Correct Use of High Temperature Resistant Castables

High-temperature-resistant castables are constructed by the vibration method, which is widely used, including the construction of dry vibration materials.

1. Preparation before construction

According to the design size requirements, check the construction quality of the previous process and clean the boiler construction site.
Transport the forced mixer, insert vibrator and trolley to the boiler construction site, install them in place, and test run them normally. The following table shows the technical indicators of the insert vibrator. It should be pointed out that the mixer is forced, the vibrator should be high-frequency, and there should be enough spare parts.

The template should have sufficient strength and rigidity, even if transported to the boiler construction site; the lighting power supply should be turned on, and clean water should be connected to the mixer.

High-temperature resistant castables are generally bagged, and materials such as anchor bricks, connectors, thermal insulation refractory bricks, calcium silicate boards, asbestos boards, refractory clay bricks, and burner bricks should be transported to the boiler construction site at any time as required.
When chemical binders are used, their concentration or density should be adjusted in advance and transported to the boiler construction site for use. Before use, they should be re-mixed and evenly mixed.

2. Verification of construction mix ratio

Bagged high-temperature resistant castables and their additives, etc., should be sampled and tested before construction according to the requirements of the design drawings or the manufacturer’s instructions, and the main properties should be tested. When the high-temperature-resistant castables do not meet the design requirements, the materials should be replaced as soon as possible and should not be sloppy. Therefore, this work is very important. From purchasing high-temperature-resistant castables, attention should be paid to their performance indicators. Qualified products should be used according to the conditions of the boiler construction site and the storage time of the materials to make the construction mix ratio of the boiler construction site.

3. Masonry and formwork of the thermal insulation layer

For the vibration construction of high-temperature resistant castables, this work also belongs to construction preparation. Before the construction of the furnace wall of high-temperature resistant castables, first lay asbestos boards, calcium silicate boards or refractory fiber felts, install metal connectors, and place anchor bricks. Secondly, lay insulating refractory bricks or pour lightweight high-temperature-resistant castables. Thirdly, support the formwork. The working surface of the formwork is first coated with oil or stickers, and then close to the working end surface of the anchor brick for support. The height of each support formwork is 600~1000mm to facilitate loading and vibration molding. When there is a fetal membrane, support the fetal membrane first, and then support the formwork. The surface of the insulation layer should be covered with plastic film to prevent it from absorbing water and affecting the performance of the castable. When the furnace wall is high, the masonry of the insulation layer should also be carried out in layers to prevent the insulation layer from tipping over when the castable vibrates.

When constructing the refractory castable furnace roof, according to the design size requirements, first firmly support the entire formwork, then apply oil; then hang the hanging bricks on the hanging beams with metal connectors. Some connectors need to be fixed with wooden wedges, while others do not need to be fixed. The hanging bricks should be placed vertically with the working surface of the furnace lining, and the distance between the bottom end face and the template surface is 0~10mm, of which more than 60% of the end faces of the hanging bricks should be in contact with the template surface. When the distance is greater than 10mm, the metal connectors should be adjusted to meet the requirements. When there are holes, the fetal membrane should also be installed firmly, and then the template should be supported.

4. Mixing

Mixing should use a forced mixer, and when the amount of material is small, it can also be mixed manually. Different types of high-temperature resistant castables have different mixing requirements; the allowable error of bagged materials or refractory aggregates and cement is ±1.0 percentage points, the allowable error of additives is ±0.5 percentage points, and the allowable error of hydrated liquid binders is ±0.5 percentage points. The amount of additives must be accurate; various raw materials are weighed and poured into the mixer, and no omissions or extra additions are allowed.

For mixing high-temperature resistant castables such as cement, clay bonded, and low cement series, first pour bagged materials, additives, and additives into the mixer as bulk materials, dry mix for 1.0 minutes, and then add water and wet mix for 3~5 minutes after uniformity. The materials can be discharged after the color is appropriate. Then transport to the face and start laying.

For mixing water glass high-temperature resistant castables, first dry mix the granules in a mixer, then add water glass solution for wet mixing, after the granules are wrapped in a water glass, add refractory powder and other materials, wet mix for about 5 minutes, then discharge the materials for use; if the dry materials are mixed, pour them into the mixer and dry mix for 1.0 minutes, add 2/3 of the water glass solution for wet mixing for 2~3 minutes, then add the remaining binder for wet mixing for 2~3 minutes, then the materials can be used. The mixing of resin-bonded carbon-containing high-temperature resistant castables is similar to this.

For mixing high-temperature resistant castables such as phosphoric acid and phosphate, first, pour the dry materials into the mixer and dry mix for 1.0 minutes, add about 3/5 of the binder for wet mixing for 2~3 minutes, then discharge the materials, and transport them to the designated location for stacking, cover them tightly with plastic film, and trap the materials for more than 16 hours. After weighing the trapped material and coagulant, pour them into the mixer for secondary mixing, and add the remaining binder and wet mix for 2~4 minutes before use.

When mixing high-temperature resistant castables, if heat-resistant steel fiber, refractory fiber organic fiber, and other additives are required, they should be continuously sprinkled into the mixing material of the mixer during the wet mixing of the castable, stirring while scattering, and never put them into a mass.

After the mixing material comes out of the mixer, if it is too dry, too thin, or lacks certain materials, the material should be discarded and no more should be added; the mixing material out of the mixer should be within 0.5~1.0h.