The ladle sliding nozzle system consists of a base brick, an upper nozzle, an upper slide plate, a lower slide plate, a lower nozzle, and a sliding mechanism. The working principle of the sliding nozzle is to adjust the flow rate of molten steel by shifting the casting holes of the upper and lower slide plates through the sliding mechanism.
Steel leakage at the joint between the upper water inlet and the upper base brick
Cause Analysis
- Steel leakage at the mud joint between the upper water inlet and the upper seat brick
(1) Steel leakage at the mud joint between the upper water inlet and the upper seat brick. During the installation process of the upper water inlet, the mud joint is not full or there are impurities in the fire mud, causing steel to seep through the mud joint between the seat brick and the upper water inlet.
(2) The upper seat brick is seriously damaged during the flushing or cleaning process, and the upper seat brick opening is larger after flushing. The sealing area between the upper seat brick and the upper water inlet is reduced or the fire mud is too thick, resulting in a larger fire mud drying and shrinking mud joint. In severe cases, the upper water inlet may creep into the ladle. Under static pressure, the molten steel gradually seeps steel along the mud joint, eventually leading to a steel drilling accident.
(3) Longitudinal cracks in the upper water inlet. Due to the poor thermal shock resistance of the upper water inlet and the large temperature difference between the inside and outside of the upper water inlet during the steel pouring process, the upper water inlet has longitudinal cracks along the length direction, and the molten steel penetrates along the cracks.
(4) The misalignment between the mechanism base and the ladle bottom mounting plate causes the upper water inlet to be fractured due to lateral force. The situation is shown in Figure 2.
Improvement measures
(1) The water-cement ratio of the fireclay should be properly adjusted, the fireclay should be moderately soft and hard, and the fireclay must be evenly mixed without impurities. Once the appropriate water-cement ratio is found, the operating specifications of each team should be strengthened to avoid fluctuations in the fireclay caused by human factors. And use barrels during use and seal with plastic film after use.
(2) Improve the anti-scouring performance of the upper seat brick and determine a reasonable service life. When replacing the upper nozzle, the pneumatic pick should hit at a suitable angle to avoid damaging the seat brick. If the inner cavity of the upper seat brick is damaged, use fireclay to repair it before installing the upper nozzle, and re-repair it if it is seriously damaged.
(3) Improve the thermal shock resistance of the upper nozzle, and install the fireclay evenly and fully.
(4) A seat brick positioning device is set at the bottom of the package, and the damage or displacement of the positioning facility caused by unpacking should be repaired in time. Ensure that the seat brick is concentric with the nozzle hole of the mechanism bottom box.
Steel leakage between the upper water inlet and the upper slide
Cause Analysis
(1) The nozzle brick creeps into the inner cavity of the seat brick. When installing the nozzle brick, evenly apply a layer of fire mud on its outer surface, and then squeeze it into the nozzle seat brick. The fire mud cannot harden in a short time. After installing the slide plate, under the action of the spring pressure, the nozzle brick creeps into the cavity of the seat brick. During the steel pouring process, the fire mud will sinter and shrink. Under the static pressure of the molten steel, the molten steel will penetrate outward along the fire mud gap between the nozzle brick and the upper slide brick. When the width and thickness of the steel sheet reach a certain level, steel leakage will occur.
(2) The sealing fire mud between the upper slide brick and the nozzle brick is too thick or too thin. During the steel pouring process, the fire mud that is too thick or too thin has a large sintering shrinkage rate, and there are many pores in the mud layer after sintering. In particular, the carbon in the aluminum-carbon fire mud is oxidized, which reduces the strength of the fire mud and is easily washed away by the molten steel. Under the action of static pressure, the molten steel passes through the contact surface and causes steel leakage. The steel leakage caused by the excessive gap between the upper slide and the nozzle caused by the nozzle being installed too deep is shown in Figure 3.
(3) The upper slide is not installed flat, the upper nozzle is installed high or the fire clay is hard, so that the upper slide cannot be installed in place. There is a gap between the upper slide and the bottom box of the mechanism. During the process of pulling the slide, the pressure center of gravity moves back and forth on both sides of the fulcrum formed on the back of the slide, which eventually causes the mud seam between the upper slide and the upper nozzle to crack and cause steel leakage.
(4) The upper slide has no positioning device and is only positioned by the mother-and-child joint. If the strength of the sealing fire clay is not high, the friction force when the slide is pulled causes the upper slide brick and the nozzle brick to shift, causing the fire clay between the contact surfaces to loosen, and the molten steel to pass horizontally along the mud seam.
(5) The ladle does not open automatically when pouring, and the oxygen tube is used to burn the eye, burning through the refractory material and causing steel leakage.
Improvement measures
(1) After the installation of the upper water inlet brick, use open flame to bake the fire clay to harden it to prevent the newly installed upper water inlet brick from creeping into the base brick cavity.
(2) Prevent the fire clay from being too thick or too thin, and strictly control the water-cement ratio of the fire clay. The installation of the upper water inlet must be standardized. The section of the sub-mouth or mother mouth of the upper water inlet should be level with or slightly lower than the mechanism slide box by 2mm. Use reasonable upper water inlet installation positioning tools to avoid human operation differences.
(3) Choose the right fire clay, which must have a certain sintering strength and resistance to molten steel erosion.
(4) Improve the self-opening rate of the ladle. When the burning eye does not open automatically, bend the oxygen tube. After the oxygen tube enters the water inlet, push it vertically upward to avoid burning the refractory material.
Steel leakage between upper and lower slide plates
Cause Analysis
(1) When casting high manganese, low carbon, and low silicon steel, the concentration of oxidizing substances in the carbon-containing slide is high. The carbon on the slide surface that contacts the molten steel is oxidized, the brick volume density decreases, and the surface strength decreases. The molten steel is easier to penetrate the lubricating plate surface, and the slide surface is more strongly corroded. During the pulling process of the slide, the surface infiltrated with molten steel and steel slag gradually increases. When the cold steel reaches a certain thickness, gaps appear between the slides and steel leaks.
(2) When casting calcium-treated steel, [Ca] in the molten steel reacts with the main component A1203 of the aluminum-carbon slide to form A aluminum-calcium series low-melting point compounds. The low-melting point compounds are washed away by the molten steel, and the upper slide forms horseshoe-shaped erosion, and the lower slide has deeper and longer grooves. When the sum of the groove lengths of the upper and lower slides exceeds the safety distance of the slide, a steel leak accident will occur when the steel casting is not closed tightly. Figure 4 shows that the calcium content of the molten steel is high and the upper slide surface has horseshoe-shaped erosion, and Figure 5 shows the grooves on the lower slide surface after calcium erosion.
(3) The mechanism slideway, track wheel and shaft are seriously worn, and the mechanism pressure is reduced. The spring is over-serviced, and the spring pressure drops significantly, resulting in a large drop in the pressure between the slides. When the pressure between the plates is lower than the static pressure of the molten steel, steel leakage between the plates occurs.
(4) The processing accuracy of the slide plate surface is low, and the gap between the upper and lower slide plates exceeds the minimum gap for molten steel to penetrate. Under the action of static pressure, the molten steel in the gap between the plates penetrates into the plates, causing steel clamping. As the pouring time increases, the penetration of molten steel increases, causing steel leakage.
Improvement measures
(1) Improve the quality of the slide plate in combination with the type of steel being smelted to improve its oxidation resistance and corrosion resistance.
(2) If the calcium content in the molten steel is high, the aluminum-carbon slide plate cannot meet the requirements, and a magnesium-carbon slide plate should be selected.
(3) Increase the inspection of the mechanism. If the slideway, small wheel, and shaft wear exceeds the specified size, they should be replaced in time. Regularly check the spring pressure and replace the new spring when the pressure value is lower than the specified value. If a gas spring is used, the spring sealing should be tested for each furnace, and the failed spring should be replaced. Ensure that the pressure between the upper and lower slide plates is not lower than the design value.
(4) Improve the processing accuracy of the slide plate surface, add an anti-oxidation coating on the slide plate surface, and improve the fit between the slide plates.
Steel leakage between the lower slide plate and the drain port
Cause Analysis
The top tightening sleeve is loose. At present, in order to improve the quality of steel billets and prevent secondary oxidation of molten steel during the steel pouring process, a long nozzle is installed under the downspout brick. During the switch pouring process, the sliding trolley moves together with the lower slide brick and the downspout brick, and the downspout drives the long nozzle to move. After multiple reciprocating movements, the top tightening sleeve that locks the downspout brick may be twisted loose, resulting in a gap between the lower slide brick and the downspout brick, causing steel leakage. Figure 6 shows that the top tightening sleeve of the downspout is loose, and steel is leaking from the mud gap between the downspout and the lower slide.
Improvement measures
When installing the drain, use a hammer to hit the top tightening sleeve to lock it in place. Before sliding the drain each time, tighten the top tightening sleeve again.
Steel leakage caused by drilling or breaking of nozzle
Cause Analysis
(1) Low melting point impurities are entrained in the refractory. The continuous casting does not open automatically and the burning eye is used. The large inclination angle of the oxygen tube causes burn damage to the diameter of the water nozzle.
(2) Water nozzle fracture. The refractory itself forms cracks after being subjected to thermal shock. When the long nozzle is installed in the continuous casting, the robot hits the water nozzle, and the water nozzle is broken by external force. The water nozzle and the bowl of the long nozzle do not match each other. During the steel pouring process, the molten steel returns to the matching gap to form adhesion. It is difficult to remove the long nozzle after the steel pouring is completed, and the water nozzle is damaged by pushing and breaking. It is difficult to find the internal damage of the refractory when it is used again. The water nozzle breaks during continuous use. Figure 7 shows the leakage caused by the external force when the long nozzle is installed.
Improvement measures
(1) Clean the refractory production environment and screen the discharged materials to avoid the inclusion of material lumps. Bend the oxygen tube during the burning operation and insert it vertically upward when it is inserted into the nozzle to avoid the oxygen tube from burning the refractory materials at a large tilt angle.
(2) Improve the thermal shock resistance of the nozzle. Design a reasonable combination of the nozzle and the long nozzle, and install a sealing ring at the joint position to reduce the phenomenon of steel sticking and steel returning.
There are many reasons for steel leakage in the sliding nozzle system of the ladle. Only by selecting suitable refractory materials, strengthening the maintenance of the sliding nozzle mechanism, improving and standardizing hot repair operations, formulating corresponding countermeasures for common causes of steel leakage in various parts, and unswervingly implementing them, can the probability of steel leakage be significantly reduced.
