Fastener + Fixing Magazine #128

Page 114

TESTING

Premium testing facilities for a safer world Nord-Lock Group has six state of the art technical centres across the world in order to best support its global customer base. The technical centres are complemented with the experience and skills of in-house engineers who perform customised tests and analysis, both at the centres and on-site for ‘real life’ testing. The biggest junker machine in the world

Nord-Lock Group’s technical centre in Mattmar, Sweden, is home to the Super Junker – which Nord-Lock states is the biggest Junker machine in the world. “The Super Junker is the only Junker machine to date that can test bolted connections up to size M48. It is compliant to DIN 25201-4, DIN 65151 and ISO 16130,” explains Nord-Lock. “The Junker test is considered the most severe vibration test for bolted connections. The size of the Junker is not the only impressive thing about it, it was also designed and built by our own engineers – highlighting their immense technical knowledge and bolting expertise.”

Over 1,000 hour of corrosion resistance

The Super Junker is not the only notable testing service developed by Nord-Lock Group. The company reports it was also the first to offer over 1,000 hour of corrosion resistance for all its steel wedge-locking washers, thanks to its modern facilities and specialised technical knowledge. Corrosion is a growing concern across all industries and the Neutral Salt Spray Test (NSST according to ISO 9227) is one of the most established methods to verify corrosion resistance. According to ISO 12944-6:2018, 1,000 hours in a salt spray chamber corresponds to at least C4 High or C5 Medium conditions. This ensures optimum performance over time, even in the most extreme environments.

Customised torque tension testing

Nord-Lock Group’s technical centre in Lyon, France, also offers services that go above and beyond for its customers. The centre’s torque tensile machine is used in accordance with ISO 16047 and measures all the important parameters needed to understand the tightening of a bolted joint. This information allows engineers to predict tightening forces and moment occurring. Deviation can also be statistically determined. Torque tension testing is performed on the customer’s specific application to provide them with the most reliable torque to apply to their specific product. www.nord-lock.com

Electrical contact resistance of bolted joints REC Fastening GmbH, known as an international fastener analysis and testing laboratory, has developed a new innovative measuring system for bolted electrical contacts – together with its sister company REC Engineering GmbH. olted electrical contacts in the high voltage range, and recently the battery technology in electronic vehicles, are coming into focus more and more often due to impending heat generation and performance losses. Until now, it has not been possible to measure the contact resistance continuously in electrical screw connections during the assembly process. The determination was usually carried out by using so-called step tests, which consist of an incremental tightening of the screw while the contact resistance is measured among the steps. Typically, the acquisition of axial clamp load or torque versus contact resistance provides a measurement curve, which is similar to typical broken rational functions. However, with REC Fastening’s new system, it is possible to carry out the synchronous recording of torque, angle of rotation and pre-tensioning force, as well as the contact resistance, during the assembly of a bolt connection.

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The measurement is carried out using the four-wire technology at two defined points on the clamped parts. The measurements are made at high sampling rates of up to 10kHz. This consequently makes it possible to analyse current conducting screw connections close to series production condition. Thanks to the interaction of the measurement, and fastening technology within the REC test beds, even assemblies with defined contact resistances can be set up. Analyses on various components of the high-voltage area, which has been done by REC, showed the influence of surface conditions. They also showed the material suitability in the section of the fastening point. The influence of the clamp load settlement caused by the relaxation or creeping under operating loads (e.g temperature, dynamics) can also be analysed under serial-production conditions. An analysis of the bolted joint enables – before the serial production starts – a punctual controlling with regard to the planned construction and

114 FASTENER + FIXING MAGAZINE ≡ ISSUE 128: MARCH 2021

assembly strategy. The general aim is to keep the contact resistances as low as possible and therefore to make the whole assembly process and the serial production safe. In order to save costs and time (with regard to assembly strategies) the REC Fastening Laboratory with its engineers, who are specialised in fastening technology, offers the validation of fastening joints with the REC µ-Ohm measuring system.


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