Focus on Producing All Kinds Of High Quality Refractory Fire Bricks !
Types and Properties of Heavy Refractory Bricks for Powder Metallurgy Electric Furnaces
There are many types of refractory materials for powder metallurgy electric furnace lining, mainly heavy refractory bricks. Including refractory clay bricks, high alumina bricks, silica bricks, fused corundum bricks, silicon carbide bricks, carbon bricks, etc. RS Refractory Bricks Manufacturer, supply high-quality refractory materials for powder metallurgy electric furnaces, contact Rongsheng, get free samples and quotes.
Clay bricks
Clay bricks are made of refractory clay or kaolin (mainly composed of Al2O3, SiO2, H2O. It also contains 6%~7% of metal oxides, such as K2O, NaO, CaO, MgO, TiO2, Fe2O3, etc.). Clay bricks are made by mixing soft clay (binder) and cooked clay and sintering them at 1300~1400℃. Clay bricks contain 30%~40% Al2O3 and the rest is SiO2.
Clay bricks are weakly alkaline refractory materials that can resist the erosion of acidic slag. However, they have poor corrosion resistance to alkaline slag and are very resistant to rapid cooling and heating. The load softening start temperature is 125~300℃, the refractoriness is 1610~1750℃, and the maximum use temperature is 1300~1400℃. Clay bricks can be used to build furnace walls, furnace tops, furnace bottoms, combustion chambers, etc. However, it is corrosive to Fe-Cr-Al resistance wire and is not suitable as its shelf brick. Moreover, it is easily damaged by CO and H2 in a controlled atmosphere.
High alumina brick refers to a refractory material with an Al2O3 content of more than 48%. It is made of high alumina bauxite (Al2O3·SiO2) and fired at about 1500℃. The refractoriness of high alumina brick is 1750~1790℃, and the load softening starting temperature is 1420~1500℃. It has good chemical corrosion resistance, but poor resistance to rapid cooling and heating. The reburning shrinkage of high alumina bricks is generally large, which is especially important for high alumina bricks containing 60%~75% Al2O3. When using high-alumina muffle furnace tubes with insufficient firing temperature or using such high alumina bricks to build the furnace roof, due to the large reburning shrinkage, after a period of high-temperature use, it is easy to cause the top to sink or collapse.
Corundum brick
Corundum brick is a high-grade refractory material with an Al2O3 content greater than 98%. According to the different raw materials used, corundum bricks are divided into two types: fused corundum bricks and alumina corundum bricks.
Corundum can be natural or artificial. Artificial corundum is generally formed by high-temperature calcination of industrial alumina (mainly γ-Al2O3). It can also be made by melting amorphous alumina raw materials in a high-temperature electric furnace, which is often called fused corundum.
Fused corundum is a refractory product made of fused corundum sand as the main raw material and adding an appropriate amount of aluminum phosphate solution as a binder. Its molding methods include ramming (or machine pressing) molding and plaster mold casting molding. Its firing temperature is 1700~1800℃, its refractoriness is 1950℃, and its load softening start temperature is 1770℃. Its resistance to rapid cooling and heating is 50 times, its density is 3.1~3.4g/cm3, and its operating temperature is 1800~1850℃.
Because corundum products have good resistance to rapid cooling and heating, high hardness, and good wear resistance, they can be used as furnace tubes for high-temperature molybdenum wire furnaces, etc. It is worth noting that corundum products require very high firing temperatures. If the firing temperature is low, the melt will also be easily re-burned and shrunk during use, and the wear resistance will also be reduced, and the resistance to rapid cooling and heating will also deteriorate, which is very important for the horizontal continuous molybdenum wire furnace tube.
Alumina corundum bricks are made of industrial pure alumina powder and added with appropriate amounts of oxides (titanium oxide, chromium oxide, etc.) and fired at above 1600℃, or pure alumina products fired with more than 98% alumina. The use temperature of such products is 1750-1850℃, and they are generally used as high-temperature kilns, electric furnace linings, furnace tubes, etc. Technical indicators of alumina corundum bricks.
Silica brick
Silica brick refers to a silicon oxide refractory material containing more than 93% SiO2. It is made of quartzite crushed and added with lime milk or other binders.
Silica brick is an acidic refractory material with strong resistance to acidic slag and weak resistance to alkaline slag. Pay attention to this when using it. The refractoriness of silica brick is 1710~1730℃, and the load softening starting temperature is almost close to its refractoriness, generally above 1620~1640℃. This is the biggest advantage of silica brick. Its disadvantage is that it has poor resistance to rapid cooling and heating. It is sometimes used to build the high-temperature part of the heating furnace, but it is not suitable for intermittent furnaces.
Magnesium brick is made of calcined magnesite (MgCO3) as raw material, which contains more than 80% magnesium oxide. Magnesium brick is an alkaline refractory material with good alkali corrosion resistance and good resistance to iron oxide corrosion. The refractoriness is as high as 2000℃, and the load softening starting temperature is 1550~1600℃. The volume shrinks slightly when used for a long time at high temperature, and the resistance to rapid cooling and heating is poor, and water cooling is only 3~5 times. Magnesia bricks are often used to build the bottom of heating furnaces. It should be noted that magnesia bricks are alkaline refractory materials, and they react to clay bricks, high alumina bricks and silica bricks to varying degrees at high temperatures.
Magnesia-alumina bricks are magnesia bricks combined with magnesia-alumina spinel (MgO·Al2O3) formed by adding 5%~10% Al2O3 to the ingredients to improve the thermal stability of magnesia bricks. The refractoriness is 2135℃. The thermal shock stability and resistance to rapid cooling and heating are better than those of magnesia bricks, and the load softening starting temperature is also improved, so it is a refractory material with excellent performance.
Silicon carbide refractory products are made of silicon carbide as raw material, with a binder (or without a binder) added to form and then fired. Its products are divided into three categories: (1) Products with clay as binder. (2) Products with other mineral binders (ferrosilicon, quartz, etc.). (3) Products without binder (recrystallization). (4) Properties of silicon carbide products with clay as binder.
Silicon carbide refractory materials have high mechanical strength, good wear resistance, resistance to rapid cooling and heating, thermal conductivity (5 to 10 times greater than general refractory materials), electrical conductivity, etc., high load softening point, and deformation starting point of about 1600℃. Its disadvantages are that it is expensive, easily oxidized when the operating temperature is higher than 1300℃, and easily corroded by alkaline slag. The denser the silicon carbide material, the better its anti-oxidation performance.
Silicon carbide refractory products are often used as electric furnace linings, muffle walls of muffle-type electric furnaces, refractory heating plates and electric heating elements.
Graphite refractory products
Graphite refractory products use graphite as raw material and soft clay as binder. There are superior, first, second and third grade varieties, with a refractoriness of 3000℃, a service temperature of 2000℃ and a load softening starting temperature of 1800~1900℃.
Alumina powder
The melting point of alumina powder is 2015℃. It is very stable in both oxidizing and strong reducing atmospheres. When the temperature is below 1900℃, it can be used in any type of atmosphere.
Pure alumina has several crystal structures at low temperatures, such as hexagonal (expressed by α), spinel (mixed oxides with the chemical formula RO·R2O3 are called spinel, expressed by β), and cubic (expressed by γ). However, these crystal forms become high-temperature stable α-Al2O3 (corundum) when heated to a temperature above 1600℃, and this transformation is irreversible.
Alumina powder can be used as a refractory material at a high temperature below 1900℃, and it is also a good heat-insulating material. This is why furnace builders often fill 50~100mm thick Al2O3 powder outside the furnace tube with electric heating elements. It is worth noting that if the atmosphere in the furnace is a carbon atmosphere, carbon particles are more likely to deposit in the alumina powder, which is very unfavorable to the Ni-Cr resistance wire and may even damage it.
Alumina products are often used as refractory linings for sintering furnaces, and are also used as electric furnace tubes or flame sleeves wrapped with molybdenum wire or tungsten wire, operating in hydrogen or decomposed ammonia atmosphere. It can also be made into small boats, observation hole sleeves, crucibles, etc. Alumina crucibles are used to melt various metals and oxides, and their chemical stability is extremely high.
