A discussion: Problems in the use of torch guniting for repairing the lining of heating equipment and production of block refractory parts. Selection of compounds for torch guniting of open-hearth roofs

Abstract

An important measure making it possible to prolong the campaign of open hearths is hot repair of them, which may be done by torch guniting.It is known that the operating time of an open hearth is determined by the service life of its roof and therefore selection of compounds providing the obtaining of a gunited coating reliably protecting the roof refractories must be considered a top priority problem.At present there is experience in the torch guniting of open hearth roofs with periclase compounds [i, 2]. In [2] the insufficient heat resistance of a periclase coating and the necessity of improving the compositions of the compounds is shown.Based on the properties of periclase-chromite refractories, which are well recommended in service in open hearth roofs, it is natural to assume that gunited coatings formed from periclase-chromite compounds must most fully answer the service requirements (high heat resistance and refractoriness, satisfactory porosity, etc.).The question of the optimum ratio of periclase and chromite in the refractories formed was sufficiently fully studied in the 1950s and 1960s. It was established that the particle size distribution of the charge has a significant influence on this ratio and to obtain highly heat resistant refractories it is preferable to use coarse grained charges.For torch guniting compounds with not less than 90 wt. % of the 5 0.09 mm fraction are used.In [3,4] the properties of peric!ase-chromite refractories the original charge of which consisted of finely ground powders of periclase and chromite with a grain size of ! 0.01 mm were investigated. However, the data presented in these works cannot be used in selection of the compounds for torch guniting not only because of the significant difference in the particle size distribution but also because of features of formation of the gunited coating including the almost complete absence of external pressure in application, the short hightemperature firing, and the presence of the low melting addition introduced by the fuel ash.In conducting the present investigations charges with weight ratios of periclase and chromite (chrome ore and siftings of it) of i00: 0, 90:10, 80:20, 70:30, 60:40, 30:70, and 0:i00 were prepared and also charges based on scrap of used periclase-chromite roof brick (PKhS-scrap) with additions of periclase powder in the following weight ratios: i00:0; 90:10; 80:20; 70:30; 60:40. The chemical compositions of the investigated materials are given in Table I.Coal concentrate waste similar in composition to coke ash (the difference in oxide content did not exceed 1%) was added as the low-melting addition. The quantity of low-melting addition was calculated based on a weight ratio of refractory: fuel = 70:30 and an ash content of 15.8%. The share of the ~ 0.09 mm fraction was 98 wt. %.