Today in 1970, US Patent 3488213 A was issued, an invention of Frank A. Bellato, assigned to Schlitz Brewing Co., for his “Method and Apparatus For Applying a Coating to the Interior Surface of a Hollow Article.” Here’s the Abstract:

A method and nozzle assembly for coating the interior surface of a barrel with wax or other coating material The nozzle assembly is adapted to be inserted within the bunghole of the barrel and includes a central reservoir which contains melted wax. The Wax is continuously pumped to the reservoir and overflows from the reservoir so that a continual flow of melted wax is achieved. The melted wax is atomized by a pressurized stream of air which is ejected through an orifice into a discharge nozzle located above the level of the wax. In addition to the primary air stream, a pair of auxiliary air jets are employed which are directed laterally towards the ends of the barrel and the auxiliary jets aid in atomizing the wax and directing the atomized wax towards the ends of the barrel.

This invention relates to a method and apparatus for applying a coating to the interior surface of a hollow article and more particularly to a method and apparatus for applying wax or similar coatings to the interior of beer barrels.