Standards for Testing Refractories

ASTM C-16 Load-testing refractory brick at high temperatures 

ASTM C-20 Apparent porosity, water absorption, apparent specific gravity, and bulk density of burned refractory brick and shapes by boiling water 

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

ASTM C-67 Brick and structural clay-tile testing 

ASTM C-92 Sieve analysis and water content of refractory materials 

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Table 10.20. ASTM standards for testing refractories ASTM standard Description...

Manual ofASTM Standards on Refractory Materials, 8th ed., American Society for Testing and Materials, Philadelphia, Pa., 1957. 

Lack of standards in testing for refractories becomes apparent when one realizes that factors such as sample size and geometry, state of stress in the lining, thermal gradient, thermal cycling and duration are difficult to scale down to a laboratory scale to simulate service conditions. Accelerated tests involving severe conditions do not always conform to realistic conditions and may lead to unrealistic results. 

Sand Rammer. The standard rammer for making test-pieces allows a 14 lb (6.25 kg) weight to fall 50 mm on sand contained in a 50 mm diam. mould three blows from the rammer are used in making a standard test-piece. Its use in compaction and workability tests for unshaped refractories is specified in B.S. 1902 Pt. 7.2. 

It is well known that corrosion of refractories used in the superstructure of glass melting furnaces can occur due to reaction with components of raw batch (also known as batch carryover) such as silica sand and soda ash and also from vapor phase species, such as NaOH. While there is a standard test available from ASTM for corrosion of refiectories from vapors (C987), there is no standard test available for testing corrosion from batch carryover. The ASTM standard, C987, requires the use of either alumina or platinum crucible for melting batch components that produce vapors, such as sodium carbonate. For the purpose of this study, the authors chose to prepare crucibles directly from the fusion-cast AZS and vibro-cast AZS products. 

The hardness determination of refractories is limited by its heterogeneous coarse-grained structure. The hardness values characterize small volumes of the material. There is no standard for the determination of the hardness for refractories for research purposes, it is possible to use ASTM Cl 327-08 [59] and ASTM C1326-13 [60] for structural ceramics. Many publications describe the determination of the fracture toughness of ceramics by measurement of cracks around the indented areas during hardness testing [61-63]. 

ASTM C768-99. Withdrawn standard ASTM C768-99 standard practice for drip slag testing refractory materials at high temperature (withdrawn 2004). 

Initially, when unshaped refractories were first used, the property requirement was kept the same as for shaped refractories, in thatthey mainly replaced linings. Later on, when the use of these refractories became widespread, new standards had to be developed. The first standards on unshaped refractories by the American Society for Testing of Metals (ASTM) were published in 1943 [3]. They were numbered as C 179 and C 181 C 179 covered "drying and firing linear change of plastics and rammings" and C 181 dealt with "workability index of plastic refractories." As noted earlier. World War II saw an increase of about 35% in unshaped refractory production. Specifications were required to obtain the required items from many manufacturers. 

Since the development of vibratable and pumpable castables, methods have been standardized for measuring the flowability of a castable, which can predict the flow characteristics. The test consists of filling up a cone with the castable refractory and then letting it flow under vibration for a specified time. The predetermined flowability characteristics define the castable s use in actual applications. 

There are two standard methods for determining the thermal shock resistance of refractory materials. For brick shapes, thermal shock resistance is measured by Ribbon Thermal Shock Testing (ASTM C-1100), and for monolithic refractories the standard method is ASTM C-1171. These tests clearly differentiate among refractory materials about their resistance to thermal shocks. 

The expansion of fireclay brick is observed in alkali-rich atmospheres and at temperatures at or below where glazing is expected or where there is prolonged alkali exposure with low concentration of alkali in a furnace atmosphere. It is well known that a new phase called kahophilite (K2O AI2O3 2Si02) will form in fireclay refractories exposed to potash (K2O) vapor. This causes a localized volume expansion of about 15% that can result in cracking and disintegration within the refractory. Potash vapor is particularly expected in combustion atmospheres where wood is the primary fuel and where glazing of ceramic ware is practiced. Alkali resistance tests can be found in standards for refractories. 

C71 -00 Standard Terminology Relating to Refractories. Annual Book of ASTM Standards Vol. 15.01. West Conshohocken, PA American Society for Testing and Materials, 2001. 

Unfortunately, an applicable uniform standard for the sampling and testing refractory gunning materials does not exist so far in Europe. Nevertheless, it is quite common to gun panels or plates. After a subsequent curing time has elapsed, which depends on the specific material, samples are cut out of a panel like that shown in Figure 9. 

Modulus of rupture at ambient temperature was introduced earlier and, as indicated, is useful for quality assurance but gives litde indication of in-service performance, unlike the same test carried out at elevated temperature. The nominal specimen size used in national and international standards for dense and insulating refractories is again 150 mm x 25 mm x 25 mm or similar, and support test span is approximately 125 mm. Specimen temperature is measured by a thermocouple placed centrally underneath the test bar. The specimens are heated to the test temperature at specified rates. Following a dwell for a set period at the test temperature, the samples are loaded to failure at a designated stress rate. The stress rate differs for dense and insulating refractories. 

Various bodies and committees produce test standards for refractory materials. Table 7 summarizes the featured test methods available from British, CEN, ISO, and ASTM bodies. 

The resistance against thermal spalling of fireclay and high alumina brick is indicated in Table 5. No standard test has been adopted for basic brick. Refractories composed of 100% magnesia exhibit poor thermal shock resistance, which is improved by addition of chrome ore. So-called direct bonded basic brick, composed of magnesia and chrome additions, exhibits good thermal shock resistance. 

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. 

The standard ASTM PCE test is relative and used extensively only for alumina—siUca refractories and raw materials (see Table 5). However, the upper service limit is generally several hundred degrees below the nominal PCE temperature because some load is generally appHed to the refractory duriag service. In addition, chemical reactions may occur that alter the composition of the hot face and therefore the softening poiat. The relationship between PCE numbers and temperature is described ia ASTM C24. 

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