DE3714161A1 - IGNITION CORD - Google Patents

Abstract

A reinforced tube suitable for use in the construction of an explosive signal transmission device. The tube 10 is constructed from a low yield strength plastic material into which has been deposited one or more reinforcing yarns 16 of a high tenacity and low elongation material in a position substantially parallel to the axis of the tube 10 during the extrusion process. The tube may be made by extrusion between a die 24 and a tip 20, the tip having a member 40 defining a channel in the tip to permit passage of reinforcing yarn therethrough and into the extrudate. <IMAGE>

Description

The invention relates to a fuse and a Vorrich device for the production of a fuse.

Explosive fuses with high tear resistance as well Detonating cords with low tensile strength are within a short time Time through energy transmission devices or elements has been replaced with no or very little Possess fragility. This signal transmission directions or elements have the advantage of increased Security and less noise, so that this especially for blasting near inhabited areas areas can be used. Such a signal supporting element is e.g. in U.S. Patent 4,290,366 ben. Another ignition device is in US-PS 35 90 739 described.

A disadvantage of the fuse, which is in a signal transmission supply device according to US-PS 42 90 366 is used, is that the fuse that is the reactive element contains loose, in the longitudinal direction by a substantial length can be deformed. In contrast, it has reactive Element within the fuse only a little elasticity act. As a result, the hose can detonate in a borehole, which in particular with explosives filled, stretched over a considerable length, while that is contained in the hose of the fuse reactive element does not stretch as much. As a result of which the one connected to the end of the fuse Detonator from the end of the contained in the fuse reactive element separately. Thus, between the End of the reactive element and the opposite A gap or an interruption at the end of the detonator arise. Accordingly, the operational safety is well known ten fuse not very high because of the described  Failure to detonate the detonator often does not occur can.

This problem of stretching and breaking fuses, as used in a device according to US-PS 35 90 739 are to be solved according to US-PS 44 93 261 be that in the fuse several fabric fibers between an inner tube and an outer tube are arranged so that the outer tube the fabric fibers and surrounds the inner tube. This arrangement has the disadvantage that it is very complex, multiple extrusions steps required and also difficulties in them has that between the inner and outer tubing no satisfactory adhesive bond is achieved if the fibers are glued in between. Because of the needed Number of two or more extrusion steps the manufacture of such fuses also not very effective.

The object of the invention is therefore to create an ignition cord that is not fragile and in one Operation can be produced.

This object is characterized by those in claim 1 Features solved.

Furthermore, it is an object of the invention to provide a device for the production of detonating cords in one operation to accomplish.

This task is accomplished by the independent device Claim 25 marked features solved.

According to the invention, a fuse and a Device for producing such a fuse created, the fuse in the extrusion process  is produced and in this one or more Reinforcement threads are arranged. In this way the production is economical and you can achieve it at the same time a good adhesive bond between the reinforcement threads and the hose wall. Furthermore, the thickness of the wall be minimal, with blow outs through the Hose wall due to the reaction of the reactive thread because of the selective arrangement of the threads in the hose wall can be prevented. With the invention The fuse is only in one device Process step producible, resulting in high production rates can be achieved.

These advantages are achieved in that the fuse has a wall made of plastic with a low against the yield point and forms a hose, in whose inner bore one or more low-stretch, tear-free Most reinforcing threads are included, which are longitudinal Prevent the entire detonating cord. The reinforcement threads are made during a single extrusion step tes arranged in the fuse. Preferably can the reinforcing threads parallel to the longitudinal axis of the ignition line run. The threads can be at a distance be arranged from the inner surface of the wall, which is at most 0.2 times the thickness of the wall.

To produce such a fuse, the device according to the invention has an extrusion nozzle, with the reinforcing threads in the wall of the fuse introduced during extrusion. The extrusions nozzle has a cylindrical peripheral wall, the front the end tapers to the longitudinal axis of the extrusion die. The front end of the extrusion nozzle also forms one External surface for the flow channel of the extrudate, if the Extrusion nozzle arranged within the extrusion die is. Inside the front end of the extrusion die  a procedure for embedding the reactive element provided in the fuse. The tapered walls of the front end form one side of the flow channel, through which the extrudate is passed and contain one or more feed-through channels, through which the reinforcing threads at certain points in the wall of the fuse be bedded. Best in a preferred embodiment the through-channels made of tubes that pass through extend through and through the wall of the extrusion die Holding devices can be fixed at certain points. On this way the arrangement of the reinforcing threads can be varied in the extruded wall of the fuse.

Further advantageous embodiments of the invention are characterized in the subclaims.

The invention is based on the in the drawings gene illustrated embodiments explained. It shows:

Figure 1 is a perspective view of the cut end of a fuse.

FIG. 2 shows a longitudinal section through a device for producing the fuse of FIG. 1;

Fig. 3 shows a cross section through a first embodiment of a fuse; and

Fig. 4 shows a cross section through a second embodiment of a fuse.

Although the fuse 10 may have any shape, it should preferably be circular in cross-section, as shown in FIG. 1. In the fuse 10 , a reactive element 14 is contained, which can consist of a reactive material, as described in US Pat. No. 4,290,366. The reactive element 14 can also consist of other known substances. The wall 12 of the fuse 10 is made of a relatively flexible, polymeric material. The term "flexible" means the bendability of the fuse 10 in the longitudinal direction. For example, 12, polyethylene, polypropylene, polypropylene copolymer polyvinyl chloride, polybutylene, ionomers, nylon or combinations thereof can be used as suitable materials for the wall. Preferably, the plastic used should remain flexible during normal operating temperatures, which are normally in the range of about -40 to + 66 ° C. In addition, the plastic used should be such that it becomes flowable and extrudable at a temperature which is lower than the temperature at which the reactive element 14 dissolves or reacts.

The outside diameter of the fuse 10 is preferably about 0.30 to 0.38 cm and the inside diameter is about 0.013 cm. The practical range for the outer diameter is approximately between 0.015 and 0.76 cm and the practical range for the inner diameter is approximately between 0.05 and 0.038 cm. The fuse may also have larger dimensions.

When choosing the outer diameter, the inner diameter and the material for the fuse 10 , the energy which the reactive element 14 will release during its reaction should be taken into account in any case, so that the elongated fuse 10 is provided with a wall 12 of sufficient strength should to prevent destruction. In this way, a random ignition of other explosive devices that are in the immediate vicinity of the energy transmission device can be excluded. Destruction or damage to the environment is also avoided in a similar manner.

Reinforcing threads 16 are embedded within the wall 12 (one of which is shown in phantom lines in FIG. 1). In the fuse tenth of Figure 1, two reinforcing threads 16 are provided. Nevertheless, only one reinforcing thread or more than two reinforcing threads can be used. Preferably, however, two reinforcing threads should be used. If more than one reinforcing thread is used, these should be arranged in the fuse cord at an equal distance from one another. The reinforcing filaments are embedded in a single step in the wall 12 during extrusion of the wall 12th

The reinforcing threads 16 consist of thread material with high tensile strength and low elongation properties. A non-conductive material should preferably be used. The most preferred fabrics for the threads are textile fibers with a tensile strength in the range of about 4060 to 52725 kg / cm ² (20,000 to 750,000 psi) and an elongation at break of 1.5 to 4%. For example, glass fibers, aramid and carbon can be used as preferred materials. A reinforcing thread 16 made of these fabrics should have a diameter of about 0.002 to 0.076 cm, a tensile strength at a load of about 4.54 to 34 kg (10 to 75 pounds) and an elongation at break of about 2 to 5%. Less preferred, but useful in some cases, are threads made of textile fibers having a tenacity in the range of about 6327 to 14060 kp / cm ² (90,000 to 200,000 psi) and an elongation at break of about 5 to 15%. Examples of this include fabrics such as polyester, nylon and rayon. The reinforcing threads can be designed as a monofilament or multifilament or can also be spun. The reinforcing thread can also consist of a combination of suitable materials. In any case, the material of the reinforcing thread must not decompose at temperatures which prevail during the extrusion of the wall 12 and which are generally in the range from approximately 177 ° C. to 232 ° C. The reactive element 14 used for the described fuse 10 decomposes or usually reacts at about 316 ° C. Therefore, the temperature range given above for the extrusion of the wall is in the safe range. The reinforcement threads should maintain their good tear properties over the intended working temperature range of -40 ° C to + 66 ° C. They should preferably remain flexible over this temperature range.

An elongated plastic tube that contains no reinforcement threads and has an outer diameter of 0.38 cm and an inner diameter of 0.013 cm and consists of LLDPE (linear low density polyethylene) generally has a yield point at an elongation of about 20% under a load of about 4.54 kg (10 pounds) and tears when stretched by several 100%. The yield point is the minimum value for the tensile stress below which a material is plastically deformed, the material being elastic below this value and becoming plastic above this value. For comparison:. A hose made of the same material and with the same dimensions, in connection with reinforcing threads 16, should typically have an elongation of 2 to 3 '% and, depending on the number, size and type of the reinforcing threads 16, with a tearing force of 13.6 kp or more tear. Preferably, the reinforcement threads should break in the event of an overload, the suddenly occurring forces which act in the region of the broken reinforcement thread on the wall 12 of the fuse cord, which bind it together and thus make it visible to the user that the fuse cord can no longer be used. The user can then simply cut out the damaged area of the fuse and continue to use the remaining sections or take other appropriate measures.

As already mentioned, the reinforcing threads can be made of any flexible, tear-resistant and low-stretch material consist. Preferably non-conductive material be used. Suitable substances come, for example se glass fibers and rayon.

The fuse is made using known extrusion processes using an extrusion die. The plastic material for forming the wall 12 is heated to the desired temperature so that it becomes flowable and extrudable. The plastic is then pressed from the melting chamber into an extrusion device. Such devices are known and generally contain a frame which carries an extrusion die and an extrusion die. The frame, the extrusion die and the extrusion die are arranged to each other so that a flow channel is formed through which the extrudate is pressed between the extrusion die and the extrusion die to produce the fuse in the desired shape. The fuse produced in this way emerges from the extrusion nozzle and is then cooled with water so that the extrudate is solidified.

As will be described below, the reinforcing thread 16 is simultaneously arranged in the wall 12 during the manufacture of the fuse in a single step. This is done with the help of a tube that extends through the extrusion die and forms a feed-through channel.

Fig. 2 shows in longitudinal section such a device with an extrusion die 20 , which is attached together with an extrusion die 24 on a frame 22 to form a flow channel 26 for the passage of the extrudate. The extrudate is introduced from the melting chamber through the inlet openings 27 into the flow channel 26 , as indicated by the arrows in FIG. 2. The extrusion nozzle 20 has a cylindrical wall 28 which at its front end 30 to the longitudinal axis 32 of the Extrusionsdü se 20 tapers, whereby a via is fen geschaf 34, through which the reactive element is inserted into the simultaneously formed detonating cord 14 which is shown in Fig. 2 in phantom lines and provided with the reference character Chen 36 . The extrusion nozzle 20 also has two feed-through channels 38 , which are formed by tubes 40 and are inserted into holes in the extrusion nozzle 22 . In this way, the tubes 40 form a passage from the inner bore 47 of the extrusion nozzle 20 through the wall 28 thereof and emerge from its outer surface 42 , which forms one side of the flow channel 26 for the extrudate. The tubes 40 are secured by suitable holding means such. B. screws 44 attached. The tubes 40 extend through the wall 28 of the extrusion die 20 to connect its inner bore to its outer surface 42 which forms one side of the flow channel 26 for the extrudate. These feedthroughs for the reinforcing threads 16 can also be formed by drilling holes in the extrusion nozzle 20 . The diameter of the tube 40 is so large that the implementation of a reinforcing thread 16 is possible depending on its diameter, but small enough to prevent backflow of the extrudate into the inner bore 47 of the extrusion die 20 . The extrusion die 20 can be made of ordinary material such as steel or stainless steel.

As shown in FIG. 2, the feed-through channels 38 thus consist of small tubes 40 which can be positioned in an adjustable manner. When the screw 44 is loosened, the position of the tube 40 can be changed. In this way, the arrangement of the reinforcing threads 16 in the wall 12 of the fuse 10 is variable. If the end of the tube 40 extends relatively far into the flow channel 26 and thus away from the outer surface 42 of the extrusion nozzle 20 , the reinforcing thread 16 is arranged closer to the outer surface of the fuse 10 . If the tube 40 is moved closer to the outer surface 42 with its end, the reinforcing threads 16 are arranged closer to the inner surface of the wall 12 . Other means can also be provided to change the position of the tubes 40 . In any case, it is possible with the extrusion nozzle 20 to place the reinforcing threads 14 at different locations within the wall 12 . The advantage of an adjustable passage 38 for the reinforcing threads by means of a tube 40 is that a simple variation in the arrangement of the reinforcing threads 14 within the wall 12 is possible. The position of the individual tubes 40 can be varied independently of one another.

Fig. 1 also shows the cross-sectional area of the fuse 10, where "t" is the nominal thickness of the wall 12 is designated. Furthermore, the distance between the inner surface 60 of the fuse 10 and the center 62 of the reinforcing thread 16 in the radial direction is denoted by "x" and the distance from the center 62 of the reinforcing thread 16 to the outer surface 64 of the wall 12 by "y" .

X should preferably be at most 20% of the wall thickness t . This has two advantages. On the one hand, the reinforcing thread 16 lies fairly close to the inner bore of the fuse 10 , as a result of which the outer surface of the wall 12 is deformed only minimally and thus remains relatively circular in cross section. A relatively circular cross section allows an increased watertight seal when a detonator is connected to one end of the fuse. The second advantage is that a relatively thick and coherent segment in the wall 12 is obtained according to the dimension "y" . This is important in order to prevent the wall 12 from tearing during the reaction of the reactive element 14 , while at the same time the thickness of the wall 12 can be kept to a minimum.

The risk of destroying the fuse 10 can also be reduced if the reinforcing threads 14 are arranged near the outer surface of the fuse 10 , where y is at most 20% of the thickness t of the wall. Nevertheless, such an arrangement should not be given before, because in this way the cross section of the outer surface 64 of the fuse is changed into an elliptical shape, as shown in FIG. 3. Such an elliptical shape is less desirable since a reliable watertight seal is much more difficult to achieve if a detonator is attached to the end of the fuse.

The arrangement of the reinforcing threads 16 closer to the inner surface 60 of the fuse, however, can interfere with the circular cross-section of the inner surface, as shown in FIG. 4, but without adverse effects on the function of the fuse. In contrast, a circular cross section of the outer surface 64 of the fuse 10 provides a good seal when connected to a detonator. For example, the nominal outer diameter of the fuse with reinforcing threads lying close to the outer surface can be 0.38 cm with a variation range from 0.36 to 0.41 cm. In contrast, a fuse with reinforcing threads lying close to the inner surface can have a nominal outer diameter of 0.38 cm with a variation range of 0.376 to 0.386 cm.

In general, the diameter of the reinforcing threads 14 can be between 0.002 and 0.76 cm. The strength of the reinforcing threads 14 can vary depending on the thickness of the wall 12 , its arrangement therein and the variation of the outer diameter to be tolerated. For a good bond between the plastic of the wall 12 and the reinforcing thread, the thickness of the wall 12 should be 0.025 cm larger than the diameter of the reinforcing thread used. For a sufficient tear strength, the thickness of the wall 12 should be twice or three times the diameter of the reinforcing thread 14 . In the case of a very thick wall 12 , the arrangement of the reinforcing threads 16 is less critical. With increasing thickness of the wall 12 and constant tensile strength of the reactive element 14 , the arrangement of the reinforcing threads 16 can be varied more without changing the shape of the fuse. For example, in many cases the wall tears at a thickness of 0.38 cm after the reactive element 14 has been ignited if the reinforcing thread 16 was in the middle of the wall 12 . On the other hand, if the reinforcing thread was placed closer to the inner surface 60 with x 0.2 +, the fuse would not break, provided the reactive element 14 had the same tear strength.

The reinforcing thread is preferably approximately parallel arranged to the longitudinal axis of the fuse. Although too a slight spiral shape can be chosen is this less recommendable, because before the reinforcement breaks kung thread causes a greater stretch of the fuse  gently, as if the reinforcing thread is parallel to the longitudinal axis of the fuse.

It is important to have a good adhesive bond between the Reinforcing thread and the wall of the fuse cord In this way, the wall slips compared to the reinforcement threads and thus an elongation avoided the fuse. A good bond is in the generally achieved by using a binder. A conventional binder can be used which is for a good bond between the mate rial of the fuse and the material of the reinforcement dens is suitable.

The binder can be applied in two ways. In one way, the reinforcing thread is coated with the binder before it is extruded into the material that forms the wall of the fuse. For example, if the wall 12 is made of polyethylene (e.g. LLDPE) and the reinforcing thread is made of glass fibers, the binder should be a polyester resin-connectable material (polyester resin compatible finish) that is applied to the glass fibers, which is then inside the wall 12 is extruded. Another method is to mix the binder with the plastic used to make the wall and then extrude this mixture to form the wall 12 of the fuse. For example, if the wall 12 of the fuse is made of polyethylene and the reinforcing thread is made of glass fibers, the binder, namely a titanate, should be added to the polyethylene when it is melted before the fuse is extruded with the glass fiber in the wall.

The reinforcing thread can be made from a single fiber such as a monofilament or from a group of twisted fibers, thereby forming a multifilament or a spun yarn. Threads formed from twisted fibers form a rough surface, whereby the connection of the thread with the material of the wall 12 can be improved because of the larger surface.

The invention is illustrated by the following examples are explained.

example 1

In this example, polyethylene was at a temperature heated to about 182 ° C and without the inclusion of a reinforcement Kungsfadens extruded so that a fuse with a Nominal outside diameter of 0.38 cm and a nominal inside diameter knife of 0.013 cm and a nominal wall thickness of 0.013 cm was made. This fuse was on closing a tensile stress acting in the longitudinal direction subject to 9.03 kp. The fuse showed under this tensile load their yield strength is about 15% stretch and cracked when stretched greater than 600%.

Example 2

In this example, a fuse according to the invention was produced by extruding the same material as in Example 1, but with two reinforcing threads embedded in the wall, the thickness of the wall being t = 0.13 cm and x = 0.025 cm. This detonating cord only expanded by 1% with a tensile load of 9.03 kp and broke with a tensile load of 17.2 kp and an elongation of 4%.

Example 3

In order to demonstrate the importance of the arrangement of the fiber in the wall of the fuse, detonators were made with a nominal wall thickness of 0.109 cm, the reinforcing thread being arranged at a location with x = 0.025, 0.051 and 0.76 cm. The detonators contained a reactive element with a tensile strength, as described in US Pat. No. 4,290,366. The reactive element consisted of a nitrocellulose and a polyester thread, which were twisted together to form a uniform reactive element with a diameter of about 0.025 cm. When the reactive element was ignited, there were no blowouts in the detonating cords with x = 0.025 cm. In contrast, the fuse with x = 0.076 cm had irregularly distributed punctures, while the fuse with x = 0.051 cm had one or more punctures at a distance of about 2.14 m. These punctures were in the form of slits.

Claims (27)

1. fuse, characterized by

• - A wall ( 12 ) made of plastic with a low yield strength and forming a hose with an inner bore; and through
• - One or more reinforcing threads ( 16 ) made of zer tear-resistant and low-stretch material, which are arranged in the wall ( 12 ) and approximately parallel to the longitudinal axis ( 32 ) of the fuse ( 10 ).

2. fuse according to claim 1, characterized in that art has a low yield strength made of polyethylene-polyvinylchloride, ionomer Polybutenes, nylon, polypropylene, polypropylene copoly mer or combinations thereof. 3. A fuse according to claim 1, characterized in that the reinforcing thread ( 16 ) has a tensile strength in the range of about 6327 to 52 725 kg / cm ² (90,000 to 750,000 pounds / inch ² ) and breaks at less than 15% elongation . 4. A fuse according to claim 1, characterized in that the reinforcing thread ( 16 ) has a tensile strength in the range of about 14 060 to 52 725 kg / cm ² (200,000 to 57,000 pounds / inch ² ) and with less than 4% elongation tears. 5. A fuse according to claim 1, characterized in that the tear-resistant and low-stretch reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon or combinations thereof. 6. A fuse according to claim 3, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon, polyester, rayon (rayon), nylon or combinations thereof. 7. A fuse according to claim 4, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon or combinations thereof. 8. A fuse according to claim 2, characterized in that the reinforcing thread ( 16 ) has a tensile strength in the range of about 6327 to 52 725 kg / cm ² (90,000 to 750,000 pounds / inch ² ) and breaks at less than 15% elongation . 9. A fuse according to claim 2, characterized in that the reinforcing thread ( 16 ) has a tensile strength in the range of approximately 14 060 to 52 725 kg / cm ² (200,000 to 750,000 pounds / inch ² ) and with less than 4% elongation tears. 10. A fuse according to claim 8, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon, polyester, rayon, nylon or combinations thereof. 11. A fuse according to claim 9, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon or combinations. 12. fuse, characterized by

• - A wall ( 12 ) made of plastic with a low yield strength and forming a hose with an inner bore;
• - A reactive fiber ( 14 ) made of self-oxidizing material, which is loosely arranged in the inner bore of the fuse ( 10 ); and through
• - One or more reinforcing threads ( 16 ) made of tear-resistant and low-stretch material, which have a tensile strength in the range of about 6327 to 52 725 kg / cm ² (90,000 to 750,000 pounds / inch ² ), with an elongation of less than 15 % tear and are embedded within the wall ( 12 ) of the fuse ( 10 ) parallel to its longitudinal axis ( 32 ).

13. fuse according to claim 12, characterized in that art has a low yield strength made of polyethylene-polyvinylchloride, ionomer Polybutenes, nylon, polypropylene, polypropylene copoly mer or combinations thereof. 14. A fuse according to claim 12, characterized in that the reinforcing thread ( 12 ) consists of glass fibers, aramid, carbon, polyester, rayon, nylon or combinations thereof. 15. A fuse according to claim 13, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon, polyester, rayon, nylon or combinations thereof. 16. A fuse according to claim 12, characterized in that the reinforcing thread ( 16 ) has a tensile strength in the range of approximately 14 060 to 52 725 kg / cm ² (200,000 to 750,000 pounds / inch ² ) and with less than 4% elongation tears. 17. A fuse according to claim 16, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon or combinations thereof. 18. A fuse according to claim 14, characterized in that the reinforcing thread ( 16 ) has a tensile strength in the range of approximately 14 060 to 52 725 kg / cm ² (200,000 to 750,000 pounds / inch ² ) and with less than 4% elongation tears. 19. A fuse according to claim 18, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon or combinations thereof. 20. A fuse according to claim 12, characterized in that the distance ( x ) of the inner surface ( 60 ) of the wall ( 12 ) to the axis of the reinforcing thread ( 16 ) is at most 0.2 times the nominal thickness (+) of the wall ( 12 ) is. 21. A fuse according to claim 20, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon, polyester, rayon, nylon or combinations thereof. 22. A fuse according to claim 20, characterized in that the reinforcing thread ( 16 ) has a tensile strength in the range of approximately 14 060 to 52 725 kg / cm ² (200,000 to 750,000 pounds / inch ² ) and with less than 4% elongation tears. 23. Detonating cord according to claim 22, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon or combinations thereof. 24. Detonating cord according to claim 20, characterized in that the reinforcing thread ( 16 ) consists of glass fibers, aramid, carbon or combinations thereof. 25. Device for producing a fuse according to one of claims 1 to 24, characterized by an extrusion die ( 24 ) for extruding a tubular fuse ( 10 ) and an extrusion nozzle ( 20 ), the outer surface ( 42 ) of which a portion of the wall of the flow channel ( 26 ) for the passage of the extrudate through the form formed by the extrusion die ( 20 ) and the extrusion die ( 24 ), a tube ( 40 ) being provided in the extrusion die ( 20 ), which forms a through-channel ( 28 ) and through which Extends outer surface ( 42 ) of the extrusion nozzle ( 20 ) into the flow channel ( 26 ) of the extrudate, whereby the passage of reinforcing threads ( 16 ) into the extrudate is possible. 26. The apparatus according to claim 25, characterized in that the tube ( 40 ) within the extrusion nozzle ( 20 ) is movable. 27. The apparatus according to claim 26, characterized by holding means ( 44 ) for holding the tube ( 40 ).