JPH04270632A - Method and device for manufacturing bubble film - Google Patents

Abstract

PURPOSE: To achieve easy control of all devices such that a partial cooling air flow is branched off by adjustable guide blades at the upstream of the die gap of a cooling ring. CONSTITUTION: There is provided a process for producing a film bubble in a film-blowing machine wherein a cooling ring 116 surrounds a film bubble 110 and has an annular die gap for cooling air, in which the cooling air throughput in the individual circumferential areas of the cooling ring 116 is controlled to correct the thickness profile of the film bubble, wherein a portion (B) of the cooling air is branched off at the positions distributed in the circumferential direction of the cooling ring for controlling the cooling air flow at the film bubble 110 by guides or guide blades 128, 144, 156, 228 capable of adjusting the amount of the branched cooling air.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for producing bubble film.

0002

BACKGROUND OF THE INVENTION Conventional bubble film manufacturing methods result in relatively large film thickness differences, which can reach up to 20% depending on the film thickness and quality of the manufacturing equipment. This thickness difference has a variety of causes, such as melt inhomogeneities, temperature differences within the melt and the tool, and mechanical and adjustment errors in the tool and cooling system. It is known to control the film thickness by varying the flow rate of the melt within the tool by the desired heating or cooling of the tool in a given circumferential area. However, such equipment and tools are very expensive, and adjusting devices for film thickness correction that operate in this manner are relatively slow to operate. This is because large delay times occur during heating and cooling of the tool area.

A method of the type mentioned at the outset, in which the thickness of the film is influenced by controlling the cooling air flow, is known from German Patent No. 3,627,129. In this method, the high temperature range of the film bubble in the cooling zone between the nozzle and the frost boundary is stretched more than the low temperature range due to the low viscosity of the melt, so that
The fact that the thickness of the film increases with stronger cooling and decreases with weaker cooling is exploited. To control the cooling air flow; a large number of pins are distributed around the circumference of the cooling ring near the air outlet, and the flow resistance in each circumferential area of the cooling ring acts as a disturbance of the cooling air flow. This can be changed by pulling out more or less of the working pin. The effect of such disturbances on the cooling air flow is due to the state of development of tube film cooling devices and the influence of tolerances on film quality in "plastics" (Schlauchfolien).
kuehlung-Entwicklungstan
d und Auswirkung von
Fehlern auf die Folien
Qualitaet in ``Kunststof
fe″) 1979, Volume 69, No. 4, 208-214
It is written on the page.

[0004] When the cooling air flows around the disturbance bodies, swirls of the cooling air occur behind these disturbance bodies and irresistible local fluctuations of the cooling air flow occur in the exit gap, so that a uniform film is not produced. Thickness is really difficult to obtain.

Another problem consists in that an increase in the flow resistance due to a disturbance body at one location in the circumference causes an increase in the dynamic pressure upstream of the disturbance body, so that the air flow rate in the adjacent circumference region increases. There is therefore a complex system of interactions between the cooling air flow rates in the various circumferential ranges, which system is hardly controllable. Because of this problem, it is difficult to control the disturbance body with the measured film thickness in different circumferential ranges such that the film thickness cross-section is adjusted in a closed-loop adjustment circuit.

Federal Republic of Germany Patent Application No. 3623
No. 548 discloses a method in which cooling air is supplied via two annular outflow gaps. Since both outflow gaps are provided with separate cooling air supplies, the air flow through both outflow gaps can be controlled independently of each other. However, the equipment proposed to implement this method
A substantially uniform flow cross section is obtained in the circumferential direction of the outflow gap.

[0007]

The problem on which the invention is based is that an independent, minute and rapid change in the cooling effect is possible in the individual circumferential areas of the film bubble and that the cooling effect is extreme. The objective is to control the cooling air flow so that significant local fluctuations are avoided.

[0008]

[Means for Solving the Problems] According to the first method of the present invention, this problem is solved by branching off a portion of the cooling air to positions distributed in the circumferential direction of the cooling ring and distributing the cooling air in film bubbles. The solution is that the flow is controlled in such a way that the amount of branched cooling air is varied by means of adjustable guide bodies or guide vanes. Furthermore, according to the second method of the present invention, this problem can be solved by narrowing or widening the width of the outflow gap for each section, thereby changing the flow velocity of the cooling air flowing out and increasing the width of the outflow gap. Changes in the flow resistance due to changes in width are compensated, at least in part, by the cooling air flow in these parts being throttled upstream of the outflow gap in relation to the gap width.

According to the basic idea of the invention, at least one cooling ring is provided which is divided into individual circumferential parts, the cooling air flow in these individual parts being controlled or regulated independently of one another. In these proposed solutions, complementary measures ensure that the cooling air flows in the individual sections do not influence each other and that no abrupt changes in the cooling effect occur around the cooling ring.

[0010] In the solution according to claims 1, 3 and 6, a part of the cooling air flow is branched off at positions distributed in the circumferential direction of the cooling ring, which are in the outlet gap or upstream of the outlet gap. The amount of cooling air applied is controlled by adjustable guide vanes or guide bodies.

[0011]

By branching off a portion of the cooling air, the flow rate in the outlet gap can be properly controlled, and a greater dynamic pressure is generated before the branching point and the cooling air is diverted to the adjacent surrounding area. Therefore, by changing the position of the guide vanes in one circumferential region, the flow rate in the other circumferential regions is not influenced. Moreover, the branching of the cooling air increases the flow velocity as it flows around the guide vanes and prevents strong vortex formation behind the guide vanes. By adjusting the guide vanes, a simple and precise control of the circumferential distribution of the cooling air flow rate and the thickness profile of the film bubble is possible.

0012

In a preferred embodiment of the device, the upper wall of the cooling ring is surrounded by a ring of branched cooling air outlet openings, each outlet opening being associated with a guide vane. The guide vanes project into the interior of the cooling ring from above and divert a portion of the cooling air to the outlet opening. The position of the guide vanes can be adjusted vertically so that the amount of diverted cooling air can be varied.

[0013] In this embodiment, the cooling ring can be divided into individual parts by means of radial partitions, such that the cooling air flows are separated from each other up to the outlet gap or to a position immediately in front of the outlet gap. In this way, the flow differences between the individual sections behind the guide vanes are prevented from canceling out again, and
Since the outlet opening and the guide vanes can then be arranged relatively far outside the cooling ring, more space is available for the operating mechanism.

In a further embodiment, the guide vanes are formed by circumferentially continuous tongues made of flexible material, the angle of attack of which can be adjusted in the individual circumferential regions by push rods or the like. With this design, a structural simplicity is achieved and the cross-section of the tongue can be streamlined so that swirls of the cooling air downstream of the tongue are avoided. Furthermore, this design avoids discontinuous transitions in the circumferential distribution of the cooling air flow.

The adjustment of the guide vanes or push rods can be carried out manually, for example by adjusting screws, or by means of suitable drives, for example electromagnetic, pneumatic or piezoelectric actuating elements. In the latter case, it is possible to adjust the cooling air flow in the individual circumferential regions by means of the film thickness measured at various points around the film bubble. Since changes in the setting of the guide vanes made within the framework of the adjustment act only in the relevant circumferential range and do not have a significant reaction on the other circumferential ranges, the operating amount of the adjusting device, i.e. the position of the guide vanes, , are sufficiently separated, so that vibrational tendencies of the regulating device are avoided and a stable regulation is achieved.

In order to further reduce the mutual influence of the cooling air flows, the flow resistance of the air flow branched off through the outflow openings is controlled to match the flow resistance of the outflow gap of the cooling ring at each position of the guide vane. It is preferable to do so. thus,
The flow and pressure conditions in the distribution chamber at the outer periphery of the cooling ring can be virtually unaffected by the adjusting movement of the guide vanes. Matching the flow resistance can be achieved using an electromagnetically controlled throttle valve or the like. However, as an alternative, it is also possible to connect the guide vane mechanically with a throttle, which narrows the associated outflow opening depending on the position of the guide vane.

The cooling action in the individual parts of the cooling ring is
It can also be varied by controlling the flow rate of the cooling air by narrowing or widening the outflow gap. If the flow rate remains the same, increasing the flow rate will increase the cooling effect. This principle is claimed in claim 8.
It is the basis of the objects of 9 and 9. A nearly constant flow rate is
The change in flow resistance caused by the change in gap width is
This is achieved by compensating for a greater or lesser restriction of the flow upstream of the outflow gap. This solution has the advantage that the total cooling air flow in each peripheral section is constant. In this way, a local reduction in the post-cooling of the film bubble above the solidification limit is prevented, and it is ensured that the film temperature during flattening and winding of the film decreases everywhere so that the film layers no longer adhere to each other. Ru. A uniformly high aftercooling effect makes it possible to reduce the length of the aftercooling section and/or to increase film extrusion.

[0018] If, in one of the solutions described above, an outflow gap is used which is divided into individual parts by partitions, the disturbances in the cooling air flow caused by these partitions affect the cooling capacity differently. . As has been found experimentally, in the closely spaced outflow gaps of the film bubble, the vortices caused by the partition walls intensify the cooling effect and thus also thicken the film. On the other hand, if the outflow gap is further away from the film bubble, the influence of different flow velocities of the outflow laminar flow becomes greater. In a case where the width of the outflow gap is uniform, a square velocity distribution cross section occurs in the circumferential direction, so the velocity is smaller near the partition wall than at the center of each part. In this case, therefore, the cooling effect is reduced in the area of the partition walls and the film becomes thinner. Various measures for avoiding these disturbance effects are proposed in claims 10 to 15.

Advantageous developments of the invention are specified in the dependent claims.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 8.

According to FIG. 1, a tubular film bubble 11
0 is extruded from the annular gap 112 of the extrusion tool 114. This extrusion tool 114 is surrounded by a cooling ring 116 through which it passes through an annular outflow gap 118.
Cooling air is supplied around the film bubble 110 through the air.

The cooling ring 116 has an annular chamber 120 defined by a lower wall 122 and an upper wall 124. In the outer peripheral region of the cooling ring, which is not shown in FIG. 1, an annular chamber 120 is connected via a retention stage with an annular distribution chamber, which is connected to a blower. Since the cooling air supplied by the blower is distributed within the distribution chamber, as shown by arrow A in Figure 1,
Via the residence stage, cooling air flows into the annular chamber 120, which is substantially uniform over the entire circumference.

The upper wall 124 of the cooling ring 116 has an outflow gap 1
Outflow openings 1 closely adjacent to each other on the radially outer side of 18
It has 26 rings. A guide vane 1 at each outflow opening 126
28, the shank 130 of which guide vane extends through a guide opening 132 in the upper wall 124 of the cooling ring and has a guide profile 134 at its lower end. There is a streamlined transition to the enlarged lower end of the outlet opening 126. The shank 130 of the guide vane is preloaded upwardly by a spring 136 and is acted upon by a lever 138 of the actuating mechanism, which lever is inserted into the housing 140 radially outside the outlet opening 126 and onto the cooling ring. It is located.

The guide vane 128 is designed in such a way that it closes the outlet opening 126 in its upper end position, so that the cooling air can flow unhindered into the outlet gap 118 . When the guide vane 128 is pushed downstream by the lever 138 , the guide contour 134 of the guide vane causes a portion of the cooling air to be diverted into the outlet opening 126 .
A partial airflow B is branched off from the main cooling airflow A. Therefore, only the remaining partial airflow C of the cooling air flows through the outflow gap 1.
18, the cooling air flow rate decreases in the outflow gap.

The circumferentially arranged outlet opening 126 and the guide vanes 128 are separated from each other by a partition wall 142 arranged in the annular chamber 120 in the radial direction. In cases where two adjacent guide vanes are adjusted to different positions, the cooling air flow rates downstream of the guide vanes are different from each other, so the bulkhead 142 prevents premature merging of the partial air flows C and flow balancing. . Thus, even though the guide vanes 128 and the outflow openings 126 are arranged relatively far apart in the radial direction of the outflow gap, the outflow gap 11 has a high angular resolution.
Control of the circumferential distribution of the cooling air flow rate at 8 is made possible. The arrangement of the guide vanes relatively far to the outside provides more room in the housing 140 for the attached operating mechanism and reduces disturbances in the cooling air flow that may be caused by the guide vanes. The advantage is that sufficient damping can be achieved before the outflow gap 118. Because the bulkheads 142 are relatively thin and constructed with edge-shaped inner and outer edges, they minimize disturbances to the cooling airflow.

In a modified embodiment, bulkhead 142
are designed as ribs protruding from the upper wall 124, and these ribs protrude into the interior of the annular chamber 120 only up to the maximum immersion depth of the guide vanes, so that the cooling ring is divided only into the upper region. Not yet. In this way, a high angular resolution is obtained in the control of the cooling air flow rate, but the continuous cooling air flow in the lower region of the annular chamber 120 achieves a certain degree of constancy of the surrounding cloth of the cooling air flow, so that it is completely Disturbance effects in the different categories are avoided.

Since the guide vanes 128 occupy the entire intermediate space between adjacent partition walls 142, flow around the guide vanes is prevented and swirls with vertical spiral axes behind the guide vanes are prevented from forming. Avoided. Guide vane 1
The downstream lower end of 28 is designed in the illustrated embodiment as a separating edge at which the cooling air flow separates.

In cases where the film bubble 110 has too large a thickness in the circumferential area lying in the cut plane in FIG. The air flow B is enlarged and the flow rate in the outflow gap is reduced. As a result, the cooling effect in the circumferential region is reduced, so that the film material can flow longer and becomes thinner when the film bubble expands. Since the excess cooling air is removed through the outlet opening 126, this cooling air does not lead to an increase in the flow rate in the adjacent circumferential area. The flow cross-section of the outflow opening 126 is chosen such that the total flow resistance determined by the cross-section of the outflow gap 118, the position of the guide vane 128 and the cross-section of the outflow opening 126 changes as little as possible upon a change in the setting of the guide vane 128. It is. The pressure in the outer region of the annular chamber 120 downstream of the partition wall 142 and in the previously connected distribution chamber is therefore practically unaffected by a change in the setting of the guide vanes.

Optionally, each of the outlet openings 126 can be provided with a throttle valve which is controlled in dependence on the position of the guide vane 128, with which the flow resistance is adjusted to a higher precision with a greater total flow resistance. so that it remains constant,
It is aligned with the position of the guide vane. In this case, the guide vane 12
It is possible to measure the flow velocity in front of 8 by a heated thermistor and adjust the throttle valve in relation to the measured flow velocity so as to obtain the desired flow resistance at each position of the guide vane. .

FIG. 2 is a partial sectional view of the upper wall 124 of the cooling ring in the area provided with the outlet opening 126 according to a modified embodiment of the invention. In this embodiment, instead of individual guide vanes, a circumferentially continuous annular tongue 144 made of flexible material is provided. This tongue 144 is attached to the inner surface of the upper wall 124 of the cooling ring and forms a guiding contour 146 into which the edge of the outlet opening 126 on the side of the outlet gap 118 continues. . The lower surface of the tongue 144 is streamlined downstream of the outlet opening 126, so that the flow of cooling air into the outlet gap is unobstructed. The blade-shaped upstream end of the tongue 144 is acted upon by a push rod 148, which is connected to a lever 138 of the operating mechanism. The tongue 144 is preloaded towards the closed position due to its inherent elasticity and is pressed against the push rod 1 in order to divert a portion of the cooling air flow to the outlet opening 126.
48 allows for elastic deflection.

In this embodiment, in addition to the outflow opening 126,
Since only one small hole for the push rod 148 in the upper wall 124 of the cooling ring is needed, excessive weakening of the wall is avoided and these outlet openings can be arranged closely adjacent to each other. For example, the outflow openings 126 are separated from each other only by thin connecting pieces, so that they act more or less like a continuous annular gap. Elastic tongue piece 1
44 is circumferentially streamlined to accommodate various positions of the push rod 148, thereby avoiding abrupt changes in the cooling air flow around the film bubble. Optionally, the continuous flexible tongue can have a cross section similar to that of the guide vane 128 according to FIG. Rather, it is guided in a groove in the wall 124 in a height-adjustable manner. In this case, the wall 124 of the cooling ring only has a small recess in the area of the groove for a push rod for operating the tongue.

FIG. 3 shows a modification of the embodiment according to FIG. In the modified embodiment according to FIG. 3, the guide vanes 128 have an approximately parabolic guide contour 134. The shape of the guide contour 134 is selected in such a way that a constriction point is formed between the guide contour and the edge of the outflow opening 126 opposite to this guide contour, the width b of this constriction point being such that the total flow resistance is It is related to the immersion depth x of the guide vane 128 so that it is not related to the immersion depth of the guide vane. Guide contour 1
The shape of 34 can be determined experimentally, but can also be approximately derived theoretically, as outlined below. In this case, the following symbols are used: x: Recessed depth of the guide vane d(x): Width of the constriction point H: Inner height of the annular chamber 120 between the inner surfaces of the walls 122 and 124 P: Annular chamber 120 upstream of the guide vane 128
pressure in the annular chamber 120 immediately downstream of the guide vane P': pressure Q1 in the annular chamber 120 immediately downstream of the guide vane; flow rate Q2 through the constriction point and outlet opening 126;
: Flow rate Q through the outflow gap 118 : Total flow rate R : Flow resistance in the part of the annular chamber behind the guide vane and the outflow gap 118

When gas flows through a narrow gap or conduit, an approximately parabolic velocity distribution occurs. The velocity is greatest at the center of the gap and drops to zero at the interface at the edge of the gap. The flow rate is obtained by integrating the velocity distribution over the gap width. Therefore, the flow rate is proportional to the pressure difference and the cube of the gap width. Therefore, the following relationship applies. Q1(x)=a1P・d(x)3
(1)
Q2(x)=a2(P-P')(
H-x)3 (2)
Q2(x)=P'(x)/R
(3)

00
[35] In these equations, a1, a2 and R are systematic constants. Equation (3) allows P' to be expressed as equation (2
), the expression for Q2 is obtained as a function of x.

It is necessary that the total flow resistance Q be independent of the immersion depth x of the guide vanes for a constant pressure P. Therefore, Q1(x)+Q2(x)=Q
(
4)

[0037] Equations (1) to (3) can be transformed into equation (
4) and solve by d, the function d(x) is generated,
This function satisfies the desired conditions. The guide contour 134 is formed by the method explained below with reference to FIG.

Various points P1, P2, and P3 are drawn on a straight line extending through points P0 and P4 in FIG. A circle with radius d(xi) is drawn around each of the points Pi (i=1, 2, 3, 4), and in this case, xi is the distance between the points Pi and P0. The arc envelope thus obtained is the desired guide contour 134.

FIG. 4 shows a modified construction of the upper wall 124 of the cooling ring. This structure has an outflow opening 1
26 into one continuous annular gap, the circumferential distribution of the cooling air flow is limited to the individual outlet openings 1
26. The upper wall 124 of the cooling ring is formed, according to FIG. 4, by an outer ring 124a and an inner ring 124b with a stepped cross section. inner ring 12
4b is bolted at its outer periphery to the outer ring 124a and is held at a distance from the outer ring 124a by a spacing piece 150, so that air flowing out of the annular outflow opening 126 can exit unhindered. Guide vane 128
is guided along the steps of the inner ring 124b.

The inner edge of inner ring 124b delimits outflow gap 118 and is only held to the outer periphery by spacing piece 150 and pin 152. The annular structure and optionally the stepped cross section reinforced by the ribs 154 make it possible to hold the inner edge of the inner ring 124b stably and without vibration.

[0041] In this embodiment, the guide vane 128 is
Preferably, it is formed as a continuous annular section made of elastic material.

According to FIG. 5, the guide vane 228 is swingably held in the outflow opening 126 by a link mechanism 230. As shown in FIG. The pivot axis 232 is formed by the rear edge of the guide vane 228 when viewed in the flow direction. Optionally, the guide vanes can be hinged to the upper wall 124 of the cooling ring. As was found through experiments, in this embodiment the guide vanes have a circular or arcuate guide contour 2, as shown in FIG.
34, the pressure downstream of the guide vane can be kept sufficiently constant.

In a further embodiment, not shown, the guide vanes can be constructed as guide bodies arranged in the annular chamber of the cooling ring, which guide bodies are rotatable about a vertical axis and are arranged in the annular chamber of the cooling ring. Like a plug, it has two passages extending at right angles to each other, one of which leads to the outflow gap and the other to the outflow opening 126. Depending on the angular position of the guide body, a larger or smaller amount of air can be drawn off through the outlet opening.

In the embodiments described above, the guide vanes 128 or 1
44 or 228 are arranged in the annular chamber 120 upstream of the outflow gap 118; on the other hand, guide vanes can also be provided directly in the outflow gap 118, as shown in FIGS. 6 to 8.

According to FIG. 6, a radially adjustable guide vane 156 of approximately wedge-shaped cross section is mounted on a streamlined retaining arm 158 such that its tip projects into the outflow gap 118. It is being FIG. 7 is a plan view of a single guide vane 156 adapted to the curvature of the outflow gap.

The deflection angle of the wedge-shaped guide vanes 156 is selected such that the portion of the cooling air flow branched off by the guide vanes is deflected to such an extent that it no longer exerts a cooling effect on the film bubble 110. If the deflection angle is small, no separation of the two partial air streams takes place, but only a radial expansion. In this case too, there is an influence on the cooling effect. This is because the radial expansion reduces the total flow velocity.

Unlike the structure shown in FIG. 6 in which the radial position of the guide vane 156 can be changed, the turning angle of the guide vane can also be changed. Instead of a wedge-shaped cross-section, the guide vanes can also have a streamlined cross-section. Furthermore, in the embodiment according to FIG. 6, it is also possible to use a continuous flexible ring instead of the individual fan-shaped guide vanes 156 with a suitable guide cross-section, so that the distance between the individual guide vane sections is Unavoidable airflow disturbances in the intermediate space are avoided. Holding arm 158
Since the radial adjustment strokes of are only approximately 2 to 3 mm, the guide vane ring can easily adapt to these adjustment movements by elastic expansion. In order to avoid an irresistible outward curvature of the ring when the radius is reduced, it is preferred that the guide vane ring is always kept under some tensile stress in the circumferential direction.

FIG. 8 shows that the guide vane 156 is connected to the outflow gap 118.
Figure 2 shows a modified embodiment, placed above the . By varying the height of the guide vanes above the outflow gap, the sensitivity of the device can be adjusted.

If the guide vanes 156 are arranged in the outflow gap according to FIG. 6 or 8, reactions to the air flow in the adjacent circumferential region of the cooling ring are largely avoided. A change in the position of the guide vanes leads to a change in the flow resistance, but if the angle of attack of the guide vanes is small enough, e.g. less than 20°, the flow resistance is small overall;
It was found that no significant reaction occurred.

FIG. 9 shows a cooling ring 316 in which a slightly modified solution principle is implemented. The width of the outflow gap 318 surrounding the film bubble 310 can be varied in this embodiment by means of a slide 320. Sliding body 3
20 is movably held between partitions 322 which divide the outflow gap into individual sections. The end face 324 of the slide defines the width of the outflow gap 318, while the lower surface 326 of the slide defines the cross section of the cooling air passage just upstream of the outflow gap.

The slide 320 is preloaded to narrow the outflow gap by means of a push rod 328 and is guided in a non-linear movement by means of a control surface 330, which is simply indicated symbolically. In order to reduce the cooling effect in this part, the sliding body 320 is moved downward and to the left along the control curved surface 330, so that the width of the outflow gap is expanded, while the cooling air passage is slightly narrowed by the surface 326. narrowed. This control surface 330 is chosen in such a way that the total flow resistance, and therefore also the cooling air flow rate, does not change practically during the movement of the slide 320. A reduction in the cooling effect is achieved because the cooling air leaves the wider outlet gap 318 at a lower velocity. Conversely, movement of the slide 320 in the opposite direction can narrow the outflow gap and thereby increase the relative velocity of the cooling air to the film bubble.

In the embodiment shown in FIG. 9, the narrowing and widening of the outflow gap 318 and the throttling of the cooling air flow in the cooling air passages are accomplished by only one component, namely the slide 320. I can do it. However, these functions can also be performed by two separate components, the drive being mechanically or electronically coupled to each other. In this case, the components used for restricting the flow in the cooling air channel can be arranged further upstream and thus closer to the outer periphery of the cooling ring.

FIG. 10 is a plan view of the outflow gap 318 of a cooling ring constructed on the same principle. In this embodiment, the end face 324 of the sliding body 320 is formed in a corrugated manner, so that the outflow gap 318 is narrowed in the center between the partition walls 322. Since the cooling air flow is braked at the surfaces of these partitions 322, the velocity distribution of the cooling air has a maximum at the center between the partitions, where a greater cooling effect occurs at uniform gap widths. The cross-section of the end face 324 reduces the cooling air flow in these areas, while creating a greater flow near the bulkhead. This compensates for large flow and velocity differences and allows the bulkhead 32
Only locally limited disturbances remain in the immediate vicinity of 2. However, these disturbances are quickly compensated for by the air flow immediately above the exit gap, so that a uniform flow rate and velocity distribution and therefore also a uniform cooling effect occur where the air flow acts on the film bubble.

The slide 320 has a certain amount of play between the partition walls 322, so that a radial adjustment movement is possible.

FIGS. 11 to 13 show a solution which serves approximately the same purpose as the device according to FIG. In all cases, the outlet gap 318 of the cooling ring is divided into sections by radial partitions 322, so that the cooling air flow around the film bubble can be controlled section by section by a control device, which is not shown.

According to FIG. 11, the inner edge of the outflow gap is provided with a disturbance edge 332 that causes turbulence. Due to the action of this disturbance edge, turbulent flow is generated around the entire circumference of the outflow gap, and these turbulent flows cover the turbulent flow that inevitably occurs at the partition wall 322, so that a uniform cooling effect can be obtained and the partition wall The influence of external disturbances is suppressed. The turbulence caused by the disturbance edge 323 also leads to better air exchange at the surface of the film bubble, so that the overall cooling capacity is increased.

In FIG. 11, the disturbance edge 232
14, which defines the outflow gap. However, if an existing device is to be equipped with a cooling ring according to the present invention, a disturbance edge can also be formed in the portion of the cooling ring 316 that forms the inner edge of the outflow gap.

The embodiments shown in FIGS. 12 and 13 are based on the principle already explained in connection with FIG. In FIG. 12, the lower surface of the upper wall 324 of the cooling ring 316 is formed in a corrugated manner, while in FIG.
The outer peripheral edge of 8 has a corrugated cross section.

The velocity of the cooling air in the portions of the outflow gap 318 delimited from each other by the bulkheads 322 is determined by the fact that the radial communication pieces 334 are arranged between the bulkheads 322, as shown in broken lines in FIG. It is also simplified. These connections cause a reduction in the flow velocity within each part of the outflow gap, so that a uniform velocity distribution in the circumferential direction occurs. The small disturbances caused by these connections and partitions are already compensated immediately above the outflow gap.

[Brief explanation of the drawing]

1 is a partial sectional view along the radius of a cooling ring of a film blowing device; FIG.

FIG. 2 is a partial cross-sectional view of a cooling air outlet device attached to a cooling ring.

FIG. 3 is a sectional view of a deriving device according to another embodiment of the invention.

FIG. 4 is a sectional view of a deriving device according to yet another embodiment of the present invention.

FIG. 5 is a sectional view of a deriving device according to yet another embodiment of the present invention.

FIG. 6 is a sectional view of the cooling ring with the outlet device arranged in the outflow gap;

7 is a plan view of a guide vane of the extraction device according to FIG. 6; FIG.

FIG. 8 shows a sectional view of a further embodiment of the outlet device arranged in the outflow gap;

FIG. 9 is a sectional view of a cooling ring with a device for varying the flow velocity in the outflow gap;

FIG. 10 is a plan view of two sectioned parts of the outflow gap;

FIG. 11 is a cross-sectional view of an outflow gap according to another embodiment.

FIG. 12 is a vertical cross-sectional view of the cooling ring immediately upstream of the outflow gap.

FIG. 13 is a horizontal cross-sectional view of an outflow gap according to another embodiment;

[Explanation of symbols]

Claims (15)

[Claims] 1. A cooling ring (11) surrounding a film bubble (110) and having an annular outflow gap (118) for cooling air.
6), in the method of manufacturing a bubble film by means of a film blowing device in which the flow rate of cooling air in each circumferential area of the cooling ring (116) is controlled in order to modify the thickness section of the film bubble, A part of the cooling air (B) is branched to positions distributed in the film bubble (110), and the cooling air flow at the film bubble (110) is controlled by a guide body or guide vane (128; 144) in which the amount of branched cooling air can be adjusted. ;
156; 228). 2. The flow resistance of the branched cooling air (B) is related to the position of the guide vanes (128; 144; 228) such that the total flow resistance is constant regardless of the position of the guide vanes. Method according to claim 1, characterized in that the method is controlled. Claim 3: The cooling ring (116) is connected to the outflow gap (118).
) with a ring of outflow openings (126) on the radially outer side of the guide bodies or guide vanes (128; 144;
228) are arranged inside the cooling ring (116) in the direction of the cooling air flow (A) so as to divert a portion (B) of the cooling air flow to the outlet opening (126). An apparatus for carrying out the method according to claim 1 or 2. 4. Each outflow opening (126) is associated with an individual guide vane (128), which guide vane is located in the opening (32) of the wall (124) of the cooling ring provided with the outflow opening. Claim 3 characterized in that it is movably guided.
The device described in. 5. The guide vanes (228) are constructed as rocking plates, and these rocking plates extend along the surface of the wall of the cooling ring with the rear end (232) as seen in the flow direction centered on the guide vanes (228). 4. Device according to claim 3, characterized in that it is swingable from the cooling ring into the interior of the cooling ring and has a guide contour (234) of semi-circular cross-section on the side closer to the outlet opening (126). 6. An outflow gap (1) viewed in the direction of the cooling air flow.
Device for carrying out the method according to claim 1, characterized in that the radial position and/or angle of attack of the guide vanes (156) arranged at or downstream of this outflow gap are controllable. . 7. The guide vane is formed by a ring (144) made of a flexible material surrounding the cooling ring (116) in the circumferential direction, and the position and/or angle of attack of this ring is distributed in the circumferential direction. Device according to claim 3 or 6, characterized in that it is adjustable by means of a push rod (148) or a holding arm (158). 8. A cooling ring (31) surrounding the film bubble (310) and having an annular outflow gap (318) for cooling air.
6), in which the flow of cooling air in the respective circumferential areas of the cooling ring (316) is controlled for the modification of the thickness section of the film bubble; ) by narrowing or widening the width of each section, the flow velocity of the outflowing cooling air can be changed, and the change in flow resistance due to the change in the gap width will cause the cooling air flow in these parts to change. A method for producing a film bubble, characterized in that it is at least partially compensated by constriction in relation to the gap width upstream of the outflow gap. 9. The outer edge of the outflow gap (318) is delimited by radially adjustable slides (320) and each slide is arranged upstream of the outflow gap viewed in the direction of the cooling air flow. A throttling device (326) is attached, and this throttling device is connected to and driven by the sliding body, and is operated so as to strengthen the throttling of the cooling air flow when the sliding body is moved in the direction of increasing the gap width. Claim 8, characterized in that
Apparatus for carrying out the method described in . 10. The outflow gap (318) is divided into individual parts by radial partitions (322), and the surface (324) of the sliding body delimiting the outflow gap is arranged so that the outflow gap (318) 10. Device according to claim 9, characterized in that the segmented part of the gap is curved forward so that it has a smaller width in the center than in the vicinity of the septum. 11. Claim 3 or 9, characterized in that the outflow gap is divided into individual parts by radial partitions and is provided with means for homogenizing the cooling air flow.
The device described in. Claim 12: An annular outflow gap (318
), the outflow gap is divided into individual parts by radial partitions (322) and the cooling air flow is uniform. An apparatus for producing a bubble film, characterized in that it is equipped with a means for producing a bubble film. 13. Device according to claim 11, characterized in that the means for homogenizing the cooling air flow are formed by a disturbance edge at the inner edge of the outflow gap which causes turbulence. . 14. Means for homogenization of the cooling air flow are formed by a corrugated contour of at least one surface delimiting an outflow gap or a cooling air passage immediately upstream of the outflow gap, whereby the outflow gap and/or each 13. Device according to claim 11 or 12, characterized in that the width of the cooling air passage is narrower in the center between the partitions than in the vicinity of the partitions. 15. Device according to claim 11, characterized in that each part of the outflow gap is divided into smaller parts by a radial connecting piece (334).