Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-03-05
2004-11-30
Tugbang, A. Dexter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S831000, C029SDIG001, C156S293000, C337S333000
Reexamination Certificate
active
06823580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a temperature-dependent switch with a temperature-dependent switching mechanism which is accommodated in a housing and, depending on its temperature, establishes an electrical connection between at least two connection electrodes provided on the outside of the housing, the housing having a lower part and a cover part, closing the latter while forming at least one join.
The invention also relates to a process for producing a temperature-dependent switch of this type.
2. Related Prior Art
Such temperature-dependent switches and processes for producing them are extensively known from the prior art.
The known temperature-dependent switches are used as safety elements which protect electrical devices from overheating and/or excessive power consumption. For this purpose, the temperature-dependent switches are electrically connected in series with the device to be protected, so that the operating current flows through the temperature-dependent switch. The switches are in this case arranged in heat-conducting connection with the device to be protected, so that the temperature of the latter is transferred to the switch.
Arranged in the switch is a bimetallic switching mechanism, which, depending on its temperature, establishes or interrupts an electrical connection between two connection electrodes on the housing of the switch. If there is too high a temperature or an excessive current flow, the temperature-dependent switch consequently breaks the current flow to the device to be protected, which can then cool down again and is protected from being damaged, respectively.
Temperature-dependent switches of this type are used, for example, in hot plates, hair dryers etc., but they are also encountered in particular as safety elements in transformers, motors, pumps, etc. To achieve good thermal coupling to the windings to be protected in these cases, the switches are frequently also wound into the coils and subsequently undergo the same further treatment steps as the coils, which are to be found for example in the transformers, motors, pumps, etc.
With respect to the construction, temperature-dependent switches of this type have a lower part and a cover part, it being possible for these housing parts to be produced from metal or from insulating material. If both housing parts are produced from metal, an insulating layer is provided between them, it then being possible for the lower part or the cover part to serve directly as a connection electrode, to which connecting leads can then be soldered. If only one of the two housing parts is of metal and the other is of insulating material, the metal housing part serves directly as the connection electrode, while a separate connection electrode, which may be a crimping lug protruding out of the housing part or else a solder head of a rivet penetrating through the housing part, is attached to the housing part of insulating material. If both housing parts are produced from insulating material, two separate connection electrodes are correspondingly required.
It is also known to provide both connection electrodes on the same housing part, that is for example on the cover part or on the lower part, which by means of a kind of current bridge can then be brought into connection with each other in temperature-dependent fashion by the temperature-dependent switching mechanism.
During the assembly of temperature-dependent switches of this type, the temperature-dependent switching mechanism is placed into the lower part, which is then closed by the cover part. This generally takes place by an upstanding edge of the lower part being flanged, if the lower part is produced from metal, or hot-pressed, if the lower part consists of insulating material. It is also known to push the cover part and lower part into each other and connect them to each other by means of snap-fittings.
The connecting point between the lower part and the cover part in this case represents a join, which may give rise to sealing problems. This is so because the temperature-dependent switches are often used in dusty or damp surroundings, so that it is necessary to prevent dust and moisture from penetrating into the interior of the switch and impairing its function. In addition, these switches must have a corresponding dielectric strength, since it is possible for the switches to carry great voltages, which must not lead to breakdown of the switch in the region of the join.
In the prior art, various possibilities are described for optionally sealing, at the customer's request, temperature-dependent switches subjected to corresponding loading.
The process customary among manufacturers of switches of this type is such that these switches are produced along with their connection hardware, that is the soldered-on connecting leads or other supply leads, before certain lots of the switches made up in this way are then provided with a special seal.
DE 196 09 310 A1 discloses a temperature-dependent switch in which the lower part is produced from insulating material and the cover part is produced from metal. The sealing between the lower part and the cover part takes place by means of a hot-pressed edge. In day-to-day operation, it has been found that this hot-pressed edge often does not provide the required tight seal with respect to dust and moisture.
DE 196 23 570 A1 discloses a temperature-dependent switch in which the lower part and cover part are produced from metal, with a Kapton film between these two housing parts being intended to provide not only the required electrical insulation but also the tight seal with respect to dust and moisture. For this purpose, a drawn-up edge of the lower part is flanged around the cover part. Here, too, it has been found that, with these and comparable switches with a flanged edge, under certain conditions the seal is not adequately tight even if an insulating film is provided.
DE 41 39 091 A1 discloses a temperature-dependent switch which, to increase the dielectric strength and to provide protection from dust and moisture, is fully encapsulated or enclosed in resin, sealing with a single-component thermosetting material taking place in a very complex process at least in the region of the connection electrodes provided with connection lugs.
Finally, DE 197 54 158 A1 also discloses the complete surrounding of a temperature-dependent switch with a shrink-fitted cap, from which the connecting leads protrude. The pushed-on shrink-fitted cap is hot-pressed or adhesively bonded.
The costs for the various subsequent treatment operations, described thus far, on switches which have already been made up lie in the range of 5% of the overall production costs, it even being possible under some circumstances for these costs to be higher still if shrink-fitted caps are used.
One disadvantage of sealing processes of this type is that the geometry of the switches changes as a result, they become more bulky and shapeless, it also being possible for the shrink-fitted caps to produce sharp edges and corners. This is disadvantageous in particular during winding into windings, because, on the one hand, very much more space than the space corresponding to the volume of the actual switch is required and, on the other hand, there is the risk of damage to the wires of the windings. In the case of the known processes, in some cases the geometry of the switch must also be designed specifically for the subsequent resin treatment, in order to create an appropriate bearing surface for the resins. Immersion processes, in which the switches are completely immersed in an immersion bath with encapsulating material, are in fact also known for this; although immersion is technologically more simple, it is disadvantageous that the switches encapsulated in this way require a lengthy drying time. In the case of an epoxy encapsulation after the connecting leads have been soldered on, there is also the risk that the unavoidable manipulations of the connecting leads during the installation of the switch wi
Harness & Dickey & Pierce P.L.C.
Nguyen Donghai D.
Tugbang A. Dexter
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