Low Temperature Zinc Phosphate Process - Freiborne Industries, Inc Low Temperature Zinc Phosphate Process - Freiborne Industries, Inc

Product Type: Freibond 2

Low temperature zinc phosphate process designed primarily for spray applications on steel with some tolerance for zinc. Advantages are subsequent saving in heating costs.


FREIBOND 2 is a highly efficient low temperature phosphate process used primarily in spray applications. It is satisfactory for coating steel and steel/zinc in mixed production.

FREIBOND 2 Make-up Chemical
NEUTRALIZER 1 Free acid adjustment
FREIDOX 2 Accelerator Chemical
FREICLEAN Alkaline Metal Cleaning Chmical
FREICON Non-chrome final seal rinse

Stainless steel, mild steel, and high temperature acid resistant plastics are suitable for processing equipment. Utilizing 300 series stainless steel equipment will significantly increase the service life of the equipment. Full cone spray nozzles, such as Spraying Systems WhirlJet® nozzles, are normally used in spray applications to ensure uniform application of FREIBOND 2.
Spray pressures should be maintained at 15 psig for optimum coating. Spray pressure above 20 psig will create inconsistencies and voids in the iron phosphate coating.

Utilization of deionized or reverse osmosis water in the system will reduce both chemical consumption and sludge generation. Application equipment should be cleaned or a regular maintenance cycle with PICKLE 2 to remove sludge and scale deposits that may interfere with application and subsequent performance.

The typical process sequence for FREIBOND 2 application consists of the following steps:

1. FREICLEAN treatment
2. Hot water Rinse
3. Water Rinse
5. Cold Water rinse
6. Cold Water Rinse
7. FREICON post treatment seal
8. Drying

Fill the tank three-quarters full with water, bring to the operating temperature of 110°CF and add 200 lbs (15-17 gals) of FREIBOND 2 and 4.5 lbs NEUTRALIZER 1 per 1000 gals of working solution. Fill to operational level with water. Just prior to processing add 3.2 lbs (2.5 pints) of FREIDOX 2 for every 1000 gals of solution.

An appropriate FREICLEAN product, followed by a rinse stage, should precede FREIBOND 2 phosphating application.

To maintain the bath’s performance it should be regularly tested and adjusted to within operating parameters. Normal processing time with FREIBOND 2 is 60 seconds. Processing parameters can vary widely based on individual processes and performance requirements. Typical operating parameters are listed below. Your Freiborne representative will help develop the proper operating parameters for your specific needs.

Indicating Paper 17 can be used to perform a quick test to ensure the bath is running on the nitrite side (Freidox 2 value is greater than zero).

The Freibond 2 treatment is typically followed by a rinse stage and a chrome free final seal rinse such as FREICON RSX.

Total Acid Test:
Pipet a 10 ml sample into a suitable beaker or Erlenmeyer flask and add 5-10 drops of Indicating Solution 3 (phenolphthalein). Titrate with Testing Solution 11 (0.1N NaOH) to a permanent pink endpoint. An addition of 1.25 gallons (16 lbs) of FREIBOND 2 per 1000 gallons will raise the Total Acid by 1 point.

Free Acid Test:
Pipet a 10 ml sample into a suitable beaker or Erlenmeyer flask and add 5-10 drops of Indicating Solution 11 (bromophenol blue). Titrate with Testing Solution 11 (0.1N NaOH) to a blue green endpoint. An addition of 0.75 gallons (10 lbs) of FREIBOND 2 per 1000 gallons will raise the Free Acid
by 0.1 points. If the Free Acid is to high an additions of 7 oz of NEUTRALIZER 1 1000 gals will reduce it by 0.1 point.


Dip a strip of Indicator Paper 17 into the working solution. If it turns pink Freidox 2 must be added, as above, until a fresh piece of paper does not change color. This is typically performed at least once per shift during operation. If it does not change color continue on to the titration, but if it turns pink the bath is on the iron side and Freidox 2 must be added in the same increments as for a new bath, until the iron is cleared.

When no change in color occurs, determine the FREIDOX 2 concentration as follows: Pipet a 25 ml sample into a 250 ml beaker or Erlynmeyer flask, add 10 – 20 drops of Testing Solution 44 (50% H2SO4) and titrate with Testing Solution 15 (0.042N KMnO4), swirling vigorously until a persistent (10 second) pink is obtained. An addition of 470 mls of FREIDOX 2 will increase the reading by 1.0 point.

General Maintenance:
During the phosphating reaction, sludge is formed as a by product of the reaction. This residue collects at the bottom of the tank and should be removed regularly so that is does not deposit on the work. The sludge is generally removed by allowing the sludge to settle to the bottom of an auxiliary tank, then the clear solution is pumped back into the processing tank from the top of the auxiliary tank. A cone shaped bottom with a bottom valve is convenient for discharging the sludge into drums for disposal. Filter pressing the sludge will recover most of the solution and lower disposal costs.

When the FREIBOND 2 solution has been heated for some time, scale will build up on the heating coils.
Periodically the coils must be removed from the tank and the scale removed by immersing in muriatic acid or by mechanical means.

FREE ACID will tend to drop below the normal range if too much FREIDOX 2 is used; or if insufficient FREIBOND 2 is added. Higher than normal Free Acid values can be obtained with excessive heating of the solution without processing work. High temperature operation can also cause this condition.

ACCELERATOR: Before testing for FREIDOX 2 (Accelerator) dip a strip of Indicating Paper #17 into the Freibond solution. If it turns pink make small additions of Freidox until a fresh strip of paper runs colorless. At this point proceed with the FREIDOX 2 test above. Accelerator is lost during intermittent use of the FREIBOND 2, or prolonged idle standing, and must be replenished accordingly.

Additional Information

Temp Range



Carbon Steel, Galvanized Steel


Paint Pretreatment, Rubber-Metal Bonding

Product Type

Conversion Coatings

Product Line



Spray or Immersion

Ordering Information

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