Do you know the retention principle of expansion joints in refractory castable construction? (1)

In the construction of firebrick masonry, we all know that there will be reserved expansion joints, so whether the refractory castable should also have expansion joints? How to keep the expansion joint of refractory castable properly? 

What size expansion joints are left for what is castable? Do you understand this? If there is no expansion joint, what will be the impact on the later use? 

Part One - Retention of expansion joints in refractory castables

The thermal expansion of refractory castable is mainly related to aggregate, and it is roughly the same as that of refractory brick masonry. 

With refractory brick masonry furnace, due to a large number of brick joints of the refractory mortar can be compressed, show the expansion of the masonry heated, so the total elongation is small, refractory castable casting concrete is poured or site of furnace lining, furnace body heat expansion after the total elongation is larger, if there are no proper expansion joints would bring lining crowded, crowded or bad result in deformation of the furnace steel structure on both ends.

1. Expansion value of refractory castable

The setting of expansion joints for integral cast refractory lining shall be specified in the design. When expansion joint values are not specified in the design, the following data may be used for the average value of expansion joints per meter of lining length for clayey or high-aluminium refractory castables: 

(1) The clay refractory castable is 4~6mm; 

(2) High alumina cement refractory castable is 6~8mm; 

(3) Phosphate refractory castable is 6~8mm; 

(4) Sodium silicate refractory castable is 4~6mm; 

(5) Portland cement refractory castable is 5~8mm.

2. Expansion joint packing

The filler and thickness of the refractory castable expansion joint should be set according to the design. When the design does not provide, it should be filled with asbestos board or plywood, and its thickness is 4~5mm.

3. Form of refractory castable expansion joint

 The forms of refractory castable expansion joints are basically divided into through joints and non-through joints, as shown in Figure 1.

4. Retention of expansion joints

The setting of refractory castable expansion joint is mainly to choose the spacing, width and form of expansion joint. The distance between expansion joints is different between the prefabricated furnace body and the furnace body cast on site.

(1) the furnace assembled by prefabricated components, such as prefabricated assembly, if the furnace body is short, there is no need to leave expansion joints between the prefabricated parts, only need to leave appropriate gaps at both ends of the furnace body; If the furnace body is long, according to the temperature of each section of the furnace body, along the length direction of the furnace body every 5~10m to leave an expansion joint, the seam is filled with asbestos rope soaked in clay mud, in order to prevent the furnace from smoking and fire at low and medium temperature.

（2）The furnace body cast on site. The spacing and width of expansion joints shall be provided for the refractory castable furnace body cast on site. For details, see Table 7-1. The values in the table apply to clay and high alumina refractory castables.

(3) The fixing of packing. The materials of the expansion joints in the refractory castable should be fixed in place before pouring or carefully filled during pouring. During the construction of block casting, the refractory castable should be divided into several blocks according to its expansion joints and separated from the expansion joints by a template for pouring. After initial setting, joint fillers should be embedded, as shown in Figure

(4) To prevent displacement. In order to prevent the displacement of the filler in the expansion joint or the local adhesion of refractory castable, 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 packing layer is separated in the cold state and contacted in the hot state in the construction environment, that is, when it becomes the slip surface, the isolation layer should be added to prevent the displacement of the packing, prevent the leakage of slurry adhesion or block the expansion gap.

5. Precautions for use

Pipes and components that pass through refractory castables shall be wrapped with asbestos ropes and pasted with asbestos boards.

For dense small tube bundles, can be wrapped in 350 linoleum paper or coated with asphalt (coated thickness of 2mm).