Everyone knows that expansion joints will be reserved during the construction of refractory brick masonry. So should refractory castables also have expansion joints? How to leave appropriate expansion joints for refractory castables? What size of expansion joints should be left for what kind of castables? Do you know these? If expansion joints are not left, what impact will it have on later use?
When refractory bricks or 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 left during the construction of refractory bricks and castables.
Refractory bricks and castables use different raw materials, and the expansion coefficients generated 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 are subjected to.
1. Forms of expansion joints of refractory castables
The forms of expansion joints of refractory castables are basically divided into through joints and non-through joints, as shown in Figure 1.
a, b-through expansion joint; c-non-through expansion joint
2. Expansion joint reservation
The reservation of expansion joints in refractory castables mainly involves the selection of the spacing, width and form of expansion joints. The distance between expansion joints of furnace bodies assembled with 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 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 joint can be filled with ceramic fiber ropes soaked in clay slurry to prevent smoke and fire from emitting outwards at low and medium temperatures in the furnace.
② Cast-in-place furnace body. 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 refractory castables.
③Fixing of fillers. The materials of the expansion joints in the refractory castables should be fixed in place before pouring or carefully filled during pouring. When pouring in blocks, the refractory castables should be divided into several blocks according to their expansion joints, and the molds should be used to separate and pour from the expansion joints. After initial setting, the joint fillers should be embedded, as shown in Figure 2.
a:δ=3~4mm
b:δ=5mm
④Prevent displacement. To prevent the expansion joint filler from displacement or local adhesion of refractory castables, the filler layer should be accurately cut and laid tightly. If necessary, nails can be nailed into the castable to stabilize the filler layer.
⑤Isolation measures. When the filler layer is separated in the cold state and in contact in the 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 displacement, prevent leakage from adhesion or blockage of the expansion gap.
3. Allowable error of expansion joint
(1) The allowable error of verticality of vertical expansion joint is no more than 2mm per meter height and no more than 15mm for the whole height.
(2) The allowable error of horizontality of horizontal expansion joint is no more than 2.5mm per meter and no more than 15mm for the whole length.
(3) The allowable error of expansion joint of power station boiler is 3~4mm.
(4) The allowable error of width of expansion joint is shown in Table 2.
