Intermediate frequency furnace

Furnace building and drying and maintenance technology

    First, build the furnace

    1, crucible refractory material

    Crucible refractory confirmation: to purchase acidic furnace lining materials from Hubei Anaijie Furnace Lining Materials Co., LTD., it is necessary to confirm the product name and model of the material supplier.

     Equipment inspection;

          Before building the furnace, the electric furnace equipment should be tested for water and pressure, trial operation, and the furnace body tilting inspection; The new paste should be dried and baked permeable, and the furnace can be laid and built after confirmation.

    2. Install alarm system.

    3. Tie the bottom of the furnace.

    a.. Layer and flatten. Use the vibrating fork to fork 3-4 times from the outside to the inside, taking 12-15 minutes. Pay attention to the principle of orderly, crossed and even. Then use the circular flat hammer from the center to the outer circle in the form of spiral vibration 2 times, taking 3-6 minutes, the flat hammer requires the second hammer pressure... 1/3 of the hammer, not missing the hammer. After ramming, scrape the surface loosely with a fork for 5-10㎜ to facilitate the interlocking between layers and prevent delamination.

    b For the second layer, the method is the same as above.

    c Level the bottom of the furnace with a level and wooden board.

    4. Place the crucible mold

    a crucible mold error ≤5㎜. The circular shape of the crucible die will cause the wall thickness of the crucible to be uneven, and the crucible die must be re-trimmed to make it conform to the requirements of the drawing.

    b Crucible mold exhaust hole diameter is 3-6㎜, spacing is 150-200㎜; If the mold is rusted, it can be used after grinding with sandpaper.

    c When placing the crucible die, pay attention to ** the wall thickness of the crucible is consistent and concentric with the coil, and the weld is left in the back half and the front side. Thick.

    d Fix the crucible mold with three wooden wedges.

    5. Installation of furnace building machine

    The pneumatic furnace building machine is composed of gas distributor, cylinder liner, gas hammer head, length adjusting rod and chain. It is mainly used for knotting the dry lining material of the medium frequency furnace. The pneumatic furnace building machine uses the gas hammer head to strike the inner wall of the crucible of the medium frequency furnace, so that the particles of the lining material fill the void with each other, so as to achieve the effect of tight lining material. The furnace building machine is designed with an automatic rotating device, which can rotate automatically during use, and can adjust the input air volume at will to adjust the vibration force size, and the knotting effect is uniform. The furnace building machine is simple to operate, one person is required to operate the crane lifting, the knotting position is determined, the air source is opened, the pressure can be adjusted appropriately during the knotting process, so that the knot is evenly knotted, and the crane can be evenly moved up and down at any time.

    6. Fill the crucible wall

    a Be sure to loosen the material that is in contact with the wall of the crucible at the bottom by 5-10㎜!

    b Add refractory materials, must carefully check each layer, be careful not to let any packaging debris and other debris mixed into the lining material!

    c If the lining material enters between the laying materials, it must be completely removed. If it cannot be removed, all lining materials must be removed.

    d Crucible wall... Add 10-15cm layer, then flatten after adding. Then use the vibration fork 3-4 times, fully exhaust, pay attention to the principle of orderly, crossed, uniform. Then continue to evenly feed, every 10-15 cm, flatten and fully vent with a vibrating fork until the entire furnace wall is filled.

    e Lower the hanging furnace builder to the lower part of the crucible, adjust the height, start the machine and tie the knot by itself, pay attention to the adjustment to a reasonable air pressure, so as not to knock the crucible out of shape if the air pressure is too large. .. Knock the layer for about 20min, and then lift the furnace building machine 15-20cm and continue to knock for 15-20min, and reciprocate until the knot reaches the furnace mouth. In the knotting process, due to the increasing density of the lining, the burden will sink and cause the material level of the furnace mouth to move down. At this time, the surface will be loosened and filled again to fill the space and fully exhaust the gas to continue to start the furnace until the lining is knotted and the material level no longer moves down.

    f Knot to 1/3 height to remove wedge blocks.

    g The lining must be finished at one time, it is strictly prohibited to stop beating, because this material has strong moisture absorption, coupled with large dust and debris in the casting workshop, which affects the life of the lining.

    7. Burner

    The lower part of the furnace nozzle can be laid with a layer of 10-20㎜ lining material dry material, and other parts can be constructed with water glass and water lining material.

    Second, the oven

    1. Insert the K-type thermocouple by the crucible wall and make it. Lower end ** In the middle and lower part of the crucible die.

    2, manually put the iron block tightly into the crucible mold.

    3. Cover the crucible mold with asbestos cloth or furnace cover, leaving only a row of pores, so that the entire furnace lining is heated evenly.

    4, must be full furnace sintering, liquid surface. The height reaches about 100㎜ from the furnace to facilitate the whole sintering.

    5, sintering specification:

    a Heat the charge to 900 ° C at 100 ° C /h and hold it there for 2h.

    b. After 900℃, take out the K-type thermocouple.

c Continue to increase the power, so that the charge begins to melt, about 5 hours to make the electric furnace completely melt into the full furnace state, when the temperature reaches 1430℃, the slag will be stripped off in time. Low power heating up to 1620℃(±20℃).

    d Heat at 1600℃-1650℃ for 1-2 hours.

    e When the hot metal temperature is greater than 1500 ° C, the temperature is generally monitored every 10 minutes.

    f Start charging when the initial charge melting reaches about 30%.

    g Each feed should be carried out before the last feed is completely melted, be careful not to produce the phenomenon of shed feed, continue to feed to the full furnace.

    6, the occurrence and treatment of hanging materials in the smelting process:

    a The melting process should be carefully added, pay attention to observe the furnace condition, so as to avoid the phenomenon of hanging.

    b The temperature of molten metal in the molten pool under the hanging material is too high, which can cause rapid ablation of the furnace lining and the risk of explosion at any time.

    c After the occurrence of hanging material, the power supply should be reduced to 25% of the insulation power to prevent the molten metal from overheating.

    d At this time, the furnace body must be tilted so that the molten metal is in contact with the hanging material and a hole is melted.

    e Turn the furnace body so that it returns to the upright position, and feed through the holes so that the molten metal comes into contact with the hanging material and melts it. Note: Do not overheat the melted metal when performing this step.

    3. Maintenance process

    1, the crucible early use, the sintered layer is thin, should try to avoid high-power power, produce excessive electromagnetic stirring, so that the furnace lining damage, usually within the first 48h does not exceed 60-80% of the total power.

    2, when feeding, should try to avoid the material hit the crucible, so that the crucible is damaged. Especially after the cold furnace, the strength of the crucible is very low, and mechanical feeding is strictly prohibited. Artificial feeding should also be particularly careful to prevent the increase of cracks, resulting in increased infiltration of metal liquid, resulting in furnace leakage accidents.

    3, after the furnace sintering is completed, the operator is required to have a strong sense of responsibility, always pay attention to check the lining condition, and keep the whole system in good condition.

    4, after the completion of the intermediate frequency furnace, regardless of any reason, the cooling water system should be recycled for about 12h, while the temperature in the furnace is below 200 ° C, otherwise it will lead to damage and even scrap of the furnace lining and induction coil.

    5, in the operation process or empty furnace, the crucible temperature is still very high, should reduce the opening times and time of the furnace cover, in order to reduce heat loss and furnace lining cracking.

    6, normal production should be full furnace, prohibit half furnace production. Lest the temperature difference is too large to crack.

    7, the normal melting should be the side of the material melting, do not allow the hot metal after clearing and then add material. In particular, the amount of waste iron is too large, resulting in large fluctuations in the liquid level of hot metal, and the hot metal is easy to penetrate into the unhealed lining above the liquid level, causing accidental penetration.

    8, the newly rammed lining should be used continuously at least 3-6 furnaces, which is conducive to the formation of a sintered layer of sufficient strength.

    9, lining cooling method:

    a After the hot metal, immediately put in a number of scraps, so that the furnace lining natural cooling.

    b Empty the hot metal and cool it naturally.

    c Empty and exhaust the hot metal, and quickly cool down with fans and air pipes.

    Suggestion: Use method a for cooling.

    10. The furnace lining should be managed by special personnel

    a Before starting the furnace, someone must confirm and agree before starting the furnace.

    b After melting a furnace, someone needs to check the degree of erosion of the furnace lining in time to determine whether the furnace lining can continue to be used and to repair it in time. Once it is found that the furnace condition is poor, affecting the safety of production, the furnace should be stopped immediately, and the relevant authorities should be notified in time.

    c furnace nozzle and furnace lining joint, easy to crack, easy to leak, each time before opening the furnace should be carefully observed, take remedial measures in time.

    d. Because of the different expansion coefficient of the collar and lining materials, cracks occur, which need to be repaired in time to avoid puncture caused by delamination.

    e. When cooling, cracks ≥2㎜ to be repaired in time.

    11. Determine whether the furnace lining is removed:

    a When the thickness of the lining is less than 50㎜, it must be removed.

    b When the furnace lining alarm current is too large, confirm the alarm device to operate without error, at this time need to disassemble the furnace.

    c When under a certain rated DC voltage, the weight of hot metal in the early and late stages is equal, the lining has no obvious local erosion, and the DC current rises by 15-20%, the lining must be removed. In the process of use, if the DC ammeter and DC voltmeter are shaken greatly, or it is found that the DC ammeter continues to rise and the DC voltmeter continues to fall, it is proved that the furnace lining has leaked, and emergency measures need to be taken immediately.

    12, if the smelting is finished, the furnace is not allowed to leave liquid iron, to avoid the furnace body temperature difference is large resulting in the crucible strain, crack.

    13, crucible cold lining is not... Smelting operation requirements (cold furnace startup depends on shutdown time) :

    a. Fill the furnace with iron blocks.

    b Cover the furnace and heat the metal charge in the furnace to 900℃ at 300℃/h.

    c Heat at 900℃ for 2 hours. During this time, no liquid metal is allowed!

    d After the end of insulation, it can be melted normally.

    e Adding order of various charges in the melting process: first add the charge with low melting point and small element burning loss, and then add the charge with high melting point and large element burning loss, ferroalloy. Then join.

    f Special attention should be paid to the charging: cold wet charge and galvanized charge should be added to other charges to slowly enter the iron liquid to avoid splashing of iron liquid. It is strictly forbidden to mix shell cases, sealed tube heads and other explosive items in metal charge.