PREPARATION OF INDUCTION FURNACES FOR PACKING

Preparation of induction furnaces for crucible stuffing. Great impact on the resistance of the crucible of the induction furnace has a careful execution of the preparatory work, which

  1. include:pressure test inductor (pressure testing);
  2. inductor test at idle;
  3. manufacture of lower and upper concrete rings (in large-capacity furnaces);
  4. inductor plastering;
  5. extract for curing and drying the coating of the inductor.

With the increase in crucible capacity, the requirements for preparatory work increase. The larger the dimensions, the greater the stresses in different parts of the furnace design that occur when it is tilted during the discharge of the metal and when the charge is charged. In order for these stresses not to lead to deformation of the lining, which entails the formation of cracks and the passage of metal to the inductor, it is necessary to increase the stiffness of the inductor. One of the rational ways to reduce the elastic deformations in the inductor of the crucible furnace when tilting is the use of structural elements made of monolithic refractory concrete and other refractory coatings on the internal surface of the inductor in the form of washings.

lining of the crucible induction furnace of refractory concrete

Image1. Elements of the lining of the crucible induction furnace, made of refractory concrete.

In large crucible furnaces made of refractory concrete and mortar, the following structural elements are performed (Img. 1): upper concrete
ring 1, the refractory coating of the inductor coil 2, the base for the support of the inductor 3, the lower concrete ring 4, the bottom of the furnace 5, the lining of the furnace lid and drain toe, sometimes the middle part of the furnace bottom – 5.6. However, more often, in order to reduce heat losses, the central (middle) part of the furnace bottom is laid out with lightweight (heat insulating) brick type SL-1.3 (Img. 2). Brick 4 is put on a plate on a solution of mortar SHT-1. To shape the circle, lightweight bricks are sawn on the machine. Along the perimeter of the hearth, asbestos-cement pipes 2 are inserted into special holes, forming holes in the concrete for the inductor screed.

Lining of the bottom of the induction crucible furnace with a capacity of 12-30 tons

Image2. Lining of the bottom of the induction crucible furnace with a capacity of 12-30 tons:
1 – refractory concrete on high alumina cement; 2 – asbestos-cement pipes forming openings for the inductor coupler; 3 – metal pattern; 4 – fireclay lightweight brick; 5 – asbestos cardboard; 6 – bottom.

Then install the metal collapsible template 3, greased with grease, and strengthen it. Refractory concrete 1 is placed on the high-alumina cement (25%) with an aluminosilicate aggregate for refractory concrete ZMKR (75%) with an Al2O3 content of at least 45% (GOST 23037-78) between the template and the outer ring of the bottom body. You can use a ready-mixed mixture of powders of fireclay and cement according to TU 14-8-214-76 grade SSHVTS. The mixture of aggregate with cement is thoroughly mixed in the mixer with forced mixing of the components, then water is added in the amount of 9-13 liters per 100 kg of dry mass (there should be no water discharge on the surface of the laid concrete, the draft of the standard cone for building concrete should not exceed 3 cm) .

The mass of one portion of the prepared concrete should be such that it can be laid before the start of setting (40 min). The compaction of the laid concrete is produced by a deep vibrator (vibrator head), which is usually used for laying concrete. After laying, the refractory concrete for curing is kept in the wet state for 48 hours, for which it is covered with a wet sacking and sprayed with water every 3-4 hours, preventing the surface from drying out. The metal form (template) is removed after 6-8 hours after laying concrete. After hardening, the lining is dried with infrared lamps aimed at concrete, or with electric heaters at a temperature of 100-120 ° C for 24 hours.

The lining of the upper concrete ring is produced by dried blocks of refractory concrete of the same composition as for the furnace bottom. The technology of laying and curing blocks for the upper concrete ring is similar to the technology for the furnace bottom, however, drying the preformed blocks for the upper concrete ring is done more thoroughly in a drying cabinet at a temperature of 100-120 ° C – 24 hours, then at 150 ° C – 24 hours at 200 ° C – 24 hours. Badly dried blocks of the upper concrete ring will emit moisture and damage the insulation of the inductor.

The inner surface of the inductor crucible furnaces for melting iron and steel is coated with a leveling coat, which gives greater rigidity to the inductor. Coating of the following composition, mass fractions,%:

Quartzite fraction of 0.1 mm, separated from quartzite, intended for the filling of the crucible. . . 75-80
High alumina cement. . . 20-25
Water (in excess of 100%) to obtain a thick mixture. . . 10-15

Quartzite and cement are mixed in a dry form, then water is added and thoroughly mixed again. The amount of water shuttered mass should be no more than 20 minutes of work. Place the application of the coating slightly moistened with water. For a uniform thickness of the applied layer, 3 distance rings with a thickness equal to the thickness of the applied layer are installed at the top, in the middle and at the bottom. The thickness of the applied layer depends on the dimensions of the furnace and varies in the range of 5-10 mm. An ironing strip is placed on these rings, moving it around the ring, removing the extra layer of coating and adding it. Applying the plastering with a trowel (trowel) with vertical stripes 15–20 cm wide, pressing hard on the plaster (solution) until the gaps between the turns of the inductor are completely filled, preventing solidification, the plastering is equal to an ironing board whose surface has a curvature equal to the curvature of the inductor.

Sliding (spacer) ring

Image3. Sliding (spacer) ring.

When the entire inductor coil is smeared and the mass is slightly hardened, remove the spacer rings and cover these places with a coating. After application, the coating is kept in the wet state for 2-4 hours, and then the AT-7 asbestos fabric 2 mm thick (GOST 6102-78) is glued in one layer. The fabric is torn into strips with a width of 400-500 mm and glued in a moist condition using high-alumina cement, sealed with water to the consistency of thick sour cream. In order to better adhere the fabric, it is pressed against the wall of the crucible with three spacer (sliding) rings (Img. 3). The same coating and gluing of asbestos fabric is produced on the furnace bottom. Before gluing, the fabric must be cut out so that when it is laid on the bottom there will be no folds. An additional thin layer of coating is applied to the surface of the glued asbestos fabric. Asbestos fabric is a reinforcement, gives a hardened layer of plastering tensile strength and reduces the possibility
cracking during operation. Such a coating serves a long time (more than 2 years) and in the case of the passage of metal through the main lining, it can be drained after the crucible shedding alarm has been triggered. In case of partial violation of the coating, it is repaired, restoring the destroyed part. Before lining the crucible, glue sheet asbestos, 5 mm thick, is glued on top of the plaster and pressed with spacer rings.

In furnaces for smelting aluminum, metal-resistant coating based on corundum with high-alumina cement is used. On top of the coating on high-alumina cement paste moistened micaceous plaster of the IFG-KAHF brand (TU 21-25-263-82) of the Petrozavodsk mica factory.

An aluminum-chromophosphate bond with finely ground chamotte or a mixture consisting of finely ground magnesite (97%) and sodium silicofluoride (3%), closed with liquid glass with a density of 1.38 g / cm3, is used as glue for micudoplast.

References:
1. Sassa V.S. Lining induction furnaces. M .: Metallurgy, 1989, 232 p.
This article was taken from this resource.