US3344386A

US3344386A - Contact connection for wire-shaped heating elements

Info

Publication number: US3344386A
Application number: US435533A
Authority: US
Inventors: Gargasson Georges Claude Le; Cadiou Marcel Joseph
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1964-02-27
Filing date: 1965-02-26
Publication date: 1967-09-26
Anticipated expiration: 1984-09-26
Also published as: DE1540976A1; DK112542B; AT263965B; BE660245A; DE1540976C3; DE1540976B2; CH444250A; FR1394979A; NL6502225A; GB1081908A; NO119643B

Description

s p 25, 1967 G. c. LE GARGASSON ETAL Filed Feb. 26, 1965- FIG? INVENTOR. GEORGES C.LE GARGASSON MAROEL J. CADIOU AGENT United States Patent Claims. (cl. sss-274 ABSTRACT OF THE DISCLOSURE A contact connection between a conductor surrounded and insulated from a metallic envelope and a metallic pin. The end of the conductor is stripped of its insulation and surrounding envelope and secured to the pin. A ceramic sleeve surrounds the exposed end of the conductor and is hermetically sealed at its ends to the envelope surrounding the conductor and the metallic pin.

This invention relates to a contact connection between a wire-shaped heating element comprising one or more electrical conductors electrically insulated 'by a powdered metal oxide and enclosed in a metallic envelope, and a plurality of associated connecting pins which are thick relative to the conductors, the ends of the conductors stripped of their insulation and envelope being soldered to the connecting pins and the envelope and the pins being surrounded by an electrically insulating mass through part of their length. Such a connection is known.

The known contact connection uses glass as the insulating mass, thus preventing ambient moisture from penetrating the powdered oxide between the envelope and the electrical conductor since absorption of moisture by the oxide would cause a considerable decrease in breakdown voltage between the conductor and the envelope.

The use of glass as the electrically insulating material in a contact connection has the disadvantage that the connection is not very resistant to mechanical oscillations or shocks. Further this connection is usable only up to an operating temperature which is lower than the comparatively low softening point of the glass employed.

An object of the invention is to provide a gasand water-tight contact connection which is very strong, which permits a high current strength and which is suitable to withstand high operating temperatures of many hundreds of degrees centigrade.

The contact connection according to the invention is characterized in that the electrically insulating mass is in the form of a sleeve soldered at its peripheral edges to the envelope and the pins in a gas-tight manner, the sleeve being of a ceramic material such as, for example, aluminum oxide over at least that portion which surrounds the area where the conductors emerge from their envelope. Preferably sintered ceramic material is used as the electrical insulating material.

By suitable choice of its density, the sintered ceramic material is permeable to light. This affords the attractive possibility for inspecting the connection visually during operation. It is then possible to ascertain whether the temperature of the conductors emerging from the envelope of the element becomes excessive. If the temperature becomes unduly high at this area and if the conductors commence to show, for example, red incandescence, this can be observed because of the transparency of the ceramic material. In this case steps may be taken to reduce the temperature, for example, by external cooling with air or water.

The sleeve of ceramic material must be soldered at "ice its peripheral edges to the metal envelope of the element and the connecting pins in a gas-tight manner. To this end, the sleeve of ceramic material could be locally metallized to permit working with copper-silver solder. Such metallizing is an expensive operation. In another embodiment of the connection according to the invention it is preferred to use a titanium-containing eutectic of silver and copper as the soldering material.

It has been found that in a connection established between a ceramic material and the envelope of the heating element by using a solder containing titanium, the titanium diffuses into the material of the envelope rendering it brittle. An embodiment is therefore preferred in which the sleeve is not made wholly of ceramic material but comprises two portions, that is to say a metallic first portion soldered to the envelope and a ceramic second portion soldered to both the connecting pins and the first portion. For the attachment of the first portion it sulfices to use, for example, a copper-silver soldered connection, the titanium-solder being used, as before, for the two operations of soldering to the second portion.

The invention will now be described with reference to the accompanying drawing, in which:

FIGURE 1 shows in cross-section one'embodiment of a contact connection between a coaxial heating cable and a connecting pin, which is in the form of a plug socket;

FIGURE 2 shows in cross-section another example of a contact connection between a heating cable having two current conductors and two connecting pins.

The wire-shaped heating element of FIGURE 1 comprises a metallic envelope 1 and a central electrical conductor 2 which is insulated from the envelope 1 by a powdered metal oxide 3. The conductor 2 is stripped of insulation at its end 4 and extends into a bore formed in a terminal portion 15 of a connecting pin 7 having the form of a plug socket. The envelope '1 and the terminal portion 15 are surrounded by a sleeve 6 of a sintered ceramic material having a density such as to be light-transmitting. The numeral 5 indicates a metal sleeve. All the connections in this example are soldered. A ring 8 likewise of ceramic material is oriented within the envelope 1 over part of its length.

The connection of FIGURE 1, in which the parts to be joined have been previously degreased carefully with the aid of a suitable liquid, was made as follows:

First a ring of soldering material, an eutectic of copper and silver, was placed on the envelope 1 at the area indicated by 11. (The position after soldering is shown.) Then the sleeve '5, which has a coefficient of expansion approximately equal to that of the sleeve 6, was slipped over the envelope '1. The sleeve 5 is made of an ironnickel compound containing 42% of nickel and the sleeve 6 is of sintered aluminum oxide. A ring consisting of solder of a titanium-containing eutectic of copper and silver was then placed in position at 12. Next the sleeve 6 and a ring of solder were arranged at 13, the envelope 1 being displaced so as to project slightly from the sleeve '6. Then the ring 8 of sintered aluminum oxide and a ring of a solder having a very high melting point were fitted at 14, the rings s and 14 contacting each other. This ring 14 is of an alloy consisting of 85% of silver and of manganese and having a melting temper-' ature of 950 C. The connecting pin 7, which is of iron nickel (42% of nickel), was then slid with its terminal portion 15 into the sleeve 6, causing the envelope 1 to be pushed back into the sleeves 5 and 6. The terminal portion 15 has a diameter such that, on the one hand, the heat within the conductor portion 4 deprived of insulation and surrounded by the ceramic sleeve 6 can be dissipated and, on the other hand, the heat produced in the terminal portion 15 due to the passage of current is negligible.

The whole was then introduced into an oven in which an atmosphere of hydrogen was maintained. Any trace of oxygen and water vapor was avoided. The temperature of the oven was approximately 1,000 C. After heating the connection for a period which depends on the diameter of the heating element and the dimensions of the contact connection, the connection was cooled while retaining the atmosphere of hydrogen in the oven.

The dimensions and the electrical properties of a contact construction manufactured in accordance with FIG- URE 1 are the following:

Millimeters Diameter of the envelope 1 2 Length a of the sleeve 5 7 Length b of the sleeve 6 7 Length c of the pin 7 18.5 Length of the terminal portion 5 Diameter of the terminal portion 15 2 length over which the end 4 extends into the terminal portion 5 is approximately 1 cm.

It has been found that a connection of the kind herein described to a heating element having a central current conductor of nickel-chromium 0.7 mm. in diameter, when exposed to air, can withstand an intensity of 30 amps. for several days and even 40 amps. have been measured in this test for a short period. The gasand water-tightness of the construction was found to be perfect. During the tests a cool flow of air was maintained at the sleeve 6. Even higher current strengths are permissible if a very cold gas (air, nitrogen CO is blown against the sleeve 6 or upon immersion in running water. The latter suggestion can be carried out because of the high gas and water-tightness of the construction.

In the embodiment shown in FIGURE 2, the heating element comprises two electrical conductors which are secured at their ends 3'6, 3'7 stripped of their insulation in bores of

nickel coupling pieces

25 and 27 in the manner shown. The two coupling pieces are insulated electrically from each other by a ceramic plate 32 and have further bores to receive iron-

nickel connecting pins

26 and 28. Further more

ceramic rings

24 and 31 are provided. The two connecting

pins

26 and 28 are maintained in position by a sleeve 29 of sintered ceramic material.

The various parts, which have previously been degreased, were assembled as follows:

A sleeve 23 consisting of a nickel-iron compound with 42% of nickel was slipped over an envelope 33 of the heating element, a ring of soldering material (an eutectic copper-silver compound) being arranged at 38. By means of this ring the sleeve 23 could be soldered to the envelope 33 of the heating element throughout its length. Then a ring 31 consisting of sintered aluminum oxide and having two apertures was slipped over the

ends

36 and 37 of the heating wires whereupon a ring 24 was brought around the heating 'wire and the two

coupling pieces

25 and 27 were slipped over the

ends

36 and 37 in the manner shown. A plate 32 of sintered aluminum oxide was arranged between the

coupling pieces

25 and 27 to avoid any contact between them. Next, rings of a silver-manganese solder were arranged at 40 and 41.

The assembly thus obtained was introduced into an oven in which an atmosphere of hydrogen at 1000 C. was maintained similarly as in the previous example.

After cooling had taken place while retaining the atmosphere of hydrogen, the assembly was removed from the oven and the sleeve 29 of sintered aluminum oxide was slipped over the rod-shaped

part

26 and 28, whereafter rings of a titanium-containing eutectic copper-silver solder were arranged at 43, 44 and 45. Then another soldering operation was carried out in the oven and the sleeve 29 attached.

Under similar conditions to those in the first example described with reference to FIGURE 1, a contact connection established as shown in FIGURE 2 in a heating element two mms. in diameter and with two heating wires, each of 0.36 mm. in diameter was found satisfactorily to withstand a current strength of 15 amps. without undue heating or any attack of the tightness of the connection being noticeable.

The dimensions of the various parts of this connection are the following:

Length (1 of the sleeve 23 mm 5 External diameter of the sleeve 23 cm 1 Length e of the sleeve 24 mm 2.5 Diameter of the sleeve 24 'mm 6 Length f of the sleeve 29 cm 1 External diameter mm from 8 to 9 What is claimed is:

'1. A connector for a heating element having at least two conductors surrounded by a common metal envelope, said conductors being insulated from. one another and from the envelope, the ends of said conductors being stripped of insulation, a ceramic member having parallel bores through which connecting pins for each of said conductors extend, metallic coupling members surrounding and secured to each of said connecting pins, each of said coupling members having a bore through which the end of the conductor extends and is secured thereto, a metal sleeve surrounding and hermetically sealed at its peripheral edges to a portion of the metal envelope, said ceramic member surrounding a portion of said conductors intermediate each of said coupling members and the metal sleeve and being hermetically secured at its peripheral edges to said metal sleeve and said connecting pins.

2. A connector as claimed in claim 1 in which the ceramic member surrounding the conductors is of lighttransmitting sintered ceramic material.

3. A connector as claimed in claim .2 in which the ceramic material is alumina.

4. A connector as claimed in claim 3 in which the ceramic member is sealed to the metal sleeve with a titanium containing eutectic of silver and copper.

5. A connector as claimed in claim 4 in which the coupling members are separated by a ceramic member.

References Cited UNITED STATES PATENTS 1,901,667 6/ 1933 'Roh 174--11.3

FOREIGN PATENTS 1,123,417 2/ 1962; Germany.

99,812. 4/ 1962 Norway.

OTHER REFERENCES Jenny, A. L., Soldered Ceramic-to-Metal Seals, Product Engineering, December 1947, pp. 154-157.

RICHARD M. WO'OD, Primary Examiner.

J. G. SMITH, Assistant Examiner.

Claims

1. A CONNECTOR FOR A HEATING ELEMENT HAVING AT LEAST TWO CONDUCTORS SURROUNDED BY A COMMON METAL ENVELOPE, SAID CONDUCTORS BEING INSULATED FROM ONE ANOTHER AND FROM THE ENVELOPE, THE ENDS OF SAID CONDUCTORS BEING STRIPPED OF INSULATION, A CERAMIC MEMBER HAVING PARALLEL BORES THROUGH WHICH CONNECTING PINS FOR EACH OF SAID CONDUCTORS EXTEND, METALLIC COUPLING MEMBERS SURROUNDING AND SECURED TO EACH OF SAID CONNECTING PINS, EACH OF SAID COUPLING MEMBERS HAVING A BORE THROUGH WHICH THE END OF THE CONDUCTOR EXTENDS AND IS SECURED THERETO, A METAL SLEEVE SURROUNDING AND HERMETICALLY SEALED AT ITS PERIPHERAL EDGES TO A PORTION OF THE METAL ENVELOPE, SAID CERAMIC MEMBER SURROUNDING A PORTION OF SAID CONDUCTORS INTERMEDIATE EACH OF SAID COUPLING MEMBERS AND THE METAL SLEEVE AND BEING HERMETICALLY SECURED AT ITS PERIPHERAL EDGES TO SAID METAL SLEEVE AND SAID CONNECTING PINS.