Induction brazing is a process that uses induction current to heat the workpiece, with the main source of heat being the resistance heating generated in the workpiece by the induction current. During induction brazing, the part of the workpiece to be brazed is placed in an alternating magnetic field, and the heating of this part of the base material is achieved through the resistance heating generated by the induction current in the alternating magnetic field.
Since the heat is self-generated, the heating speed is fast. The oxidation of the workpiece surface is less than in the furnace brazing, and it can prevent the growth of the grain size of the base material and the occurrence of recrystallization. It can also achieve local heating of the workpiece.
Induction brazing is widely used for brazing of steel, stainless steel, copper and its alloys, high-temperature alloys, etc. It can be used for both soft brazing and hard brazing. It is mainly used for smaller workpieces, especially for symmetrical shaped workpieces, such as tubular joints, flange connections, shafts and discs, etc., and it is easy to achieve automation and rapid local heating, which is suitable for mass production.
Induction brazing equipment mainly consists of an AC power supply and an induction coil, as well as some auxiliary clamping and positioning fixtures. The AC power supply can be divided into low-frequency, intermediate frequency and high-frequency according to the frequency. Low-frequency is rarely used for brazing, while intermediate and high-frequency are commonly used. The frequency of the generator in the field of induction brazing is 30-150kHz, or even higher, depending on the size of the welding area and the thickness of the material.
There are two ways to place the induction coil: one is to place it outside the container, relying on the inductor to heat the welded joints, and the material of the container is a conductor; the other is to place the induction coil inside the container, and the welded joints are directly heated by the induction coil. In this case, glass containers are often used to facilitate the observation of the brazing process.
The induction coil is a component that transfers induction current and is designed according to specific joint designs, especially for complex shaped joints, which are usually completed by empirical and experimental methods. When encountering components with different brazing cross-sectional sizes, the heating method can be adjusted by combining various basic design forms.
The induction coil should ensure fast and uniform heating, high efficiency, etc. The induction coil is usually made of 4-12mm round or flat pure copper pipes, and water is used for cooling during operation. The wall thickness of the pipe should be less than the depth of current penetration, generally 1-1.5mm.
There should be a gap between the induction coil and the welded joints to avoid short-circuiting, but in order to improve the heating efficiency, the gap between the turns of the induction coil and between the induction coil and the welded joints should be minimized. When induction brazing, some auxiliary tools are often needed to clamp and position the workpiece. When designing, the parts of the fixtures adjacent to the induction coil should not be made of metal to avoid induced heating. The joint clearance for induction brazing is usually 0.038-0.051mm, mostly using silver-based brazing materials.
Various brazing materials can be used for induction brazing. Since the brazing heating is fast, the brazing materials and brazing flux are pre-assembled during assembly. Induction brazing can be carried out in the air or in a vacuum or protective atmosphere. In this case, both the workpiece and the induction coil can be placed in the container, or the container containing the workpiece can be placed in the induction coil, and the container can be evacuated or filled with protective gas.