Passivation Equipment

Passivation System using Nitric or Citric Acid

New England Sales offers sales and service on manual, semi, or fully automated passivation systems.   We supply systems which use Nitric Acid or Citric Acid.    We service the northeast including the 6 New England states (we are based in Boston, MA area) and NY.

Stainless steel derives its corrosion resistant properties from its chromium content. The chromium, in the presence of air, especially oxygen, forms a thin, hard adherent film of chromium oxide on the surface of the alloy. It is this chromic oxide layer that is inert (passive) to the surrounding environment and gives stainless steel its corrosion resistant properties.

Passivation, according the ASTM A380, is "the removal of exogenous iron or iron compounds from the surface of stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination, but will not significantly affect the stainless steel itself." ASTM A380 also describes passivation as "the chemical treatment of stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film."

Typically, passivation is performed with a nitric acid bath from 20 to 50% by volume. Temperatures range from ambient to 160 degrees F. Immersion times can be as long as two hours and even include the addition of a chromate salt. Nitric acid is by far the most accepted means by which passivation is performed.


The following Case History is of a Nitric Acid Passivation System for precision aerospace components. The system consists of five stages comprising five RAMCO MK Immersion Washers. The line runs from right to left. Ventilation ductwork is provided for all wet stages. Roller conveyor sections are on each platform and in between stages as required to provide smooth lateral transfer of baskets from stage to stage. The materials of construction include 304 stainless steel , 316L stainless steel, Alloy 20Cb-3 heating elements and Nema 4X control panels (see below).


 

THE PROCESS:

WASH - The parts are batch loaded into 18L x 18W x 6H stainless steel baskets and placed on the first transport elevator in Stage One. Using a high alkaline detergent at 170 degrees F the parts are washed using vertical agitation.

RINSE - The basket is laterally transferred over special platform roller conveyor sections onto Stage Two. Using hot water at 150 degrees F the parts are rinsed using vertical agitation.

PASSIVATION USING NITRIC ACID - The basket is laterally transferred over special platform roller conveyor sections on to Stage Three. Using a 25% solution of nitric acid at 135 degrees F the parts are passivated using vertical agitation.

RINSE - The basket of parts is then laterally transferred over platform roller conveyor to Stage Four. Using DI water at 150 degrees F the parts are rinsed using vertical agitation.

 

HOT AIR BLOWOFF DRYING - The basket of parts is then laterally transferred over platform roller conveyor to Stage Five. Using hot air at 180 degrees F the parts are dried. RAMCO Hot Air Knife Blow-Off Dryers get maximum evaporation providing rapid drying without excessive heat.
Nitric Acid Passivation

Stainless steel derives its corrosion resistant properties from its chromium content. The chromium, in the presence of air, especially oxygen, forms a thin, hard adherent film of chromium oxide on the surface of the alloy. It is this chromic oxide layer that is inert (passive) to the surrounding environment and gives stainless steel its corrosion resistant properties.

ASTM A380 describes passivation as "the removal of exogenous iron or iron compounds from the surface of stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination, but will not significantly affect the stainless steel itself" ..... and "the chemical treatment of stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film."

Simply stated, utilizing a mild oxidant, such as a mineral or organic acid solution, to promote the removal of excess iron from the surface of the stainless steel will enhance the formation of a chromic oxide layer thereby enhancing its corrosion resistant properties.

Typically, passivation is performed with a nitric acid bath from 20 to 50% by volume. Temperatures range from ambient to 160 degrees F. Immersion times can be as long as two hours and even include the addition of a chromate salt. Nitric acid is by far the most accepted means by which passivation is performed.

 

The following Case History is of a Nitric Acid Passivation System for precision components. The system consists of seven stages comprising two MKT Consoles and a single stage Nitric Acid MK Series.

 

Due to the nature of Nitric Acid and its fumes the electrical and pneumatic systems are built for corrosive environments. This includes Nema 4X electrical components and enclosures as well as special pneumatic components specifically designed for this application.
Citric Acid Passivation

 

Stainless steel derives its corrosion resistant properties from its chromium content. The chromium, in the presence of air, especially oxygen, forms a thin, hard adherent film of chromium oxide on the surface of the alloy. It is this chromic oxide layer that is inert (passive) to the surrounding environment and gives stainless steel its corrosion resistant properties.

Passivation, according the ASTM A380, is "the removal of exogenous iron or iron compounds from the surface of stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination, but will not significantly affect the stainless steel itself." ASTM A380 also describes passivation as "the chemical treatment of stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film."

Simply stated, utilizing a mild oxidant, such as a mineral or organic acid solution, to promote the removal of excess iron from the surface of the stainless steel will enhance the formation of a chromic oxide layer thereby enhancing its corrosion resistant properties.

Typically, passivation is performed with a nitric acid bath from 20 to 50% by volume. Temperatures range from ambient to 160 degrees F. Immersion times can be as long as two hours and even include the addition of a chromate salt. Nitric acid is by far the most accepted means by which passivation is performed. Recently, however, there has been an increase in the amount of industries that have successfully implemented citric acid into their passivation procedures.

Citric acid is an organic acid unlike nitric which is a mineral acid. It reacts with the iron much better than nitric and does not attack elements in stainless steel alloy which nitric acid does. And citric acid, overall, is a less harmful chemical than nitric acid. Nitric acid raises problems with environmental disposal, health and safety, environmental pollution, increased environmental liability and regulation, and overall complexity to utilize it. Citric acid on the other hand is derived from oranges, utilized in food and beverage products, is acceptable in some instances to go right to drain, depending upon contaminants and local environmental regulations, and much more friendlier when it comes to worker health and safety.

Even the process aspect of citric acid passivation is easier. Stainless steel must be cleaned prior to any passivation procedure. All surfaces contaminated with oil, grease, chips, grinding dust, lapping compound, buffing compound, coolant, and/or swarf must be removed.

For more information on this and other passivation system call our factory at 800-553-3650.

For more information on citric acid passivation chemicals and processing go to Stellar Solutions.

 

 

Above are three different citric acid passivation systems designed and built at RAMCO. The lines were developed based on the batch load size/weight, cleanliness level of the parts prior to passivation, and the required throughput per hour.
 

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