Pyrometric Cone Equivalents

Refractoriness. Most refractories are mixtures of different oxides, sometimes with significant quantities of impurities. Thus, they do not have sharp melting points but a softening range. Refractoriness is the resistance to physical deformation under the influence of temperature. It is determined by the pyrometric cone equivalent (PCE) test for aluminosiHcates and resistance to creep or shear at high temperature (see Analytical methods). 

Refractoriness. Refractoriaess is determined by several methods. The pyrometric cone equivalent (PCE) test (ASTM C24) measures the softening temperature of refractory materials. Inclined trigonal pyramids (cones) are formed from finely ground materials, set on a base, and heated at a specific rate. The time and temperature (heat treatment) requited to cause the cone to bend over and touch the base is compared to that for standard cones. 

Maximum use temperatures are reported on refractory data sheets in terms of pyrometric cone equivalent (pee). In essence, this pee defines the temperature at which a small standard sized cone of the material slumps due to softening. Table 18-1 lists the pee numbers with the corresponding temperature limits and generic types of brick which fall within the various pee ranges. These reported pce s indicate a refractory s maximum use limit when exposed to a gas-fired environment however, they may actually soften at much lower temperatures due to reactions with the atmosphere they are containing. 

Table 18-1 Approximate Pyrometric Cone Equivalent (PCE) Values of Generic Classes of Fireclay and High Alumina Refractory Brick...

If the refractoriness of a material is to be determined, it must be cut or shaped into a cone of the same shape which is then heated at the specified rate together with several standard cones. The high-temperature behaviour of an unknown material is thus compared with that of a known material. The refractoriness is then specified by the number of that standard pyrometric cone whose tip would touch the supporting plaque simultaneously with a cone of the refractory material under investigation (pyrometric cone equivalent, PCE). 

PCE. Abbreviation for pyrometric cone equivalent, a scale of melting or fusion points of refractory materials, based on comparison with the temperature at which pyrometric cones melt. 

Table 9.7 Data compiled by Nassau, K. (1994) Gemstone Enhancement, 2 Ed., Butterworth-Heinemaim, Oxford, p. 220, modified with applications from the American Iso-static Presses, Inc. data sheet. ANSI (American National Standards Institute) symbols, except for G, C, and D. Table 9.8 The pyrometric cone equivalent test is described in ASTM Standard C24-56.

As a rule of thumb, an insulating material is considered a refractory material if its melting or solidus temperature is well above the melting point of pure iron (1539°C), i.e., if it exhibits a Seger s pyrometric cone equivalent of No. 26 or more (Table 10.19). Moreover, the maximum operating temperature of a refractory material is usually 150°C lower than its pyrometric cone equivalent. 

Table 10.19. Temperature equivalents (°C) of pyrometric cones and pyrometric cone equivalents ...

Cone No. Heating rate for large cones Heating rate for small cones Pyrometric cone equivalent (PCE)... 

ASTM C-24 Pyrometric cone equivalent of fireclay and high-alumina refractory materials... 

ISO 528 1983 Refractory products - determination of pyrometric cone equivalent (refractoriness)... 

Because of the heterogeneity of their composition and structure, ceramic refractories do not exhibit a uniform melting point. The refractoriness is characterized by the optical determination of the pyrometric cone equivalent (according to Seger), that is, the temperature at which the tip of a cone made of the sample material softens to the point that it touches the base plate. Reference cones with well-established pyrometric cone equivalents at temperature intervals of 10 °C and above, along with the test cones made from the sample material, are heated in the same furnace so that it is possible to make an accurate comparative temperature determination for the softening point of the refractory material to within approximately 20 °C. 

DIN 51063. Testing of ceramic raw and finished materials. Pyrometric Seger cone. Part 1 determination of the bending point (pyrometric cone equivalent), Part 2 testing of Seger cones. ISO 1146 1988 Pyrometric reference cones for laboratory use - specification. 

Ceramic grade - Grades for ceramics are finely groimd (typically 200, 270, or 400 mesh), controlled for PCE (pyrometric cone equivalent), free of dark impurities, and white-firing without specking. 

Moving toward service-related properties such as pyrometric cone equivalent (P.C.E.), hot modulus of rupture (HMOR), and permanent linear change (P.L.C.) gives us a little more information on a product s maximum service temperature and stability on heating. 

The pyrometric cone equivalent gives an indication of the refractoriness of a material, that is, its ability to withstand high temperatures in an unstressed situation. The method appUes particularly to aluminosilicate materials. A standard refractory... 

The pyrometric cone equivalent of a material is affected by the presence of impurities in the material such as iron and alkalis, which reduce the P.C . value, by acting as fluxes. Determination of the P.C.E. can ensure that a refractory selected for a particular application is operating well below the onset of melting. 

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