A flexible edge-dam or side-dam chain is made by stringing discrete separate edge-dam blocks, usually of metal, onto a looped endless flexible metallic tension member such as a ribbon, followed by welding that ribbon into a loop before assembling the last edge-dam block, using the split-block technique described in U.S. Pat. No. 3,865,176 of Dompas et al. The looped edge dams are normally used in pairs which travel along with the belt or belts to complete the defining and sealing of a mold cavity or space. Alternatively, a pair of wire ropes may replace the ribbon.
The edge dams of the prior art are described in the patents referenced herein, which are all assigned to the same assignee as the present invention. The mutually abutting faces of the dam blocks have normally been flat or effectively lying in one plane as shown in the referenced patents. This plane of abutment is normally perpendicular to the mold cavity. On the whole, these prior-art edge dams have nearly solved the above problem of presenting to the freezing metal a continuous, unbroken surface to be cast against. However, the strap or wire ropes which carry the blocks and unite them into a chain require to be fitted loosely into the corresponding slots or holes in the blocks in order to permit self-adjustment of each block along the length of the strap or wire ropes. Yet, this needed looseness may permit tilting of the blocks when in the casting section of the casting machine, especially the tilting of tall blocks used for casting thick sections such as wire bar.
The looped edge dams should present to the molten metal a smooth, continuous, substantially unbroken surface. Slightly tilted or cocked dam blocks cause the edge of a frozen metal slab to be correspondingly jagged or discontinuous. Then cracking or breaking may occur at such points of stress concentration, whether immediately, or during rolling, or later during fabrication of finished products. The problem can be especially acute in casting the generally rectangular bar which is to be drawn into wire, notably copper wire. The intense wire-drawing process results in laps at such discontinuities and consequently slivers and cracks. Fine wire may break within the dies as a result, or wire may locally overheat in electrical service.
A second undesirable result of tilted or cocked edge-dam blocks is that uneven contact with stationary longitudinal edge-dam guides results. Such guides are used in the casting of bar shapes. They are a significant heat sink; by their contact with the outer faces of the passing edge-dam blocks, the guides extract heat and pass the heat to the cooling water in the channel drilled through each of them. Uneven contact between guides and dam blocks not only slows down the freezing process; the sharp discontinuities of cooling-rate between adjacent misaligned edge-dam blocks compounds the above-mentioned problems by adding crystalline discontinuities and internal stresses. Moreover, the resultant temperature differences cause the immediate rolling of the hot cast bar to be unevenly severe in hot work from point to point.