Method for estimating and controlling flow pattern of molten steel in continuous casting and apparatus therefor

A method for estimating flow pattern of molten steel in continuous casting, comprising the steps of:

• continuously casting a molten steel injected into a mold through an immersion nozzle;
• measuring temperatures of a copper plate in width direction of the copper plate on longer side of the mold at a plurality of points using a temperature measurement device;
• estimating a flow pattern of the molten steel in the mold based on a distribution of the copper plate temperatures at individual measurement points;
• and
• determining a heat flux being transferred from the molten steel in the mold to a cooling water for the mold copper plate using the mold copper plate temperatures measured by the temperature measurement device, thickness of the mold copper plate, distance between a surface of the mold copper plate on the molten steel side and a tip of a temperature measurement element, temperature of the cooling water for the mold copper plate, thickness of a solidified shell, thickness of a mold powder layer, and temperature of the molten steel in the mold;
• deriving a convection heat transfer coefficient, corresponding to the heat flux, between the molten steel and a solidified shell;
• and
• determining flow speed of the molten steel along the solidified shell based on the thus derived convection heat transfer coefficient.

A method for estimating flow pattern of molten steel in continuous casting, comprising the steps of:

• continuously casting a molten steel injected into a mold through an immersion nozzle;
• measuring temperatures of a copper plate in width direction of the copper plate on longer side of the mold at a plurality of points using a temperature measurement device;
• and
• estimating a flow pattern of the molten steel in the mold based on a distribution of the copper plate temperatures at individual measurement points;
• the temperature measurement device for the mold copper plate comprising a plurality of temperature measurement elements which are buried in rear face of the mold copper plate for continuous casting, the temperature measurement elements being located in a distance range of from 10 to 135 mm from the level of molten steel in the mold to the direction of slab-drawing, a distance between a surface of the mold copper plate on the molten steel side and a tip of the temperature measurement element being 16 mm or less, while keeping not more than 200 mm of intervals of the temperature measurement elements in the mold width direction and allotting thereof over a range corresponding to a whole width of the slab.

A method for estimating flow pattern of molten steel in continuous casting comprising the steps of:

• continuously casting a molten steel injected into a mold through an immersion nozzle;
• measuring temperatures of a copper plate in width direction of the copper plate on longer side of the mold at a plurality of points using a temperature measurement device;
• and
• estimating a flow pattern of the molten steel in the mold based on a distribution of the copper plate temperatures at individual measurement points;
• the step of estimating the flow pattern comprising estimating a deflected flow of the molten steel in the mold based on the measured temperatures by comparing a maximum value and a position of the maximum value of the temperatures of mold copper plate at right half width with a maximum value and a position of the maximum value of the temperatures of mold copper plate at left half width of the mold to a center of the mold width.

A method for judging surface defect on a slab obtained by continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements in a distance range of from 10 to 135 mm from a position of meniscus in a mold to a direction of slab-drawing along a width direction of a rear face of a mold copper plate;
• measuring a distribution of temperatures of a mold copper plate in a width direction thereof;
• and
• judging the surface defect on the slab on a basis of the distribution of temperatures in the mold width direction,
• the judgment of surface defect being carried out by judging the surface defect of the slab based on a maximum value in the temperature distribution in the mold width direction.

A method for judging surface defect on a slab obtained by continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements in a distance range of from 10 to 135 mm from a position of meniscus in a mold to a direction of slab-drawing along a width direction of a rear face of a mold copper plate;
• measuring a distribution of temperatures of a mold copper plate in a width direction thereof;
• and
• judging the surface defect on the slab on a basis of the distribution of temperatures in the mold width direction,
• the judgment of surface defect being carried out by judging the surface defect of the slab based on a minimum value in the temperature distribution in the mold width direction.

A method for judging surface defect on a slab obtained by continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements in a distance range of from 10 to 135 mm from a position of meniscus in a mold to a direction of slab-drawing along a width direction of a rear face of a mold copper plate;
• measuring a distribution of temperatures of a mold copper plate in a width direction thereof;
• and
• judging the surface defect on the slab on a basis of the distribution of temperatures in the mold width direction,
• the judgment of surface defect being carried out by judging the surface defect of the slab based on an average value in the temperature distribution in the mold width direction.

A method for judging surface defect on a slab obtained by continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements in a distance range of from 10 to 135 mm from a position of meniscus in a mold to the direction of slab-drawing along a width direction of a rear face of a mold copper plate;
• measuring a distribution of temperatures of a mold copper plate in a width direction thereof;
• and
• judging the surface defect on the slab on a basis of the distribution of temperatures in the mold width direction,
• the judgment of surface defect being carried out by judging the surface defect of the slab based on a difference between the average value of the temperature distribution in the mold width direction and the average value of a typical temperature distribution in the mold width direction at the slab-drawing speed.

A method for judging surface defect on a slab obtained by continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements in a distance range of from 10 to 135 mm from a position of meniscus in a mold to a direction of slab-drawing along a width direction of a rear face of a mold copper plate;
• measuring a distribution of temperatures of a mold copper plate in a width direction thereof;
• and
• judging the surface defect on the slab on a basis of the distribution of temperatures in the mold width direction,
• the judgment of surface defect being carried out by judging the surface defect of the slab based on a larger value of, centering an immersion nozzle located at center of a mold, the difference between a maximum value and a minimum value in the temperature distribution at left half width of the mold and the difference between a maximum value and a minimum value in the temperature distribution at right half width of the mold.

A method for judging surface defect on a slab obtained by continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements in a distance range of from 10 to 135 mm from a position of meniscus in a mold to a direction of slab-drawing along a width direction of a rear face of a mold copper plate;
• measuring a distribution of temperatures of a mold copper plate in a width direction thereof;
• and
• judging the surface defect on the slab on a basis of the distribution of temperatures in the mold width direction,
• the judgment of surface defect being carried out by judging the surface defect of the slab based on an absolute value of a difference between a maximum value in a temperature distribution at left half width of the mold and a maximum value in the temperature distribution at right half width of the mold, centering an immersion nozzle located at center of the mold.

A method for detecting flow of molten steel in a continuous casting process comprising the steps of

• locating a plurality of temperature measurement elements orthogonally to a direction of slab-drawing at a rear face of a mold copper plate for continuous casting;
• measuring mold copper plate temperatures using the plurality of temperature measuring elements;
• applying low pass filter treatment to each of the thus measured mold copper temperatures assuming a range of cut-off space frequency of larger than [2/(mold width W)] and less than 0.01, the space frequency f of the molten steel flow being defined by f=1/L, where L designates varying wave length (mm);
• and
• estimating a state of flow of molten steel in the mold on a basis of the temperature distribution of the mold copper plate, which temperature distribution was treated by the low pass filter.

A method for detecting flow of molten steel in continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements orthogonally to a direction of slab-drawing while keeping a distance between adjacent temperature measurement elements to a range of from 14.8 mm to [0.443×(mold width W)/6] mm;
• measuring temperatures of a mold copper plate using the thus located temperature measurement elements;
• deriving a spatial movement average of the thus measured mold copper plate temperatures;
• and
• estimating a state of molten steel flow in the mold based on a temperature distribution of the spatial movement average mold copper plate temperatures.

A method for evaluating irregularity in heat-release in a mold in continuous casting, comprising the steps of:

• locating a plurality of temperature measurement elements orthogonally to the direction of slab-drawing at a rear face of a mold copper plate for continuous casting;
• measuring temperatures of the mold copper plate using the thus located temperature measurement elements;
• applying low pass filter treatment to each of the thus measured mold copper temperatures;
• and
• evaluating the irregularity in heat-release in the mold on a basis of a difference between the measured mold copper plate temperature and the mold copper plate temperature that was treated by the low pass filter.

A temperature measurement device for mold copper plate comprising:

• a plurality of temperature measurement elements buried in rear face of a mold copper plate for continuous casting process;
• the temperature measurement elements being located in a distance range of from 10 to 135 mm from a level of molten steel in the mold to a direction of slab-drawing;
• a distance between a surface of the mold copper plate on a molten steel side and a tip of the temperature measurement element being 16 mm or less;
• the temperature measurement elements comprising at least five temperature measurement elements in one wavelength of a flow speed profile of the molten steel near a meniscus.

A method for controlling a quality of steel in continuous casting, comprising the steps of:

• continuously casting a molten steel injected into a mold through an immersion nozzle;
• measuring temperatures of a copper plate in a width direction of the copper plate on a longer side of the mold at a plurality of points using a temperature measurement device;
• and
• estimating a flow pattern of the molten steel in the mold based on a distribution of copper plate temperatures at individual measurement points;
• and
• the step of estimating the flow pattern comprising estimating a flow pattern of the molten steel in the mold based on quantity and positions of peaks of temperatures of the mold copper plate in the mold width direction to detect a flow state of the molten steel in the mold.

A continuous casting method, comprising the steps of:

• injecting a molten steel into a mold through an immersion nozzle;
• measuring temperatures of a copper plate in a width direction of the copper plate on a longer side of the mold at a plurality of points using a temperature measurement device;
• estimating a flow pattern of the molten steel in the mold based on a distribution of the copper plate temperatures at individual measurement points;
• the step of estimating the flow pattern comprising estimating a flow pattern of the molten steel in the mold based on quantity and positions of peaks of temperatures of the mold copper plate in the mold width direction;
• adjusting at least one variable selected from the group consisting of a magnetic field intensity of a magnetic field generator attached to the mold, a slab-drawing speed, an immersion depth of an immersion nozzle, and an Ar gas injection rate into the immersion nozzle, so as to establish a specified flow pattern.

A continuous casting method, comprising the steps of:

• injecting a molten steel into a mold through an immersion nozzle;
• measuring temperatures of a copper plate in a width direction of the copper plate on a longer side of the mold at a plurality of points using a temperature measurement device comprising temperature measurement elements;
• estimating a flow pattern of the molten steel in the mold based on a distribution of the copper plate temperatures at individual measurement points;
• the temperature measurement elements being located in a distance range of from 10 to 135 mm from a level of molten steel in the mold to a direction of slab-drawing, a distance between a surface of the mold copper plate on a molten steel side and a tip of the temperature measurement element being 16 mm or less, while keeping not more than 200 mm of intervals of the temperature measurement elements in a mold width direction, and allotting thereof over a range corresponding to a whole width of the slab;
• adjusting at least one variable selected from the group consisting of a magnetic field intensity of a magnetic field generator attached to the mold, a slab-drawing speed, an immersion depth of an immersion nozzle, and an Ar gas injection rate into the immersion nozzle, so as to establish a specified flow pattern.

A method for estimating flow speed of molten steel in a mold, comprising the steps of:

• measuring a temperature of a copper plate of the mold using a temperature measurement element buried in the copper plate;
• determining a heat flux being transferred from the molten steel in the mold to a cooling water for the mold copper plate using the mold copper plate temperature measured by the temperature measurement device, a thickness of the mold copper plate, a distance between a surface of the mold copper plate on the molten steel side and a tip of a temperature measurement element, a temperature of the cooling water for the mold copper plate, a thickness of a solidified shell, a thickness of a mold powder layer, and a temperature of the molten steel in the mold;
• deriving a convection heat transfer coefficient, corresponding to the heat flux, between the molten steel and a solidified shell;
• and
• determining a flow speed of the molten steel along the solidified shell based on thus derived convection heat transfer coefficient.