Analysis and prevention of lining problems of induction furnace

1. Cracking of furnace lining: the occurrence and prevention of vertical cracks and horizontal cracks

2. The occurrence and prevention measures of flake or thin layer lining peeling phenomenon

3. Occurrence and prevention of abnormal melting corrosion of furnace lining:

1. Uneven corrosion of smooth glassy lining surface:

2. The lining surface is not smooth and uneven corrosion:

3. Abnormal serious melt loss at the bottom:

4. Abnormal serious melting loss at the bottom and lower cone (melting of the shape of the foot):

5. Abnormal serious melting of the lower cone:

6. Abnormal serious melting loss of furnace wall:

7. Abnormal serious melting damage on the upper part of the furnace wall:

4. Discussion on different color or decolorization of furnace lining:

5. Occurrence and prevention of abnormal wear of furnace lining:

1. Ribbon groove wear:

2. Localized pocket-like wear:

3. Irregular wear at the same level:

4. The overall lining shows irregular wear:

6. Occurrence and prevention of metal penetration and penetration:

1. Shark fin-like infiltration/penetration phenomenon:

2. Metal penetration or a dark layer at a certain depth of the lining:

3. There is impurity intrusion in the local position of the furnace lining:

7. The occurrence of slag accumulation or hanging slag phenomenon and prevention countermeasures:

1. Formation and deposition of low melting point slag:

2. Formation and deposition of high melting point slag:

Viii. The generation and prevention of the phenomenon of electrical phase imbalance or excessive current:

1. Appear in the initial sintering process:

2. In the process of restarting after stopping the furnace:

3. In the process of restarting after the current trip:

4. In the process of reactivating the furnace lining after repair:

9. Abnormal phenomenon judgment and disposal of dry vibration ramming materials:

1. Particle segregation and particle size anomalies:

2. Disposal when silica content is too low:

3. Disposal of impure materials when found:

10. The occurrence and prevention countermeasures of unstable service life:

    Abstract: Tracing and discussion on the problem of lining resistant material for centerless induction furnace

Although the service life of the lining of a centerless induction furnace is mainly determined by its operating conditions and operating environment; However, it cannot be avoided that whether to stop the furnace for repair depends on the extent of damage to the refractory lining. It is rarely necessary to stop the furnace for repair because of problems with electrical equipment or mechanical equipment and water cooling or oil pressure equipment. The design of working furnace lining will be corroded. However, some users often have the illusion that all the problems can be blamed on the lining material, and ignore it. The big reason is that the operating conditions and operating environment, and even mistakenly believe that thicker lining will have a longer service life. In fact, the thicker lining is not conducive to melting efficiency, and it is not easy to form a good sintering layer, and there will be a high corrosion rate in the early stage of use.

As mentioned above, the corrosion loss rate of the furnace lining is greatly related to the operating conditions and operating environment. Such as: the impurity composition and content of the added earth metal (iron block and return charge); How to add to the furnace; What kind of molten iron is melted; And what kind of additives to add; Melting operating temperature; The height of molten iron; Is the continuous or intermittent operation of various operating factors, will directly cause chemical melting corrosion of furnace lining; Effects of mechanical and stress damage and thermal shock cracking and spalling. At the end of the operation of the lining, if the lining puncture phenomenon occurs, carefully and carefully at the bottom of the furnace; Pyramis; It will be helpful to improve the lining material and prolong the service life to take appropriate samples for analysis and study of the furnace wall and upper part.

This paper collects the problems and phenomena that often happened in the past, and discusses the causes and solutions in depth, which can be used as a reference book.

1. Cracking of furnace lining: the occurrence and prevention of vertical cracks and horizontal cracks

A. Vertical cracking phenomenon: more often occurs in the larger induction furnace lining, mainly due to the cooling shrinkage caused by stress cracking, its prevention countermeasures are:

1. According to the instructions of sintering operation (temperature rise and sintering temperature curve), the furnace lining should produce a sintered layer of sufficient thickness to resist the stress cracking caused by cooling shrinkage.

2. Avoid air cooling of silica lining, and should be kept above 800℃; Air cooling is not allowed, even for intermittent operations. The correct method is: first of all, clear the hot iron, and then lift into the red hot iron block, cover the furnace cover, do not close the cooling water, continue to keep heat above 800℃.

3. As far as possible 24 hours, uninterrupted continuous production operation; If it is necessary to stop production at ** *, it should also be insulated as mentioned in item 2 above.

4. If you want to check the furnace lining when stopping production, do not use a fan to cool the furnace wall to prevent the phenomenon of cold cracking.

B. Horizontal cracking phenomenon: mainly due to particle size segregation and construction caused by the layer, such as dry punching materials through transportation and movement in the bag has caused particle size segregation; Or uneven cloth in the furnace; Or the furnace tools and processes are poor; Or mold gaps resulting in fine powder outflow; Or layer indirect surface poor reasons. Second; It may be caused by mechanical impact or vibration during production operation, and its prevention countermeasures are:

1. Before hitting the furnace, check whether the packaging of the dry punching material is complete and whether the material in the bag has particle size segregation. If there is particle size segregation, it should be evenly mixed again before it can be used.

2. Check whether the inner mold is intact, whether the joint part is close, if there is a break or gap, it should be repaired.

3. Uniform cloth is needed when feeding... Can not be a single point of fabric, in order to prevent the uneven fabric caused by particle segregation situation.

4.. The best selection of the construction vibration tools (high vibration frequency) and mold equipment (cruciform internal mold vibration or three-arm air hammer) recommended by the original company can reduce the lack of construction technology, shorten the construction process, improve the density of the furnace lining (about 10% higher than the manual furnace), and improve the durability of the furnace lining.

5. If the furnace is played by hand, the flat head type gas hammer can not be used, and the fork type or cross type hammer should be used to prevent the occurrence of inter-layer phenomenon.

6. Moderate vibration or furnace, can be obtained. Good filling density, too much or not enough are harmful.

7. When making the bonding layer, the surface should be made into flowers first to facilitate the bonding effect of the material

8. Record and compare the amount of material used in each furnace to judge and understand the construction status of the furnace lining.

9. Reduce and reduce the mechanical impact on the furnace lining, improve the unnecessary vibration of the working platform.

2. The occurrence and prevention measures of flake or thin layer lining peeling phenomenon

During the melting process, some lining materials can sometimes be observed suspended on the surface of the hot metal, which is a flake or thin layer of lining stripping phenomenon. The possible causes of this phenomenon are: the excessive drying and heating rate, resulting in the water steam explosion and resulting in the separation of the furnace lining surface; Dry ramming material itself contains too much residual water; The use of iron mold crucible heating, but not in the iron mold crucible pre-vent, resulting in the water gas can not effectively escape from the furnace lining surface; Wet ramming or pouring material and coil mud for safety backing, which have not been completely dried and are caused by residual moisture; Dry ramming material itself sticky; The result of uneven distribution of the sinter, or the result of particle segregation. The countermeasures are as follows:

1. Boric acid and borogane are commonly used dry ramming materials of the sintering agent, the former contains crystal water, so its temperature curve to be slightly slower than the latter. The size of the furnace and the thickness of the lining will also affect the temperature curve. The following temperature rate can be used as a reference:

2. Residual water of dry ramming material must be controlled below 0.5%; Generally, the company's products are controlled below 0.3%; Also, materials must be stored indoors; Pay attention to moisture and prevent direct sunlight; Too cold or too high is not suitable.

3. If the iron mold crucible is used for heating, it is necessary to reserve air holes in the iron mold crucible to facilitate the elimination of water vapor. At intervals of approximately 225mm, a diameter of 2 to 3mm is required. Of course, in the vibration ramming furnace lining, it is necessary to close the ventilation hole, and then open the ventilation hole after completion.

4. In the early drying process, auxiliary heating equipment, such as gas fire breathing equipment or electric heat pipe and other devices can be used to prevent the flame from directly impacting the furnace lining surface, and pay attention to the air circulation to discharge water vapor and extend the drying time. The design of conical induction coil and conical furnace lining requires a high drying temperature and the opening of cooling water. Try to avoid forming a dry and hard layer on the lining surface.

5. Do not add additional additives to the dry beating material to avoid sticking; The sinter is not evenly distributed.

6. Improve the furnace construction process and tools to prevent the particle segregation of the furnace lining

3. Occurrence and prevention of abnormal melting corrosion of furnace lining

Uniform corrosion is the design principle of refractory furnace lining. Under the operating conditions of a 24 hour continuous operation of a centerless furnace, producing products of a single type of composition, and making 66~80% of the residual hot metal liquid level, the original unit resistant material consumption of the silica dry beating material should be between 1~2 kg per ton of hot metal, and a normal silica dry beating furnace lining should be clearly visible after use : a. The working layer surface, which accounts for about one-third of the thickness of the lining, is the so-called vitreous surface layer. b. Second, accounting for about one-third of the thickness of the lining, is the so-called hard sintered layer. c. The remaining third, near the induction coil, is a powdery non-sintered layer. Of course, different insulation and insulation designs will more or less change the thickness distribution of the three layers; The thickness of the general lining at the end of service is about 40% of the thickness of the original lining.

A. The lining surface is smooth and glassy, but there is uneven corrosion:

Excessive sintering agent, resulting in rapid melting corrosion of furnace lining; High mobility; Low viscosity slag; Resulting in rapid corrosion of lining; Or more alkaline slag, and acid (silica) lining reaction, resulting in rapid corrosion of the lining. The improvement and prevention measures are as follows:

1. First, use the same product again to observe and confirm the occurrence of the same phenomenon; Subsequently, the product containing a lower amount of sintering agent was tested twice to observe and confirm the improvement effect; Or try the product containing a lower amount of sintering agent twice to observe and confirm the improvement effect.

2. Slag has a direct and huge influence on the corrosion of refractory lining; If the user is not careful, stable and careful to manage and control the content and composition of slag, it will be difficult to understand and improve the corrosion of furnace lining.

3. If it is confirmed that the slag is alkaline, the lining material of alkaline (magnesium oxide) or neutral (high alumina) should be selected.

B. Uneven corrosion, and at the end of use, the surface is loose, like no sintered layer phenomenon:

It may be due to the lack of sintering work, or the insufficient sintering agent of the dry punching material itself, resulting in the result. The improvement and prevention measures are as follows:

1. Conduct sintering operation according to sintering operation standards; Or slightly lengthen the sintering time

2. Select the dry beating material with higher sintering agent content for test, observe and confirm the improvement effect.

C. Abnormal serious melt loss at the bottom:

May be due to poor construction technology, especially in the middle; Large centerless furnace bottom ramming is not solid; Or due to the impact and impact during the feeding, the result is caused by the improvement and prevention countermeasures are:

1.. The best selection of construction vibration tools recommended by the original company (high vibration frequency) can reduce the lack of construction technology, shorten the construction time, improve the density of the furnace lining, and improve the durability of the furnace bottom. Or on the normal thickness of the bottom of the furnace, add a layer of 50~100mm thick lining as a buffer to resist the charging impact of the huge iron block.

2. If the construction process of manual ramming is working, try to let the construction personnel enter the furnace, or stand on the top of the furnace for ramming, be sure to solid the bottom of the furnace.

3. Try to avoid feeding large iron blocks and iron blocks with sharp angles (should be cut in advance) to avoid direct damage to the furnace bottom.

4. If the above measures can not effectively solve the problem, it is most likely that the position of the induction coil is too low, or the adiabatic insulation at the bottom of the furnace is excessive, causing the bottom of the furnace to overheat and accelerate the corrosion rate. Improvements should be discussed with the furnace equipment company.

D. Abnormal and severe melting of the bottom and lower cone (melting of the image foot shape):

Like foot or pear shape corrosion phenomenon, the main reaction mechanism is the chemical reaction of carbon to reduce silica lining, which can be expressed by the chemical reaction equation SiO2+2C→Si+2CO. The main reason for this phenomenon is that the hot metal remaining in the centerless furnace is caused by the chemical reaction after a long time and too high temperature. The improvement and prevention measures are as follows:

1. Strictly control the liquid level of hot metal. Regardless of the high or low level of the residual molten iron, the rate of molten iron melting per unit hour is generally the same; If the liquid level height of more than 66% of the original volume can be maintained regularly, it can not only save the electric energy consumption of the iron, but also effectively prevent the corrosion phenomenon like foot or pear shape. As for the production of large castings, try to arrange the furnace before the weekly break, and clear the hot metal.

2. If there is no large casting or ladle to carry hot metal before the furnace is shut down during the week, the hot metal can be poured out to make small iron blocks and left for later use. It must be noted that the low liquid level of hot metal is easy to cause overheating, resulting in chemical corrosion reaction.

3. In daily operation, if the liquid level of residual hot metal is low, small iron blocks should be slowly added, which will quickly sink and melt, and the liquid level of hot metal can be raised. Do not add large iron block, it is less easy to melt, when it sinks into the bottom of the furnace, but will increase the bottom temperature too fast, resulting in overheating phenomenon.

E. Abnormally severe melting of the lower cone:

Due to the structure of the inclined Angle, the lower cone slope is not easy to be compacting in the construction technology of manual vertical ramming. Therefore, in the production operation, it is easier to be damaged. The improvement and prevention measures are as follows:

1. Start from the design structure, do not use the design with the lower cone as far as possible; Straight tube type with slightly inclined lining is less of a problem. The internal mold crucible and vibration construction tools recommended by our standard are adopted. The best solution.

2. Or as much as possible to slow down its bevel slope (about 20°), that is, to lengthen its oblique line; This method, although in the initial operation will reduce the iron volume, but it is a solution.

3. If the existing design cannot be changed, only with the help of manpower, a small amount of feeding, slowly solid the lower cone

F. Abnormal serious melting loss of furnace wall:

If the iron block containing high rust and other iron oxide components is used under the operating conditions, the iron monoxide (F e O) is easy to react with the silica (SiO2) lining to produce a low melting point (1205℃) F a y a l i t e (2FeO˙SiO2) mineral phase, resulting in rapid corrosion reaction of silica (SiO2) lining. It is best to avoid as far as possible the use of iron blocks containing high rust components and other iron oxide components, but if it is unavoidable, its improvement and prevention measures are:

1. Keep the liquid level of molten iron as high as possible to avoid high output power of molten iron and prevent excessively high operating temperature.

2. Melt iron blocks containing high rust and other iron oxide components as soon as possible, stirring if necessary; Do not set the operating temperature to maximum.

3. Remove the slag as soon as possible and often, so that the rust can be quickly melted into the hot metal

4.. Good use of slow and fixed feeding speed; If the one-time feeding method is used, add an iron block in the back. Maintain bath temperature and operating conditions below 1400℃.

5. Add metallurgical grade silicon carbide (SiC), which has the effect of carburizing and silicon-increasing, and is also a very effective solution. When adding rust material, add an appropriate amount of silicon carbide, and maintain the operating conditions below 1400℃; In 12 to 15 minutes, silicon carbide will decompose into carbon and silicon, and the rust of the iron oxide reduction to iron, to prevent the formation of low melting point (1205℃) of the F a i I e (2FeO˙SiO2) mineral phase, and then ** lining is not melted corrosion. In many real furnace experience, it is shown that the lining life of the furnace can be significantly improved under the operating conditions of adding silicon carbide. It can be explained by the following reaction equation: Below 1400 ° C, the formation of a y i I e should be avoided :SiO2+2FeO→2FeO˙SiO2 above 1400 ° C, the first silicon carbide decomposition into carbon and silicon :Si I C →Si i+ C, carbon and silicon will reduce iron monoxide :Si+2FeO→SiO2+2Fe C +Fe O→F e +C O

Some of the silicon will rob the oxygen in the hot metal, forming silicon dioxide: Si+O2→SiO2(to prevent the corrosion of silicon dioxide in the refractory lining) and some of the carbon will reduce the silicon dioxide, provide new silicon, and then reduce the iron monoxide:

G. Abnormal serious melting damage on the upper part of the furnace wall:

The abnormal serious melting loss in the upper part of the furnace wall can be divided into slag line part and the part above the induction coil. The melting loss of slag line is mainly caused by the erosion reaction of slag. The damage of the part above the induction coil is mainly due to the low temperature, it is not easy to form a sintered layer, the mechanical strength is insufficient, and it is unable to resist mechanical damage. The improvement and prevention measures are as follows:

1. In the process of melting operation, try to close; Adjust the height and position of the iron surface to enlarge the slag line; The distance of the lower part is used to disperse the corrosion part and achieve the effect of average melting loss.

2. Or in the slag line part, choose the most perfect material to achieve the effect of average melting corrosion of the whole furnace lining.

3. In the parts above the induction coil, choose products with higher sintering agent to facilitate sintering.

4. Use small block feeding, or use funnel feeding device to avoid the impact of large block feeding.

5. Make regular repairs.

4. Discussion on different color or decolorization of furnace lining

A. The overall lining is light pink:

It is a pale pink color due to the trace elements contained in natural raw materials. There is no improper and harmful, will not have any adverse effects, do not worry.

B. The overall lining is light gray:

The same reasons as above; Or it may be due to the addition of too much rust, resulting in Fayalite(2FeO˙SiO2) mineral phase, if there is a faster corrosion rate at this time, the following improvement measures should be taken:

Use clean iron that does not contain rust. Or according to the degree of corrosion, an appropriate amount of silicon carbide (Si C) and ferrosilicon (F e Si i) are added to reduce iron monoxide and slow down the corrosion of the furnace lining.

C. Some lining thickness is dark black or metallic:

It may be due to the infiltration of hot metal, its prevention and improvement measures.

D. After dismantling the furnace, a lot of black spots can be seen in the overall furnace lining

This is due to the oxidation and reduction reaction of hot metal, carbon monoxide (CO) gas produced, infiltrated and deposited in the gas hole of refractory furnace lining, resulting in carbon accumulation phenomenon; If the carbon accumulation phenomenon is too serious, it will lead to conductive furnace lining and produce arc. Its prevention and improvement measures are:

1. Try to avoid too high temperature (overheating) and too long heat preservation operation when pumping out hot metal; Otherwise, the carbon in the molten iron will begin to react with the lining to produce carbon monoxide (CO) gas. (See the introduction of the third ˙F in this article)

2. Correct construction of furnace construction technology, reduce the porosity of refractory lining, reduce the construction of non-dense lining parts.

3. Strictly control the carbon content of the additive.

5. Occurrence and prevention of abnormal wear of furnace lining

A. Band groove wear phenomenon, especially at the vertical or horizontal joints of the inner mold, and the lower cone:

When the iron mold crucible is used for preheating and sintering, high hot spots are easily generated due to the thickness of the joint welding points, which causes the furnace lining along the welding points to suffer from excessive temperature. The inner mold of the lower cone is difficult to make, resulting in uneven or uneven phenomenon; Its prevention and improvement measures are:

1. Smooth the welding points of the iron mold crucible.

2. Trim the iron mold crucible at the lower cone.

The possible reason is that the local water is concentrated here and cannot be effectively eliminated in the baking process; Or in the furnace, there is a foreign body (slag or unclean matter) involved, not removed. Its prevention and improvement measures are:

1. Pay attention to the setting of the exhaust hole of the iron mold crucible and check the design of the insulation layer.

In addition, if there is a renewal of the coil cement or safety backing, whether it has been baked in advance.

2. Pay attention to the removal of foreign matter (slag or unclean matter) in the furnace process.

C. Irregular wear at the same level:

It is more common in the position of the bottom and the lower cone of the large centerless furnace, there is more than 90° irregular mechanical wear phenomenon. Possible causes are: in the furnace, foreign matter or unclean matter and dust fall to the furnace lining; Or the cone under the crucible of the iron mold is not placed properly, resulting in uneven thickness of the furnace lining, and hot spots are generated during sintering and operation. The prevention and improvement measures are as follows:

1. Before the iron mold crucible is placed, compressed air should be used to clean it and cover it to prevent foreign bodies or unclean things and dust from falling; Pay attention to the removal of foreign matter (slag or impurity) during the furnace process.

2. Even if the iron mold crucible can be correctly placed when placed, it should still be tried to confirm whether the spacing between the lower cone and the starting block is symmetrical and uniform.

    3. Properly fix the iron mold crucible, so that the iron mold crucible will not move during the furnace

    D. The overall lining shows irregular wear:

    This phenomenon can be summarized as the particle size segregation phenomenon, the product itself after handling; Or incorrect feeding methods; And incorrect construction technology; The phenomenon of moisture stripping during baking, the product itself contains high residual moisture, or the material can not be used in real time after opening the package, or the furnace lining can not be baked after the construction ramming, and the moisture in the atmosphere is absorbed by the furnace lining; In the furnace; Foreign matter or impurity and dust fall into the furnace lining. Its prevention and improvement measures are:

    1. At present, the special packaging form of the dry punching material of the product itself can effectively prevent the particle segregation caused by transportation and complete moisture resistance; And the residual water of the product is generally controlled below 0.3%, which can be used with confidence.

    2. According to the product instructions, the dry punching material must be stored indoors, to prevent direct sunlight, moisture and constant temperature conditions; And to prevent other dust pollution (add a layer of plastic film cover).

    3. Once the material is opened, it should be used immediately to prevent the absorption of water in the atmosphere, especially in the humid and high temperature summer.

    4. Before using dry beating materials, use compressed air to clean the working area; Centerless furnace construction mold and tools; As well as dry packaging, remove dust and foreign matter.

    5. For the correct feeding and proper construction tools and the exact furnace process, please refer to this article (1).

    6. After finishing the bottom or wall of the furnace, before it is not immediately baked, plastic film should be laid to prevent the absorption of atmospheric water.

    6. Occurrence of metal penetration and penetration phenomena and prevention countermeasures

    A. Shark fin-like infiltration/penetration phenomenon:

    The main reason of this phenomenon is that molten iron penetrates into the fissure of the furnace lining. The main reason for the fissure of the lining is too fast temperature rise. The prevention and improvement measures for cracks caused by improper cooling and water vapor are:

    1. Please refer to the prevention measures of cracking in (a) of this article.

    2. Under long-term use, the cooling cracking of the furnace lining is unavoidable; In the silica lining, the temperature is raised again about 700℃, if given enough time, due to its swelling characteristics, the cracking will gradually close. Therefore, the hot metal must be cleared before cooling; When heating up again, it should be slow, and after the cracking will gradually close, it can be sintered and operated normally.

    B. Metal penetration or a dark layer at a certain depth of the lining:

    This phenomenon is commonly seen in the same furnace lining, melting different components of steel or hot metal; Due to the demand for different operating temperatures, and steel or hot metal also has different degrees of viscosity and permeability; At higher operating temperatures, steel or hot metal quickly penetrates into refractory lining, and its prevention and improvement measures are as follows:

    1. Try to avoid how to operate.

    2. If it is necessary, the production of high-temperature varieties can be concentrated first, and then the production of lower-temperature varieties can reduce the occurrence of this phenomenon. Avoid, high; Low temperature operation.

    C. There is impure foreign body intrusion in the local position of the furnace lining:

    The main cause of this phenomenon is that the foreign matter is not taken out and driven into the lining of the furnace by carelessness in the furnace; Or local areas are not solid, and caused by hot metal intrusion, its prevention and improvement measures are:

    1. To carry out clean-up work in accordance with the regulations; When the furnace, if found foreign bodies, should be removed. Clothing of construction personnel. Good not to have pockets, so as not to have cigarettes in the pockets; A lighter; Loose change; Pen or other debris dropped in the dry punching material.

    2. In addition, if there is another centerless furnace is working next to it, the isolation net should be set up in the middle to prevent sparks and other foreign objects from spraying out.

    3. For the correct feeding method, appropriate construction tools and the exact furnace process, please refer to this article (1).

    Vii. The occurrence and prevention of slag accumulation or hanging phenomenon

    Confirm the cause of hanging slag, and take samples for chemical analysis, microstructure and mineral phase analysis if necessary. It is easier to prevent slag accumulation than to remove hanging slag. However, if the use of flux, it may damage the refractory lining, speed up the corrosion reaction of the lining. If it is not easy to remove slag at the low liquid level of molten iron, the molten iron can be cleared and used in the ladle for slag removal.

    A. Formation and deposition of low-melting slag:

    Mainly due to the low operating temperature, low melting point slag (Si+O2→SiO2) viscosity increase and accumulation phenomenon, its prevention and improvement measures are:

    1. Occasionally increase the melting temperature to melt the accumulated slag.

    2. Occasionally raise the liquid level of hot metal to melt the accumulated slag.

    3. Cover, reduce the loss of surface temperature, melt the accumulated slag.

    4. Often adjust the liquid level of hot metal up and down to prevent corrosion of slag line in a single part

    B. Formation and deposition of high melting point slag:

    The slag deposition reaction of silica composition is generated by the reaction of silicon and ferric oxide at about 1400℃, and the chemical reaction equation is :2FeO+Si→2Fe+SiO2. It is characterized that high content of SiO2 and FeO can be found in the sampling analysis of slag.

    The recovered castings are not cleaned in advance, and the casting sand included in them produces the accumulation of stone (3Al2O3) or needle-like alumina (Al2O3) mineral slag with high melting point. Its characteristics are that high content of mollite and alumina can be found in the analysis of slag sampling. Or in the alkaline process, the acidic (SiO2) lining material is mistakenly selected, and the prevention and improvement measures are:

    1. The recycled castings must be cleaned in advance, and the casting sand must be removed.

    2. Use clean iron blocks to avoid using high amounts of rust; Sediment; And iron blocks containing high alumina minerals.

    3. Keep the operating temperature of the furnace bath slightly higher than 1400℃, not too high, in order to prevent the formation of highly corrosive slag. (2FeO+ SiO2→2FeO˙SiO2)

    4. Add silicon carbide (SiC), see this article (3 ˙F). In addition, the chemical reaction of silicon carbide and iron monoxide will produce exothermic phenomenon, providing part of the effective and perfect heat source, contributing to the benefit of local heat extraction, the reaction equation is:

SiC+3FeO→3Fe+SiO2+CO+4430 kcal / kg

    5. Try to avoid the selection of iron silicon containing aluminum metal components, use metallurgical grade silicon carbide.

    6. In alkaline working environment, neutral (3Al2O3) or alkaline (M g O) working lining should be selected; Although the unit price is higher, but the right medicine, and there will be lower operating costs.

    7. In an alkaline working environment, if an acidic (SiO2) working lining is selected, it must endure a shorter service life. If there is slag accumulation, some broken glass can be added to reduce the melting point of the slag.

    The generation and prevention of the phenomenon of electrical phase unbalance or excessive current

    At the end of the use of refractory lining, when more than 50% of the lining thickness is corroded, the occurrence of electrical phase imbalance or excessive current phenomenon is normal; Otherwise, it is an anomaly and should be discussed.

    A. Appears in the initial sintering process: if the safety backing or coil cement is not properly baked, or the water gas of the dry-beating furnace lining is not effectively removed, resulting in the phenomenon of water gas conduction, its prevention and improvement measures are as follows:

    1. Bake the safety backing or coil cement properly in advance.

    2. At the temperature of 95℃, heat preservation for a long time; Calculated in units of furnace lining thickness per centimeter, less than each centimeter needs to be maintained for more than 15 minutes; Slowly heat up to 700 ° C and keep warm again.

    B. After the furnace is shut down for air cooling, when it is cooled again:

    Due to shrinkage cracking, it is caused by infiltration of hot metal, and its prevention and improvement measures are as follows:

    1. Try to take the best, uninterrupted continuous production operation.

    2. To stop production, air cooling should also be avoided, refer to the instructions in this article (A)

    3. If it is necessary to air cool down, rapid cooling should also be avoided, and fan blowing should be avoided. When it is heated again, the temperature is slowly raised to 700℃, and the heat is held again for a long time, and then the heating operation is carried out after the crack is closed.

     C. After the power interruption, when again ** * :

    Because there is no cooling effect, hot metal penetrates into resistant wood lining; Or when the cooling water interference and insufficient flow, its prevention and improvement measures are:

    1. Set up backup cooling device,** in the case of power jump, can be immediately switched to use.

    2. Minimize the time for stopping power supply.

    D. appears in the process of restarting the furnace after repairing the furnace lining:

    It may be because the metal attached to the lining surface is not removed first, causing the metal to exist between the old and new lining; When the power is transmitted again, there are local overheating and even cracking phenomena, and its prevention and improvement measures are:

    1. To clean the hot metal, there is no residue in the furnace and residual hot metal deposited on the lining surface, and then hot repair.

    2. If the cold room repair is carried out, it is necessary to check the furnace lining surface and cracks in detail, and there is no residue and residual hot metal accumulation; If it is found, it must be removed and then repaired.

    Ix. Judgment and disposal of abnormal phenomena of dry vibration ramming materials

    A. Particle segregation and particle size anomalies:

    At present, the special packaging form of the dry beating materials of the products of various companies can effectively prevent the particle size segregation caused by transportation, and basically there should be no such problem; It is possible that the sampling method is not correct, resulting in abnormal results. Recommended disposal procedure:

    1. According to different industrial standards, correctly collect samples and record product names in detail; Production lot number; Appearance condition; Sampling position and sampling method; And divided by the method of four; Half of the field tests; The other half are outsourced for verification.

    2. Detailed tracking of material usage and service life or other anomalies.

    B. Disposal when silica content is too low:

    If lower grade raw materials are used, of course, the product will have a lower silica content. Recommended type:

    The low content of silica will directly affect its physical and chemical properties, and the service life may be low; When in use, it is necessary to carefully observe the corrosion condition. If you do not have confidence, you can use it above the induction coil, which is not in direct contact with hot metal and molten slag, and will not affect the service life of the overall lining.

    C. Disposal of impure materials when found:

    It may be contaminated during the production process, or contaminated during handling and storage, or contaminated by careless handling when opening the bag and hitting the furnace. Its prevention and improvement measures are:

    To carry according to; To store; Opening and furnace instructions to prevent external contamination; If a foreign body is found in the furnace, it should be removed immediately. If it is determined that the foreign matter is found to be from the product when the package is opened, the production batch number should be recorded in detail and the original packaging sample should be retained, contact the supplier for disposal, and carefully observe whether the same situation occurs in other packages.

    10. The occurrence and prevention countermeasures of the instability of service life

    Unstable service life or a sudden decrease in service life, the possible causes of which are extremely difficult to explain; Records of past use and operation must be examined and compared in detail; Only then can it be possible to find out the causes, and then it is possible to find ways to improve.

    In the case that there is no problem with the material and the furnace process, more than 80% of the occurrence probability is caused by small changes in the operation; And this small change; It is often ignored by operators. It is necessary and important to keep detailed records of past operations. When you are facing and solving these problems, you should follow these steps:

    1. Stay calm so that you can clearly identify the problem and remedy or improve it

    2. Record the causes and consequences of the occurrence in detail, check and compare the past operation records in detail.

    3. On-site observation, interview and sample collection, must get... Hand messages and data; Hearsay must be verified before being recorded.

    4. Adopt the inductive evolution method of mathematical logic to find out the relevant factors and analyze them

    5. Only change the improvement method of one variable at a time, so as to find out the cause and correct measures.

    Problem and solution check reference table

    1. Is it a single emergency? Repeat each step and process carefully and accurately, observe and record the phenomenon as it occurs, in order to determine the possible cause of its occurrence.

    (2) If it is a repeatable phenomenon, whether it only occurs in the same centerless furnace, and other furnaces do not have this phenomenon, it may be due to human negligence; At this time should pay attention to the management of personnel, especially in the furnace, to pay special attention to cleaning work. If it can occur in several furnaces, it is necessary to check and compare the past operation records of these furnaces in detail, try to find common ground, and then cross-analyze and compare; For example, the maintenance and use of the water cooling system, the type and composition of iron blocks used, and the type of additives; Amount and composition of addition, etc. Sometimes, it is important to note that improvement measures have other consequences; For example: carburization will produce hot melt corrosion, increase the output voltage will produce strong stirring effect, improve the mechanical loss of furnace lining

    3. Perhaps it is the dry punch product itself, caused by the use of new raw materials; Detailed record of the production lot number of the product used in order to track the variation of the production product.

    4. Check the production lot number of the inventory, ensure the management principle of first come first serve, and confirm the performance indicator of the product; Replace with new products if necessary.

    5. Supervise and record the furnace process, the amount of materials used, the baking process, the erection of iron mold crucible, the construction tools and the furnace process, and the heating sintering operation in detail; If any difference is found, the customer must be informed.

    6. What is the heating rate and time of drying at 100 ° C with water and gas, and the insulation operation at 800 ° C, whether the instructions have been followed or what is different from the past operation, and whether there is a heating record for tracing?

    7. During the sintering operation, whether the establishment of the bath height is fast enough, whether the sintering temperature and time are sufficient, and whether there is a temperature record to trace. Other thermocouples or seg cones may be used for temperature monitoring.

    8. New furnace lining. Final service life, by. The operation of the first four days has a great impact; Personal advice, first four days. To maintain uninterrupted operation and maintain the molten metal level at a condition of 66 to 80%; At this time, the furnace lining can form a good sintering layer, if the furnace must be stopped during the process,800℃ insulation operation is necessary. On the contrary, if the above conditions cannot be achieved in the early stage, the service life of the furnace lining may be affected.

    9. Early stage. Good use of clean iron blocks, and produce a single class of products.

    10. After that, normal production operation will be resumed. In principle, clean iron should be used, which helps to extend the life of the lining.

    11. Note and document delays and delays in production operations, such as hot metal composition analysis; Adjustment of composition or alloy; Ladle too late to pour hot metal, etc.; Will extend the hot metal in the furnace holding time; And the result of overhot melt of molten iron corrosion lining

    12. Observe and record the type, quantity and composition of additives added in detail, and analyze the composition and change of slag, which is helpful to understand the corrosion damage mechanism of furnace lining.

    13. Detailed inspection and comparison of the composition of slag and the use of slag removal agents are helpful to understand the corrosion damage mechanism of furnace lining.

    14. Check and compare the damage of furnace equipment in detail; Repair or update to understand the impact on the life of the lining.

    15. Detailed audit and comparison of operation methods; The situation of shift operation and furnace shutdown, as well as the situation of electric tripping or other accidents, to understand the impact on the life of the furnace lining.

    16. For the operating environment of the furnace and the working attitude and changes of the operator, it should also be observed and recorded in detail to help understand the damage of the refractory lining.

    17. Human habit is another factor that should be taken into account, any change of the furnace or the operator will have a greater or less impact on the construction and use of refractory lining; It is helpful to understand the damage of refractory lining by observing and recording the changes of personnel and their habits in detail.

    18. Recording any results observed, tabulating and comparing them will help to understand the factors affecting the life of lining materials.

    19. Identify possible causes and list possible measures and methods for improvement; Remember to make one change at a time to validate the effect. Don't make too many changes at the same time to avoid confusion or counter-effect.