Hot modulus of rupture

There are some apparatus and methodical limitations in the HMOR measurement. The MOR is defined as the maximum stress a rectangular test piece of specific dimensions can withstand in a three-point bending test until it breaks, expressed in N/mm or MPa. Test piece dimensions are 150 mm x 25 mm x 25 mm. 

According to ASTM C-583-00 [75] and ISO 5013-85 [76], the three-point bending apparatus is used, and the rate of heating below 980 °C should be below 330 °C/h and not exceed 110°/h after 980 °C with exposure at least for 3 h. For castables and chemically bonded materials, the exposure at the temperature of testing should be above 12 h. The HMOR values are calculated according to the equation for the three-point bending test [Eq. (1.11)]. 

The MOR is an important variable in the characterization of refractory materials. Along with other thermophysical properties, the maximum load at high temperatures is an important parameter for the quality control and development of furnace 

The standard method for the reheat change is ASTM Cl 13-14 [77], For heat insulation material, the volume is calculated by directly measuring dimensions, and the time of exposure may be 2 and/or 5 h (it should be noted in the specifications). 

Some producers indicate in the specifications that the time of exposure at max temperature is 6 or 12 h (because the reheat change may not take place within 2 h or may take place but not through the end). Unfired refractory or heat insulation materials may sinter at service, and their dimensions may diminish. An example is unfired vermiculite materials on a sodium silicate binder. For such materials, exposure at the service temperature should be 50 h or even 100 h during testing. Usually, the value for the reheat change according to the procedure just described is like the value obtained in a dilatometer, but sometimes the values might differ a httle. 

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Hot modulus of rupture, HMOR the high-temperature flexural strength bending strength, measured at high temperatures. 

Strengths of refractories are measured as cold compressive strength, cold modulus of rupture, or hot modulus of rupture. Hot modulus of rupture provides the best indication of the performance of a refractory material in use. 

Hot Modulus of Rupture (ASTM C-583). The hot modulus of rupture provides the indication of a refractory material about its flexural strength at elevated temperatures. Since refractories are used at elevated temperatures, the hot modulus of rupture is the true indicator of the suitability and performance of a refractory at high temperatures. Hence, in recent years, the hot modulus of rupture has been prescribed and required by users as the most important test criterion for selection and use of refractories. 

The type denoted as Tabular alumina—comndum matrix is made from coarse supercalcined alumina aggregates and reactive calcined alumina fines to produce a direct bonded microstructure where alumina-to-alumina bonding (corundum-to-comndum) predominates. This provides an obvious increase in hot modulus of rupture (Table 12). The microstmcture of this type of brick is shown in Figure 10. In the lower field, a tabular alumina aggregate particle resides, and it is connected to the matrix through bonds with smaller corundum crystals. 

Figure 14 Effect of spinel content on the hot modulus of rupture of Al203-spinel castables. (From Ref. 43.)...

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. 

To determine the modulus of rupture (breaking force in pounds per square inch) of petroleum wax (ASTM D-2004), a wax slab, 8 x 4 x 0.15 in., is cast over hot water. Small strips, about 3x1 in., are cut from the center of the slab. The strips are placed lengthwise on the support beams of the apparatus, and a breaking beam is placed across the specimen parallel to the support beams. A steadily increasing load is applied by water delivered to a bucket suspended from the breaking beam. The modulus of rupture is calculated from an equation relating the thickness and width of the test specimen to the total weight required to break it. 

Figure 3. Dependence of Homogeneous Particleboard Modulus of Rupture on Hot Press Time for Various Resins.

Tables 2-4 show the effect of the dry/cold. moderate, and humid/hot environments on the tensile properties of the adhesive FM 300K tested at the 10 "/s. lO /s. and lO Vs strain rates, respectively. The values of the yield strength, the yield strain, and the offset obtained with the SED method and the corresponding values from the 0.2 % offset method are shown. The tensile strength, rupture strain, and elastic modulus are provided for information. On average, the time to rupture of the specimens tested at the lO /s, lO /s, and lO Vs strain rates were 4 seconds. 6 minutes, and 15 hours, respectively. The data are listed in ascending order of yield strength. The tensile properties listed in parentheses at the bottom of each cell are averages for replicate specimens. For ease of comparison, these averages are summarized in Table 5.

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