What If the Nozzle of Continuous Casting Is Blocked?

Continuous casting nozzle blockage is a difficult problem encountered by many steel plants on site, which not only increases the maintenance workload, but also affects the process quality, causes accidents and affects the cost. Generally speaking, the following ways can be considered:

1. Strengthening filtration and water treatment is still the foundation. First, strengthen the filtration and water quality control of the water supply system. However, this is not enough. A simple parallel double filter should be added behind the valve chamber. Its advantages are:

1) Pressure gauges are set at the front and back to make it clear whether the filter is blocked;

2) Do not occupy the operation time when cleaning is required;

3) Cleaning is very convenient.

For nozzles with important applications, it can be considered to add a filter at the joint of the spray pipe or at the inlet of the nozzle. This can solve the corrosion of the pipeline in the valve chamber and prevent sundries from accidentally falling during maintenance.

2. Select nozzles with good wear resistance. From the use of a factory, the original nozzle must be removed and cleaned within half a month, and most of them are not easy to use after reinstallation. After replacement, it can be used for 3-4 months without blockage and damage under the same water supply conditions. The reason is that the inner surface of the new nozzle has good wear resistance and is not easy to bond. It has been analyzed that the blockage of the nozzle is mainly iron oxide, calcium oxide and silicon oxide. These materials, like cement and paint, continue to bond and accumulate in the nozzle cavity, eventually blocking the nozzle.

3. Use nozzles with large through-holes: nozzles with the same flow but different manufacturers have different through holes; The nozzle structure is different, and the through-hole is also different. For example, under the same pressure and flow, the through-hole of a new elliptical nozzle of Japan spray company is twice that of the ordinary elliptical nozzle widely used in slab, and it is not easy to be blocked. Choose a new nozzle, such as 120. Rectangular nozzles are longitudinally arranged for billets or slabs. Not only can the spraying distance be longer to prevent the nozzles from being damaged or burned, but also the coverage area of one nozzle is equivalent to two or more general conical nozzles. The flow of a single nozzle is large and the through-hole is large, so it is naturally not easy to block.

If you are interested in the continuous casting machine, please contact me.

Email: marketing2@hanrm.com; kerrirollingmill@gmail.com.

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Performance Requirements and Development Direction of Steel for Rolls

Different kinds of metal materials, rolling methods and rolling mills have different requirements for roll characteristics. Therefore, there are many kinds of rollers. The rolling mill is also different due to the different shapes of metal materials (plates, tubes, bars, wires) after forming. Some rolling mills are equipped with different types of rolls, and different types of rolls are used in rolling. The following mainly describes the work roll used by the hot-rolled steel sheet mill and in direct contact with the rolled piece.

1. Roll Manufacturing Method

Rolls for steel rolling production can be manufactured by forging, casting, powder sintering and other methods. Hot rolling work rolls are mainly cast rolls. In the past, the roller was not a composite structure, but a single material. In order to make the roll high-performance, the roll is developed into a composite structure roll with the high degree of freedom of outer material. The casting methods of the composite roll are mainly the centrifugal casting method and the continuous casting forming composite method.

The inner layer of the centrifugal casting roll is ductile iron, and the inner layer of the continuous casting forming composite roll is cast steel. Cold rolling work rolls are mainly forged rolls. Cast and forged rolls are made of various materials. Adopt the corresponding roll manufacturing method according to the material. After the roll is rolled, the surface properties of the roll change due to wear and tear. At this time, the deteriorated layer on the roll surface can be removed by grinding and other methods before it can be used again.

2. Performance Requirements of Hot Strip Mill Roll

The hot strip mill is divided into the rough rolling section and the finish rolling section. The finish rolling section is divided into the front section and the rear section. Because hot rolling is carried out at a high temperature, the roll is required to have wear resistance at high temperatures. Therefore, the main material used for the roll is the casting material containing a large number of carbides. The rolling load and heat load of the roll in the roughing section are large, so the roll material should be a casting material containing a large number of carbides.

However, starting from finish rolling, the material of each stand roll can be changed to the material with less carbide content. The cast roll using carbide is generally a roll with a composite structure. The outer layer of the roll is made of hard material, so the outer layer of the roll has wear resistance and orange peel resistance. The inner layer of the roll is made of strong and tough materials, so that the roll will not break due to torque and screw-down force.

The rough rolling section has a large reduction rate, large rolling load, and high rolling temperature, so the rough roll uses materials with high strength and good heat resistance. The finishing roll is made of materials with good wear resistance and orange peel resistance. In addition, the rollers used in the finishing section should also be made of accident-resistant materials. That is, when a rolling accident occurs in the post-finishing section, the roll will not produce deep cracks and cause damage.

3. Development Direction of Roll Steel

The front roll of the finishing mill emphasizes wear resistance and orange peel resistance. In the past, high Cr cast iron rolls were used, but high-speed steel rolls have been used since the 1990s. At present, high-speed steel rolls are basically used in the front section of the finishing mill in Japan. At present, the use of high-speed steel roll is expanding, but in different countries and regions, the use rate of high-speed steel roll is different. High Cr cast iron is mainly used for various purposes as cold working wear-resistant cast iron. The carbon content of high-speed tool steel for cutting tools is about 1%, while the carbon content of high-speed steel for casting rollers is more, about 2%.

The roll material of roughing section is high-speed steel, and high hardness carbides are also used to obtain wear resistance. Therefore, the carbon content is also increased. The addition of Mo and W makes the matrix of steel produce secondary hardening during tempering, and improves the heat resistance and wear resistance. This method is the same as that of high-speed tool steel. The rolls in the finishing section is required to have good wear resistance and orange peel resistance. In the past, high alloy steel was used.

The wear resistance of high-speed steel is 3-5 times higher than that of high Cr cast iron and high alloy steel, so high-speed steel is also used for the roll at the end of finish rolling. However, high-speed steel was not used in the last finishing mill because of the roll crack damage caused by the rolling accident in the last finishing mill. The crack damage degree and accident resistance of high-speed steel roll is not as good as high-alloy roll.

In order to improve the wear resistance of high alloy roll, V and other alloy elements are added to steel, and high hardness carbide MC is used to improve the wear resistance. This kind of roll is an improved high alloy roll. The C content of high alloy roll and improved high alloy roll is higher, about 3%. Therefore, the carbides in improved high alloy roll, except MC, are mainly cementite.

In addition, graphite with an area ratio of several percent in the structure of the improved high alloy roll can lubricate the thermal bonding of steel plates in the event of rolling accidents. In addition, about 4% Ni is added to the improved high alloy roll steel to form bainite or martensite in the matrix and improve the wear resistance of the matrix. The rolling efficiency is improved by using high-speed steel in the front section of finish rolling. However, there is a problem of low rolling efficiency when using improved high alloy rolls in the rear section. At present, the development of high alloy rolls with improved performance is underway.

If you are interested in any kind of rolls, please contact me freely.

Email: marketing2@hanrm.com; kerrirollingmill@gmail.com.

TAKE A LOOK AT THE OTHER OUR ARTICLES
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