Cromagem – Processo, Aplicação, Vantagens

Chrome plating – Process, Application, Advantages

What is chrome plating?

The chrome plating process is a method of applying a thin layer of chromium to a substrate (metal or alloy) through an electroplating procedure.

In simple terms, electroplating is achieved by passing an electrical current between two electrodes that are immersed in an electrolytic bath composed of chromic acid. One of the electrodes will be the substrate to be coated. During the flow of electricity between the two electrodes, chromium atoms are deposited in a layer on the electrode to be coated.

Chromium is a corrosion-resistant metallic substance, while other metals, such as steel, are easily corroded by moist air. Chromium cannot be deposited from solution, only chromic acid (CrO3) and water. There must be one or more acid radicals present in the bath that act as catalysts to cause or assist in the cathodic deposition of chromium. The purity of the chromic acid used is generally not specified or established, but rather the nature. The end of the chromium process will coat the metal surface.

Chrome plating is not difficult to cover, the part has been properly cleaned using the following requirements met:

  • Preparation of the chromic acid (CrO3) solution. (Do not purchase hydrogenated chromic acid crystals (H3CrO4))
  • Bath temperature control (plating solution)
  • Preparation of lead (peroxide) anodes
  • Bath agitation method (bubbles)
  • Plating current density control and duration (controller)
  • Ventilation (for safety)

All that remains is the time requirement – ​​so don't let the apparent complexity of the task discourage you because the results are very worth it indeed.

Chrome plating process steps:

hard chrome Hard chrome process

Chrome plating a component typically includes these steps:

  • Degreaser to remove heavy dirt
  • Manual cleaning to remove all residual traces of dirt and surface impurities
  • Various pre-treatments depending on the substrate
  • Placement in the chrome plating tank, where it is allowed to heat up to the temperature of the solution
  • Application of electroplating current for the time necessary to achieve the desired thickness
  • There are many variations to this process depending on the type of substrate being coated. Different substrates need different etching solutions, such as hydrochloric, hydrofluoric and sulfuric acids. Ferric chloride is also popular for corrosion of nimonic alloys. Sometimes the component enters the plating tank while it is electrically energized.
  • There are two main types of chrome plating:

    Decorative chrome plating.

    This type employs a nickel layer and a chromium layer. Nickel gives the surface of the object a shine and a polished appearance. Once the nickel layer has been deposited, a layer of chromium is added on top of it. The chromium layer helps to increase the corrosion resistance of the material and also improve scratch and wear resistance. Decorative chrome plating generally has a total thickness of less than 0.001 inch.

    Hard chrome plating.

    This type is typically used in industrial environments where aesthetic appeal is not the main concern. Hard chrome plating, although it can improve the corrosion resistance of the material to which it is applied, is primarily used to increase the wear resistance of certain components. Hard chrome plating is commonly applied to various types of steel and is almost always thicker than decorative chrome plating.

    Hard chrome plating (industrial hard chrome plating):

    Hard chrome plating is an electroplating process in which chromium is deposited from a chromic acid solution. The thickness of hard chrome plating varies from 2 to 250 µm. Various types of hard chrome include microcracked chrome, microporous chrome, porous chrome and crack-free chrome. It is essential that microcracked and porous coatings have a minimum thickness of between 80-120 µm to provide adequate corrosion resistance. Microcracked chrome has a Vickers hardness of 800-1000 kg/mm2, while uncracked chrome has a Vickers hardness of 425-700 kg/mm2. The formation of microporous chromium is achieved by a specialized electroplating method that involves the use of inert suspended particles. Porous chrome plating is developed by engraving electroplated chrome. They are designed to retain lubricant, for sliding and rolling applications.

    Chrome plating is used for wear and corrosion resistance, in addition to its tribological characteristics (low friction). However, there are environmental concerns associated with disposing of the galvanizing solution. This has caused many chrome plating users to seek alternative plating methods. One option is to replace hard chrome with high-velocity oxyfuel (HVOF) sprayed coatings of cermet materials such as WC/Co (Tungsten Carbide/Cobalt). HVOF spray-on coatings can offer superior protection against wear and corrosion.

    CHROME PLATING APPLICATIONS
    Hard Chrome can be applied to all types of stainless steel alloys, most ferrous metals and some non-ferrous metals including copper and brass. Contact our application engineers to discuss the feasibility of applying Hard Chrome to other metals such as aluminum.

    Matte black chrome plating Matte black chrome plating

    Hard Chrome improves the performance of:

    • Piston rings and valves
    • Tools and dies
    • Printing of wear roller surfaces
    • Brake discs
    • Automobile engine, powertrain and suspension parts
    • Motor shafts
    • Landing gears and aircraft components
    • Machine parts
    • Medical devices
    • Fasteners
    • Commercial firearm components (not for personal firearms)
    • Gears

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