Mechanical plating & Sherardizing( Mechanical rolling Sherardizing) XZB Composite Mechanical Plating 1. BASIC PRINCIPLE Mechanical plating was developed by Erith Clayton of The Tainton Co. Baltimore, Maryland, in the late 1940's and early 1950's. Since then many important improvements were made to form the todays mechanical plating technology. Mechanical plating operates at room temperature using open tumbling barrels to provide the necessary mixing and tumbling action. Components to be coated in the barrels are tumbled with glass beads, water, surface preparation chemicals, promoter chemicals, and metal powders. The chemical conditioners remove oxides from the coating metal surface. Rotational energy from the barrels cause the glass bead impact media interacting with the small metal particles to uniformly "cold-weld" powdered metallic particles onto the surface of parts, finally to achieve a smooth, uniform and dense plating layer with the required plating thickness. The coating thickness of mechanical deposits can be characterized by their relative thickness. Standard plating builds are typically 8-12 microns, which compete against coatings applied by electro-deposition. The heavier galvanizing process deposits 40-50 micron coatings and competes against the hot dip galvanizing process. Generally, thin coatings of less than 25mm are known as mechanical plating and heavier coatings up to 25mm -110mm as mechanical galvanizing. Mechanical plating is used primarily to give ferrous-based parts coatings of zinc, tin, aluminum and alloys or mixture of these metals in various combinations. Other soft, ductile metals such as brass, copper, lead, gold, silver and indium can also be plated. Mechanical plating has the unique ability to deposit combination coatings, alloys, and layered or sandwich coatings known as composite mechanical plating. Typically deposits are smooth matte to semi-bright in appearance. The brightness can be improved to a degree by a water polish after coating deposition; however, they should be considered functional deposits since the highly leveled and fully bright appearance of an electroplated surface cannot be achieved. 2. TECHNOLOGY SPECIFICATIONS There are many international standards defined mechanical plating processes. Listed below are just some of the many current specifications: American Association of State Highway and Transportation Officials (AASHTO) AASHTO M298-87 "Coatings of Zinc Mechanically Deposited on Iron and Steel" American Society for Testing and Materials (ASTM) ASTM B695-85 "Standard Specification for Coatings of Zinc Mechanically Deposited " ASTM B696-86 "Standard Specification for Coatings of Cadmium Mechanically Deposited" Ford ESF-M1P67-A "Plating, Mechanical - Zinc" ESF-M1P68-A "Plating, Mechanical - (Tin/Cadmium)" General Motors GM4345M and GM4344M "Corrosion Protective Coatings - Zinc Plating" GM4346M "Corrosion Protective Coatings - Cadmium Plating" United States of America MIL-C-81562B "Coatings, Cadmium, Tin-Cadmium and Zinc (Mechanically Deposited)" 3. MAIN BENEFITS Mechanical plating has a number of advantages over conventional plating and coating processes, which are listed as follows: 1) Mechanical deposits can be readily applied onto a diverse range of substrates, including ferrous metals, copper alloys and stainless steels; of particular note is its ability to process die-castings and powder-sintered materials (powder metallurgy). 2) No hydrogen embrittlement and detempering. This ensures that in many applications mechanical plating has become the preferred coating method for hardened fasteners and stressed components. This also eliminates the need for the costly pre-plate and post-plate baking operations as associated with electro-deposition high-strength steels. Since the mechanical process operates at room temperature, it will not detemper heat-treated parts. 3) Mechanical deposits provide a uniform coating thickness in nature, no stickers and with smooth and silver-bright in appearance. The coating thickness distribution is generally better than comparable electroplated and galvanized coatings. This means that threaded parts do not require resizing after processing. The process can plate up to 75 µm and still maintain a uniform deposit. It also has the ability to process flat parts, such as washers, without masking. 4) Mechanically applied zinc deposits offer good corrosion protection. Their performance is comparable to those applied using electro deposition. The general corrosion performance of coating systems measured by the 5% neutral salt spray test, ASTM B117 is shown in Figure 1. 5) Mechanical processing uses relatively simple, non-cyanide, non-toxic chemistry that is consumed during each process cycle. The high process efficiency of more than 90% means that only small zinc levels are present in wastewater, thereby treatment is easy and waste treatment costs are reduced. 6) The mechanical process is cost effective, requiring comparatively little energy. Unlike electro-deposition, it does not require any special jigging or anode configuration. Its economics is especially attractive for deposits above 10-15 microns. Figure 2 offers a greater cost analysis for this comparison. 4. APPLICATIONS OF MECHANICAL PLATING Mechanical plating offers a credible and cost-effective coating alternative to electro deposition and hot dip galvanizing technologies. The coating thickness of less than 25 mm (known as mechanical plating) are widely used in the automotive industry on hardened steel parts as a replacement for electroplating. Coating of 25 mm or greater (known as mechanical galvanizing) can be used as an alternative to hot-dip galvanizing on fasteners and other small components and used for extended outdoor corrosion protection. Parts suitable for mechanical plating include screws, blots, nuts, washers, J-nuts, U-clips, and self-tapping screws. Components suitable for mechanical galvanizing include structural bolts, washers, nuts, nails, pole line hardware, conduit hardware, and chain hardware. Various substrates that are suitable for mechanical plating include high-carbon beat treated spring steel, case hardened steel, leaded steel, high strength low alloy steel, low carbon steel, malleable iron and sintered steel. The process can also coat zinc die-castings, brass, copper, and sintered copper. Generally speaking mechanical plating products are supplied to diverse markets such as the automotive, aerospace and construction industries. 5. QUALITY ASSURANCE The quality of mechanical plating products in XZB Company is required very rigorous at each stage of the production. The specifications on mechanical plating or galvanizing mentioned above are strictly followed by XZB Company. All the tests concerning corrosion and the 5% neutral salt spray resistance are carried out by the 66th station of Tianjin Station of Supervision & Inspection on Product Quality. The monitoring of the thickness of plating coating during production is verified by electromagnetic measuring and in some required situation by metallographic section inspection. 6. PRODUCTION CAPACITY XZB Company is possessed of 18 equipments for mechanical plating or galvanizing production, and the annual productivity can reach 30,000 ton. It is one of the largest mechanical plating production enterprises in China. XZB Company is the group member of Chinese Society for Corrosion and Protection (CSCP) and China Chemical Anti-corrosion Technology Association (CCATA) respectively. XZB Company has paid more attention on the research & development of new technology, new materials and new products for corrosion and protection, and has founded the XZB-MSE Joint Laboratory with the school of materials science and engineering, Tianjin University to perform the research of advanced composite mechanical plating or galvanizing technology. The mechanical products have been sold to many regions and countries in Asia, America, Australia, Europe and Africa etc. In China many companies have contracts with XZB for producing various mechanical plating parts. Such as: Beijing Da Rui Xing nail production Co., Ltd.; Beijing Shi Dan Li metal industry Co., Ltd.; Tianjin Jia Na metals industry Co., Ltd.; Tianjin Zhi Tong hardware products Co., Ltd. etc. Fig.3 Mechanical plating Zn coating on the surface of nails Fig.4 Mechanical plating for various components and nails XZB Mechanical rolling Sherardizing 1. BASIC PRINCIPLE Sherardizing was a method of producing a protective Zn/Fe alloy coating on iron and steel products and therefore giving high protection against corrosion and abrasion. The conventional sherardizing was placed components in a still closed chamber in the presence of a mixture of zinc dust, and the chamber was heated at temperature ranging from 350-500C. Now the process is developed and performed in a mechanical rolling closed container while it is heated in furnace at temperature 420C approximately. With the aiding of mechanical rolling energy, the duration of thermal diffusion process to form the Zn/Fe alloy layer was apparent reduced and the procedure had greatly enhanced the efficiency and quality of production. Recently a relatively new sherardizing technology was developed by the XZB Company, in which the nano powder of rare earth was added in the sherardizing mixture as an activator. It was shown that the sherardizing mixture by adding the nano powder of rare earth had more benefits to improve the original sherardizing process and the performance of surface alloying layer. The new sherardizing process was possessed of the lower consumed energy and higher efficiency as compared with the original sherardizing. Malleable grey iron and cast iron, carbon steels, low alloy and sintered steels are all suitable for sherardizing. Sherardized Coating forms two layers of zinc-iron alloy, a diffused gamma layer which contains 21 to 28% of iron and a compact delta layer which contains 8 to 10%. 2. TECHNOLOGY SPECIFICATIONS There are many international standard defined sherardizing: B.S.4921-1988 Specification for sherardized coatings on iron or steel; B.S.7371-1998 Coatings on metal fasteners: Specification for sherardized coatings; The French standard NF A 91-469. The Dutch standard NEN 5253 et 2694; The Chinese standard JB/T 5067-1999 Sherardizing of iron and steel articles. 3. MAIN BENEFITS The advantages of using sherardizing for the treatment of surfaces of ferrous metals and cast iron, compared to other methods, are incontestable. Main features are listed as follows: 1). The thickness of the coating remains regular and uniform, even on irregular or complex shaped and recessed components, 2). The thickness can be controlled according with the requirements of users, which is ranging from 10-100mm with the error non less than 10%, 3). With excellent corrosion resistance, neutral salt spray resistance test after 1600 h without rusting and guarantee avoiding rusting in 10-15 years (50-70mm), 4). Exceptional adhesion due to the diffused zinc/iron alloy coating, 5). Resistance to abrasion: micro hardness = 471 HV, relatively high degree of wear: resists shocks and scratches, can only be worn off or chemical removed, 6). Resistance to heat corrosion: will oxidize rather than melt and then only at temperatures of above 1000 C. 7). Non-hydrogen embrittlement, lower treatment temperature and non-effects on the mechanical properties of components, non-pollution for the environment, 8). Matt grey textured surface, excellent base of paints and organic coatings as well as adhesives. 4. VARIOUS APPLICATIONS OF SHERARDIZING Sherardizing has been and is, used in many different fields off application: - In Hong-Kong, to protect the cable hooks along the walls of the mass transit railway, - In London, for the metal fittings and fasteners used during the construction of the Channel Tunnel, the London Ring Main and the jubilee Underground, - In the mining industries, - In rail track fittings, - In certain telecommunication systems, etc... The exceptional effectiveness and durability as a treatment anti-corrosion and anti-abrasion, makes it the perfect answer to innumerable applications. Screws and bolts Normal and high resistance ( type 10.9 -12.9), Regularity of the thickness of the coating, identical from the base to the top. Any tapping of the bolts or nuts is unnecessary. Resistant to shocks during the screwing. No weakening. Chains Conservation of the mechanical resistance. No risk of peeling, due to the good adhesive qualities of the coating. Washers and flat components Regularity of the thickness of the coating. The components do not stick to each other during the treatment. Metallic pins and pegs Excellent holding properties of the coating, even after assemblage. Nails and studs The protective coating is not at all altered by the shock of the hammer. The uniformity of the coating, no dripping effect. The dry process is particularly well adapted to these components. Adhesive and collage Rubber and anti-vibration pieces. Cast iron joints Good adherence on cast iron. The building and marine construction industries, the naval and offshore industries, the automobile industries, and civil engineering...The number of industries or areas involved is endless. Fig.1 Examples of sherardizing applications 5. THICKNESS OF THE COATING Sherardizing allows us to obtain a regular and uniform coating even over components that have very complicated forms or areas that are barely accessible (tubes, hollow areas, etc...), The duration of the anti corrosion protection depends mainly on the thickness of the coating: it's possible to apply a layer of 15 and 70 microns, of which a part is diffused in the steel. THE COATINGS ARE CLASSED BY THEIR AVERAGE THICKNESS. Category of the coating NN Localized thickness of the coating (µm) Category 45 45 Category 40 Category 30 30 For outside use. Category 20 Category 15* 15 For inside use and certain outside uses. * Standard sized nuts and bolts in the category 15 can be treated without alteration of their dimensions. 6. QUALITY ASSURANCE The quality assurance of products in XZB Company is very rigorous at each stage of the production. The international specifications on sherardizing mentioned above were strictly follows by XZB Company. All the tests concerning corrosion and salt spray resistance are carried out by the 66th station of Tianjin Station of Supervision & Inspection on Product Quality. The monitoring of the thickness of coating during production is realized by electromagnetic measuring and in some necessary condition by metallographic section inspection. 7. PRODUCTION ABILITY XZB Company is possessed of two-product line of 4.5m and one product line of 2m for sherardizing respectively and can deal with components with length as long as 4.5m, the annual productivity can reach 12,000 ton. It is one of the largest sherardizing enterprises in China. XZB Company is the group member of Chinese Society for Corrosion and Protection (CSCP) and China Chemical Anti-corrosion Technology Association (CCATA) respectively. XZB has paid more attention on the research and development of new technology, new materials and new products for corrosion and protection, and has founded the XZB-MSE Joint Laboratory with the school of materials science and engineering, Tianjin University to perform the research of advanced mechanical rolling thermal diffusion coating technology. Fig. 2 Sherardizing Zn/Fe alloying coating on the surface of bolts For further information please contact: Tianjin XZB Iron & Steel Anti-corrosion Engineering Co., Ltd. Add: 500m North of Yi Xing Bu flyover Bridge, Jing Wei Road, Bei Chen District, Tianjin 300402 MR.Wang huize(Thomaswang) Tel: 86-22-81406277 FAX:86-22-26990104 e-mail:thomaswang@sohu.com