The wet tensile strength of moulding sands largely depends on their content of active bentonite. Too little bentonite may lead to cracks or spalling in the sand mould, resulting in casting defects, such as scabbing. With the new WJ1 tester, foundrymen can measure the wet tensile strength in next to no time and adjust the bentonite content as required. The innovative system is the world’s first to operate fully electronically, using a calibrated load cell, a digital display for the measured results and, as an option, an interface for data transfer.
The tester measures the tensile force at which a standard test specimen breaks in a tensile test. The specimens are produced by filling sand into a testing tube and pressing in a liftable ring at the top end of the tube. The tube with the specimen is placed into the instrument and heated at approximately 300 °C. The heating is continued until the fracture surface that will result from the imminent breakage will have reached the top rim of the specimen tube. According to practical experience, this will take approximately 35 seconds.
By this heating procedure, a condensation zone is generated in the specimen which in sand casting is a critical parameter for the avoidance of scabbing. Upon reaching the end of the heating time, the ring is automatically pulled upwards causing the specimen to break. The tensile force measured during the breaking process is equal to the wet tensile strength. It is indicated on the digital display in N/m². The entire procedure takes place fully automatically. The operator starts the measurement by the push of a button and can take the readings within a minute. The instrument does not have to be attended as it performs the measurement.
_{(Jung Instruments GmbH)}