01. Construction Preparation
According to the design dimensions, inspect the construction quality of the previous process and clean the site. Transport the forced mixer, immersion vibrator (vibrator bar), and wheelbarrow to the site, install them, and test run them to ensure they are functioning normally. It should be noted that a forced mixer must be used, the vibrator bar should be high-frequency, and sufficient spare parts should be available. The formwork should have sufficient strength and rigidity and be transported to the site promptly; connect the lighting power supply and clean water to the mixer. Low cement refractory castables are generally packaged in bags. Anchor bricks, connectors, insulating refractory bricks, calcium silicate boards, refractory fiber felt, asbestos boards, refractory clay bricks, and burner bricks should be transported to the site as required. When using chemical binders, their concentration or density should be pre-adjusted and transported to the site for use. Before use, the mixture should be re-stirred evenly.
02. Verification of Construction Mix Proportion
Before construction, bagged refractory castables and their admixtures should be sampled and tested according to the design drawings or the manufacturer's instructions, and their main properties should be verified. If the refractory castable does not meet the design requirements, the material should be replaced as soon as possible; this is crucial. Therefore, this work is very important, and attention should be paid to its performance indicators from the time the refractory castable is purchased. For qualified products, the on-site construction mix proportion should be determined based on site conditions and the material's storage time.
03. Insulation Layer Construction and Formwork
For vibration construction of low cement refractory castables, this work also falls under construction preparation. Before constructing the refractory castable furnace wall, firstly, ceramic fiber boards are laid, metal connectors are installed, and anchor bricks are placed; secondly, insulating refractory bricks are laid or lightweight refractory castable is poured; thirdly, formwork is erected. The working surface of the formwork is first coated with oil or paper, then pressed tightly against the working end face of the anchor bricks for support. Each formwork erection should be 600-1000mm high to facilitate material loading and vibration molding. When a formwork template is present, it should be erected first, followed by the formwork. A plastic film should be applied to the surface of the insulation layer to prevent water absorption and its impact on the performance of the castable. When the furnace wall is high, the insulation layer should be constructed in layers to prevent it from collapsing during casting vibration. During the construction of the refractory castable furnace roof, the entire formwork should be firmly erected according to the design dimensions, and then oiled. The hanging bricks should then be suspended from the hanging beams using metal connectors. Some connectors require wooden wedges to secure the hanging bricks, while others do not. The hanging bricks should be installed perpendicular to the furnace lining working surface, with a bottom face 0-10mm from the formwork surface, and at least 60% of the hanging brick ends should be in contact with the formwork surface. If the gap exceeds 10mm, the metal connectors should be adjusted to meet the requirements. When holes are present, the formwork template should also be firmly installed before erecting the formwork.
04. Mixing Forced mixing should be used.
For smaller quantities, manual mixing is also acceptable. The mixing process varies depending on the type of refractory castable. For bagged materials or refractory aggregates and cement, the allowable error is ±1.0%; for additives, ±0.5%; and for water and liquid binders, ±0.5%. The amount of additives must be accurate. All raw materials must be weighed and added to the mixer without omission or over-addition. For cement-based, clay-bonded, and low cement refractory castables, first, add the bagged materials, additives, and other bulk materials to the mixer and dry-mix for 1.0 minute. After uniform mixing, add water and wet-mix for 3-5 minutes until the material is uniform in color before discharging. Then transport the mixture to the working face and begin distribution. For mixing water glass refractory castables, it is best to first dry-mix the refractory granules in a mixer, then add water glass solution for wet mixing. After the granules are coated with water glass, add refractory powder and other materials, and wet mix for about 5 minutes before discharging and setting aside. If the dry materials are mixed together, pour them into a mixer and dry-mix for 1.0 minute, add 2/3 of the water glass solution and wet mix for 2-3 minutes, then add the remaining binder and wet mix for 2-3 minutes before use. The mixing of resin-bonded carbon-containing refractory castables is similar. For mixing phosphoric acid and phosphate refractory castables, first pour the dry materials into a mixer and dry-mix for 1.0 minute, then add about 3/5 of the binder and wet mix for 2-3 minutes before discharging and transporting to a designated location for stacking. Cover tightly with plastic film and allow to settle for at least 16 hours. After weighing the prepared material and accelerator, pour them into the mixer for secondary mixing, and add the remaining binder and wet mix for 2-4 minutes before use. When mixing refractory castables, if heat-resistant steel fibers, refractory fibers, and organic fibers need to be added, they should be continuously and continuously sprinkled into the mixer during the wet mixing process, mixing as they are added, and never added in clumps. If the mixture is too dry, too thin, or lacks a certain material after exiting the mixer, it should be discarded and not reused; the mixture should be used within 0.5-1.0 hours. Material that has initially set and hardened should be discarded.
05. Vibration Molding
The mixture should be transported to the construction site promptly. When pouring the furnace bottom, the material thickness should be approximately 200mm, then vibrated with a plate vibrator. If using a vibratory rod, the material thickness should be 200-400mm. When constructing the furnace wall, begin laying the material from one end or at the expansion joint, with a thickness of 300-400mm. Immediately after laying, vibrate with a vibrator, continuing the process continuously. The formwork should also be continuously erected. Where expansion joints are encountered, add expansion joint material and maintain the design requirements. During vibration molding, if using a plate vibrator, move it continuously with overlapping edges to prevent missed vibrations. When using a vibrator, insert it slowly into the material layer, move it continuously, and withdraw it slowly to prevent leaving holes and missed vibrations. The vibrator must not collide with the formwork, anchors, or insulation layer. Ideally, the vibrator should be kept at least 120mm away from the formwork and wall. The lining generally requires at least two consecutive vibrations until surface slurry returns, venting is minimal, and there is no settlement.
Construction of the furnace roof lining also begins from the end, with a thickness of 250-300mm. Move the vibrator along the furnace length and width between the hanging bricks, avoiding collisions with the hanging bricks. Construction can only continue when the refractory surface has returned to its designed thickness. During construction, expansion joint material and temperature measuring hole formwork should be installed. After the entire furnace roof lining is completed, the insulation layer can be applied, but the metal connectors for the hanging bricks must not be embedded in it. Once the entire refractory castable lining is completed and has initially set and gained strength, the formwork can be removed and the site cleaned. Simultaneously, curing should be carried out according to the requirements of refractory castable type.
