A brief analysis of the characteristics of induction heating of non-ferrous metals using medium frequency annealing equipment

Aluminum, brass, copper, titanium and other non-ferrous metals can also be induction heated using medium frequency annealing equipment. However, the properties of different non-ferrous metals vary greatly. From the perspective of thermal conductivity, copper and aluminum have good thermal conductivity, while alloys have poor thermal conductivity. Any metal heated in air undergoes an oxidation process. However, when titanium alloys are heated above 600°C, in addition to forming oxide scale, they will also absorb oxygen, nitrogen, and hydrogen (surface contamination). The surface temperature cools quickly after coming out of the furnace, resulting in a large temperature difference between the inside and outside, leading to cracking during the forging process and aggravating the uneven distribution of the internal and external deformation of the billet.

Compared with steel, titanium alloys are more viscous and have poor fluidity. In the induction heating specifications, slow (slow) preheating must be followed, and then heated to the forging temperature. The original blank is removed from the surface, coated with glass powder, and the heating furnace remains slightly oxidized. atmosphere. Ingot extrusion: The ingot is heated in a metal sleeve. The metal sleeve material is made of material that does not react with the base metal at the extrusion temperature, generates a low melting point eutectic, has similar mechanical properties to the base metal, and does not bond with the mold material. metal materials, such as copper and mild steel. Power frequency (50Hz) is usually used, and medium frequency heating is only used when the diameter is less than 120mm. Aluminum has good thermal conductivity, allows fast heating, and short heating time. First, the induction heating frequency is 50Hz. Low and medium frequencies are only used when the diameter is less than 120mm. The induction heating frequency selected for copper is wider than that of aluminum.

The degree of surface oxidation of non-ferrous metals when heated is related to the alloy composition, ingot size, heating temperature, heating time and atmosphere in the furnace. For example, alloys such as white copper, tin bronze, low zinc brass, aluminum bronze are easily oxidized at high temperatures, and The oxide film is incomplete and should be heated in a slightly reducing or neutral atmosphere. The oxide film formed by heating high-zinc brass, copper alloys containing manganese and cadmium, and nickel alloys is thin and hard with high density, which can reduce further oxidation and can be heated in a micro-oxidizing atmosphere. Oxygen-free copper is heated in an oxidizing atmosphere. The penetration of oxygen into the copper not only produces surface oxidation, but also intergranular oxidation, which can generate water vapor with the hydrogen adsorbed during casting, causing cracking in hot rolling or blistering during annealing. Therefore, oxygen-free copper should be heated in a reducing or neutral atmosphere.

The methods to reduce oxidation and control the atmosphere in the furnace when heating non-ferrous metals are similar to those used when heating steel, such as using medium frequency annealing equipment for induction heating, flame furnaces to adjust the ratio of air and fuel, control the degree of combustion, control furnace pressure and use protective atmosphere etc.