|Title of Invention||
A FLEXIBLE ELECTRICAL HEATER SUITABLE FOR FLAT SURFACE MOUNTING AND A METHOD OF MAKING THE FLEXIBLE ELECTRICAL HEATER.
|Abstract||The invention relates to a flexible electrical heater suitable for flat surfacemounting. It comprises of a nichrome foil element with a cladding of kapton polyamide film. It has acrylic adhesive to insulate the nichrome foil element and insulated lead wires welded at both ends of the nichrome foil filament.|
The invention relate to a flexible electrical heater suitable for flat surface mounting and a method of making the fiexible electrical heater.
Reliable passive thermal control element such as multilayer insulation blanket, optical solar reflectors thermal control coatings play an important role in thermal control system of a spacecraft. Such thermal control systems are often augmented witN an active thermal control element such as an electrical heater. The function of these on-board electrical heaters is to provide fine temperature control to systems such as cameras, batteries etc. They also provide requisite power compensation for non-operating high dissipating packages during eel ipse or in transfer orbit.
Contemporary electrical heaters available for flat surface mounting have mica insulation with circular wire or flat wire resistor elements to produce heat. The electrical heater using mica insulation require complex mounting method using clamps and therefore not quite suitable for spacecraft application. Further tL electrical heater used in spacecraft should have low oMtgassing characteristics, good flexibility, fast warm up, wide operating temperature, simple for application and high reliability.
Accordingly a flexible electric heater with kapton insulation was developed satisfying the requirements of the electrical heater for using in spacecraft. However, they can ^lso be used for moderate heating application in chemical industries, pharmaceutical industries, food warming systems and in research and development laboratories etc.
The process of manufacturing the flexible electrical heater comprises the following steps :
1. Cladding of nichrome foil with kapton film,
2. Chemical etching of nichrome foil.
3. Welding of lead wire..
4. Encapsulation of leads and coverlay cladding.
Thus the invention provides a flexible electrical heater suitable for flat surfuct mounting comprising total element with a clading of kapton polyamide film havinq acrylic adhesive insulating the nichrome foil element and insulated lead wires welded at both ends of the nichrome foil filament.
The invention also provides a method of manufacturing the flexible electrical heater described hereinabove, comprising the iteps of clading one side of a nichrome foil with a kapton film
Havinq acryjlic adhesive, making a heater element of desired
geometry by iphoto masking and chemical etching the nichrome foil with kapton film clading on one side; welding lead wires from the two ends of the heater element; and cladding the exposed side of the heater ,element with kapton film with acrylic adhesive.
The invention will be discussed in detail with reference to
the accompanying drawings, in which :
j Fig. 1 is a flexible electrical heater in accordance with the invention and
Fiq. 2 is a fixture for producing the cladding of nichrome foil and kaptan film in the flexible electric heater according to the invention.
A nichrome foil (8) of appropriate size is placed over a kapton polyamide film (7) coated with an acrylic adhesive holding between two release sheets (6) and pressed between two platens (5) of a pressing machine. The locating pins (9) hold the assembly of nichrome foil (B), kapton polyamide film (7) and the release sheets (6) in pomitian while prmnnlnm* Wh#n %H» pressure on the assembly reaches a predetermined level, preferably around 50 PSI, the assembly is heated slowly while evacuating the space between the platens (5) till a predetermined temperature and vaccum level is reached. Preferably heating rate is kept at about 10° C/minute till a
temperature! of about 105° C and a vacuum of about 13 milli bar
are reached. Subsequently the pressure and temperature applied
on the assembly was increased to higher predetermined values.
}he increased temperature is preferably about 190° C and the
increased pressure is preferably about 150 PSI. The assembly is
held at this elevated temperature and pressure for a period of
i time typically for about 45 minutes. The specimen is then
allowed to cool slowly to ambient temperature preferably at the
rate 10° C/minute. Using a photo mask prepared to obtain the
desired geometry and resistance for the heating element, the
nichromfe foil is masked with photo resist and etched in acid
solution to obtain a heating element (1) embeded on a kapton film
(2). The process of making the element (1) of desired shape and resistance by photolithographic process and chemical etching is known in the art. A suitable etchent contains 3 molar concentrate ferric chloride and 10*/. HC1. For best results it is advisable to heat the etchent to 40 to 45°C. The photo mask remaining on the heating element may be removed by stripping with 2V. sodium hydroxide standard stripper. Lead wires (3) are welded to the ends of the nichrome foil heating element (1). Preferably gold plated multistrand lead wires with teflon insulation may be used. Gold pl*t«d kov«r transition nichrome element (1) and lead wires (3) are welded to the transition tabs (4) for better reliability. While welding the lead wires the welding tabs may have to be de-laminated for effecting proper contacts. They may be laminated back to kapton film using acrylic adhesive under elevated temperature and pressure similar to that used earlier. The exposed side of the heating element is then claded with kapton film coated with adrylic adhesive under elevated temeprature and pressure. Preferably the heating element with kapton film coated with acrylic adhesive on the exposed surface is kept between resilient members such as neoprine sheets and held by a C-clamp and heated in an oven for a period of time. Heating at a temperature of
190° to 2001 C for about 45 minutes provides excellent result.
1. A flexible electrical heater suitable for flat surface mounting comprising a nichrome foil element (1) with a clading of kapton polyamide film (2) having acrylic adhesive insulating the nichrome foil element (1) and insulated lead wires (3) welded at both ends of the nichrome foil filament.
2. The heater as claimed in claim 1, wherein the thickness of the kapton film clading (2) having acrylic adhesive over the nichrome foil element (i) is less than 0.25 mm.
3. The heater as Calimed in claim wherein the and wires
are welded to the nichrome foil element through a transition tab
(4) of gold plated kovar.
4. A method of manufacturing the flexible electrical heater
claimed in claim 1, comprising the steps of clading one side of a
nichrome foil with a kapton film having acrylic adhesive, making
a! heater element of desired geometry by photo masking and
chemical etching the nichrome foil with kapton film clading on
one side; welding lead wires from the two ends of the heater
element; ancj cladding the exposed side of the heater element with
kaDtort film with acrylic adhesive.
5. The method as claimed in claim 4, wherein the lead wires are
welded to the ends of the heating element through gold plated
kovar transition tabs.
6. The method as claimed in claim 4f wherein the lead wires are
welded to the heating element after de-laminating the ends of the
heating element from the kapton film.
7. A flexible electrical heater suitable for flat surface
mounting, substantially as hereinabove described and i1 lustrated
with reference to the accompanying drawings.
8. A method of manufacturing the flexible howere
substantially as hereinabove described and illustrated with
reference to the accompanying drawings.
|Indian Patent Application Number||2594/MAS/1997|
|PG Journal Number||40/2007|
|Date of Filing||13-Nov-1997|
|Name of Patentee||INDIAN SPACE RESEARCH ORGANISATION ,|
|Applicant Address||SPACE, ANTARIKSH BHAVAN, NEW B.E.L. ROAD, BANGALORE 560 094|
|PCT International Classification Number||H05B3/54|
|PCT International Application Number||N/A|
|PCT International Filing date|