Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
2000-10-10
2002-07-23
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S541000, C439S271000
Reexamination Certificate
active
06423952
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 199 48 819.3, filed on Oct. 9, 1999, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a heater arrangement such as a heater cable including a connector and/or a terminating element at an end thereof, and using a fluoropolymer material to provide a seal. The invention further relates to a method of manufacturing such a heater arrangement.
BACKGROUND INFORMATION
Heater arrangements of the above mentioned general type are used for heating pipe systems such as water lines, water tanks, valves and armatures as well as structural components in which liquid products are to be transported, in order to achieve an active frost protection to prevent freezing of the liquid being transported therein when the surrounding ambient environment drops to temperatures below the freezing temperature. Especially in aircraft, which are subjected to extremely low outside temperatures during long flights, it is possible that the various water lines including fresh water lines and waste water lines will freeze if an adequate frost protection is not provided. This could lead to the failure of the entire fresh water or waste water system of the aircraft and, for example, make it impossible for the passengers to use the toilets or the like. For this reason, it has become commonly known to use such heater arrangements, especially in the form of heating bands or heating cables, on the water systems of aircraft.
The heating bands that are used for such heater arrangements conventionally comprise a heating element as well as connecting conductors or conductor strands. The heating element itself is insulated and protected by an insulating layer of a fluoropolymer synthetic plastic. Onto this inner jacket of fluoropolymer, a protective shielding conductor braid is arranged, and then a plastic outer protective jacket or sheath encloses this heater arrangement. The heating bands are typically commercially available as “yard goods”. In other words, the heating band is available in the form of a long continuous coil, and an appropriate length of the heating band is simply cut from the coil and must then be assembled or fabricated with other components to meet the need of the particular application, as follows.
A connecting member must be provided on at least one end of the heating band in order to enable the interconnection of several heater arrangements or the connection of a respective heater arrangement to a source of electrical power. In order to achieve this, an end of the heating band is “stripped” to remove the protective jackets or sheaths on the inside and the outside, so as to expose the connection conductors. The heating element portion itself is shortened so that the connection conductors are sufficiently exposed to reach an adequate length so as to then be used as an interconnection line. The individual strands of the protective conductor braid must be combed out and then twisted together, and then connected to an additional extension line. The respective lengths of the connection conductors and of the extension line of the protective braid are matched or adapted to each other so that they respectively end flush with one another.
The transition region between the heating band and the connection lines or conductors must be sealed in a pressure-tight manner that is also resistant to chemical influences and substantial temperature variations, which requires a rather complicated and time consuming process. This is necessary if the heater arrangement is to be used in an aircraft, because for such applications, the influences of vibrations, greatly varying temperatures, low pressure conditions, and the influence of various aggressive chemical agents must necessarily be taken into account so that it can be ensured that the heater arrangement does not fail due to such influences.
In the above context, to achieve such a sealing of the transition region at the connection end of a heater band, the prior art calls for a process in which at least respectively one adhesive and/or potting mass is manually applied to each connection area and then covered with a shrinkable tubing such as a heat shrink tube. Moreover, a complex adhesive pretreatment is necessary, whereby the following steps must be carried out in order to achieve a sufficient bonding between the epoxy adhesive and the fluoropolymer plastic surface (e.g. fluorinated ethylene propylene-FEP) of the heater band: the outer and inner jackets or sheaths must be abraded or otherwise roughened; the region to be adhesively bonded must be cleaned with a solvent or cold cleaning agent, for example ethanol; an etching compound, for example TETRA-ETCH, must be applied to the area and allowed to take effect; then the etchant must be washed away using de-ionized water and subsequent cleaning with a solvent or cold cleaning agent; then the heating band must be dried in a circulating air oven; and finally after the above pretreatment, the epoxy adhesive must be applied and the adhesive bonding of the shrinkable tube must be carried out within a limited period of time.
Since several shrinkable tubes are adhesively bonded in several layers, the time and complexity involved in the above fabrication process for fabricating this connection area is multiplied accordingly. Moreover, when the finished connection area is subjected to mechanical loads, for example during installation or due to operational vibrations, it has been found that the adhesively bonded joints can become separated, especially because the cured epoxy adhesive is relatively rigid while the fluoropolymer plastic such as FEP remains relatively flexible, so that the two materials are not very compatible with each other in relation to mechanical flexure.
A further difficulty or disadvantage with the conventional process for fabricating the connection areas as described above is that a specialized workplace with its own air exhaust or air processing system is necessary for carrying out at least the etching step of the process. Namely, the use of such etching compounds raises environmental concerns as well as health and safety concerns for the workers carrying out the above process. Finally, the disposal or reprocessing of the etching compounds involves additional costs and difficulties.
The above processes are also necessary for fabricating a terminating member on a terminal end of such a heater arrangement. Namely, for such a terminating member it is similarly necessary to carry out an etching process to prepare the components for a subsequent adhesive bonding using an epoxy adhesive on the FEP material of the protective jacket or sheath.
U.S. Pat. 5,998,772 (Kirma et al.) and U.S. Pat. 6,126,483 (Kirma et al.), which are both commonly owned with the present application, disclose heating conductor arrangements that can be coupled to one another or connected to an appropriate electrical power supply by means of special connection modules. Generally, these patents call for a connection technology in which the transition or joint area is provided with a split housing, whereby the interior space of the housing is completely filled with an adhesive and potting compound after completion of the necessary connections, in order to provide a reliable protection against the penetration of moisture or liquid. In the event that fluoropolymer (e.g. FEP) sheaths or jackets are used, in order to achieve a good adhesion of the potting compound with the FEP surfaces, the disclosed systems and processes would also require an adhesive pretreatment, for example using an etching technique. Thus, the above mentioned disadvantages such as a time intensive and complicated pretreatment process, health and safety risks while using various etching compounds such as TETRA-ETCH, as well as the necessary disposal or reprocessing of the etching compounds, will also be expected to apply in the context of these patented technologies.
The present invention is rela
Airbus Deutschland GmbH
Fasse W. F.
Fasse W. G.
Pelham Joseph
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