Abrasion In Refractory
The test procedure sprang from the developmental days of the FCCU vessel. The method attempted to simulate a fine abrasive flowing through a duct at high velocity scratching the refractory.
The exterior photograph shows the feed system for the abrasive, which is 1,000 grams of No. 36 silicon carbide grit. Recall that silicon carbide is a 9, just below diamond in the Mohs scale. A venturi device is used to control the flow so that the test runs for 450 seconds. A 65-psi dry air supply propels the grit against a target. The pressure inside the box is relieved through a simple dust collector.
ASTM C-704 abrasion tester
Inside the box is a glass tube nozzle that directs the silicon carbide grit. The grit is propelled against a target which is a 4” x 4” x 1” thick plate of refractory. If the specimen is a brick piece, the sample is just dried before testing.
If the specimen is a castable, the sample is dried then heated to 1500°F for 5 hours, cooled, and then tested. The initial weight of the specimen and its density is accurately recorded.
The abrasive cuts a round cavity into the specimen. After the test, the final weight of the specimen is recorded, and the volume of the cavity is calculated from the measured density. The results are expressed as cubic centimeters of lost volume. Less resistant materials have high weight loss, so a large number is bad. A small number of abrasion loss is good.
Below left is a photograph of a C-704 test plate of a material that had poor abrasion resistance. You can see the grit cut a hole completely through the specimen.
C-704 Test Plate - Poor Abrasion Resistance
Above right is a C-704 test plate for a 70% alumina brick, our RESCAL 70D. An abrasion loss of about 10 cc’s is typical for many alumina firebricks, this refractory should handle moderate abrasion. I would rate materials with C-704 results between about 8 cc’s and 12 cc’s as moderately good in abrasion resistance. As a further note, abrasion resistance tends to track with the cold crushing strength of refractory, and 70% alumina brick has CCS values of about 6,000 psi to about 7,500 psi.
Not all brick refractories in the same alumina class will have equal abrasion resistance. In the adjacent photo, sample on the left looks well bonded and will probably give good crushing strength and ASTM C-704 result. The sample on the right lacks matrix, which is the fine particles, looks poorly bonded, and gave poor in abrasion resistance in service. So, a key feature for abrasion-resistant refractories is the design of the matrix.
On the left is a test plate for an 80% alumina phosphate-bonded brick, ALUMEX P-85-HS. It has a very low abrasion result at just under 4.0 cc. Phosphate-bonded alumina refractories typically show excellent abrasion resistance because phosphates have high intermolecular bonds and readily react with alumina. ALUMEX P-85-HS has a cold crushing strength of about 14,000 psi. Anything with a C-704 test below 5 cc’s as extremely abrasion-resistant.