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Preparation before construction
1.1 Preparation of raw materials
The finished refractory castable shall be subject to necessary technical inspections before construction, and it shall be put into use after confirming that it meets the design requirements.
The self-provided ones on the construction site should be selected according to the technical requirements proposed by the design. The selected aggregates and powders should be re-examined according to their physical and chemical properties and particle gradation. The selected bonding agent should be tested according to its technical requirements.
1.2 Determination of mix ratio
The finished refractory castables are usually constructed according to the mix ratio and requirements specified in the construction manual provided by the manufacturer.
If the site is self-provided, sampling and trial matching shall be conducted in the laboratory. When the construction requirements are met, test blocks are made and inspected according to the specified items. When the inspection results meet the design requirements, the final construction mix ratio can be determined.
1.3 Preparation of the template
The formwork used for construction should be selected according to the characteristics of the project structure and the size of the project. The types of formwork include: fixed, suspended and tooled, etc. The template material is usually steel mold and wooden mold.
When the formwork is set up, the following requirements shall be met:
(1) The size is accurate and meets the design regulations.
(2) The support is firm, the formwork combination installation is convenient for construction, and the lap joint is tight and does not leak.
(3) For refractory castables with strong corrosive or cohesiveness, an isolation layer should be provided in the template.
(4) The wooden slats reserved for expansion joints should be fixed firmly to avoid displacement during vibration.
(5) The formwork should be painted with protective oil before construction to prevent sticking.
1.4 The production and installation of anchors
Anchors are generally divided into two types: metal and non-metal. One end of the anchor is welded to the furnace iron shell and supporting steel frame, and buried in the refractory castable to play a supporting and connecting role.
The setting of the anchors should be in accordance with the design regulations, usually metal anchors are used in low-temperature parts, and ceramic anchor bricks are used in high-temperature parts.
The metal anchors adopt different forms according to the different parts of the furnace body structure. The metal anchors of the furnace wall and vault include V-shaped, L-shaped and Y-shaped.
Generally, the front end of the metal anchor is buried to 2/3 of the thickness of the furnace wall; the anchor brick is generally exposed on the heating surface.
The installation distance of metal anchors depends on the thickness and height of the furnace wall. Generally, the horizontal spacing is about 50~600mm, and the vertical spacing is about 450~500mm.
When anchoring bricks are used, the distance between the side wall part is mostly 300~500mm, and the furnace top part is about 200~300mm.
Construction Conditions
The construction conditions are:
(1) Choose and install one or several forced mixers according to the construction amount required by the project. The inside of the machine should be kept clean. The installed machinery can be used only after passing the trial operation.
(2) The construction site should be cleaned up in advance, and if necessary, it should be cleaned with water or blown with compressed air.
(3) The pouring material lining with anchoring device should be checked for the position and welding of the metal anchor or the metal anchor-seat of the anchor brick.
(4) Check the installation size, firmness and joint condition of the template.
Stir
When mixing, follow the manufacturer’s material instruction manual for mixing.
Pouring and vibration
The pouring of refractory castables should be vibrated by vibrating machine in layers. The vibrating machine should adopt plug-in vibrating rod or flat vibrator. Only in special circumstances can manual vibrating be used. When using a plug-in vibrating rod, the thickness of the casting layer should not exceed 1.25 times the length of the vibrating rod’s active part; when using a flat-plate vibrator, its thickness should not exceed 200mm.
The castable should generally be poured continuously, and the next layer of castable should be poured before the first layer of castable initially sets. If the construction gap exceeds its initial setting period, it should be treated according to the requirements of construction joints.
Curing and demoulding
Due to the different types of varieties, the maintenance time and maintenance environment requirements are also different.
Precautions for the maintenance of silicate refractory castables:
1) It is suitable for watering and curing to make the cement in the product form dehydration and hardening during the hydration process. The maintenance of high-alumina cement castables is particularly important, because the cement hydrates quickly. And produce a large amount of exothermic reaction, which is easy to cause cracks on the surface.
2) Wet curing should be covered and watered after the castable has started to harden. The number of times of watering should be sufficient to keep the castable in a sufficiently moist state.
3) The heating rate of steam curing should be 10～15℃/h, and the maximum should not exceed 20℃/h; the cooling rate should not exceed 40℃/h.
Precautions for maintenance of sodium silicate castable:
Its strength increase is produced during the dehydration process of silica gel. Therefore, it should be maintained in a dry environment for curing, rather than watering for curing.
Precautions for the maintenance of phosphoric acid refractory castables include:
1) Avoid curing with water or steam, but curing in a dry environment.
2) If the ambient temperature is low, low-temperature drying is required after pouring.
