| 摘要 |
<p>A method of forming a layer of coating of tin on an inner surface of a copper pipe by passing a substitutional electroless tin plating liquid through an inner portion of the pipe, comprising a first plating step in which the plating is done by regulating a deposition rate of a layer of coating of tin so that a value obtained by dividing a total copper ion concentration in the portion of the plating liquid which has passed through the inner portion of the copper pipe and just flowed out therefrom by a concentration of bivalent tin ions in the same plating liquid becomes not more than 0.8, and a second plating step in which the plating is done with the temperature of the plating liquid set higher than that of the plating liquid in the first plating step. A plating liquid preferably used is a plating liquid containing 0.05-0.3 mol/l of positive bivalent Sn ion, 0.5-2.0 mol/l of thiourea, 0.5-2.0 mol/l of sulfuric acid, 0.05-2.0 mol/l of alkyl benzene sulfonic acid and 0.5-5.0 g/l of nonionic surface active agent. A corrosion resisting internally tin-plated copper pipe used as a water supply pipe, a hot water supply pipe and a heat exchanger pipe can be manufactured in the form of a long size coil, and a layer of coating of tin thus formed has small scatter of thickness, and high adhesion and a high corrosion resistance.</p> |
