When customers browse the documentation on silicon carbide rods heater and molybdenum rods, they often see the word thermal stress. What does thermal stress mean? What is the connection between silicon carbide rods and silicon molybdenum rods?
First explain what is called thermal stress. According to Baidu Encyclopedia's explanation, when the temperature changes, the external stress caused by the object and the mutual restraint between the internal parts, so that the stress that can not be completely freely expanded and contracted is called thermal stress, also called temperature change stress. Take the glass for an example. We all know that when the glass is placed on the flame, it will burst after a while. Because at this time the glass is heated on one side and not on the other. Due to the characteristics of thermal expansion and contraction, the heated side is trying to expand rapidly at this time, while the unheated side is dragging the hind legs of the heated side, the expansion speed is not so fast, which is thermal stress, because the glass is brittle, Would rather break and not give in to each other, eventually leading to bursting.
(For convenience of description, the following focuses on silicon carbide heater, silicon carbide rods and molybdenum rods are similar.) Let us look at what thermal stress looks like in silicon carbon rods. First, the silicon carbon rod is regarded as a cylindrical shape (the silicon carbide heating elements is actually a hollow cylinder, which is also for convenience of description and understanding). When the temperature rises, the external temperature is lower due to the lower external contact temperature. It is slightly lower, and the internal temperature is relatively higher, so the internal expansion force is larger than the external expansion force. At this time, thermal stress is generated, and the inside is supported by the outside to expand. When the temperature is lowered, the outside is cooled by the atmosphere in the contact furnace, and the internal temperature is slower. At this time, the outside wants to shrink sharply and the inside shrinks not so fast, which also generates thermal stress. Silicon-silicon rods Molybdenum-molybdenum rods are gradually warmed down and cooled, and their strength is much larger than that of glass. Therefore, they do not burst like glass, but they also have certain effects, such as the surface of the silica protective film.
When producing silicon carbide heater, it is necessary to use silicon carbide particles with various particle sizes mixed in a certain proportion. Why not use uniform size silicon carbide particles?
If a uniform larger particle of silicon carbide is used, the bulk density is not high enough, which will cause a large number of small holes in the silicon carbon rod. Such a SIC Rod heater is not good in integrity, and is not sturdy and is more susceptible to oxidation. If the silicon carbide particles with smaller particle size are uniformly used, the strength of the silicon carbon rod produced will not be too good, the production difficulty will be greater, the electricity consumed will be larger, and various problems such as incomplete sintering and bending will be easily caused. The use of different sizes of silicon carbide is to ensure the maximum bulk density while ensuring the strength of the silicon carbon rod, so that the silicon carbon rod will be stronger, more durable and better in oxidation resistance.
The proportion of silicon carbide used by various silicon carbon rod manufacturers in the production of silicon carbon rods may vary slightly because of the different equipment and environment. If you want to judge the quality of the SIC Heating Elements from the appearance, you can try it. It is recommended to use the old rod that cannot be used. After breaking, look at whether the section of the rod is smooth and the integrity is strong. The unsmooth overallity may be that the sintering is not complete enough or the particle size coordination is not well mastered. Such silicon carbide elementsare not strong enough to use and have poor oxidation resistance.