DE3724514A1 - Process for the continuous production of branch caps or dividing caps from plastic which recovers its shape on heating - Google Patents

Abstract

In a process for producing branch caps or dividing caps from plastic which recovers its shape on heating, an extruded plastic pipe is first of all crosslinked and expanded. After the expansion, regions of the inner surface of the pipe are joined by fusion welding. The caps are subsequently produced by severing in the region of the weld and between two weld regions.

Description

The invention relates to a method for continuous Production of branch caps or distribution caps heat-recoverable plastic, wherein the Plastic material cross-linked, over the Crystalline melting point heated, widened and in the expanded state is cooled, in which continuous operation, a tube is extruded and at intervals parts of the inner surface of the tube be joined together by fusion welding and finally the caps are separated from the tube, being in the area of the weld as well as between two weld seam areas the pipe is severed.

Under branch caps or dividing caps are molded parts to understand which at one end is a relatively large one Opening and at the opposite end at least two have correspondingly smaller openings. Such Shrinkable caps become the conclusion of multi-core cables and wires needed, the Cap is placed on the cable end and through Heat is brought to shrink. The ends of the Cores are thereby through the smaller openings passed, whereas the larger opening in the rule surrounds the cable sheath. Due to the shrinking is a achieved moisture-proof termination of the cable end.  

It has been such caps as injection molded parts prepared and after crosslinking the openings widened. This procedure is quite complicated and therefore not economical.

From GB-PS 14 54 838 a method is known, with which such caps in a continuous manner can be produced. A tube is extruded and immediately after extruding through Pressure tool intermittently parts of the inner Surface welded together. That way fabricated structure is crosslinked and after crosslinking heated to a temperature above the Crystallite melting point of the crosslinked plastic lies. When heated, the pipe is replaced by a Expander passed, which consists of a tube in which between the plastic pipe and the pipe a negative pressure is generated, which is an expansion should cause. Alternatively, it is also suggested that Inside of the plastic pipe with an overpressure too apply. After widening, the caps of separated from the tube. In this known method has it turned out to be disadvantageous that during expansion no body with a uniform surface is present. at the production of such caps, it is necessary that the degree of expansion is constant, d. H. it is one outer shape required, to which the expanded Can create pipe. It is easy to see that after the structure produced by the known method because of his irregular surface does not evenly to the Form surface can create. So it can only be done here Produce caps with relatively irregular dimensions.

From EP-PS 00 46 077 it is known vorgereckte Making body of a polymeric material and a Melting between one or more parts of the Body to produce. Then at least the Weld area for increased strength networked. In a preferred embodiment  described that an uncrosslinked expanded tube is made and parts of the inner surface of the expanded tube are connected to each other. Subsequently, the structure thus produced is crosslinked and the caps separated from the tube. By the final networking becomes the expanded state largely fixed, so that the shrinking property of Caps left a lot to be desired.

The present invention is based on the object specify a method by which the said Distribution or branch caps in an economical manner be made with almost the same dimensions can, which have a large shrinkage capacity.

This object is achieved in that according to the Invention the welding after crosslinking and Widening is done. Opposite that from the GB-PS 14 54 858, the advantage of the invention still exists in that the risk of tearing the weld in the Expansion does not exist, since the expansion before the Welding was done. Opposite the procedure according to EP-PS 00 46 027 shows the inventive Method has the advantage that much higher Shrinking forces in the moldings are "frozen". The EP-PS 00 46 027 uses a shrink mechanism, the the expansion of uncrosslinked material provides. The subsequent networking leads to previous Findings that a shrinking effect after the Crosslinking without subsequent expansion does not occur.

Compared to the previous level of knowledge has completely Surprisingly shown that for many applications a perfectly adequate weld also Crosslinked materials can be achieved, where limiting must be mentioned that both in terms of expected shrinking forces as well as the height of the Degree of crosslinking does not exceed certain limits can be. The process according to the invention  produced caps are used wherever high shrinkage rates are not needed.

After a particularly advantageous development of The method according to the invention is the welding Ultrasonic welding done. At this Welding causes the supplied energy that only the surfaces to be welded together be transferred in the molten state.

As starting material for the production of the caps is advantageously a hose used by Coextrusion was made, with the inner layer consists of a hot melt adhesive. In the Welding is the hot melt adhesive layer from the Area of the weld displaced so that the networked Plastic material comes into contact with each other and can be welded.

As it has proven particularly useful a pipe by coextrusion, its inner layer is not networkable, and thus easy to close.

For some applications, it is desirable that the Cross section of the branches is very small. For these cases It has proved to be expedient that the width of the Weld transverse to the longitudinal direction of the tube so large is chosen that between the branches enough Material remains and that this material after the Welding is removed.

The welding is advantageously carried out immediately after widening in the same operation. This can the material contained in the material after expansion Heat content for welding to be exploited with. In this approach, it has to be advantageous proved that the tube after the expansion but before Welding from the outside is cooled so that at least the outer surface of the tube to less than 100 degrees C.  has cooled. The inner surface of the tube remains because of poor thermal conductivity on one much higher temperature level, whereas the outer Surface has cooled down so far that they are for the Welding required mechanical forces can record and transmit.

With particular advantage is as a material for the pipe used a polyethylene grafted to the silane groups are. The amount of silane groups is calculated so that a degree of crosslinking of the polyethylene of at most 25% is reached. The degree of crosslinking can be higher be if a hose with two concentric Layers is used, the inner layer of a thermoplastic non-crosslinkable plastic z. B. Polyethylene exists.

The invention is explained in more detail with reference to the embodiment schematically illustrated in FIGS. 1 to 4.

By means of an extruder 1 , a tube 2 is extruded from a crosslinkable plastic in a continuous operation and wound onto a storage drum 3 .

The plastic used is preferably polyethylene, grafted onto the silane.

You first create a mixture that is composed of:

50 parts High density polyethylene 25 parts Ethyl vinyl acetate copolymer 25 parts Carbon black batch (40 parts carbon black - 60 parts ethyl vinyl acetate copolymer) 0.5 parts Anti-aging agent (Anox HB) 0.1 parts calcium stearate

The mixture is in a manner not shown in one Extruder processed and processed into granules.

This granular mixture is added to 1% by weight of a crosslinking agent in a mixer. The crosslinking agent is composed of 98 parts of vinyltrimethoxysilane, 1.2 parts of peroxide (Parkadox 14) and 0.8 part of dibuthyltin dilaurate as a catalyst. From the mixer, the finished mixture is fed directly into the hopper of the extruder 1 . The grafting of the silane on the PE molecules is then carried out after homogenization by melting within the extruder at temperatures above 140 degrees C.

The extruded tube 2 is then optionally in a manner not shown. On the storage drum 3 in the presence of moisture z. B. in a humidity chamber at about 50 degrees C crosslinked.

After crosslinking, the tube 2 is withdrawn from the storage drum and heated in a continuous manner to a temperature above the crystallite melting temperature. A glycol bath 4 is expediently used for this purpose. The heated tube is then expanded in a calibration device 5 to the desired level. For this purpose, the calibration device 5 is subjected to negative pressure, which ensures that the heated tube is sucked against the mold surface of the calibration. Immediately behind the calibration device 5 , the welding device is arranged. This consists of two mutually-on and away from each other movable rollers 6 and 7th When moving together press the rollers 6 and 7 portions of the inner surface of the expanded tube 2 a together. As a result of the pressure applied by the rollers 6 and 7 and the high temperatures required for the expansion, the surfaces of the expanded plastic tube 2 a contacted with each other weld together. Depending on the number of rollers 6 and 7 or if it is profiled rollers, according to the number of circumferentially extending elevations, the number of adjacent welds may be different.

The rollers 6 and 7 are cyclically moved against the continuously transported through the system pipe, so that in the longitudinal direction of the tube 2 a seen alternate sections with welds and sections without welds. For the transport of the tube provides a trigger device, not shown. Behind the pair of rollers, a cutting device 8 may be provided which cuts through the continuously passing pipe 2 a in the region of the welds and between two welds.

Instead of the rollers 6 and 7 advantageously not shown sonotrodes can be used, so that the welding is carried out by ultrasonic welding. FIG. 3 shows an example of a so-called two-finger cap made in the manner described above. The cap consists of a substantially hollow cylindrical part 8 , whose cross section corresponds approximately to the cross section of the expanded tube 2 a . By the U-shaped weld 10 two fingers or branches 11 and 12 are formed, whose cross-section is circular or oval depending on the strength of the crosslinked material. The plastic material between the legs of the U-shaped weld 10 has been removed by a punching operation. This approach will be preferred if the cross-section of the branches 11 and 12 should be small compared to the cross-section of the section 9 .

However, the weld 10 may also be linear in the direction of the longitudinal axis of the tube 2 a . In this case, the cross sections of the branches 11 and 12 are larger and correspond to almost half the cross section of the tube 2 a or of the section 9 .

If one chooses the position of the weld 10 so that it does not run in the middle of the tube 2 a , then you get branches 11 and 12 with different sized cross sections. Such an embodiment will be used advantageously when z. B. from an electrical cable only one or a few wires are to be diverted.

The method described is also suitable for producing so-called four-finger caps. For this one will use instead of the two rollers shown 6 and 7, two more offset by 90 degrees on the pipe 2 a attacking unrepresented roles. A cap produced by such a method is shown in FIG. 4 in a perspective view. The section corresponding to the cross section of the pipe 2 a is denoted by 13 and the four branches by 14, 15, 16 and 17 . At 18 , the weld is designated. Three branches will use three rolls offset by 120 degrees.

The rollers 6 and 7 are advantageously rotationally driven at least during the time in which they attack on the tube 2 a and produce the weld at a speed corresponding to the passage speed of the tube 2 a .

Claims (9)

1. A process for the continuous production of branch caps or distribution caps made of heat-recoverable plastic, wherein the plastic material is crosslinked, heated over the crystallite melting point, expanded and cooled in the expanded state, in which a tube is extruded in a continuous operation and at intervals parts of the inner surface of the Tube are joined together by fusion welding and finally the caps are separated from the tube, wherein both in the region of the weld and between two weld seam sections, the tube is severed, characterized in that the welding is carried out after crosslinking and expansion. 2. The method according to claim 1, characterized that the welding by ultrasonic welding he follows. 3. The method according to claim 1 or 2, characterized characterized in that during the extrusion of the tube by coextrusion a two-layer pipe is made, the inner layer of a Hot melt adhesive exists.   4. The method according to claim 1 or 2, characterized characterized in that during the extrusion of the tube by coextrusion a two-layer pipe is made, the inner layer of a Thermoplastics remains, which remains uncrosslinked. 5. The method according to claim 1 or one of the following characterized in that the width of Weld transverse to the longitudinal direction of the tube so is chosen large, that between the branches enough material remains and that this material is removed after welding. 6. The method according to claim 1 or one of the following characterized in that the welding immediately after widening in the same Operation takes place. 7. The method according to claim 6, characterized that the tube after the expansion but before the Welding from the outside is cooled so that at least the outer surface of the tube cooled to less than 100 degrees C. 8. The method according to claim 1 or one of the following characterized in that as a plastic Polyethylene is used, the silane groups grafted on, and that the amount of Silane groups are sized so that a Degree of crosslinking of the polyethylene of at most 25% is reached. 9. The method according to claim 1 or one of the following characterized in that in the region of Weld another perpendicular to it Weld is produced whose width is chosen is that through the separating cut a T-shaped Weld remains on each branch cap.