If you want to know the life of sic heater, you should understand the furnace type, design and cycling make a difference. This question should be considering electric furnace with a muffle operating at 1000-1100°C. In this temperature, the resistance of silicon carbide heater will be lower and stable. Check the value of resistance, ampere and voltage, as well as furnace max temperature you wanted. You will know whether need to replace silicon carbide heating elements:
1. Beginning with a change of sic heater, measure the amperage and voltage to the individual silicon carbide heating elements on a quarterly basis. Calculate their resistance and watt input to determine whether they are balanced or not. If a particular element shows erratic readings or large changes in resistance from one set of readings to the next, it is time to replace it. Note: Silicon carbide heater should be changed in sets depending on how many sic heater are in series with one another (sometimes in pairs, sometimes more).
2. Also, there is a relatively simple procedure that should be done to take the guesswork out of knowing when to change elements. With all new sic heater, lower the furnace temperature (and monitor it during this procedure) and place the power controller (SCR) in manual mode calling for 100% power. Take a digital meter with extra long leads and, CAREFULLY touching the silicon carbide heater on either end, measure the voltage drop across the element. Note: Do not take this reading by touching the straps as they run slightly cooler and your reading won’t be as accurate. Measure the current using a clamp-on ammeter around the straps and calculate resistance and watt input. Record this information for future reference. When the elements have doubled in resistance, it is time to change sic heater. Repeat these measurements every quarter.
3. When you see that the silicon carbide heater have degenerated to about 2/3 of their original resistance value, it is time to change to the next highest tap on the transformer.
4. If you are fully “tapped up” – on the highest tap setting on the transformer – and a particular zone begins to “struggle” (when it has difficulty maintaining your temperature set point), then you know it’s time to change all of the sic heater in that zone.
In a word, the choice of silicon carbide heater depends on many factors. For example, silicon carbide heating elements are capable of higher operating temperatures and higher watt loadings than say metallic elements. They are self-supporting and can be used in furnaces either too wide or too long to be spanned by other element types and are relatively easy to change while hot. SiC heater are used extensively in electric furnaces running continuously at or above 1100°C and for other processes where the temperature range lies between 1300°-1500°C.
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