Metal spraying is the process that uses compressed air or inert gas to spray molten, corrosion-resistant metal onto a metal surface to form a protective coating.
What is Metal Spraying?
Metal spraying, also called metallization, is a method of coating metal surfaces with thin films of melted atomized metals. As they are sprayed onto the metal surface, ionic reactions create a strong attractive force to hold the metal film to the base metal.
In metal spraying, the coating material is melted and atomized in a special spray sink or spray gun and sprayed onto the base material. Oxyacetylene flames are generally used, but other gases are sometimes used. A coated wire is automatically fed through a flame core, and as the wire is melted it atomizes and sprayed onto the base material by a compressed airflow. This atomizing process can be used with almost any metal that can be made into wire. Another type of spray gun sprays powdered material through a flame. The advantage of this method is that it can be used with materials other than metals, such as metal-ceramic composites, oxides, and cemented carbides.
Preparations Before Metal Spraying:
Since the bond between the coating material obtained by metallization and the base material is purely mechanical, the base material must be properly pretreated. To obtain a good mechanical bond, the substrate surface must be clean and free of oil.
A most common method of surface preparation is sandblasting. The grit is sharp enough to produce a truly rough surface. For cylindrical surfaces that can be turned on a lathe, it is effective to machine a very coarse thread and then roll it lightly with a roller cutter. Another improvement that can be used for flat surfaces is to use a grooving knife to cut a series of parallel grooves on the surface and then use a knurling knife to cut facets between the grooves. If the plated surface requires subsequent machining, the substrate surface should be prepared by roughing or grooving.
What are the Applications of Metal Spraying?
Metallization has many important uses in product design. Protective coatings such as zinc and aluminum are sprayed onto steel surfaces for corrosion resistance. Because metallization can metalize almost any metal or non-metallic surface, it provides a method of coating a conductive surface onto a poorly conducting or non-conducting surface. Copper or silver is often sprayed onto glass or plastic to create a conducting surface. After metallization, items can be treated in a variety of ways, such as by polishing or brushing, or can be left in the sputtered state. Metallization is often used as a decorative solution in the manufacturing and construction industries.
The Spray Coating Process:
- Degreasing treatment: clean with acetone or alcohol.
- Surface treatment: corona discharge treatment, ultraviolet irradiation treatment, etc.
- Bottom surface coating/hardening treatment: The bottom surface coating process can improve adhesion between the surface and the spray coating. Bottom surface coating and hardening treatments are only preparations before coating. There are used to prepare base materials that have poor adhesion to coatings such as steel.
- Sputtering process: Materials used for electrodes can be Al, SUS304, etc.
What Metal Spraying Processes are there?
Vacuum metal spraying process:
The vacuum coating process is a physical method of plating metal onto a substrate. Coating takes place in a vacuum chamber, where the metal is melted and becomes gaseous when it reaches its vaporization point. The gaseous molecules then condense on the target substrate, forming a relatively uniform coating. The vacuum system consists of a sealed chamber where the coating process takes place and multiple pumps outside the enclosure that pump air out to reach the vacuum required for the process. A power source supplies high voltage electricity to an electrode connected to a series of insulators containing tungsten filaments that evaporate the metal. There are eight to ten major steps in the vacuum metallization process. Generally, a spray coating takes 2 to 3 hours to complete.
Substrates suitable for vacuum metallization include metals (tin, steel, aluminum, etc.), plastics (ABS, polypropylene, styrene, etc.), and glass. To obtain a perfect, flawless coating, the raw substrate surface must be free of contamination such as release agents, fingerprints, dirt, dust, oil, and grease.
Nano spraying, or nano-sputtering, is a process in which a silver ammonia solution is sprayed on the surface of a workpiece with a spray gun forming a silver mirror surface. A protective solvent can be added to the surface to form different colors. Advantages of the nano-sputtering electroplating process are that nano-sprayed products have better adhesion, impact resistance, corrosion resistance, water resistance, weather resistance, wear resistance, and scratch resistance, and have good anti-rust performance and excellent hardness. Compared with traditional electroplating, it is less polluting to the environment.
Nano spraying is can be used for the surface treatment of fine precision products as well as for large items such as automobiles and large electrical appliances. They are also be used for surface decoration and protection spraying in many other industries.