mill scale

English

Noun

mill scale (uncountable)

1. The flaky surface of hot rolled steel, which will protect the steel against atmospheric corrosion until it is removed or flakes off. The scale should be removed before paint is applied.
   • 1951 October, “Preventing Rail Corrosion”, in Railway Magazine, page 648:

     Recently the Great Northern Railway, U,S.A., which has a considerable mileage of line bordering the Pacific seaboard, has put in service mobile equipment for applying anti-corrosion treatment to rails. An old motor-car has been adapted to carry two oxy-acetylene flame-cleaning heads, which simultaneously clean both sides of both rails of all mill-scale and rust as the car is hand-propelled forward; men follow to brush away the loosened material; the final operation is that of spraying both rails, by means of paint guns carried on a trolley, with a corrosion-resisting compound.