SU916060A1 - Method of horizontal continuous casting of hollow blanks - Google Patents

Description

The invention relates to metallurgy, and more specifically to the methods of horizontal continuous casting of pipes and other engineering blanks.

The known method of continuous casting of hollow ingots, by which, for example, a significant part of the heat of crystallization is removed through the wall of the mold, moreover, graphite of considerable density and with a small grain of _{10 is} used as the material for the manufacture of the wall of the mold and the mandrel [1].

The closest in technical essence to the present invention is a method of continuous casting hollow billets, including the supply of metal in the annular gap 15 between the outer mold and the inner mandrel, which during freezing of the envelope on the mandrel at the moment of hangup or strain stops the metal in the mold and reduces the speed ₂ θ stretching by 50-95%, after reaching the level of metal, the thinning site can withstand it until the meniscus hardens, after which they increase the speed of stretching until the shell is torn off [2].

2

The disadvantage of this method is the decrease in the performance of the process, caused by the need to reduce the speed of extrusion up to 50% and stop the supply of metal in the mold. When keeping the workpiece before the meniscus hardens, the hardening of the outer and inner surfaces of the latter occurs in one zone of its cross section. Thus, with cyclic pulling of the workpiece, it is possible to form isolated zones with an uncured melt, the solidification of which, under the conditions of difficulty compensating for shrinkage phenomena, leads to the formation of loosening and cracking, which causes a decrease in the quality of the workpiece. The resulting defects are often the main reason for stopping the process, which consists in breaking the workpiece along a weakened section.

The purpose of the invention is to increase the productivity of the process and improve the quality of continuously cast hollow billets.

This goal is achieved by the fact that in the method of horizontal continuous

916060

casting hollow billets, including the supply of liquid metal in the annular gap between the mold and the mandrel and cyclic pulling of the solidified billet, at the beginning of the blanking process, displace the cooled core zone relative to the cooled mold core during the blanking of the blank by an amount equal to 2-8 times the thickness of the hollow billet wall, and further casting is carried out at the offset position of the mandrel.

FIG. 1 shows a solidification scheme for horizontal continuous casting of a hollow billet according to a known method; in fig. 2 - solidification scheme for the proposed method with a periodic step of extrusion, equal to Ζ, and cooled down.

In the case of continuous casting of the billet by a known method, i.e., when pulling a hollow billet with a cooled mandrel and combined cooling zones (Fig. 1a), the process of solidification of the billet proceeds as follows. At the beginning of the cycle, before the preform is stretched, the crystallization front in the wall along the longitudinal section of the preform takes the form of a wedge hole (Fig. 1b). During the billet stretching period, the crystallization front shifts to a draw step (Ζ), burning off part of the crystallized alloy held by friction on the surface of the mold and mandrel, exceeding the tensile strength forming the stationary crust zone 1 (Fig. 1c). On the extruded part of the workpiece, a zone of continuous solidified-2 is formed. The zone of fracture 3 fills the incoming portions of the liquid metal (liquation phase).

During the subsequent shutdown and holding period, an increase in the hardened layer occurs, and the rate of increase at the top 4 of the wedge hole is significantly reduced due to the formation of a gas gap between the workpiece and the external crystallizer, and the output of the base of the well from the cooling zone of the crystallizer, which leads to the formation of isolated zones 5 of an unhardened alloy . Subsequent solidification of the alloy in these zones leads to the formation of internal defects in the body of the workpiece (segregation triangles).

When considering the kinetics of the solidification front (see 1 g, e), it can be seen that the rate of growth of the crust in the continuous hardening zone of the wedge hole is lower than in the stationary crust zone, and the zone of rupture between them - (due to continuous influx of liquid metal) remains unhardened (liquation belt or crater), which contributes to the formation of wall accretions in the form of protruding needles and spherical droplets in the gap between the wall of the mold and the workpiece. The formation of the solidification front corresponds in time to three Periods of T ,, b and T ₃ .

A diagram of the formation of a wall of a hollow billet according to the proposed method with spaced cooling zones on the surface of the mold and dord by the amount b is shown in FIG. 2 a. At the end of the pause before the next step of the tension, the solidification front asymptotically approaches the conical surface, without significant bends (Fig. 2b). In the process of pulling the workpiece, a stationary crust forms only on the surface of the mold (Fig. 2c). At the initial pause moment, the crystallization front looks like an asymmetric wedge as the axis approaches the surface of the mandrel (the position of the mold front during the pause period at the time point corresponds to that shown in Fig. 2 d). Then, during a pause, at time points ~ _r and Щ, the crystallization front is aligned and, at the end of the pause, approaches the conical surface again (Fig. 2e).

Thus, the proposed separation of crystallization zones excludes the conditions for the formation of isolated zones of unhardened metal and, consequently, is inherent in the known process of occurrence of defects - segregation triangles, saps in the form of needles, spherical drops, etc., which significantly improves the quality of continuously cast billets. The choice of limits for the movement of the cooled section of the mandrel is justified by the fact that the movement of the cooling zone of the mandrel relative to the cooled zone of the mold during the extrusion of the workpiece by an amount of 2-8 times the thickness of the hollow billet improves the performance of the casting process by increasing the solid crust simultaneously .

When moving the cooled zone of the mandrel relative to the cooled zone of the mold less than 2 times the thickness of the hollow billet, the kinetics of the crystallization front is almost the same as shown in FIG. 1 a, b, c, d, d, and exceeding the amount of movement of the cooled part of the mandrel 8 of the thickness of the hollow billet can contribute to the breakthroughs of the metal on the outer surface of the crust.

Economic efficiency from the use of the proposed method of continuous casting hollow billets will be about 25 thousand rubles. per year due to an increase in the productivity of the process by 15% and an improvement in the quality of blanks by 10–15%.

Claims (1)

Claim The method of horizontal continuous casting of hollow billets, including the sub-916060 chu liquid metal in the ring zazbr between the mold and the mandrel and cyclic pulling of the hardened billet, characterized in that, in order to improve the performance of the process and improve the quality of the workpieces, at the beginning of the process of stretching the workpiece, the cooled zone of the core relative to the cooled zone of the mold , rav6 The thickness of the wall 2-8 is full of billet, and further casting is carried out at the offset position of the mandrel.