When refractory castables are used for the lining of industrial kilns, the lining structure will be deformed and expanded due to the influence of thermal stress formed by temperature changes and temperature gradients. Therefore, expansion joints should be set during the construction of refractory bricks and castables.
Refractories castables use different raw materials, and the expansion coefficients produced after heating are also different. The size of expansion during masonry is mainly determined by the properties of the refractory bricks or castables used and the temperature they withstand.
1. Form of expansion joints of refractory castables
The forms of expansion joints of castables are basically divided into through joints and non-through joints
2. Setting of expansion joints
The setting of expansion joints of castables mainly involves selecting the spacing, width and form of expansion joints. The distance between expansion joints of furnace bodies assembled from prefabricated parts and furnace bodies cast on site is different.
① For furnace bodies assembled with prefabricated components, if the furnace body is short, there is no need to leave additional expansion joints between the prefabricated parts, and only appropriate gaps need to be left at both ends of the furnace body; if the furnace body is long, an expansion joint can be left every 5~10m along the length of the furnace body according to the temperature of each section of the furnace body, and the joints are filled with ceramic fiber ropes soaked in clay slurry to prevent smoke and fire from emitting outward at low and medium temperatures in the furnace.
② Furnace body cast on site. The spacing and width of expansion joints for furnace bodies of refractory castables cast on site. Please refer to Table 1. The values in the table are applicable to clay and high-alumina castables.
③ Fixation of fillers. The materials of the expansion joints in the castables should be fixed in place before pouring or carefully filled during pouring. When the block casting is constructed, the castables should be divided into several blocks according to their expansion joints, and the templates should be used to separate and pour from the expansion joints, and the joint fillers should be embedded after initial setting
④ Prevent displacement. In order to prevent the expansion joint filler from shifting or local refractories castables from sticking, the filler layer should be cut accurately and laid tightly. If necessary, nails can be nailed into the castable to stabilize the filler layer.
⑤ Isolation measures. When the filler layer is separated in a cold state and in contact in a hot state under the construction environment, that is, it becomes a sliding surface, it is advisable to add an isolation layer to prevent the filler from shifting, preventing leakage from sticking or blocking the expansion gap.
3. Allowable error of expansion joints
(1) The allowable error of vertical expansion joints is no more than 2mm per meter in height and no more than 15mm in total height.
(2) The allowable error of horizontal expansion joints is no more than 2.5mm per meter in horizontality and no more than 15mm in total length.
(3) The allowable error of expansion joints of power station boilers is 3~4mm.
4) Allowable error of expansion joint width
General industrial furnaces allowable error +2 -1
Converter allowable error +2
Industrial boilers +5 -0
Power station boilers +3 -3
5) All types of refractory castables cast on site shall be provided with expansion joints in accordance with the requirements of the design drawings, and the width error shall be +3mm and shall not be less than the specified width.
When constructing the furnace bottom, the expansion joints of refractory bricks or castables shall be staggered between the upper and lower brick layers and the same layer of the furnace bottom. When building the furnace wall, the expansion joints left between the inner and outer layers and between the upper and lower layers can also be staggered. When constructing the circular wall, a gap shall be left between the outer shells to compensate for expansion.
During the construction of the vault, the expansion joints of the refractory bricks and refractory castables should be left straight at both ends. When leaving, the longitudinal expansion of the vault and the upward expansion of the furnace wall should be considered. When the vault length is greater than 5 meters, in addition to leaving expansion joints at both ends, expansion joints should be left in the middle of the vault according to the segmentation of the vault length, and the expansion joints of the staggered vaults should be left straight.
The expansion joints of each layer of the multi-layer vault should be staggered, and the expansion joints should be covered with a layer of flat bricks. If it is a dry-laid vault of silica bricks, 1-2mm cardboard should be inserted into the radiation joints of the vault every 3-5 bricks to compensate for the expansion.
If the suspended furnace roof uses refractory bricks or castables, expansion joints should be left around the furnace roof.
