|
(11) | EP 0 573 430 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
|
|
| (54) |
ELECTRIC TUBULAR HEATING ELEMENT COMPRISING A TEMPERATURE CONTROLLER THEREFOR ELEKTRISCHER ROHRHEIZKÖRPER MIT EINER TEMPERATURKONTROLLEINRICHTUNG ELEMENT DE CHAUFFAGE ELECTRIQUE TUBULAIRE AVEC UN REGULATEUR DE TEMPERATURE |
|
|
|||||||||||||||||||||||||||||||
| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to an electric tubular heating element comprising a tubular metal casing which contains a coil of resistance wire surrounded by an insulating material, and a temperature controller connected in series with a resistance-wire coil and arranged at one end of the metal casing and comprising an insulating sleeve which contains a bimetal switch and has an outer terminal forming a terminal of the tubular heating element, and an inner terminal which later, when the temperature controller is mounted in the tubular heating element, contacts a terminal connected to the resistance-wire coil.
[0002] The prior art encompasses electric tubular heating elements of this type. The temperature controller used in the prior-art tubular heating elements is of single-use type, such as a fuse, or of reclosing type, such as a bimetal switch.
[0003] Single-use temperature controllers have the disadvantage that the entire tubular heating element has to be replaced when the controller has blown. It is true that the temperature controller can be made replaceable, but this involves safety problems.
[0004] Such temperature controllers as bimetal switches, which always return automatically when the temperature falls to the normal value, are not usually sanctioned by the authorities for safety reasons.
[0005] The object of the present invention is, therefore, to provide at tubular heating element with a temperature controller not impaired by the drawbacks of the prior art.
[0006] Such a temperature controller must meet the following requirements.
a) It should be of recloseable, not single-use, type, but should not reclose automatically when the temperature drops.
b) The heat conduction from the resistance-wire coil to the temperature-sensing part of the temperature controller should be satisfactory.
c) After opening, it should be insensitive to the ambient temperature as to maintaining the open position.
d) It should be mountable in the tubular heating element after this has been completed.
e) It should be mountable in a tubular heating element of comparatively small diameter, e.g. 8 mm or even 5.4 mm.
f) It should cause a distinct opening at a given excessive temperature.
[0007] EP-A-0 204 850 discloses an electric tubular heating element having a temperature controller consisting of a bimetal switch which always returns automatically when the temperature falls to the normal value. This electric tubular heating element does meet only a few of the above requirements. It could be made recloseable manually by the introduction of a manually recloseable bimetal switch, such as described in e.g. DE-A-3 644 514 and DE-A-3 320 730. DE-B-1 125 567 discloses an electrical tubular heating element having a reclosable bimetal switch and a parallel-connected resistor element.
[0008] According to the invention, the above requirements are met by an electric tubular heating element which is of the type stated in the introduction to this specification and which has the characterising features stated in claim 1. Preferred embodiments of the electric tubular heating element according to the invention, have the features stated in claims 2-7.
[0009] In a preferred embodiment, the inner and outer terminals have tongues facing one another, the bimetal switch and the resistor element being fixed one on each side of said tongues. To this end, rivets may be used, one of which may also constitute the fixed contact of the bimetal switch.
[0010] According to the invention, the resistor element advantageously is a PTC-resistor, i.e. a resistor element whose resistance has a positive temperature coefficient.
[0011] The temperature controller according to the invention meets the above requirements a) - f) in that
1) it employs a bimetal switch with a parallel-connected resistor for maintaining the open position (requirement a),
2) it comprises a casing having such an inner connection that the temperature controller can be mounted last, i.e. after the tubular heating element otherwise is complete, e.g. stress-relieved, which would not be possible if the temeprature controller had been mounted (requirement d),
3) the bimetal spring proper is live and disposed at the centre of the temperature controller, which is facilitated by the fact that the resistor element is arranged on that side of the bimetal spring which is opposite to the opening direction thereof. This arrangement permits maximum width of the bimetal spring, which is important in preventing the bimetal spring from being overheated by the current throughflow, and in enabling such a design of the bimetal spring that it produces a snap action when opening (requirements e and f)
4) the centrally disposed, live bimetal spring, which constitutes the temperature-sensing element, is, when in closed position, connected in excellent thermally conductive manner to the resistance-wire coil by the inner terminal and the pin (requirement b), and
5) the employed casing is insulating (both as to electricity and as to heat), such that the required electric strength and the desired independence of the ambient temperature can be achieved, especially in combination with the centrally disposed and live bimetal spring (requirement c).
[0012] The invention will be described in more detail below, reference being had to the accompanying drawings, in which
Figs 1 and 2 are longitudinal sections of two embodiments of a tubular heating element with one and two, respectively, temperature controllers according to the invention,
Fig. 3 is a longitudinal section of a preferred embodiment of a temperature controller according to the invention,
Fig. 4 is a plan view of a bimetal spring in the temperature controller of Fig. 3, and
Fig. 5 is an end view of a resistor element in the temperature controller of Fig. 3.
[0013] The inventive electric tubular heating element shown in Fig. 1 consists of a tubular metal casing 1 which has a resistance-wire coil 2 extended between two terminals in the form of pins 3 and 4. The resistance-wire coil is surrounded by, and insulated from the casing 1 by means of, a pulverulent insulating material 5, such as magnesia powder. The two ends of the wire coil are in conventional manner fixed to the inner ends of the pins 3, 4, e.g. by welding. A temperature controller 6 is according to the invention mounted in the left end of the tubular heating element, as seen in Fig. 1. The temperature controller 6 has an inner terminal in the form of a contact socket 7 (Fig. 3) which encloses and electrically contacts the terminal pin 3 of the resistance-wire coil 2. The oppositely directed terminal 8 of the temperature controller 6 projects from the end of the tubular heating element in the form of a pin and forms the second electric terminal thereof. The metal casing 1 extends a certain distance along the terminal 8, i.e. it contains substantially the entire temperature controller 6, and an end bushing 9 of steatite or polymers forms a seal between the metal casing 1 and the terminal 8 and also serves to maintain the latter in place.
[0014] The terminal 4 may be either directly connected to the resistance-wire coil 2 or connected thereto via a temperature controller corresponding to the controller 6.
[0015] Fig. 2 illustrates an alternative tubular heating element, in which the terminals 3', 4' of the resistance-wire coil 2' are provided at the same end of the metal casing 1'. The other end of the metal casing 1' is closed, and the resistance-wire coil 2' extends from one end of the casing 1' to the other and back embedded in an insulating material 5'. In this embodiment, two temperature controllers 6', 6" according to the invention are each connected to a terminal 3', 4'. The temperature controllers 6' and 6" in the embodiment of Fig. 2, unlike that of Fig. 1, are not substantially contained in the metal casing 1' but in an extension piece thereof which consists of a bushing 10 and a tubular member 11. The tubular member 11 is mounted in the bushing 10 which in turn is fixedly mounted on the metal casing 1'. Further, the bushing 10 has a threaded portion for fixing the tubular heating element. The outer terminals 8', 8" of the temperature controllers 6', 6" are electrically connected to two conductors in an electric cable 12 through which current is supplied to the resistance-wire coil 2'.
[0016] The preferred embodiment of an inventive temperature controller shown in Fig. 3 comprises a sleeve 13 of an insulating material, such as plastic, preferably of a circular cross-section corresponding to e.g. the cross-section of the metal casing 1 in Fig. 1. The terminals 7 and 8 are mounted each in one end of the sleeve 13, the terminal 7 consisting of a cylinder 14 which is made in one piece with a contact socket 15 slotted in the longitudinal direction, and a tongue 16 facing away from the socket and disposed in a plane through a diameter of the cylinder 14. The terminal 8 consists of a pin which is fixedly mounted in an end wall of the sleeve 13 and has a tongue 17 extending into the free space inside the sleeve 13. The tongue 17 is located in the same plane as the tongue 16.
[0017] One end of a resistor element 19 is fixed to the tongue 17 by a rivet 18. The other end of the resistor element 19 is fixed to the tongue 16 by a rivet 20. One end of a bimetal spring 21 is fixed to the tongue 16 by the rivet 20 on that side of the tongue 16 which is opposite to the resistor element 19. The bimetal spring 21 extends in over the tongue 17 and, when in closed position, contacts the rivet 18 which thus forms the fixed contact of the bimetal switch formed by the rivet and the bimetal spring 21. Thus, the bimetal spring 21 is located substantially at the centre of the casing 13 and has the shape illustrated in Fig. 4. In cross-section, the resistor element 19 has the shape shown in Fig. 5. For fixing the resistor element 19 and the bimetal spring 21 to the tongues 16 and 17, respectively, holes have been formed in the tongues 16 and 17 and in the resistor element 19 and one end of the bimetal spring 21, as shown in Figs 4 and 5.
[0018] When mounting the temperature controller of Fig. 3 in e.g. the tubular heating element of Fig. 1, the contact socket 15 will contact the pin 3, and the terminal 8 will form one terminal of the tubular heating element. It should here be observed that the sleeve 13, after the details housed therein have been mounted, has been given a decreasing diameter at its free end, just beyond the contact socket 15, thereby ensuring the electric strength between the contact socket 15 and the metal casing 1.
[0019] The resistor element 19 can be made of any suitable material of sufficiently high resistivity, but a material whose resistance has a positive temperature coefficient is preferred, since it ensures the desired limitation of the current through the tubular heating element after the bimetal switch has been tripped.
[0020] If a tubular heating element according to the invention is overheated when in operation, the bimetal spring 21 will, at a given temperature, rise from the fixed contact 18, thereby breaking the normal path of the current through the resistance-wire coil 2. A slight current, depending on the resistance of the resistor element 19, will continue to flow through the resistance-wire coil 2 via the resistor element 19. Thus, this element is heated and the generation of heat is so dimensioned that the bimetal spring 21 cannot bend back and contact the fixed contact 18. To reconnect the tubular heating element, thus also the slight current through the resistor element 19 must be interrupeted.
characterised in
that the bimetal switch (18, 21) comprises a bimetal spring (21) disposed along the centre of the insulating sleeve (13) and having one end connected directly to the inner terminal (7) and, when the bimetal switch is in a closed position, having its other end connected to the outer terminal (8) for current throughflow;
that a resistor element (19) is contained in the sleeve (13), has one end fixed to the inner terminal (7) and the other end fixed to the outer terminal (8), is disposed on that side of the bimetal spring which is opposite the opening direction of the bimetal switch, and has such a resistance that the heat generated by the resistor element when the bimetal switch is tripped open and the resistor element is supplied with current, is sufficient to maintain the bimetal switch in open position by heating the bimetal spring; and
that the inner terminal (7) has a contact socket (15) which is contained in its entirety in the insulating sleeve (13), which is insulating both as to electricity and as to heat.
ein rohrförmiges metallisches Gehäuse (1; 1'), das eine Wicklung aus Widerstandsdraht (2; 2') enthält, der von einem isolierenden Material (5; 5') umgeben ist, einen Temperaturwächter (6; 6', 6"), der in Reihe mit der Widerstandsdrahtwicklung geschaltet und an einem Ende des metallischen Gehäuses angeordnet ist und eine isolierende Büchse (13) aufweist, die einen Bimetall-Schalter (18, 21) enthält und einen äußeren Anschluß (8), der einen Anschluß des rohrförmigen Heizelementes bildet, und einen inneren Anschluß (7) enthält, der mit dem in dem rohrförmigen Heizelement montierten Temperaturwächter einen Anschluß (3) kontaktiert, der an die Widerstandsdrahtwicklung (2) angeschlossen ist,
dadurch gekennzeichnet,
daß der Bimetall-Schalter (18, 21) eine Bimetall-Feder (21) umfaßt, die entlang des Zentrums der isolierenden Büchse (13) angeordnet ist und ein Ende direkt mit dem inneren Anschluß (7) verbunden hat, und, wenn sich der Bimetall-Schalter in einer geschlossenen Stellung befindet, sein anderes Ende für den Stromdurchfluß mit dem äußeren Anschluß (8) verbunden hat;
daß ein Widerstandselement (19) in der Büchse (13) enthalten ist, ein Ende an dem inneren Anschluß (7) befestigt hat und das andere Ende an dem äußeren Anschluß (8) befestigt hat, auf derjenigen Seite der Bimetall-Feder angeordnet ist, die der Öffnungsrichtung des Bimetall-Schalters gegenüberliegt, und einen solchen Widerstand aufweist, daß die durch das Widerstandselement erzeugte Wärme, wenn der Bimetall-Schalter geöffnet wird und das Widerstandselement mit Strom versorgt wird, ausreicht, um den Bimetall-Schalter durch Erhitzen der Bimetall-Feder in geöffneter Stellung zu halten; und
daß der innere Anschluß (7) eine Kontaktbuchse (15) aufweist, die in ihrer Gesamtheit in der isolierenden Büchse (13) enthalten ist, welche sowohl gegen Elektrizität, als auch gegen Wärme isoliert.
caractérisé en ce que
le bilame (18, 21) se compose d'un ressort de bilame (21) disposé le long du centre du manchon isolant (13) et ayant une extrémité reliée directement à la borne intérieure (7) et, lorsque le bilame est dans une position fermée, ayant son autre extrémité reliée à la borne extérieure (8) pour le passage du courant;
en ce qu'un élément de résistance (19) est contenu dans le manchon (13), a une extrémité fixée sur la borne intérieure (7) et l'autre extrémité fixée sur la borne extérieure (8), est disposé sur le côté du ressort de bilame qui est à l'opposé de la direction d'ouverture du bilame, et présente une résistance telle que la chaleur générée par l'élément de résistance, lorsque le bilame est basculé en position ouverte et l'élément de résistance est alimenté avec du courant, est suffisante pour maintenir le bilame dans une position ouverte en chauffant le ressort de bilame; et
en ce que la borne intérieure (7) possède une embase de contact (15) qui est contenue dans sa totalité dans le manchon isolant (13), qui est ainsi isolant à la fois pour l'électricité et pour la chaleur.