DE2126751A1 - Coaxial high-frequency cable with cavity insulation - Google Patents

Description

High frequency coaxial cable with cavity insulation The invention relates to is based on coaxial radio frequency cable with cavity insulation between Inner and outer conductor is provided. This cavity insulation consists of a the inner conductor extruded thermoplastic plastic tube, which in Distances caused by the pressure surge of a gaseous or liquid medium to a annular bladder widened with a diameter adapted to the outer conductor and then with removal of the medium by means of a mounted in the press head is formed into a disc which can be moved back and forth in the pressing direction.

Coaxial high-frequency cables with cavity insulation, which in general Also referred to as spacers, are in a wide variety of embodiments already become known. There are HF cables with a helix as a spacer, i.e. a strand of plastic that is helically wrapped around the inner conductor is. This spacer can be applied relatively easily and in one continuous process, but involves a relatively large amount of insulating material in between Inner and outer conductors, so that the attenuation is too high for many cases; it also fulfills the important requirement for the cable core to be longitudinally watertight in no way. Another embodiment of the spacer consists of washers, what a Distances to each other attached to the inner conductor or can be applied by injection molding. The disadvantage of this spacer lies in the fact that the discs are only applied discontinuously with complex machines and in many cases there is therefore no economical production.

The German Offenlegungsschrift 1 665 221 already describes a high-frequency cable became known, as described at the beginning. This known cable is however, between the panes, which are formed from the plastic, a relative There is a thick plastic tube that lies against the inner conductor and seals it surrounds. This accumulation of insulating material also provides such a spacer for some cases, such as for transmission at very high frequencies, electrical not good because the attenuation is too high. Furthermore, through the thick, The tube completely surrounding the inner conductor also easily builds up heat on the inner conductor arise, so that the transferable power is adversely affected.

The invention is based on the object of specifying a high-frequency cable, its continuously applied cavity insulation all mechanical and electrical Requirements in an optimal way is sufficient.

For a high-frequency cable, this task becomes the one outlined at the beginning Type solved according to the invention in that the wall thickness of the plastic tube is much smaller than the wall thickness of the panes.

The advantage of the invention can be seen in the fact that now #to wipe a thin tube rests on the inner conductor of the disks, but this the disks compared to the cable types with individual disks increased stability gives. The slices themselves are still thick enough to provide mechanical strength to guarantee. However, the hose in between is so in its cross-section reduced that only little mass is available and the IIF cable according to the invention accordingly has reduced damping.

Exemplary embodiments of the subject matter of the invention are shown in the drawings shown.

In Fig. 1 is a longitudinal section through a LiF cable according to the invention pictured. Fig. 2 shows a longitudinal section through a press head of a device for the production of the HF cable in two working phases, each above and below the Center line and FIG. 3 shows a variant of FIG. 2.

The inner conductor of the HF cable is denoted by 1, and the outer conductor 2 is based on the inner conductor with the interposition of the cavity insulation, which is formed from the discs 3 and the thin tube 4 in between, away. As can be seen from Fig. 1, the discs 3 are made of a relatively thick Material that ensures the mechanical strength of these discs, while the intermediate tube is much thinner than the discs is. An outer plastic sheath 5 can also be attached over the outer conductor 2 be.

To increase flexibility and strength, the ladder l and 2 are designed to be wavy.

According to FIG. 2, the inner conductor 1 is a coaxial high-frequency cable through the press head 6 of an extrusion press, not shown, in the direction of the arrow 7 passed through; A guide tube 8 is also attached to this press head, which has channels through which a medium, for example a gas or even a liquid can be pressed through, which exits the press head Plastic tube 10 expands to form a bladder 21, namely to a diameter that of the inner diameter of the outer conductor 2 of the HF cable to be applied later is equivalent to.

This limitation is created by the ring slide 11, which has a chamber 12 corresponding to the required dimensions. The ring slide 11 with the shaft tube 13 is in Fig. 2 above the center line in retracted Position (expansion process) and below the center line in the forward position (Evacuation process) to be seen. It is driven by a cam, magnetic or hydraulic drive in the press head 6 in the axial direction, i.e. in the direction of the double arrow 14, movable back and forth.

The cross section of the openings in the press head 6 through which the Plastic passes through, is now reduced at periodic intervals and again enlarged. For this purpose, the ring slide 11 can easily be used, which at his in the press head 6 protruding end to the shaft tube 13 is formed with transverse channels 15, which the inner sliding bearing surface of the stationary Housing of the press head 6 alternately covered and during the back and forth movement releases. The plastic mass flow is reduced so that in the spaces Only a thin tube 4 remains between the panes 3 and is attached to the inner conductor 1 creates. This measure can be achieved by simply throttling the plastic mass flow to be achieved; however, it is also possible to use this plastic mass flow completely to interrupt and thereby the already extruded plastic tube 10, which is still warm to drag on.

The throttling can be done at any point of the mass flow, So for example according to FIG. 3 also at the nozzle mouth 16 by reducing the Outlet cross-section.

Around the inner pane walls for mutual contact and if necessary To bring about welding, the previously injected gaseous or liquid Medium again sucked out of this extension, including the channels 17 between the Guide tube 8 and the inner conductor l serve. When the inner wall of the ring slide 11 is profiled, for example has radial grooves, stiffening ribs are formed on the disks 3, which are indicated by the dashed lines.

The outer diameter can be reduced by cooling the inner ring slide wall of the discs 3 depending on the requirements of the individual types of plastic due to quench hardening fix. For this purpose, a heat insulating layer 18 in the ring slide 11 is useful. The molding process can also be cycled from the outside via an annular groove 19 and its pipe connection 20 support the vacuum acting on the rear wall of the pane.

After the bladder 21 with the trigger movement over the suction channels 17 is run, the pressing occurs on the front, which is arched as a result of the pressure surge Wall of the panes 3 to the rear pane wall through the interaction of the outside atmospheric or, in contrast, increased external air pressure, internal vacuum and Ring slide movement. A pressurized air application now initiated via the annular groove 19 between slide wall and disc 3 facilitates removal if necessary. The functions of the ring slide 11 with the shaft tube 13 are throttling, Calibrating, shaping, tempering or

Cooling and fixing, transporting and guiding the plastic mass.

As a gaseous substance for inflating the plastic insulation, for example Suitable for air. In special cases, inert gases are required for improvement the weldability. Well-known insulating oils or fluorocarbons are used as liquids, such as heptacosafluorotributylamine, in question. As a plastic for the insulation itself all thermoplastics, especially polyethylene, are suitable.

Claims (4)

Patent claims ) Coaxial radio frequency cable with cavity insulation between Inner and outer conductors, which are made from a thermoplastic extruded around the inner conductor Plastic tubing is made at intervals by the pressure surge of a gaseous or liquid medium to form an annular bubble with an outer conductor matched Expanded diameter and then with removal of the medium by means of a in the press head mounted ring slide movable back and forth in the pressing direction is formed into a disk, characterized in that the wall thickness of the plastic tube (4) is much smaller than the wall thickness of the disks (3). 2. A method for producing a high-frequency cable according to claim 1, characterized in that to form the cavity insulation from the press head (6) Exiting plastic mass flow in each case during the exit of the hose areas (4) between the discs (3) from the press nozzle opposite the discs (3) forming areas is throttled. 3. Apparatus for performing the method according to claim 2, characterized characterized in that the ring slide (ll) on his in the press head (6) -projecting end is designed so that the openings (15) for the supply the plastic compound in one end position of the ring slide (il) partially or are completely closed. 4. Apparatus for performing the method according to claim 2, characterized characterized in that the ring slide (li) is designed so that the nozzle mouth (16) partially or completely closed in one end position of the ring slide (11) is.