Refractory plastic is a kind of unshaped refractory with high plasticity for a long time, and it is in the form of hard mud paste. It consists of a certain grade of refractory aggregate, fine powder, appropriate amount of binder, plasticizer, and preservation Agent and water.
In the past ten years, my country's large and medium-sized steel companies have adopted refractory plastics as a whole or part of the working lining of the furnace roof and furnace wall of the steel rolling heating furnace, which has increased the service life of the heating furnace and achieved good economic benefits.
The fire-resistant plastic developed at the beginning is widely used in the lining of boiler and other thermal equipment. The operating temperature is generally below 1200℃, and phosphoric acid or phosphate thermo-rigid binder is mainly used. By the middle of 1970s, China developed refractory plastics for metallurgical industrial furnaces, and the service life of steel and stepping heating furnaces is more than 7 years, which is higher than ordinary castable, thus effectively promoting the development of refractory plastics.
To the 1980s, the clay bond and low cement series of refractory castable rapid development, its performance is better than refractory plastic, and has a higher room temperature strength, vibration molding, construction is convenient, so it has constantly replaced refractory plastic. But in the 1990 s, refractory plastic varieties, quality, construction equipment and production technology by leaps and bounds of progress has been made in various aspects, widely used in iron and steel, non-ferrous metallurgy, petrochemical and other industries of industrial kiln, as the service life of the heating furnace of steel rolling working lining is 30 times with material cement castable, service life up to 15 years, and has obtained the good use effect and considerable economic benefits. Due to the numerous advantages of refractory plastics, and with the increasing requirements of the life of refractory materials in industrial kilns, as well as the gradual deepening of the recognition degree of the design unit of industrial kilns, the application scope and amount of refractory plastics will be further improved.
Classification of Refractory Plastic
Refractory plastic has a variety of different classification: according to the material of the aggregate can be divided into clay, high aluminum, Mullite - rigid jade, rigid jade, containing chromium, aluminum - silicon carbide, zirconium refractory plastic; According to the normal temperature hardening property can be divided into thermal rigid, gas rigid refractory can be plastic, now the market appeared in the heat rigid, gas rigid binder composite use of refractory can be plastic, for the time being called thermal rigid, gas rigid composite binder refractory can be plastic; According to the type of chemical binder can be divided into phosphoric acid, phosphate, aluminum sulfate, sodium silicate, resin bonded refractory plastic; According to the construction method can also be divided into ramming, spraying type refractory plastic and other different categories.
Refractory Progress of Refractory Plastics
China in the initial stage of the use of refractory plastic, generally for thermal rigid refractory plastic, the binder mainly used liquid phosphate or aluminum phosphate, this type of refractory plastic has a higher room temperature, high temperature strength, but the storage period is short. The price is also on the high side.
Due to the high cost of refractory refractory plastics and short storage period, refractory research personnel in the late 1970s, the development of aluminum sulfate as a binder of gas refractory refractory plastics. Due to the good performance of gas rigid refractory plastic, the cost is relatively low, in the 1990s was widely promoted.
Thermal and rigid refractory plastics have their own advantages and disadvantages, but their advantages and disadvantages can be made up for each other. In the late 1990s, gas-hard and thermal refractory composite binder with mature technology was developed successfully. After practical application, good results have been obtained.
Thermal Rigid Refractory plastic
Refractory refractory plastics mainly use 85% phosphoric acid or aluminum phosphate as binder. Before use, they are diluted with water into a solution with a density of 1.2~1.3g/cm3. Because the solution is easy to react with the iron in the fine powder, the hardening speed of the plastic can be accelerated, the plasticity is reduced, and after ramming the lining is easy to swell, therefore, a certain amount of inhibitors, preservatives and other admixtures must be added. Admixtures mainly include oxalic acid, tartaric acid, molasses, citric acid, NH-66, lignin sulfonate, etc., among which oxalic acid and tartaric acid have good effects. When the dosage is appropriate, the storage life of refractory plastic can be up to 3~6 months.
During production, 60% of the total binder solution was mixed with refractory aggregate and fine powder, and then the binder was trapped for 24h. The remaining binder and admixture were added in the second mixing, and the mixture was evenly mixed and then entered into the next production process.
Thermal-rigid refractory plastic has the advantages of higher normal temperature and high temperature strength, medium temperature strength does not decline, good thermal shock resistance, strong spalling resistance, especially for the use of high strength requirements are particularly suitable. Such as the circulation vulcanization bed boiler with high - strength wear - resistant plastic, generally using aluminum phosphate as a binder of hot - rigid refractory plastic. The following are the physical and chemical performance indexes of high aluminum wear resistant plastic for the circulating vulcanized bed boiler (upper part of furnace and cyclone separator) :
Sample chemical composition (%) : A12O3 61.13, SiO2 26.25, Fe2O3 3.43, P2O5 1.87, Na2O 2.09, K2O 0.31, TiO2 1.76; The apparent porosity is 12.68%, the volume density is 2.63g/cm3, the thermal conductivity is 1.35w /(m·K) on the hot surface at 900℃, the fire resistance is >1750℃, the starting point of the weight-softening temperature is 1612℃, and the 4% is 1655℃.
Due to the high price of phosphoric acid and aluminum phosphate, the cost of refractory plastic materials is also high. Although the storage life of the heat-resistant refractory plastics has been improved by adding the additives, the storage life of 3 ~ 6 months cannot fully meet the storage requirements. If the plastic can be exported to foreign countries, because the transport time is long, its preservative is not easy to meet the requirements. Hot and hard refractory plastic storage environment requirements are strict, need to be stored in a cool, humid warehouse, especially in summer when the temperature is high, hardening speed will be accelerated to shorten the storage period. The phosphoric acid and aluminum phosphate are relatively strong, and they are easy to react with the iron in the fine powder and produce the swelling phenomenon. Therefore, the materials need to be trapped, and the production process is relatively complex.
Physical Properties of Wear Resistant Plastic Samples
| The Process Temperature ℃ |
The line Rate % |
Compressive Strength MPa |
Flexural Strength MPa |
| 110 |
-0.16 |
41.0 |
14.2 |
| 815 |
-0.18 |
52.9 |
18.6 |
| 1100 |
-0.15 |
84.8 |
25.0 |
| 1500 |
-0.21 |
93.6 |
26.7 |
Pneumatic Refractory Plastic
To the end of the 1970s, developed a gas rigid refractory plastic, and its technology is constantly improving. In the 1990s, the gas rigid refractory plastic technology after continuous improvement has been very mature, its good performance, low price, has been widely promoted. Large and medium-sized steel mills, such as Baosteel and Wuhan Iron and Steel Co., LTD., adopt gas rigid refractory plastic on the newly built heating furnace item and furnace wall T as lining, which improves the service life of the heating furnace and obtains good economic benefits.
Aluminum sulfate is generally used as a binder for gas - rigid refractory plastics. Since the price of aluminum sulfate is only 15% of that of aluminum phosphate, the cost of gas-rigid refractory plastic is relatively low, and its low price lays a certain foundation for market promotion. The gas-hard refractory plastic has a long storage period of more than 12 months, which can fully meet the requirements of transportation and construction time; In production, there is no need for trapped materials, and the binder solution can be directly added to the material to stir evenly.
(1) Stricter requirements on raw materials. Gas-rigid refractory plastics have stricter requirements on raw materials, especially on soft clay, because the main properties of refractory plastics come from soft clay. Soft clay not only plays the role of a binder, but also a plasticizer, which has a great impact on the plasticity, storage life, construction performance, high temperature refractory performance of refractory plastic. As can be seen from the data in Table 3, the properties and characteristics of soft clays from different producing areas are different, while the advantages and disadvantages of several soft clays can be complementary. Therefore, in order to make refractory plastic has a good comprehensive performance, often compound use two or more than two kinds of soft clay.
(2) Compensation refractory plastic shrinkage technology. Some technical measures have been taken to compensate the shrinkage of refractory plastics due to the dehydration and sintering shrinkage of soft clay. (1) Introduce the blue SPAR group minerals and make use of the volume expansion generated by mullite at 1300~1500℃ to compensate for the shrinkage; (2) A12O3 material was introduced, and the volume expansion generated by the reaction with SiO2 to produce Mullite was used to compensate for the contraction; The type, addition and particle size composition of soft clay are preferred, and the ultrafine powder <1 m (such as A12O3) is selected to replace part of the soft clay, which can reduce the firing shrinkage of refractory plastic; Select raw materials, strict control of raw materials Fe2O3, Na2O and K2O impurities and low melt.
Uniform expansion technology is adopted to ensure the integrity of the construction lining. On the basis of preventing the shrinkage of refractory plastics, we carefully match the raw materials and accurately design the formula, so that refractory plastics can expand uniformly with the increase of temperature, not in a certain temperature section to produce excessive expansion, and ensure the integrity of the construction lining. The figure I below shows the change rate of the heating line of a high alumina refractory plastic after uniform expansion
Thermal Hard and Gas Hard Composite Binder is Refractory and Plastic
Thermal hardness and gas hardness refractory plastics have their own advantages and disadvantages, but the advantages and disadvantages of the two plastics can be made up for each other. Therefore, researchers of refractory materials have developed a composite binder with excellent properties of thermal hardness and gas hardness refractory plastics. The composite use of aluminum phosphate and aluminum sulfate, give full play to the advantages of thermal and rigid and rigid refractory plastic, and overcome the disadvantages as far as possible, this kind of refractory plastic in practical application has also obtained a good use effect.
The strength of thermal-hard and gas-hard composite binder is appropriate for refractory plastics. As can be seen from the indicators in Table 1, such plastics have appropriate strength at room temperature and high temperature. Long storage period, up to more than 10 months, can fully meet the requirements of transportation time and construction time; Due to the use of composite binder, material cost is moderate, the market price is appropriate, conducive to market promotion; During the production, the binder and admixture can be added directly into the material for even mixing, without material trapping, and the production process is simple.
Technical improvement measures for refractory plastics with thermal-hard and gas-hard composite binder:
(1) Use a variety of effective admixtures. One of the obvious technical improvement measures of this kind of refractory plastic is to use a variety of effective and efficient preservative, plasticizer and other trace additives, so that the material has a longer storage life, plasticity and other properties.
(2) The design of the formula is more reasonable and accurate, with more emphasis on comprehensive performance. Such as a large number of high quality coking stones, light mullite and other low thermal conductivity of raw materials, to ensure the low thermal conductivity of plastic, so as to improve the heat preservation performance of the kiln.
(3) Pay more attention to the innovation of refractory plastic production equipment. The technical indexes of production equipment are constantly improved to meet the requirements of different refractory plastic materials for different performance.
From the research institutions and the market to learn, especially in the past ten years in the domestic steel rolling reheating furnace of the use of hot-hard, gas-hard composite binder refractory plastic performance is good, has also been recognized by users.
4. Application Prospect of Refractory Plastics
Because the hot hard refractory plastic has the advantages of high intensity, applied to require high strength, wear resistance of material to use parts of the more appropriate, so hot hard refractory plastic on such as petrochemical industry boiler can obtain good development: hot hard, rigid composite binder refractory plastic has good performance and suitable price, in the metallurgical industry furnace and dosage will further expand the scope of application of; Spraying type refractory plastic has many unique advantages such as high construction efficiency, low labor intensity, etc. This kind of plastic can also be promoted vigorously in the future.
At present, metallurgy, petrochemical and other industries strongly advocate energy saving and consumption reduction, reduce production costs and thus improve economic benefits, therefore, the refractory life requirements are also increasing. Refractory plastics are used in the lining of industrial kiln, which greatly improves the life of furnace and the performance-to-price ratio of materials, and attracts more and more attention. With the continuous progress of refractory plastics technology and construction machinery, the range and amount of refractory plastics will be further improved.
