Steelmaking ladle nozzle between nuisance steel causes and improvement measures

Steel mill ladle is a metal container which belongs to contain high temperature steel, after receiving converter steel in the production process, it is lifted to continuous casting area by overhead crane for steel pouring operation, there is a set of slide plate mechanism at the bottom of the ladle, which consists of steel structure and refractory material. Above the intermediate ladle of continuous casting, the slide plate mechanism is opened manually, and the molten steel in the ladle automatically flows into the tundish, completing the conversion of molten steel between containers. At the bottom of the ladle, the liquid steel sealing relies on the tight fit between the slide plate, the slide gate plate mechanism is driven by hydraulic pressure, the slide plate periphery is composed of matching resistant materials such as the upper and lower nozzle, etc. The slide plate mechanism at the bottom of the ladle is shown in Figure 1.

Ladle bottom slide mechanism
Ladle Bottom Slide Mechanism

1.Location and cause analysis of ladle steel nuisance

1.1 Steel nuisance position

The position of the nuisance steel is between the ladle nozzle and the upper slide plate, As shown in figures 2.

lalde nozzle position
Figures 2 Lalde Nozzle Position

1.2 Analysis of the causes of steel nuisance in smart ladles

In response to several smart ladle leakage accidents of nuisance steel, professional and technical personnel combined with the design department, the use of units, maintenance departments for many follow-up, discussion, found the following design defects.

(1) The strength of the ladle nozzle parcel exposed outside the ladle well block is low.

Intelligent ladle on the upper nozzle wrapped in the well block length of 140 mm, the length of 115 mm in the seat of the external brick, the nozzle and well block rely on refractory cement bonded together as a whole length of only 140 mm, the overall strength is worse than the conventional packages (conventional ladle nozzle completely wrapped in the seat of the internal brick, the length of 255 mm). The sealing and bonding between the nozzle and the steel structure relies on the sealing mud refractory material, the two do not belong to the same kind of material, can not be fused together, and the expansion coefficient of the two at high temperatures is large, which will form a cavity, the nozzle and the overall strength of the well block is poor. The field installation diagram is shown in Figure 3.

Nozzle Installation Dimensions3
Figure 3 Nozzle Installation Dimensions
nozzle installation4
Figure 3 Nozzle Installation

(2) The addition of a slag detection coil in the mounting plate results in a non-tight fit.

The slide mechanism relies on the mounting plate for fixation, and the mounting plate is connected to the bottom of the bag with 4 bolts welded and fixed, and the total thickness of the mounting plate is 70 mm, in which the lower slag detection coil is added, with a thickness of about 35 mm, and the inner diameter is larger than that of the mounting plate, and there is a deviation of about 15 mm, which results in the formation of a misalignment. The comparison of the mounting plates of the smart package and the conventional package is shown in Figure 4.

Ladle Slide Gate figure4
Ladle Slide Gate

Close fit of nozzle to nozzle seat tiles during installation of plain packet upper nozzle.

In the smart ladle spout installation process, between the nozzle and the nozzle well block due to the detection coil in the cavity of the mounting plate, the two are not a close fit, as shown in Figure 5.

Ladle nozzle and well block installation5
Figure 5 Ladle nozzle and well block installation

(3) The slide bar of the mechanism is designed to be made of 45# steel, which has low strength at high temperature.

Sliding plate mechanism in the operation process, mainly relying on the slide bar compression spring, slide bar material design for 45 # steel, in the high temperature state of strength and toughness of the weak, in the operation process of different degrees of wear and tear, the surface of the convex and concave, resulting in the upper slide plate and the nozzle between the steel and nuisance steel, and ultimately burned out of the mechanism, the occurrence of leakage of steel accidents.

(4) The slide plate of the smart package was initially designed as a teardrop shape, relying on the four corners of the block, also known as the top tightener (with the slide plate contact edge is linear) for fixation, the block and the slide plate are in line contact with each other, the wrapping force is not enough. The slide plate and fixing method on site is shown in Figure 6.

Slide Gate fixation
Slide Gate Fixation

(5) The design size of the spout top table inside the nozzle well block is small. In the middle and late stages of use, the internal surface of the well block cavity and the top platform of the nozzle (made of aluminium-magnesium-carbon material) appeared to be oxidised, eroded and peeled off, and were forced to come off the line earlier.

The upper nozzle of the ladle is installed inside the nozzle well block, the well block and the bottom of the package into one, in each ladle offline inspection, sand process, it is necessary to use the oxygen pipe to clean the impurities inside the nozzle also known as cleaning the nozzle. The material of the nozzle well block is aluminium-magnesium-carbon, and there is a top table inside, which mainly fixes the position of the front end of the upper nozzle. In the process of cleaning the nozzle, oxygen will gradually erode the surface of the internal cavity of the well block and the front end of the top platform, resulting in oxidation of the internal cavity of the well block surface peeling, peeling, and the front of the top platform erosion. After installing the new nozzle, the nozzle loses the top support force, and will be displaced inwards during manual installation, and at the same time, due to the oxidation of the inner cavity of the well block, the mud gap between the spout and the well block increases, and the strength of the parcel is weakened, as shown in Figure 7.

well block erosion
Figure 7 Well Block Erosion

In addition, there are some problems in the actual operation on site.

① In the process of replacing the upper nozzle and upper slide gate plate, manual labour is required to use external force for the installation of the upper nozzle. When installed, due to the short sintering time of the sealing clay between the nozzle and the nozzle well block, the overall bond strength is weak, the nozzle will be displaced towards the inside of the well block (after the erosion of the internal top platform of the nozzle well block), resulting in an increase in the gap between the nozzle and the upper skateboard’s sub-mother clasp; At the same time, the strong surface pressure of the slide gate plate and the cylinder pulling force leads to the loosening of refractory cement between the upper slide gate and the upper nozzle, resulting in the occurrence of the steel nuisance. From the position of the steel, all in the same direction of the slide movement.

② The use of pressure between the sliding plate is 7 MPa, in order to reduce the clamping of steel and between the plate nuisance steel, by adjusting the spring and pressure gear, the sliding gate plate surface pressure is adjusted to 11 MPa. In the production of the open casting, pulling the lower sliding plate (the upper sliding plate and the upper nozzle with fixed immobility), a strong extrusion pressure is transferred to the upper sliding plate, the upper sliding plate and the upper nozzle is stressed, the nozzle may be moved towards the internal well block (the nozzle well block of the inner top table erosion, nozzle well block, the internal surface of the top platform of the seat, oxidation, spalling). (the internal top platform of the well block erodes, and the surface of the inner cavity of the well block oxidises and peels off). At the same time, under the strong pulling force of the cylinder, the upper slide plate produces lateral displacement, and the refractory cement between the upper slide plate and the upper nozzle loosens, resulting in the emergence of nuisance steel.

2.Follow-up improvement measures

Aiming at the above smart ladle in the use of the process of the defects exposed to research and analysis, combined with the scene to carry out some rectification.

(1) Modification of the lower slag detection coil embedded in the smart ladle mounting plate

The lower slag detection coil is embedded in the mechanism of the internal mounting plate, and with the mounting plate holes due to dimensional deviation to form a misalignment, constituting a cavity, in order to eliminate this hidden danger, to produce a protective sleeve, inlaid in the coil outside, not only to fill the position of the cavity, eliminating the misalignment, but also to increase the protection of the coil. The field modification is shown in Figure 8.

Detection Coil Protective Sleeve8
Figure 8 Detection Coil Protective Sleeve

(2) Intelligent package upper and lower slide plate transformation

In the actual production process, the lower slide plate is driven by the slide plate mechanism for movement, the upper slide plate is always in a static state, so as to achieve the upper and lower slide plate holes aligned to achieve the state of liquid steel flow and closure. In order to ensure that the upper slide plate will not be displaced in the process of use, the fixed block of the slide plate (attached to the entire mounting plate above) is not changed, while the upper and lower slide plate is modified from the original teardrop shape to octagonal, as shown in Figure 9. So that the fixed way of the slider is changed from line contact to face contact, increasing the contact area and increasing the strength of the package.

Modified slide gate plate
Figure 9 Modified Slide Gate Plate

(3) Improvement of the material of the slide bar in the slide plate mechanism

Due to the repeated action of high temperature and friction of the slide bar in the slide gate mechanism in the movement of the lower slide mechanism, the slide bar shows different degrees of wear. Subsequently, the material of the slide bar was changed from 45# steel to 40Cr, and the annealing process was carried out at the same time, which increased the abrasion resistance and toughness of the slide bar, prolonged the service life of the slide bar, and the amount of abrasion was reduced, and the symptom of the steel clamping between the slide plates also disappeared.

(4) Modification of the top platform inside the nozzle well block

During the use of ladle well block, its internal top platform is constantly eroded due to the use of oxygen to clean the nozzle, and the nozzle appears to move internally during the use, causing the sealing mud between the upper nozzle and the upper sliding plate to loosen, which results in seepage and nuisance of steel, and in serious cases, leads to leakage of steel. In view of this design defect, the technicians combined with the field personnel to improve the top table and inner diameter inside the well block. Specific improvements in size, that is, in the original size of 20 mm above the increase in the contact area of the nozzle and the top platform, thus reducing the erosion rate of the well block, extending the service life, slowing down the nozzle in the use of the process of the chances of internal displacement, to eliminate the upper nozle, the upper slide between the seepage of steel, steel breeding accidents. At the same time, for the nozzle well block transformation, the corresponding upper nozzle has also been modified, the specific dimensions shown in Figure 10.

Upper nozzle modification dimensions10
Figure 10 Upper nozzle modification dimensions

(5) According to the actual situation on site, sum up the operation experience and formulate the operation standardised operation.

① Due to the intelligent mechanism in the process of replacing the nozzle and slide plate operation is cumbersome, long time, in order to ensure the safety of the mud mouth between the upper slide plate and the upper nozzle, will be manually mixed on-site filler fire clay (sealant mud) changed to moulding rubber mud cake. On the one hand, effectively extend the mud mouth sintering time, on the other hand, make the sealant mud mud volume has been effectively controlled, to achieve the mud mouth between the mud volume full, the upper and lower slide plate between the purpose of uniform force.

② Regular replacement of all institutions track, slider, spring, track wheel, axle, to achieve a balanced force between the slide gate.

③ Regularly replace the lower nozzle sets and trolleys of all mechanisms to reduce the influence of spare parts on aperture alignment and solve the problem that the lower nozzle cannot be locked.

④ Formulate standards for replacement of slide plate mechanism and resistant material, implement standardised operation, and conduct field operation process training from time to time to strengthen workers’ operation concept and operation habit.

After practicing, figuring out and summarising the use of the new intelligent ladle in the steelmaking plant, and through the careful analysis and study of many accidents, a series of modifications were finally made to the ladle slide mechanism, and the ladle slide mechanism is now used relatively smoothly. According to the field data collection statistics, the annual accident rate is reduced by 25%. In the subsequent use process, professional and technical personnel need to continue to follow up and constantly make adjustments and improvements to achieve safe production on site.

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