Types of Finishing Services
Below are descriptions of some of the more common types of material finishing or industrial finishing techniques used in industry today.
What is Painting (Wet Spray)?
Wet-Spray Painting is the process of applying a liquid paint or finish coating to the surface of a part or product (often metal). This traditional method of applying a surface coating functions by passing liquid paint from a canister through a feed line that is pressurized (from a compressor) and then ultimately out of the nozzle of a gun. The process can be compared to that of a can of spray paint in principal, as the functions are essentially the same. Industrial paint sprayers, however, are much more highly controllable and result in more even deposition of paint and overall better finishes. The thickness of paint on the surface is also controllable and varied based on paint flow out of the gun, rate of traverse speed of the gun and amount of layers.
What is Powder Coating?
Powder Coating is a finishing process where a coating of dry powder is applied electrostatically to the surface of a material. Once applied the material is heated or ‘baked’ to melt or cure the powder into a uniform plastic covering on the surface and create a strong bond. In this process it is very important that the part be well cleaned prior to coating to ensure that the powder adheres properly to the surface. Tight control of temperature and time during the bake are critical to ensure good adhesion. The result is a very thick and hard layer on the surface.
Wet-Spray Painting v Powder Coating,
Wet-Spray and Powder Coat, each have their place in industring finishing. Powder coating provides a thicker and harder overall finish than wet-spray, however the thickness is more controllable with wet-spray and much thinner layer thicknesses can be achieved. Because of the nature of the process powder coating typically creates a more uniform surface finish. Powder coating is a more environmentally friendly option, as there are no volatile organic compounds utilized in the process. For smaller runs wet-spray is often a less expensive option, and the overall investment in equipment is much higher with powder coating than wet-spray.
What is Silk Screening?
Silk Screening or Screen Printing is a method of printing where a fine mesh screen is placed over the surface of a part and ink is passed through the screen onto the part. Sections of the screen are blocked off preventing ink from passing in these areas, thus creating a design stencil and allowing for intricate patterns to be created. The screens are typically held in a frame and the ink is then poured into the frame. A squeegee is passed over the screen, ensuring complete coverage of ink on the material below the screen. This process also enables multiple layers and colors to be stacked to create dynamic designs.
What is Metal Plating?
Metal Plating is a process where very thin layers of metal are formed on the surface of a substrate, often a different type of metal. The metal deposition can be performed either through an electroplating process where electric current is used to bond the plating metal to the substrate, or an electroless process where a chemical bonding process is used.
There are several techniques used in electroplating but in general a flow of electric current is used to create opposite charges in the substrate (material to be plated) and plating metal. The two metals, now functioning as a cathode and anode are attracted to each other and gradually a build up of the plating metal is electrically deposited on the substrate.
In electroless plating metal, chemical solutions (in a bath) are used to create a spontaneous chemical reaction when the metal substrate is introduced to the bath. One common form of this style of plating is electroless nickel plating.
The major benefits of metal plating are corrosion resistance and aesthetics, as well as durability and surface hardness, surface friction reduction and enhanced paint adhesion, among others. Some common plating metals include: Zinc, Chrome, Nickel, Copper, Tin, Silver and Gold.
What is Anodization?
Anodization is a technique used for creating a protective outer layer on a metal part through a controlled oxidation process. This electrochemical process works by immersing the electrically charged metal substrate in an electrochemical bath which then stimulates oxygen ions in the solution to react with the surface of the metal. The result is a hardened, wear resistant outer surface, that serves to provide aesthetic improvements amongst other benefits. Only certain non-ferrous metals are suitable for anodization, aluminum being most popular among them. Unlike a plating process or other coatings, the oxidation layer becomes part of the underlying metal, and therefore is not subject to peeling. Because the oxidized surface is porous, anodizing can be paired with additional color/dye processes which enable a wide range of different surface coloring for anodized parts.
What is Passivation?
Passivation is a surface finishing process used mainly for stainless steel to make it more resistant to corrosion. This non-electrolytic process (unlike anodization) makes use of an acid bath which removes iron particles and other contaminants from the surface of the stainless steel. Once removed the higher chromium concentration on the surface reacts with oxygen in the air to create a thin oxide layer (chromium-oxide) on the surface of the material. This in turn makes it more resistant to rust, as rust is iron-oxide, created when iron on the surface reacts with oxygen.
What is Abrasive Grit Blasting?
Abrasive grit blasting, also known synonymously as sandblasting, is a process where a grit media is combined with highly pressurized air or water and released as a stream through a nozzle onto an object in order to both clean and refinish or reshape a material surface. Sandblasting is actually a specific type of abrasive blasting that utilizes sand as the abrasive grit. Other abrasive media can be used to create different surface characteristics and textures, such as glass beads, plastics, metals (often called shot blasting) and walnut shells among many others. The major characteristic differences between media are smoothness and texture of the surface finish, and the amount of material to be removed.
Our Metal Finishing Process and Approach
At AKI we can provide any of the above finishing processes to finished goods that we provide. Many of these services we provide through our in house capabilities and for those that we don’t we rely on our strong group of partners that we work closely with to compliment our capabilities. Whether you have a need for a small volume of simple parts to high volume or highly complex integrated solutions, we can support your needs.
We can support a variety of materials, from steel to stainless steel to aluminum and more. We cover industries from medical, to energy to defense to instrumentation and robotics and more. Have a current or upcoming project? Have a member of our team contact you to discuss.
What are the Advantages of Metal Finishing?
The primary drivers of metal finishing are for surface protection and aesthetics, however many other benefits can be attained through the processes listed above. Improved hardness to surfaces can make components more durable, smoother surfaces can reduce friction enhancing bearing or raceway surfaces, reduced surface porosity can improve cleanability of the components. Left untreated many types of metals can oxidize and corrode leading to eventual failure, loss of performance, and unsightly appearance. For these reasons metal finishing is a post-processing step used in a majority of metal manufacturing projects.