Electroplating for aluminum casting parts

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Usually there is an anode (positively charged electrode), which is the source of the material to be deposited; the electrochemistry which is the medium through which metal ions are exchanged and transferred to the substrate to be coated; and a cathode which is the substrate (the negatively charged electrode) to be coated.

Plating is done in a plating bath which is usually a non-metallic tank (usually plastic). The tank is filled with electrolyte which has the metal, to be plated, in ionic form.

The anode is connected to the positive terminal of the power supply. The anode is usually the metal to be plated (assuming that the metal will corrode in the electrolyte). For ease of operation, the metal is in the form of nuggets and placed in an inert metal basket made of non-corroding metal (such as titanium or stainless steel).

The cathode is the workpiece, the substrate to be plated. This is connected to the negative terminal of the power supply. The power supply is well regulated to minimize ripples as well to deliver a steady predictable current, under varying loads such as those found in plating tanks.

As the current is applied, positive metal ions from the solution are attracted to the negatively charged cathode and deposit on the cathode. As a replenishment for these deposited ions, the metal from the anode is dissolved and goes into the solution and balances the ionic potential.

In the case of materials such as gold, the anode is not sacrificial (gold does not dissolve easily !), but it is made out of material that does not dissolve in the electrolyte, such as titanium. The deposited gold comes out of the solution. Plating is an oxidation-reduction reaction, where one material gives up electrons (gets oxidized) and the other material gains electrons (gets reduced). The anode is the electrode at which oxidation occurs, and the cathode is the electrode at which reduction occurs.

Electroplating is the process of using electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material such as a metal, for example. Electroplating is primarily used for depositing a layer of material to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property. Another application uses electroplating to build up thickness on undersized parts.

Preparing aluminum casting parts for Plating.

The first thing you should be aware of when preparing your parts for plating is that in most cases you will have to polish the metal to a mirror finish. Plating will not cover any of the imperfections in the metal. Whatever imperfections were left in the metal will still be there after the part has been plated. The exception to polishing and buffing parts to a mirror finish is copper plating. The copper plate fills the imperfections.

Thus when aluminum casting part is prepared for plating, it should be polished and buffed to a mirror finish. Although you do not have to start with a 120-grit wheel, the depth or height of the imperfections will determine the grit you use, followed by the finer grits down to a 240-grit set-up polishing wheel or a 320-grit cartridge roll. The buffing procedures depend on the surface quality of the aluminum casting parts you are working with.

Make sure that you keep an ample supply of compound on the sisal, since it may easily create deep scratches in the aluminum casting part if run dry. To make sure you have removed all of the sisal buffing lines, do a crosscut. This should point out any buffing lines you may have missed. There is no need for a color buffing operation when parts will be plated.

chrome plating, chromium plating

Chrome plating or chromium plating is a bright decorative process that can be used on a wide range of parts and equipment.

Chrome plating is a finishing treatment utilizing the electrolytic deposition of chromium. The most common form of chrome plating is the thin, decorative bright chrome, which is typically a 10 micro meter layer over an underlying polished nickel plate. Thicker deposits, up to 1000 micro meter, are called hard chrome and are used in industrial equipment to reduce friction and wear and to restore the dimensions of equipment that has experienced wear.

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