For the iron out of the ditch, in addition to the material itself, the construction method is very important. It is briefly described as follows:
Pounding Molding Method
This method is a construction technique used for lining iron outlet ditches, previously applied in small blast furnace iron outlet ditches. It has been carried out manually or with a wind hammer. Since the 1970s, on-site mechanical tamping has gradually developed into the use of automatic pounding hammers suitable for different parts of the structure.
Cast Construction Method (N-Cast Method)
In the late 1970s, the cast construction method was developed in Japan. This method uses a vibrator inserted into the ditch material to vibrate it directly, and the ditch material contains more moisture. This method has several advantages:
(1) it can retain part of the residual lining and improve the utilization rate of the lining material;
(2) the ditch lining has a uniform structure, low porosity, and good durability; and
(3) it reduces the labor intensity of the workers and improves the on-site construction environment.
The disadvantages are high noise levels and a long drying time.
Vibratory Molding Method (VF Method)
The ditch material is poured into the iron trough and into an inner mold equipped with a vibrator. While applying vibration at a frequency of several thousand hertz, pressure is also applied. The thixotropic properties of the low-moisture ditch material are used to promote the flow and densification of the refractory material. As the process continues, the molding die gradually sinks to form the desired shape of the ditch. The moisture content of the ditch material used in this method is between 4% and 6%.
Compared with the pounding method, this method offers higher efficiency, reduced refractory material consumption, and improved quality of the iron trough. However, the densification of the ditch lining is better on the permanent layer side, while it is poorer on the inner mold side.
Core Mold Dry Vibration Molding Method (SVP Method)
The construction machinery used in the core mold dry vibration molding method is relatively complex. The inner mold is equipped with high-, medium-, and low-frequency vibrators. After the mold is positioned, the material is added from the side and compacted through vibration to form the ditch lining.
This method uses vibration molding with dry materials, which can be rapidly dried without cracking, thus saving time. It is especially suitable for single-outlet fixed ditches. In addition, the absence of moisture helps reduce porosity, increase densification, and extend the service life of the iron trough.
Large Bricks and Precast Masonry Method
The iron trough is precast and molded in special molds according to the shape and size of the iron trough. Currently, this method is developing rapidly. All processes-including molding, drying, curing, and baking-are completed in a refractory factory. Masonry can be completed quickly, and the precast iron trough can be put into use immediately. This method is especially suitable for the iron trough and tap hole areas.
The advantages of this method are that the lining can be baked in advance, avoiding the limitations of tapping schedules, and the performance of the castable material is not affected by on-site construction conditions. As a result, high-strength iron trough materials can be obtained, and the service life of the trough is relatively extended.
The disadvantages are that the outer dimensions of the precast components cannot be too large, as the baking conditions may not meet the required standards. Additionally, when used in iron troughs, the joints between precast components can become weak points in the structure.
Self-flowing Castables
Following the development of self-flowing castables in France, self-flowing iron trench castables have been studied in Japan. This material does not require vibration during construction and relies on its own weight and the displacement difference of the material to achieve self-flow, resulting in degassing, smoothing, and densification. It is a viscous-plastic material with a low yield value and certain plastic viscosity, developed based on rheological principles.
Its advantages are:
(1) no need for vibration, allowing the material to be automatically poured and densely packed, greatly reducing labor intensity;
(2) if pumped during construction, labor is reduced and efficiency is improved;
(3) compared to vibrated castable materials, it is more adaptable and can be cast into any shape.
Iron Ditch Repair Method
Localized damage to the lining of the blast furnace iron outlet ditch-particularly in the slag line and iron flow line areas-develops relatively quickly, and is more severe when the proportion of slag and iron is higher. For this reason, hot spray patching materials can be used to repair the ditch lining and achieve damage equalization, thereby improving its service life.
The refractory spray patching materials commonly used for repairing blast furnace iron outlet ditches are generally high-alumina–silicon carbide, Al₂O₃–SiC–C, and mullite–silicon carbide materials. Spray patching is usually carried out after removing residual iron deposits from the lining following iron discharge. Spraying can begin when the temperature is between 400 and 900 ℃, or it can also be performed at room temperature.
Each spray patch layer typically has a thickness of 70 to 150 mm. The disadvantages of this method are the large rebound loss of spray patch material, insufficient density, and a tendency to delaminate.
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