With the NEMA apparatus for repeated scrape abrasion, ultimate so ftening by R22 was found to be the same for AI/PE, PEl and PE/PE and FU regardless of their initial value. The differences between enamels which appear significant after short exposures to R22 became smaller as the exposure time was increased. The scape resistance of Polyimide wire was unaffected by R22.Using Emmons's overload test apparatus, data on the burnout resistance , the retained dielectric strength after a temperature excursion and the blister resistance of enamels in R22 were determined. All these three characteristics were studied using essentially a single test, by varying test parameters.In general, the burnout resistance in R22, and after exposure to liquid R22, was found to be sharply lower than that determined in air. A 16 hour soak in R22 vapor gave an abnormally high burnout resistance compared to a 3 day liquid soak or to no soak at all. The effect of soaking time in liquid R22 is smaller on burnout than it is on softening.The ranking of enamels based on burnout temperatures in air did not necessarily hold true when tests were made in refrigera nt. AI/ PE ranked higher than PE/PE in air , but ranked lower in refrigerant. The difference between AI/PE and PEl seemed significant in air, bu t it became considerably smaller in refrigerant.The thermal excursion test gives results consistent with those from the burnout test in refrigerant. However, the test becomes more discriminating when comparisons between enamels are made at more than one temperature, and hence shows considerable merit.Blistering characteristics were obtained from visual observations of the thermal excursion test specimens. A separate blister test was not used. The merits of performing the blister test in this manner are discussed and the minimum temperature at which blistering occurs is proposed as a figure of merit. AI/PE was found to be more blister prone than PEl or PEAL However, all of them blistered at 120°C after a ten day soak in liquid R22.Because the interactions of an enamel and refrigerant 22 are time dependent. it is suggested that the rate of absorption of R22 IntroductionRefrigerant 22, monochlorodifluoromethane, (R-22) has a high solvent power and tends to dissolve or to be absorbed to some extent in many polymeric materials. Enameled wires when immersed in R-22-oil systems as in hermetic motors are softened by the R-22 in the system. In addition to the softening effect on the enameled wire, blisters in the enamel may occur due to the combined effects of long periods of absorption followed by resistance heating of the windings. This tends to release the R-22 vapors rapidly through the enameled wire coating.Polyesters, modified polyesters, polyesterimides and polyesteramide-imides have been tested and used in R-22 hermetic systems because of their good solvent resistance and thermal stability. Aromatic polyimides and polyamide-imides have excellent solvent resistance and thermal stability and are also being used in hermetic systems.
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