The masonry of a hearth resistance furnace is generally composed of a refractory layer and a heat-insulating layer. The selection of refractory layer materials is often determined based on factors such as the maximum operating temperature of the furnace, the load-bearing requirements of the furnace bottom, and economic indicators. For the repair of the old furnace masonry, refractory bricks of the same material type, brand, and specification as the original are generally used. After masonry, it should be restored to its original state.
01: Refractory mortar for furnace repair
This mortar is required to be resistant to high temperatures and have fire-resistant, slag-resistant, and airtight properties. Generally, refractory mortar is composed of refractory brick powder and a small amount of adhesive. ① Thin mortar for brick joints with a thickness of 1mm: 1m3 dry material + 600L water. ② Semi-concentrated mortar for brick joints with a thickness of 2mm: 1m3 dry material + 500L water. ③ Concentrated mortar for brick joints with a thickness of 3mm: 1m3 dry material + 400L water. When laying silica bricks, use 5~6 parts by mass of silica powder + 1 part by mass of refractory clay. For laying clay bricks, use 60%~70% (mass fraction) of clay clinker powder + 30%~40% of finely ground refractory raw clay. Laying semi-acidic bricks is the same as laying clay bricks; magnesium bricks should be laid dry, and the seams should be filled with magnesium brick powder.
02 Bricklaying method for furnace
There are three bricklaying methods according to different situations and requirements.
① Dipping method. When the mortar joint is required to be 1mm, use the dilute mortar dipping method for laying. After dipping the bricks with dilute mortar, place them in the laying position and tighten them with a wooden hammer or hard rubber hammer.
② Squeezing method. On the surface of the already laid bricks, use a mortar shovel to spread the mortar; then use your hand to push the bricks along the mortar so that the side is close to the already laid bricks, and the mortar is squeezed out of the masonry joints; then use a wooden hammer or hard rubber hammer to tighten.
③ Scraping method. Spread the mortar on the surface of the laid bricks. First use a mortar shovel to scrape the mortar onto the side of the previous laid brick, and then hold the brick to be laid close by hand, so that a good vertical joint can be obtained. When scraping and squeezing the mortar to lay bricks, use a mortar shovel to fill the unfilled brick joints with mortar after each layer. It is strictly forbidden to wet the refractory bricks with water, otherwise cracks will occur during heating and damage the furnace body.
03 Arch masonry method
The furnace arch masonry method is divided into two types: ring masonry and staggered masonry. The ring masonry method is suitable for masonry of the furnace arch of a continuous furnace with inconsistent furnace temperatures in each section, or a furnace roof with a high furnace temperature, rapid damage, and frequent demolition and repair, or a very short furnace roof. The staggered masonry method is suitable for masonry of furnace arches and flue arches with consistent furnace temperatures in each section. a) Filling layer insulation furnace roof structure b) Diatomaceous earth brick insulation furnace roof structure a) Staggered masonry method b) Ring masonry method
04 Expansion joint reservation
When the furnace is heated, the furnace body refractory bricks will expand. Therefore, expansion joints must be left to prevent damage to the masonry and the metal frame of the furnace shell. For furnaces with a short length, the expansion of the furnace body can be compensated by the compression of the ash joints. In large furnaces, special wide joints must be used for compensation. Generally, the expansion joints are filled with slightly moist refractory mud mixed with 20%~30% (volume fraction) asbestos to give it a certain degree of elasticity. At the same time, in order to prevent the furnace wall from being permeable, the expansion joints are staggered and reserved, and should not run through the entire thickness of the masonry, otherwise it will reduce the strength of the masonry and increase the permeability of the furnace.
