In the production of the largest arc furnace

https://www.lmmgroupcn.com

6 common types of refining devices outside the ladle furnace and the types of refractory materials used

The ladle degassing refining method is the main method of refining outside the furnace (also known as secondary steelmaking). Out-of-furnace refining is the process of transferring the molten steel smelted in a roughing furnace (electric furnace and converter) to another high-temperature vessel (mainly a ladle) for refining: Refining is a process of using different metallurgical treatment methods and devices outside the furnace according to the type of steel to be smelted.

Basic knowledge of continuous casting and 11 issues for improving the quality of continuous casting slab

 1. What are the causes of longitudinal cracks on the surface of continuous casting slabs and their prevention methods?

Longitudinal cracks on the surface of continuous casting slabs will affect the quality of rolled products. For example, a longitudinal crack with a length of 300mm and a depth of 2.5mm leaves a 1125mm layered defect on the rolled plate. Severe longitudinal cracks will cause leaks and rejects.

Safe operation process of continuous casting and pouring steel

01 Tundish preparation

1. Check the wall, bottom and baking conditions of the tundish;

2. The middle contractor shall determine the middle contract number used on duty according to the middle contract situation, write it on the blackboard and explain and sign on the "Tundish Packaging Safety Use Record Sheet" in the duty room (such as: normal, spare, new package and baking status, Out of service);

Reasons and preventive measures of steel breakout in continuous casting machine

 One of the main operational failures encountered in continuous casting is "breakout". When the cast stream slab shell ruptures, the static molten steel in the slab shell overflows and blocks the machine, requiring expensive downtime. In order to pull out the breakout shell, it is necessary to extend the downtime caused by the breakout, because it may block the guide roller or the foot roller, and air cutting is required to clean the blockage and pull out the billet shell. When the temperature of the broken steel billet shell decreases, it needs to be cut into small pieces and taken out of the machine with a straightening machine. The straightening machine is designed to gradually straighten the cold billet shell in the stable stage. The upper roll can provide enough Lift the gravity to create a curved cast stream that is not too long. Therefore, the breakout has a major impact on the effectiveness of the casting machine—influencing productivity and production costs.

Matching principle of continuous casting machine and steelmaking and rolling

Classification method of continuous casting machine

At present, continuous casting machines have been widely used in steel mills, with various forms and different uses. The name of the continuous casting machine is also very inconsistent. Now introduce the classification method of continuous casting machine according to general habits:

Slide gate plate and nozzle installation

Before installing the upper nozzle on the online ladle, first check the usage of the nozzle block. If there are pits or cracks, use the repair material to repair, and then perform the next step.

Take the upper nozzle brick for trial installation, check the gap between the nozzle brick and the seat brick and the positioning of the nozzle brick. It is forbidden to smash off the upper nozzle head before installing.

Take the upper nozzle brick for trial installation, check the gap between the nozzle brick and the seat brick and the positioning of the nozzle brick. It is forbidden to smash off the upper nozzle head before installing.

When installing the nozzle, the nozzle brick should be smoothly fed into the seat brick, and the mud at the bottom of the nozzle brick should be prevented from falling off and creating gaps during operation.

The water inlet must be replaced when the following conditions exist during installation and use.

The installation and positioning distance of the upper nozzle exceeds the standard range, resulting in the clamping of steel between the upper nozzle and the upper sliding plate or the phenomenon of inability to pull.

The horizontal or vertical aperture of the water inlet exceeds 85mm.

LMM GROUP One stop service for steel industry

Slide gate plate nozzle

EAF steelmaking replacement of graphite electrodes

LMM GROUP One stop service for steel industry

Graphite Electrode

Continuous casting mold flux knowledge

 1. What is the role of continuous casting mold powder?

During the pouring process, powdery or granular slag is continuously added to the molten steel surface of the mold, which is called mold flux. The role of mold powder has the following aspects:

(1) Thermal insulation to prevent heat dissipation;

(2) Separate the air to prevent oxygen in the air from entering the molten steel to cause secondary oxidation, which will affect the quality of the steel; (3) Absorb and dissolve the inclusions that float up from the molten steel to the slag interface to purify the molten steel;

(4) There is a layer of slag film between the mold wall and the solidified shell for lubrication, reducing the drawing resistance and preventing the adhesion of the solidified shell and the copper plate; (5) Filling the air gap between the blank shell and the mold to improve Heat transfer in the mold.

A good mold flux should be able to fully play the role of the above five aspects to achieve the purpose of improving the surface quality of the cast slab and ensuring the smooth flow of continuous casting.

When and how to add mold flux for continuous casting is the most beneficial?

In the actual production process, the performance of mold powder is closely related to the operation of adding slag. The continuous casting production practice of domestic and foreign steel mills has proved that even if the mold powder is selected correctly, failing to use it correctly will cause no quality problems in the cast slab. When adding protective slag to the mold, the mold slag must be evenly distributed on the molten steel surface in the mold. When the molten steel level fluctuates, drifts, stops casting and other failures occur during the pouring process, corresponding measures must be taken. In the actual operation process, the following items should be paid attention to when adding mold powder.

The composition and use skills of the slide gate late nozzle

The sliding nozzle is composed of upper and lower sliding plates and 4 refractory bricks for the upper and lower nozzles. The pouring of each ladle of molten steel must pass through the upper and lower sliding plates and the upper and lower nozzles, so they are very strict. Firstly, they must have sufficient strength at high temperatures to withstand the static pressure of molten steel, and secondly, the upper and lower sliding plates are required. The sliding surface should be very smooth, flatness should be high, to ensure tight contact, to ensure that no molten steel leaks during the pouring process, but also to be resistant to erosion, erosion, and good thermal stability, so as to withstand sudden changes in temperature. Erosion and slag erosion.

The sliding nozzle device is composed of upper and lower slide plates made of refractory materials and a mechanical drive structure, and is installed outside the bottom of the ladle. The upper slide is fixed, and the lower slide is movable. According to the skateboarding method, it can be divided into three categories:

1) Linear reciprocating;

2) Linear propulsion;

3) Rotary type.

By driving the pull rod, the sliding plate slides back and forth in a straight line. When the casting holes on the upper and lower sliding plate blocks are staggered, the upper nozzle hole is filled with drainage sand, and the steel ladle can be loaded; when the casting holes overlap, the drainage sand automatically flows out. Pouring, and the pouring speed can be controlled by the degree of overlap of the casting holes.

The sliding plate is a key component that determines the function of the sliding nozzle, and plays a role of controlling and regulating the flow of molten steel. Due to the repeated contact of the sliding plate with high-temperature molten steel (especially the casting hole), the corrosion damage is serious and the use conditions are harsh. The skateboard is required to have good performances such as high strength, corrosion resistance, and peeling resistance. During the casting process, ensure that no molten steel leaks between the skateboards. The skateboard must have the following properties:

(1) Flatness of sliding surface ≤0.05mm;

(2) High mechanical strength;

(3) Strong corrosion resistance to molten steel and molten slag;

(4) Excellent anti-oxidation performance;

(5) Good thermal shock stability.

The sealing protection of the ladle sliding nozzle is mainly at the connection between the upper nozzle and the upper slide, and the lower slide and the lower nozzle. In the pouring process, generally after pouring one or two furnaces of molten steel, the lower slide plate and the nozzle must be replaced and reassembled. The sealing protection adopts fibrous or mortar gaskets to ensure the high cleanliness of the molten steel and the uniformity of the internal quality of the casting slab.

Sliding nozzle hydraulic transmission:

Large and medium-sized ladle generally use hydraulic transmission devices to solve the problem of opening and closing sliding nozzles. Hydraulic transmission is driven by liquid (common oil) as the working medium. Because the liquid has almost incompressible characteristics, when the liquid is filled with a closed container (consisting of oil pumps, pipes, valves, cylinders, etc.), the liquid is pressurized by the oil pump, and it can lose this pressure through pipes, valves, etc. It is transmitted to the oil cylinder very small, causing the oil cylinder to move and realizing hydraulic operation. Reasons for steel leakage between sliding nozzles and preventive measures

(1) The reason for the leakage of the gap between the drain and the lower sliding plate: the sliding plate is not baked after pre-installation; the cement is not evenly coated during installation, resulting in gaps; there are bricks in the cement, making it loose.

Preventive measures: The fire mud must be clean during installation, the joints must be evenly seamed, and can only be used after baking and drying.

(2) The reason for the leakage of the upper and lower slide plates: the sliding surface is not flat; the upper and lower slide plates are cracked at the edge of the injection hole; the adjustment operation is not tight or the front and back are uneven.

Preventive measures: pay attention to choosing flat skateboards. Do not use skateboards without steel hoops to prevent cracking at the edge of the injection hole; the adjustment operation should be tight and even before and after.

(3) The reason for the leakage of the gap between the upper nozzle and the upper sliding plate: the upper sliding plate and the upper sliding plate are not evenly coated with mud; the mass in the fire mud causes the male and female mouths to be insufficiently deep and disconnected; the gap is too large.

Preventive measures: the fire mud should be clean, and the joints should be evenly cracked.

LMM GROUP One stop sevice for steel industry slide gate plate nozzle 

Design and Analysis of Continuous Straightening of Arc Continuous Casting Machine

 1 The function of the straightening machine

The arc continuous caster is the main force in the production of cast slabs in the iron and steel industry. Square billets, rectangular billets and round billets are generally produced by arc continuous casters, occupying a dominant position, even for continuous casters with straight arc arrangements. It is also necessary to use a circular arc section for transition, and straightening of the cast slab is still required after the arc section. The stretching and straightening machines of the square billet and round billet arc continuous casters are centrally arranged near the horizontal line. The stretching and straightening machines in the continuous casting production process need more than two. The conventional continuous casting machines for billet production will be arranged with two stretching and straightening machines. In one frame, a five-roller tension leveler is formed. The function of the tension leveler is:

(1) Balance the sliding force of the slab: use the upper and lower rolls of the tension leveler to hug the slab in the sky to prevent the slab from falling down and maintain continuous production. This is also the basic parameter of the hydraulic design of the tension leveler, such as the use of a 16-meter radius casting machine for production. For the φ600mm round billet, 35 tons of sliding force is generated due to the high potential energy, which requires multiple tension leveling machines to work together to generate a friction force capable of balancing 35 tons. Figure 1 shows the drawing and leveling machine group of Wuxi Xuefeng Great Circle Continuous Casting Machine, where 5 drawing and leveling machines are used. The use of a 9-meter radius casting machine to produce 150mm billets also has a sliding force of 1.5 tons. This only requires the friction generated by a pair of rollers to balance this sliding force. Figure 2 shows a typical five-roller tension leveler. For billet production, continuous casters with an arc radius of 6~10m are generally used, and most of them are in the form of a five-roll straightening machine, as shown in Figure 2. The initial stage completely relies on the friction generated by a pair of pull rolls to balance the casting or guiding The spindle weight, so as to maintain normal production.

Picture 1: Continuous caster stretching and straightening machine group

Picture 2: Fully water-cooled billet continuous casting stretch-straightening machine

(2) Constant casting billet drawing speed: According to the operation requirements, the frequency converter controls the drive motor and the speed of the reducer to transmit the power to the rollers of the drawing and leveling machine. The rollers and the casting are under the action of the hydraulic pressure of the hydraulic cylinder. The slab produces friction, so that the slab that is steadily falling will drive the rollers according to the requirements of the drawing speed, so that the casting slab will slide in a continuous and stable manner according to the requirements of the drawing speed. In fact, from the force analysis, the tension leveler is actually a slab Sliding speed stabilizer.

(3) Feeding of the induction bar: The casting and drainage of continuous casting is carried out through the induction bar. At the beginning of the operation, the tension leveler is used for transmission, and the induction bar is also fed into the induction bar through the second cold room through the second cold room. Place it in the inner cavity of the copper tube, as shown in Figure 3. After the starter head is ready, the starter is ready for pouring. When the continuous casting starts, the tension leveler friction drives the starter rod downwards, the solidified slab head is connected with the starter head, and the cast slab descends with the starter rod. After the slab head is separated from the starter bar, the rigid starter bar continues to rise by the friction of the clamping roller of the starter storage device and enters the starter bar storage device; the flexible starter bar passes through The roller table before and after cutting enters into the idler bar storage roller table, and the flexible idler bar storage device lifts it out of the roller table and puts it aside.

Figure 3: The photo of the starter rod entering the crystallizer through the second cold room

(4) Straightening the slab: the slab with a radius of curvature of R is transformed into a straight slab with an infinite radius of curvature through the straightening action of the tension leveler. Even if the vertical bending continuous caster is used, the slab needs to be The curved shape from the radius of curvature is transformed into a cast slab with a straight length by the action of a straightener.

Therefore, the design of the tension leveler needs to consider the size of the cast billet section, the radius of the casting machine, the motor power, the speed ratio and strength of the reducer, and the number of the tension leveler's clamping rollers and the size of the hydraulic cylinder should be reasonably configured.

2 Calculation of the output pressure of the tension leveler

2.1 The pressure output by the hydraulic cylinder of the tension leveler

Take an example to illustrate the force analysis of the tension leveler. See Figure 4 for the actual object of the tension leveler.

Figure 4:Five-roller tension leveler

The force analysis of the tension leveler is shown in Figure 5. This is an independent tension leveler, and its force analysis is consistent with the five-roller tension leveler.

Figure 5: Schematic diagram of tension and leveling machine force

The force output by the hydraulic cylinder can be decomposed into horizontal force and vertical force. The angle is α=25.8298°. The horizontal force of the hydraulic pressure at the ball head is Fh=fcosα, and the vertical force is Fv=fsinα. The hydraulic pressure is transmitted by the hydraulic cylinder. The resulting dynamic torque is equal to the resistance torque of pressing the upper roll, and N is the vertical pressure exerted on the casting billet, so:

Fcosα*700+Fsinα*(170+900)=900N 900N=1096F N=1.2177F

It can be seen that through the structure design of the upper roller of the tension leveler, the effect of amplifying the hydraulic pressure is achieved, which increases the positive pressure of the tension leveler. This structure is widely used in the tension leveler of square billets and round billets.

The design of the big round billet stretch-leveling machine, when producing a Φ330mm round billet, α is equal to 56.35°, as shown in Figure 6. According to the above analysis of the structure, N=1.33F.

Figure 6: Tension and straightening machine of large circle continuous casting machine

2.2 The tension and straightening machine pressure required to send the starter rod

The hydraulic pressure output by the tension leveler is a function of the cylinder diameter and the pressure. For example, the cylinder diameter is φ140mm, the hydraulic pressure is 20bar, and the output pressure of the hydraulic cylinder is 3.785 tons. Take the Wuxi Great Circle Continuous Casting Machine as an example, under the action of this hydraulic pressure , The pressure exerted on the casting billet is 4.09 tons, the friction force generated is 1.23 tons, and the friction force generated by five tension levelers is 6.14 tons, which can hold the φ280mm round billet produced by the continuous casting machine with a radius of 11 meters. It is in stable production.

The coefficient of friction between the high-temperature cast slab and the roller of the tension leveler is calculated according to 0.3. I have done this test many times to verify the coefficient of friction, which is roughly the data. The starter bar is in a cold steel state, and its friction coefficient is much smaller. It is also through many tests of its own. This friction coefficient is about 0.1~0.15, so the cold billet pressure required to send the starter bar is much larger, such as The Wuxi Xuefeng large circle continuous casting machine used a pressure of more than 120bar to send the flexible starter bar. It should be noted that the flexible starter bar sends the starter head into the copper tube. Generally, the tension leveler below only has 2~3 racks. If the dead weight of the ingot bar is large, a higher hydraulic pressure is needed to balance the sliding force of the ingot bar, as shown in Figures 7-9.

Figure 7: The ingot bar emerges from the crystallizer to install the ingot head

Figure 8: R11 meter round billet continuous caster's starter rod is sent to the mold for pouring

Figure 9: The ingot bar pulls the cast slab down

The process of sending the spindle rod requires the maximum hydraulic pressure output by the tension leveler, mainly:

(1) The friction coefficient between the roller of the leveler and the starter bar is small.

(2) The influence of the dead weight of the starter rod. For large-section cast billets, the starter rod needs to have a certain dead weight, so as to maintain the dead weight of the starter rod to pull the cast billet to overcome the resistance of the mold, so sufficient friction must be paid by the tension leveler Force to balance the sliding force caused by the rising of the ingot bar. Tang Gong has always insisted that overcoming the mold pulling resistance is the sliding force generated by the dead weight of the ingot bar and the slab, so it must have a certain height and dead weight potential energy to overcome the mold resistance, which is the basic condition for stable continuous casting production. Can not expect the tension leveler to generate tension to overcome resistance.

(3) Flexible starter bars are generally used for large-section cast billets. The basic radius of the casting machine is large, and the cast billet and the starter bars have large potential energy, so a large hydraulic pressure is required to generate sufficient friction to balance the sliding force.

At the end of casting of the continuous caster, the moment the billet leaves the copper tube, due to the absence of the mold drawing resistance, if the billet size is large, the weight per unit length is greater than the weight of the ingot bar, which is caused by the weight of the billet. The sliding force is the largest. At this time, the tension leveler needs the greatest hydraulic pressure to hold the cast slab in the sky. Therefore, the design of the hydraulic station of the continuous casting machine stretching and leveling machine requires a high pressure of more than 160 bar, which is to send the ingot bar and start to use the continuous casting. Once the stretching and leveling machine most of the rollers are pressed against the high temperature casting billet, it can be converted to The pressure of the hot billet is much lower than the hydraulic pressure of the delivery spindle.

3Continuous straightening curve

3.1 Determination of the straightening curve equation

Figure 10 is the tension leveler design of ASIMCO for the Iran project. I simplified it here. The cast billet is 200mm square billet, the basic radius of the caster is R9 meters, and the rigid starter bar. The angle inside is selected as 3.542°:

Tanα=0.061898433

This angle is the angle between the tangent line of the lower roll of the draw roll and the horizontal line. If this is the starting point of the curve between the draw roll and the intermediate roll, the corresponding slope of the curve is tan(α).

Figure 10: Schematic diagram of continuous straightening machine

The derivative of the curve is the slope of the aforementioned great circle at the tangent point. Assuming that the center of the coordinate is on the center of the basic radius of the continuous casting machine, then the abscissa of the tangent point is x=-9000*sin3.542=-556.02171, and the equation of the circle is :

The derivative is:

Let's put the coordinate origin on the intersection of the middle roller surface of the five-roller tension leveler and the vertical centerline. According to consensus, the cubic parabola equation is generally used to determine the straightening curve. The cubic parabola equation is:

Derivation of the above formula:

The value of k can be given according to the initial conditions, namely:

For the cubic curve, the slope at the tangent point, the distance from the tangent point to the vertical roller surface below the pulling roller a=175*sin3.542=10.81153397mm, so for the cubic curve the abscissa x = 1125-10.81153397 = 1114.188466mm , Into the formula, you can find k = -1.6621x10-8, so that the equation of the cubic curve can be determined.

3.2 Calculation of the descending height of the intermediate roller and the straightening roller in the straightening section

We find the descending distance between the intersection of the intermediate roll surface and the vertical centerline to the tangent point of the continuous casting reference circle on the drawing roll, and let x=-1114.188466mm, which can be calculated as 22.98884mm, plus the vertical point of the drawing roll The amount of descent h=175-175*cos3.542=0.334288616mm, the amount of descent of the centerline of the lower roller and the middle roller of the pulling roller = 22.98884+0.334288616 = 23.3212862mm. In this way, all the geometric parameters of the so-called continuous straightening of the tensile straightening machine are determined.

The drop amount on the drawing is 23.53mm, which is a little different from my calculation. I estimate that some designers use an empirical formula in the calculation of the K value, so there is a little difference. This difference does not affect the production and use of the equipment, but from three times From the perspective of the square curve, the deduced formula is accurate, but I think this error will not have any negative impact on straightening.

Whether the cast slab is bent and deformed according to the continuous straightening curve we stipulated, in fact, the object still follows the principle of minimum action during the deformation process, that is, it runs in the direction of the least force during the deformation process.

A lower roll is added between the pull roll and the straightening roll. The purpose is to convert single-point straightening into two-point or continuous straightening, but I always think it should be two-point straightening, and it should be based on the principle of continuous straightening. The calculated descent of the intermediate roller and the straightening roller takes into account the elastic recovery of the object after straightening, that is, exceeding the required straightening amount, giving the casting billet space for recovery. Therefore, the design of the roller for straightening is lower.

On the R9-meter and R8-meter billet continuous casters, we can see that the straightening roll is lifted during normal production, and the straightening force is generated by the weight of the cast slab, but the intermediate roll is separated from the lower surface of the cast slab. This amount is about 2mm, of course, also left the lower roller surface of the straightening roller. Observe that the two lower rollers of the straightening roller and the middle roller do not rotate. This is the single-point straightening mode, as shown in Figure 11. From the long-term production practice, no impact on product quality has been seen. Therefore, there is no need to believe in the so-called continuous straightening, that is, two-point straightening and single-point straightening are no problem.

I used to be a steel rolling engineer. The rolled rebars need to undergo bending and reverse bending tests. Sometimes, in order to observe the bending of the steel bar under extreme conditions, I bend the steel bar to 135°, and then consciously bend it to 90~180°. The deformation conditions are very harsh, and the strain has reached more than 15%, but basically no cracks on the surface of the steel bars can be seen, indicating that the steel can adapt to large strain deformation. Although the slab straightening is the as-cast structure, the slab under high temperature still has a certain degree of plasticity, and straightening cracks will not appear at a small strain rate.

Once the pouring was stopped due to power failure, the φ280mm cast slab has been cooled to below 500°C. In order to reduce the workload, continue to turn on the straightening machine to pull it out after the power is turned on, carefully observe the surface of the cast slab, and then cut the low-magnification sample. Nothing is found Any crack defect, according to the normal billet delivery, everything is normal, indicating that as long as it is not straightened in the dual phase zone, it will not affect the billet. The rolling straightening process is everywhere, and the straightening deformation is very large. The workmanship is normal, and generally no straightening defects will occur.

I think the continuous straightening roll system layout idea should be the same as the roll system layout idea in the secondary cooling chamber of the vertical bending continuous casting machine from a straight section to an arc section, and it can also be designed with reference to the above calculation. Vertical bending continuous casters are rarely used on billets and round billets. I always think that the cleanliness of molten steel must be completed in the refining process. You cannot expect to remove inclusions in the tundish and mold, and in the mold The downward scouring action of the inner molten steel creates agitation of the molten steel in the cavity. It is difficult to have the conditions for the inclusions to float up. It does not require the straightness provided by the vertical bending continuous caster to float the inclusions. The vertical bending continuous caster is complicated in equipment. Maintenance is troublesome and there are many spare parts, so there is no need to increase the trouble. The arc continuous caster is fully capable of doing it.

Figure 11: Lifting the straightening roll during the production of the billet continuous caster, relying on the billet's own weight to straighten it

The problems that arise in the production process can always be solved through on-site efforts, continuous adjustment and continuous improvement. As long as the on-site engineering and technical personnel, management managers and on-site employees continue to learn and practice, they can use the existing equipment Produce higher-level steel grades under horizontal conditions.

The purpose of writing this article is to solve the problem, expounding the ingot process and the straightening process, hoping to solve the existing problems, and at the same time expounding some theories on the casting slab straightening, hoping to give you a clear concept. Understand this starter and straightening process. At the end of the article, the progressive straightening parameters are deduced. Everyone is engaged in the work related to the continuous casting machine. It may be useful to understand this design.

The straightening process design of the continuous casting machine is ideal. However, due to the installation error and the wear of the rollers of the tension straightening machine in actual production, it is impossible to carry out continuous straightening completely in accordance with the ideal state. The casting billet straightening process has For larger latitude, I have seen a continuous casting machine that has been installed incorrectly. The elevation and position of the roll surface of the pull-straightening machine are different by tens of millimeters. The production is also normal. A set of good equipment and technology needs to be given to the operator. Certain wide-capacity, over-precision process equipment is still difficult to maintain for large-scale industrial steel production.