Encapsulated electrically resistive heater
View Patent ↗Electrically resistive heating element, with metal strip electrodes secured thereto, and with electrical wires secured to said metal strip electrodes, is encapsulated with thermoset-molding compound.
1. Method of making an encapsulated electrically resistive heater, said method comprising:
(a) providing a mold having a cavity therein,
(b) centrally positioning an electrically resistive heating element in said cavity,
(c) said cavity having a length and width greater than the length and width of said electrically resistive heating element, thereby to provide a space between said cavity and said electrically resistive heating element, said space extending completely around the sides of said electrically resistive heating element
(d) said electrically resistive heating element having a first face and a second face opposite said first face,
(e) said second face contacting the bottom of said cavity,
(f) applying a first thermosetting molding compound to said first face of said electrically resistive heating element,
(g) forcing a press into said mold against said first thermosetting molding compound, thereby to force said first thermosetting molding compound against the first face of said electrically resistive heating element and into said space,
(h) allowing said first thermosetting molding compound to cross-link,
(i) removing said electrically resistive heating element from said mold, reversing said electrically resistive heating element and reinserting said electrically resistive heating element into said cavity, said first thermosetting molding compound contacting the bottom of said cavity,
(j) securing electrodes to said second face of said electrically resistive heating element,
(k) applying a second thermosetting molding compound to said second face of said electrically resistive heating element,
(l) forcing a press into said mold against said second thermosetting molding compound thereby to force said second thermosetting molding compound against the second face of said electrically resistive heating element and into contact with said first thermosetting molding compound in said space,
(m) allowing said second thermosetting molding compound to cross-link,
(n) removing the now-formed encapsulated electrically resistive heating element from said mold,
(o) removing a portion of said encapsulation from around the ends of said electrodes to permit connection to a source of electricity.
2. Method as in claim 1 , wherein step (j) may be performed when said electrically resistive heating element is in said mold.
3. Method as in claim 1 , wherein step (j) may be performed before said electrically resistive heating element is reinserted into said mold.
4. Method as in claim 1 , wherein:
(p) said electrodes comprise metal strips secured to said electrically resistive heating element, and wires connected to said metal strips,
(q) a portion of said encapsulation is removed from around the ends of said wires.
5. Method as in claim 1 , wherein:
(p) said electrodes are secured to said electrically resistive heating element adjacent opposite sides of the said electrically resistive heating element.
6. Method as in claim 1 , wherein said electrically resistive heating element is heated in said mold prior to application of said first thermosetting molding compound to a temperature that will facilitate molding and cross-linking said first and second thermosetting molding compounds.