A TERMINAL FOR ELECTRICAL RESISTANCE HEATING ELEMENT AND A METHOD FOR THE MANUFACTURE OF SUCH TERMINALS

Abstract: A terminal for electrical resistance heating elements, comprising a thin, resistance thread of a highly temperature resistant material, particularly MoSi₂, which at at least one end thereof has a lead-in electrode of a material having a better conductivity than that of the resistance heating element and having a greater cross-sectional area than that of the resistance thread. The terminal (10) comprises an outer thin-walled sheat­ ing (12) of stainless steel, one end of which is shaped as a sleeve (13) and the other end which is flattened into a flat connecting tongue (14) having a bore (15). The sheating (12) contains a filling (16) of alumina wherein one end of the resistance thread (11) is molten in.

Description: The invention relates to a method for the manufacture of a terminal for electrical resistance heating elements. Already previously an electrical heating resistance element with terminals has been proposed (SE-A-7305185-6), wherein the resistance element comprises a thin thread of a highly temperature resistant material, preferably essentially comprising molybdenum disilicide, MoSi₂, which thread has, at least at one end thereof, a terminal of a material of better conductivity than that of the heating resistance element material, preferably a thread-shaped terminal of aluminum, and having a cross sectional area which is considerably greater than that of the resistance thread. A characterizing feature of this previously proposed resistance element is that the end portion of the resistance thread is molten into the end portion of the terminal. Resistance elements of the just described kind have been found to operate satisfactorily in many cases but they have also certain limitations and drawbacks. Thus, it may sometimes be somewhat elaborate to melt in the end portions of the resistance element into the end portion of the terminals, which normally consist of an aluminum thread. Further, a terminal in the shape of an aluminum thread has certain limitations with respect to the connection of the thread itself to a conducting element such as a pole screw or the like. The present invention aims at providing a method for the manufacture of a terminal which does not exhibit the just mentioned drawbacks and which has certain pronounced advantages as compared to the previously proposed terminals for elements of the just mentioned kind. To the just mentioned end it is proposed that the manufacture of the terminals should be carried out so as is defined in claim 1. The invention will be disclosed in more details below with reference to the accompanying drawing. Fig. 1 is a plan view of one embodiment of the terminal according to the present invention, picked as an example only, arranged at the end of a thin resistance thread of a highly temperature resistant material; Fig. 2 illustrates the terminal of fig. 1 in axial longitudinal section in the plane II-II in fig.1; Fig. 3 is an axial longitudinal section of a blank for the manufacture of a terminal according to fig. 1 and 2; Fig. 4 illustrates, similarly in an axial longitudinal section, a first step of the manufacture of a terminal from a blank according to fig. 3; Fig. 5 illustrates schematically a melting step for melting in the end of the resistance thread into the terminal. The terminal, generally denoted 10 in fig. 1, 2 and 5, is adapted for the connection of an end of a resistance element 11 to a current conducting member, not shown. The invention has been created in connection with certain works with electrical heating resistance elements of the kind which are composed of a thin thread of a highly temperature resistant material, preferably essentially comprising molybdenum disilicide, MoSi₂, and the invention will be disclosed below essentially with reference to such elements although it is by no means restricted to be used only for such materials. The terminal 10 comprises an outer, comparatively thin-walled sheating 12 from an electrically good conducting material, which may be formed by pressing, but which is still rigid and which further has comparatively low tendency to oxidation. A material which is particularly suitable for this purpose is stainless steel. One end of the sheating 12 is shaped as a sleeve 13, whereas the other end is shaped as a flat connecting tongue 14 with a bore 15 or any other opening to receive a pole screw or a similar current conducting member (not shown). The terminal 10 contains a filling 16 of pliable, good conducting material, preferably aluminum. With reference to figs. 3 - 5 the manufacture of connecting terminals according to the present invention is carried out in such a manner that a thread 17, e.g. of aluminum, having a jacket 18 of a suitable material, e.g. stainless steel, is first cut into blanks 19 of suitable lengths, such as is shown in fig. 3. Then one end of the blanks 19 is compressed so as to form the flat connecting tongue 14. This tongue is then, by boring or punching, provided with an opening 15 to receive a conducting member. Of course the rod shaped blank material may be provided with the flat connecting tongue 14 in advance of cutting off the blank from the rod shaped blank material and if desired it is also possible to take up the opening 15 in the same step. As a last step the aluminum filling is melted in the uppermost portion of the terminal 10, e.g. during direct passage of current after having been switched in between two current conducting electrodes 20 and 21, such as is shown in fig. 5, whereupon finally the end of the element 11 is dipped down into the aluminum melt and held fixed therein until the melt has again solidified. The terminal according to the invention is very sturdy and will therefore maintain the element thread in a securely fixed position. Further the terminal has a very great conductive area and big contact surfaces for which reason the current density will be rather low. Further the terminal has great radiation surfaces, which means that the contact temperature will be maintained low, despite the fact that the element temperature may normally be permitted to become rather high. The terminal according to the invention has the special advantage that the portion of the element thread 11, which is normally subjected to the so called silicide pest and therefore is unnecessarily early deteriorated, is now shortened very much, or close to eliminated entirely. This portion, which is otherwise normally subjected to the silicide pest, is the portion which is disposed between the red or even white glowing glow zone portion and the glow zone end which is considerably colder due to the heat conduction to the terminal. It should be mentioned that the highly temperature resistant thread may have a diameter of from about 0.4 and up to about 2.0 mm, or slightly more. The aluminum thread 17, which forms the filling of the terminal, may have an original diameter of about 0.4 mm and up to about 6.0 mm or slightly more, depending on the application, and the stainless steel sheating may have an initial wall thickness of from 0.2 mm up to about 0.4 mm.

Claims: A method for the manufacture of a termination for electrical resistance heating elements, comprising a thin thread of a highly temperature resistant material, preferably essentially comprising molybdenum disilicide, MoSi₂, which thread, at at least one end thereof, is provided with a terminal (10) of a material having a better conductivity than that of the material of the resistance thread and having a cross-sectional area which is essentially greater than that of the resistance thread, characterized in that a rod (17) of a suitable filling material, preferably aluminum, having an outer jacket as a sheeting of a suitable material, for instance stainless steel, is cut into blanks (19) having a suitable length, which blanks comprise the sheeting (12,18) and the filling (16,17) therein, and in that one end of the blanks is compressed into a flat connecting tongue (14) which is provided with an opening (15) to receive a current conducting member and in that finally the filling (16) is melted in the uncompressed end of the terminal (10) for example during direct passage of current between two electrodes (20, 21), which are held against the outer surface of the sheeting, and the end of the element thread is dipped down into the melt and held fixed therein until the melt has again solidified.

Inventors: BIZZARRI, VENANZIO
Applicants: KANTHAL AB
Application year: 1985
Main classification: H01R11
IPC codes: H01C1, H01C17, H05B3, H01R11, H01R4