The rails are quenched and heat treated using a medium frequency induction heating machine. Are you using the correct cooling method?

When rails are quenched and heat treated using a medium-frequency induction heating machine, the cooling method is usually determined based on technical requirements and cross-section size. There are currently two commonly used cooling methods - spray cooling and jet cooling. Today, the editor will introduce to you these two cooling methods.

Spray cooling uses spray (a mixture of water and air) to directly cool heated steel treads. Its performance characteristics are:

1. The cooling is uneven and the nozzles are easily clogged, causing local cooling to be too fast and leading to the formation of structures such as martensite.

2. It is sensitive to surface conditions. If there is rust, oil, etc. on the surface, the cooling rate will be very different, resulting in low hardness or the emergence of martensitic structure.

3. The hardness decreases from the upper fillet of the rail to the lower jaw, resulting in reduced wear resistance.

Jet air cooling uses high-efficiency nozzles to spray and cool the three sides of the heated rail with a single compressed air. The outlet pressure is 0.2-0.3MPa. Its characteristics are:

1. Uniform cooling, stable pressure, and good surface hardness uniformity after cooling.

2. It can avoid the generation of martensite, obtain pearlite structure, and avoid peeling, falling off and damage during use.

3. There is almost no change in the fillet and jaw hardness of the rail, it is not sensitive to surface conditions, the process is reliable, and the design is safe.

Currently, spray is a relatively mature process, but spray (a mechanical mixture of water and air) has problems such as uneven cooling, low hardness, shallow hardened layer, poor wear resistance, and short service life. The air jet uses a single medium, cooling evenly, completing the transformation of austenite to pearlite structure, ensuring qualified hardness and structure, and meeting the use requirements of rails. However, it should be noted that the steel type cooled by jet air should have a eutectoid composition, and its carbon content should be above 0.70%.

From the above analysis, it can be seen that spray cooling and air jet cooling each have their own advantages and disadvantages. Therefore, in the actual production process, we should choose the appropriate cooling method according to our own requirements.