Electroless Nickel Plating
Electroless nickel produces an alloy with truly unusual properties. These properties have made electroless nickel very useful in a broad range of functional applications. Most applications take advantage of the hardness, lubricity, corrosion resistance, electrical and magnetic properties, as well as its ability to cover complex geometries and internal as well as external surfaces.
Some applications of the process are discussed in the following paragraphs, followed by a chart listing applications by industry sector.
APPLICATIONS OF ELECTROLESS NICKEL
Petroleum and Chemical Industries
Petroleum and chemical industries are the largest users of electroless nickel
for corrosion protection. High phosphorus coatings of 25 to 125 μm
(1 to 5 mils) thickness are commonly used to resist corrosion and erosion in
aggressive brines acids and gases. Common applications include valves,
chokes, blow-out preventers, mud pumps, sucker rod and submersible
pumps, pipe, heat exchangers and separators, packers, safety valves,
production tubing and all types of downhole tools.
Medical and Pharmaceutical
Electroless nickel is also used for medical and pharmaceutical equipment because of its superior corrosion and wear resistance. This equipment is often subject to severe abuse, but must remain completely reliable. Electroless nickel provides almost complete resistance to these environments
and frequently allows steel or aluminium to be used instead of more expensive stainless steel.
Typical medical applications are scissors, suture needles, clamps, forceps and hubs for disposable hypodermic needles. In the pharmaceutical industry extruders, sizing screens, pill sorters and filling equipment are common applications.
Printing and Textile Industries
The use of electroless nickel for the cylinders and rolls used in the printing and textile industries has grown greatly during the past several years. The ability of the coating to deposit uniformly allows the cylinder to be machined to size, balanced and plated without subsequent finishing or grinding. Typical coating thicknesses are 25 to 50 μm (1 to 2 mils). The life of the equipment is also greatly extended by the lubricity and wear resistance of electroless nickel. Other common textile applications include thread guides, fibber feeds,
fabric knives, heddles, bobbins, shuttles, rapiers, ratchets, knitting needles and picks.
Aerospace
In the aerospace industry, electroless nickel is used to protect the surface of light metals, such as aluminium, from corrosion and wear. It also enhances the appearance of these metals with a polished, stainless steel look. The coating is used on a variety of aircraft parts, including engine components, structural air frame and landing gear pieces, refuelling systems, compressor blades, and servo valves. Its uniform thickness, and its ability to coat the inside of holes and recesses, makes electroless nickel an ideal coating for welded tanks and complex hydraulic valve and manifold systems.
Firearms
Electroless nickel has gained significant use in commercial and military firearms. A 6 μm (0.25 mils) thick deposit provides an attractive corrosion resistant and long wear surface. These coatings also allow better fit and smoother action of internal parts, reduced leading of the barrel, and improved protection against gas by-products.
Packaging and Handling
With packaging machinery and food handling equipment, electroless nickel is also used because of its excellent wear and corrosion resistant. The coatings provide an attractive finish and help to ensure the cleanliness of the part. Electroless nickel is used to handle such diverse products as sodium hydroxide, food grade acids and fish oils. Its uniform deposit is especially useful for hydraulic cylinders, worm feeds and extruders, shafts, chain belts and other close fitting parts. Common food handling applications include
pneumatic canning machinery, hamburger moulds and grills, bun warmers, baking pans, frying and chocolate moulds.
Mining
Equipment for mining operations is a growing application for electroless nickel coatings. Mining environments are both very corrosive and abrasive. Mine waters are typically acidic and cause high rate of attack of unprotected steel. In addition, the dust produced during mining can result in severe erosion. Electroless nickel coatings have been found to withstand these conditions with little attack. Common applications are hydraulic components, frame, cylinder heads for jetting pumps, pipeline connections and tubing, and mine engine components.
Wood, Pulp and Paper
Wood handling, pulp and paper equipment operate under conditions of severe corrosion and abrasion. The salt and organic acids present in woods can cause high rates of attack on common materials. Electroless nickel coatings provide good protection against these conditions and are presently being used for knife holder cover plates and for abrading plates for woodcutting and chopping machines.
Automotive
Except for plated plastics, components for the automotive industry historically have provided only a limited market for electroless nickel. With the longer lives and greater reliability now required for automotive components, however, more and more applications for the coating are being developed. Some existing applications are pad holders for disc brakes and brake cylinders, synchromesh gears, piston rods, shock absorbers, steering assemblies,
mufflers, exhaust pipes, exhaust manifolds and lock components.
Moulds and Dies
The ability of electroless nickel coatings to provide uniform deposits, even into deep recesses helps to ensure that the finish will replicate the original surface. The natural lubricity of the coating provides smooth flow during injection and quick and easy release of the part. Because of its high hardness at elevated temperatures, electroless nickel minimises erosion and abrasion of moulds and dies and helps to extend their lives. The coating also provides excellent protection against the corrosive fumes produced during moulding such plastics as ABS, PVC, polycarbonate, acrylics and materials with
thermoplastic additives. Similarly, electroless nickel has been found to provide a superior coating for zinc diecast dies and glass moulds.
Electronics
Co-axial connectors, headers, housings and cases, heat sinks, diode cans, shutters, interlocks and memory disks and drums are among the many electronic applications presently plated with electroless nickel. For electronic components the coating is used for its combination of superior corrosion resistance and solderability. Other important considerations with these components are the coatings uniform thickness and its consistent electrical, thermal and physical properties.
Salvage and Repairs
Electroless nickel coatings are very cost effective for salvage and repair. Because of its superior adhesion, uniform and accurately controlled thickness, and excellent wear and corrosion resistance, these coatings are often used to
selectively build up worn or mis-machined parts. Thicknesses of 125 to 250 μm (5 to 10 mils) are common, although repairs with as much as 1000 μm (40 mils) are occasionally made. The cost savings from such repairs are often substantial, since they not only allow mis-machined parts to be used and thus avoid their remanufacture, but this also allows the manufacturing facility to increase the production of new parts and improves productivity.