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Questions&Answer

1.How to keep long life-time of SiC heating elements?

To keep a long life-time of SiC heating element,we need to know:

Operating Temperature
The higher the application temperature, the shorter the life will be.Oxidation of elements accelerates,as well as life-time shortened especially when the furnace chamber temperature higher than 1600℃. Therefore,we suggest that the elements surface temperature shall not be heated too much,and  it is necessary to minimize the difference between furnace chamber temperature and the elements temperature.
Surface Loading
The surface loading density (W/cm²) is the electric powder loaded in a square centimeter of the heating surface.It is prove that the larger the surface loading density (electric power) of the element, the higher the surface temperature, the faster the resistance increase,which resulted in the shorter the life of elements.
Type of Furnace Operating
There are two types of operating ways for furnace heating,one is continuous heating processing,the other is intermittent operating.Considering element life time, SiC heating elements will have a longer life-time in continous operating than intermittent operating. Silicon carbide heating elements rod oxidize in the surface, where a silica film is formed. This film gradually thickens along with its using, resulting in an increase in the resistance of the heating element. The silica film abnormally expand and contract around its crystallizing point(1270℃). If  temperature goes up and down repeatedly around this temperature by intermittent operating, the film will be destroyed repeatedly and oxidation will be increased,in this case, the resistance increase rapidly,and life-time shortened.

2.What is important for us before we use MoSi2 heating elements rods to the furnace?

Drying processing of furnance

The new furnace or the furnace that haven’t been used for a long time should be dried before use. The regular drying temperature is 100℃- 200℃. However,MoSi2 heating element tube should not be working under low temperature for long time,so that,for large sized furnace with a long drying time, it’s better to use other heating element instead to dry furnace. For the small sized furnace, its drying time is short-aound several hours, we could use MoSi2 rod to be the heating elements to dry the furnace.At beginning of the drying processing,better fully open the furnace gate,then half- opened when rising of temperature, and closed when the temperature rises over 1000℃.

3.How to replace the heating elements?

Replacement of MoSi2

If it is found that one element is damaged during operation, you should determine where it is and prepare a made up one simultaneously. Then loose the screw which links the lead wire of the damaged element and the bus, clear out the ceramic cotton and pull out the through brick. Afterward, insert the new element from the furnace top, link the lead wire, block the gap with ceramic cotton and start raising temperature.

Replacement of SiC

Generally speaking,all the SiC heating elements working in a furnace should be replaced together. To make sure using SiC heating elements rod with same or similar resistance in one furnace,it is very important for life-time of SiC heating elements.SiC heating elements with large difference in resistance are not permit to be installed together.