Observation of Pips Formed on Ag/SnO2 Contacts in DC14 V-21 A Resistive Circuit

Abstract

In order to study the growth of transferred pips, we operated Ag/SnO 2 12 wt% contacts mounted on an electromagnetic relay in a DC14V-21 A the resistive circuit as make-only contacts, and took photographs of the transferred pips formed on a cathode surface. In this experiment, the pip shape was different depending on whether the movable contact was the cathode or anode. When the movable contact was the cathode, pip grew high, and became 0.7 mm height at maximum. Sometimes, the pip collapsed. Sticking occurred, when the pip shape became H/Dr ≥ 2.5 and H/Ga ≥ 0.5, where H is pip height, Dr is diameter of pip root, and Go is gap length of open contacts. Judging from this result, we can predict that when a pip grows to H/Dr ≥ 0.5 and H/Ga ≥ 0.5, sticking will easily the occur. When the movable contact was the anode, no tall pip was formed, because of pip breakages. Sticking occurred for three samples although the pips grew to H/Dr ≥ 0.5 and H/Ga ≥ 0.5. In this case we could not obtain a numerical relationship between of the pip shape and the occurrence of sticking.