Keywords: cooling, water, saltwater, caustic soda solution, Water purification, Sodium chloride aqueous, Sodium carbonate, Common concentration, Usage temperature, Cooling characteristic,

Comparison and application of cooling performance of water, saltwater, caustic soda solution, and sodium carbonate solution

Table: Properties of Water, Salt, and Alkali Solutions

　　The use of low concentration sodium carbonate aqueous solution is the same as that of sodium chloride aqueous solution, but its cooling capacity is slightly lower At high concentrations, it is easy to absorb carbon dioxide and gradually change its composition

Media name	Water purification	Caustic soda aqueous solution**	Sodium chloride aqueous solution	Sodium carbonate solution
Common concentrations		5%-15%	5%~15%	3%-20%
Usage temperature	≤40℃	≤60℃	≤60℃	≤60℃
Cooling characteristics	(1) The steam film stage is long and prone to producing bubbles, which can cause soft spots on quenched workpieces. (2) Is the cooling rate in the range of 300-200 ℃ higher than 650~550 ℃ High speed in the range	Due to the addition of salt and alkali, the steam film stage is greatly shortened, and the cooling capacity is significantly improved. As the salt and alkali content increases, the maximum cooling rate continues to increase. However, when the salt and alkali content approaches the saturation solubility of water, the cooling rate decreases due to the increase in solution viscosity. At the same concentration, the cooling capacity of caustic soda aqueous solution is the highest, followed by sodium chloride aqueous solution, and then sodium carbonate aqueous solution
Scope of application	Small section carbon steel (immersion quenched)	Carbon steel (quenching of tools and parts with simple shapes and high hardness requirements)	Carbon steel (effective thickness 30-100mm, quenched with salt water or salt water oil)	The use of low concentration sodium carbonate aqueous solution is the same as that of sodium chloride aqueous solution, but its cooling capacity is slightly lower
	Low alloy structural steel with larger cross-section (water air water intermittent quenching) Induction heating spray quenching of carbon steel and low-alloy steel		Alloy structural steel (40Cr, 40CrMoV, effective thickness 50~150mm, 38CrabMoAl effective thickness>80mm to be quenched with salt water and oil)	15%~20% sodium carbonate aqueous solution suitable for quenching bearing steel with effective thickness>25mm
hardenability*	—	7mm	6mm	4.6mm
Stability	Good, with reduced cooling ability after using oil and soap	At high concentrations, it is easy to absorb carbon dioxide and gradually change its composition	Good	White precipitate formed when encountering BaCl2
Surface condition of the workpiece	Relatively smooth	Smooth and silver gray in color	It is relatively smooth, and the workpiece is prone to rusting if not treated with rust prevention in a timely manner	Relatively smooth

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