In modern steel casting process, refractory nozzle brick plays a vital role. It is not only the control hub of molten steel flow, but also the key factor to ensure the smooth casting process and improve product quality. This paper will introduce the structure, performance, application and manufacturing process of nozzle brick in detail to help readers fully understand the important part of this refractory.

I. Structure and design of nozzle brick

Nozzle brick is a kind of refractory material installed at the bottom of ladle, and its main function is to control the outflow speed and direction of molten steel. Structurally, the nozzle brick is usually cylindrical or conical, with the upper part as the inlet end and the lower part as the outlet end. The inlet end is usually designed as an arc, which is helpful for the smooth inflow of molten steel and can reduce the impact force of molten steel when it enters the nozzle brick, thus reducing the erosion of the nozzle brick. The outlet end is designed as a straight cylinder, so as to ensure that the molten steel can flow out stably and form a uniform stream, and avoid splashing and turbulence of the molten steel.

The internal channel design of nozzle brick is also very important. In order to ensure the smooth flow of molten steel, the inner wall of the channel is usually finely machined to make its surface smooth and reduce the friction between molten steel and the inner wall. In addition, the size and shape of nozzle brick will be customized according to different casting processes and ladle capacity. For example, the size of nozzle brick used in large ladle is larger to meet the rapid outflow demand of a large amount of molten steel; In the small ladle, the nozzle brick with smaller size will be used to realize accurate control of molten steel flow.

II. Performance Requirements of Shuikou Brick

As a refractory material, nozzle brick must have a series of excellent properties to adapt to the high temperature, high pressure and high corrosive casting environment.

(1) Fire resistance

The fire resistance of nozzle brick is one of its most basic and important performance indexes. In the process of iron and steel casting, the temperature of molten steel is usually above 1500℃, so the nozzle brick must have high fire resistance to ensure that it does not melt or deform at high temperature. Generally speaking, the fire resistance of nozzle brick should reach above 1700℃, so as to ensure its stable structure and performance under the action of high temperature for a long time.

(2) Thermal shock resistance

In the process of casting, nozzle brick will be frequently subjected to sharp changes in temperature. For example, when molten steel flows into the nozzle brick, the temperature of the nozzle brick will rise rapidly; After the molten steel flows out, the nozzle brick will cool quickly. This rapid change of temperature will cause thermal stress to the nozzle brick, which will lead to cracks and even cracks. Therefore, the nozzle brick must have good thermal shock resistance and can maintain the structural integrity under the condition of rapid temperature change. The thermal shock resistance is usually measured by the thermal expansion coefficient and thermal shock resistance times of nozzle bricks. The nozzle brick with low thermal expansion coefficient has less thermal stress when the temperature changes, so it has better thermal shock resistance.

(3) Corrosion resistance

The erosion of nozzle brick by molten steel and slag is one of the main factors affecting its service life. The chemical composition of molten steel and the acidic or alkaline substances in slag will cause chemical erosion to the nozzle brick, and the flow of molten steel will also cause mechanical erosion to the nozzle brick. Therefore, the nozzle brick must have good corrosion resistance, which can resist the chemical erosion and mechanical erosion of molten steel and slag. The corrosion resistance mainly depends on the chemical composition and microstructure of nozzle brick. For example, nozzle bricks with high aluminum content usually have better corrosion resistance, because aluminum can react with oxides in molten steel to form stable compounds, thus forming a protective film on the surface of nozzle bricks to prevent further corrosion.

(4) dimensional accuracy and shape regularity

The dimensional accuracy and shape regularity of nozzle brick are very important for its installation and use in casting process. If the nozzle brick is inaccurate in size or irregular in shape, it may lead to poor flow of molten steel and even breakout. Therefore, in the production process, the nozzle brick must undergo strict size detection and quality control to ensure that its size accuracy is within the allowable error range, and its shape is regular, its surface is smooth, and there are no defects such as cracks and missing corners.

III. Application of nozzle brick

Shuikou brick is widely used in various fields of iron and steel casting industry, mainly including ladle, tundish, crystallizer and other parts. In the ladle, the nozzle brick is installed at the bottom of the ladle to control the speed and flow of molten steel from the ladle into the tundish. By adjusting the opening of nozzle brick, the molten steel flow can be accurately controlled, thus ensuring the liquid level stability of molten steel in tundish. In tundish, the function of nozzle brick is to distribute molten steel evenly to each crystallizer, so as to ensure the consistent flow of molten steel in each crystallizer, thus improving the quality and dimensional accuracy of billet. In the crystallizer, the nozzle brick is used to control the speed and direction of molten steel flowing into the crystallizer, so that molten steel can enter the crystallizer smoothly and form a good solidification interface to avoid defects in the slab.

IV. Manufacturing of Shuikou Brick

The production and manufacture of nozzle brick is a complex process, which involves the selection of various raw materials, batching, molding, sintering and other technological links.

(1) Selection of raw materials

The main raw materials of nozzle brick include refractory aggregate, binder and additives. Refractory aggregate is the main component of nozzle brick, and materials such as high alumina, corundum and silicon carbide are usually selected, which have high refractoriness, high hardness and good corrosion resistance. The function of binder is to bond the refractory aggregate together to form a green body with certain strength. Commonly used binders are phosphate, asphalt, resin, etc. Additives are used to improve the performance of nozzle brick. For example, adding antioxidant can improve the oxidation resistance of nozzle brick, and adding expansion agent can compensate the shrinkage of nozzle brick during sintering.

(2) batching and mixing

According to the design requirements and performance indicators of Shuikou brick, various raw materials are mixed according to a certain proportion. Then put the ingredients into a blender for mixing, so that the raw materials are fully and evenly mixed together. In the process of mixing, the stirring time and speed should be strictly controlled to ensure the uniformity of the mixture.

(3) forming

The mixed materials are made into the blank of Shuikou brick by molding process. The molding methods mainly include press molding, pouring molding and isostatic pressing molding. Press molding is to put the mixed materials into a mold and apply pressure through a press to shape them. Casting molding is to make the mixed materials into slurry, then pour it into the mold and shape it by natural drying or heating drying. Isostatic pressing is an advanced forming technology, which makes the density of the blank more uniform and the strength higher by isostatic pressing the material under high pressure.

(4) sintering

The formed blank needs to be sintered to become the final product. Sintering is to put the green body into a high-temperature furnace and heat it at a certain temperature and atmosphere, so that the binder in the green body is decomposed and volatilized, and sintering reaction takes place between refractory aggregates to form a nozzle brick with certain strength and performance. Sintering temperature and sintering time are the key factors affecting the quality of Shuikou brick. Different raw materials and formulas require different sintering process parameters. Generally speaking, the sintering temperature is between 1300℃ and 1600℃, and the sintering time ranges from several hours to dozens of hours.

(5) Quality inspection

The sintered nozzle brick needs to undergo strict quality inspection, including size inspection, appearance inspection and performance inspection. The size inspection mainly checks whether the size of the nozzle brick meets the design requirements, while the appearance inspection checks whether there are cracks, missing corners, air holes and other defects on the surface of the nozzle brick. Performance testing includes fire resistance testing, thermal shock resistance testing, corrosion resistance testing, etc. Through these tests, the quality of nozzle brick can be ensured to meet the standard requirements.

V. Development Trend of Shuikou Brick

With the continuous development of iron and steel industry, higher requirements are put forward for the performance and quality of nozzle brick. In the future, the development of nozzle brick will present the following trends:

(1) High performance

In order to meet the harsh casting environment such as high temperature, high pressure and high corrosiveness, the nozzle brick will develop towards high performance. By improving raw material formula and optimizing production process, the fire resistance, thermal shock resistance and corrosion resistance of nozzle brick are improved, its service life is prolonged and production cost is reduced.

(2) Functionalization

In addition to the traditional function of controlling molten steel flow, the future nozzle brick will have more functions. For example, nozzle bricks with anti-oxidation, anti-thermal spalling and self-lubrication functions are developed to meet the needs of different casting processes.

(3) intelligence

With the continuous development of automation technology and information technology, the manufacturing of nozzle brick will gradually realize intelligence. By introducing automatic production equipment and intelligent control system, the automation and intelligence of Shuikou brick production are realized, and the production efficiency and product quality stability are improved.

(4) Environmental protection

Under the background of increasingly strict environmental protection policy, the production and manufacture of Shuikou brick will also pay more attention to environmental protection. The use of environmentally friendly raw materials can reduce the emission of waste gas, waste water and waste residue in the production process and realize the sustainable development of Shuikou brick production.

VI. Conclusion

As an indispensable refractory in steel casting, nozzle brick's structural design, performance requirements, application scope and manufacturing process have an important impact on casting technology and product quality. With the continuous development of iron and steel industry, nozzle brick will also be constantly innovated and improved to meet higher performance requirements and wider application requirements. In the future, high performance, functionalization, intelligence and environmental protection will become the main development direction of Shuikou brick, which will provide a strong guarantee for the sustainable development of steel casting industry.