Research and Development
refractoriness under load (RUL) and creep in compression (CIC) of refractory
Refractoriness under load (RUL, according to ISO 1893) is a measure of the deformation behavior of refractory ceramic products subjected to a constant load and increasing temperature. The temperature range in which the softening occurs is not identical with the melting range of the pure raw material; however it must be reliably determined with the RUL 421 to check the use of refractory products in high-temperature applications.
Creep in compression (CIC, according to ISO 3187) refers to the percent of shrinkage of a refractory test piece under a constant load and exposed to a constant high temperature over a long period of time. The creep in compression test is also carried out in the RUL 421 to a maximum temperature of 1700°C. With its sturdy design, the RUL 421 is well suited for these long-running thermal and mechanical loads.
The same test-piece dimensions of 50 mm in diameter and 50 mm in height are used for both the RUL and the CIC tests. For the high-precision differential measuring system for determination of the deformation, the cylindrical test piece has a co-axial bore of 12.5 mm.
Selection and application of the load on the test piece are reproducible and independent of the deformation through use of the hood-type furnace with counterweights.
By reducing the load on the test piece to negligible values (as compared to the surface of the test piece), precise dilatometer measurements on large and even inhomogeneous samples can be carried out in the RUL 421 at temperatures up to 1700°C.
Modulus of Rupture (MOR) of refractory
The modulus of rupture (MOR) is an important variable in the characterization of refractory materials. Determination of the maximum load at high temperatures is a property which, along with other thermophysical properties, is an important parameter for quality control and development of furnace linings. The modulus of rupture is defined as the maximum stress a rectangular test piece of specific dimensions can withstand in a 3-point bending test until it breaks, expressed in N/mm2 or MPa. The International Standard Test Method is described in ISO 5013; test piece dimensions: 150 mm x 25 mm x 25 mm. For determination of the modulus of rupture of refractories up to a temperature of 1500°C and a maximum load of 5000 N (60 N/mm2), NETZSCH offers the model 422 D/3. This model is designed for continuous testing with a 3-point bending device. With optional devices for load and deformation measurement and/or constant deformation rate, additional information about the limits of elasticity and crack propagation in ceramic test pieces can be obtained. The modulus of rupture model 422 E/4 is used to test small single test pieces in accordance with the 4-point load method with a distance between support edges of 40 mm. Inserting the test piece is simplified by the user-friendly split shell furnace (maximum temperature 1450°C). This unit uses a differential measuring system like that used by the for accurate determination of the test piece deformation.
Equipment for the Determination of Hot Modulus of Rupture (HMOR)
Another test normally carried out to determine the mechanical behavior of refractory material is the Hot Modulus of Rupture (HMR), this mechanical parameter is defined as a material’s ability to resist deformation under load, at a given temperature.The HMRrepresents the highest stress experienced within the material at its moment of rupture.
Permanent Linear Change ( PLC)
Permanent Linear Change (PLC) is a factor used to judge the suitability of refractories in ranges of temperature limits. Refractory materials can undergo mineral formation, phase transformation or shrinkage when heated. These processes may result in either volume expansion or reduction. Upon cooling to room temperature, the material will possibly be larger or smaller than the original dimensions. PLC is the property of shaped refractory to retain their original size after undergoing through a given temperature-time treatment and subsequent cooling down to room temperature. It is a crucial parameter for the design of refractory lining.
The EN 993-10 Standard was issued in 1998 and is based on the PRE/R19 elaborated in 1972.
Cold Crushing Strength ( CCS)
The Cold Crushing Strength (CCS) represents the ability of a product to resist failure under compressive load at room temperature. It has an indirect relevance to refractory performance, and is used as one of the indicators of abrasion resistance. The higher the CCS of a material is the greater should be the resistance to abrasion. Refractories with high CCS are also expected to have higher resistance to slag attack. The determination of cold crushing strength (CCS) is also highly important in case of refractory insulating bricks where bricks have to be porous as well as strong. For the measurement of the CCS, according to EN 993-5, a steadily increasing compressive load is applied to the refractory test piece by a compressive machine until the test piece fails. The EN993-5 Standard was issued in 1998 and is based on the PRE/R14 elaborated in 1967.
Bulk density/ open porosity
The bulk density (BD) is the amount of refractory material within a volume (kg/m3). An increase in bulk density of a given refractory increases its volume stability, heat capacity and resistance to slag penetration. The apparent porosity or open porosity (oPo) is the volume of the open pores, into which a liquid can penetrate, as a percentage of the total volume of the refractory. This property is important when the refractory is in contact with molten charge and slag. A low apparent porosity prevents molten material from penetrating into the refractory and therefore enhance it resistance to corrosion.
Several methods can be employed to measure the BD and oPo of materials, the EN 993-1 is a so-called imbibition method. The BD and oPo are there determined by weighing the mass of dry test piece, then its apparent mass when immersed in a liquid which it has been impregnated under vacuum, and then its mass in air while still soaked with liquid.
The EN 993-1 was issued in 1995 and is based on the PRE/R9 and PRE/R10 (PRE Recommendation) elaborate in 1966. The EN 1402-6 was first issued in 1998 and revised in 2003 and is based on the PRE/R28 elaborated in 1977.
Thermal conductivity of insulating refractory materials
Measurements of thermal conductivity with the heat flow meter, laser flash method, hot disk method and hot wire method are compared on two kinds of refractory materials: Insulating Boards and Insulating Fireclay Bricks. Heat losses, humidity, anisotropy and heterogeneity can explain the variation in thermal conductivity values obtained with the different techniques. If they are taken into account in the analysis, discrepancy within 10% can be found. The choice of the technique depends on the investigated material and on the level of information required