A heating element is a resistance heater that converts electrical energy into heat. It has diverse uses - from household appliances such as hair dryers, dishwashers or baking ovens to industrial application areas in the electrical high-temperature furnace. One example of metallic/ceramic materials for use in high temperatures is molybdenum disilicide (MoSi2).
Heating element geometries
Heating elements of molybdenum disilicide can be produced in many different shapes or geometries in individual sizes. Typical shapes include the U-shape, W-shape, L-shape, which can be bent both in the cold zone or the heating zone. In addition to these standard designs, individual special geometries can be implemented as well. This includes panorama, block and coil shapes, as well as rods.
Heating element sizes
Determination of a heating element size requires some information. The information Lu (cold zone), Le (heating zone), a (shank distance), c (diameter of the cold zone) and d (diameter of the heating zone) is needed for a U element, for example.
A W element additionally requires the values B (height of the heating zone from the upper to the lower edge) and S (number of the shanks a1, a2, a3). An L element requires indication of where the bend is to be and at which angle the bend is to be applied. The dimensions are usually indicated in millimetres.
Heating elements become round bodied
It is also a normal reaction, which is due to electric fields in terms of attraction and repulsive forces. A slightly round bodied deformation does not generally effect the performance or function. It is advisable to check the circuit (series or parallel circuit) and the connections.
Heating elements crack (mechanical crack)
This phenomenon happens in various ways. One possibility results in an user error and occurs, when too much force is applied to fix the heating elements with the contact straps or the double holders. Finesse is needed in the truest sense of word. Furthermore it is necessary that the heating elements are really straight installed through the furnace roof into the furnace chamber. A slightly tilting can already lead in a mechanical crack.
Heating elements lengthen
This is a normal reaction. As a rule, the lengthening involves rather larger heating elements with a heating zone (Le) of approx. >500mm. In general the phenomenon does not lead to any problem during operation. As soon as the elements threaten to touch the furnace bottom, they should be replaced, otherwise the insulation will be damaged.
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