What are the main uses of phosphating?
The main uses of phosphating are: Corrosion protection in conjunction with organic coatings, such as paints and polymer films. Facilitation of cold-forming processes, such as wire drawing and tube drawing, or deep drawing. Corrosion protection in conjunction with oils and waxes.
What is phosphating of metals?
Phosphating of metals is one of the most important of surface treatment methods and a number of modern metal finishing procedures would not be possible without it. The main areas of application of phosphating are; * Corrosion protection with no subsequent treatment. Phosphating can be executed using a variety of sequential processes.
What are the different types of phosphating systems?
Then, too, some of the individual stages can be combined, for example, cleaning and phosphating. Of the many phosphating systems which have been proposed, the following are of industrial importance: zinc phosphate, iron phosphate, manganese phosphate.
Is phosphating a conversion coating?
The process of phosphating aluminum and steel parts is typically listed as a conversion coating because the process involves metal removal as part of the reaction. However, it is not like anodizing or black oxide in that the phosphate coating is actually a precipitation reaction. Q. How many types of phosphating are there? 3 Types of Phosphating.
What is the purpose of phosphating?
The main benefits that phosphating provides is strong adhesion and corrosion protection. Typically, phosphate coatings are applied to steel parts because iron in the steel is required for the coating to form....Zinc Phosphate Coating.Phosphate Coating StatisticsTop CoatsOil or Paint2 more rows
Which chemicals is used in phosphating process?
Chemistry of phosphating process The main components of a phosphating solution are: Phosphoric acid (H3PO4); Ions (cations) of bivalent metals: Zn2+, Fe2+, Mn2+; Accelerator - an oxidizing reagent (nitrate, nitrite, peroxide) increasing the coating process rate and reducing the grain size of the deposit.
How is phosphate coating applied?
Phosphate coatings are usually applied to carbon steel, low-alloy steel and cast iron. The coating is formed with a solution of iron, zinc or manganese phosphate salts in phosphoric acid, and is applied either by spraying the solution onto the substrate or by immersing the substrate into the solution.
What is the meaning of phosphate coating?
Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron, zinc, or manganese phosphates, to achieve corrosion resistance, lubrication, or as a foundation for subsequent coatings or painting. It is one of the most common types of conversion coating.
How do you make phosphating solution?
Preparation method: first with 15kg water, 10kg zinc oxide is completely dissolved in acid-resistant container, add 20kg85% phosphoric acid after being sufficiently stirred for and continue stirring, add 0.7kg citric acid after fully reaction, 13kg zinc nitrate, 0.2kg nickel nitrate, 9kg manganese nitrate, 0.3kg ...
How do you remove phosphate coating?
Traditional phosphate removal methods rely on chemical strippers like hydrochloric and sulfuric acid. Other strongly alkaline and chelated solutions are just as dangerous. If you want to get rid of chemicals during phosphate coating removal, laser cleaning may be the solution you're looking for.
Does phosphate coating prevent rust?
All phosphates are fairly porous, so they do not provide complete protection from rust. They serve primarily to provide a stable base for an additional process or coating. For additional protection from corrosion, oil is often applied over a phosphate coating.
What color is phosphate coating?
gray to blackPhosphate coating is the crystalline coating applied on the ferrous metals to inhibit corrosion. The phosphate coating lends a gray to black appearance of the surface.
How thick is phosphate coating?
For most indoor applications a 50 micron coating thickness (2 mils) is adequate as long as it will hide the metal. For outdoor applications a higher film thickness is generally recommended (75 micron or more, 3 mils).
Why is phosphating done before powder coating?
Why is phosphating done? The process of Phosphate coating is employed for the purpose of pretreatment prior to coating or painting, increasing corrosion protection and improving friction properties of sliding components. Metal coating offers both zinc phosphate and manganese phosphate coating.
How does phosphate prevent corrosion?
The phosphate process achieves a chemical alteration of the surface of a part, with the intent of creating corrosion resistance. The phosphate process for metal actually creates a new substance through a chemical reaction.
What is a phosphate wash?
Phosphating or phosphate conversion coating is a manufacturing process and chemical treatment in which an acidic bath solution reacts with the metal part or weldment.
What is phosphating metal?
Phosphating of metals is one of the most important of surface treatment methods and a number of modern metal finishing procedures would not be possible without it. The main areas of application of phosphating are;
What is phosphate coating?
Phosphate coating can be defined as the process in which the phosphate coating solution forms an insoluble phosphate layer on a metal surface by dipping, spraying or any other method. For the formation of this type of coating the content of the prepared solution must contain hydrogen ion (H + ), phosphate anion ...
How does metal pretreatment affect coating weight?
The effect of metal pretreatment on coating weight depends on the phosphating temperature. At high bath temperatures, the phosphate crystals form on the blasted steel are largely of uniform size and very fine. On samples which have only been degreased, very large and very small crystals co-exists, whereas on blasted steel, there is much more uniform coverage of very small crystals.
Why do you rinse between the steps of a metal processing?
There is normally a rinse between the individual processing steps in order to remove the solution layer from the metal surface and to avoid carry-over of this as an impurity to the subsequent stage. According to circumstances, the processing sequence may be longer or shorter. Thus, for example, pickling can be omitted if no corrosion products are present on the metal surface. Then, too, some of the individual stages can be combined, for example, cleaning and phosphating.
Can steel be phosphated?
To suggest that a large range of steels are capable of being phosphated is not to imply that, in all cases, these are suitable for industrial applications. Thus it has been found that deep- drawn steel, as widely used in automobile industry, can be phosphated, painted and subjected to accelerated corrosion testing.
Can phosphate be formed on clean surfaces?
Phosphate coatings which adhere well to the basis metal and which, so far as possible , cover it completely, can only be formed on clean surfaces which are free from rust, scale, soot and other corrosion products.
Does pretreatment affect phosphate coating?
The nature of the pretreatment steps used before the phosphating itself, e.g., in the cleaning, can considerably affect the growth rate of the phosphate coating, its thickness and the crystal size. These effects can be chemical or mechanical and sometimes both together. The effect of metal pretreatment on coating weight depends on ...
What is phosphating process?
Q. What Is the phosphating Process? Phosphating is the process of converting a steel surface to iron phosphate. This is mostly used as a pretreatment method in conjunction with another method of corrosion protection.
What are the applications of phosphate?
What are the main applications of phosphating? The main applications of phosphating are: Corrosion protection in conjunction with organic coatings, such as paints and polymer films. Facilitation of cold-forming processes, such as wire drawing and tube drawing, or deep drawing.
What is manganese phosphate used for?
Manganese Phosphate: Used primarily on friction and bearing surfaces to prevent meal-to-metal contact and reduce wear. This coating is also used as a base for dry film lubricants. The following is a typical phosphating procedure: Cleaning the surface, Rinsing, Surface activation, Phosphating, Rinsing, Neutralizing rinse (optional), and Drying.
Why is phosphate coating used?
Why is phosphating done? The process of Phosphate coating is employed for the purpose of pretreatment prior to coating or painting, increasing corrosion protection and improving friction properties of sliding components . Metal coating offers both zinc phosphate and manganese phosphate coating.
What is phosphorating in metals?
3 Types of Phosphating. Phosphating is a conversion coating applied to Steel and Iron components. In its basic form, the process involves immersing a component in a dilute solution, which converts the surface of the metal into a layer of microscopic Phosphate Crystals.
Is phosphate a precipitation reaction?
However, it is not like anodizing or black oxide in that the phosphate coating is actually a precipitation reaction.
What is phosphate coating?
Phosphate coatings are usually applied to carbon steel, low-alloy steel and cast iron. The coating is formed with a solution of iron, zinc or manganese phosphate salts in phosphoric acid, and is applied by either spraying the solution onto the substrate, or immersing the substrate into the solution. When steel or iron parts are placed in the ...
What is the most common phosphate chemistry?
The most common phosphating chemistries are iron phosphate, zinc phosphate, and manganese phosphate. There are also other phosphating chemistries such as Plaforizing™ which are non-traditional in their chemistry and application since they are single step and typically an organo-phosphate that react with both the organic contaminants and the metal surface.
What temperature should phosphate be?
Some chemistries have been developed that work well at room temperature. In general, there has been a trend from high temperatures, 90 F to 200 F, to much lower temperatures, 70 F to 140 F, resulting in energy savings.
What happens when iron is placed in phosphoric acid?
When steel or iron parts are placed in the phosphoric acid, this causes a metal reaction which locally depletes the hydronium (H3O+) ions, raises the pH, and causes the dissolved salt to fall out of the solution and precipitate on the surface. The acid and metal reaction also creates iron phosphate, which may be deposited.
Does phosphate help with rust?
In rust creep testing, the rust creep is reduced when phosphate is present under the paint.
Is phosphate a stand alone coating?
layer or powder coat layer compared to no conversion layer under the organic coating. Phosphate can be used as a stand-alone coating for other purpose s such as lubricity in parts forming but the other functions are beyond the scope of this report.
What is the process of phosphate bath?
Process. The process takes advantage of the low solubility of phosphates at medium or high pH. The bath is a solution of phosphoric acid, containing the desired iron, zinc or manganese cations and other additives. The acid reacts with the iron metal producing hydrogen and iron cations: Fe + 2 H.
What is phosphate conversion coating?
Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron, zinc, or manganese phosphates, to achieve corrosion resistance, lubrication, or as a foundation for subsequent coatings or painting. It is one of the most common types of conversion coating.
How to make phosphate coating?
A phosphate coating is usually obtained by applying to the steel part a dilute solution of phosphoric acid, possibly with soluble iron, zinc, and/or manganese salts. The solution may be applied by sponging, spraying, or immersion. Phosphate conversion coatings can also be used on aluminium, zinc, cadmium, silver and tin.
What are the different types of phosphate coatings?
Types. The main types of phosphate coatings are manganese, iron, and zinc. Manganese phosphate coatings are used both for corrosion resistance and lubricity and are applied only by immersion. Iron phosphate coatings are typically used as a base for further coatings or painting and are applied by immersion or by spraying.
What happens when you put zinc phosphate in a bath?
When depositing zinc phosphate or manganese phosphate the additional iron phosphate may be an undesired impurity. The bath often includes an oxidizer, such as sodium nitrite, to consume the hydrogen gas — which otherwise would form a layer of tiny bubbles over the surface, slowing down the reaction.
What is the best coating for phosphate?
The performance of a phosphate coating depends on its crystal structure as well as its thickness. A microcrystalline structure is usually best for corrosion resistance or subsequent painting. A coarse grain structure impregnated with oil may be best for wear resistance. These factors can be controlled by varying the bath concentration, composition, temperature, and time.
Can zinc phosphate be used as a lubricant?
While a zinc phosphate coating by itself is somewhat abrasive, it can be turned into a lubricating layer for cold forming operations by treatment with sodium stearate ( soap ). The soap reacts with the phosphate crystals forming a very thin insoluble and hydrophobic zinc stearate layer, that helps to hold the unreacted sodium stearate even under extreme deformation of the part, such as in wire drawing.
What is phosphating used for?
The most common use for phosphating is pretreatment of parts before they enter a powder coating system.
What are the controls for phosphate conversion?
The most important process controls in phosphate conversion coating are: Time – The longer the contact time, the more time to chemically react. The process must be long enough to allow the chemistry to form a uniform coating. Temperature – Chemistries typically become more aggressive at elevated temperatures.
What is phosphate coating?
Phosphating or phosphate conversion coating is a manufacturing process in which an acidic bath solution reacts with the metal part or weldment and combines with or causes a chemical conversion that transforms the surface of the metal part into a protective layer, which is uniform and inert to the environment.
What is the most important stage of powder coating?
The most important stage of powder coating phosphate wash is properly preparing the parts by cleaning residues left from prior processes like welding, grinding, and drawing residues such as machining oils, grease, dust, and rust and then iron phosphate coa ting. This is commonly achieved in a multistage alkaline cleaning, rinsing, phosphating, and rinsing immersion tanks or spraying system. Iron phosphate can sometimes combine washing/cleaning with phosphating depending on initial part cleanliness.
What is Chromium Phosphate used for?
Chromium phosphate. Chromium phosphate is most commonly used for aluminum alloy based parts. While this process is effective, like zinc phosphate, it uses heavy metals which need to be recovered for environmentally friendly disposal.
What is the effect of pH on coating?
Concentration and pH – The more acid in concentration accelerates the coating process and can result in a heavier total weight of the coating .
Where does zinc phosphate start forming?
Zinc phosphate crystals start forming at anodic surfaces on the part surface and stop forming when the part surface area is consumed, ie. they hit another crystal.
What happens when a phosphorating process tank is emptied?
When this happens the process tanks will need to be emptied and the solids will need to be shoveled out. This is costly as the entire tank needs to be drained and sent to wastewater treatment or hauled away. It is also a downtime that leads to a lot of labor.
What is phosphate coating?
This application is applied to steel that creates a thin layer of iron, zinc, or manganese phosphates to improve corrosion resistance and promotes better paint bonding. While many manufacturers use phosphate conversion coating, it also creates a few challenges. Met-Chem specializes in keeping process tanks clean, treating this wastewater through evaporation, a batch waste treatment system, or a continuous flow treatment system.
What is evaporation system?
Many companies are turning to evaporation systems to treat phosphating wastewater. An Evaporation System can reduce your need to haul away Expensive Wastewater. The equipment would Pay for Itself in a manner of years. Met-Chem offers two types of evaporation, Thermal and Atmospheric.
Process Bath Materials
Since the corrosive effects of alkaline degreasing solutions are not much, it is suitable for the bath material to be made of standard steel with protective coating or a hard plastic material such as polypropylene.
Water Quality
The quality of the water used in the process baths and rinsing baths in the phosphating lines has a certain importance. Generally; It is suitable to use mains water in degreasing, acid cleaning, activation, phosphate coating and post treatment baths because it is economical.
Phosphate Sludge Formation and Its Cleaning
The +2 valence iron (Fe +2 ), which is formed as a result of the etching reaction in the phosphate coating solution, is converted to +3 valence (Fe +3) thanks to oxidizing additives. It is mainly iron III phosphate (FePO 4) which is called as phosphate sludge.
What is zinc phosphate used for?
In most operations where the corrosion resistance of finished workpieces must be especially high, conversion coatings are applied using zinc phosphate. This approach is widely used in the wire drawing works, automotive industry and in certain sectors of the appliance and electronics industries. Similarly, zinc phosphating is often specified by the armed services, especially for equipment that may be exposed to severe environments. Moreover, many operations using electrocoating or powder coatings, particularly when a one-coat finish will be exposed to the weather, pretreat workpieces with zinc phosphate.
How many stages of phosphating are there in a zinc plant?
Zinc phosphating lines are normally based on 5- stage to 6-stage plants. They differ little in the pre-phosphating stages. The 5-stage type includes a rinse between cleaning and phosphating steps. In the case of the 6-stage type, there are either two cleaning and one rinse stages or one cleaning and two rinsing steps.
How long does it take to dry phosphated paint?
Circulating air ovens, operating at 120-180 °C with a drying time of 5-15 minutes are typically used for such drying.
What is the pH of a cleaning solution?
Cleaning is usually based on alkaline or strongly alkaline solutions in the concentration range 1-5%, and pH 10-13. Compared to the cleaners used in the spray mode, the cleaners used for immersion contain larger amounts of silicate and sodium hydroxide.
Does zinc phosphate need activation?
Activation is mandatory for zinc phosphating and in its absence, because of the relatively high pH values involved, a thick and coarse-crystalline coating is formed which is quite unsuited of subsequent painting. Conditions for the rinse, post-rinse and drying stages differ little from spray phosphating. SPRAY PROCESS.
Overview
Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron, zinc, or manganese phosphates, to achieve corrosion resistance, lubrication, or as a foundation for subsequent coatings or painting. It is one of the most common types of conversion coating. The process is also called phosphate coating, phosphatization, phosphatizing, or phosphating. It is also known by the trade name Parkerizing, especially when a…
Types
The main types of phosphate coatings are manganese, iron, and zinc.
• Manganese phosphate coatings are used both for corrosion resistance and lubricity and are applied only by immersion.
• Iron phosphate coatings are typically used as a base for further coatings or painting and are applied by immersion or by spraying.
Process
The process takes advantage of the low solubility of phosphates at medium or high pH. The bath is a solution of phosphoric acid (H3PO4), containing the desired iron, zinc or manganese cations and other additives. The acid reacts with the iron metal producing hydrogen and iron cations:
Fe + 2 H 3O → Fe + H 2 + 2 H 2O
The reaction consuming protons raises the pH of the solution in the immediate vicinity of the su…
Parkerizing
Parkerizing is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of a chemical phosphate conversion coating. Parkerizing is usually considered to be an improved zinc or manganese phosphating process, and not to be an improved iron phosphating process, although some use the term parkerizing as a generic ter…
Uses
Phosphate coatings are also commonly used as an effective surface preparation for further coating and/or painting, providing excellent adhesion and electric isolation.
Phosphate coatings are often used to protect steel parts against rusting and other types of corrosion. However, they are somewhat porous, so this use requires impregnating the coating with oil, paint, or some other sealing substance. The result is a tightly adhering dielectric (electric…
See also
• Chromate conversion coating
• Iron pillar of Delhi
Sources
• MIL-HDBK-205, Phosphate & Black Oxide Coating of Ferrous Metals: a standard overview on phosphate and black oxide (bluing) coatings
• Budinski, Kenneth G. (1988), Surface Engineering for Wear Resistance, Englewood Cliffs, New Jersey: Prentice Hall, p. 48
• Brimi, Marjorie A. (1965), Electrofinishing, New York, New York: American Elsevier Publishing Company, Inc., pp. 62–63.
External links
• Henkel Surface Technologies—Current owner of Parco-Lubrite (a manganese phosphating process) and other Parkerizing rust-prevention coatings. (Parco is a registered trademark of Henkel Surface Technologies.)
• Coral Chemical Company—Current owner of Coral Eco Treat (vanadium conversion coating process)