Equipment requirements to conduct vibration testing according to the new DIN 25201

Article originally published in FastenerEurAsia, January/February 2013 – part 2 of 4 of Morten Schiff’s series on the new DIN 25201.

Old-style vibration testing of fasteners to determine self-loosening behavior just needed a basic Junker Test bench and the fastener. In this second of four articles explaining the requirements of the new DIN 25201, Vibrationmaster CEO Morten Schiff explains that test requirements just got a whole lot tougher.

Junker Testing’s new requirements

Vibration testing to determine the self-loosening behavior of fasteners according to the new DIN 25201 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. And a considerable advance on the old DIN 65151 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 program will depend on this initial stage.

A washer meeting specific DIN standards must be included

The new DIN 25201 spells out in detail that the test fittings should include the bolt and nut in standardized 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: it must be compliant with DIN EN ISO 7093-1; the surface of the washer must be ground, with the roughness also complying with DIN 7093-1. Its shape and flatness must comply with DIN EN ISO 4759-3. The washer’s contact surfaces should be coated with molybdenum disulfide paste and its hardness must be in the 200 HV (Vickers Pyramid Number) ranges for strength grades up to 8.8 and 300 HV for strength grades above 8.8. During testing, the washer should be fixed in place and not allowed to turn. All these requirements are new, and much more demanding than previously.

To start the reference test, the fastener must be placed securely in a Junker Test Bench and the displacement varied until the point when it self-loosens after 300 load cycles, plus or minus 100 load cycles at a frequency of 12.5 Hz. Once this initial reference test displacement has been discovered, the fastener should undergo three subsequent reference tests to ensure that the effective displacement is correct and the results are consistent. This means running the same test again, but with fresh fastenings and washers and under exactly the same conditions.

Maintaining consistency is very important, because the test report (to be described in the fourth article in this series) will require the exact test conditions to be precisely recorded. Clearly, just with what we have covered so far, the new DIN 25201 already exceeds the requirements of the old DIN 65151.

Next in the series – Part 3: The new DIN 25201: reference testing and verification testing.

References

• DIN 65151: 2002-08 Dynamic testing of the locking characteristics of fasteners under transverse loading conditions (vibration test), Deutsches Institut für Normung e.V., Berlin 2002
• DIN 25201-4: 2010-03 Annex B Test specification for demonstrating the resistance to self-loosening of secured bolted joints, Deutsches Institut für Normung e.V., Berlin 2010