Refractory gunning mix is the kind of refractory material applied by the high-speed gunning method. Refractory gunning mixes include gunning material used for damaged lining patching and coating material used for new lining construction. Refractory gunning work can be done without mould, so it is labor-saving and have a shorter working schedule. Gunning refractory mix can be classified into two categories according to physical states: cold gunning method and molten spraying method. The cold gunning method relies on hydrous cementitious material to make the refractory material adhere to the lining. Cold gunning method can further be divided into 5 types: dry gunning method, semi-dry gunning method, wet gunning method, slurry gunning method, and mixing gunning method. The molten spraying method is the one uses a high-temperature flame or plasma arc to melt refractory material and spray it to the lining. According to the raw material category, it can be divided into acid-resistant gunning mixes, aluminum silicate fire-resistant gunning mixes, ceramic gunning mixes, magnesium gunning mixes, etc.
Nowadays, the wet gunning method is widely used due to the advantages of no dust pollution, a better working environment, less rebound during gunning, and material saving.
Acid-resistant gunning mixes are made of acid-resistant aggregate and powder, adding water glass or Portland cement and admixtures. It is mainly used for the protective layer of hot blast stove dome steel plates and various chimneys. The acid-resistant gunning refractory can also be poured, and spraying or pouring can be selected according to the construction conditions on-site.
Ceramic Gunning Mixes
Ceramic gunning mixes are the most widely used gunning refractory. The lining can be built as a whole, and it can also be repaired by gunning. During the construction, the bulk material is conveyed by air, and sprayed to the part that needs to be used or repaired by the spray gun, and can also be smeared. At present, the use of lime kiln lining has become a trend in the market. The method is to replace the re-built refractory brick lining when repairing the kiln lining but to rebuild the furnace lining on the surface of the remaining brick lining or furnace shell to restore its lining working layer. This method is characterized by good integrity and can delay the relining and overhaul time.
The aluminum silicate gunning refractory mix’s main components are Al2O3 and SiO2. Aluminum silicate gunning mix includes heavy, semi-lightweight, and lightweight types. Heavy gunning mix’s bulk density is no less than 1.8g/cm3, the bulk density of semi-lightweight gunning mix is between 1.3~1.8g/cm3, and the bulk density of lightweight gunning mix is less than 1.3g/cm3. Heavy gunning mix is mainly used as working lining or patching material, semi-lightweight gunning material can not only be used as heat-insulating lining but also be used as working lining of low and medium-temperature atmosphere furnaces, while lightweight gunning material is mainly used as thermal insulating lining.
Al2O3-SiO2 Gunning Mix Physiochemical Index
Item
ASG-1
ASG-2
ASG-3
Bulk Density g/cm3 110 ℃
1.8-2.0
1.25
1.8-1.9
Modulus of rupture (110℃) Mpa
8
13
3
Crushing Strength 110℃ Mpa
45
—
10
Linear Change Rate % 110℃ ≥
0.1
0.3
0.2
Thermal Conductivity W.(m.K)-1110℃
0.7
0.28
0.65-0.75
Application
Chimney inner lining of Sintering factory and power plant
Aluminum silicate gunning refractory mix is mainly used at the flue and chimney inner lining of industrial furnaces, at the insulating lining of blast furnaces and hot blast furnaces, at the cyclone separator inner lining of rotary kiln, at the insulating lining and working lining of catalytic cracking equipment of petrochemical industry, at ladle and tundish insulating lining and so on.
Magnesium gunning mixes are used in the alkaline atmosphere of the furnace lining. The outstanding performance of an alkaline fire-resistant gunning refractory coating is that it is suitable for use in linings with high temperatures and strong slag erosion. For example, the lining of the tundish, slag is soaked for a long time, and the use of alkaline gunning refractory paint is more uniform than that of alkaline smear. Moreover, it will not have side effects on molten steel, and it can also remove residual steel slag shells during spraying.
The performance of the alkaline refractory gunning coating material is to be used in a furnace with high temperature and alkaline atmosphere. It is characterized by no bursting or peeling during spraying and baking, and a good heat preservation effect. The most important thing is that it has good corrosion resistance to molten steel and slag, and it is easy to remove the residual steel slag shell after use. When removing the residual steel slag shell, the working lining will not be damaged, and the disassembly property is good.
So what are the conditions for alkaline fire-resistant gunning refractory coatings to be sprayed? First of all, it does not require a lot of pressure and moisture when spraying, and the material has good fluidity in the conveying pipeline and the material is evenly discharged. It has good adhesion to the working lining and does not fall back and collapse. React with different molten steel, or will not cause secondary oxidation of molten steel.
There are many ways to combine alkaline refractory gunning mixes, such as water glass, phosphate, magnesium sulfate, composite phosphate, high alumina cement, and alumina cement.
It should be noted that different furnaces and temperatures should be combined with different binders. It cannot be used in any furnace with the same process, otherwise, the gunning mixes will be cracked. The three combinations of water glass, alumina cement, and phosphate should be used with caution. Improper use will lead to phosphating, cracking, or shortened service life.
In order to obtain alkaline fire-resistant gunning mixes with good performance, in addition to the correct selection of binders, it is also necessary to select admixtures such as water-retaining agents, plasticizers, dispersants, hardeners, anti-dispersants, and explosion-proof fibers. In this way, the water retention performance, anti-explosion performance, and anti-deflecting effect of the alkaline gunning refractory coating can be adjusted.
RS Kiln Refractory Manufacturer
RS Kiln Refractory was founded in the early 1990s. With more than 20 years of innovation and technical reformation, RS brand refractory products such as mullite brick, carbon brick, alumina brick, magnesia brick, silica brick, corundum brick, clay brick, high alumina castable, low cement castable, ceramic fiber textiles have exported to more than 60 countries and regions, our refractory products are tested by numerous customers and are trustworthy.
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