Home Refractory Knowledge Castable Heating Curve

Castable Heating Curve

Heating Curve is a key link in the construction and use of unshaped refractory materials. However, in actual production, OSYMEN found that some constructors tend to ignore the details of the heating, which leads to the decrease of the service life of the kiln. Therefore, today, on this topic, I will bring you the operation method of the heating after the construction of various types of thermal equipment castables.
Its function is mainly to remove free water and chemically bound water in the lining body and obtain high temperature performance.

Proper Heating Curve can improve the life of the kiln and thermal equipment. Otherwise, if the water is not removed smoothly, the lining will crack, reduce the strength, and even cause the lining to peel off or explode. Dense, high-strength castables such as low-cement series refractory castables are prone to such phenomena because it is difficult to remove moisture.

Weight loss rate of refractory castables with different binders
The figure below shows the weight loss rate of refractory castables with different binders. It can be seen from the figure that the weight loss rate after drying at 110℃ is 55%-80%, and in the temperature range of 200-300℃, the cumulative weight loss rate generally reaches 70-90%. This shows that there is more dehydration in the low temperature stage, mainly free water, and some bound water; as the temperature continues to rise, bound water and crystal water are continuously excluded. When it reaches 500 °C, the water content of the castable is only about 10%. At the same time, it can be seen that the weight loss rate at each temperature is slightly different for different types of refractory castables. Therefore, the formulation of the heating curve is also different.

heating system

The heating system of monolithic refractories is related to factors such as material varieties and properties, construction methods, lining thickness and use conditions. Therefore, when formulating the heating curve of the lining, all aspects should be fully considered. The general principle is before 600℃, should be slowly heating up and keep warm, so that the moisture in the lining can be fully discharged.

Heating system for monolithic refractories lining
The following table shows the heating system of monolithic refractories lining. After keep warm at 600℃, can also be keep temperature at 800℃ 8-16h, the heating rate is generally 20-35℃/h; In general, the specific lining heating curve can be formulated with reference to the system. The heating time of dense castables such as low-cement series refractory castables should be 24-48h longer than the given time in the table.

Temperature Control, oC

0-150

150

150-350

350

350-600

600

Lining Thickness <200 mm

Heating, oC/ hours

15

 

15

 

15

 

Time

10

24

13

30

17

16

Cumulative Time (hours)

10

34

47

77

94

110

Lining Thickness 200-400 mm

Heating, oC/ hours

15

 

10

 

10

 

Time

10

32

20

32

25

24

Cumulative Time (hours)

10

42

62

94

119

143

Lining Thickness >400 mm

Heating, oC/ hours

15

 

10

 

10

 

Time

10

40

20

40

25

24

Cumulative Time (hours)

10

50

70

110

135

159

 

Heating system for Plastic refractories
The following figure shows the heating curve of the plastic lining of the heating furnace. Although the lining is built with exhaust holes, the material is like plasticine, and the water is difficult to be discharged, so the heating time of the lining is longer. Some heating for 15-30 days. Generally, heating for about 12 days. Individual cases, there are heating 8 days.

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Heating system for Clay castable lining
The following figure is the heating curve of the clay castable lining of the heating furnace. There are many kinds of clay bonded refractory castables and they are widely used. The water add is 6%-10%, and the water easy to discharged when heating at low temperature, leaving the exhaust channel, so the heating time of the lining is shorter, generally about 7days. If the lining construction is completed, the natural curing or interval time is longer, the heating time can be shortened, generally 5-6D.

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Heating system for dense castable lining
Dense, high-strength, low-cement series and clay-bonded refractory castables have been widely used. During the lining baking process, if the operation is slightly careless, large pieces of the lining will peel off, and even explosion accidents will occur. Therefore, it is possible to mix explosion-proof agents, appropriately extend the baking time at 300-600°C, and need careful operation, which can basically prevent accidents. The figure below is the bake curve of the dense castable liner. In kilns and thermal equipment such as heating furnaces, soaking furnaces and power frequency induction furnaces, the linings are constructed on site with low-cement series refractory castables, and baked with this curve, generally no problems occur. Therefore, for the baking of dense or high-strength refractory castable linings, this curve can be referred to.

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It should be noted that in the dense castable, adding polypropylene fiber, metal aluminum powder and other quick-drying explosion-proof agents, the heating time can also be shortened, generally about 6d. If time permits, heating time should be guaranteed to be greater than 8d, which is conducive to the improvement of furnace life.

Heating system for main groove of blast furnace
The following figure shows the baking curve of the lining of the main channel of blast furnace iron extraction. The lining is made of ultra-low cement refractory castable of rigid jade and mixed with aluminum powder explosion-proof agent, so that it can be baked quickly without peeling and explosion. Under the condition of production, due to the non-working lining has a certain temperature, so the iron can be baked 40h; The lining body of blast furnace iron outlet ditch and slag iron line are easy to be damaged, repaired with the same material, and generally baked for 20h, can be used through iron. This kind of material is also called fast drying refractory castable.

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Baking curve of refractory castable for high – tech ladle
The figure below is the baking curve of refractory castable for high-tech ladle. The lining thickness of ladle is 170mm at the upper part and 210mm at the lower part. The castable contains quick-drying explosion-proof agent. Gas baking is adopted, air-fuel ratio is strictly controlled, and the temperature difference between upper and lower ladle is within 30℃.

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Last updated: 2024-01-03
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