Parkerizing is a method used on ferrous metals such as wrought iron, cast iron, steel and alloy steel, offering added protection from corrosion. This process is not suitable for non-ferrous metals like a copper, brass, aluminium, and plastic items. It can also be used to improve the wear resistance of materials by adding a surface coating. In the commercial world this process is used to improve the surface roughness, corrosion resistance, wear resistance and protection from indentation and scratches. The process is also known by a number of alternative names such as:-
- Phosphate coating
Description of parkerizing
The apparatus used in the parkerizing process consists of three tanks. They are completely separate from each other as they contain different components which should never be mixed together.
The first tank holds a solvent solution which is prepared for specific material with impurities. This is used to clean the impurities from the work piece surface. In the second tank there is a phosphoric solution also known as the parkerizing solution. This tank also contains a heating element which is used to heat the solution – this process is carried out at a fixed elevated temperature. Clean water is the only substance in the third tank which is flowing/rotating inside the tank at normal speed. This tank is used to clean the parkerizing solution from the surface of the work piece and bring the process to a close.
Detailed steps of parkerizing
A more detailed description of the parkerizing process is as follows:-
- First clean the surface of metallic parts that need to be coated through the parkerizing method. Cleaning is required to remove dirt, grease, oil and other contaminants from the material surface. Usually this preparation process is done by using a soft brush which removes all contaminants from the material surface.
- Parkerizing process starts with a hot water rinse tank where the work piece is immersed for 3-5 minutes. After this the metallic parts are removed from the hot water rinse and submerged in the parkerizing solution. This is carried out for 3-10 minutes at a steady operating temperature of between 190FO and 195FO. This process can be enhanced further by immersing again for 5-10 minutes at a temperature range adjusted to between 68FO and 92FO.
- Clean the parkerized parts by using the flowing water of a rinse tank and a stiff brush to scrub the parts thoroughly – this also ends the parkerizing reaction on the surface. After the part is removed from the solution tank, it is left hanging on a rack above the tank to allow excess solution to drain back into tank. After this action is completed, remove it from rack, inspect it and then move to packing and storing.
There are many different applications for parkerizing which include:-
- The parkerizing process is perhaps best known for use with firearms product – creating additional protection from corrosion and from general wear and tear
- It is also used on automobiles parts to protect unfinished metal parts from rust or corrosion
- This type of process is traditionally used for protection of ferrous metals – especially military arms manufacturing parts
- Parkerizing is used on large a scale by the Marine Corps to protect against corrosion of various equipment
- Aircraft and space vehicle parts often receive enhanced protection against wear and rusting using parkerizing
The parkerizing process can be used on an array of ferrous materials such as:-
- Alloys steel
- Carbon steel
- Cast iron
- Wrought iron
Mechanical design guidelines
In order to ensure the process is carried out on a uniform basis, there are a number of mechanical design guidelines:-
- The thickness of the layer coated during the parkerizing process is limited to 0.01 to 5 micrometres
- Each part cross section is limited to 1 meter square and volume to 1 cubic meter
- Surface finish of the final product can be up to 1 micrometre with lower limit of 0.2 micrometre
- Only use approved salts and chemicals for acidic solution
- The temperature of phosphoric solution should be maintained in the required range – according to the surface of metal and type of metal/alloy.
- For better result completely submerged each work piece in the solution – if not completely submerged then a defective/low quality finish will be the end result
- All geometric shapes, even a threaded body, are possible but sharp corners should be avoided
- For the thickness of the layer the tolerance limit for this process is about 1 to 2 micrometres
- Parkerizing is often used as a generic term for cleaning material surfaces of oil, grease, rust and dirt
- When cleaning metal parts use special soft brushes, cotton wastage and then rinse through warm water
- Once the metallic body has reached the desired colour, remove from the agent and place them in a cold water rinse
- Parkerizing must not be conducted on aluminium parts; it will contaminate the parkerizing solution
Economics of the process
Cost is obviously a major factor and it is fair to say that on the whole parkerizing compares well to the alternative processes.
- Moderate labours skills are required for this process hence the moderate labours costs
- The cost can be relatively high for lower volume runs and is more cost effective for higher volumes and batch production
- A moderate level of safety equipment is used during this process which increases the overall cost
- Initial equipment costs can be relatively high for parkerizing
Advantages of parkerizing
Parkerizing offers a number of major advantages over comparable procedures:-
- Parkerizing protects the metal surface from corrosion
- Provides wear resistance and also increased resistance from scratching
- Chemicals that are used in this process are easily available
- Time consumption for this process is lower compared to other similar processes
- Overall the process can be completed at very low cost
Disadvantages of parkerizing
There are some drawbacks to the parkerizing process which include:-
- Parkerizing is only suitable for ferrous parts and is not suitable for other materials such as plastic
- Personnel protective equipment/high safety practices are required in this process because of the presence of chemical solutions
- Relatively thin layering offers low levels of protection, the thicker the layers the better
- Environmental engineering (McGraw Hill series) by Howard’s peavey.
- US environmental protection agency recommendations.