New anti-corrosion surface coating protects vital hydralic components

Joint ‘TriCem 3800’ development by Surface Technology plc and Sun Hydraulics® results in enhanced protection against salt water attack for Ocean Power Delivery’s ‘Pelamis’ wave power machine.

The Armourcote® division of Surface Technology plc and specialist hydraulics components manufacturer Sun Hydraulics® – both based in Coventry – have worked closely together on the development of a new multi-layer anti-corrosion and anti-wear surface coating – ‘TriCem 3800’ – specifically to protect vital hydraulic components used in the innovative ‘Pelamis’ wave power generation system, designed by Edinburgh-based Ocean Power Delivery Ltd.

The 120-metre long Pelamis wave energy converter is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. Power from all the joints is fed down a single umbilical cable to a junction on the seabed. Several devices can be connected together and linked to shore through a single seabed cable.

A 750kW prototype machine has been subjected to intensive testing off Orkney for a number of years, and three production specification machines will soon be commissioned off northern Portugal as part of the world’s first commercial “wave farm”.  When complete, this project will embrace over 30 machines and generate 22.5MW, to meet the demand of some 15,000 Portuguese households.

The Scottish Executive also recently announced a £4 million funding package to support a £10 million Scottish Power Pelamis wave generation project in Orkney, and a 5MW project is planned for the seabed 10 miles off Hayle in Cornwall by E.ON UK and Ocean Prospect, involving seven Pelamis machines.

The hydraulic systems which form the heart of the Pelamis machine required specialist expertise, and Ocean Power Delivery have worked in close co-operation with Sun Hydraulics on the design, configuration and manufacture of the systems employed.  Sun Hydraulics is one of the world’s leading designers and manufacturers of high performance screw-in hydraulic valves and manifolds and specialises in the development of customised products.

Barry Lovell of Sun Hydraulics, said:  “Because of the highly corrosive salt water environment the Pelamis hydraulics have to operate in over many years, we were presented with the challenge of producing custom valve and manifold components with exceptional corrosion resistance and good handling characteristics.

“The large SG iron manifolds, in particular, have several cartridge cavities, ports and tapped holes, are difficult to handle and are potentially vulnerable to corrosion.  We therefore have to protect both the external and internal surfaces with a coating that ensures maximum corrosion resistance. In addition, the coating has to be thin to meet the required tolerances, allow bores to be protected from rust during storage and facilitate final assembly without damaging the surface.”

Sun Hydraulics approached the Armourcote® division of Surface Technology plc at an early development stage for a suitable solution.  The two companies have worked closely together on many surface protection projects and share a customer-focused philosophy based on a strong “problem solving” capability.

This initial approach coincided with the development by Armourcote of a new electrodeposited multi-layer, thin-film coating – ‘TriCem 3800’ – with superior anti-corrosion properties, which met all the necessary criteria and, following rigorous salt-spray and wear tests, was subsequently adopted by Sun Hydraulics for coating the critical Pelamis manifold.

2000+ hours salt spray corrosion resistance

Described by the company as “the next generation in black metal finishing technology”, TriCem 3800 has a smooth, lubricious and hydrophobic, glossy black surface and has been proved to exhibit more than 2000 hours’ salt spray corrosion resistance to aggressive white corrosion.  Film thickness is less than 20 microns.

The coating also has a high bond strength and adheres to a wide range of substrates, including all steel alloys, sintered metal, aluminium, brass and copper, as well as SG iron.  It is available in WEEE/RoHS and ELV compliant versions and contains no cyanides, ammonia or arsenic, so also conforms to current environmental legislation, and is especially suitable for environmentally sensitive applications.

Andrew Courtney, Operations Director at Armourcote, said:  “The zinc plated black finishes used traditionally for hydraulic components provide reasonable surface coverage but do not give the 100% penetration into blind holes and threaded areas that that we can achieve with TriCem 3800, so can leave bare surface areas vulnerable to corrosion attack.

“Added to this, the passivation and plating techniques we have developed for the new coating ensure good throwing power and highly uniform surface coverage – even in deeply threaded areas – important where precise tolerances are essential.”

Armourcote is confident that in most thin-film coating applications, TriCem 3800 can achieve significant production benefits in terms of enhanced surface protection and reduced process times, and will exceed the performance of zinc, zinc alloy and electroless nickel plated finishes in applications where corrosion resistance, high surface durability and the optimum life of components are primary requirements.

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