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Manufacturing technology of induction smelting furnace lining

Time:2021-08-20   Nums:1091

The lining material of induction smelting furnace belongs to consumables. To withstand high temperature metal liquid, the operator must master the materials and processes related to furnace lining.

Common materials include: crucible mold, crucible (or furnace liner), quartz sand, magnesia, high alumina sand, ramming material, spinel, furnace mouth material, coil mastic, scanning acid, boron anhydride, glass water, asbestos board, asbestos cloth, glass fiber cloth, etc. the combination needs to be selected according to the enterprise's own situation.

There are generally two methods for furnace building process of induction furnace

The first method: use the furnace liner to build the furnace (for those who are not skilled in building the furnace: it is highly recommended!)

1. Clean the inside of the furnace body. Mixed filling materials for furnace building (magnesia, quartz sand and bauxite can be used as filling materials). Proceed as follows:

a. Choose by hand. It mainly removes blocks and other impurities.

b. Magnetic separation. Magnetic impurities must be completely removed.

2. Selection of binder: use industrial boric anhydride (B203) or boric acid (H3BO3) as binder, and the addition amount is 2% ~ 2.5%.

3. Selection and proportion of furnace building materials

a. It should be noted that not all SiO2 & Ge; 99% quartz sand can be used as lining material of induction furnace, and the important thing is the particle size of quartz. The coarser the grain, the less the lattice defects, the better (for example, the crystal quartz sand has high SiO2 purity, white and transparent appearance), and the larger the furnace capacity, the higher the requirements for the grain.

b. Grain size composition and proportion of quartz sand for furnace lining:

For example, above 2T furnace: 3.35 ~ 1.70mm (6 ~ 8 mesh 3) 10% ~ 15%,

1.70 ~ 0.85mm (10 ~ 20 mesh 4) 25% ~ 30%,

0.85 ~ 0.425mm (20 ~ 40 mesh 5) 25% ~ 30%,

0.106 ~ 0.053mm (100-200 mesh 10) 25% ~ 30%.

For example, below 1.5T furnace: 1.70 ~ 0.85mm (10 ~ 20 mesh 4) 20%,

0.85 ~ 0.425mm (20 ~ 40 mesh 5) 30%,

0.425 ~ 0.2mm (40 ~ 70 mesh 6) 20%,

0.106 ~ 0.053mm (100-200 mesh 10) 30%.

The above models can be used after being mixed evenly. No water is required.

4. Put asbestos cloth around the induction ring to keep it flat.

5. Add filler and tamp at the furnace bottom (make the inner bottom of the furnace liner level with the first induction ring).

6. Lift the furnace liner vertically with two lifting ropes and hoist it into the induction ring.

7. Place the furnace liner vertically in the middle of the induction ring (if it is not installed correctly, the service life of the furnace liner will be directly affected)

8. Fill the filler between the furnace liner and the induction ring, 3-5cm at a time, tamp it layer by layer until 5-8cm from the furnace mouth, brush the furnace liner mouth and the filler with glass, and then cast the furnace collar.

9. Connect the furnace collar sand evenly on the furnace liner and hammer it with a rubber hammer (ensure that it will not crack after opening the furnace)

10. Build the furnace collar with furnace collar sand

Precautions for use of furnace liner

The service life of the furnace liner is directly related to the installation and the operation of the furnace worker. As long as it is installed in place and operated according to the regulations, the satisfactory effect of the furnace liner can be achieved. Please pay attention to the following items:

1. Baking and sintering specification

The baking and sintering process can be roughly divided into three stages:

a. In the baking stage, the crucible mold is heated to 600 ℃ at the speed of 25% / h and 50% / h respectively for 4h, so as to remove the moisture in the furnace lining.

b. In the semi sintering stage, raise the temperature to 900 ℃ at 50 ℃ / h for 3h, and then raise the temperature to 1200% at 100 ℃% / h for 3h. The heating rate must be controlled to prevent cracks.

C. During high-temperature sintering in the complete sintering stage, the sintering structure of the crucible is the basis for improving its service life. With different sintering temperature, the thickness of sintering layer is insufficient, and the service life will be significantly reduced. During the baking process, a certain amount of iron is added to enhance the heating effect of the induction coil. With the continuous baking and sintering, a relatively stable electromagnetic force is generated through low-power power power transmission to stir the molten iron, so as to heat the furnace lining up and down evenly. In addition, the temperature of three phase transformation zones of quartz sand is strictly controlled, so as to promote the full phase transformation of quartz sand and improve the first sintering strength of furnace lining.

2. After the installation of the furnace liner, clean up the sundries in the furnace. When the new furnace liner is opened, the blanking must be handled with care. Do not throw large iron blocks into the furnace liner to avoid damaging the furnace liner. When the installed new furnace liner is opened for the first furnace, the power should not be pulled too fast, which is conducive to the combination of the furnace liner and fixed filler

3. Pay close attention to the changes of furnace liner during use and deal with it in time

4. After the furnace liner is used for a certain number of times, the wall of the furnace liner becomes thinner. When the wall thickness of the furnace liner is about to be less than 1 cm, it should be stopped and replaced with a new furnace liner

Second method: use crucible mold to build furnace (only those who have rich experience in building medium frequency electric furnace)

1. Clean the inside of the furnace body. Mixed filling materials for furnace building (magnesia, quartz sand and bauxite can be used as filling materials). Proceed as follows:

a. Choose by hand. It mainly removes blocks and other impurities.

b. Magnetic separation. Magnetic impurities must be completely removed.

2. Selection of binder: use industrial boric anhydride (B203) or boric acid (H3BO3) as binder, and the addition amount is 1.5% ~ 2%.

3. Selection and proportion of furnace building materials

a. It should be noted that not all SiO2 & Ge; 99% quartz sand can be used as lining material of induction furnace, and the important thing is the particle size of quartz. The coarser the grain, the less the lattice defects, the better (for example, the crystal quartz sand has high SiO2 purity, white and transparent appearance), and the larger the furnace capacity, the higher the requirements for the grain.

b. Grain size composition and proportion of quartz sand for furnace lining:

For example, above 2T furnace: 3.35 ~ 1.70mm (6 ~ 8 mesh 3) 10% ~ 15%,

1.70 ~ 0.85mm (10 ~ 20 mesh 4) 25% ~ 30%,

0.85 ~ 0.425mm (20 ~ 40 mesh 5) 25% ~ 30%,

0.106 ~ 0.053mm (100-200 mesh 10) 25% ~ 30%.

For example, below 1.5T furnace: 1.70 ~ 0.85mm (10 ~ 20 mesh 4) 20%,

0.85 ~ 0.425mm (20 ~ 40 mesh 5) 30%,

0.425 ~ 0.2mm (40 ~ 70 mesh 6) 20%,

0.106 ~ 0.053mm (100-200 mesh 10) 30%.

The above models can be used after being mixed evenly. Add a small amount of water.

4. Put asbestos cloth around the induction ring to keep it flat.

5. The thickness of knotting furnace bottom is about 280mm, and sand is filled in four times. During manual knotting, uneven density shall be prevented, resulting in non compact furnace lining after baking and sintering. Therefore, the feeding thickness must be strictly controlled. Generally, the thickness of each sand filling shall be; l00mm; Force evenly to avoid uneven density. When the furnace bottom knotting reaches the required height, scrape it, and then place the crucible mold. In this regard, pay attention to ensure that the crucible mold is concentric with the induction ring, adjust vertically up and down, closely combine the pattern with the built furnace bottom as far as possible, clamp it with three wooden wedges after adjusting the peripheral clearance to be equal, and lift heavy objects in the middle to press it, so as to avoid the displacement of quartz sand when knotting the furnace wall.

6. According to the size of the induction ring of the furnace body, the thickness of the lining of the knotting furnace fireplace is 70-120mm, the cloth shall be uniform, and the thickness of the filler each time; 40mm, be sure to tamp firmly layer by layer 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.

7. Baking and sintering specification

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

a. In the baking stage, the crucible mold is heated to 600 ℃ at the speed of 25% / h and 50% / h respectively for 4h, so as to remove the moisture in the furnace lining.

b. In the semi sintering stage, raise the temperature to 900 ℃ at 50 ℃ / h for 3h, and then raise the temperature to 1200 ℃ at 100 ℃ / h for 3h. The heating rate must be controlled to prevent cracks.

C. During high-temperature sintering in the complete sintering stage, the sintering structure of the crucible is the basis for improving its service life. With different sintering temperature, the thickness of sintering layer is insufficient, and the service life will be significantly reduced.

8. Pay close attention to the changes of the furnace liner during use and deal with the situation in time. After using a certain furnace number, the wall of the furnace liner becomes thinner. When the wall thickness of the furnace liner is about to be less than 5cm, it shall be stopped and the furnace shall be rebuilt

3、 Furnace front operation

After the furnace lining is knotted, how to operate correctly and reasonably is the key to prolong the service life of the induction furnace and ensure life safety- Generally, before operating the induction furnace, check whether the water flow of the water cooling system is smooth, whether the water pressure and temperature of the cooling water are normal, whether there is water leakage, and whether the furnace tilting system can work normally. During the operation, be careful not to touch or touch randomly. One person operates and one person monitors. It is strictly prohibited for miscellaneous personnel to enter the machine room to prevent electric shock. Dry molten materials shall be used in the smelting process, and the materials shall be handled with care and fed frequently. When the melting of molten materials in the furnace reaches the needs, they shall be poured out in time to avoid increasing the loss of furnace lining at high temperature; Frequently observe that when the outside of the furnace body is found to be red, which is the precursor of furnace leakage, measures such as shutting down the power supply and pouring out the molten material in the furnace should be taken in time to avoid the occurrence of furnace leakage accident. It should also be noted that when the furnace lining becomes too thin to continue to use, the old furnace lining should be smashed and the new furnace lining should be rebuilt to prevent furnace leakage.

In addition, the dust in the machine room, power cabinet and the copper bar connected to the induction coil shall be cleaned frequently to prevent insulation reduction and failure. Regularly check whether the water flow and water pressure of each cooling water circuit are normal. Regularly tighten the connecting bolts and nuts of all parts to prevent poor contact from burning the parts. Regularly maintain the pumping motor of the water cooling system and the motor of the hydraulic station, clean the hydraulic oil, and ensure the normal water supply and oil supply of the equipment. Regularly check the rated voltage and current of the equipment to prevent the failure of the protection circuit. Regular, correct and careful maintenance is an important guarantee for prolonging the service life and ensuring safety of induction smelting furnace.

Yiphee Electric Furnace Co.,Ltd specializes in producing induction furnace.Tel(WhatsApp):+86-13450756789, yiphee@yiphee.cn


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