Electroplating is a process of coating an object, usually metallic, with one or more relatively thin, tightly adherent layers of some other metal by means of electrochemical process. Electrochemical process involves electrical and chemical energy.
Principles of Electroplating
In electroplating, the object to be plated is immersed in a solution containing dissolved salts of the metal to be deposited. The set up is made up of a cathode and an anode with the object to be plated usually the cathode connected to the negative (-) terminal of a direct current source. To complete the electrical circuit, another metal is connected to the positive (+) terminal and both are immersed in the solution. This metal is made up of the same material as the metal to be deposited and is called the anode. When current is applied, the electrical energy carried is converted to chemical energy by decomposition, a reaction in which the elements are divided into positive and negative charged ions. The movement of positively charged ions towards the cathode surface results to metal deposition.
Preparation of Work Surface
The most important step in the entire plating operation is the surface preparation of metals or the cleaning process. This is because the appearance and acceptance of the article depend primarily on a sound finish achieved with a clean and active substrate. Likewise, improper cleaning process leads to rejects and decreased profitability.
Before the desired coating can be applied to the component, the surface to be plated should be clean and free of all “foreign” matters like heavy scale of oxide films, rust, workshop soils & oils, grease, dirt, and any other material. All these should be removed to ensure strong adherence of electrodeposited metal to the piece. This is achieved through the following methods:
1. Descaling – this is done by polishing, tumbling and blasting with sand, grit or vapor. This is then followed by pickling process where the component is immersed in acid to remove rust, scale, tarnish, light oxides and dirt.
2. Polishing – this is done after the surface has been subjected to grinding or wire brushing. This method alters the surface of the metal through the use of a variety of abrasives: coarse, medium, fine and so on. This operation smoothens the surface of the metal.
3. Buffing – this method further smoothens the metal surface and improves its appearance by the application of very fine abrasives to produce different types of finishes (e. g., satin finish, brushed or butler finish, mirror brightness finish, etc.)
4. Alkaline soak clearing – the component is dipped in hot alkaline solution to remove oil and wax.
5. Electrolytic cleaning- this process is performed on the metal surface prior to electroplating. It is more efficient than soak cleaning and considerably minimizes chemical attack on the metal surface. The component becomes the cathode (direct cleaning) or anode (reverse cleaning) or alternately the cathode and anode in an alkaline solution.
6. Ultrasonic cleaning – the use of high-frequency waves called ultrasonic waves enhance cleaning efficiency of components with complex shapes like jewelry, electronic and other precision parts.
Effects of Improper Cleaning
- Deposits on substrate poorly adhere
- Non-uniform appearance of deposit
- Pitting of deposit
- Unplated areas
- Poor corrosion resistance
- Micro-roughness of deposit
- Contaminated baths
Equipment and Accessories Needed
- Plating Tank
- Anode: e.g., Nickel, Copper, tainless Steel, Silver
- Air Blower/Agitator
- Racks and Jigs
- Copper Bus Bar
- Bench Grinder
- Wire Wheel Brush
- Polishing Wheel
- Buffing Wheel
- Measuring Glassware (Beaker, Graduated Cylinder)
- a. Copper Plating on Low Carbon Steel
- b. Nickel-Chromium Plating on Aluminum And Its Alloy
- c. Gold Plating on Zinc-Based Alloys Including Die Castings
- d. Silver Plating on Copper, Brass and Other Copper-Based Alloys
For more info, contact:
Engr. ROBERT O. DIZON
Assistant Secretary, DOST and OIC, MIRDC
MIRDC Compound, Gen. Santos Ave., Bicutan, Tagig City
E-mail: [email protected]
Telephone: 837-0431 to 38