3.3. As to Cooling

Quenching tank:

In order to quickly cool down the workpieces, the tank is filled with water or oil, for example, and it must constantly be kept cool. That is ensured by means of cooling coils, but also by the regular feed of coolant (with simultaneous discharge). Workpieces have to be moved in quenching tanks so that cooling down is effected as quick as possible; thus, steam bubbles quickly come off the workpiece.

The quicker cooling is effected, the higher is the degree of hardness!

As to mild cooling processes, heated quenching media can also be applied in heated tanks (hot baths).

Figure 16 - Quenching tank

Quenching media:

According to the desired properties of the workpieces, rough or mild quenching media are used.

Rough quenching media	-	great strength and little elasticity of the workpiece to be treated
Mild quenching media	-	little strength and higher elasticity of the workpiece to be treated

Quenching media	Effect
Acidified water	very rough
Salt-containing water (10% salt)	rough
Ice-cold water (2° C)	very powerful
Pure water (20° C)	powerful
Soluble oil emulsion or hot water (40° C)	less powerful
Petroleum, oil, train oil	mild
Compressed air	very mild
Air	very mild

The rougher the quenching medium, the harder is especially the case of the workpiece!

Temperature data may be given in various units. Apart from the units "degree centigrade" used herein, the units "Kelvin" or "Fahrenheit" may be used.

Conversion table for temperature data

Centigrade	Kelvin	Fahrenheit
0°C =	273 K =	32 F
100°C =	373 K =	212 F

Which requirements are made on quenching tanks?
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What are the effects of the use of a rough quenching medium onto the workpiece?
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