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    Home > Coatings News > Paints and Coatings Market > The influence factors and construction methods of bauxite-based spray coating.

    The influence factors and construction methods of bauxite-based spray coating.

    • Last Update: 2020-09-05
    • Source: Internet
    • Author: User
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    Keywords:
    -spray
    coatings
    ,
    bauxite
    dry, semi-dry, wet, flame spraying foreword:
    With the development of
    -refrasive materials
    industry and social progress, some labor intensity, slow construction of refrater materials are gradually replaced, indetermine refrater materials in the metallurgical industry increasing use. In the indetermity refrater material is the largest amount of pouring materials, followed by spray coating. Spray coatings are widely used in thermal equipment such as kilns and can be used to spray new linings and to repair furnace linings. It can be used to construct and repair furnace lining and coat it into protective layer in cold state, and it is also suitable for repairing furnace lining in hot state.
    spray coating developed and produced by Crane Wall Zhongsheng Furnace Engineering Co., Ltd. solves the problem that the ordinary construction method of refractory materials cannot be operated in complex or special-shaped parts. In addition, the spray coating construction does not require a support template, can be directly on the spray surface set anchor firmware for construction or on the surface of refrasive material spray. As can be known from the above, spray coating is an effective technical measure to speed up the construction progress, shorten the repair time, extend the life of the kiln and reduce the consumption of refrasive materials.
    general overview of
    1 spray coating
    spray coating is an indeter form refraction material constructed by mechanical injection using pneumatic tools. Refraction spray coating in the pipe with the help of compressed air or mechanical pressure to obtain sufficient speed, through the nozzle to the spray surface, can form a solid
    coating
    . The spray method can be divided into wet method, dry method, semi-dry method and flame method
    4
    category, and according to the status of the material accepted by the spray surface can be divided into cold material spray method and molten material spray method.
    Fire-resistant spray coating and the same variety of fire-resistant pouring materials are basically similar, the difference is that the critical granularity of fire-resistant bone material is small, generally 3 to 5mm, refragent powder, ultra-micro-powder and binding agent combined with more, generally 35% to 45%. Because the composition of the material is similar, the condensation hardening process of the spray coating and the physical and chemical changes at high temperatures are basically the same. The key technologies are adhesion, adhesion, strength and sintering. These properties are not only closely related to the material itself, but more importantly, are restricted by mechanical equipment such as jets and construction process parameters, but also by factors such as the status and conditions of use of the injectors.
    must have the nature of spray coating:
    (1) has a certain particle grade distribution to ensure that the material has a certain amount of liquidity;
    (2) spray coating must have a certain plasticity and solidification, so that the material can be very good adsorption to the spray coating, and can quickly solidify and have a certain strength;
    (3) to control the water, to ensure that the material can be moisturized without causing flow.
    should pay attention to:
    (1) injection of air pressure and air volume, to avoid rebound and fall off;
    (2) the distance and angle between the nozzle and the subject, so as to avoid the material spraying to the spray surface is too large or too small, to ensure uniform spraying;
    (3) when sprayed, too thick to peel off.
    specific considerations will be discussed in more detail later.
    2 Factors affecting the performance of bauxite-based spray coatings
    Bauxite spray coatings are bauxite as the main raw material, calcium bauxite cement, silicon powder as a binding system, according to the situation to add blue crystal, red pillar stone, etc., the use of three stones at high temperature Mole petrochemical to offset sintering contraction. In order to improve its performance and add some
    additives
    . In order to promote condensation hardening and add some coagulants and so on. Now in the ZS-CM formula of the spray coating of Crane Wall Furnace Engineering Co., Ltd., the effect of a small amount of added material in the spray coating is analyzed.
    the effects of 2.1 silicon micropowrines,
    studies have found that improving the fineness of fine powders in refrainable materials can promote sintering of products, resulting in a range of excellent properties. Silicon micro-powder has attracted much attention because of its high ratio surface area and high surf activity, which brings a series of excellent properties to refrailable material products.
    2.1.1 line shrinkage
    Figure 1 micro-powder content and heat treatment temperature on the rate of sample line change
    Silicon micro-powder surface defects, surface mass activated and disordered more, with high energy, high activity characteristics, which can promote the sintering process. With the increase of heat treatment temperature, silicon micro-powder is gradually transformed into liquid phase, which is conducive to the filling of pores, and under the effect of surface tension, the distance between the sample particles is closer, so the shrinkage of the material increases. After the sample was heat treated at 1500 degrees C, with the increase of silicon micro-powder content, the line shrinkage of the sample decreased gradually until expansion was produced. This is because silicon powder reacts with brown corundity to form a molybton, which at the same time produces volume expansion, resulting in a reduction in the line contraction of the test subject until expansion is produced. When the mass fraction of silicon micro-powder is 5%, the line shrinkage of the material after different heat treatment temperature is not very different, and the material shrinkage rate is very small, if the material shrinkage rate is too large, it will cause the coating in use due to shrinkage caused by cracking, and therefore will reduce the life of the material.
    2.1.2 volume density
    at low and medium high temperatures, the volume density increases with the increase of silicon micropowr content, which is conducive to filling the internal pores of the sample. However, when the sample after 1500 degrees C heat treatment, the volume density of the sample with the increase of silicon micro-powder content showed a decreasing law of change, because silicon micro-powder and brown cumin reaction, the formation of molybton, at the same time will produce volume expansion, resulting in loose internal structure of the sample. With the gradual increase of silicon micro-powder content, the amount of molybton formation also increased correspondingly, and the expansion of volume became more and more obvious, resulting in a gradual decrease in sample volume density.
    2.1.3 Folding strength and pressure resistance
    At lower temperatures, si-OH bonds formed after hydration of the surface of silicon micro-powder particles are dehydrated and aggregated to form a solid Si-O-Si bond Due to the combined micro-powder mesh chain structure, the micro-powder long chain reaction is as follows:
    SiO2-Si-OH-HO-Si-SiO2-SiO2-Si-Si-Si-Si-SiO2-H2O.
    With the increase of this mesh chain structure, the binding performance of silicone is also stronger, so at low temperature 110 degrees C with the increase of silicon micro-powder content of the sample's folding strength and pressure resistance strength also increased accordingly. At medium and high temperatures of 1000 and 1300 degrees C, silicon micro-powder and brown cumin react to form molybton, the intensity increases. Therefore, with the increase of silicon micro-powder content, the anti-fold strength and pressure-resistant strength of the sample also increased accordingly. After the sample has been heat treated at 1500 degrees C, the folding strength and pressure resistance of the sample are reduced and then increased with the increase of silicon micro-powder content. This is because there is a liquid phase generation, resulting in the material melting, so its strength value is relatively large. After that, with the increase of silicon micro-powder content, the amount converted to molybton also increased accordingly, so the strength of the sample's folding and pressure resistance increased accordingly.
    2.1.4 thermal expansion coefficient
    The coefficient of thermal expansion of bauxite-based spray coatings decreased with the increase of silicon micro-powder content under the same temperature conditions.
    2.1.5 Conclusion
    (1) In this experiment, the mass score of the best silicon micro-powder for the preparation of bauxite-based spray coating was 5%;
    (2) after 110 degrees C drying, 1000, 1300 degrees C heat treatment, bauxite-based spray coating folding strength and pressure resistance strength with the increase of silicon micro-powder content;
    (3) the coefficient of thermal expansion of bauxite-based spray coating decreased with the increase of silicon micro-powder content.
    2.2 effects of sodium aluminumate
    spray coating construction needs to have a better working time and faster hardening, if the spray coating after spraying to the furnace lining, in a longer period of time not hardened, there will be paint collapse. In this case, it is necessary to spray paint after construction can be hardened in a faster time, to prevent the material due to slow hardening collapse.
    the samples with 0.1% and 0.2% sodium aluminate were added to the experiment and compared with samples without sodium aluminate.
    2.2.1 Condensation Hardening
    After the experimental results of Crane Wall Furnace Engineering Co., Ltd. proved that at room temperature, the hardening time of spray coatings without adding sodium aluminate is longer, and the test coagulation hardening time of adding sodium aluminate is significantly shorter, so adding sodium aluminumate to the spray coating can play a role in promoting the hardening of spray coatings. The hardening time is shortened and the working time is shortened accordingly, which is not conducive to the dressing work after the construction of the spray coating, and the addition of excessive sodium aluminumate will also reduce the strength of the material's health and pressure resistance. Therefore, taking into account the effect of different sodium aluminumate addition on spray coating working time, hardening time and health pressure resistance, it can be seen that the optimal addition of sodium aluminumate under the experimental conditions is 0.1%. Its action is as:
    CaO. Al2O3 plus H2O- CaO Al2O3.10 H2O (six parties) (below 20 degrees C to 22 degrees C),
    CaO Al2O3 plus H2O plus 2CaO Al2O3.8 H2O (Six Parties) - Al2O3.3 H2O (-25 degrees C) -
    3CaO Al2O3.6 H2O (Six Parties) and Al2O3.3H2O (35 to 45 degrees C).
    in the spray coating to add coagulant sodium aluminumate, so that cement parts
    China aluminum
    calcium acid, aluminum acid calcium and other accelerated into the solution to extract hydrate, so accelerate the hydration reaction of cement, so that cement can be hardened more quickly, so that the spray coating shortens the hardening time, but also reduce the working time.
    2.2.2 volume density and line shrinkage
    Sodium aluminumate is a low melting point salt substance, added to the spray coating, at high temperature is easier to promote the sintering of the material, resulting in decreasing pores, increased density, so the volume density of the test site increased. At the same time, during sintering process, the liquid phase is produced inside the sample, under the effect of surface tension, the distance between the particles of the sample is pulled closer, so with the increase of sodium aluminumate content, the line shrinkage rate of the sample gradually increased.
    2.2.3 folding strength and pressure strength
    after drying the sample at 110 degrees C, the folding strength of the sample decreased with the increase of sodium aluminumate mass fraction; With the increase of sodium aluminate mass score, after 1300 degrees C heat treatment, the resistance strength of the test was not significantly changed with the increase of sodium aluminumate mass fraction, and after 1500 degrees C heat treatment, the resistance strength of the test was increased with the increase of sodium aluminumate mass fraction. After the sample was dried at 110 degrees C and after 1000 degrees C and 1300 degrees C heat treatment, the pressure resistance strength of the sample decreased with the increase of the quality score of sodium aluminumate, and after the heat treatment of 1500 degrees C, the pressure strength of the sample increased with the increase of the mass score of sodium aluminumate. It can be seen that the addition of sodium aluminumate in the spray coating will have a certain impact on the strength of the material after low temperature drying and pressure resistance, but on the material temperature, medium and high temperature of the folding strength has played an increased role, while affecting the material temperature, medium and high temperature pressure strength. Although the folding strength and pressure resistance strength of the high temperature of 1500 degrees C have been increased, but due to the melting phenomenon of the sample, the surface of the sample has cracks, thus reducing the temperature of use of the material.
    2.2.4 Conclusion
    (1) The optimal addition of sodium aluminate under the experimental conditions of Crane Wall Furnace Engineering Co., Ltd. is W (Na2O. Al2O3) - 0.1%.
    (2) adds sodium aluminumate to the coating, the temperature at which the spray is used is reduced.
    construction techniques for 3 paints were used in
    early days, the spraying methods were dry and wet. Among them, the advantages of dry spraying has been widely used. However, dry spraying has the disadvantages of large dust and more rebound, poor performance of the construction body, so it developed a semi-dry spray technology, so as to obtain low moisture and high filling construction body, and has the advantages of dust-free construction, spray coating attachment rate, so it was quickly popularized and applied.
    the purpose of developing semi-dry spraying is to avoid the complicated premixed operation of wet method. Because the advantages of wet method are obvious, the technical interest now turns to wet spraying.
    later developed flame spraying, which has a very good effect compared to the previous wet spray. The flame spray coating is firmly integrated with the furnace lining, densely organized, high fire resistance and strong corrosion resistance, which can significantly improve service life and reduce the cost of furnace materials.
    3.1 dry spray
    dry material from the silo into the rotating cloth bucket, cloth cloth barrel rotation at a certain angle, its upper port and compressed air channel connected, the material is compressed air is piped to the nozzle near the encounter with water, in the nozzle material mixed with water is sprayed to the spray surface.
    : Wet and dry spray equipment structure and process
    the use of dry spray should pay attention to the following things.
    (1) add water appropriately. Too little material can not be very good wetting, dry material is easy to bounce back;
    (2) jet pressure and air volume should be appropriate, too large particles on the jet surface impact is too large, easy to rebound, too small, insufficient adhesion force easy to fall off.
    (3) the distance angle between the nozzle and the spray surface should be appropriate to avoid the material being sprayed too large or too small to the spray surface. The spray gun moves up and down left and right to ensure uniform thickness.
    (4) the thickness of each spray should not be too thick, too thick easy to peel off, not more than 50mm.
    (5) control the plasticity and solidification of the material, so that the material can be very good adsorption on the spray coating, and can quickly solidify and obtain a certain strength.
    3.2 Wet spraying
    The wet spray developed by Hebi Zhongsheng Furnace Engineering Co., Ltd. is to pump the fluid pouring material through the pipe to the nozzle, where it is high-pressure gas.
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