In the early days, gunning mass methods included dry and wet methods. In the early days, gunning construction was only used on converters, and later gradually applied to blast furnace bodies, torpedo tank cars, electric furnaces, ladles, vacuum degassing devices, etc. Among them, dry gunning with advantages has been widely used.
1. Comparison of the three
At present, gunning materials are the most common repair materials, and this situation may not change in the future. The reason for the large-scale use of gunning materials is that it can be constructed at any temperature from normal temperature to high temperature, and the operation is also very simple.
Gunning mass construction methods can be divided into dry, semi-dry and wet methods according to the way the materials are transported.
The dry method is a method of transporting dry powder without water and adding water to the nozzle.
The semi-dry method is a method of transporting powder with partial water and adding the remaining water to the nozzle.
The wet method is a method of transporting mud with water added.
The key to gunning technology is to have a set of spraying devices that can operate normally. Different materials are sprayed with different devices, and their performance and parameters are also different.
The spraying devices include double piston pumps and extrusion pumps, both of which are forced feeding pumps. The mud pumped by the double piston pump is transported by high-pressure air injected through the compressed air inlet, and then mixed with the rapid coagulant injected behind the nozzle, and then sprayed out through the nozzle. The extrusion pump is that the mud is not transported by compressed air, but directly mixed with the injected rapid coagulant behind the nozzle. The coagulant is quantitatively injected with dry high-pressure air, the purpose of which is to prevent the coagulant from getting wet and causing pipeline blockage.
The new wet spraying system consists of a material mixer, a high-pressure pump for pressurizing materials, a liquid coagulant supply device, piping (hose or conduit) and a special nozzle. In order to reduce the labor load of the operator, the piping uses a pipe and nozzle with an inner diameter of 4cm.
In this wet spraying method, the key equipment is a high-pressure pressure pump. The pump uses a double piston pump with a discharge port diameter of 7.5cm with a swing ball. The swing ball swings back and forth between two cylinders with controllable oil pressure. One cylinder sucks the material, and the other cylinder is connected to the material outlet through the swing ball. The series of operations of the swing ball and the two cylinders can produce a stable material flow. The performance comparison of the pressure pump and the previous pump is shown in Table 7-1-1. In order to stably pressure-feed low-moisture, high-viscosity, low-cement gunning castables, an extrusion or screw pump and an air pressure sprayer are used. The pressure should not be too small.
2. Grasp the following points
(1) Ensure stable pressure-feed performance. The particle size composition of low-cement gunning mass is closely related to the pressure-feed characteristics. The particle size composition of particles with a maximum size of 5mm and 1mm accounts for 60~80%, which can ensure stable pressure-feed performance. In addition, as the amount of added water increases, the pipe will be blocked during the pressure-feed process. Therefore, in order to achieve stable pressure-feed performance, it is necessary to adjust the optimal particle size composition range of low-cement gunning castables.
(2) Adjustment of hardening speed. The type and amount of the accelerator that imparts hardening properties have a great influence on the strength of the construction body. For aluminate solution (accelerator A), the strength increases rapidly with the increase of its addition amount. For silicate solution (accelerator A), the strength increases with the addition amount within a certain range, but after exceeding a certain amount, its strength shows a downward trend.
In actual construction, when the vertical construction surface is thick, it is necessary to increase the strength of the construction body rapidly; and when the surface of the construction body after spraying needs to be processed, it is better to increase the strength slowly. Therefore, it is very necessary to select appropriate accelerators and addition amounts according to construction conditions.
(3) Formation of dense construction body. Analysis of the relationship between the amount and pressure of spraying air and the organizational structure of the construction body shows that when the amount of spraying air is small, the porosity of the construction body is very high; when the amount of spraying air is large, the coarse particles rebound and the porosity is also high. Therefore, there is an optimal range of spraying air volume to achieve the densification of the construction body, but the density is not related to the spraying pressure.
