Refractory castables (also known as refractory concrete) vary widely in their aggregate materials, binders and admixtures. The construction methods of several kinds of refractory castables, such as Portland cement refractory castables, aluminate refractory castables, water glass and phosphoric acid (or phosphate) refractory castables, are listed below.
Preparation of refractory castables before construction
(1) Preparation of raw materials: The finished refractory castables should be subjected to the necessary technical inspection before construction, and confirmed that they meet the design requirements before they can be put into use.
(2) Determination of the mix ratio: The finished refractory castables are usually constructed according to the mix ratio and requirements specified in the construction instructions provided by the manufacturer.
(3) Configuration of the template: The template for the construction of the refractory castable should be selected according to the characteristics of the engineering structure and the amount of engineering. The types of templates are: fixed, hanging and tool. The template material is usually a steel mold and a wood mold.
When the template is supported, the following requirements shall be met:
1) Accurate and in accordance with design regulations.
2) The support is firm, the formwork combination is easy to construct, the joints are tight and the slurry is not leaking.
3) For corrosive or cohesive refractory castables, a barrier layer shall be provided in the formwork.
4) The wooden slats for the expansion joints should be fixed firmly to avoid displacement when vibrated.
5) The template should be coated with protective oil before construction to prevent sticking.
(4) Manufacture and installation of anchors: The anchors are generally divided into metal and non-metal. One end of the anchor is welded to the kiln shell or the supporting steel frame, and is embedded in the refractory castable to support and Connection effect.
The setting of refractory castable anchors shall be in accordance with the design regulations. Metal anchors are often used in low temperature parts, and ceramic anchor bricks are used in high temperature parts.
The metal anchors adopt different forms according to different parts of the furnace structure, and the metal anchors of the furnace wall and the dome have V shape, L shape, Y shape and the like.
Generally, the front end of the metal anchor is buried at 2/3 of the thickness of the furnace wall; the anchor brick is generally exposed on the heating surface.
The installation spacing of the metal anchors depends on the thickness and height of the furnace wall. Generally, the horizontal spacing is about 550~600mm, and the vertical spacing is about 450~500mm.
When anchoring bricks are used, the spacing of the side wall portions is usually 300 to 500 mm, and the top portion of the furnace is about 200 to 300 mm.
Construction conditions of refractory castables
The construction conditions mainly include:
(1) Select and install one or several forced mixers according to the construction dosage required for the project. The machine should be kept clean and the machinery installed in place should be used after passing the test run.
(2) The construction site should be cleaned beforehand, if necessary, with water or with compressed air.
(3) The castable lining with anchoring device shall check the position and welding of the metal anchoring seat of the metal anchor or anchoring brick.
(4) Check the size, firmness and seam of the formwork installation.
Stirring of refractory castables
Stirring is carried out with the manufacturer's material instruction manual while stirring.
Pouring and vibrating
The casting of refractory castables shall be stratified by vibrating machine tools. The vibrating machine should use a vibrating rod or a flat vibrator. Manual vibration can only be used in special cases.
When inserting a vibrating rod, the thickness of the casting layer should not exceed 1.25 times the length of the vibrating rod. When using a flat vibrator, the thickness should not exceed 200 mm.
The castable should generally be continuously poured. Before the first layer of castable is initially set, the next layer of castable should be poured. If the construction gap exceeds its initial setting period, it shall be carried out according to the requirements of the construction joint.
Maintenance and demoulding
Due to the variety and type of refractory castables, the curing time and maintenance environment requirements are also different. Commonly used refractory castable maintenance system can refer to Table 4-6
5 points about the construction of refractory castables
Maintenance considerations.
The precautions for the maintenance of silicate refractory castables are:
1) Silicate refractory casting 枓 is suitable for watering and curing, so that the cement in the product forms dehydration and hardening during hydration. The maintenance of high alumina cement castables is particularly important because the cement hydration in the high alumina cement castables is enhanced rapidly, and the exothermic reaction of the large children is generated, which easily causes cracks on the surface.
2) Wet curing should be covered and watered after the start of hardening of the castable. The number of times of watering should be sufficient to keep the castable in sufficient moisture.
3) The heating rate of the Portland cement refractory castable for steam curing should be 10~15°C/h, the maximum should not exceed 20°C/h; the cooling rate should not exceed 40°C/h.
The precautions for the maintenance of water glass castables are:
The strength increase of the water glass castable is produced during the dehydration of the silica gel. Therefore, it should be maintained in a dry environment, and should not be watered for maintenance.
The precautions for the maintenance of phosphoric acid refractory castables are:
1) Phosphoric acid refractory castable should not be cured with water or steam, but should be cured in a dry environment.
2) If the ambient temperature is low, then low temperature drying is required after pouring.
U) Precautions for demoulding. The precautions for demolding are:
1) Without load-bearing formwork, it should be removed when the strength of the castable material can ensure that the surface and edges are not damaged by demolding.
2) The load-bearing formwork should be removed only when the castable reaches 70% strength.
