DE1941356U - ELEMENT OR CABLE WITH METAL SHEATH AND MINERAL INSULATION. - Google Patents

Description

.A-136 378 * 3/12/66

Wiletorfer Strasse 32

Pp F. Led® ⁵ "® ⁷ March 11, 1966

ISOPAD LIMITED

Barnet By-Pass, Boreham Wood, Hertfordshire, England.

Provided with metal jacket and mineral insulation Element or cable.

Priority; British patent application

No. 11098/65 of March 16, 1965

The invention relates to an element or cable provided with a metal jacket and mineral insulation.

Various types of seals have heretofore been used, but all of them have had to be made with great care to avoid the possible ingress of moisture. In the case of seals which ^{are intended to work at temperatures below 100 °} C., satisfactory supervision of the seals is difficult and even seals which appear to be perfectly in order can fail under working conditions. Waterproofing for Betri $$ above this temperature are usually based on a vitreous compound, but such seals have the disadvantage that the glass-like statements to crazing tends which _f the ingress of moisture permit followed by local reduction of the resistance of the insulation possibly leading to Short circuits and failure of each termination.

The invention now relates to an element or cable provided with a metal jacket and mineral insulation one end, the element extending beyond the jacket and insulation, and to one end

outer conductor is connected, and the end is sealed by a Hohr made of plastic, which is shrunk onto the end, around the end of the jacket and the connection with the outer one seal head.

Some embodiments of the invention will now be described, for example, with reference to the drawings, which represent;

Figo 1 to 3s Different stages in a preferred one Embodiment of the invention

Pig. 4s section through a flameproof

Stuffing box and element provided with a metal jacket according to the invention immediately before installation, and

Pig »5; a side view of the flame-proof Stuffing box and the element after installation »

1 to 3 explain the application of the invention to an element with a metal jacket and mineral insulation, consisting of an outer metal jacket 1, magnesium oxide insulation 2 and a central conductor 3, which is made of resistance material such as copper, nickel, nickel chrome ο «the like. can be in a case wherein the element is to be used as a heating unit »

In order to enable connection with the middle conductor 3, the outer jacket and the magnesium oxide insulation cut away by about 6 mm, exposing the conductor for that length, and a narrow ring-shaped one Groove 4 is formed in the metal jacket of the element about 6 mm from the end. The purpose of this Groove will be apparent from the following description. The conductor 3 is then connected to an outer conductor low resistance 6 connected, e.g. Ausfeupfer, by means of a small crank 7? which creates a strong mechanical bond between the two conductors,

A tube or sleeve 8 made of irradiated plastic is then brought over this connection connection, the wall of the sleeve being composed of layers. The outer layer has a high shrinkage capacity when heated to a given temperature, and the inner layer is plastic at this temperature, sleeve 8, the length of which is preferably between six and eight times the diameter of the element, is then heated, preferably using a hot air gun in order to shrink the outer layer and to allow the inner layer to flow around the crank, filling the cavity. The inner layer then forms an insulating seal in intimate contact with the conductors 3 and 6 and the crank 7 ₅ and the outer layer forms a tight seal around the connection »

The aforementioned annular groove 4 creates an anchorage for the sleeve as it shrinks and also forms one Barrier against possible ingress of moisture through capillary action in the finished connection.

One form of sleeve has an outer layer made of PVC, which is ^{heated to about 150 0} G in order to cause shrinkage! it can work steadily at temperatures from -50 to 110 C. »A sleeve of this type will usually be suitable where the wattage ^ per 30 cm of a heating element whose outer side diameter is between 3? 14-4 nam, will not exceed 20. For higher strengths and working temperatures, a sleeve with an outer layer of PTFE with a filling of generally the same material, sold under the trade name PEP, is used. Shrinkage at a temperature of about ⁰ C 3I6, again conveniently by means of a hot air gun, causing. The connection is suitable for continuous operation from -50 to 200 ⁰ C for element wattage of 40 watts per 30 cm-

With these compounds, the complete assemblies can be immersed, heated and in water can be re-immersed in water, and this cycle can be repeated many times without removing the insulation suffers from connections. Tests have shown that after immersion in Water can withstand up to about $ 80 of the voltage, whichever the element alone would withstand under ideal conditions. This was determined by means of an impulse test 1500 volts alternating current and 2000 volts direct current for a minute.

If maximum voltage resistance is desired, Apply a layer of a suitable compound against the exposed surface of the magnesia prior to shrinking of the sleeves pressed «When shrinking, the connection is pressed against the exposed surface of the magnesium oxide pressed and forced to penetrate the air spaces, which when the middle Conductors can be left free and what is generally the cause of ionization and premature Are failures.

A moisture-proof closure of the described Construction can be used to advantage in a flameproof gland construction, as shown in Fig.

and 5 explained. The gland, which comprises main part 11, Msa nut 12 and compression olive 13, is to be screwed over the element before the final connection is made, and the complete assembly is then located in a flameproof switch box with the sealed connection, inside the flameproof housing, screwed in. The sealed connection created by the heat-shrunk sleeve prevents any short-circuiting due to the ingress of moisture along the outer jacket of the element and is in this regard '; consider the usual combinations that use a metal cap soldered to the element »

Claims (1)

! A.136 378-12.3.66 Protection claims, 1. Provided with metal jacket and mineral insulation Element or cable with one end in which the conductive part extends beyond the jacket and the insulation and to an outer one Conductor is connected, characterized in that the end by a pipe made of plastic that is shrunk onto the end, around the end of the jacket and the To seal the connection with the outer conductor. 2a element or cable according to claim 1, characterized characterized in that the tube is also shrunk into an annular groove which is open the metal jacket is formed near its side. or cable 3. Element / according to the preceding claims, characterized characterized in that the connection is made by means of a mechanical crank. or cable 4. Element / according to the preceding claims, characterized in that the tube an insulating packing made of other plastics in intimate contact with the element, outer conductor and the connection between them. 5. Element or cable according to claim 4, characterized marked that the pipe from P.T.F.E. and the pack of 3? .E “P. is. 6. Element or cable according to the preceding claims ^. in combination with a mechanical flameproof gland assembly that tightly surrounds the metal jacket with the sealed cable end located at the end of the gland which is ₍ in use) inside the flameproof housing.