A Roll Caster to Cast Clad Strip

Abstract

A tandem-type roll caster that can cast a three-layered clad strip was developed by mounting one twin roll caster on another twin roll caster. In this caster, the base strip is cast by the upper twin roll caster, and the overlay strips are cast by the lower caster. The three strips are metallurgically bonded by the lower caster. This study investigated three aspects of this caster. First, the clad ratio could be controlled by the solidification lengths of strips from the upper and lower twin roll casters, and a clad ratio of 1:8:1 was attained. Second, although it is known that fabrication of clad strips from Al-Mg alloy and other Al alloys is very difficult, the clad strip with the Al-Mg alloy as the base strip or the overlay strip could be cast. Finally, by adding scrapers, the caster could cast the clad strip with a base strip having a lower melting point than the overlay strip. Element strips of the clad strip are made by many processes, such as direct chill (DC) casting, scraping of the ingot surface, heat treatment, hot rolling, and cold rolling. Typically, surface treatment and hot rolling are used to clad the strips. Since many processes are required, clad strips require consume much energy. Therefore, producing clad strips is expensive. A vertical-type tandem twin roll caster was developed to cast clad strips. This caster has the advantages of process saving and energy saving, and so can fabricate economical clad strips. In the fabrication of clad strips, control of the clad ratio is very important. In the brazing sheet for automobile radiators, the base strip is made from AA3003 and the overlay strips are made from AA4045, and the clad ratio is usually 1:8:1. In the present study, a clad strip with a clad ratio of 1:8:1 was attained. The cladding by hot rolling of Al-Mg and other aluminum alloys, which is considered to be a very difficult process, was also investigated. Clad strips with either a base strip or an overlay strip of an Al-Mg alloy were cast by the roll caster. Although the cladding was not easy, the Al-Mg alloy could be cast into the clad strip. In addition, a clad strip with a base strip having a lower melting point than that of the overlay strip was investigated. Such cladding cannot be cast by the vertical-type tandem twin roll caster as mentioned above because the base strip is re-melted from the heat of the overlay strips. In the present study, a scraper was developed and adopted to cast a clad strip with a base having a lower melting point than that of the overlay strips. This type of clad strip could be cast because the scrapers prevented the re-melting of the base strip. In this paper, these three aspects of fabrication are reported.