Salt bath hardening is a fast and efficient process that delivers visible results.
By design, salt baths can be divided into internally or externally heated baths and electrode baths.
Internally and externally heated salt baths
This type of bath is designed for hardening high-speed steel, various metal sheets and profiles at 450–525 °C. The baths are 6 to 8 meters long and can reach a power of hundreds of kilowatts.
Externally heated baths are round or rectangular steel vessels placed in a shaft with heating elements. In internally heated units, tubular heaters are placed directly inside the bath.
Internally heated baths have much lower heat losses than externally heated ones, and they use almost ten times fewer heating elements. They are also safer to operate.
Electrode salt baths
An electrode salt bath is a salt-filled bath with electrodes immersed in it. This design ensures uniform and fast heating, which makes it especially popular for hardening tools.
Electrode salt baths with offset electrodes, made as round or rectangular rods, are becoming increasingly common. In the bath, the electrodes are placed 20–25 mm apart. The current passing between them heats the salt and creates intense thermal circulation: salt particles rise and spread along the upper edge.
Hardening high-speed steel in a salt bath is 5 times faster than in a gas-fired or electric furnace, and the heat is distributed evenly over the entire surface of the part.
Another advantage is that only part of a tool, such as a drill, can be heated to the required temperature. The drawbacks of salt bath hardening of high-speed steel are that immersing a wet tool causes heavy splashing of salt, and the fumes from the bath are harmful to health. That is why strict adherence to safety rules is essential.
Today there are single-phase and three-phase electrode salt baths with a power of 20–150 kW, rated for temperatures up to 1300 °C.
Salt bath hardening, like barium bath hardening, is widespread in Ukraine. During hardening in molten salt, parts are coated with a layer of salt, which provides good protection against oxidation.
The most important thing in metal hardening is following the process correctly. When everything is done right, the result is hard and strong hardened steel.