Month: March 2021

Combination Method of Alumina-Magnesia Castable

KilnRefractory

In recent years, due to the vigorous development of out-of-furnace refining technology and continuous casting technology, the ladle is also used as a vessel for holding molten steel and molten steel refining equipment, which greatly extends the residence time of molten steel in the ladle. This is accompanied by an increase in the tapping temperature and more severe smelting conditions. As a result, the service life of the inner lining of the ladle is greatly reduced. The ladle uses alumina-magnesia castables, including spinel-containing castables, and it has always been a development trend for integral casting.

High-Quality Alumina-Magnesia Refractory Castable
High-Quality Alumina-Magnesia Refractory Castable

The Combination Method of Alumina-Magnesia Castable

Binder is an important part of alumina-magnesia castables. The bonding methods used for alumina-magnesia castables are generally calcium aluminate cement bonding, silica micro-powder bonding, hydrated alumina bonding, sol bonding, magnesium silicon water bonding, and so on.

Cement bonding

At the initial stage of development of alumina-magnesia castables, pure calcium aluminate cement is used. This is because the cement calcium aluminate will react with the Al2O3 in the matrix to form CA6, which is a highly refractory phase. However, as the number of cement increases, the fluidity of the castable decreases. At the same time, due to the excessive content of CaO at high temperatures, it will react with SiO2, Al2O3, and MgO in the matrix to generate a low-melting phase, which will reduce the high-temperature performance of the castable. Some refractory researchers have studied the effect of the amount of water added in cement on the thermal expansion behavior of alumina-magnesia castables after high-temperature firing. The results show that with the increase of cement addition, the phases of CA2 and CA6 in the sample increase, and the linear change rate of the sample after high-temperature heat treatment increases. In addition, some people have studied the influence of silica powder, magnesia, and cement on the properties of high-purity alumina-magnesia castables. The study pointed out that the pure calcium aluminate cement and the Al2O3 fine powder in the matrix start to react at about 1000°C to form CA2 and CA6, and the reaction is accompanied by volume expansion. It can reduce the intensity ratio after high- and medium-temperature firing, and also contribute to the improvement of the high-temperature performance of the sample.

MgO-SiO2-H2O combination

There are many kinds of researches on the combination of MgO-SiO2-H2O. The combination of MgO-SiO2-H2O is used in the alumina-magnesia castable. On the one hand, due to the polymerization of SiO2 gel formed by the interaction of SiO2 powder and water, the amount of water added is reduced, and the fluidity of the castable is greatly improved. On the other hand, the combination of MgO-SiO2-H2O can inhibit the hydration of magnesia, but too much silica powder will form a low-melting phase with impurities in the matrix. At the same time, the forsterite phase formed by the reaction of magnesia and silica powder in the matrix has poor thermal shock stability at high temperatures.

Composition Materials and Properties of Low Cement Alumina-Magnesia Refractory Castables

The slag resistance of low-cement alumina-magnesia refractories is similar to that of alumina-magnesia spinel castables but superior to alumina-spinel castables. Therefore, it is selected by users at home and abroad, especially in the Japanese steel ladle. In addition, the material is used in the desalinization pouring channel of the large-scale blast furnace tapping channel, and its life is longer than that of the Al2O3-SiC-C iron channel material.

The high-tech basis of low-cement alumina-magnesia refractory castables is high-grade raw materials and scientific formulas. Construction, baking, and careful process operation and maintenance are the guarantees of its long life. This material is used on a ladle of about 100 tons, and the ladle age is 60 ~ 120 times.

The performance of low cement alumina-magnesia refractory castables is excellent. The content of MgO is not more than 8%, and the content of Al2O3 is 89% ~ 97.6%, indicating that the material is excellent. The linear changes after firing are all positive values, the pores are low, and the strength is high, which is beneficial to the use of castables.

Low-cement alumina-magnesia refractory castables are developed on the basis of sodium silicate alumina-magnesia refractory castables and have been used on medium and small ladles with good results. When higher-grade refractory raw materials are used and the material formula is designed with scientific methods, high-tech low-cement alumina-magnesia refractory castables can be successfully formulated. It can be used on large and medium-sized ladle to improve the age of the ladle.

For more detailed information about refractory castables for kiln furnaces, please visit the website of Rongsheng Kiln Refractories Website: https://kilnrefractory.com/.

How to Choose Refractory Plastic or Low Cement Castable for the Top of the Heating Furnace?

KilnRefractory

Use refractory plastics or low cement castables in different areas of the heating furnace roof? The temperature of the heating furnace varies greatly from the preheating section, heating section, and soaking section, and each part has different functions. When choosing plastic refractory or low-cement castables, the use performance and price factors must be considered, as well as the convenience of construction and the storage of products.

Unshaped Refractory Material for Heating Furnace Roof
Unshaped Refractory Material for Heating Furnace Roof

Refractory plastic can not damage its packaging before construction. If the packaging material is damaged, the plastic can lose its plasticity. When storing and keeping the plastic, pay attention to the integrity of the plastic packaging.

If low cement castables are used, anchors must be welded. If the plastic material is fixed on the furnace roof by anchoring bricks, the tightness of the plastic material and the anchoring brick affect the quality of the plastic furnace roof.

Ramming around the anchor is very important when the fire-resistant plastic is constructed. Make wooden molds based on the shape of anchor bricks. When the plastic is rammed, a wooden mold is used to mold the plastic around the anchor bricks, and then the anchor bricks are inlaid in the mold. Pram around the anchor brick with the wind to make it come in close contact with the plastic. But be careful not to smash the anchor brick.

But plastic is more shrinking. After removing the mold, use an expansion joint knife to cut a 30-50mm expansion suture on the surface with an interval of about 1.5m, which means that the plastic surface is cut into 1.5m square blocks. But if the plastic shrinks, it will only crack in the opened expansion joint, and no cracks or cracks will appear.

If low cement castables are used, 20 anchors per square must be welded. Support the mold first, then pour the low-cement castable, take off the film after 24 hours, and then grill according to the barbecue system.

In short, whether fire-resistant plastic or low-cement castable is used, depends on the situation. If there is no condition to store plastics, low cement castables can be used. If the construction of low cement castables is inconvenient, refractory plastics can also be used.

How Long is the Setting Time of the Refractory Plastic?

Refractory plastic is an amorphous material that can maintain good plasticity for a long time. Next, we come to understand some characteristics of the refractory plastic from the setting time of the refractory plastic.

The Setting of Refractory Plastic

The refractory plastic can be in the form of a mud paste, or it can be separated from the powder and the binder. If you are in a hurry for construction or repair, it can be made into a mud paste. If the construction time is long, the powder and the binder can be packaged separately, so that they can be mixed and used during pre-construction.

The plasticity of the plastic has a great influence on the bonding strength and volume stability of its hardened body. It is the properties of clay that control the properties of refractory plastics. The plasticity is related to the properties and dosage of the clay, which increases with the increase of the binding dosage. If the binding dosage is too high, the fire resistance and plasticity are not strong, and it is best to control it at 5%-10% so that the plasticity of the plastics will not decrease during the shelf life. The binding agent is a special glue preparation.

The refractory plastic can be taken out from a sealed container during construction, or a special bonding agent can be added on-site to trap the material. The trapping time cannot be less than 10 hours. Then lay it between the hanging bricks or anchoring bricks and tamping with a hammer. In particular, the plastic can be processed into any shape before being hardened.

Refractory plastic In order to facilitate the drainage of water, holes should be punched at regular intervals. Expansion joints should also be set according to the design. If the part to be constructed is integral, first construct on the bottom form and then hoist it after drying.

The setting time of refractory plastic is 1-3 hours for the initial setting and 6-8 hours for the middle setting. It can reach 60-80% strength after one day of curing, 85%-95% of the strength is reached after 3 days of curing, and it can be used after 7 days of final strength.

Unshaped Refractory Material Sales

Rongsheng refractories production and sales factory have advanced and fully automatic monolithic refractory production lines. The annual output is 80,000 tons. Our unshaped refractory products mainly include various refractory castables, ramming mass materials, refractory plastics, low cement castables, wear-resistant refractory castables, etc. We can customize the formula of unshaped refractory materials according to the specific needs of customers. Our monolithic refractory products have a high rate of return orders from our monolithic refractory customers. Customers’ trust in us stems from our strict control of product quality. And we are committed to providing customers with high-quality customer service. To purchase high-quality unshaped refractory products, please contact us. We will provide you with the most suitable products for your project production needs according to your specific construction needs.