What is Chrome plating – Process , Application , Advantages
What is chrome plating?
The chrome plating process is a method of applying a thin layer of chromium onto a substrate (metal or alloy) through an electroplating procedure.
In simple terms, electroplating is achieved by passing an electric current between two electrodes which are immersed in an electrolyte bath comprising of chromic acid. One of the electrodes will be the substrate which is to be plated. During the flow of electricity between the two electrodes, chromium atoms are deposited in a layer on the electrode to be plated.
Chromium is a metal substance that resistant to corrosive while other metal like steel are easily to corrode affected by wet air. Chromium can’t be deposited from solution only chromic acid (CrO3) and water. There must be present in bath one or more acid radicals which act catalyst to bring about or aid in the cathodic deposition of chromium. The purity of chromic acid used is often not specified or established and yet the nature. The end of the process chrome will coated the surface of metal.
Chrome plating is not difficult covered on the part has been properly cleansed using the following requirements met:
- Preparation of the chromic acid (CrO3) solution..(Do not acquire the hydrogenated ( H3CrO4 ) chromic acid crystals)
- Temperature control of the bath (plating solution)
- Preparation of lead anodes (peroxide)
- Agitation method of the bath (bubbles)
- Plating current density control and duration (controller)
- Ventilation (for safety)
All that remains is the requirement of time – so don’t let the apparent complexity of the task discourages you because the results are very worthwhile, indeed.
Stages of Chrome Plating Process :
Chrome plating a component typically includes these stages:
- Degreasing to remove heavy soiling
- Manual cleaning to remove all residual traces of dirt and surface impurities
- Various pretreatments depending on the substrate
- Placement into the chrome plating vat, where it is allowed to warm to solution temperature
- Application of plating current for the required time to attain the desired thickness
- There are many variations to this process, depending on the type of substrate being plated. Different substrates need different etching solutions, such as hydrochloric, hydrofluoric, and sulfuric acids. Ferric chloride is also popular for the etching of nimonic alloys. Sometimes the component enters the chrome plating vat while electrically live.
There are two main types of chrome plating:
Decorative chrome plating.
This type employs a layer of nickel and a layer of chromium. The nickel gives the surface of the object its shine and its polished look. Once the nickel layer has been deposited, a chromium layer is added on top of it. The chromium layer helps increase the corrosion resistance of the material and also improve the resistance to scratching and wear. Decorative chrome plating usually has a total thickness under 0.001 inch.
Hard chrome plating.
This type is typically used in industrial settings where aesthetic appeal is not the primary concern. Hard chrome plating, while 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 ) :
Hard chrome plating is an electroplating process in which chromium is deposited from a chromic acid solution. Thickness of hard chrome plating ranges from 2 to 250µm. Various types of hard chrome include micro-cracked chromium, micro-porous chromium, porous chromium and crack free chromium. It is essential that the micro-cracked and porous coatings have a minimum thickness between 80-120µm in order to confer adequate corrosion resistance. Micro-cracked chromium has a Vickers hardness of 800-1000 kg/mm2, while crack-free chromium has Vickers hardness between 425-700 kg/mm2. The formation of micro-porous chromium is achieved by a specialised plating method involving the use of inert suspended particles. Porous chrome plating is developed by etching electrodeposited chromium. These are designed to retain lubricant, for sliding and bearing type applications.
Chrome plating is used for wear and corrosion resistance in addition to its tribological (low friction) characteristics. However, there are environmental concerns associated with disposal of the plating solution. This has led to many users of chrome plating seeking alternative coating methods. One option is to replace hard chrome with high velocity oxy-fuel (HVOF) sprayed coatings of cermet materials such as WC/Co (Tungsten Carbide/Cobalt). The HVOF sprayed coatings can offer superior wear and corrosion protection.
APPLICATIONS OF CHROME PLATING
Hard Chrome can be applied to all types of stainless steel alloys, most ferrous metals, and some nonferrous metals including copper and brass. Please contact our application engineers to discuss the feasibility of applying Hard Chrome to other metals such as aluminum.
Hard Chrome improves the performance of:
• Piston rings & valves
• Tools & dies
• Printing wear roll surfaces
• Brake discs
• Auto engine, drive train and suspension parts
• Motor shafts
• Aircraft landing gears and components
• Machinery parts
• Medical devices
• Commercial firearm components (not for personal firearms)
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