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Screw manufacturers rely on testing technology from ZwickRoell

ZwickRoell delivers high-capacity testing machines to well-known manufacturers of screws and nuts in force ranges of 400 kN, 600 kN and 1200 kN once again. In addition to highly accurate and repeatable test results, it is crucial that the testing machine and software offer simple and efficient operation.

The testing of screws with threads up to M39 is defined by the ISO 898-1 standard. For threads larger than M39 (Fmax > 1200 kN), ZwickRoell offers proven solutions based on ISO 898-1.

The various test methods specified in the standards are already preprogrammed in the testXpert III testing software. Also, the minimum break forces required by the standard are stored in the testing software and are compared to the test results, enabling efficient and reliable testing. To assist with gripping the specimen in the testing machine, self-aligning tension grips with head mountings and threaded mountings are used, which ensures compliance with the minimum specimen length specified in the standard. For performing strain measurement on screws, the makroXtens extensometer is used. The sensor arms can remain on the specimen until after break whereby an automatic determination of strain at break A is possible.

When combined with the corresponding mandrel and die, the self-aligning tension grip can also be used to perform proof load tests (tensile and compression tests) on nuts according to ISO 898-2. The nut is loaded at the force specified in the standard and maintains it for 15 seconds. The nut is considered to have passed the test if the nut can be twisted off manually from the mandrel.

Hardness testing

In addition to tensile tests, hardness tests are also a part of quality assurance for screws. Johann Maier, a leading German manufacturer of high performance fasteners, relies on a ZHU250CL universal hardness tester for quality assurance. The hardness tester with closed loop control for test load application covers tests according to Vickers, Brinell, and Rockwell methods as standard. Tests on high-performance screws.

Fatigue testing

In addition to static loads, fasteners are generally subjected to frequent cyclic loading, including vibrations. Fatigue tests on screws are most quickly and efficiently performed in a Vibrophore, which can apply cyclic loads with a maximum force of up to 1000 kN in a frequency range up to approx. 285 Hz, using grips designed specifically for screws and other fasteners. The magnetic drive, which generates controlled resonance in the system, including the specimen, requires minimal power during this test, resulting in highly cost-effective testing.