Radio wave phase method of quality control for refractory slabs for sliding gates

Abstract

In pouring steel from ladles, successful use has recently been made of sliding gate valves in which the crucial elements are refractory slabs [i]o These slabs operate in stringent conditions, and therefore severe technical requirements are imposed on them (TU [2]~ The present quality control of these slabs, which involves testing two specimens from each batch of 400 sets for mechanical strength and open porosity, is inadequate for reliable estimation of the production of crucial components.It is necessary to check each slab separately, as each set has to permit stable pouring of 130-700 tons of steel.In this article we describe the results of investigations on nondestructive quality control of composite (MSP-95) and biceramic (MPB-95) magnesite (peric!ase) slabs .For nondestructive testing of the mechanical properties (open porosity, apparent density, and compressive strength) of refractory artifacts made of dielectric materials, at the All-Union Institute of Refractories (VIO) we have developed a radio-wave phase (uhf) method [3-5] based on measurement of the velocity of transmission of radio waves through the test articles.The method is contactless and permits local monitoring, i.e., measurement of the properties in a limited zone determined by the area of the beam (ray) of electromagnetic radiation.The velocity of transmission of radio waves is measured by means of the phase change of the wave passing through the article relative to that for passage along the same path in air.When radio waves pass through an infinite dielectric medium with low loss (in which the dielectric loss angle tangent is tan ~ < 10-2), the relation between B and the dielectric constant of the medium [6, p. 44] is as follows: 2=where % is the wavelength in free space, in centimeters; c, relative dielectric constant; and d, geometrical path length of the wave in the dielectric medium, in centimeters.We can approximately assume that the radio waves pass through a layer in the articles. Consequently, the relation between B, e, and ~ will take the formwhere r = --4~d ;and ~m is the measured phase lead [7].Since the dimensions of the monitored articles can vary, as the parameter (to be measured by the nondestructive method) by which the properties of an article is to be judged (on the basis of a calibration graph) we choose the corrected phase lead,

Nondestructive radiowave method of inspection and its role in increasing product quality

“…'2-0.3 g/cm 3, as the result of which the change in porosity within the limits of a single part is as high as 6% in absolute value [4][5][6][7]. A significant difference in density of parts frquently leads to the fact that the readings of the mechanical properties (open porosity, apparent density, compressive strength) determined on specimens are beyound the allowable limits although on the average for the part these readings are satisfactory.…”

“…The results of investigationof the interrelationship between the dielectric permeability of refractory parts and their microstructure and strength properties [5,13,14] showed that there is a clear relationship between 8 and the compressive strength as the result of their common relationship to the change in apparent density. From the values of it is possible to determine other indices related to the change in Papp"…”

“…The coefficients a and b depend upon the chemical composition of the material and for parts of a single type are constants [2][3][4][5]7,i0,Ii,12]. The correlation coefficients between P and 8 are 0.8 and more.…”

“…It has been experimentally established that from the rate of passage of superhigh frequency range radiowaves it is possible to approximately determine the moisture content ~of powders, compounds, and green parts [20], the activity of powders [21], and the degree of uniformity of green parts [5], to invesitgate sintering processes, and to record phase transformations in a material [13].…”