the so-called “periodic pumping”, which was previously unavoidable with internal cooling with air compensate, otherwise a tube with periodic widenings and constrictions is created and accordingly the film thickness cannot be kept constant. For mechanical calibration, the blow tube is generally guided during its cooling through a cylindrical hollow basket, the parts of which have a calibrating effect, e.g. rings with a small diameter Friction coefficients that support the outer surface of the hose, as described, for example, in US Pat. Nos. 3,596,321 and 3,749,540 and in DE-OS 19 50 758 and 2004881.

Mechanical tube calibration has disadvantages, however, since it usually leaves traces on the outer surface of the tubular film and is therefore less suitable for high-quality, in particular transparent products, apart from the comparatively complicated structure of the equipment required for this and the problematic conversion to other hose diameters.

It would therefore be desirable and an object of the invention to use larger specific cooling air volumes for the internal cooling of blow hoses without mechanical hose calibration. 10 This goal cannot be achieved with the means of the prior art; for example, in US Pat. No. 2,170,011 to reinforce the internal cooling, a specific configuration of the outflow nozzle for the internal air flow is described; In addition to other methods, it is proposed (see FIG. 2 of US Pat. No. 3,170,011) to guide the internal air flow in a closed circuit and to cool the air circulating in this circuit; the inside air flow is controlled in the primary or skin air flow with a variable blower and regulated to a lesser extent with at least one secondary or secondary air flow; For this purpose, a branch line with a shut-off valve is arranged in the line of the main air flow in front of and behind the fan in order to increase or decrease the effective total air flow as required. Furthermore, the width of the flattened hose, viewed in the running direction of the hose, is continuously measured behind the squeeze roller in order to use the signals of the deviations of the hose width from the desired value for actuating the valves in the branch lines. If the hose width is too large, the hose width meter actuates the valve in the branch line, viewed in the direction of flow of the primary air stream, behind the blower, i. H. the outlet end of the secondary air flow, and opens the associated branch line, so that the total flow entering the dynamic bubble is reduced by the amount of air leaving the secondary flow. As a result, the hose is expanded less, the hose width decreases towards the desired value and the valve at the outlet end of the secondary flow 35 closes. If the hose width is too small, the hose width meter actuates the valve of the branch line in front of the blower, i.e. H. the inlet end of the secondary flow, so that the total flow entering the dynamic bubble around the suctioned in the secondary flow, d. H. amount of air supplied is increased. The hose is consequently expanded again more, the hose width increases towards the setpoint and the valve at the inlet end of the secondary flow closes.

This type of internal cooling, known from US Pat. No. 3,170,011, with regulation of the internal air flow through the continuously measured hose width has the disadvantage, according to the later mentioned US Pat. No. 3,596,321, that it is not possible to achieve a sufficiently uniform hose diameter, which can be achieved with the high inertia of the regulation of the indoor air flow based on width measurement is explained.

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The experiments of the inventor leading to the present invention have shown that the regulation of the internal air flow, which is dependent on the hose width measurement and is proposed in US Pat. No. 3,170,011, is so unstable that it is effective for internal cooling and therefore sufficient Withdrawal speeds required specific cooling air volumes, the periodic pumping described in DE-OS 20 04 881 is inevitable or even a continuous hose production is impossible at all.

Furthermore, it was found that the inertia of the regulation of the interior air flow, which is dependent on the hose width, causes the disadvantages mentioned, but rather that a characteristic feedback function of this system is much too large and possibly even increasing amplitudes, i. H. a strong periodic pumping.

65 It is therefore an object of the invention to switch off the tendency to periodic pumping in a method having the features mentioned in the preamble of claim 1 or at least to reduce it to such an extent that effective internal cooling without mechanical

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Calibration and still sufficient consistency of the tube thickness can be achieved safely.

This object is achieved according to the invention by keeping the maximum flow rate of the entire secondary air less than 1%, preferably less than 0.5% of the flow rate of the primary air flow, and by coupling the setting of the primary air flow with the control of the secondary air to the setting adjust the primary air flow if the setpoint deviation of the hose width within a predetermined period of time, for. B. 5-20 seconds, is not resolved by controlling the secondary air. With the first-mentioned measure according to the invention, the variability of the controlled function (flow rate of the secondary air) and thus the bandwidth is limited; the second measure shifts the position of the variability range until the regulating function (hose width) again influences the regulated function (flow rate of the secondary air).

Without being restricted to any particular theory, it can be assumed that even with a constant pressure difference between the dynamic bubble and the outside air, periodic pumping occurs, e.g. triggered by minimal temporary changes in viscosity of the plastic polymer mass emerging at the ring slot; Such changes in viscosity can be physically caused by slight temperature fluctuations and / or inhomogeneities in the polymer compositions and are practically unavoidable. If, as a result of such a change in viscosity, with a constant pressure difference, there is a temporarily greater widening of the hose and the resulting “bead” reaches the squeeze rollers, a “pressure surge” can be caused when the bead area is laid flat with the squeeze roller, which leads to an induced new expansion the hose in the plastic area, d. H. between the ring slot nozzle and the frost line.

The control loop proposed in US Pat. No. 3,170,011, FIG. 2, with a direct and unlimited coupling of regulating function and regulated function reinforces this effect; In addition, the closed air flow there does not dampen this tendency to intensify periodic pumping, but at best increases it.

In the method of the invention, the primary air flow is therefore generally conducted in an “open” circuit, that is to say one with ends open to the ambient air; a fan is preferably arranged near each end, which has a blowing effect at the inlet end and a suction function at the outlet end; both fans are expediently used by a common drive axis, e.g. that of an electric motor, operated synchronously and have practically the same performance values, e.g. typically in the range of 200 to 1000 m3 / h.

The regulatory function, d. H. the width of the tube is preferably measured contrary to the teachings of the prior art, in particular contrary to US Pat. No. 3 * 170 * 011, before passing through the pair of squeeze rollers and not behind it.

The entire secondary or secondary air is usually, as is known per se from US Pat. No. 3,170,011, guided in an "open circle", ie with two ends open to the atmosphere, and preferably two controlled secondary air streams are used, but not as in the prior art, both act on the blown-in primary air flow, but in each case on the blown-in or blown-out part of the primary air flow, preferably alternately and not cumulatively.

If, for example, the blower on the input side of the primary air flow for an output of 500 m3 / h. and the preferably equally designed and synchronously running, suction-switched fan on the output side of the primary air flow can draw off the same amount of air accordingly, the maximum flow rate of the entire secondary air is less than 2.5 m3 / h. Such a limitation can be achieved by appropriate cross-sectional dimensions of the line of the controlled secondary air flow or the lines of the controlled secondary air flow or by means of appropriately fixed throttles.

The primary air flow is preferably adjustable at least at the outlet end, e.g. B. with known volume flow controllers, as known for example from air conditioning technology and in the trade, for. B. from Luwa AG, Zurich, Switzerland.

The at least one controlled secondary air flow is generally branched off between the blower at the associated primary air flow end or its setting member and the ring slot nozzle and can accordingly blow off secondary air (behind the blower switched blower). Preferably, all of the secondary air is alternately directed to a blowing and a suction secondary air stream, i. H. appropriate lines, distributed and with a common control body, for. B controlled a pendulum slide valve that either blocks both secondary air lines or partially opens one line to the atmosphere.

To control the secondary air, the hose width is measured continuously, e.g. B. with a sensor on each edge of the flat tube; each sensor is e.g. B. connected to a potentiometer, so that a signal can be generated via a comparator circuit, which corresponds to the extent and direction (negative or positive deviation) of the actual width deviation of the hose from a predetermined target width. Such sensors and comparator circuits are in themselves, for. B. from CH-PS 504'371, known and commercially, for. B. from the company Afex AG, Uznach, Switzerland, so that a detailed description is unnecessary.

The preferably electrical signal of the target width deviation of the flat tube can be used directly or after amplification to control the secondary air, for. B. by the possibly amplified signal actuates the drive of the pendulum slide valve mentioned above in order to either branch off a secondary air stream which is blowing off from the input line of the primary air stream - which reduces the total air stream entering the dynamic bubble and accordingly also the hose width - or an intake secondary air stream into the output line of the primary air stream let in, which reduces the total air flow drawn from the dynamic bladder and accordingly increases the hose width. As soon as the target width is reached again, the secondary air flow can be switched off completely.

After the maximum flow rate of the secondary air is narrowly limited according to the invention, the signal of the setpoint deviation can correspond to such an enlargement or reduction of the hose width, which can no longer be completely compensated with secondary air; the inventive coupling of the secondary air control, which acts as a fine control of the total air flow, with the setting of the primary air flow, which acts as a coarse control, adjusts the latter after a predetermined time interval, i. H. the flow rate of the primary air flow is increased or decreased with a predetermined delay until the secondary air control is again sufficient to compensate for the setpoint deviation of the hose width.

The most appropriate delay may depend on the sensitivity of the hose between the ring slot nozzle and the frost line, e.g. B. on the thickness and / or the viscosity of the polymer mass. In general, the delay is 1-30 seconds, preferably 5-20 seconds, and can be optimized in each case with a few attempts.

The outer surface of the extruded tube between the ring slot nozzle and the frost line can be cooled with conventional external cooling rings or preferably with the aid of two superimposed annular blowing nozzles, which are separated from one another by an intermediate suction zone (suction ring), as explained in more detail below. The interior blowing air is expediently divided, for. B. with two annular slot nozzles, from which the inner surface of the hose can be acted on at approximately the same height as the outer surface of the blow nozzles for external cooling. This enables pneumatic support of the extrudate before reaching the frost line.

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Furthermore, it has proven to be advantageous if the total air flow of the internal cooling inside the dynamic bubble is passed through a condensation zone; As a result, oil-like Al separations on the inside of the hose and / or the system parts coming into contact with the outflowing total air flow can be avoided or significantly reduced. Such deposits usually consist of impurities that are contained in the polymer mass or are formed when they are heated.

The invention further relates to a device for performing the method explained above. This device has the features mentioned in claim 11. Preferred variants of the device are described below and have the features mentioned in claims 12-18.

The drawings serve to further explain the method and device according to the invention. Show it:

Fig. 1 is a schematic representation of a preferred embodiment of the device for a preferred method, and

Fig. 2 shows the semi-schematic broken representation of the blow head of a preferred device.

From the blow head 10 of the device 1 is viscous thermoplastic material with an elevated temperature of z. B. 160-250 ° C to form the blow hose 19, which solidifies between the ring slot nozzle 101 and the frost line F. The hose 19 is on its outer surface by an outside cooling air stream, for. B. from at least one cooling air ring 12, and from an internal cooling air flow, for. B. from the blowing end 131 of the internal cooling 13; the internal cooling air flow is drawn off at the suction end 132.

Inside the hose 19, a dynamic air volume 199, i. H. a dynamic bubble formed, which has a slight excess pressure of typically 5-10 mm water column from the atmosphere and from the hose 19 between the ring slot nozzle 101 and the pinch roller pair 11, z. B. of two oppositely driven and pressed against each other rollers 111, 112, is included. Before the inlet of the hose 19 into the pair of squeeze rollers, a conventional flat guide, e.g. B. from two pairs of rollers 113, 114 may be arranged.

The greater the flow rate of the internal cooling air flowing through the dynamic bubble, the greater the cooling rate of the inside of the hose and the greater the tendency of the hose to "periodic pumping" explained above.

In order to ensure reliable hose production with at most minimal fluctuations in the hose thickness even at high flow rates of the internal cooling air without the usual mechanical external calibration of the hose 19, the total air flow of the internal cooling that receives the bladder 199 is controlled by continuously using the device 18 and preferably before passing through the squeeze rollers 11, the hose width measured partially serves as an indirect or delayed control variable.

As indicated schematically in FIG. 1, the more or less flat hose 19 is scanned with the aid of a pair of sensors 181, 182. The term "width measurement of the hose" used here encompasses both the measurement of the width of the completely flattened hose and the width of the hose which has not yet or not completely flattened, ie its largest diameter in a cylindrical or oval state. You can use mechanical sensors or contactless ones Use scanning equipment and also place the measuring point closer to the frost line F than shown in Fig. 1.

The position values continuously sensed by the sensors 181, 182 are mostly converted into electrical quantities in the transducers 183, 184 and fed into a comparator 185. As a result, lateral displacements of the position of the hose are initially compensated for without any actual change in width or diameter, and the positive or negative deviation of the resulting actual value of the hose width from a preselected, ie. H. The setpoint that can be set on the comparator 185 is determined. The comparator generates a signal which indicates both the direction of the deviation ("positive" deviation if the actual width is too large or "negative" deviation if the hose width is too small) and the size of the deviation, eg. B. in the form of a varying and either positive or negative DC voltage.

This signal is, preferably after amplification z. B. with a known buckling amplifier, for actuating a drive, io z. B. an electric servo motor 149, which actuates the secondary air control 14.

The term “secondary air” or “secondary air flow” used here means the secondary air or secondary air flow branched off from a main or primary air flow, which by its nature is a “passive” or “induced” flow, i. H. is kinetically dependent on the primary air flow and can only work together with it.

In the method according to the invention, the dynamic air volume 199 is generated by a total air flow as it is blown or sucked through the 20 blow line 152 and the suction line of the interior air duct 15; the entire secondary air can in principle be guided through a single one and not as shown in FIG. 1 and, according to the invention, preferably through two secondary air lines 171, 172 with opposite flow directions (arrows 25 SL-1 or SL-2).

Accordingly, the secondary air stream SL-1 branched off from the primary air blowing line 154 and passing through line 171 is a blowing stream by which the total air flow entering the hose is reduced, while the stream SL-2 branched off from suction air line 151 and going through line 172 is a suction flow by which the suction flow entering the inlet 153 of the suction fan increases, i. H. the current emerging from the volume 199 through the line 151 is reduced.

The secondary air flow control 14 has the effect that either both 35 secondary air lines 171, 172 are closed or that only one of these lines is fully or partially open.

The flow rate of the secondary air, i.e. H. either SL-1 or SL-2, is limited according to the invention to a certain maximum value, namely to less than 1%, preferably less than 0.5% 40 of the flow rate of the primary air flow. In this case, the volume / time quantity is preferably used in each case, but in principle the mass / time quantity can also be used. The primary air flow rate is determined by the amount of air / time that is fed from the pressure blower 162 through the associated optional adjustment device 16b into the line 154, i.e. the air flow rate. H. before branching line 171 is blown. The maximum flow rate of the secondary air can be limited by the cross-section of the lines 171, 172 or by throttles (not shown) in these and, if necessary, controlled by conventional flowmeters. The effective flow rate of the secondary air is determined by the slide 141, which is preferably designed as a pendulum slide , d. H. is rotatably mounted in the housing 147 and is movable between a first end position and a second end position.

The slide 141 is connected to the servomotor 149, as shown schematically by the broken line in FIG. 55, and can be brought into one of the two end positions of the slide 141 or any intermediate position by the servomotor and held in one of these positions as long as by the signal of the comparator 185 conditional.

60 Both in the first and in the second end position, the slide 141 actuates or closes an electrical switch 145, 146 and thereby sets the associated time relay 140 or 143 in motion, which is preferably a conventional switching delay with a z. B. between 1 and 30 seconds adjustable duration of the delay is 65.

After the delay interval set and typically after 1-20 seconds, preferably after 1-10 seconds,

the respective switch 140, 143 sets the drive 161 of the setting

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direction 16a in progress, the z. B. is a conventional lifting spindle motor, and preferably via an intermediate conventional pulse generator 142 and 144. Such pulse generators generate electrical pulses with adjustable or fixed length of typically 0.5 to 2.5 seconds and adjustable or fixed intervals of typically 1-10 Seconds.

The blower 162 used to generate the primary air flow is driven by one end of the (not shown) axis of the motor 169, the other end of the axis actuates the blower 161. Both fans 162, 161 are preferably designed for practically the same delivery rate. The blower 162 is "blowing", i.e. switched in such a way that it draws air from the environment through its suction end 160 and blows into the primary air line 154 through an optional adjusting device 16b.

The blower 161 is "sucking", i.e. switched in such a way that it sucks in the air from the line 153 and blows it into the atmosphere through the adjusting device 16a coupled to the secondary air regulator 14 and an optional throttle 168.

For rough adjustment, the adjusting devices 16a, 16b and the throttle 168 can be operated by hand.

The device 1 works as follows: in the position of the slide 141 shown in FIG. 1, the primary air flow generated by the blower 162 is blown into the dynamic air volume through the blow line sections and cools the inner surface of the hose 19 which is continuously pressed out by the annular slot nozzle 101 and which is formed by the Pinch roller pair 11 continuously laid flat and pulled in the direction of arrow A, z. B. on a corresponding Wicklcr.

The internal air flow is drawn through the open suction end 132 of the suction line 151 via the connection 153 into the blower 161 and is blown into the atmosphere from there.

As soon as the actual width of the hose 19 measured by the device 18 deviates from a predetermined target value, e.g. B. typically depending on the hose width by 0.1 to 5 mm, the comparator 185 generates a signal corresponding to the deviation and actuates the slide 141 via the servo motor 140, which means that if the hose width exceeds the positive value of the hose, the end of the secondary air line 171 in the housing 147 more or less is opened and a corresponding secondary air flow SL-1 is now diverted past the slide 141 through the housing opening 148 into the atmosphere and a correspondingly lower air flow reaches the volume 199 through the line 152. This reduces the hose width, which, with a delay corresponding to the withdrawal speed of the hose 19 and the distance between the frost line and the width measuring point, produces a decreasing signal of the positive setpoint deviation at the comparator 185.

In the opposite case, d. H. with increasing signal of the negative setpoint deviation, the housing-side end of the secondary air line 172 is more or less exposed by the slide 141, so that a corresponding secondary air flow SL-2 from the atmosphere through the opening 148 of the housing 147 past the slide 141 through the line 172 into the passes through the port 153 from the suction fan 161 drawn internal air flow; this reduces the air flow flowing through the suction line 151, so that the undiminished blown air flow in the line 152 causes an increase in the hose width.

When the end of the secondary air line 171 or 172 lying in the housing 147 is completely open, the slide 141 is in one of its two end positions and then actuates either the switch 145 or the switch 146 and thereby sets the associated time relay 143 or 140 in motion. As soon as the delay time preset on the respective relay has expired, the associated pulse generator is started and actuates the motor 161 of the adjusting device 16a in such a way that it opens more strongly when the setpoint is exceeded, i.e. H. the volume of the air flow canceled by the blower 161 is increased, or more closed if the setpoint is undershot, and accordingly the volume of the air flow sucked off by the blower 161 is increased.

In any case, the division 16a is changed until the slide 141 leaves the respective end position and the power supply to the motor 161 is switched off by opening the associated limit switch.

2 shows a broken-off, semi-schematic representation of a preferred embodiment of the air duct for internal and external cooling and of the integrated condenser, which is preferably arranged in the interior of the hose.

The hose 29 emerging from the ring nozzle 201 is viscous until it reaches the frost line and is accordingly particularly sensitive. For a quick, effective and gentle cooling of the inner surface of the hose, the internal cooling air introduced through the blow line 252 is distributed to two superimposed nozzle rings or ring slot diaphragms 24, 23 which act on the inner surface of the hose in two corresponding different ring zones.

Preferably, the Ausschnkühlluft is distributed to at least two blowing or cooling rings 221, 222, each acting approximately on those areas of the hose which are simultaneously acted upon directly by the nozzle rings 24, 23.

In any case, it is advantageous to improve the cooling between adjacent, superimposed outer blow rings, e.g. B. the rings 221, 222, a suction zone, for. B. the suction ring 223, to be arranged or which is connected by a perforated wall 224 with a (not shown) suction fan.

The condenser 28 shown in FIG. 2 is preferably combined with the internal air supply and discharge lines to form an integral, approximately cylindrical element 27. The outer wall 271 is closed except for the nozzle rings 23, 24, so that the internal cooling air drawn off through the line 251 is introduced at the upper end of the element and between the inner surface of the wall 271 and the outer surface of the cylindrical coaxial condenser through a cylindrical gap with a relatively small width and can be performed relatively large length.

A preferably liquid coolant, such as tap water, is guided through the hollow jacket 281 via the lines 282, 283. The contaminants which separate out in relatively small amounts during operation of the condenser 28 are mostly oily and can be removed in the course of normal maintenance of the system. For this purpose, the upper part of the jacket 281 is preferably removably attached to the element 27.

Various variations are within the scope of the invention. For example, the setting 16b can be connected to a drive or can be omitted entirely. It is also possible to work with a single controlled secondary air flow. Further changes to the specially described process steps and device parts result from the expert knowledge.

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Claims (18)

658 425 1. Process for the production of blown tubular films by a) extruding thermoplastic material from an annular slot die of an extrusion press to form a tube b) expanding the extruded tube with the help of a dynamic air volume that is practically enclosed by the tube and cooling it on its inner surface, and c) air cooling the outer surface of the hose without mechanical calibration, where d) the dynamic air volume is generated from a total air flow which is determined by a primary air flow and the secondary air of at least one controlled secondary air flow, and e) the flow rate of the secondary air is changed if the continuously measured hose width is of a predetermined value Setpoint deviates, characterized in that one 0 keeps the maximum flow rate of the total secondary air less than 1% of the flow rate of the primary air flow, and g) couples the setting of the primary air flow with the control of the secondary air in order to adjust the setting of the primary air flow if the setpoint deviation of the hose width within a predetermined period of time by the control the secondary air is not eliminated. 2. The method according to claim 1, characterized in that the primary air flow is guided in an open circuit and is set at least at one end. 2nd PATENT CLAIMS 3. The method according to claim 1 or 2, characterized in that the hose width is measured continuously on the practically flattened hose in front of the pair of nip rollers. 4. The method according to any one of claims 1-3, characterized in that the maximum flow rate of the secondary air is less than 0.5%, e.g. is kept to a maximum of 0.25% of the flow rate of the primary air stream. 5. The method according to any one of claims 2-4, characterized in that the primary air flow is generated by a fan near its input and output end and that the two fans have practically the same power and are operated synchronously by a common drive. 6. The method according to any one of claims 1-5, characterized in that the primary air flow is adjustable at least at the exit end. 7. The method according to any one of claims 2-6, characterized in that the at least one variable secondary air flow is branched from the primary air flow between the end of its setting or the outlet thereof from the dynamic air volume. 8. The method according to any one of claims 1-7, characterized in that the outer surface of the extruded tube between the ring slot nozzle and the frost line is first passed through a first outer cooling air blowing zone, then through a suction zone and finally through a second outer cooling air blowing zone. 9. The method according to claim 8, characterized in that a first part of the total air flow of the internal cooling against the inner tube surface of the extruded tube in the area of the first outer cooling air blowing zone and a second part of the total air flow of the inner cooling air flow is guided against the inner tube surface in the area of the second outer cooling air blowing zone. 10. The method according to any one of claims 1-9, characterized in that the total air flow, which forms the dynamic air volume, is guided inside the hose through a cooled condensation zone. 11. Device for performing the method according to claim 1, with an annular slot nozzle (101) for pressing out a hose (19) made of thermoplastic material, a pair of squeeze rollers (11) removed from the annular slot nozzle (101), a device (12i for cooling the outer surface the hose, an internal air guide (15) for expanding the hose (19) and for cooling the inner surface of the hose between the ring slot nozzle (101) and the pinch roller pair (11), at least one device (16) for adjusting the flow rate of the primary air flow the inside air duct (15), at least one secondary air duct (17) branched off from the inside air duct (15), a device (18) for continuously measuring the hose width and for generating a signal of the setpoint deviation of the hose width, and a device (14) for control the secondary air duct with the signal of the setpoint deviation, characterized in that the device (16) for setting the Flow rate of the primary air flow is connected to a drive (161) for changing the setting and that the device (14) for controlling the secondary air flow is connected to a timer (140) in order to change the device (16) after a predetermined duration of the setpoint deviation Adjust the flow rate of the primary air flow until the setpoint deviations are compensated again by controlling the secondary air flow. 12. The device according to claim 11, characterized in that the inner air duct (15) has a suction line (151) and a blow line (152), that at the outflow end (153) of the suction line (151) a suction fan (161) and at the inflow end (154 ) of the blower line f 152) a pressure blower (162) is arranged, the suction blower (161) and the pressure blower (162) having approximately the same power values and being connected to a common motor (169) for synchronous actuation. 13. The apparatus of claim 11 or 12, characterized in that a first secondary air duct (171) from the suction line (151) and a second secondary air duct (172) is branched off from the blower line (152), both secondary air ducts (171, 172) in of the control device (14), which is preferably designed as a pendulum slide valve (141), which is connected to a drive (149), which in turn is connected to the signal transmitter (185) of the device (18). 14. The apparatus according to claim 13, characterized in that the control device (14j has two Endstellimgsschaiter (145, 146) and two timers (140, 143) and two pulse generators (142, 144), each pulse generator with the drive (169) Adjusting device (16) is connected to actuate it when the slide (141) remains in an end position for a predetermined period of time. 15. The device according to any one of claims 11-14, characterized in that the blow line (252) of the inner air duct (25) guided through the blow head (21) opens into two superimposed nozzle rings (24, 23) which between the blow hose (29) the ring slot nozzle (201) and the frost line (F). 16. Device according to one of claims 11-15, characterized in that the device (22) for external cooling of the blow hose (29) has two superimposed blow rings (221, 222) and a suction ring (223) located between them. 17. The device according to claims 15 and 16, characterized in that the nozzle rings (24, 23) for internal cooling are approximately at the same height as the blowing rings (221, 222) for external cooling. 18. Device according to one of claims 11-17, characterized in that the blow head (21) carries a condenser (28) which has at least one approximately hollow cylindrical cooling jacket (281) which is connected to coolant lines (282, 283).