1 year ago

MDA Technologies 5/2014

MDA Technologies 5/2014

Safe hydraulics thanks

Safe hydraulics thanks to high-precision tube connection technology Harald Pott High efficiency, varying temperature conditions and frequent load changes – hydraulic systems in stationary and mobile machinery are constantly subjected to stresses. Corrosion-resistant, highprecision tube connection technology is vital to ensure maximum long term functionality. Author: Dr.-Ing. Harald Pott is technical director at VOSS Fluid GmbH in Wipperfürth Small components with big system features. Secure and reliable processes in the creation of hydraulic tube connections are crucial for reliable and economical operation of modern production machinery, across all industries. The desire to achieve better energy-efficiency is a central issue here – but as machine efficiencies increase, the loads acting on the hydraulics and pneumatics. In order to ensure that plant and machinery such as plastics injection moulding machines and huge mining excavators will operate reliably in tough conditions, coupling components meeting leak-tightness requirements and offering durable corrosion protection are required. This means that users not only have to choose suitable, system-compatible coupling components but must also focus their attention on correct, professional assembly and choice of a competent supplier. Voss Fluid GmbH manufactures tube coupling systems and is a system partner of machinery manufacturers all around the world. The company’s product portfolio includes tube couplings for stationary and mobile hydraulic systems, cutting-ring and flared screw couplings, tube-forming systems, flange couplings, valves and accessories. “Superficial” quality with professional depth The surface finish of tube couplings is one of the main quality requirements. This is the prerequisite for long-lasting corrosion protection and highly functional and therefore economical components. Here, Voss Fluid 44 MDA Technologies 5/2014

machine elements uses its proprietary, durable and lasting Voss coat zinc-nickel finish for all tube couplings. This coating meets all requirements of the EU directive on end-of-life motor vehicles, which has prohibited the use of surface coatings containing hexavalent chromium compounds since 2007. In cooperation with independent research institutes and universities such as the Aalen University of Applied Sciences, a corrosion protection system which, compared with similar base materials, is ten times better than conventional zinc coatings has been developed. As opposed to pure zinc surfaces, zinc-nickel does not corrode to produce noticeable white rust, but only forms a light grey discoloration. Nickel release by this coating is 50 times lower than the limit values specified in EC Regulation 1907/2006 for articles intended to come into direct and prolonged contact with the skin. In direct comparison, a Voss coat surface achieves a limit value 2230 times lower than a 2-euro coin. The hard-nickel content of this coating makes the surface not only environmentally safe, but also more resistant to wear under the mechanical stresses which the hydraulic couplings are exposed to during transportation, assembly and everyday use. Voss coat consists of a zinc-nickel base coat which is subsequently passivated before being sealed. These three layers prevent the base material from corroding and thus sustainably improve the quality of the coupling components. The zinc-nickel finish achieves the best corrosion resistance class K5, according to VDMA standard sheet 24576. This class applies to a optimum assembly torques. This has led to distinctly lower torques than those required with other zinc-nickel coatings. Depending on the coupling part a lubricant and partial internal coating is used in some applications, e. g. for union nuts. A competitive edge: in-house electroplating A key factor in achieving such high-quality coatings of tube couplings is Voss Fluid’s in-house electroplating plant, meeting high technological standards as well as conforming to currently valid environmental protection regulations for mixed residential/ commercial areas. It is one of Europe’s most modern plants and is optimally designed for the various internal coating process stages – a degree of specialisation that would have been impossible with an outsourcing arrangement. In comparison to conventional electroplating, this process has been optimised with regard to component damage prevention, layer distribution, visual appearance and coefficients of friction – ensuring qualitative reproducibility of the 6,600 different articles which form the basis for an even greater product spectrum. Mass, size and geometry are just some of the programme parameters – 12 on average – that are stored in the production control system for each individual article. These data are important requirements for achieving perfect coating of the different coupling parts every time. The electroplating current, the length of time the item remains in the bath 01 Larger coupling parts with weights of up to 2.5 kg and easily-damaged external threads are put on the racks manually in order to prevent potential damage during the coating process Dr.-Ing. Harald Pott: “VOSS Fluid GmbH lays the foundation to success with its consulting competence and applications know-how.” surface protection effect which has been proved to prevent red rust development for at least 720 hours and white rust development for at least 360 hours. Under laboratory conditions, a salt-spray test of unassembled parts in accordance with DIN EN ISO 9927 even showed that these resisted corrosion for more than 2,000 hours. A real-life-conditions test using random samples of products from mass production after handling and assembly showed that the base material had not corroded even after 1,000 hours. The coefficients of friction of mating parts of cutting-ring couplings have been continually improved in further development and production processes in order to achieve and the handling processes are specifically and clearly defined for every article. The racks and baskets used to move the coupling parts through the plant are a proprietary development. Larger coupling parts weighing up to 2.5 kg and easilydamaged external threads are put on the racks manually in order to prevent potential damage during the coating process. In the preparation process, the items are cleaned ultra sonically to remove contamination or residues from holes and hollow sections. Smaller components are placed in drums for the coating process. These are filled incrementally via a conveyor belt in order to keep the dropping height to 02 Smaller parts with internal threads are placed in drums for the coating process


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