The use of the ribbon test method in conjunction with measurement of M.O.E. by transient vibration has proved of significant assistance in the comparison of various refractory grades for thermal shock resistance and is now proving a useful tool in the development of new products. It is hoped that, once the parameters of the test are more fully understood and standardised, it will be only necessary to measure elastic modulus before and after 10 cycles or perhaps even 5 cycles will be sufficient.
L’utilisation de la méthode d’essai Ribbon en liaison avec la mesure du module d’élasticité par vibrations transitoires, a été d’une grande aide dans la comparaison de plusieurs sortes de réfractaires du point de vue de leur résistance aux chocs thermiques; elle constitue maintenant un bon outil dans le développement de produits nouveaux. On peut espérer, une fois qu’on comprendra mieux les paramètres de cet essai, qu’il suffira de mesurer le module d’élasticité avant et après 10 cycles, ou même seulement 5 cycles.
Dans le but d’améliorer le contrôle des produits et matériaux réfractaires, les Laboratoires de Réfractaires et Minerais ont recherche une méthode : non-destructive, rapide, simple, peu coûteuse. L’appareil utilisé conçu pour mesurer le module d’élasticité des meules à partir de la fréquence de résonance répond à ces critères. Les L.R.M. ont donc entrepis une étude afin de déterminer les possibilités exactes offertes par cet appareil pour le contrôle des produits et matériaux réfractaires.
Mathematical relations were evaluated and equations are presented correlating non-destructive sonic measurements, using either ultrasonic velocity or modulus of elasticity, with modulus of rupture for five representative fired refractory product types, including high alumina (90%), mullite (70% alumina), super-duty fireclay (42% alumina), vitreous silica (99% silica) and carbon. The experimental relations were tested for additional brands and found to yield predicted strengths that were within 0.5% to 6% of the actuals strengths for refractory products having properties similar to the model refractory product used to develop the correlation equation. For refractory products with properties that were dissimilar to the model refractory, the predicted strengths differed from the actual strengths by >20%.
Depuis de nombreuses années, le contrôle sonique est utilisé sur les briques réfractaires d’aciérie pour détecter l’apparition de fissures au choc thermique, pour déterminer la dispersion des caractéristiques physiques d’un lot de fabrication, pour contrôler et trier des pièces don’t la tenue est essentielle. Cet article a pour but de préciser les possibilités de ce type de contrôle et de déterminer des corrélations entre modules d’élasticité ainsi mesurés et caractéritiques physiques de réfractaires.
Correspondant à la tangente de l’angle à l’origine sur la courbe effort-déformation du matériau, le module d’élasticité est plus facilement et plus précisément mesuré par les méthodes ultrasonique et sonique. Cette dernière se fait par entrée en résonance avec excitation par vibration continue de fréquence variable, ou par choc.
Les essais menés sur des lots provenant de trois fournisseurs ont permis de tracer des histogrammes de répartition par classe et de rechercher des corrélations linéaires entre caractéristiques physiques et modules d’élasticité.
Cette méthode doit être considérée comme complétant utilement les contrôles traditionnels sur les éléments réfractaires et comme primordiale sur les éléments don’t la bonne tenue en service est impérative.
The impulse excitation technique has been used sucessfully for many years to determine the hardness of grinding wheels and honing stones. Investigations were carried out at the Minarals & Refractories Laboratories to determine if this method could be used to access the quality of refractories.
This nondestructive method uses an instrument originally developed to determine the modulus of elasticity of grinding wheels. Because it measures the frequency of fundamental vibrations, the instrument also should provide excellent results in testing refractory products.
Tests were performed with random batches from three suppliers of ladle brick to determine linear relationships between physical characteristics and the modulus of elasticity. This testing method is of prime importance for studying parts whose proper in-service behavior is essential.
The accuracy and advantages of the non-destructive resonant frequency technique (impulse excitation technique) for the final inspection of conventional refractory products are discussed. Mathematical models and correlations for alumina brands are presented.
SiC-based kiln furniture has a maximum service temperature of 1600°C. Beyond that point, mullite-corundum materials are required. Here it is important that high hot bending strength resp. thermal fatigue in conjunction with adequate thermal shock resistance be achieved through selectively designed microstructures and appropriate raw materials.
Refractories are the “Backbone of Industry”. Despite their great importance, refractories are frequently misunderstood, overlooked, and/or abused. The results can be extremely disruptive, costly, and even tragic. This paper defines seven main reasons for refractories problems in industry, and notes seven other contributing factors. Many practical examples are included. Based on an improved understanding of the reasons for refractories problems, as well as a thorough review of all related factors, it is possible to reduce or eliminate unnecessary and unexpected major expenses.
TiZrC and TiZrB2 solid-solution materials were synthesized by conventional powder production methods. These materials exhibited nonlinear, and generally superior, mechanical properties when compared to the end-member constituents.
The knowledge of the modulus of elasticity (MoE) of refractories and its dependence on the temperature is necessarily for
° the calculation of the stress-deformation state of kiln linings as a basis for optimizing the kiln construction and for calculating of the allowable speed op the heat up and cool downs.
° the non-destructive quatlity control.
To determine the MoE (ultrasound or resonance frequency) dynamic or static
( dependence of the stress on the deformation by measurement of the mechanical strength) methods are used. The different measurement methods deliver deviant results. To understand these differences, experiments with the following four different refractories were carried out :
° two different mullite bonded corundum refractories – without/with ZrO2 addition
° two different magnesia refractories – with/without ZrO2 addition.
For all four the MoE were measured by different dynamic and static methods. According to the measurement method different values of MoE were received. This is caused by the rheological behaviour of the refractories. At room temperature there is a nearly elastic behaviour. At elevated temperatures non-elastic irreversible time dependent deformations appear. In the application of the MoE values in practice, above all the time coarse of the loading must be taken into account.