CH684887A5 - Process and apparatus for the production of thin-walled tubes - Google Patents

Abstract

What is proposed is a process for the production of hollow fibres or capillary tubes from liquefiable masses, which is characterised in that, - to form a tubular strand (as a precursor of a hollow fibre obtained during the production operation) in a spinneret-like device, a first mass enters a first annular channel through part orifices of the latter from a collecting space and flows through the said channel, and in that, during exit from this channel, a second mass is fed to the resulting tubular strand inside the tubular strand from a second channel surrounded by the first channel, - in that, to form the hollow fibre, the tubular strand exiting from the first channel is drawn off, a limited radial drafting being achieved as a result of the introduction of the second mass and an axial drafting being achieved as a result of the draw-off, at the same time with a narrowing of the dimension of the tubular strand to form the finished hollow fibre, and - in that, as a result of the drafting operations, the narrowing in wall thickness is less than double the narrowing in diameter. For carrying out the process, an apparatus is described and is illustrated by means of various embodiments. It is characterised in that the collecting spaces 1' and 1'' for the two spinning masses M1 and M2 are formed and limited by bottom and wall parts 3 and 2 of the apparatus, and in that arranged in the region of the bottom is at least one centre of channel systems which consists of an annular channel 5, worked at least partially into the bottom material, for the feed of the first mass M1 and of a second channel 8, running through the centre of the first channel 5, for the feed of the second mass M2. Figure 1 shows a special embodiment in this respect. Here, the annular channel 5 passes only over part of its circumference through the bottom 3, but otherwise terminates blind in the wall and bottom material. The first mass M1 passes through part orifices 4 into the annular channel 5 surrounding the second channel 8, through which the second mass M2 can flow. <IMAGE>

Description

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description

The present invention relates to methods and devices for the spinning manufacture of thin-walled tubes, which also include capillaries and hollow fibers. The choice of terms depends on the cross-sectional size. So tubes are called capillaries if they are in the range of more than 1 mm cross-sectional dimension, in the range of less than 1 mm, the term hollow fibers is usually used. In the following, the term "tube" is intended to cover all areas up to several centimeters in cross-sectional extent.

The production of such thin-walled tubes according to previously known methods encounters difficulties if they are to have a very small wall thickness (s) to diameter (d) ratio. This is particularly the case when s: d values have to be below 1:10. Even s: d values of up to 1: 150 are aimed for. But then such thin-walled tubes only become interesting for a whole range of applications.

In order to ensure that the s: d ratios are as small as possible, new and better methods and devices for carrying them out must be sought.

A known process for the production of hollow glass fibers works according to the fiber drawing technique. For example used in the manufacture of optical fibers. One assumes a so-called preform, including of a quartz rod with a diameter of 10 to 20 mm, which has the same cross-sectional structure as the fiber drawn from the rod. One end of the preform is heated so that a fiber can be drawn off from the melt formed there.

For glass hollow fibers, the preform is e.g. from a glass tube that has the same wall thickness: diameter ratio s: d as the fiber to be drawn from it. A reduction in the s: d value given in the preform during the drawing process of the fiber is practically impossible, the geometric relationships of the tube are also reflected in the fiber. However, the production of a preform with exact circular cross sections for very small s: d values is only possible within narrow limits and involves considerable difficulties.

The pulling out of the fiber without additional measures, which cannot be carried out here, to support and expand a thin fiber wall until it solidifies sets limits.

Another known possibility, especially for the production of hollow fibers from glass or other inorganic materials that are meltable, is a method according to German patent DE 2 555 899 C2 dated 12.12.1975, according to which hollow fibers can be produced from a glass melt which practically arise after a melt spinning process, which is superimposed by using a blowing process, in order to make a relatively thick-walled melt tube immediately after emerging from a spinning device by blowing up. The use of the blowing process, which is made possible by supplying a gas component to the inside of the spinning tube, can easily cause instability during the inflation process, which can be caused by pulsation of the fiber tube (up to fluctuations between full fiber and hollow fiber with a very thin fiber wall) or even by bursting Hose wall makes noticeable.

The characteristic specified in the above-mentioned process: the ratio of tapered diameter: tapered wall thickness should be equal to or less than 1: 2, indicates the need to include the inflation of the spinning tube in the spinning process in the process specified there.

The reason lies primarily in the constructive and patented design of the device for carrying out this method: the use of a displacement body to form a spinning gap through which the spinning melt emerges from the spinneret. During the manufacture and the thermal load during the operation of such a device, there are relatively large tolerance fluctuations for the spinning gap, so that the formation of a thin-walled hollow fiber below an s: d value of 1:10 cannot allow constant fiber production. A particularly disadvantageous effect (due to the tolerances) is the eccentricity in the position of the displacer inside the bore of the nozzle opening, which already predicts thinner wall thickness ranges during the formation of the spinning tube, which can be caused by the blown-in filler gas or the broken fiber can lead to the withdrawal process.

The task of ensuring exactly geometrical wall thickness relationships for the hollow fiber to be produced is solved by the proposed measures. This also applies to the processing of other liquefiable masses and is not limited to glass.

The method steps characterized in the first claim switch off the flow around a displacement body (described in the sense described above) and the inflation process on the spinning tube is limited to such an extent that the pulsation processes described above are largely restricted by the tapering of the wall thickness between the spinning tube wall thickness when it emerges from the spinneret and the finished hollow fiber wall thickness is kept small.

So (to prevent instability problems in the blowing process) a kind of extrusion process is included in the melt spinning process (compared to the known spinning process mentioned above).

When processing thermoplastic materials, the extrusion process is made possible by increasing the viscosity immediately before the spinning tube is produced. While processing

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of glass for the production of hollow glass fibers (or glass capillaries), therefore, higher temperatures are used in the area between the melting zone and the spinneret than in the actual nozzle area (exit zone for the melt = nozzle mouth). The same applies to the processing of thermoplastics, such as Polycarbonate.

The process can also be used for wet spinning processes. By supplying a precipitant into the interior of the spinning tube, it is “inflatable” to a limited extent, taking into account a slight tapering of the wall thickness.

The limitation of the inflation value also means, with regard to the design of the spinning device, that relatively narrow spinning gap widths must be selected. An example is:

Then a spinning nip with s: d = 1:12 results in a hollow fiber with s: d f = 1:15.

The tapering of the spinning tube diameter emerging from the nozzle to the finished hollow fiber diameter reaches a value of 12: 0.2 = 60, the tapering of the wall thickness as the spinning tube emerges to the finished hollow fiber wall reaches a value of 1: 0.013 = 76.9.

The ratio of the diameter taper to the wall thickness taper is then 60: 76.9 = 1: 1.28.

The wall thickness taper is therefore less than double the diameter taper.

A widening of the spinning nip with the same outside diameter of the spinning nip would require a higher radial stretching in the case of a hollow fiber with the same s: d, i.e. require a greater degree of inflation and thus a higher wall thickness rejuvenation. In the sense of the present invention, this should be avoided in order to better stabilize the spinning process and to enable the reproducible production of very thin-walled hollow fibers or capillaries.

Such products with sometimes very extreme s: d values up to 1: 100 (and even less) are required for insulation materials made of plastic or glass capillaries in the dimensions of 1 to 3 mm in diameter (in special cases up to 10 mm) . To ensure a constant process in the production process of such «hollow fibers», one can orientate oneself on the conditions mentioned above, which in practice means: The spinning gap width must be very small in relation to the spinning gap diameter. If you want to create capillaries with a diameter of 1 mm with an s: d = 1:50, the spinning process takes place in a stable range e.g. with a spinning gap width of 1 mm and a spinning gap outer diameter of 30 mm. The degree of taper for diameter: wall thickness is 1: 1.67.

The choice of a very small spinning nip width now has the consequence that high demands must be made on the tolerance accuracy for the spinning nip when producing a suitable spinning device, and on the other hand that there are no significant factors during the thermally highly stressed spinning operation (especially in the case of Gias) Tolerance changes may occur.

The type of construction with a displacement body within a hole, as described above, does not guarantee a constant tolerance. Centering bridges for better positioning of the displacement body in the spinning gap disturb the material flow in the narrow spinning gap widths in question, because such bridges must be arranged as close as possible to the nozzle mouth, otherwise their effect is weakened.

The present invention now proposes, for the configuration of a spinneret-like device for carrying out the method steps listed in claim 1, the features described in patent claims 6 to 11, with which it is possible to take into account the relationships described above.

At the point where the material flows out of the first mass from the spinneret device (nozzle mouth), an annular (also circular) channel ends, which at its beginning (inside the nozzle) only connects part of its circumference to the collecting space in which the first mass is located is located. The channel is preferably arranged in the region of the wall parts of the device adjoining the collecting space, in such a way that it only partially penetrates the collecting space floor and otherwise ends blindly in the wall. As a result, the core of the “hollow channel” remains. For the most part, the core is still the bottom or wall of the spinning device and remains optimally stable with high thermal load capacity. In this way, it guarantees the central position of the spinning gap outside diameter to the spinning gap inside diameter.

The incorporation of the hollow channel can be done by laser, ultrasound, grinding processes, electroerosion etc. work methods that allow very tight tolerances. Hollow drills or milling cutters or hollow grinding tools are also suitable for circular channels.

Such processing methods can be used for different spinneret materials. Depending on the type of spinning mass used, these include Platinum, ceramics (e.g. aluminum oxide), Ni-Cr alloys, CrNi steels.

Spinning gap outer diameter Spinning gap width outer fiber diameter fiber wall thickness

: 12 mm

1 mm 0.2 mm

0.013 mm

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When machining operations with electrical discharge machining are used, the Hohikanai can be designed with a conical cross-section in such a way that the cross-section of the spinning hollow channel at the nozzle mouth is smaller than in the inflow area of the first mass within the nozzle material. This advantageously results in a pressure build-up as the viscous spinning mass flows through to the nozzle mouth and thus an optimal distribution of the mass within the spinning tube formed on the nozzle mouth.

The incorporation of hollow channels into the spinneret device is superior to a construction method using displacement bodies (see above) in several points and ensures the described requirements for an exact construction during production and operation. Among others, to:

- The axial direction of the outer and inner diameter of the annular gap is absolutely the same, since both gap walls can be created at the same time.

- The width of the annular gap can also be carried out with the closest tolerance.

- The standing core of the hollow channel (as part of the spinneret bottom or the spinneret wall) does not require any positioning, in contrast to a displacement body, the position of which is difficult and which can easily change its position under thermal stress.

- For multifilament nozzles, it is not absolutely necessary that the axial directions of the channels (for the first spinning mass) have to match one another. Displacer designs require this, which leads to expensive measures in the machining steps of the spinneret parts and their adjustments during assembly.

The channel arrangement in the wall of the spinning device offers a simple possibility for supplying the second material mass or the gaseous spinning component. Since the channel center lies within the wall, a corresponding feed hole can run through the entire length of the wall. This bore can optionally be additionally lined with suitable feed pipes. If tubes with a very small inner diameter and extreme length are used, this has a stabilizing effect on the inflation process in the emerging spinning tube when gaseous spinning components are added.

For multi-jet nozzles for the simultaneous production of several hollow fibers or capillaries, it is advantageous to arrange several channels in the bottom-wall area of a spinning device and to create connections from each of the channels via partial openings to the collecting space delimited by walls and floors.

This construction also allows adaptation to industrial systems. Such multifilament nozzles can e.g. be connected to glass trough melt feeds.

Of course, it is also possible to feed plastic granules or glass balls or glass pieces to the spinning device and to melt them in their collecting space. The delivery rate can be controlled by a suitable choice of the level of the melt sump or by applying a delivery pressure to the melt.

Finally, a further variant of the channel arrangement in a spinning device should be mentioned, which can preferably be used for monofilament nozzles, that is to say in the event that “one-hole” nozzles are to be used. The channel would not be placed in the wall area, but in the floor area, below the collecting space for the first mass to be processed. As can also be seen from the following drawings, the channel runs only inside the spinneret bottom in the lower part, without penetrating the bottom. By arranging partial openings between the upper end of the duct and the bottom of the nozzle, access to the spinning mass is made possible for the duct. For the most part, this is the "bottom" of the spinning device.

In order to delimit the feed for the second spinning mass or gas component, which is enclosed by the sewer, from the collecting space, it is either possible to feed the second spinning mass to the feed via holes drilled in the floor or to install a duct guide running through the collecting space.

The following drawings illustrate different variants for advantageous designs of the spinneret-like device according to the invention. The drawings are schematic and distorted on a scale for clarity.

The drawings show the formation of some spinneret variants, namely for circular ring channels.

When using such nozzles for processing thermoplastic materials, the nozzles must be heated, which has not been included in the drawings. Industry-standard methods can be used for this, such as infrared radiation by means of electrical resistance heating, by gas or oil heating or also by high-frequency or low-voltage exposure.

The drawings show in detail:

Fig. 1: Longitudinal and cross section of a multifilament spinneret for 3 channel systems

Fig. 2: Longitudinal and cross section of a Multifil spinneret for 3 channel systems in the spinneret bottom

Fig. 3: Longitudinal and cross section of a multifilament spinneret for 4-channel systems with a common central feed for the second spinning component

Fig. 4: Longitudinal and cross section of a monofilament spinneret

Fig. 5: Longitudinal and cross section of a monofilament spinneret with conically incorporated spinning channel

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Fig. 1 shows in longitudinal and cross section a multifilament spinneret for three channel systems for the simultaneous production of 3 hollow fibers or capillaries. These are created by subtracting the spinning mass flowing out of the channel ring gaps 5, e.g. a glass melt. This is liquefied after being fed in the direction of arrow M1 in the collecting space V. This collecting space is delimited by the wall 2 and the floor 3. The upper level of the spinning mass is indicated here by the line P. The level can be selected so that there is sufficient delivery pressure on the mass to be spun out on the floor of the collecting room. The mass flows into the channels 5 through partial openings 4 and flows out at the nozzle mouth as a liquid tube 6, from where it is drawn off by a (not shown) extraction device and tapered in diameter and wall thickness, so that finally the desired hollow fiber or capillary in it cooling and solidification occurring.

To support the fiber wall and to taper it during the spinning process, a second spinning component, e.g. an inert gas such as argon is introduced into the inside of the hose 6. The supply takes place in the direction of arrow M2 via tube 7 and collecting space 1 "through the cannula 8. The latter is placed in the spinneret wall by the inserted tube 8 'with a predetermined inner diameter and a predetermined length such that it opens out in the center of the channel 5. The feed pipes 7 can be connected to each other outside the nozzle and connected to a common feed line, which is not shown in the drawing.

Another possibility for the arrangement of the channels of the two spinning components can also be seen in FIG. 2 in longitudinal and cross-section. Likewise drawn as a multi-nozzle for three channel systems, the channels 5 are incorporated in the region of the base 3 in which they end blindly and are connected to the collecting space 1 'by partial openings 4. The second mass, which is also thought of as a gaseous spinning component, is supplied through the nozzle wall 2 and through bores into the center of the respective channel system. The channel 5 surrounds the outlet bore 8. Each channel system is assigned a feed for the gaseous spinning component, which can be connected to a common feed line outside the spinneret.

Further number designations in FIG. 2 are analogous to FIG. 1.

3 shows in longitudinal and cross-section how, according to FIG. 2, the channel arrangement of the annular gaps 5 in the base 3 of a spinneret can be made by the feed for the second component centrally through the area of the collecting space 1 'and not through the nozzle wall 2 runs. Four channel systems for four hollow fibers or capillaries to be produced simultaneously are shown here. The spinning mass is filled in the direction of arrow M1 through a cover 10 which closes off the nozzle (by means of seal 9). This makes it possible to increase the delivery pressure to the liquefied mass in the collecting space 1 ', the level of which lies at line P, by introducing a delivery gas, e.g. compressed air kept under slight overpressure. In this case, the feed pipe 11 on the cover 10 is to be sealed against the atmosphere and the spinning mass is introduced via a lock (not shown).

The centrally fed second spinning component is distributed radially from the center of the bottom 3 to the individual channel systems, which are connected to the center by bores. If these holes are made in production as far as the edge of the nozzle bottom, they must be dowelled or welded tightly there.

Here, too, the remaining number designations are analogous to FIG. 1.

Another exemplary embodiment is shown in FIG. 4, this time as a monofilament nozzle (in longitudinal and cross-section) for producing a single hollow fiber or capillary.

For the processing of certain glass qualities, the inner surfaces of the spinneret wetted by the glass spinning mass must be platinized or the nozzle parts made entirely of ceramic material, e.g. high-purity aluminum oxide. Both are e.g. inert against E-glass (a low-alkali glass).

Fig. 4 shows a ceramic version (except for the suspension 12 made of metal). The lower nozzle part 13 with the channel system 5 can even consist of a solid platinum / rhodium alloy, as is used in industry in the production of full glass fibers.

The channel ring gap 5 is worked into the bottom of the nozzle 13 and encloses in its center the channel 8, which receives the second spinning component from the collecting space 1 ". This component is fed in from the direction of the arrow M2. The collecting space 1" is formed by the two tubes 14 and 15. The tube 14 has the function of the nozzle wall numbered 2 in FIGS. 1 to 3. The first spinning mass is refilled in the direction of arrow M1.

5 shows a further variant for a metal, e.g. made of a platinum / rhodium alloy, lower nozzle part 13 a, analogous to nozzle part 13 of FIG. 4.

The annular hollow channel here has a smaller width, denoted by 5 a, in the outer region of the nozzle bottom at the nozzle mouth than in the inner end region, denoted by 5 b. The channel width extends conically in the direction of the channel length into the region of the partial openings 4 through which the first mass can enter the annular channel. As shown here as a variant, the partial openings 4 can be formed as depressions which form connections to the annular hollow channel for the entry of the first mass.

For this purpose, reference is also made to FIG. 1, which shows a different design of the partial openings 4

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shows. However, the annular hollow channels can also have different channel widths in the direction of the channel lengths in the same way, as are shown in FIG. 5.

Claims (12)

Claims 1. A process for the production of hollow fibers from liquefiable materials, characterized in that - That to form a tube as a preliminary stage of a hollow fiber formed during the manufacturing process in a spinneret-like device from a collecting space, a first mass enters through partial openings of a first, annular channel, flows through it, and that when it emerges from this channel, the resulting tube a second mass, which is supplied from a second channel, which the first channel surrounds, inside the tube, - That the tube emerging from the first channel is withdrawn to form the hollow fiber, a limited radial stretching being achieved by the introduction of the second mass and an axial stretching being achieved by pulling off the tube, with the dimensions of the tube becoming finished and - That the tapering of the wall thickness is less than twice the diameter taper due to the stretching processes. 2. The method according to claim 1, characterized in that the first mass flowing through the annular channel thermoplastic properties, such as. Glass and that the second mass is an inert gas, e.g. Is argon. 3. The method according to claims 1 and 2, characterized in that the viscosity of the thermoplastic mass in the channel is higher than that which it has in the collecting space. 4. The method according to claim 1, characterized in that the first mass is a soluble substance, such as e.g. Polyacrylonitrile in aqueous solution of sodium thiocyanate NaSCN, and the second mass is a liquid, e.g. Water. 5. The method according to claim 1, characterized in that the first annular channel has an annular cross-section and the second channel enclosed by it lies in the center of the circular ring for the purpose of exactly centric outflow of the second mass into the interior of the hose emerging from the first channel, which of the first mass is formed. 6. Device for carrying out the method according to claim 1, characterized in that the collecting spaces for the supply of the first and the second mass of floor and wall parts of the device are formed and limited and that in the area of the floor at least one center of channel systems is arranged, which consists of an at least partially machined into the soil material annular channel for the supply of the first mass and a second channel running through the center of the first channel for the supply of the second mass. 7. Device according to claim 6, characterized in that the annular channel is completely incorporated into the soil material without penetrating it, and is connected to the first collecting space through partial openings and that the second channel is connected to the second collecting space through feed bores which run between the partial openings of the annular channel. 8. Device according to claim 6, characterized in that the annular channel penetrates only part of its circumference through the floor, but otherwise ends blind in the wall and / or floor material and that partial openings are formed for the entry of the first mass into the annular Channel. 9. Device according to claims 6 and 8, characterized in that the channel for the second mass, which passes through the center of an annular channel arranged in the region of the floor / adjacent wall parts, runs through the entire wall length extending over the annular channel and there simultaneously forms the second collecting space for the second mass. 10. Device according to claims 6 to 9, characterized in that the annular channel in the outer region of the bottom has a smaller width than in the inner end region of the channel, there in particular in the connection region of the partial openings for the entry of the first mass. 11. Device according to claims 6 to 10, characterized in that the annular channel is incorporated in the material of the device. 12. Device according to claims 6 to 10, characterized in that the annular channel has an annular cross section and is incorporated in the material of the device. 6