Abstract
The present paper sums up some observations concerning sideledge in industrial aluminium cells. Furthermore, some laboratory experiments with freeze formation on a gas-cooled cylinder (coldfinger) immersed into bath and metal are reported. The freeze formed during contact with bath did not melt away when the coldfinger was lowered deep into the metal; this is in accordance with a recently suggested hypothesis concerning sideledge facing the metal. It appeared, however, that the freeze melted away rapidly at a zone near the metal-bath interface, even though stirring or wave motion was not applied. This observation gave rise to a new interpretation of the conditions at the ledge-metal-bath boundary. It is suggested that the deep depression or “trench” formed at that zone is caused by a high heat transmission coefficient between metal and ledge at the meniscus formed near the ledge-metal-bath boundary.