CN102211161A - A method and device for improving the quality of continuous casting large-diameter hollow metal tube billets - Google Patents

Abstract

The invention discloses a method and a device for improving the quality of continuous casting large-diameter hollow metal tube blanks. In the method and device, an electromagnetic coil is arranged outside the outer mold, and a spiral stirring magnetic field generator is placed in the inner mold at the same time. On the outside of the outer mold, a medium and high-frequency magnetic field is applied to the molten metal poured into the pouring cavity formed by the inner and outer molds, and at the same time, inside the inner mold, a magnetic field is applied to the molten metal in the casting cavity Low, power frequency spiral stirring magnetic field. The invention uses electromagnetic coils to focus on the outer surface quality of the hollow tube, and the spiral stirring magnetic field generator can effectively improve the inner surface quality and internal quality of the tube, and remove non-metallic inclusions, bubbles, segregation, cracks and other defects , and can significantly improve the macroscopic solidification structure of the tube blank. The invention is suitable for continuous casting of hollow steel blanks with an inner diameter of more than 100mm, and also suitable for continuous casting of hollow steel blanks of other types of alloys.

Description

A method and device for improving the quality of continuous casting large-diameter hollow metal tube billets

technical field

The invention belongs to the field of preparation of seamless large-diameter hollow metal tube blanks, and in particular relates to a method and a device for improving the quality of continuous casting hollow metal tube blanks such as steel tube blanks.

Background technique

With the rapid development of my country's electric power, petrochemical and other industries, the demand for high-quality seamless large-diameter hollow steel pipes continues to increase. Due to the harsh working environment, there are strict requirements on the quality of the inner and outer surfaces of the pipe and the solidification structure. The common processing method of seamless large-diameter hollow steel pipes is to obtain pipes through continuous casting hollow billets through subsequent rolling, drawing and other processes. The quality of continuous casting hollow billets directly determines the quality of metal pipes. Hollow billet continuous casting technology refers to pouring high-temperature molten steel into the cavity (casting cavity) formed by the inner and outer crystallizers on the vertical continuous casting machine, solidifying and forming a billet shell with a certain thickness, and then continuously pulling it out. Hollow cast slab. Although the method of continuous casting to prepare hollow steel billets has the advantages of high production efficiency and high metal utilization rate, it often has disadvantages such as non-metallic slag inclusions, pores, segregation, surface indentation, and coarse solidification structure. In order to improve the quality of the hollow billet, the invention patent application (application number 02109370.9) discloses a method for electromagnetic continuous casting of the hollow billet. During the continuous casting process of the hollow billet, a stirring magnetic field or electromagnetic coil is applied outside the outer mold, or simultaneously A composite magnetic field of a stirring magnetic field and an electromagnetic coil is applied. This method is only suitable for the continuous casting process of small-diameter hollow billet. For the continuous casting of large-diameter hollow billet, the electromagnetic generator required by this method is very bulky. On the one hand, there will be high manufacturing costs and difficult installation. Disadvantages, on the other hand, the improvement effect on the surface quality of the slab, especially the inner surface quality is not obvious. In 2006, the article "Out-of-phase electromagnetic continuous casting of hollow billets" published in "Journal of Nonferrous Metals of China" proposed a method of placing power frequency electromagnetic coils in the inner and outer molds during the continuous casting process of aluminum alloy hollow billets. The method can effectively improve the surface quality and solidification structure of the aluminum billet, but for the continuous casting of the steel metal billet whose density is much higher than that of the aluminum alloy, due to the heavy weight, the effect of applying the electromagnetic coil to improve the solidification structure is not obvious . The patent application CN101298094A published in 2008 proposes a method to improve the quality of the hollow tube blank by applying an electromagnetic coil to the outer mold and placing a rotating or traveling wave stirring magnetic field generator in the inner mold. , segregation, cracks and other defects on the outer surface can also significantly improve the solidification structure of the tube billet, but if you choose to apply a rotating stirring magnetic field generator in the inner mold, the rotation of the molten steel will inevitably make the non-metallic inclusions gather to the center , although the surface quality of the slab has been improved, it is possible that the inclusions in the central area will increase and the quality will be reduced, which will cause defects in the subsequent rolled products, and when a rotating magnetic field is applied, segregation will easily occur inside the slab under a large magnetic field strength. Defects, commonly known as "white bright bands", require stricter control of magnetic field strength. If a traveling wave stirring magnetic field generator is applied in the inner mold, the molten steel in the mold will generate convection, scour the solidification interface, accelerate the floating of inclusions and gases, and disperse on the surface of the liquid metal in the mold, which can improve the quality of the slab Internal quality, but the effect of improving the surface quality can not meet the requirements.

Contents of the invention

In view of the above reasons, the present invention provides a new method for improving the quality of continuous casting large-diameter hollow metal tube blanks, and a device using the above method; A spiral stirring magnetic field generator is placed in the inner crystallizer, and the external electromagnetic coil can focus on solving the outer surface quality of the hollow tube blank, while the internal spiral stirring magnetic field generator can effectively improve the inner surface quality and internal quality of the tube blank .

Its technical solutions are:

A method for improving the quality of continuous casting large-diameter hollow metal tube blanks, comprising the following steps:

Step 1, on the outside of the outer mold of the hollow metal billet continuous casting equipment, apply a medium and high frequency magnetic field to the metal melt poured into the pouring cavity formed by the inner and outer molds; the medium and high frequency magnetic field The frequency is 1000Hz～50000Hz;

Step 2, on the inner side of the inner mold of the hollow metal billet continuous casting equipment, apply a low, power frequency spiral stirring magnetic field to the metal melt poured into the pouring cavity formed by the inner and outer molds; the spiral stirring The frequency of the magnetic field is 3Hz ~ 50Hz;

During the continuous casting process, the molten metal is continuously poured into the pouring cavity, and step 1 and step 2 are carried out at the same time, and the bottom mold of the pouring cavity is pulled at a certain speed to obtain a continuous casting hollow tube blank.

The above-mentioned metal tube blank is a steel tube blank, and the metal melt is molten steel.

A device for improving the quality of continuous casting large-diameter hollow metal billets, including medium and high-frequency electromagnetic coils arranged outside the outer mold of hollow metal billet continuous casting equipment, and arranged inside the hollow metal billet continuous casting equipment The low and power frequency spiral stirring magnetic field generator inside the crystallizer; the above medium and high frequency electromagnetic coils are fed with alternating current, and the frequency of the current is 1000Hz~50000Hz; the above low and power frequency spiral stirring magnetic field generator is generated by The electromagnetic inductor of the spiral stirring magnetic field, the cylindrical shell for protecting the electromagnetic inductor, and the cooling water circuit for cooling the electromagnetic inductor are composed. The electromagnetic inductor is made by winding an electromagnetic coil on an iron core. Arranged by the Mu winding method, three-phase alternating current is passed in, the phase difference between each phase current is 120°, the frequency of the alternating current is 3 Hz to 50 Hz, and the angle between the core axis of the above-mentioned iron core and the yoke is 30° °~60°, under the action of the magnetic field of the three-phase alternating electromagnetic coil, the direction of the electromagnetic force generated inside the molten metal poured into the pouring cavity is perpendicular to the direction of the magnetic force line, forming a spiral stirring swirl inside the molten metal.

The above-mentioned cooling water circuit includes a cooling cavity formed between the electromagnetic inductor and the inner wall of the cylindrical shell, and the cooling water inlet and the water return port in the cooling cavity are arranged on the cylindrical shell; The structure cools the electromagnetic inductor.

The above-mentioned iron core includes a vertical mandrel, and the electromagnetic coil is a copper tube coil, and the copper tube coil is nested on the vertical mandrel according to the Kramm winding method, and several vertical mandrels are arranged on the vertical mandrel, from top to bottom The magnetic yokes are arranged in sequence, and each magnetic yoke is approximately conical, and the angle between the side wall of the magnetic yoke and the axis line of the vertical mandrel is 30°-60°.

The present invention has the following beneficial technical effects:

In the present invention, an electromagnetic coil is applied outside the outer mold, and a spiral stirring magnetic field generator is placed in the inner mold at the same time. The electromagnetic coil can focus on solving the outer surface quality of the hollow tube billet, and the spiral stirring magnetic field generator can effectively improve the quality of the tube. The internal surface quality and internal quality of the billet can remove non-metallic inclusions, air bubbles, segregation, cracks and other defects, and can significantly improve the macroscopic solidification structure of the tube billet. In addition, placing a spiral stirring magnetic field generator in the inner crystallizer, on the one hand, is easy to operate, on the other hand, the magnetic field generator is small in size and high in efficiency, and is especially suitable for being placed inside the inner crystallizer for pouring The molten metal in the cavity produces a spiral stirring effect.

Description of drawings

Below in conjunction with accompanying drawing and specific embodiment the present invention will be further described:

Fig. 1 is a schematic diagram of the structural principle of an embodiment of the device in the present invention, and also shows the relevant parts of the hollow metal billet continuous casting equipment (machine).

Fig. 2 is a schematic diagram of the structure and principle of the low and power frequency helical stirring magnetic field generator in the mode of Fig. 1 .

Fig. 3 is a schematic diagram of the spiral stirring principle of the low and power frequency spiral stirring magnetic field generator.

Detailed ways

Referring to Fig. 1, Fig. 2 and Fig. 3, a device for improving the quality of continuous casting large-diameter hollow metal billet, the device is suitable for hollow metal billet continuous casting equipment (machine), the continuous casting equipment includes external mold 3, The inner crystallizer 4 forms a pouring chamber 8 between the inner mold 4 and the outer mold 3 , and the bottom of the pouring chamber 8 is provided with a pullable bottom mold 5 . The above-mentioned device includes medium and high frequency electromagnetic coils 1 arranged outside the outer crystallizer 3 , and a low and power frequency helical stirring magnetic field generator 2 arranged inside the inner crystallizer 4 . The above-mentioned medium and high-frequency electromagnetic coils are fed with alternating current, and the frequency of the current is 1000Hz-50000Hz. Above-mentioned low, industrial frequency helical stirring magnetic field generator 2 comprises cylindrical housing 201, is arranged on the iron core 202 inside cylindrical housing, is arranged on the electromagnetic coil 203 on iron core 202, and the inner cavity of cylindrical housing is Cooling cavity 204, the cylindrical shell is provided with cooling water inlet 205 and water return port 206 in the cooling cavity, and the electromagnetic coil 203 arranged according to the Kramm winding method is fed with three-phase low-frequency alternating current, and the frequency of the alternating current is 3Hz-50Hz, the electromagnetic coil is cooled by the cooling water entering the cooling cavity, and the heat generated by the electromagnetic coil 203 is taken away. The included angle between the yoke formed by the iron core 202 and the mandrel axis of the iron core is 30°-60°, under the action of the magnetic field of the coil, the molten metal 7 (such as molten steel) poured into the casting cavity The direction of the electromagnetic force generated inside is perpendicular to the direction of the magnetic force line, and a spiral stirring swirl is formed inside the metal melt, that is, when the yoke is tilted downward at a certain angle, the magnetic force line generated in the metal melt (metal melt) The direction corresponds to it, and also forms a certain angle with the horizontal direction. According to the left-handed spiral rule, the direction of the electromagnetic force generated in the metal melt is perpendicular to the magnetic force line of the coil, so under the action of such electromagnetic force, the metal melt Spiral electromagnetic stirring is generated in the body; focus on Figure 3, the spiral curve in the diagram represents the direction of the spiral stirring swirl, the symbol B represents the magnetic induction intensity, and its direction is the direction of the magnetic force line, the symbol F represents the electromagnetic force, and the symbol I represents the induction current. More specifically: the above-mentioned iron core 202 includes a vertical mandrel 2021, and the electromagnetic coil 203 is a copper tube coil, which is sleeved on the vertical mandrel. The magnetic yokes 2022 are arranged in sequence, and each magnetic yoke 2022 is approximately in the shape of a truncated cone, and the included angle between the side wall of the magnetic yoke and the axis of the vertical mandrel is 30°-60°.

A method for improving the quality of continuous casting large-diameter hollow metal tube blanks, comprising the following steps:

Step 1, using the medium and high frequency electromagnetic coil 1 to apply a medium and high frequency magnetic field to the metal melt 7 poured into the pouring cavity on the outside; the frequency of the medium and high frequency magnetic field is 1000 Hz to 50000 Hz;

Step 2, using a low-frequency and power-frequency spiral stirring magnetic field generator 2 to apply a low-power frequency spiral stirring magnetic field to the molten metal 7 poured into the pouring cavity; the frequency of the spiral stirring magnetic field is 3 Hz to 50 Hz;

During the continuous casting process, molten metal such as molten steel is continuously poured into the pouring chamber, and steps 1 and 2 are performed simultaneously, and the bottom mold 5 of the pouring chamber is pulled at a certain speed to obtain a continuous casting hollow shell 6 .

In the present invention, a low and power frequency spiral stirring magnetic field generator is arranged inside the inner crystallizer, that is, the difference between applying a spiral stirring magnetic field inside the inner crystallizer and stirring magnetic fields in other prior art:

1. Compared with rotating and traveling wave stirring magnetic fields, the spiral stirring magnetic field in the present invention has more advantages

Applying a helical stirring magnetic field can generate a helical rotating force, causing the molten metal such as molten steel to produce a spiral upward or downward stirring motion. Compared with a rotating stirring magnetic field and a traveling wave stirring magnetic field, it can more effectively improve the quality of the slab. Surface quality, internal quality and solidification structure.

The spiral stirring magnetic field can promote the separation and floating of inclusions, gas and molten metal, and gather to the center of the liquid surface, which is beneficial to the removal of inclusions and can avoid defects such as inclusions and pores. Experiments show that: under the condition that the stirring force is basically the same, the content of inclusions in the ingot under the action of spiral stirring is significantly lower than the content of inclusions in the case of rotary stirring and traveling wave stirring, and the content of inclusions in the slab under the action of spiral stirring The content is only half of the rotary stirring.

The distribution of electromagnetic force in the helical magnetic field is conducive to the formation of uniform stirring in a large area, and has a significant role in promoting the formation of equiaxed crystals. Compared with rotary stirring and traveling wave stirring, the equiaxed crystal rate obtained by spiral stirring is the highest. Expanding and refining the equiaxed grain zone can increase the crack resistance of the slab, eliminate the central shrinkage cavity, and reduce the central porosity and central segregation.

2. The advantages of applying a spiral stirring magnetic field in the inner crystallizer than applying it outside

By applying a spiral stirring magnetic field in the inner mold of the continuous casting hollow billet, there are the following advantages:

1) The above-mentioned helical stirring magnetic field generator has a reasonable and compact structure, has the characteristics of small size, higher power utilization rate, etc., and will not hinder the application of an electromagnetic field at the outer crystallizer, which is easy to operate.

2) Applying a spiral stirring magnetic field in the inner mold will make the electromagnetic force on the inner mold side of the tube blank greater than that on the outer mold side, so the flow rate of the melt near the inner mold side is greater than that of the outer mold side melt This is more conducive to improving the surface quality of the slab on the inner mold side (such as better elimination of inclusions on the inner surface, reducing ripples, etc.) High), and because the inner surface of the tube blank is not easy to be milled, if there are defects on the inner surface, it will directly lead to pipe defects. Therefore, applying a spiral stirring magnetic field in the inner mold can improve the quality of the billet more effectively than placing a stirring magnetic field outside the billet.

The method proposed by the invention is suitable for continuous casting of hollow steel billets with an inner diameter of more than 100mm, and also suitable for continuous casting of hollow steel billets of other types of alloys.

It should be noted that under the teaching of this specification, those skilled in the art can also make various modifications such as replacement and simple combination without departing from the scope of protection of the claims of the present invention, all of which fall into the scope of this specification. within the scope of protection of the invention.

Claims (5)

1. A method for improving the quality of continuous casting large-diameter hollow metal tube blanks, characterized in that it comprises the following steps: Step 1, on the outside of the outer mold of the hollow metal billet continuous casting equipment, apply a medium and high frequency magnetic field to the metal melt poured into the pouring cavity formed by the inner and outer molds; the frequency of the medium frequency magnetic field is 1000Hz~ 9000Hz, the frequency of high-frequency magnetic field is 10000Hz～50000Hz; Step 2, on the inner side of the inner mold of the hollow metal billet continuous casting equipment, apply a low, power frequency spiral stirring magnetic field to the metal melt poured into the pouring cavity formed by the inner and outer molds; the spiral stirring The frequency of the magnetic field is 3Hz ~ 50Hz; During the continuous casting process, the molten metal is continuously poured into the pouring cavity, and step 1 and step 2 are carried out at the same time, and the bottom mold of the pouring cavity is pulled at a certain speed to obtain a continuous casting hollow tube blank. 2. The method for improving the quality of continuous casting large-diameter hollow metal tube blanks according to claim 1, characterized in that: the metal tube blanks are steel tube blanks, and the metal melt is molten steel. 3. A device for improving the quality of continuous casting large-diameter hollow metal billets, characterized in that it includes medium and high-frequency electromagnetic coils arranged outside the outer mold of the hollow metal billet continuous casting equipment, and arranged on the hollow metal billet The low and power frequency spiral stirring magnetic field generator inside the inner crystallizer of the continuous casting equipment; the above-mentioned medium and high frequency electromagnetic coils are fed with alternating current, and the frequency of the current is 1000Hz-50000Hz; the low and power frequency spiral stirring The magnetic field generator is composed of an electromagnetic inductor that generates a spiral stirring magnetic field, a cylindrical shell that protects the electromagnetic inductor, and a cooling water circuit that cools the electromagnetic inductor. The electromagnetic inductor is made of an electromagnetic coil wound on an iron core , the electromagnetic coils are arranged according to the Kramm winding method, and the three-phase alternating current is fed in. The phase difference between each phase current is 120°, and the frequency of the alternating current is 3 Hz to 50 Hz. The included angle between them is 30°～60°. Under the action of the magnetic field of the three-phase alternating electromagnetic coil, the direction of the electromagnetic force generated inside the molten metal poured into the pouring cavity is perpendicular to the direction of the magnetic force line, forming inside the molten metal. Spiral stirring swirl. 4. A device for improving the quality of continuous casting large-diameter hollow metal tube blanks according to claim 3, characterized in that: the cooling water circuit includes a cooling cavity formed between the electromagnetic inductor and the inner wall of the cylindrical shell , and the cooling water inlet port and the water body return port in the cooling chamber are arranged on the cylindrical shell; the electromagnetic inductor is cooled by the external water direct cooling cooling structure. 5. A device for improving the quality of continuous casting large-diameter hollow metal tube blanks according to claim 3, characterized in that: the iron core includes a vertical mandrel, the electromagnetic coil is a copper tube coil, and the copper tube coil is in accordance with the gram The Lamb winding method is nested on the vertical mandrel, and there are several yokes arranged in sequence from top to bottom on the vertical mandrel. The included angle of the axis line of the straight mandrel is 30°～60°.

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