A division of R.W.L. Hardchrome and Engineering Pty. Ltd. Maryborough. Queensland. Australia.

Home | Company Profile | Workshop Facilities | Salvageable Parts | Properties & Applications | Photo Gallery | E-mail Us

SULPHAMATE NICKEL Properties and applications of heavy nickel electro-deposits. As a metal nickel has an atomic number of 28 and occurs in group 8 of the periodic arrangement of the elements, after iron and cobalt and above palladium and platinum. It resembles iron in strength and toughness but is more like copper, which follows it with an atomic number of 29, in resistance to oxidation and corrosion. More than 50 % of the nickel produced is normally incorporated in alloys with iron. Nickel steels containing from 0.5 to 10% nickel possess special properties of strength and toughness and are used in great quantities in the manufacture of all types of commodities. Stainless steels containing from 2 to 26% of nickel are resistant to corrosion, tarnish and stain and are used extensively wherever these properties are required in association with strength and toughness. Heat-resistant steels, which also contain from 2 to 26% of nickel, are used to meet the high temperature requirements of furnace and jet-engine parts as well as components for the glass, ceramic, metal and chemical manufacturing industries. Electro-deposited nickel has many of the characteristics of extreme corrosion prevention met with in the pure metal, and it also has a melting point in the range of that of the base metal of 1,450oC. In fact, the only occurrence with nickel electro-deposits when they are subjected to high temperatures, is that the nickel tends to soften to some extent while adhesion improves due to migration of the nickel crystals into the crystal structure of the base metal underneath the deposit. HARDNESS The hardness figure of massive nickel varies from 200 to 220 VPN. However, nickel that has been produced by electro-deposition is usually somewhat harder than this due partly to the finer grain structure of electro-deposited non-metallic materials. It has been shown that the hardness of deposits achieved by electroplating varies in accordance with the plating conditions and the particular solutions being used. Thus, it is normally possible to achieve deposits with a hardness in the range of 400 VPN. The tensile strengths of nickel deposits are not easy to measure although results can be obtained if a stripped deposit is tested in a tensile testing machine designed for handling thin foil. It has been established that nickel deposits applied under normal plating conditions can vary in tensile strength between 40,000 and 65,000 lb per sq. in. (30 and 45 h bar). INTERNAL STRESS The internal stress of a nickel deposit may be tensile or compressive according to the particular plating solution employed, the additions that are made to it and the conditions under which it is operated. In general terms, Watts-type solutions produce deposits with low tensile stress (or even a small compressive stress if the correct addition agents are used), the harder and faster nickel solutions tend to have much higher tensile stressed deposits, while the lowest stresses, either tensile or compressive, are obtained from sulphamate solutions. FRETTING CORROSION When two metal parts are in very close contact, such as in press or interference fits, and the two metal parts are subjected to alternating stresses, then the phenomenon known as fretting corrosion is likely to occur. The occurrence of this is typified by the light brown powder which can often be seen when a ball race or gear wheel is drawn off its shaft. In a series of tests that were carried out to establish the best metals to use to prevent this type of phenomenon, it was found that nickel and steel were the best combinations. Thus, in any application where fretting is to be kept to a minimum, the treatment of either the shaft or the mating part with a nickel deposit will practically cure fretting corrosion. In practice, the shaft which has had a ball race seating salvaged by depositing nickel and finish grinding to suit a new ball race will perform in a superior manner to the original shaft. AS A MEANS OF SALVAGE Undersize engineering components can very often by salvaged by building up with an adherent nickel deposit. The fact that they are undersize can generally be attributed to the heavy use that they have had in service or to an error during their initial manufacture. Nickel is used mainly for salvaging surfaces which are for static fits such as ball-race seatings (where it is superior even to the original steel), gear seatings, flywheel seatings, fixed splines, threads, taper seatings etc. Any part that has been worn in service on a static-fit diameter can normally be salvaged in nickel. The procedure is first to machine the diameter to remove any bad scoring or corrosion, then to build the part up to an oversize by deposition and finally machine to the original limits.