Refractory castable products are widely used in high-temperature industrial production due to their quality and characteristics, and have broad market prospects. However, the construction of refractory castables is relatively simple and does not pick the construction site. However, various regulations in construction must still be strictly enforced, and precautions in construction must be raised to prevent possible problems after construction in advance. There are also different precautions for refractory castable construction in different seasons.
Refractory castable furnace lining construction regulations
1. The following regulations shall be met when pouring refractory castable furnace lining:
1) The construction site should be cleaned first;
2) The steel bars or metal anchors in the refractory castable should be set on the non-heated surface;
3) When the refractory castable is in contact with refractory bricks or insulation products, anti-water absorption measures should be taken to isolate them. Foam boards and plastic sheets can be used for isolation during construction and removed after construction;
2. The surface of the formwork used for pouring the furnace lining should be smooth, have sufficient rigidity and strength, and be simple in structure. The support and removal of the formwork should meet the following regulations:
1) The support is firm and easy to install and disassemble, and the joints do not leak;
2) Corrosion For refractory castables with strong corrosion or adhesion, an isolation layer should be set in the formwork to take anti-adhesion measures;
3) The wooden strips reserved for expansion joints should be firmly fixed to avoid displacement during vibration;
4) The thickness dimension is accurate and the allowable deviation is +2~-4mm;
5) The formwork should not be installed on the castable if the strength does not reach 2MPa;
6) The formwork can be supported horizontally in layers, sections or blocks. The height of each formwork should be determined according to factors such as the ambient temperature of the construction site, the pouring speed and the setting time of the castable. Generally, it should not exceed 5m;
7) The load-bearing formwork should be removed when the castable reaches 70% of its strength. The non-load-bearing formwork should be removed when the castable reaches 70% of its strength. Remove when the strength of the castable can ensure that the surface and edges of the furnace lining are not damaged by demolding;
8) Thermo-hard castables should be baked to the specified temperature before demolding;
3. The construction joint of the furnace lining should be determined before the construction of the refractory castable, and the construction should be carried out continuously. The thickness of the furnace lining of the same type of refractory castable should be formed at one time, and layered construction is not allowed. If it is interrupted for some reason, it should be treated as a construction joint and comply with the following regulations:
1) The construction joint should be left on the center line of the two adjacent rows of anchors;
2) Construction joint interface type:
a. When the furnace lining thickness δ≤50mm, it can be made into a straight joint
b. When the furnace lining thickness δ>50mm, it should be made into a step joint
3) Different When pouring double-layer furnace lining of different types of refractory castables, the construction joints should be staggered, and the staggered distance should not be less than 100mm;
4) The joint surface of hydraulic refractory castables should be fully moistened during pouring or spraying, and the joint surface of air-hardening and thermosetting refractory castables should be evenly brushed with binder solution, and loose and residual refractory castables at the joint surface should be removed;
5) When the poured refractory castables continue to be poured, the joint surface should be carefully rammed to make the new and old castables tightly combined;
4. The gap size, distribution position and structure of the expansion joint of the integrally cast furnace lining should comply with the design requirements, and the filling materials should be filled according to the design requirements. When the design does not specify the gap size of the expansion joint , the average value of the expansion joint of the furnace lining per meter long, the following data can be used in clay and high-alumina castables:
1), aluminate cement refractory castable 6~8mm;
2), phosphate refractory castable 6~8mm;
3), water glass refractory castable 4~6mm;
4), silicate cement refractory castable 5~8mm;
5. The surface expansion line of lightweight refractory castable can be set during pouring or cut after pouring. When the thickness of the furnace lining is greater than 75mm, the width of the expansion line should be 1~3mm and the depth should be 1/3~1/4 of the thickness of the furnace lining. The spacing of the expansion lines should be 0.8~1m and set in a well shape;
6 1. When the thickness of the furnace lining of the heat-insulating refractory castable is ≤50mm, the manual coating method can also be used for continuous pouring and manual tamping. After pouring, the surface of the furnace lining should be flat and dense and should not be pressed;
7. When the thickness of the furnace lining of the lightweight refractory castable is δ<200mm, the part with the inclination angle of the furnace lining less than 60 can be tamped by hand. The material should be evenly distributed during pouring. Use a rubber hammer or a wooden hammer in a plum blossom shape, press half a hammer to compact it, and then vibrate it with a portable flat vibrator to compact it. The surface of the furnace lining should be flat and dense without loose particles;
8. The refractory castable should be vibrated during the formwork casting, and the mechanical vibration should comply with the following regulations:
1) The castable should be uniform and continuous during pouring When there is a construction break during the continuous layered pouring, the pouring of the second layer of castables should be completed before the initial setting of the previous layer of castables. The free fall height of the castables shall not exceed 5m;
2) The height of the pouring layer using an inserted vibrator should not be greater than 300mm. The vibrator rod should be inserted into the lower layer of castables about 50mm. The moving distance should not be greater than the radius of action of the vibrator rod, and the vibration time should not be too long to allow the internal bubbles to overflow and present the floating slurry and no longer sink;
3) When pouring and vibrating refractory castables, the formwork and support should be observed. If deformation is found, timely measures should be taken;
9. Semi-wet mechanical spraying of refractory castables is suitable for thermal insulation refractory castables, lightweight refractory castables, Dense refractory castables, but alumina hollow ball refractory castables shall not be constructed using semi-wet mechanical spraying, and shall comply with the following regulations:
1) Conditions for spraying construction
a. Water pressure shall not be less than 0.6MPa
b. Compressed air pressure shall not be less than 0.4MPa and air volume shall not be less than 79m3/min
c. The working environment shall have ventilation facilities
d. Determine various parameters through trial spraying
2) Spraying shall be carried out in sections and continuously once, spraying to the designed thickness. If the furnace lining is thick and needs to be sprayed in layers, the second layer shall be sprayed before the initial setting of the previous layer of sprayed material, and the rebound material attached to the support or pipeline shall be removed in time.
3) The material and water should be uniform during spraying, and there should be no dry material interlayer or flow on the continuous spraying spraying surface. The spraying direction should be perpendicular to the sprayed surface. The distance between the nozzle and the sprayed surface should be 0.8~2m, and the nozzle should continuously perform spiral motion to evenly distribute the aggregate.
4) The spraying thickness should be checked in time, the over-thick part should be flattened, the under-thick part should be sprayed in time, the spraying surface should not be calendered, and the rebound material is strictly prohibited.
5) The moisture content should be measured at least once per shift.
6) When the expansion line is left on the surface, it should be cut in time after the spraying is completed.
10. The maintenance of the refractory castable lining should be carried out according to the design regulations or the construction instructions of the material manufacturer. If there is no regulation, the commonly used refractory castable maintenance system should be in accordance with the following table:
1) Wet maintenance should be carried out after the castable hardens, and the surface of the lining should be kept sufficiently moist. The relative humidity of natural maintenance is preferably 35% to 75%.
2) The heating rate of steam curing should be 10 to 15℃/h, and the cooling rate should not exceed 40℃/h
3) When curing CA-50 aluminate cement refractory castable, it should be determined whether to take measures to reduce the surface lining temperature according to the climatic conditions. Strengthen early maintenance and natural conditions maintenance at least 1d later.
4) The maintenance of CA-60CA-70CA-80 aluminate cement refractory castables should be based on the Al2O3 content of cement in the castables and the amount of cement used. It should be selected whether to cover the surface with plastic cloth in a natural state or wet maintenance.
5) The castables shall not be subjected to external force and vibration during the maintenance period.
11. The quality inspection of refractory castable construction shall be carried out with 3 engineering test blocks of 40×40×160mm per group on site. The production and maintenance of the test blocks shall be consistent with the construction conditions of the furnace lining. The castable test blocks shall be retained in batches of 20m3 of each brand of castable in the sub-project, and no less than 2 groups of test blocks shall be inspected. If the number is less than this, a batch inspection shall also be carried out.
12. The surface of the refractory castable lining shall not have defects such as peeling, cracks, holes, etc. Slight mesh cracks and a small amount of pores are allowed when there are no special requirements in the design.
13. The refractory castable prefabricated furnace lining shall be lifted, transported and assembled only after the curing period reaches 70% of the compressive strength. During this process, measures should be taken to prevent cracks, and gravity knocking shall not be applied during assembly.
14. When repairing defects in the refractory castable furnace lining, the defects that affect the structural performance of the furnace lining shall be studied and handled in conjunction with the design, supervision and construction units, and shall comply with the following regulations:
1) At least one anchor nail shall be chiseled out at the repaired part of the refractory castable furnace lining, and the joint surface shall be made into an inner eight-shaped (dovetail) shape.
2) The curing method of the repair material shall be consistent with the original furnace lining.
3) The repaired part shall be carefully filled with water-hardening refractory castable, the joint surface shall be fully moistened, and the joint surface of the air-hardening and heat-hardening refractory castable shall be evenly brushed with a binder solution.