Metal founding – Means to shape metallic material – Continuous or semicontinuous casting
Patent
1997-04-04
1998-09-01
Batten, Jr., J. Reed
Metal founding
Means to shape metallic material
Continuous or semicontinuous casting
164459, B22D 1104
Patent
active
057997195
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a continuous casting mold for casting a strand of polygonal cross section, comprising side walls delimiting a mold cavity of polygonal cross section, wherein side walls have a center region extending in the casting direction and exhibiting a first taper and side regions laterally adjoining the center region and exhibiting a taper that is less than the first taper.
A continuous casting mold of this type is known from EP-A - 0 179 364. According to this document, the interfacial angle between adjacent side walls of the continuous casting mold diminishes in the moving direction of the strand, i.e. in the casting direction, provided that the tensile stresses in the edge region which are caused by the shrinkage of the strand shell continuously diminish and/or compensate each other. Hereby, detaching of the strand shell from the cooled mold wall in the region of the comers is to be avoided with a view to achieving uniform shell growth, particularly a shell having a uniform thickness. This is, however, disadvantageous, namely for the following reason:
In conventional continuous casting molds, a particularly pronounced shell growth results in the edge or corner region of the strand already in the initial solidification phase of the strand, and thus directly below the meniscus, due to the two-dimensional heat transport taking place in the edge region. Hereby, the rigidity of the strand shell in the edge region increases to such an extent that the ferrostatic pressure inside the strand is no longer sufficient for pressing the strand shell against the mold side walls in the edge region. Hence contact loss in the edge region will ensue. Due to this contact loss, further cooling of the strand in the edge region can only be effected by heat radiation, but no longer by heat conduction.
As a consequence, the shell growth will immediately fall short of that of adjacent strand zones which rest against the side walls of the continuous casting mold. Directly at the edge of the strand the cessation of heat transmission is, however, compensated for by heat conduction through two-dimensionally acting heat radiation. Thus, there form zones of weak spots having slighter shell thickness, each closely adjacent to the edges of the strand, said zones of weak spots extending in the longitudinal direction of the strand. These local shortfalls in shell growth lead to the strand shell being inhomogeneous and thus richer in tension and more susceptible to cracking and results in a risk of breakout. As the strand passes through the mold, these weak spots move slightly away from the comer regions of the mold toward the center of the side walls.
Attempts to avoid detachment of the strand shell from the cooled side walls of the mold in the region of the comers by the method described in EP-A - 0 179 364, namely by diminishing the interfacial angle in the casting direction, will first of all cause an increase in the extraction force for the strand due to an enhanced degree of friction. Furthermore, excessive cooling of the edge regions will ensue as contact between the edges of the strand and the comers of the mold is effected along the entire length of the mold--at least theoretically--, leading to a further increase in the frictional forces acting between the strand and the continuous casting mold. If, finally, contact loss does occur in the edge region, the above-described effect, i.e. the formation of local weak spots, will be added.
SUMMARY OF THE INVENTION
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a continuous casting mold in which uniform shell growth is ensured in conjunction with only slight frictional forces acting between the strand and the continuous casting mold. In particular, lifting off of the strand shell in the edge or corner region of the strand is to be effected so selectively that there will be no more weak spots located adjacent to the edges or corner and any risk of breakout in these regions will be signific
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"Convex approach to faster billet casting", Steel Times International, vol. 18, No. 6, Nov. 1994, Redhill, Surrey, GB, pp. 18-19.
Thone Heinrich
Wimmer Franz
Batten, Jr. J. Reed
Voest-Alpine Industriean-lagenbau GmbH
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