Common forms of damage to heating coils in quenching inductors for semi-circular crankshafts

Burn of coil
1. The coil collides with the workpiece. The reason is that the coupling gap is too small, which may be due to coil deformation or excessive wear of the spacing positioning block. According to the regulations of the induction heating equipment factory, the wear of the interval positioning block cannot exceed 0.3D (D is the distance between the effective ring inner diameter and the contact end of the positioning block).
2. If the surface of the shaft neck is not cleaned thoroughly, residual iron filings will be magnetically attracted and agglomerated, forming a shell layer with engine oil residue. The shell will form a conductor between the coil and the workpiece, generating sparks when heated and energized, causing both the journal surface and the coil to burn simultaneously. Therefore, whether the crankshaft neck is cleaned thoroughly before quenching is an important factor determining the service life of the sensor.

Coil burnout
Coil burnout is a common form of failure. The reason is that when a large current passes through the coil, there is insufficient or no cooling. The latter is usually due to operational errors, which often occur when the machine tool has water shortage protection; However, insufficient cooling requires careful analysis.
1. Insufficient water flow can cause blockage of the coil channel during use due to debris and scale buildup. In the past, a customer reported that the black adhesive tape wrapped around the pipe joint hung into the water inlet, causing a decrease in water flow and burning out the coil.
2. Scale blockage is caused by the high hardness of the cooling water. When the CaO content in the water is less than 60mg/L and the water temperature is higher than 45 ℃, scale will form, which will intensify with the increase of water temperature.
3. There should be no air in the water that affects the cooling of copper pipes. The enemy is that the water contains air, and bubbles cause oxidation of the high-temperature copper pipe. This oxide layer is a poor conductor of heat, which slows down the cooling of the copper pipe. Therefore, modern cooling systems have adopted closed circulation systems; And advanced cooling systems are equipped with centrifugal air separators, which can remove even the smallest bubbles.
4. Cooling water should not be too pure. Distilled water should not contain salt or impurities, and is generally considered the ideal cooling water; However, water that is too pure has lower cooling performance than water that contains salt. Therefore, some factories have stipulated that the content of CaO in water should be greater than 10mg/L (German hardness greater than 1 degree) to improve its cooling capacity.

Bubbling on the conductive surface of the coil
There are multiple reasons for this. In terms of copper material quality, oxygen free high conductivity copper should be used first to prevent the combination of oxygen-containing copper and hydrogen, which can produce water vapor. The pressure generated by water vapor can lead to the formation of cracks or bubbles. In addition, when a large current passes through a conductor and bubbles appear in the water due to insufficient cooling, black copper oxide is produced on the inner wall of the copper tube, and bubbles are often found on the working surface. The mechanism is currently being studied.

Welding joint cracking and conductive tube cracking
The reason is due to the continuous rapid cooling and heating of this part, so the design should avoid excessive current density and large differences in the cross-section of the transition section. When a conductor is energized, the temperature increases in small areas of the cross-section and decreases in large areas, resulting in uneven thermal expansion and contraction;