Refractory Testing

RUL/CIC 421 -Apparatus For Determining Refractoriness Under Load
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.

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 HMOR 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 RUL/CIC 421 for accurate determination of the test piece deformation.

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), i.e. 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 (designated SK xx or ISO xxx) 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 approx. 20°C.



The NETZSCH PCE 428 test bench has a mechanical lever, which positions the base plate for the sample and reference cones in the hood furnace from below; a viewing window in the furnace lid with a radiation filter and surface mirror allow visual determination of the pyrometric cone equivalent. The maximum temperature for this melting point determination is 1700°C (complies with SK 31, ISO 170), in accordance with DIN EN 993-12. The furnace is equipped with a single temperature controller.



The NETZSCH PCE 428 is operated independent of software.