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Aluminum Industry

refractory for aluminum melting and holding Furnace

Aluminum Industry

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refractory for aluminum melting and holding Furnace

Refractory selection criteria for aluminum smelting holding furnace
Not sticky
Low silica, iron oxide and calcium oxide content
Resistance to molten aluminum water infiltration
Thermal stability
Sufficient strength against mechanical shock
Different alloy materials
Cemented carbides contain high Mg, Zn, Cu, low Si. In general, refractories are susceptible to erosion.
Soft alloys contain high Si, which is good for refractory
Therefore, for the refractory material in contact with aluminum water, in order to reduce the problem of long corundum tumor during use and to achieve long life of the lining, a suitable refractory material can be selected from the following aspects:
1. Select a refractory material containing an anti-adhesive agent. Anti-adhesive agent mainly produces effects through two aspects: A, anti-adhesive agent and aluminum water have a large wetting angle and do not react with aluminum water; B. refractory material also containing anti-adhesive agent has very low after sintering Porosity, low porosity will prevent the penetration of aluminum water. The following figure shows the results of the anti-adhesion test of two materials with the same alumina content, no anti-adhesive agent and anti-adhesion test with anti-adhesive material.
2. Reduce the content of silica, especially free silica, in the refractory. The higher the proportion of silica in the material, the easier it is to infiltrate corundum; the ALU-FLO 94AR and ALU-FLO 87AR developed and produced by Zhongzhu have very low silica, which is recommended for use in demanding environments or further Extend the life of the lining;
3. Use low cement and low moisture castables. Because the traditional castable contains more CaO and has a larger amount of water, the density of the material is poor, the pores are many, and the aluminum water is easy to permeate. The salts used in the smelting process, such as CL salt and F salt, react with CaO in the cement to destroy the material. structure. Medium Casting Refractory All materials in contact with aluminum water are low cement castables, which maximize the density of the material, reduce the porosity and improve the resistance of the material to aluminum water penetration.
In the process of using aluminum furnace lining, due to a large number of cracks in the furnace wall and flaking of the furnace lining, the overall expansion of the side wall causes the steel structure of the furnace to be deformed or the temperature of the furnace wall is too high, and the heat dissipation is serious. All of this is related to the occurrence of corundum slag in the refractory material of the furnace wall. The main chemical reactions occur are:
 3(Al2O3 - SiO2 ) + 8Al →6Si + 13Al2O3 
Aluminum reacts with silicon oxide in the furnace lining refractory material to reduce Si, which causes aluminum water to increase silicon, and at the same time increases the proportion of alumina in the furnace wall refractory material. The reaction is expansion reaction, which will destroy the lining refractory structure. Show).
Alcoa alkali corrosion test for roof and upper wall material? K2CO3 + NaCO3 @ 900oC 5 hours
The carbonate base mainly forms a low melting point phase with the furnace-lined alumina silica, thereby reducing the service life, and the carbonate further reacts with the cement hydration phase:
 Na2CO3+ CAH10→ CaCO3+Na2O.Al2O3+ 10H2O
Medium-casting refractory selects low impurity content (low Fe2O3, low Na2O), low cement and ultra-low cement castable in the upper furnace wall and furnace bottom, and adopts micro-powder technology and new water-reducing agent technology to make the material very dense. The structure of the body, medium-cast refractory for the upper wall materials ULTRA-FLO 71 and ALU-FLO 80 have good resistance to alkali corrosion.
Alkali corrosion test of ULTRA-FLO 61 material
Low cement castable mixing and construction
The water for mixing must reach the drinking water standard, and the pH is 6-7. Strictly control the amount of water added, and the amount of water added to the material should be accurately weighed.
Pouring; the stirring temperature of the injection should be between 15oC and 30oC, and the optimum temperature is 21oC. When the construction is carried out below the recommended temperature, external heating measures shall be taken to increase the temperature of the construction environment;
The mixing time is controlled within 5~10 minutes, and it is recommended not to exceed 10 minutes. The material to be mixed and mixed must be poured within 30 minutes;
The vibration of low moisture castables is critical. The vibrating rod should move up and down in the castable. When the vibration is over, the vibrating rod should be slowly pulled out;
After the casting is completed, the material can be molded after 18-24 hours depending on the hardening of the material, but the material must have been completely hardened. Care should be taken not to damage the surface of the material during demolding;
After demolding, it should be kept at room temperature for 24-72 hours and then sintered.
Low cement castable baking and sintering
At any time, especially for unsintered linings, the ambient temperature must be above 5 °C to prevent the lining from being frozen;
The furnace lining must be started after 72 hours of natural drying from the lining construction;
In the initial sintering (before the 340 degree heat preservation is finished), use the auxiliary heat source to heat, it is recommended not to use the reverberatory furnace to bring the burner to prevent the local material from heating up too quickly;
At any time, the temperature rise control is mainly based on the highest temperature, but the thermocouple should be avoided to be in direct contact or too close to the heat source; at the beginning of each insulation stage, the temperature difference of each thermocouple should be less than 100 degrees, otherwise the heat preservation time should be extended;
If there is pressure steam discharge during the sintering process, the temperature should be stopped and kept at this temperature until the pressurized steam disappears, and the sintering process is continued;
It is recommended that after the furnace lining is finished, it should be put into use directly. Do not use the cold furnace frequently. Any furnace lining may crack in the frequent heating process of the cold furnace. Please note that after the furnace temperature rises to the production temperature, the joint mine recommends that the furnace temperature not fall down immediately and maintain the normal operating temperature for at least one month to release the thermal stress.
When the lining needs to be cooled, first clean the aluminum water and slag, then cool to 100 degrees at a speed of no more than 50 degrees / hour, and then open the furnace door. When the furnace needs to be reheated, please refer to the furnace re-melting process, and then add aluminum water after the 740 degree insulation.
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