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      Brief introduction of low cement castable

      Jan 26, 2021
      Low cement castable refers to a castable with a lower amount of cement. The cement dosage of refractory cement castables is generally 15% to 20%, and the cement dosage of low cement castables is about 5%, and some even reduce to 1% to 2%. The purpose of reducing the amount of cement is to improve the fire resistance of the castable.
       
      Low cement castables rely on the addition of several special raw materials to obtain good performance: First, pure calcium aluminate cement, due to the high content of effective mineral CaO·Al2O3, can obtain the required strength with less mixing. The second silica fume is glass beads with an SiO2 content between 93% and 98% and an average particle size of about 0.5μm. After adding silica fume, the castable has good fluidity, low water requirement for molding, and low sintering temperature, which improves the performance after heat treatment. Third, alumina powder is easier to participate in the reaction and improve the fire resistance of the material. Fourth, the water reducing agent, which can be adsorbed on the surface of the powder, and then generate electrostatic repulsion to disperse the powder, so as to further play the role of fine powder.
       
      Advantages of integral casting of low cement castables
      Low-cement castable is a high-tech refractory developed on common castables by using rheological principles, the tightest packing theory and ultra-fine powder technology. It has the characteristics of low porosity, small pore size, high density, good volume stability, high strength and small water addition, and it overcomes the characteristics of a significant drop in strength of ordinary castables at 800~1200℃, and increases with temperature And increase, so that the thermal shock of the furnace body can be more than doubled.
       
      Use of low cement castable
      1. Preparation before construction
      According to the technical requirements of the drawings, a comprehensive and detailed inspection and acceptance of the furnace steel structure, baseline, holes and other parts should be carried out. Check the bricklaying and anchoring bricks of the side wall insulation layer. The shape and size of the anchoring bricks and hanging bricks should be checked and accepted one by one. There should be no transverse cracks. The position of the bricks should meet the design requirements, and the anchoring hook with the furnace shell should be maintained. Or the hanging beam on the top of the furnace is vertical. In order to prevent the side wall light insulation brick from absorbing water, a layer of asphalt should be painted on its surface. It is necessary to check whether the support of the inner mold is firm, not to move, and the surface is covered with cloth; the template should also be set firmly, and the surface is brushed with oil to facilitate demolding. Check whether the mixer, vibrating rod, etc. work normally; whether the driving is normal, if there is a failure, it should be repaired in time, or other hanging appliances must be prepared, and the pouring must not be interrupted. Clean up the debris at the pouring site to ensure it is neat and clean.
       
      2. Construction points of of low cement castable
      (1) First, pour the bagged low cement castable into the mixer, determine the number of bags according to the capacity of the mixer, dry mix for 12 minutes, and then add water according to the construction requirements, strictly control the amount of water added, and mix for 2 to 3 minutes. After the material is uniform in color, the material is discharged.
       
      (2) At the beginning of pouring, the mixture should be vibrated while pouring, and the construction should be continuous. After the vibrating rod is inserted into the material layer, it should move continuously and vibrate repeatedly for more than two times until the surface returns to the slurry, the exhaust is less, and the material surface does not settle. At the same time, the vibrating rod must not touch the insulation layer, template, tire mold and anchor brick. When the furnace wall is constructed, the height of one-time pouring is 300-350mm.
       
      (3) Pay attention to the setting of expansion joints and the setting of pressure and temperature measurement holes. According to the requirements, expansion joints should be left on the side walls and furnace roof. The side walls are made of 60mm PVC plastic panels. The contact parts between the furnace roof and the side walls are made of 50mm aluminum silicate refractory fiber felt. 11 expansion joints are left horizontally on the furnace roof. Fill 6mm corrugated plastic board.
       
      (4) The construction process should generally be continuous pouring, and the expansion joint should be used when it is interrupted, and the template should be firmly supported. This should also be the case when the furnace top pouring is interrupted. When re-construction, the stubble must be handled well.
       
      (5) The amount of water added should be strictly controlled during the construction process. Under the premise of ensuring good fluidity, water consumption should be minimized. Otherwise, it will affect the solidification strength. Once out of the mixer, it should be used up within 0.5h. If the construction is interrupted or spilled, it must be discarded and not used.
       
      3. Maintenance and mold removal of low cement castable
      After the low cement castable has been poured, it should be kept in a natural environment for 24 hours after it is fully formed. When the temperature exceeds 30 ℃, it should be protected from direct sunlight. It is not allowed to hit hard during the demolding process to prevent the furnace wall from being damaged. After removing the mold, repair the local damage on the surface in time. If the vent is sealed by mud, it should be punched and repaired.
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