To improve the appearance and product value, decorative plating will be applied on top of the layers consisting of the bottom layer (base plate) spread over mechanically conditioned substrate and the medium layer applied for enhanced corrosion resistance. The following combinations are common for each application:
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| * | Satin nickel and Velours® nickel are the plating process product names. Both have semi-bright satin finish. |
Surface conditioning of substrates is an extremely important process prior to performing surface treatment, including electroplating. The required surface patterns vary from heavy conditioning on pre-plating substrates to light conditioning, where texturing is applied within the plating film.
| This is a conventional method of surface polishing that uses abrasive compounds applied around cloth wheels to polish the material.This polishing method can produce a wide range of surface roughness, from emery buffing using abrasive compounds glued to the buff for rough polishing to a grazing finish applying an oil-based abrasive compound each time. The buffing materials are also available in various forms, such as cotton, e.g. calico, and hemp, thick cardboard, fibers, animal hair, and scratch cloth with metal wires stitched into it. |  |
| In this method, a barrel containing workpieces is rotated to polish workpiece surfaces. This method can be performed in several ways, such as lapping that uses only workpieces or with a chemical solution to facilitate the polishing, and stone polishing that use workpieces with polishing stones and/or aqueous solution. |  |
| Oscillation is applied to the tumbling barrel so that workpieces are polished in areas other than the sliding surfaces of workpieces and polishing stones. Polishing speed of this method is several times faster than that of polishing by tumbling only. |  |
| This is a polishing method using an endless belt with abrasive compounds glued onto it. Polishing tasks can be performed more efficiently because of the broader polishing surface compared to emery buffing. |  |
| This is a method for creating a satin finish on the workpiece surface by spraying metal particles or ceramic powders using pneumatic pressure or centrifugal force. |  |
To add patterns to plating layers, methods, including diamond-cutting and spin texturing, are available. Of course, scratches made by such methods are extremely shallow.
The metal cleaning processes vary depending on the material or size of an item you are going to clean, the purpose of cleaning, or the degree of contamination. In general, the metal cleaning consists of the following processes:
Acid picking used to be a common method of removing serious contamination, such as red rust, mill scales, or scales from heat treatment in the air. Today, the dirt removal methods without using water, such as shot blasting, are becoming more common from the viewpoint of environmental conservation.
For products requiring hairline, satin finish, or matting after surface treatments, prepare the surface base in advance. Create hairlines using emery wheels or wheel brushes in various sizes and prepare a satin finish using sand, grit, or glass beads.
These treatments do not work well if any oily spot exists on the product. Be sure to remove all the grease from the products prior to performing these treatments.
To remove oil-based stains, prepare a solution by dissolving surfactants or chelating agents into an alkaline solution. Soak the product and heat the solution to 40 to 60℃. Stir the liquid or swing the product in the solution to remove dirt.
To remove oxide films generated by metal processing or to eliminate relatively mild contamination of metallic origin, perform acid pickling using 10 to 20% hydrochloric acid or sulfuric acid. Add a dissolution inhibitor to prevent hydrogen embrittlement or excessive dissolution of the basis metal.
Both acid and alkaline solutions are available. In practice, alkaline solutions are more common. Although the bath composition is not so much different from alkaline degreasing, this method can perform more precise cleaning by lifting up dirt from the substrate using hydrogen and oxygen generated from electrolysis of water along with the cleaning process by oxidation-reduction.
Oxidation or reduction occurs on the metal surface depending on whether the product is positively charged or negatively charged. Select an appropriate reaction based on the type of basis metal and the degree of contamination. It is also possible to use both reactions by adopting periodic reverse current electrolysis or pulse electrolysis method that can change the polarity in a cyclic manner.
Perform neutralization if the final process of pretreatment and the next surface treatment alkalify or acidify the products. For example, neutralize and activate the surface using acid picking after electrolytic cleaning that alkalified the product.
Water contains metal ions such as Ca (calcium) and Mg (magnesium). It is well known that the larger amount of such metal ions will hinder foaming and compromise the cleansing effect. In the industrial cleansing, these ions are also detrimental because they turn into insoluble salts after reacting with alkaline materials.
The agents used to increase the cleansing effect by deactivating these metal ions are called sequestering agents. The following types of agents are available:
Polymeric phosphate-based agents are very common. Sodium tripolyphosphate is the most popular item as it is inexpensive and excels in sequestering abilities for Ca and Mg because its alkaline level is perfect for detergent additives. However, it is not so effective for trivalent ions such as ferrous ions. [Table 1] shows sequestering agents of polymeric phosphate.
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This type of agents is also called "chelating sequestering agents" because it transforms metal ions into stable compounds by retrieving metal ions to form a chelating complex (the term "chelate" came from the word meaning "crab's claw").
The following agents are available:
Citric acid, glycolic acid, gluconic acid and their salts. [Table 2] shows an example of the ion sequestering amount.
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Nitrilotriacetic acid, ethylenediaminetetraacetate (EDTA), etc.
Hydroxy-ethylenediamine tetra-acetic acid, for example.
Sequestering agents are added to alkali degreasing, boiling degreaser, and electrolytic cleaning bath and more. They form stable and inactive compounds by quickly reacting with metal ions in the cleaning solution or metal ions of the dirt particles liberated from metal products after cleaning.
In other words, the cleaning by these agents works because the metals that could hinder the cleaning effect in the solution lose their abilities to combine with other ions (metal ions are sequestered).
