Refractories compression, resistance

Thermomechanical properties, e.g. softening under load, creep in compression, refractoriness under load and thermal shock resistance. 

According to the data in Table 25.5 and to Eq. (25.6) the compressive strength of filaments of refractory materials such as carbon and silicon carbide have compressive strengths about 10 times as large as those of organic fibres. This would seem to be a serious restriction to the use of organic polymers such as aramids in their application in composites. For most of the applications this restriction is of minor importance, however, since long before ac max is reached, instability in the construction will occur. The resistance of a column or a panel under pressure is proportional to the product of a load coefficient and a material efficiency criterion ... 

From previous considerations it is apparent that this type of refractory canno b( . as heat-resisting as the previous class. However, for first-class materials the soft-( iiing point should not he lower than that of cone 28, about 1,635°C. or 2,975°F. The M rmanont contraction or expansion upon reheating to 1,400°C. is, as a rule, low and should not exceed 0.5 per cent. The porosity may vary between 20-28 per cent, liie rc sist ance to compression at temperatures of 1,350°C. is high and the contraction should in no case exceed 4 per cent at the temperature given and under a load of 40 lb. per s(iuare inch. 

Magnesite bricks show in the cold state a compression strength of approximately 2,000 to 3,000 lb. per square inch. Their resistance to abrasion and impact is not marked owing to the comparatively weak bond. The electrical resistivity of magnesite refractories has been found by Stansfield, MacLeod and McMahon to be 6,200 ohms per cm. at 1,300°C. 420 at 1,400° 55 at 1,500° 30 at 1,550° and 25 at 1,565°. 

A relatively new development is the combination of metals and ceramic in compacts called cermets. The purpose is to combine the high refractoriness, resistance to osidation, electrical insulation, and retention of compression strength on heating—all properties d ceramic bodies—with the ductibility and thermal shock resistance of metals. ... 

SHS compound Refractoriness C C) Heat resistance (thermal cycles) Compression strength (MPa) Wetting angle at1600°C... 

Usually for the estimation of the mechanical properties of the refractories, specialists use cold crushing strength (CCS or compressive strength), (flexural) bending strength (modulus of rapture, MOR), and elastic modulus (or Young s modulus). In the specification of refractory materials that will be subjected to abrasion, erosion, and wear, usually the characteristics of wear resistance are included. In research practice, the hardness, fracture toughness, and some other characteristics may be taken into account. 

Practical considerations and experience tell us that in the metallurgy of Al, refractories are subjected to chemical wear, abrasion, and chemical attack, but they rarely go out of service because of cracking due to overloading. From a scientific point of view, the investigation of refractory brittleness is interesting [71], yet in industrial practice, people are usually satisfied with characteristics such as compression, flexural strength, elastic modulus, and abrasion resistance. The exception is carbon cathode blocks. 

According to the withdrawn standard ASTM C-1100 [115], the determination of the relative resistance of refractories to thermal shock conditions resulting from changing heating and cooling cycles was induced by gas burner and compressed air, while the observation of cracks due to the thermal cycles was visual. 

Figure 2 Collection of test pieces made of unshaped refractories. Description from left to right (Top) Two bricks for measuring thermal conductivity (230 x 114 x 76 mm) Shape A according to EN cup for slag tests (100 x 100 x 100 mm, hole 50 mm in diameter and depth). (Middle) Test piece for measuring abrasion resistance according to ASTM C 704 (114 x 114 x 40 mm) test piece according to special specifications for petrochemical industry (230 x 50 x 50 mm) drilled 50 mm cylinders out of a shape B (one with 12.5 mm hole for determination of Refractoriness Under Load or Creep Under Compression). (Bottom) Shape B according to EN 3 cubes for petrochemical specifications (50 x 50 x 50 mm) Shape C according to EN.

Most lining systems are three-dimensional and therefore experience three-dimensional compressive thermal expansion states. This explains why refractory linings can resist large compressive thermal expansion forces that create stresses beyond the one-dimensional crushing stress. This also explains why the expansion force of the refractory lining system can cause distortions in the steel support structure and also why the refractory will not necessarily fail at high values of compressive stress. 

---