What are the commonly used materials for the metal shell of heating elements and heating tubes?

The four most common materials that make up the shell of the electric heating element electric heating tube are copper, aluminum, iron, and stainless steel. Titanium alloy is also used in a small amount, and Incoloy tube is a new type of material that has emerged in recent years.
1. Aluminum tube
The maximum surface temperature of aluminum tubes is not greater than 260 ℃, and it is mainly used for low-temperature embedded heating of household appliances and ultra-low temperature air drying. However, it must be noted that aluminum pipe electric heating elements should not heat aluminum materials, as the aluminum surface is prone to oxidation, and the aluminum metal structure exhibits looseness and poor density. The electric heating element made of aluminum pipes has a low density of magnesium oxide, so it is only suitable for occasions with low power density or low working temperature.
2. Copper tube
Basically, it is a copper tube, and in a few occasions, brass tube is also used. The maximum surface temperature of the tube is 177 ℃, mainly used to heat liquids such as water and oil.
3. Iron pipe (also known as steel pipe)
The commonly used grade is 10 # steel, although sometimes 20 # steel is also used. However, due to the high carbon content of the 20 # steel pipe, its hardness is high and it is easy to damage the mold during compression. The maximum allowable working temperature on the surface of steel pipes is 400 ℃, because after exceeding 400 ℃, the oxidation heat loss on the surface of the pipes increases. Its main heating objects are liquids (spray painting is required when heating oil and water to avoid rusting), metal molds, embedded components in household appliances, as well as many static or flowing air (usually with an air temperature not exceeding 300 ℃), nitrates, lye, etc.
4. Low carbon steel pipe
Generally, it is below 4 #, which is close to pure iron and also derived from Bondi tube and Heiklin tube. That is, copper with a thickness of 0.02mm is plated on the surface of the tube to solve the problem of rust on the surface. It is mainly used for pipe materials of household appliances, and due to its low carbon content, it can be bent without annealing when compressed by electric heating.
5. Stainless steel pipe
According to the American Iron and Steel Institute (AISI) type name:
302, 303, 304, 316, 321, and 347 models have a maximum operating temperature of 760 ℃;
309s maximum working temperature: 816 ℃;
310 type maximum working temperature: 871 ℃;
403, 405, 410, 416, 501 models have a maximum operating temperature of 649 ℃;
430 type maximum working temperature: 704 ℃;
442 type maximum working temperature: 760 ℃;
446 type maximum operating temperature: 816 ℃
Stainless steel pipes are mainly used for mold heating, ovens, drying channels, liquids with high temperature and high pressure (especially under high pressure, due to the density of the pipes, their compressive strength is strong), as well as weak acids. However, stainless steel pipes have poor mechanical strength at high temperatures.
6. Nickel alloy tube
According to the American Society of Mechanical Engineers (ASME) type name:
Maximum working temperature of 400 type alloy: 482 ℃;
Maximum working temperature of 600 type alloy: 982 ℃;
Maximum working temperature of 800 type alloy: 927 ℃;
825 alloy maximum working temperature: 593 ℃;
840 type alloy maximum working temperature: 927 ℃;
7. Titanium tube
The main feature is acid and alkali resistance, especially suitable for strong acids and alkalis. However, the fatal disadvantage of titanium tube materials is that they are difficult to weld and bend, and are prone to fracture. Generally, vacuum annealing can solve this problem, but titanium welding rods are used for welding.
8、Incoloy
Incoloy is a nickel chromium iron alloy. There are many types of Incoloy alloys, such as Incoloy800, Incoloy800H, Incoloy800HT, Incoloy825, Incoloy840, Incoloy901, Incoloy825, Incoloy20, Incoloy320, etc.