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DIN 25201 - Important new standard for testing fasteners By Morten Schiff, Vibrationmaster ApS Not re-testing fastener stock to DIN 25201 could cause product ranges to become obsolete. The following explains the important differences between DIN 25201 and its predecessor, DIN 65151, when conducting Junker Testing of fasteners for self-loosening behaviour.
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new age of fastener testing was heralded in 1969 when Gerhard Junker published his classic paper, ‘New criteria for selfloosening of fasteners under vibration’, in the Transactions of the Society of Automotive Engineers. The Junker Test, as it became known and was later prescribed by the original DIN 65151, tested the self-loosening behaviour of fasteners under transverse loading conditions by vibration testing. It has been a byword of trust, safety and security in the fastener industry. But now that has all changed with the publication in 2010 of the new DIN 25201. Certainly the new DIN standard builds on the original DIN 65151 defined by Junker, but it also takes things much further in setting out exactly how to conduct vibration testing of fasteners. For the first time, the new DIN allows researchers, test engineers and clients worldwide to conduct fastener vibration tests that genuinely compare like with like. This also gives greater confidence to engineers specifying components, because the testing standards of critical fasteners are so much tougher than under DIN 65151. But there are still manufacturers and customers in the fastener industry unaware that the old standard, DIN 65151, has been superseded, and that a much tougher new test regime is in place. They are in danger of losing competitive advantage, and their products could simply drop out of the market. That’s because, unless a re-testing programme is initiated, many fastener products lacking test certification to DIN 25201 will begin to disappear from engineers’ specifications.
Demanding new test requirements While the original DIN 65151 only specified that vibration testing must be conducted using a Junker Test Bench, the new DIN 25201 sets out exactly how the
testing must be completed. It introduces new mandatory requirements to conduct reference and verification tests that compare the self-loosening behaviour of bolted joints, requires the use of a washer during testing and sets out strict test reporting procedures. Vibration testing must be completed using a test block that, when the schematic provided of the test equipment to be used is examined, is to all intents and purposes a Junker Test Bench. A considerable advance on the old DIN test conditions is that the new test must match the likely application and operating conditions of the fastener as closely as possible. The first stage of the test is called the ‘reference test’. The aim is to discover the effective displacement at which the bolt starts to self-loosen, so that the performance of the securing element, or locking mechanism, can be effectively tested. The rest of the testing programme will depend on this initial stage.
A washer meeting specific DIN standards must be included The new DIN spells out in detail that the test fittings should include the bolt and nut in standardised dimensions, and a washer, which is another new feature. The washer is now included to play the part of the surface that would normally support the fastener when used in practice. All test subjects must be new, unused and not previously tested or stressed. They should conform to a manufacturer’s standard product specification so that the results can apply to a range of standard fastener products made of the same materials and to identical specification. The quality standards of the test fittings should be in quality categories A or B. Even the washer’s parameters are detailed. The parameters must be compliant with DIN EN ISO 7093-1, the surface of the washer must be ground,
124 Fastener + Fixing Magazine • Issue 71 September 2011
The new DIN 25201 at a glance • Introduces a comparative assessment of the self-loosening characteristics of bolted joints. • Introduces a reference test to determine at what effective displacement the unsecured bolted joint loses its preload. • Introduces verification tests on a secured bolted joint, which confirms that the preload is not lost at the same effective displacement at which it was lost in the reference test. • Details exact methodology of how the reference and verification tests must be conducted. • Requires a surface washer compliant with DIN EN ISO 7093-1 for hardness/ roughness and DIN EN ISO 4759-3 for plane parallelism and flatness. • Introduces strict reporting requirements. • Specifies the test equipment to be used, such as a Junker Test Bench (as it was with DIN 65151). • Demands that every bolt size must undergo testing —the results of testing one fastener size can no longer be applied to another. • To learn more about the important differences between DIN 25201 and its predecessor, DIN 65151, when conducting Junker Testing of fasteners for self-loosening behaviour, contact the author or visit the Vibrationmaster website at: www.vibrationmaster.com