Method of and apparatus for withdrawing strand in horizontal continuous casting installation

A method of withdrawing a strand in a horizontal continuous casting installation, wherein said strand is intermittently withdrawn by repeating a cycle of withdrawing the strand from within a mold connected to a tundish of the horizontal continuously casting installation, through a mold tube provided downstream of the mold, over a predetermined stroke by means of strand withdrawing means, and retracting the withdrawn strand over a relatively short stroke, said method comprising the steps of:

• presetting, in control means of said withdrawing means, one cycle of a strand withdrawing and retracting characteristic;
• controlling said withdrawing means based on said strand withdrawing and retracting characteristic for each said cycle by said control means;
• determining an instruction signal based on a comparison of a detection signal generated by detection means which detects an amount of withdrawal and retraction, with said strand withdrawing and retracting characteristic;
• feedback controlling said withdrawing means in response to said instruction signal;
• detecting a temperature at an exit end of said mold tube;
• decreasing the withdrawing speed of said withdrawing means when said detected temperature exceeds a predetermined value;
• causing the withdrawing operation of said withdrawing means to return to a control according to said strand withdrawing and retracting characteristic of said withdrawing means when said detected temperature returns to a normal value;
• providing at least one temperature detecting means in a mold tube near a break ring provided between said tundish and said mold;
• calculating a mean value of a periodic variation of the temperature detected by said temperature detecting means;
• setting a first value obtained by subtracting a first set temperature from said mean value before a set time as a lower control temperature for changing said withdrawing speed;
• setting a second value obtained by adding a second set temperature to said mean value before said set time as an upper control temperature for changing said withdrawing speed;
• changing the withdrawing speed when a presently detected temperature detected by said temperature detecting means decreases below said lower control temperature or increases above said upper control temperature;
• setting a value obtained by subtracting a third set temperature from said lower control temperature at a time of initiating changing of said withdrawing speed as a restoring temperature utilized for restoring said withdrawing speed;
• restoring said withdrawing speed to the original speed when a presently detected temperature detected by said temperature detecting means exceeds said restoring temperature;
• and
• restoring said withdrawing speed by an operator when said presently detected temperature exceeds said upper control temperature.

An apparatus for withdrawing a cast strand in a horizontal continuous casting installation, including withdrawing means having upper and lower pinch rolls which intermittently withdraw and retract a strand by repeating a cycle of withdrawing the strand over a predetermined stroke from a mold provided for a tundish of the horizontal continuous casting installation, and retracting said withdrawn strand over a small stroke, and servomotor means for driving the pinch rolls, said apparatus comprising:

• control means preset with a strand withdrawing and retracting characteristic of one cycle;
• detecting means for detecting strand withdrawing and retracting quantities for producing a detection signal;
• means for comparing said detecting signal with said strand withdrawing and retracting characteristic for producing an instruction signal;
• means for sending said instruction signal to said servomotor means, said servomotor means comprising servomotors provided for said pinch rolls, respectively, to drive the respective pinch rolls independently;
• speed reduction means interposed between each servomotor and each pinch roll, said speed reduction means including a double lead type worm gear driven coaxially with each of said servomotors, a worm wheel meshing with said worm gear and secured coaxially to each of said pinch rolls, and means for finely adjusting an axial position of said worm wheel;
• and
• rotary driving means including a backlashless type coupling for connecting said servomotor to said worm gear.