How to Improve the Temperature Resistance of Induction Furnace Lining？

   Methods of Improving the Temperature Resistance of Induction Furnace Lining

Furnace lining refers to the furnace wall of induction furnaces or other furnaces used to refine metals. It is an important part of the working process of medium frequency furnace. The quality of furnace lining can directly affect the working efficiency of the electric induction furnace. As high-temperature smelting equipment, the temperature resistance of the furnace lining must be the main standard to judge the furnace lining. So how can we improve its temperature resistance? Today, let's discuss how to improve the temperature resistance of the induction melting furnace lining.

The temperature resistance of furnace lining mainly depends on the physical, chemical properties and mineral composition of the refractory used in furnace lining. On the premise of selecting raw and auxiliary materials, the sintering process is the key process to obtaining a good microstructure of furnace lining and give full play to its high-temperature resistance. The densification degree of lining sintering is related to the chemical composition, particle size ratio, sintering process, and sintering temperature of refractory. After introducing the relevant factors, we will officially start to introduce the methods to improve the temperature resistance of the electrotherm induction furnace lining.

1. Remove the mica paper when building the furnace

One of the ways to improve the temperature resistance of the inductherm induction  furnace lining is to remove mica paper when building the furnace.

2. Treatment of crystal quartz sand for furnace building

Manual selection: mainly remove blocks and other impurities;

Magnetic separation: magnetic impurities must be completely removed;

Dry ramming material: it must be dried slowly, with the drying temperature of 200 ℃ - 300 ℃ and heat preservation for more than 4 hours.

3. Selection of binder for medium frequency electric furnace

Boron anhydride (B2O3) is used instead of boric acid (H3BO3) as binder, and the addition amount is 1.1% - 1.5%.

4. Selection and proportion of appropriate furnace building materials:

(1）Selection of furnace building materials: it should be noted that not all quartz sands with SiO2 ≥ 99% can be used as furnace lining materials of induction furnace. The important thing is the size of quartz grains. The coarser the grains are, the less the lattice defects are, the better. (for example, crystal quartz sands have high SiO2 purity and white and transparent appearance.) The larger the furnace capacity, the higher the requirements for grains.

(2）Proportion of furnace building materials: proportion of quartz sand for furnace lining: 6-8 mesh, 10% - 15%, 10-20 mesh, 25% - 30%, 20-40 mesh, 25% - 30%, 270 mesh, 25% - 30%.

5. Knotting of furnace lining

The knotting quality of the furnace lining is directly related to the sintering quality. When knotting, the sand particle size is evenly distributed without segregation. The density of the sand layer after knotting is high, and the probability of cracks after sintering is reduced, which is conducive to improving the service life of the induction furnace lining.

6. Knotting at the bottom of the furnace

The thickness of the furnace bottom is about 280mm, which is filled with sand in four times. During manual knotting, it is necessary to prevent uneven density everywhere, and the furnace lining after baking and sintering is not dense. Therefore, the feeding thickness must be strictly controlled. Generally, the thickness of sand filling shall not be greater than 100mm/time, and the furnace wall shall be controlled within 60mm. Multiple people shall operate in shifts, 4-6 people in each shift, knot for 30 minutes each time, and change people. Rotate and rotate slowly around the furnace with uniform force to avoid uneven density.

7. Knotting of the furnace wall

The thickness of the furnace lining is 110-120mm. Dry knotting materials are added in batches. The distribution is uniform. The thickness of the filler is no more than 60mm. Knotting for 15 minutes (manual knotting) until it is flush with the upper edge of the induction ring. After knotting, the crucible mold is not taken out, and it plays the role of induction heating during drying and sintering.

8. Observe baking and sintering specifications

In order to obtain the three-layer structure of furnace lining, the baking and sintering process is roughly divided into three stages:

(1) Baking stage: heat the crucible mold to 600 ℃ at the speed of 25 ℃ / h and 50 ℃ / h respectively, and keep it warm for 4h, so as to completely eliminate the moisture in the furnace lining.

(2) Semi sintering stage: raise the temperature to 900 ℃ at 50 ℃ / h for 3h, and raise the temperature to 1200 ℃ at 100 ℃ / h for 3h. The heating rate must be controlled to prevent cracks.

(3) Complete sintering stage: during high-temperature sintering, the sintering structure of medium frequency electric furnace crucible is the basis for improving its service life. With different sintering temperatures, the thickness of the sintering layer is insufficient and the service life is obviously reduced.

The above is the method to improve the temperature resistance of the medium-frequency furnace lining. In addition, I would like to remind you that when the medium frequency furnace is cold started, you must preheat at low temperature and gradually increase it, which can effectively improve the service life of the furnace lining.

If you have any questions or inquires, please email at [email protected].