Understanding the Manufacturing Process of Heating Elements
Electric heating elements are used in liquid heating vessels such as electric kettles, coffee makers, deep fat fryers etc. In particular, the invention of kettle heating elements concerns heating using thick film heating tracks.
The use of thick film heating elements is increasing in hot water applications such as kettles and coffee makers. Conventionally, the base of the vessel for the liquid to be heated is defined by a thick film heating element. The heating element itself comprises a metal substrate on one side of which there is an insulating layer, and a printed circuit heating track is provided over the insulating layer as well. When the heating element is mounted in the vessel, the base of the vessel is defined by the side of the substrate opposite the heating track, so that the heating track and insulating layer are disposed outside the vessel and thereby do not make contact with the liquid to be heated.
The power of the heating element can be increased by the use of thick film heating tracks and an additional advantage is the ease of cleaning the inside of the vessel, when it is compared to vessels using conventional sheathed immersion heating elements. The inside appearance of the liquid heating vessel can also be improved by using a flat heating element.
An immersion heating element is a thick film resistive heating track which is deposited between insulating layers and provided on a stainless steel support plate. For an immersion heater, the heating track must be covered by an insulating layer, because both sides of the heating element are in contact with the liquid to be heated. The top insulating layer must also function as a mechanical protection layer, and thus requires a sufficient thickness to resist incidental damage i.e. during cleaning.
For a conventional thick film heating element, which defines a portion of the vessel for the liquid to be heated, the insulating layer is fired at a first temperature on the metal substrate, and the thick film heating track is deposited over the insulating layer and fired at a second, lower temperature. Consequently, the insulating layer beneath, since it can withstand much higher temperatures, and has a higher firing temperature itself don't get damaged by the firing stage for the heating track.
The use of thick film heating elements is increasing in hot water applications such as kettles and coffee makers. Conventionally, the base of the vessel for the liquid to be heated is defined by a thick film heating element. The heating element itself comprises a metal substrate on one side of which there is an insulating layer, and a printed circuit heating track is provided over the insulating layer as well. When the heating element is mounted in the vessel, the base of the vessel is defined by the side of the substrate opposite the heating track, so that the heating track and insulating layer are disposed outside the vessel and thereby do not make contact with the liquid to be heated.
The power of the heating element can be increased by the use of thick film heating tracks and an additional advantage is the ease of cleaning the inside of the vessel, when it is compared to vessels using conventional sheathed immersion heating elements. The inside appearance of the liquid heating vessel can also be improved by using a flat heating element.
An immersion heating element is a thick film resistive heating track which is deposited between insulating layers and provided on a stainless steel support plate. For an immersion heater, the heating track must be covered by an insulating layer, because both sides of the heating element are in contact with the liquid to be heated. The top insulating layer must also function as a mechanical protection layer, and thus requires a sufficient thickness to resist incidental damage i.e. during cleaning.
For a conventional thick film heating element, which defines a portion of the vessel for the liquid to be heated, the insulating layer is fired at a first temperature on the metal substrate, and the thick film heating track is deposited over the insulating layer and fired at a second, lower temperature. Consequently, the insulating layer beneath, since it can withstand much higher temperatures, and has a higher firing temperature itself don't get damaged by the firing stage for the heating track.
Step-by-step Process of Manufacturing
Firstly an electrical insulating layer is deposited over one side of the first and second substrates and each insulating layer are fired at a first firing temperature.
Secondly, a thick film consisting of an electrical conductive heating track are deposited over the insulating layer of one of the substrates, and then the heating track are fired at a second firing temperature which is less than or equal to the first firing temperature.
The third step consists of mounting the first and second substrates together, with the insulating layers facing each other.
According to the method of the invention, the insulating layers are provided over separate substrates and can be deposited and fired without any effect on the heating track, which is subsequently applied to one of the substrates.
The final step of mounting the substrates together preferably comprises applying a bonding agent over the insulating layer of one of the substrates, pressing the substrates together and firing the heating element at a third firing temperature less than the second firing temperature, for solidifying the bonding agent. The bonding agent may consist of a lead glass composition, which may typically have a firing temperature of roughly 500° C.
Secondly, a thick film consisting of an electrical conductive heating track are deposited over the insulating layer of one of the substrates, and then the heating track are fired at a second firing temperature which is less than or equal to the first firing temperature.
The third step consists of mounting the first and second substrates together, with the insulating layers facing each other.
According to the method of the invention, the insulating layers are provided over separate substrates and can be deposited and fired without any effect on the heating track, which is subsequently applied to one of the substrates.
The final step of mounting the substrates together preferably comprises applying a bonding agent over the insulating layer of one of the substrates, pressing the substrates together and firing the heating element at a third firing temperature less than the second firing temperature, for solidifying the bonding agent. The bonding agent may consist of a lead glass composition, which may typically have a firing temperature of roughly 500° C.