More about Phosphate Coatings . . .
Types of Phosphate Coatings
Phosphate coatings are available in three types: Zinc, manganese, and iron phosphate. Each of these coatings have their own unique properties. Zinc and manganese phosphates produce more complex layers of crystals which absorb lubricants more readily. This makes these coatings effective in reducing galling, pick up and scuffing. Iron and zinc phosphates are used as under coatings for steel and other metals prior to painting to enhance paint adhesion and corrosion protection. Manganese phosphate is more resistant to alkalinity and also more suitable for wear applications or where heavy thicknesses are required. All phosphate coatings are good rust preventatives for use during the manufacturing process.
Deposit Thickness of Phosphate Coatings
Phosphate coatings can range from less than 0.1 to over 2 mils in thickness. Industry standards usually express the coating requirements by weight per square meter or milligrams per square foot, rather than in actual thickness of the deposit. Coating weight requirements are generally dependant upon the type of phosphate process involved.
Iron phosphates typically yield lighter coating weights of 30 - 80 mg/SF Zinc phosphates usually yield heavier coatings of 150 - 2500 mg/SF Manganese phosphates are able to yield the heaviest coatings at well over 3500 mg/SF
Applications For Phosphate Coatings
Zinc Phosphate Coatings can be applied by either spray, immersion, or a combination of spray and immersion. Zinc Phosphate coatings can be used in the following applications:
Applications for Zinc Phosphate
- Pulleys
- Springs
- Slides
- Fasteners
Heavy zinc phosphate coatings are typically used to retain rust preventive oils and waxes. Zinc phosphate provides maximum corrosion protection and extended service life. The coatings provide good corrosion protection by bonding the final finish (stain, oil, wax or paint) to the treated material. The treatment produces a uniform coating and is particularly good for corrosion protection of threaded areas and parts that have small holes or recesses.
Manganese Phosphate coatings are most commonly used because of their excellent break-in or wear resistance properties. They prevent metal-to-metal contact between moving parts and they have extremely good oil retentive properties, which increases both lubricity and corrosion protection. Because of this, Manganese phosphate is a common under coating called up by the military for equipment requiring oil or greased parts.
Another common use for Manganese Phosphate is as undercoating prior to dry film lubricants. The manganese phosphate coatings are very effective corrosion protection. Typical parts that are coated with Manganese phosphate are:
Applications for Manganese Phosphate
- Bearings
- Gears
- Internal-combustion parts
- Piston Rings
- Camshafts
- Cylinder Liners
- Transmission Gears
The Manganese Phosphate coatings are usually dark grey in appearance without any post treatments applied. Because nearly all parts coated with Manganese Phosphate are given an oil post treatment, the coatings often appear black due to the oil coating.
Iron Phosphate coatings are primarily used as base coatings for paint in order to increase adhesion to the iron or steel substrate. It can also be used for bonding fabrics, wood, and other materials to these surfaces as well. Iron Phosphate coatings are usually applied as part of the painting process. The coatings are so thin that they can corrode very quickly if a post treatment is not applied. To avoid the need for extra cleaning to remove the post treatment when painting is required, the phosphate coating is built right into the painting production line.
To view the properties and benefits of phosphate coatings click here.
