AN APPARATUS FOR THE CONTINUOUS CASTING OF METAL BARS,PIPES AND SHEETS

Abstract: An apparatus for the continuous casting of metal bars, pipes or sheets, comprising a chill mold (4) for receiving the molten metal (1), a cooler (3) fitted around the chill mold (4), a refractory lining (2) which protects the cooler (3) from the molten metal, members (9) for withdrawing the metal bar (7), pipe or sheet from the chill mold (4), and a highly thermally conductive medium which fills the gap (6) between the cooler (3) and the chill mold (4).

Description: An apparatus for the continuous casting of metal bars, pipes and sheets The present invention relates to an apparatus for the continuous casting of metal bars, pipes and sheets, and particularly to an apparatus which has a chill mold for receiving the molten metal, a cooling member fitted around least the rear part of the chill mold as seen in the with¬ drawing direction, a refractory lining protecting at least the cooling member, and members for the continuous with¬ drawing, from the chill mold, of the bar, pipe or sheet which has solidified in the chill mold. The object of the present invention is to promote the transfer of heat from the material being cast and thereby increase the casting rate and obtain a more advantageous crystal structure in the casting, at least when copper or copper alloys are being cast. Previously known there are devices for the continuous cast of metal bars, pipes or sheets, having a chill mold made o a refractory material for receiving the molten metal, and around the chill mold there has been 'fitted a cooler with water or molten metal flowing in its ducts. The chill mold may be made of graphite, and during casting the heat trans¬ ferred from the solidifying molten metal and the solidifie metal is directed further to a cooling medium circulating i the cooler. It is very important -that this transfer of heat is effective, for it decides the rate at which the continuo casting can be carried out. A metal bar, pipe or sheet contracts when solidifying and cooling, and thereby a gap forms between the piece being cast and the chill mold; the gap is known to complicate th OMPI transfer of heat from the piece being cast to the chill mo This gap cannot be completely eliminated because, if it is then there is the risk that the casting adheres to the chi mold if the mold converges in the withdrawing direction. Owing to the low heat conductivity of air and gases, even very narrow gap caused by contraction constitutes a considerable obstacle to the transfer of heat. Therefore, among experts the idea has prevailed that this gap due to contraction between the chill mold and the casting is the reason why the transfer of heat in the existing casting apparatus is considerably less advantageous than it ought to be if only the transfer of heat in the chill mold, the transfer of heat in the cooling material and the heat transfer coefficient in the cooling ducts of the cooler ar taken into account. It has now been shown surprisingly that the " above-mentione general conception has been correct only in part-. Measurem and calculations which have been performed have shown that in the casting apparatus used there appears considerable heat resistance also in the interface between the chill mo and the cooler. This heat resistance is particularly significant in the continuous casting of metal sheets. The probable reason for this is that, owing to the thermal expansion movements of the material, gaps form between the chill mold and the cooler, and it has been impossible to prevent the formation of such gaps even by means of bolt joints. Studies have now shown that if the reducing effect of these gaps on the transfer of heat could be eliminated, it would be possible to improve the efficiency of the casti apparatus substantially even if nothing were done with respect to the air gap between the casting and the chill mo The formation of gaps between the chill mold and the cooler could theoretically be eliminated by means of tight bolt joints or by a suitable design of the surfaces of these t members, but in practice this has not produced the desire results. For this reason-, -an attempt has now been made to find other solutions to this problem. The object of the present invention is therefore to provi an apparatus for the continuous casting of metal bars, pi or sheets, an apparatus in which the transfer of heat fro the solidifying melt and the cooling metal piece is more effective than previously so that the casting rate can be increased and simultaneously a product with improved crys structure can possibly be obtained. The main characteristics of the invention are given in accompanying Claim 1. In the alternative according to the present invention, the gap or gaps between the chill mold ' and the- cooler are fill with a medium having a good thermal conductivity, such as molten metal or molten salt, in which case this gap is advantageously connected to an outside expansion vessel. I practice it is easy to find usable materials with a good thermal conductivity in the professional literature of the field, so that listing such materials in this context has been considered unnecessary. It can, however, be mentioned that a metal melt containing tin at least about 50 % by weight has proven to be one such thermally conductive material. Filling a gas space between two solid surfaces with molten metal in order to improve the transfer of heat is in principle known per se. This procedure has even been propo for use in casting apparatus in order to improve the trans of heat between the chill mold and the casting during the continuous casting of metal bars, pipes and sheets. The OMPI procedure has not, however, produced the desired results b has' involved obvious and very great practical difficulties in the form of, for example, leakages. For this reason thi procedure has not gained any practical significance. Durin » the development of the present invention it was surprising to observe that most of the thermal resistance appeared between the chill mold and the cooler and not mainly betwe the chill mold and the casting, as had been assumed previousl . Furthermore, it was surprising that the procedure which ha previously been applied to the improvement of the transfer of heat between the chill mold and the casting and been fo difficult to use for that purpose proved to be highly applicable to the improving of the transfer of heat betwee the chill mold and the cooler. Thus, in the alternative according to the " present inventio a liquid with a good thermal conductivity, such as a molte metal, is used for filling the gap between the chill mold and the cooler. In this alternative the heat-transferring medium does not come into contact with the metal being cas and, owing to the drop of temperature between the walls of the chill mold, the boiling point of the heat-transferring medium need not necessarily be higher than the solidificat point of the metal being cast. Also, there is no fear of leakage problems in this case. In order to achieve the advantages of the invention it is by no means necessary that the molten metal or salt is in a flowing motion, but it can just as well be completely stationary. The effectiveness of the heat-transferring med is based on its thermal conductivity, which is far superio to that of gas, a decisive factor in this connection. OMPI It is important that the heat-transferring material fills completely as possible the gaps between the chill mold an the cooler so that no gas pockets appear in these spaces. Therefore, it is advantageous to connect the gap or gaps an 'expansion vessel for the heat-transferring medium so t heat-transferring medium can flow into the gap or gaps between the chill mold and the cooler and back as the vol of the gaps varies according to the thermal expansion movement of the surrounding walls. The invention is described below in greater detail with ^ reference to the accompanying drawing, in which Figures 1 and 2 depict cross sectional side elevations of two preferred embodiments of the invention. In .the drawing, the melt to be cast is .indicated by refere numeral 1. The melt to be cast can be in a melt con-tainer the wall of which in general is indicated by 2 and to whic a chill mold 4 made of graphite is attached to receive the melt. Outside the container wall 2 there is, fitted around the chill mold 4, a cooler 3, in which ducts for the cooli medium have been made in a known manner. The melt 1 flowin into the chill mold 4 yields heat to the walls of the chil mold 4 and forms, at a certain distance from the inlet of the chill mold 4, a solidification front, which is indicat by a dotted line in the drawing. The solidified metal is withdrawn in the form of a bar 7 from the chill mold 4 by means of withdrawal members 9. While solidifying and cooli the metal contracts somewhat so that a gap 5 forms between- the bar 7 and the chill mold 4. In addition there is betwe the chill mold 4 and the cooler 3, or there has been separately made, a gap 6, which in accordance with the invention is filled with a medium which transfers heat wel Thus the transfer of heat from the chill mold 4 to the coo 3 is more effective than normally. In the case represented by Figure 2, the gap 6 between the chill mold 4 and the cooler 3 is connected by means of a pipe 8 to an expansion vessel 10, which is partly filled w a medium which transfers heat well. The expansion vessel 1 is at a higher level than the gap 6,inwhich there thus prevails a metallostatic pressure when molten metal is use as the cooling medium. The metal in the expansion vessel c be maintained in a molten state by, for example, fitting a heating resistor around the vessel. It is evident that the present invention can be applied to continuous casting in any direction. If the present invent is applied to an upward continuous casting and if the solidification front is formed above the surface of the me reference numeral 2 in Figure 1 indicates a refractory lin which prevents the melt from coming into direct contact wi the cooler 3, which in this case must.be lowered at least partly to a level below the melt surface. OMPI

Claims: Claims 1. An apparatus for the continuous casting of metal bar pipes or sheets, comprising a chill mold (4) for receivin the molten metal (1) , a cooling member (3) fitted around rear part of the chill mold (4) as seen in the withdrawin direction, a refractory lining (2) which protects at leas the cooling member (3) , and members (9) for the continuou withdrawing of the bar (7) , pipe or sheet which has solid in the chill mold (4) from the chill mold (4) , c h a r a c t e r i z e d b y a highly thermally conductive medium which fills the gap (6) between the chi mold (4) and the cooling member (3) . 2. An apparatus according to Claim 1, c h a r a c t e r i z e d i n that the-said highly thermally conductive medium is in a molten state at least during the casting. 3. An apparatus according to Claim 2, c h a r a c t e r i z e d i n that the gap (6) between the chill mold (4) and the cooling member (3) is connected (8) to an outside expansion vessel (10) . 4. An apparatus according to any of the above claims, c h a r a c t e r i z e d i n that the highly thermally conductive medium is a metal mel which contains tin at least approx. 50 % by weight. OMPI

Inventors: HEIKKILAE HANNU K, OEHMAN GOERAN A, STENFORS RAULI I
Applicants: HEIKKILAE HANNU K, OEHMAN GOERAN A, OUTOKUMPU OY, STENFORS RAULI I
Application year: 1981
Main classification: B22D11
IPC codes: B22D11