A MODERN MIXED CHROME PASSIVATE FOR GALVANIZED / GALVALUME COATED STEEL STRIP

ADVANTAGE:

• A mixed chrome product to minimize bronzing effect.
• Room temperature application
• No heating / no cooling of bath solution
• Self-healing properties of typical Cr 6 + application
• Reasonable bath life if application is done by spray- squeeze method also
• Excellent anticorrosion properties
• No post rinse system
• Free of chelating agent & hence ease of effluent treatment

CHARACTERISTICS OF PRODUCT (TYPICAL):

• Appearance : Reddish Green colour liquid.
• Sp. Gravity at 200 C : 1 – 1.28 (typical)
• Total chrome content : 60.0 g/ L (approximate)
• p H (neat) : Acidic

INITIAL BATH PREPARATION:

• Run the tank total empty before new makeup.
• Add 130 – 200 L SUPASS for 1000 L bath.
• Fill the tank about 3 / 4 full with water.
• Add the recommended quantity of SUPASS.
• Add sufficient water to bring the solution up to the working level.
• Mix well to make the solution homogeneous.
• However, the concentration of make up solution depends on the desired chromium layer thickness and on the plant conditions of each installation ( smoothness, hardness and pressure of the squeezing rollers) as well as on the composition of the substrate to be passivated.
• The smaller the bath volume, the longer the bath life.
• Solution can be consumed faster than it can load with zinc contamination.

APPLICATION PARAMETERS:

EQUIPMENT:

Holding tank, pump, piping and solution trays should be constructed of Stainless steel, preferably type 316 stainless steel. The holding tank and piping may be constructed of lined with plastic (PVC, PTFE etc).

Squeeze rolls should be constructed of chromic acid-resistant rubber.

For roll- coating application, the applicator rolls should be constructed of chromic acid-resistant rubber, and the pick- up rolls should be chromium plated or constructed of Stainless steel.

A filter (50 - 100 mesh) should be installed in the fluid line between the outlet side of the pump and the fluid tray.

Squeeze Roll Settings (Typical):

• Material : Hypalon
• Hardness : 40 - 55 deg. shore
• A Roughness : 5 - 10 micrometer

Oven drying / Dryer:

The SUPASS treated strip must be dried as quickly as possible to ensure uniform deposition of coating. The strip must pass through a dr y off unit adequate to remove the water. Air movement within the oven should be sufficient to remove evaporated water, but must not physically disturb the deposited wet film.

Once applied the SUPASS solution film must not be disturbed before it has dried completely. Care must be taken to avoid physical contact with the strip before the film has dried. The PMT of the strip should be in the range of 550 C– 750 C.

BATH MAINTENANCE :

The bath solution is replenished with SUPASS concentrate and proportional water to be added to maintain constant concentration range. Addition sequence should be first chemical and then water for top up.

To raise 1% (w/v) SUPASS, add 1 kg SUPASS per 100 L bath solution.

Zinc content in the bath:

Zinc content should ideally be controlled below 2000 ppm and under no circumstances it should exceed 3000 ppm zinc since this will lead to reduced performance. A turbidity will be developed of this contamination label zinc & this should be considered at bath discardal criteria.

To avoid high zinc build up in the bath:

• Run bath temperature as low as possible (maximum 400C).
• Short reaction distance to the squeeze rolls (maximum 1.0 meter).
• Drying temperature 70 – 800C (PMT).

Consumption idea:

Consumption depends on required coating weight & tendency of zinc build up in the bath. However, 75 ± 2 ml SUPASS per 100 m2 of strip is sufficient enough to get optimum performance. The loss of passivation chemical due to leakage / spillage & discardal is not considered in the above calculation.

a) CONCENT RATIO

a.Principle:

Iodometric titration of hexavalent chrome.

1.Apparatus:

• Measuring cylinder
• Iodometric flask ( 250 ml)
• Burette
• Pipette (10 ml)

2.Reagents :

• Sample solution to be tested Potassium iodide
• Starch indicator
• 0. 1 ( N) Sodium thiosulphate solution

3.Procedure:

• Measure out 10 ml of the bath solution into a 250 ml Iodometric f lask.
• Add 100 ml clean water to dilute.
• Add 10 ml 50 % sulphuric acid.
• Add 2 g of potasium iodide or 20 ml 10 % Potassium iodide solution.
• Swirl the f lask to mix the contents.
• Keep the f lask in the dark for 5 minutes.
• Titrate with 0 . 1 ( N) sodium thiosulphate solution using starch as indicator to a clear or pale green end point.
• Record the ml of Sodium thiosulphate as T.

Calculation :

Concentration of SUPASS % by weight ( w/ v) = T X 0 . 637 Concentration of SUPASS% by volume ( v/ v) = T X 0 . 553

b) ZINC CONTENT BY TITRATION TECHNIQUE:

Zinc content can be determined by Atomic absorption spectroscopy, colorimetric or titration techniques. The titration technique is not as sophisticated as other two techniques but for simplicity & without the help of costly instrument it can be used as a rough guideline.

Principle:

Complexometric titration by EDTA

Apparatus:

• 100 ml measuring cylinder
• 5 ml Pipette
• 250 ml Erlenmeyer flask
• 50 ml Burette

Reagent :

• 0.1 N EDTA
• Buffer solution (100 g/L NaOH and 240 ml/L 98% acetic acid in DM water)
• Indicator (1.0% Xelenol orange-tetrasodium salt + 99% KNO3 mixture)

Procedure

• Pipette 5 ml into 250 ml Erlenmeyer flask.
• Add 100 ml DM water, 20 ml buffer solution and a spatula tip of indicator.
• Titrate with 0.1 (N) EDTA from red brown to yellow or to light green (depending on the Cr+3 content).
• Note the consumption of EDTA as S ml.

Calculation :

• Zinc (g/L) = S X 1.3074

Remark:

However, for a particular line, the analysis of zinc might not be required regularly. The discardal frequency could be established during trial on the basis of tonnage of production.

DISPOSAL :

SUPASS waste contains hexavalent chromium. Follow the effluent treatment by chemical reduction with Sodium Bisulphite. The supernatant l liquid may be discharged only after meeting the Local regulation for hexavalent and trivalent content in discharged water. The sludge may be dumped into specified dumping ground or can be stored / sold to authorised agent as per local regulations.

SAFETY :

SUPASS is highly acidic & toxic in nature and contains both hexavalent & trivalent chromium compounds. Do not store near combustibles and reducing materials.
Avoid breathing solution, vapour or mist SUPASS can cause severe burns in contact with eyes and skin and may be harmful i f swallowed. W hen handling, wear rubber gloves, rubber apron, rubber boots, safety goggles and face shield. W ash thoroughly after handling.

STORAGE :

No special storage system is required. The SUPASS on long exposure at low temperature may give some precipitation which could be re dissolved by keeping i t in a warm place. I t may generate gas on long storage. Take care during opening the l id of the container.

BEST BEFORE END :

1 year from month of manufacture.

PACKING :

20 / 30 / 50 / 200 kg HDPE Container / 1000 kg IBC or as per the contract.