The use of inserts made from self-hardening liquid mixtures (SLM), which make it possible to mechanize the process of lining the top part of a mold, reduces the head cutting waste of high-quality electric steel to 11-12% [i]. A further decrease in the head waste can be achieved by using exothermal inserts made from SLM. These exothermal inserts are of particular interest.In order to evaluate their behavior during metal casting, we prepared experimental tiles Of trapezoidal shape of the following dimensions: lower base, 95; upper, 60; height 65, and depth i0 mm. The composition of the tiles was 80% sand, 6% ferrochrome slag, 8% iron ore, and 6% exothermal component.To 100% of the batch, we added 7% bonding material in the form of sodium silicate water glass with a density of 1.4 g/cm 3.For the exothermal component we used aluminum (5%) plus 1% NaCI (composition No. i); FeSi iron silicide (composition No. 2); or SiCa calcium silicide (composition No. 3). The tiles were prepared by casting.To evaluate the resistance of the tiles to abrasive wear, we determined their crumbling tendency, which is characterized by the weight loss from the surface layer of a specimen per unit time when the specimen is rolled around the wall of a meshed drum rotating at a frequency of 60 rpm. The properties of the tiles are given in Table i.Tool (U7A) and bearing (ShKhlS) steels were melted in a 50-kg induction furnace and cast in square molds with the head adapters lined with the experimental tiles. The clear surface of the metal was warmed with a graphite sol. The ingots were removed and cut open on an electrochemical-mechanical machine tool along the axis of the longitudinal section.
Heat-insulating inserts ("hot tops") have recently become very popular for the lateral heat insulation of metal in the riser part of ingots. Their use has reduced the level of top trimming by 3-5% [1, 2].The literature contains inadequate data on the physicoceramic and heating properties of these inserts and on the effect of these properties on the depth of penetration of shrinkage defects inside the ingot. The thermal conductivity of the lining material in the riser has a most marked effect on the shrinkage depth during crystallization of the ingots.Methods involving spheres, hollow cylinders, and ellipsoids are recommended for determining the thermal conductivity of refractories, as these are the most precise, convenient, and low-inertial methods [3][4][5]. However, the sphere and ellipsoid methods [3, 4] involve the need for precision grinding of the materials, precision preparatory work, and the preparation of specimens of complex configuration.The hollow cylinder method [5] is more acceptable. Although it involves minor errors (2-5C]o) due to the leakage of heat through the faces of the cylinder, it admits of the use of simple specimens. An analysis of the errors shows that the maximum values do not exceed 8%. Therefore, the hollow-cylinder method was used for these experiments.The specimens whose composition corresponded to hot tops (Table 1) were made in the form of cylinders. The carefully blended mixture was poured into a mold and compacted using a tamper or a vibrotable. To check that the specimens and hot tops had the same properties, measurements were made of the main characteristics affecting conductivity: density and porosity. When these factors coincided the specimens were tested for thermal conductivity.
As a result of the reconstruction of the shop, the furnace was shut down for the main maintenance after being used for 1 year.When the lining was inspected, it was established that it was still in a reasonable working state.The wear on the walls in the slag zone was 40-60 mm (20-25% of the original thickness).There was only very slight wear (5-10mm) below the level of the slag zone.As a result of the work carried out, a Soviet lining for LFR-2 CTO baleout pot furnace has been developed and tested.The resistance of this lining is as good as that of the lining made from imported mass.
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