Galvanized surfaces are very prone to react with acidic and alkaline environments. They develop white rust in contact of poorly ventilated moisture covered surface. The reaction is catalyzed in presence of acidic gases such as sulphur-di-oxide, Carbon-di-oxide, nitrous/nitric oxides etc present in urban and industrial atmospheres. In marine atmosphere, presence of chloride further aggravates this phenomenon. During packing, storage, transportation and usage, the galvanized steel surface comes in contact with humidity leading to white rust formation. The Passivation coating, that inhibits the formation of white rust, is applied by passing the zinc coated steel sheets/tubes through a passivating bath containing the passivating chemical solution, and subsequently by drying the sheets/tubes/structures. In some plants, the sheets are passed through spray chambers and squeeze rolls for uniform application. Chrome based passivators are established to be the most effective in protecting the galvanized surfaces from white rusting and retain lusture of the surface. Unfortunately, hexa-valent chrome is highly carcinogenic and is being discouraged its use in plants. A recent trend is the use of mixture of majour amount of tri - valent + minor amount of hexa valent chrome for passivation of galvanized products. Tri - valent chrome is non-toxic and completely safe for use. Galvachrome is designed with this concept and it incorporates 90% tri-valent + 10% hexa-valent chrome. FEATURES Film formed is highly resistance to salt spray test ( > 120 hours). Composite colourless film of Tri+hexa Chrome+ other anions and cations. Blue to greenish appearance due to thin and uniform film. Better primer & paint bonding on passivated surface.
PROCEDURE FOR USE OF Galvachrome Fresh Baths:
- Dosing: Should be maintained in the range of 1 - 3 % (V/ V) of total volume of the passivation bath.
- Temperature: Room temperature to 75 0 C.
- Contact time: 5 to 30 seconds, depending on the type of operation.
- Caring after passivation: Materials should be stored at least 48 hours in aerated shed.
- Control of composition of passivation bath : Maintainance of pH of bath is enough for satisfactory functioning of Galvachrome.
pH of bath = 1.5 to 2.0
Disposal of passivation bath:
There is no need to dispose off the bath prepared by Galvachrome . In case insoluble powder settled at the bath disrupts operation after long time of use, the bath can be filtered to remove insoluble residue. Steps involved for use of Galvachrome:
- GALVANIZE
- Cool to temperature below 600 C
- Treat in Galvachrome bath
- Squeeze / Hot air dry. Standard operating
procedures:
Bath material of construction: Acid resistant brick wall or 304 SS tank.
Dilution of Galvachrome: Galvachrome can be diluted with water in any propoprtion .
Operating Conditions Addition in the bath: @ 1 - 3% Vol / Vol.
Operating Temperature: Ambient to 750 C
Contact Time: 5 second to 30 seconds.
Hot air blower temperature : 75 - 900 C
Safety precautions:
Normal precautions related to handling of chemicals. In case of accidental spillage at floor,sprinkling of soda ash followed by washing with water , Skin contact should be avoided. In case of accidental contact, the affected part should be thoroughly cleaned with soap and water. Oral inhaling is dangerous. Immediate medical help should be taken.
APPEARANCE: Dark green-yellow liquid.
PACKING: 20, 35, 45 ,100 and 200 liters HDPE carboys.