Two plastic tank floats in separate toilets in one dwelling failed within a relatively brief period of time. Examination of the floats and of a brass connecting rod revealed that the fracture occurred at the base of the threaded hole in the nipple and was brittle in nature. The fracture surfaces were coated with zinc oxide. It was concluded that the failure resulted from improper repairs and/or adjustments, including the use of a cosmetic zinc oxide cream as a lubricant. The cream initiated deterioration of the originally ductile plastic, causing it to become brittle and fragile.
David O. Leeser, Failure of Two Plastic Toilet-Tank Floats, Handbook of Case Histories in Failure Analysis, Vol 1, Edited By Khlefa A. Esaklul, ASM International, 1992, p 434–436, https://doi.org/10.31399/asm.fach.v01.c9001127
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