The present invention relates to a new and improved construction of oscillatory or reciprocating mold of the type having a hollow mold cavity or compartment which is curved or arc-shaped in the direction of travel of the strand for cooling an essentially rectangular steel strand which is forming, the aforesaid continuous casting mold comprising a first cooling device for indirect cooling of the strand and a second cooling device equipped with strip-shaped support surfaces and between such support surfaces intermediately disposed cooling water channels, there cooling water channels being equipped with water infeed means.
During the continuous casting of steel, especially at high casting speeds, it is extremely important that there be produced as uniform and as thick as possible strand shell or skin upon departure of the cast strand or casting out of the mold.
Due to the contraction of the strand shell within the mold such lifts off of the mold walls and, depending upon the cross-section of the strand and the taper of the hollow mold cavity or compartment, produces an irregular contact of the strand with the walls of the mold viewed over the periphery of the strand. Due to this irregular contact of the strand with the mold walls there is formed, especially at the lower portion of the mold, a strand shell which is of varying thickness at the outlet end of the mold and possesses the well known drawbacks, such as for instance, diamond profile, fissures, metal breakouts and so forth.
Hence, for the purpose of producing strands having a uniform thickness of the shell over the periphery of the strand at the outlet end of the mold it therefore was beneficial to use short molds equipped with a subsequently arranged spray cooling device. However, the thickness of the strand shell at such mold is thin at the time that the strand departs from the mold and thus severely prone to the metal breakout phenomena, so that even the slightest defects at the strand shell can precipitate metal breakout. Thus, from the standpoint of counteracting metal breakout long molds are preferred. But such long molds possess at the lower region thereof an extremely small cooling efficiency or capacity, and considered with regard to the periphery of the mold, an irregular cooling capacity. Thus, such molds are not suitable for high-speed casting operations where there should prevail safeguards against metal breakout, especially when casting billet- and bloom-cross-sections.
There is known to the art an oscillating or reciprocating mold having an arc-shaped or curved mold cavity which, viewed in the direction of travel of the strand, possesses two different successively arranged cooling devices. The first cooling device consists of cooled walls which indirectly cool the strand shell or skin forming therein. Directly following such first cooling device is the second cooling device which is equipped with support surfaces and intermediately located strip-shaped cooling water channels. These cooling water channels which are open at the strand infeed side are provided with water infeed means for the direct cooling of the strand. However, this mold construction is associated with the drawback that the vapor forming in the cooling water channels can ascend in the shrinkage gap between the mold walls and the strand in the indirectly cooled mold portion up to the level of the molten metal bath and thus can cause explosions. Apart from this drawback such mold construction, however, possesses a still further shortcoming. With incipient metal breakouts, which again close due to solidification in the cooling water channels, there are formed with respect to the strand surface protruding whisker- or teardrop-like irregularities. In the case of a larger incipient metal breakout such a resulting repaired location, even along a shorter path, can completely fill the entire hollow space of the cooling water channel. Due to the relative movement between the oscillating mold and the moving strand there are effective at such repaired locations shearing moments due to the straight lateral boundary surfaces of such channels, which can again tear open such locations. Consequently, on the one hand there is considerably reduced the metal breakout-preventing effect of such cooling device and, on the other hand, there is considerably increased the danger of explosions which arise due to penetration of water into the torn or broken open strand shell.