DE2022282A1 - Ceramic insulated heater element - Google Patents

Abstract

A self supporting ceramic body containing a resistive heater material, e.g. a wire, is filled with an interposed buffer material in which the wire is embedded. The body is a hypoceramic of a fused homogeneous mixture of alumina with other metallic or non metallic oxides fired in the low temp. range 400-1200 degrees C. The buffer material is fire resistant and electrically insulated, firing at >1200 degrees C e.g. magnesium silicate or magnesium oxide. The method of prodn. ensures freedom from air inclusions hence increasing the electro-thermal efficiency of simple, stable, relatively cheap elements.

Description

Ceramic electric heating element and process for its manufacture 1) The invention relates to an electrical ceramic heating element and a method for placing the ceramic heating element.

Electric heating elements usually fall into two groups. One type is due to that in a granular or dusty or particulate form, for example Insulating compound embedded and pressed-in resistance material, such as a resistance wire, characterized, while the electrical heating elements of the other system are so-called are flat heating elements. In principle, the very common tubular heating elements belong on the type of heating elements embedded in an insulating compound. The efficiency of the flat heating elements is inexpensive, but their commercial application is in many I? allen hindered by the fact that the particularly düYu? e VYiderstamdasicht in the operational Use can be easily damaged.

A significant technical disadvantage of the types of heating elements in which the resistance material is inserted into an electrical insulating compound, exists in the absolutely necessary securing of the necessary for the embedding and a body or vessel with adequate mechanical strength, e.g. a hot plate casting or the metal tube of the tubular heating element.

In many cases, the internal shape of the body or vessel is expediently designed so that the unfavorable Thermal conductivity properties of the insulating compound as an embedding material are eliminated, which are related to the fact that the insulating material has a considerable amount of air pockets contains.

This profiling formed in the interior of the heating element body (e.g. in the case of hot plate castings, the formation of inner metal channels) can be achieved through it is very difficult to manufacture cast metal with dimensional accuracy. If, on the other hand, the insulating material is pressed into the heating element body with a profile tool, the jumps Deformed bodies when the embedding material is pressed in. Precision casting makes it more expensive on the other hand, the production of the element body is considerable.

The inventive new electric Keresnik heating elements require not the expensive element body with the diac components mentioned.

The electric ceramic heating element consists of a combination of one self-supporting body made of ceramic itiaterial and an electrical manufacture or resistance material that forms in the course of a technical process is characterized according to the invention in that it is the resistance material, such as a vein stand wire, in the self-supporting ceramic body in an intermediate Contains dilation buffer material embedded.

The ceramic heating element according to the invention is produced in the following way.

a): lit an appropriately designed injection molding or pressing tool is made from a burnout at low temperature from 40Q to 900 to 100000 ceramic base material made a profiled part body. In this part of the body a profiled recess corresponding to the power of the heating element, e.g. in the form of grooves, formed by pressing or injection molding.

b) In the system of excavations formed according to a) - e.g.

with a correspondingly designed injection molding tool insert according to the performance, e.g. i3. at 500 W heating power a 2.3 mm thick, electrically insulating dilation layer or buffer schicate c) In the channel-like system of kushebungen one of the desired heat output is appropriate resistance material, such as a heating wire or a heating coil, housed.

d) It is applied to the raw heating element base obtained e.g.

also with an appropriately sized injection molding tool insert another dilation buffer layer (buffer cover layer) is applied.

e) The heating element part obtained is appropriately designed with the The top layer of ceramic base material is sprayed onto the tool or pressed on.

The row heating element produced according to the invention according to a) to e) can be used in the ceramics industry for the production of ceramics at low Burnout temperatures (400 to 1100 ° a) customary processes by drying, pre-burning and burn out together with the resistance material, e.g., a heating coil the ceramic heating element according to the invention are formed An important The requirement in the method according to the invention is the use of a ceramic Base material whose burnout temperature is in the range of 400 to 9000C, at most but is 1100 ° C. Generally are at these low burn zone temperatures To burn out the desired types of ceramic (hypoceramic), such as P8 7/3 FK or 6/4 FK. It is therefore most expediently selected the ceramic protective layer so that the burnout temperature of the dilation buffer material is not reached.

In general, the composition of the ceramic protective and Carrier shell of the heating element body, characterized in that it meets the requirement after a low burnout temperature is sufficient and from the mixture accordingly selected metal oxides and non-metal oxides, such as CaO, BaO, SiO2 , En ° 2 etc., in a homogenized one selected according to the dilatation requirements Ceramic base mixture with a crystalline component, such as Al203 Das Ratio of the composition of the selected metal oxides, non-metal oxides and the crystalline components can be the electrical heating power of the heating element be changed accordingly.

The main requirement with regard to the protective ceramic is that this also is resistant to thermal shock.

The cracks occurring during operation are the result of incorrect adapted dilatation factors. By choosing the composition accordingly and the grain size can in extreme cases also be a burned out at low temperature Kind of ceramic heating element that does not have a dilation buffer layer owns.

The material composition of the dilation buffer layer contains in a variable amount of electrically well insulating metal oxide and silicate components with high melting point.

Fire-resistant electromagnesium oxide can be used as a buffer material high degree of purity or fire-resistant magnesium silicate of high degree of purity applied with a layer thickness corresponding to the electrical power of the heating element will.

The drying of the raw heating elements can take place in the temperature range of 50 to 400 whether with heat treatment stages from 80 to 1000C.

On the surface of the heating elements according to the invention a (up to 8000C) heat-resistant, water-repellent and water-impermeable coating an appropriately selected hydrophobic substance, such as, for example, a modified one Ethyl silicate, or metal oxide enamels selected for the electrical performance, optionally produced by metal spraying. The waterproof one Protective layer can also be applied to the surface of the heating elements by means of plasma spraying are made from metal oxides.

The so-called dilation buffer material of the electrical according to the invention Ceramic heating elements are used to improve processing through injection molding or pressing plasticized with organic hydrocarbons. During the burning this material turns completely or partially into powder form.

for example, in a ceramic heating element according to the invention the following materials are used: Composition of ceramic Protective layer: Hypoceramics, type 7/3 70% crystalline aluminum oxide 30% vitreous melt Composition of the dilation buffer layer: 60% heat-resistant aluminum oxide (Al23) high degree of purity 40 0 heat-resistant silicon dioxide (SiO2) of high degree of purity Composition of the water-repellent enamel layer: Cover enamel made of 20 ° TiO2 25 0/0., B203 20 d CaF2 35 where PbO 100% The one produced by the process according to the invention electric ceramic heating element can be used in the manufacture of contemporary electro-thermal technology Apparatus and devices, e.g. for convection and radiation units and in the case of heat storage, in fixed and portable stoves for household and commercial use, be used for soldering irons, immersion heaters, hotplates, irons, etc. It can with decorative ceramics and commercial ceramics and with a modeled metal frame can be used in combination.

The heat storage core of electrical heat stores made of ceramic, Cast iron or a Saizschmelze can with directly built-in according to the invention Heating elements, e.g.

In the case of heat storage cores on a ceramic basis, through injection molding or pressing.

In the accompanying drawings, which illustrate the method according to the invention To explain, A shows a grooved ceramic semi-heater body according to the invention, B in an advanced manufacturing stage in the groove of the heating element body housed resistance material and C the finished, with the top layer provided heating element.

The illustrations explain the invention for only one possible application of the ceramic heating element according to the invention, but numerous others can be used Heating element constructions are carried out according to the invention.

-Patent claims-

Claims (10)

P a t e n t a n s p r ü c h e 0 Electric ceramic pickup element made from a combination of ceramic material and an electrical one or resistance material that forms in the course of a technical process, in that it is the resistor material, such as a Resistance wire, in the self-supporting ceramic body in an intermediate Contains dilation buffer material embedded. 2. Electrical ceramic heating element according to claim 1, characterized g e It is not noted that the ceramic body is susceptible to a low temperature range from 400 to 1200 ° C depending on the electrical power of the heating element Fired material from the homogenized mixture of melts of lethal oxides and light metal oxides such as CaO, BaO, SiO2, MnO2, - as well as crystalline body components, like Al203. 3. Electrical ceramic heating element according to claim 1 and 2, characterized it is not noted that the dilatation buffer material is above 12000C flammable, fireproof and electrically insulating, appropriately selected material, such as magnesium silicate or magnesium oxide. 4. Electrical ceramic heating element according to claim 1 to 3, characterized It is not noted that the ceramic body is made from a ceramic base material low burnout temperature of 400 to 1200 ° C, especially hypoceramics, this through a suitable choice of the grain structure to a low coefficient of expansion from z = 1 to 1.5. 10 6 has been set. 5. Electrical ceramic heating element according to claim 1 to 4, characterized it is not noted that there is a heat-resistant, water-repellent and waterproof cover made of a hydrophobic material, such as ethyl silicates or metal oxide enamels. 6. Sheet metal ceramic heating element according to aAnspruch 5, thereby g e no indication that it has a water-impermeable metal coating, which has been applied to the surface after metal spraying. 7. Electrical ceramic heating element according to claim 5, characterized g e k It is noted that it has a waterproof coating that has been applied to the surface by plasma spraying. -8th. Method of manufacturing the electric ceramic heating element according to claim 1 to 7, characterized in that one part of the self-supporting body made of the ceramic base material by injection molding or Presses that have a profiled recess for the resistance material is provided, the recess with that when burned out partially or completely dilation buffer material transforming into powder form fills or covers the Resistance material is inserted into the recess and the combination obtained is carried out covers a corresponding sprayed or pressed ceramic molding and burns in a manner known per se at 400 to 1100.degree. 9. The method according to claim 8, characterized in that one more dilatati on the resistance material accommodated in the recess on buffer layer by spraying on, pressing or pouring. 10. The method according to claim 8 to 9, characterized in that g e k e n n -z e i c n e t that the dilation material with plasticizing additives, in particular with hydrocarbons, in the plasticized state before burning out of the heating element takes place.