How to Reserve Expansion Joints for Refractory Bricks and Castables?

When refractory bricks or castables are used in the refractory lining of industrial kilns, due to the influence of temperature changes and thermal stresses formed by temperature gradients, the lining structure will deform and expand. Therefore, expansion joints should be left during the construction of refractory bricks and castables.

The raw materials used in refractory bricks and castables are different, and the expansion coefficients produced after heating are also different. During masonry, the size of expansion is mainly determined by the nature of refractory bricks or castables and the temperature it withstands. 

Reserved Expansion Joints for Refractory Bricks in Rotary Kiln

The expansion of refractory brick and castable heating surface at the highest temperature is (unit: mm):

• Clay brick masonry: 5-6
• High alumina brick masonry: 7-8
• Corundum brick masonry: 9-10
• Silica brick masonry: 12-13
• Magnesia brick masonry: 10-14
• Clay castable masonry: 4-6
• Phosphorus salt castable: 5-8
• High alumina cement castable: 6-8
• Water glass castable: 4-6

Rules for reserved expansion joints

Clay bricks and lightweight brick masonry whose temperature is lower than 800°C do not need to leave expansion joints. However, expansion joints are still required for clay bricks with too long dimensions. The location of the expansion joint must avoid the stressed part. If there are holes in the furnace body frame and lining, the expansion joints should be separated and the spacing should not exceed 2m.

The expansion joints of refractory bricks or castables at the bottom of the furnace should be staggered in the upper and lower bricklayers and the furnace bottom of the same layer. When building the furnace wall, the left expansion joints can also be left in a staggered pattern between the inner and outer layers and in the upper and lower layers. When the circular wall is constructed, a gap should be left between the shells to compensate for expansion.

In the vault construction, the expansion joints of the refractory bricks and the castable should be left straight at both ends. Consider the vertical expansion of the vault and the upward expansion of the furnace wall when setting it aside. When the length of the dome is greater than 5 meters, in addition to leaving expansion joints at both ends, expansion joints must be set in the middle of the dome according to the segmentation of the arch length. The expansion joints of the staggering vault are left straight through.

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 dome made of silica bricks, cardboard of 1-2mm should be inserted every 3-5 bricks in the radial joint of the dome to compensate for expansion.

If refractory bricks or castables are used for suspended furnace roofs, expansion joints should be left around the furnace roof.

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