The service life of cement rotary kiln lining is closely related to the construction of refractory castables for the lining. Therefore, we should pay attention to the following points when constructing castables in cement kilns:
(1) Before the construction of castables, the following inspections should be strictly carried out:
1) Check the appearance and cleanliness of the equipment to be casted.
2) Check the integrity of the construction machinery and tools. Vibrating tools and other tools must have intact spare parts.
3) Check the type, size, layout and welding quality of the anchors. Metal anchors must be well compensated for expansion.
4) Check the measures to prevent castable water loss in the surrounding refractory brick lining and insulation layer.
5) Check the packaging and factory date of the castables, and conduct a pre-experimental check to see if they are invalid.
6) Check the construction water. The water quality must reach the quality of drinking water.
If the above items are unqualified, they should be treated and qualified before construction. Expired and invalid materials shall not be used. During the construction of castables, ensure that there is no power outage and no interruption of construction.
(2) The formwork for castable construction can be made of steel plate or hardwood board, and the surface must be smooth.
The formwork must be strong enough, rigid, not deformed, not shifted, and not leaking. The formwork must be firmly fixed to avoid mold expansion due to vibration. The gap between the formwork and the joint must be small to avoid slurry exposure. Steel formwork should be coated with release agent, wooden formwork should be painted with waterproof paint, and reusable formwork should be cleaned and then painted before use.
(3) The amount of water added to the castable should be strictly controlled according to the instruction manual and should not exceed the limit. Under the premise of ensuring construction performance, the amount of water added should be less rather than more.
(4) The mixing time of the castable should be no less than 5 minutes. A forced mixer should be used during operation. When mixing, it is advisable to dry mix in advance, then add 80% of the water used for mixing, and then slowly add the remaining water depending on the dryness and wetness until a suitable working consistency is obtained. When mixing different castables, the mixer should be cleaned first.
(5) Castables must be used in whole barrels or bags. The mixed castable is generally used up within 30 minutes. In a high temperature and dry working environment, this period should be shortened appropriately. Castables that have already set or even agglomerated must not be poured into the mold frame, nor should they be mixed with water for reuse.
(6) The castable poured into the mold frame should be immediately vibrated and compacted in layers with a vibrating rod. The height of each layer should not exceed 300mm, and the vibration interval should be about 250mm. Try to avoid touching the anchor when vibrating, and do not vibrate or re-vibrate at the same position for a long time. After seeing the slurry on the surface of the castable, the vibrating rod should be slowly withdrawn to avoid segregation and voids in the castable layer, and ensure that the gas in the castable is discharged. After the casting is completed, the castable body cannot be subjected to pressure and vibration before solidification.
(7) When casting a large area, construction should be carried out in blocks.
The area of each casting area should be about 1.5m2. Generally, 3-5mm plywood is used as expansion joint. Plywood should be placed on the working surface of the casting material. Expansion should be reserved according to the design and should not be omitted. The depth of the expansion joint should be about half of the thickness of the casting material. If the casting height of the casting material is low, an expansion joint should be reserved between 1.2-1.5m. The expansion joint should be reserved at the position of the anchor interval.
(8) After the surface of the casting material is dry, the part exposed to the air should be immediately covered with plastic film or straw bag. After the initial setting, it should be regularly watered to keep its surface moist. The curing time is at least two days, and water should be frequently sprinkled within the first day. After the final setting of the casting material, the side formwork can be removed and watering can be continued. However, the load-bearing formwork can only be removed after the strength reaches 70%.
(9) After the formwork is removed, the casting body should be inspected in time.
Quality problems such as honeycombs, peeling and voids should be dealt with and repaired in time. When the problem is serious, the defective part should be chiseled off to expose the anchor, then filled and compacted with tamping material of the same quality, and maintenance should continue. It is prohibited to use cement mortar to level it to cover up the problem.
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