Special attention should be paid to the following 5 procedures in the construction of high-aluminum and low-cement castables for the lining of rotary kilns:

1. Determination of expansion joints

According to the previous experience in the use of high-alumina and low-cement castables, expansion joints are a key factor affecting the service life of rotary kiln castables. The expansion joints during the pouring of the rotary kiln lining are determined as follows:

(1) Annular seam: a section of 5m, the method of sandwiching 20mm aluminum silicate fiber felt between the surrounding pouring body, the fiber is compacted after expansion, and the expansion stress is buffered.

(2) Flat seam: every three pouring bodies are sandwiched with a 100mm deep five-ply board in the inner circumferential direction, and the working end is left seam, a total of six.

(3) When pouring, 25 exhaust plugs are used per square meter to release a certain expansion stress while the kiln is exhausted.

2. Determination of construction temperature

The suitable construction temperature for high-alumina and low-cement castables is 10~30℃. If the ambient temperature is low, the following measures should be taken: (1) Enclose the surrounding construction environment, increase warm-keeping facilities, and prevent freezing. (2) Hot water mixing at 35-50°C (determined according to the on-site pouring test vibration).

3. Mixing

Depending on the capacity of the mixer to determine the amount of one-time mixing. After the mixing amount is determined, add the pouring material in the packaging bag and the small packaging additives in the bag into the mixer at the same time. First start the mixer to dry-mix for 2~3min, then add the first weighed water to 4/5, stir for 2~3min, and then determine the remaining 1/5 of the water according to the viscosity of the mud. Pouring, combined with the situation of vibrating mud, determine the amount of water added. After the amount of water added is determined, it must be strictly controlled. Under the circumstance of ensuring vibratory mud boiling, water should be added as little as possible (reference water addition for this castable is 5.5%-6.2%).

4. Construction

The construction time of high-alumina and low-cement castables is about 30 minutes. The dehydrated or coagulated materials cannot be mixed with water and should be resolutely discarded. The vibrating rod is used to vibrate to achieve compaction. The vibrating rod must be backed up, so that the spare rod can be activated when the vibrating rod fails.

The construction of the castable should be carried out in strips along the axis of the rotary kiln. The construction surface should be cleaned up before each pouring. There should be no dust, welding slag and other debris. At the same time, check the welding of the anchors and whether the surface asphalt paint is treated. In place, otherwise, remedial measures should be taken.

In the split construction, the construction of the strip casting should be carried out in the lower part of the kiln body from the kiln end to the direction of the kiln head. The support of the formwork shall be carried out between the anchor nail and the steel plate. The steel plate and the anchor are firmly inlaid with wooden blocks. The support mold has a height of 220mm, a width of 620mm, a length of 4-5m, and a central angle of 22.5°.

The construction of the second pouring body should be carried out after the final solidification of the strip and the removal of the mold, and the method of supporting an arc-shaped formwork shall be adopted on one side of the kiln to be closed and poured from the kiln head to the kiln tail. The rest can be deduced by analogy.

When the castable is vibrated in construction, the mixed mud should be added into the tire mold while vibrating. The vibration time should be controlled so that there is no obvious air bubbles on the surface of the pouring body. The demoulding time should be determined by the ambient temperature of the construction site, and the demoulding should be ensured after the castable is finally set and has a certain strength.

5. Baking of the lining

The baking quality of the lining of the rotary kiln directly affects the service life of the lining. In the previous baking process, due to lack of mature experience and good methods, in the low temperature, medium temperature and high temperature baking process, the method of injecting heavy oil was used to burn, and the temperature is difficult to control: when the temperature needs to be controlled at 150 When the temperature is below ℃, heavy oil is not easy to burn; when the temperature is higher than 150℃, the heating rate is too fast, and the temperature distribution in the kiln is very uneven, the temperature of the lining at the burning place of heavy oil is about 350~500℃, and the temperature of other parts But it's on the low side. In this way, the lining is easy to burst (previous castable linings have burst during the baking process), which affects the service life of the lining.

How to bake low cement castable for rotary kiln

The rotary kiln uses shaped refractory bricks as the lining material. Because the refractory bricks are high-temperature sintered products and do not contain moisture, the purpose of the kiln is to roast the joint materials of the refractory bricks to achieve a tight bond between the bricks. Kiln time is short. When the unshaped refractory castable is used as the lining, it is made by mixing bulk materials with water. Because the castable is not fully pre-fired, the structure is unstable at low temperature, the water content is relatively large, and the kiln speed is too fast. The lining cracks due to the rapid discharge of water, so the kiln should be properly extended according to the situation when it is not in use.

Determine the heating rate according to different lining materials

In the lining made of unshaped refractory material, during the low temperature stage of the heating process, the castable mainly undergoes a series of dehydration changes. Due to the very close matching of low cement series castables, coupled with the filling effect of ultra-fine powder (with a particle size of less than 5 microns) on the gaps of the castables, the inner lining has high density, low porosity and poor air permeability. The moisture in the lining material is mainly discharged in the form of gas. If the temperature rises too fast, the vaporization rate of water will increase, and the gas discharge will increase. When the water turns into water vapor, the volume will increase, and the volume of water vapor will increase as the temperature rises. Once the pressure generated by gas expansion exceeds the liner The limit that can withstand causes cracks, peeling or peeling of the lining body. Therefore, the heating rate of low cement series castables should be lower than other types of castables, especially when the temperature of the lining is below 600℃, a longer heating time should be maintained in order to fully discharge the water.

In addition, since active SiO2 is added to low cement series castables, when the temperature of the lining is higher than 900°C, mullite reaction will occur between the aluminum oxide and silicon dioxide in the lining material to form mullite Produce volume effect, offset part of the volume shrinkage of refractory castable, and promote the improvement of lining strength. The mullite chemical process is a key process that affects the high-temperature performance of cement series castables. Therefore, at the end of the kiln, the heating rate should be controlled at a low temperature and the holding time should be relatively long, so that the mullite chemical reaction can proceed fully.

Determine the heating time according to the specifications and shapes of the industrial furnace

When the kiln volume is small and the flue gas flow is relatively short. Since the temperature in the kiln is easy to be uniform and balanced, the heating time can be appropriately shortened. For some bulky thermal equipment such as rotary kilns, it is difficult for the temperature of each part to reach a balance within a certain time. Therefore, the heating time should be longer to reduce the temperature difference of each part of the lining and avoid The lining body shrinks unevenly and cracks occur.

Determine the drying system according to the lining construction method and lining conditions

Lining construction methods and health conditions are different, and the kiln system should also be different. The inner lining has a long curing time, vent holes, and a small thickness. The temperature rise can be faster; the curing time is short, the winter is built, the lining is dense, the thickness is high, the moisture content is high, or the furnace construction quality is not ideal. The time should be longer. After the low cement series refractory castables are lined with the furnace, the furnace should be cured for no less than 7 days at an ambient temperature of 15-25°C. The furnace built in winter should also be lined with insulation measures. During the construction of the castable, in addition to ensuring the technical conditions of the castable mixing time, vibration time, vibration intensity, etc., it should also be drilled on the lining body every 150~250mm, and the depth is about 1/3~2/ of the thickness of the lining body. 3, the diameter of the vent hole is about 4mm.

Determine the oven control temperature according to the lining temperature in the high temperature working zone

During the drying process, the temperature control parameter should be the temperature of the lining. For large kilns with temperature steps, since the lining temperature of each part cannot be raised at the same time, the surface temperature of the lining in the area in direct contact with the flame should be taken as controlled object. In this area, the lining is generally located in the high temperature working area, which is the vulnerable part of the kiln lining and also the sensitive part to flame temperature changes. The heating speed and range of the lining in this area can reflect whether the heating of the entire kiln lining is reasonable.

Special attention should be paid to the following 5 procedures in the construction of high-aluminum and low-cement castables for the lining of rotary kilns:

1. Determination of expansion joints

According to the previous experience in the use of high-alumina and low-cement castables, expansion joints are a key factor affecting the service life of rotary kiln castables. The expansion joints during the pouring of the rotary kiln lining are determined as follows:

(1) Annular seam: a section of 5m, the method of sandwiching 20mm aluminum silicate fiber felt between the surrounding pouring body, the fiber is compacted after expansion, and the expansion stress is buffered.

(2) Flat seam: every three pouring bodies are sandwiched with a 100mm deep five-ply board in the inner circumferential direction, and the working end is left seam, a total of six.

(3) When pouring, 25 exhaust plugs are used per square meter to release a certain expansion stress while the kiln is exhausted.

2. Determination of construction temperature

The suitable construction temperature for high-alumina and low-cement castables is 10~30℃. If the ambient temperature is low, the following measures should be taken: (1) Enclose the surrounding construction environment, increase warm-keeping facilities, and prevent freezing. (2) Hot water mixing at 35-50°C (determined according to the on-site pouring test vibration).

3. Mixing

Depending on the capacity of the mixer to determine the amount of one-time mixing. After the mixing amount is determined, add the pouring material in the packaging bag and the small packaging additives in the bag into the mixer at the same time. First start the mixer to dry-mix for 2~3min, then add the first weighed water to 4/5, stir for 2~3min, and then determine the remaining 1/5 of the water according to the viscosity of the mud. Pouring, combined with the situation of vibrating mud, determine the amount of water added. After the amount of water added is determined, it must be strictly controlled. Under the circumstance of ensuring vibratory mud boiling, water should be added as little as possible (reference water addition for this castable is 5.5%-6.2%).

4. Construction

The construction time of high-alumina and low-cement castables is about 30 minutes. The dehydrated or coagulated materials cannot be mixed with water and should be resolutely discarded. The vibrating rod is used to vibrate to achieve compaction. The vibrating rod must be backed up, so that the spare rod can be activated when the vibrating rod fails.

The construction of the castable should be carried out in strips along the axis of the rotary kiln. The construction surface should be cleaned up before each pouring. There should be no dust, welding slag and other debris. At the same time, check the welding of the anchors and whether the surface asphalt paint is treated. In place, otherwise, remedial measures should be taken.

In the split construction, the construction of the strip casting should be carried out in the lower part of the kiln body from the kiln end to the direction of the kiln head. The support of the formwork shall be carried out between the anchor nail and the steel plate. The steel plate and the anchor are firmly inlaid with wooden blocks. The support mold has a height of 220mm, a width of 620mm, a length of 4-5m, and a central angle of 22.5°.

The construction of the second pouring body should be carried out after the final solidification of the strip and the removal of the mold, and the method of supporting an arc-shaped formwork shall be adopted on one side of the kiln to be closed and poured from the kiln head to the kiln tail. The rest can be deduced by analogy.

When the castable is vibrated in construction, the mixed mud should be added into the tire mold while vibrating. The vibration time should be controlled so that there is no obvious air bubbles on the surface of the pouring body. The demoulding time should be determined by the ambient temperature of the construction site, and the demoulding should be ensured after the castable is finally set and has a certain strength.

5. Baking of the lining

The baking quality of the lining of the rotary kiln directly affects the service life of the lining. In the previous baking process, due to lack of mature experience and good methods, in the low temperature, medium temperature and high temperature baking process, the method of injecting heavy oil was used to burn, and the temperature is difficult to control: when the temperature needs to be controlled at 150 When the temperature is below ℃, heavy oil is not easy to burn; when the temperature is higher than 150℃, the heating rate is too fast, and the temperature distribution in the kiln is very uneven, the temperature of the lining at the burning place of heavy oil is about 350~500℃, and the temperature of other parts But it's on the low side. In this way, the lining is easy to burst (previous castable linings have burst during the baking process), which affects the service life of the lining.

How to bake low cement castable for rotary kiln

The rotary kiln uses shaped refractory bricks as the lining material. Because the refractory bricks are high-temperature sintered products and do not contain moisture, the purpose of the kiln is to roast the joint materials of the refractory bricks to achieve a tight bond between the bricks. Kiln time is short. When the unshaped refractory castable is used as the lining, it is made by mixing bulk materials with water. Because the castable is not fully pre-fired, the structure is unstable at low temperature, the water content is relatively large, and the kiln speed is too fast. The lining cracks due to the rapid discharge of water, so the kiln should be properly extended according to the situation when it is not in use.

Determine the heating rate according to different lining materials

In the lining made of unshaped refractory material, during the low temperature stage of the heating process, the castable mainly undergoes a series of dehydration changes. Due to the very close matching of low cement series castables, coupled with the filling effect of ultra-fine powder (with a particle size of less than 5 microns) on the gaps of the castables, the inner lining has high density, low porosity and poor air permeability. The moisture in the lining material is mainly discharged in the form of gas. If the temperature rises too fast, the vaporization rate of water will increase, and the gas discharge will increase. When the water turns into water vapor, the volume will increase, and the volume of water vapor will increase as the temperature rises. Once the pressure generated by gas expansion exceeds the liner The limit that can withstand causes cracks, peeling or peeling of the lining body. Therefore, the heating rate of low cement series castables should be lower than other types of castables, especially when the temperature of the lining is below 600℃, a longer heating time should be maintained in order to fully discharge the water.

In addition, since active SiO2 is added to low cement series castables, when the temperature of the lining is higher than 900°C, mullite reaction will occur between the aluminum oxide and silicon dioxide in the lining material to form mullite Produce volume effect, offset part of the volume shrinkage of refractory castable, and promote the improvement of lining strength. The mullite chemical process is a key process that affects the high-temperature performance of cement series castables. Therefore, at the end of the kiln, the heating rate should be controlled at a low temperature and the holding time should be relatively long, so that the mullite chemical reaction can proceed fully.

Determine the heating time according to the specifications and shapes of the industrial furnace

When the kiln volume is small and the flue gas flow is relatively short. Since the temperature in the kiln is easy to be uniform and balanced, the heating time can be appropriately shortened. For some bulky thermal equipment such as rotary kilns, it is difficult for the temperature of each part to reach a balance within a certain time. Therefore, the heating time should be longer to reduce the temperature difference of each part of the lining and avoid The lining body shrinks unevenly and cracks occur.

Determine the drying system according to the lining construction method and lining conditions

Lining construction methods and health conditions are different, and the kiln system should also be different. The inner lining has a long curing time, vent holes, and a small thickness. The temperature rise can be faster; the curing time is short, the winter is built, the lining is dense, the thickness is high, the moisture content is high, or the furnace construction quality is not ideal. The time should be longer. After the low cement series refractory castables are lined with the furnace, the furnace should be cured for no less than 7 days at an ambient temperature of 15-25°C. The furnace built in winter should also be lined with insulation measures. During the construction of the castable, in addition to ensuring the technical conditions of the castable mixing time, vibration time, vibration intensity, etc., it should also be drilled on the lining body every 150~250mm, and the depth is about 1/3~2/ of the thickness of the lining body. 3, the diameter of the vent hole is about 4mm.

Determine the oven control temperature according to the lining temperature in the high temperature working zone

During the drying process, the temperature control parameter should be the temperature of the lining. For large kilns with temperature steps, since the lining temperature of each part cannot be raised at the same time, the surface temperature of the lining in the area in direct contact with the flame should be taken as controlled object. In this area, the lining is generally located in the high temperature working area, which is the vulnerable part of the kiln lining and also the sensitive part to flame temperature changes. The heating rate of the lining in this area,

The heating range can reflect whether the heating of the entire kiln lining is reasonable.