MISUMI Europa GmbH provides coating processes for components across its comprehensive products range to supplement bronzing, chromium plating, anodisation and nickel galvanisation surface treatment techniques, with advantages for an enormous range of applications.
According to data from the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research, the financial losses due to corrosion represent an estimated four percent of gross national product for all industrialised countries each year.
Sophisticated surface engineering processes can be employed to optimise components for an enormous range of uses. Besides barrier functions designed to increase corrosion resistance, other advantages such as improved wear resistance as well as electrical or optical functions can usually also be exploited.
MISUMI Europa now offers Low Temperature Black Chrome Plating (LTBC) for the following product groups: linear shafts, linear ball bearings, splines and nuts, profiled rail guides, ball-type linear drives, bushings, washers and socket cap screws. The layer thickness of the coatings is in the micro metre range, meaning component geometries are not affected, and the original properties of the material are retained in full.
A black, alloyed surface is created in an electrochemical reaction that takes place below 0°C; part of this surface forms an alloy-like diffusion layer in the boundary area of the metal. In doing so, the base material and the layer become integrated and inseparably bonded with one another. This means that the layer cannot peel or flake, and there is even no wearing effect as a result of mechanical influences. The new surface forms an even film, which provides much more effective and resilient protection against rust formation on the chrome ceramic base than conventional techniques. This improved corrosion prevention and reduced abrasion help to markedly increase the service life of components. Reliable corrosion protection is guaranteed for more than 10 years in most cases; up to 20 years or beyond is possible.
LTBC-coated components such as shafts exhibit an exceptional ratio of hardness to elasticity. Their surfaces are resistant to cracking, and are highly resistant to bending under reversing loads. The average tolerances of the components are not affected for technological purposes. Not only are LTBC-coated components ideal for use in applications with stringent specifications regarding corrosion resistance, but they also satisfy requirements for minimised reflection due to the black colour of their coating.
More than just protection
As in the LTBC process, chemical nickel plating, unlike other coating processes, also produces layer thicknesses in the micro metre range. The layer can be formed on most base materials, including construction steel, cast iron, alloyed or stainless steel, aluminium, copper, brass or bronze. This process is available from MISUMI for the following product groups amongst others: linear ball bearings, bushes, bearing units, discs, struts.
The process requires no external voltage and creates uniform layer thicknesses up to a maximum of 2 µm with no periphery effects. Chemically nickel-plated components from MISUMI not only exhibit an attractive looking finish, but are also highly resistant to corrosion. They are particularly resistant to organic acids, salts, corrosive alkaline liquids, and dilute inorganic acids. The coating protects iron and steel from oxidation and still provides a high degree of surface hardness. The resistance to abrasion exhibited by the chemically formed nickel layer is a vast improvement on that of galvanised nickel plating due to its significantly higher degree of hardness. The coating can be made even harder and its resistance to abrasive wear further increased through tempering. Even if a component is bent or heated after coating, the film remains in place and does not flake off, as is often the case when nickel is deposited by galvanising.
A convincing test result
In order to be able to evaluate the corrosion protection offered by LTBC coating and chemical nickel plating effectively in a comparative test, the housing of a linear ball bearing with round flange underwent salt water spray testing for 168 hours.
Samples of roller bearing steel (1.3505/100Cr6) and stainless steel (1.4125/X105CrMo17) were tested as well as a chemically nickel plated component and a component with an LTBC coating. The standardised test procedure corresponds to the cyclical test set forth in JIS H 8502 (procedure as complex corrosion test) and was conducted on each test piece consecutively under the following conditions:
- Salt water spray test (5% NaCl, 35°C) 2 hours
- Drying (60°C) 4 hours
- Atmospheric humidity (85% rel. hum., 50°C) 2 hours
The appearance of the test pieces was compared with their respective conditions at the start of the test after 72 hours (interim result) and after 168 hours. The result was conclusive: Comparison of the components (Fig. 1: Test chart) clearly indicates that the housing coated via the LTBC method shows hardly any traces of corrosion. The component that was nickel plated chemically only showed slight vulnerability, unlike those produced from roller bearing and stainless steels.
In general, stainless steels that are capable of being tempered (martensitic) tend to corrode more readily than austenitic steels, though the latter cannot be tempered. Accordingly, the roller bearing steel variant with a highly effective coating is the better choice in some cases.
New technological developments are tending to require that component materials meet more stringent specifications, with the result that such materials be better equipped to withstand higher pressures, more extreme temperatures, or aggressive substances. Investment in coated components is repaid in the long term, because efficient corrosion protection helps to lower operating costs.
Users can find a summary of other types of coating in the latest issue of the main MISUMI catalogue, which lists more than 500,000 components. The options for the individual components are shown in the material composition table and are defined using the individually generated product code when the order is placed.
本文转自：China Industry News
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