High-temperature system with three furnaces

Tensile tests on metals are one of the most frequent applications in materials testing. The ranges of application of high-quality metals and in particular alloyed steels are extended continuously. For example, these steels are used for applications under mechanical load and at high ambient temperatures. Classical examples are e.g. exhaust valves of combustion engines or turbine blades.
For the manufacturer of such high-quality metals it is a matter of course to test materials at the corresponding temperatures and to prove the required strengths.

The function and procedure of the tensile test at an increased temperature does not differ from the tensile test at room temperature, the only difference being that tensile tests at higher temperatures are carried out in a furnace at a prescribed temperature. The tensile forces required for the specimens are applied via tensile rods led in through the furnace wall. The sensor arms of the extensometer are led into the furnace through a slot for the direct extension measurement. The extensometer itself is located outside the furnace.
A decisive factor for the duration of the tensile test in addition to the standardized test speeds and the temperature dwell time, is the heating and cooling time of the high-temperature furnace. The temperature dwell time is required to ensure the complete heating of the specimen after having reached the test temperature. Following the test, specimens and tools have to cool down before being changed.

Steel manufacturers test their materials during production. Increasing output numbers require shorter test times and specimen throughput times. The duration of the test itself is predefined by the standardized test speeds and the dwell time. To obtain the highest possible specimen throughput rate, specimen feed times have to be reduced to a minimum. By using a rotary rack with three furnaces, Ulm-based manufacturer of testing machines Zwick has found a possibility to reduce the specimen feed times for high-temperature tests.

While one furnace is always positioned in the test axis for the performance of a test, the other furnaces cool down, are re-equipped and heated up. With the electronic temperature control of all three furnaces specimen throughput times can be reduced considerably.
While it is possible to test approx. 4-5 specimens per shift with one furnace at a temperature dwell time of 10min and a test temperature of 900°C, the high-temperature rotary rack of Zwick allows to increase the specimen throughput to approx. 20 specimens per shift during current operation.