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Abstract

Сontents

Introduction

In connection with the intensive development of scientific and technical processes, the requirements for constructional materials to ensure the greatest productivity of machines are constantly growing. Thermal units for a long time can be used in conditions of sudden temperature fluctuations, exposure to corrosive media, erosive and corrosive wear, all this negatively affects their service life, as well as the quality of the products. As practice shows, the use of high-quality, and, therefore, more expensive materials for the laying of production furnaces is not always possible or appropriate, as a result of which cheaper products are usually used which are less resistant to the action of various destructive factors. In turn, this leads, first, to the rapid deterioration of the lining of apparatuses and the increase in waste, most of which goes to dumps, and secondly, the consumption of raw materials for raw materials for the production of new materials for masonry of furnaces increases.

To extend the service life of the lining of industrial furnaces and other thermal units, as well as to reduce the formation of industrial waste and more rational use of natural resources, protective coatings of various compositions are used, consisting of refractory powders of specified granularity and a binder. Coatings are applied in the form of coatings and shotcrete masses, not only to protect the refractory lining and prolong the life of the furnace, but also to repair the heat units both in cold form and at high temperatures without stopping them.

1. Theme urgency

The relevance of the study is related to the presence in our region of a large number of metallurgical, coke chemical and other industries using high-temperature heat devices, which necessitates the extension of the service life of furnace lining.

2. Goal and tasks of the research

The purpose of this work is to study the main properties and characteristics of existing refractory coatings, methods of their control (such as density, porosity, water absorption, mechanical strength and thermal resistance), as well as to study the effect of various additives on the properties of refractory coatings and to develop the possibility of replacing traditional refractory aggregates technogenic products.

3. Importance and application of products

Refractory coatings are powders of various refractory materials of a certain granularity, into which various additives are added for binding. These coatings are applied to the working surface of refractory lining by the method of shotcrete with the help of special apparatuses, and in some cases manually in the form of coatings, to protect them from premature wear from exposure to slags and other destructive reagents, as well as to repair damage, both during stops and during the operation of furnace units, which generally contributes to the extension of the service life of the masonry [1]. The thickness of the coating layer should be 3 – 7 mm. If the thickness is thicker, the coating can crack during drying and fall off, with lower thickness its resistance decreases. The grasping and hardening of the coatings occurs as a result of the drying and sintering of the mass when heated.

The composition and granularity of the coatings are determined by the way they are applied, by the kind of masonry being repaired or protected by them and by the conditions of service. The composition of the mass contains a filler with grains less than 2 mm in size and with a content of fine fractions of less than 0.2 – 0.5 mm of the order of 50 %, a chemical bond, a plasticizer and water. Refractory aggregate is usually selected by analogy with the nature of the protected masonry. Plasticizers are bentonites or plastic refractory clays, introduced in an amount of 5 – 10 %. The chemical bond may be soluble glass, chromates, phosphates, magnesium salts, slags, ferruginous additives, administered in amounts of 1 – 15 %. However, the use of these additives is permissible only in cases where a decrease in the refractory properties of the mass can not worsen its resistance to service [2].

For example, the mass for repairs of the dinas masonry of coke ovens contains 90 to 95 % of chamotte and 5 to 10 % of refractory clay. To bind the mass, orthophosphoric acid is added in an amount of 15 – 17 % over the weight of the dry components [3].

For hot shotcrete open-hearth and electric arc furnaces chromium-magnesite masses with different contents of chromite, chromium-magnesite and magnesite powder are used. About 5 – 10 % of plastic refractory clay is injected into these masses. In some cases slag or scale is also introduced.

In masses for furnaces of non-ferrous metallurgy with dinasic masonry, a dynas or quartzite with 5 – 10 % clay is used, and for chromium-magnesite and magnesite masonry – a battle of chromium-magnesite brick, chromite ore, magnesite metallurgical powder.

To protect the chamotte lining of steam boilers and various furnaces, chromite, chamotte, chamotte-corundum clay, containing 6 % clay, of a similar type, is used to protect chamotte lightweights [4].

Requirements to cover requirements are very diverse. In some cases, high resistance against high thermal loads is required, in others, high physicomechanical characteristics are required. More often than not, refractory coatings require good adhesion to the linings to be repaired or protected by them, small volumetric changes during drying and high temperatures, resistance to chemical and mechanical damage.

In many cases, the coating requires a set of properties that ensure its long-term operation under operating conditions. Naturally, all this complex of properties is difficult to combine in one material. However, when analyzing the relevant literature [1 – 12], it can be concluded that with proper selection of the ratio of the main components of the coating mixture and the introduction of appropriate additives, it is possible to substantially increase the operational properties of protective coatings.

A great opportunity opens up the use of composite coatings [6], which are a combination of two or several dissimilar materials, allowing the fullest use of the advantages of individual components. The combination of components with different properties makes it possible to obtain coatings of the required characteristics.

Conclusion

The duration and efficiency of high-temperature industrial units depends on the level of their technical operation, the timely diagnosis of emerging defects and the quality of preventive maintenance. Timely implementation of the required volume and application of the most rational preventive repairs with the use of refractory coatings, can significantly extend the service life of industrial furnaces.

In the future it is planned to expand the range of additives in order to improve the properties of coatings such as:

References

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