Heat exchanger prodn. by expanding bores in rolled metal block - employing weld-stop powder comprising metal oxide and opt. talc and metal silicate

摘要

The parent patent described a method for producing a flat heat exchanger by producing bores in a metal block, applying a weld-stop agent to the bores, elongating the block by rolling in the direction along the bores and then expanding the bores. The weld-stop agent comprises a dry powder mixt. of talc and a metal oxide and/or silicate, a dry pulverulent metal oxide which is soluble in dilute acid or a mixt. of at least two such metal oxides. The weld-stop agent adheres uniformly well to the bore walls but is readily removed after bore expansion. Any weld-stop residues left in the bores are too small in amt. to affect heat transfer or cause corrosion of the heat exchanger material.