Chemical browning bath for metals - where one electronic temp. comparator maintains bath at constant temp. and concn. by adding water when specified bath temp. is exceeded

摘要

The bath is provided with heaters so it can be kept at its b.pt; and a temp. sensor is immersed in the bath to determine its actual temp. (Ta). The sensor feeds signal (Ta) to a controller, which is supplied with a desired bath temp. (Tref), and compares the two values. When Ta exceeds Tref, the controller switches on a pump so that water is fed into the bath, pref. from a water rinsing bath located next to the browning bath. The browning bath pref. has heaters employed to attain a temp. (To) which is below Tref. Once the bath has reached temp. (To), the heating power is reduced to a lower value. The controller pref. has a lamp indicating that Tref has been exceeded, and an acoustic alarm operated when Tref has been exceeded for a prescribed time. Used e.g. in a browning bath consisting of a 35% NaOH lye with optimum working temp. (Tref) of 142 deg.C. The invention holds both the operating temp. and the NaOH concn. constant, both essential factors if a constant colour is to obtd. on metals immersed in the bath.