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Continued from page 11


PAG quenchants are a copolymer of ethylene oxide and propylene oxide. PAG polymer quenchants are used in the aerospace industry to control and minimise the distortion occurring in the quenching of aluminium. Typically these quenchants are governed by AMS 3025 [5]


, and are either Type I or


Type II quenchants. Type I quenchants are single PAG polymers, while Type II quenchants are multiple molecular weight PAG polymers. Each offers different benefits. Because of the higher molecular weight of the Type II PAG quenchants, lower concentrations can be used.


PAGs exhibit inverse solubility in water. They are completely soluble in water at room temperature, but insoluble at elevated temperatures. The inverse solubility temperature can range from 60°C to 90°C depending on the molecular weight of the polymer, and the structure of the polymer. This phenomenon of inverse solubility modifies the conventional three-stage quenching mechanism [4] great flexibility to control the cooling rate.


and provides


The cooling rate of these polymers can be readily varied to suit the specific application by changing the concentration, quenchant temperature, and the amount of agitation.


The concentration of the polymer influences the thickness of the polymer film that is deposited on the surface of the part during quenching. As the concentration increases, the maximum rate of cooling,


and the cooling rate in the convection phase decrease. The benefits of quenching aluminium in the PAG quenchants are shown in Figure 2.


Agitation has an important effect on the quenching characteristics of the polymer quenchant [6]


. It


ensures uniform temperature distribution within the quench tank, and it also affects the quench rate. As the severity of agitation increases, the duration of the polymer-rich phase decreases and eventually disappears, and the maximum rate of cooling increases. Agitation has comparatively little effect on the cooling rate during the convection stage when using polymer quenchants.


In this short article, we’ve discussed the benefits of using PAG quenchants to control the distortion of aluminium parts, while still maintaining properties. PAG quenchants can be used effectively to reduce distortion, and costly straightening, without compromising on the desired properties of the part being worked.


References [1] SAE International, Heat Treatment of Wrought Aluminium Alloy Parts, Warrendale, PA: SAE International, 2015.


[2] K. Speith and H. lange, Mitt. Kaiser Wilhelm Inst. Eisenforssch, vol. 17, p. 175, 1935.


[3] A. Rose, Arch. Eisenhulles, vol. 13, p. 345, 1940. [4] G. Totten, C. Bates and N. Clinton, Eds., Handbook of Quenching and Quenchants, Metals Park, OH: ASM International, 1993.


[5] SAE, “AMS 3025E Polyalkalene Glycol Heat Treat Quenchant,” SAE, Warren, PA, 2018.


[6] P. M. Kavalco, L. C. Canale and G. E. Totten, “Distortion Reduction by Aqueous Polymer Quenching of Aluminium Alloys,” Industrial Heating, vol. 2, no. February, p. 39, 2011.


[7] P. M. Kavalco, L. C. Canale and G. E. Totten, “Quenching of Aluminium Alloys: Property Prediction by Quench Factor Analysis,” Heat Treating Progress, pp. 23-28, May/June 2009.


Figure 2. Comparison of distortion using different quenchants for two different aluminum alloys, AA 2024 (top) and 7475 (bottom). From top to bottom, for each alloy, the quenchants are cold water; hot water at 60°C; 12% PAG, and 20% PAG. Same agitation was used for all samples [6]


.


LINK www.houghtonintl.com


12


LUBE MAGAZINE NO.149 FEBRUARY 2019


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