Determination of the technological parameters of guniting

Abstract

At present guniting is widely used in the repair and preparation of the linings of thermal equipment with the use of chamotte guniting compounds containing aluminocalcium cements [1][2][3][4]. The necessary properties of the gunited concrete coatings are determined by the operating parameters of the guniting machine, including the pressure of compressed air in the dry aereated mixture hose, the pressure in the moistener hose, and the distance from the nozzle to the surface to which the coating is being applied.It is known [5, 6] that the pressure of the compressed air and the distance from the nozzle to the surface being gunited determine the pressure of the stream of compound on the surface, upon which depends the density and strength of the layer of gunited concrete coating and also the amount of spring-back.The moisture of the gunited compound is regulated by the pressure of the moistener. A high moisture content leads to slipping or runoff of the compound from the surface while the compound held to the surface forms a gunited cement coating with high porosity and low strength. Low moisture content produces increased dust formation, an increase in losses of compound with the spring-back, and a reduction in the strength of the layer of gunited concrete coating.The basic requirements for linings of gunited concrete in thermal equipment are high strength and low porosity [7, 8], which determined the necessity of searching for the guniting parameters in mass preparation of the linings of new thermal equipment. For a solution of this problem experimental guniting was done on a stand equipped with an SB-67A guniting machine and a tank with a VK-5/24A-U2 peripheral pump.For the guniting a dry mixture* of 25% cement and 75% type AShA chamotte powder of class No. 4 according to All-UnionState Standard (GOST) 23037-78 was prepared. The temperatures of the hardener (water), the air, and the lining were constant (20~ Cement of two types was used, type 500 alumina to GOST 969-77 and VTs-75 high alumina to Technical Specification (TU) 21-20-25-76.In guniting the coefficient of adherence, the ratio of the weight of the compound adhering to the surface (the layer of gunited coating) to the weight of the original compound, was investigated. After preparation of the samples (cutting out) from the layer of gunited concrete, a moist hold for 72 h, and drying at II0~ for 5-8 h their compressive strength was determined according to and the open porosity to GOST 2409-80.About 70 tests were made and 57 groups of values of the guniting parameters and the properties of the gunited coating (adhesion, strength, and porosity) according to the task formulated were obtained. From the results obtained the original data was set up for calculation on a Mir-I computer of the optimum guniting parameters. For this the guniting parameters were adopted as the independent variables (Table i). The boundaries of variation of the independent variables were determined experimentally and the level of variation by analysis of the parameters of guniting,...

Evaluation of the propoerties of gunited concrete coatings and refractory parts

“…Gunited concretes of alumina cement with a chamotte filler and of high-alumina cement with a mullite-corundum filler containing 41 and 65%, respectively, of AI203 in the compound were compared withgeneral purpose class B chamotte parts with a 28% AI203 content apd type 8hPD-39 parts for blast furnaces~ The properties of the gunite concretes were determined on specimens prepared with rational guniting parameters from compounds with the optimum substance and grain size compositions [3,4]. The properties were determined by known methods (Table i).…”

Gunited concrete linings of conveyer sintering machines

“…The optimum parameters determined in [3] and intended for simple structural elements also were adjusted in relation to the length of coverage of the guniting.…”