Ronuk Industries

TRI BLUE 556
TRIVALENT BRIGHT
BLUE PASSIVATE FOR ZINC

TRI BLUE 556 is a trivalent chromium based process; designed to give a bright, pale blue finish to electroplated zinc surfaces. The process is suitable for use on zinc deposits from all common electrolytes. TRI BLUE 556 is supplied as a highly concentrated liquid of density 1.31 +/- 0.020 & is eco friendly.

IMPORTANT NOTE:

Before using the product, please ensure that this complete document and relevant Health & Safety sheets have been read and understood.

MAKE–UP:

PARAMETER	ALKALINE ZINC / CYANIDE ZINC	ACID ZINC
Concentration PH Immersion time Agitation Temperature	10 – 15 ml/l 1.6 – 2.0 30 – 50 seconds Air Agitation 27oC – 32oC	15.25 ml/l 1.8 – 2.2 30 – 50 seconds Air Agitation 27oC – 38oC

The precise concentration will be dependent on the desired appearance and individual plant characteristics and shall vary from component to component, type of plating and plant configuration.

Fill the tank approximately three- quarters full with main water and add the required amount of TRI BLUE 556 solution with mixing. Make up to the operating level and temperature and again remix.

EQUIPMENT:

In existing installations, tanks already in use for blue passivataion can be used for TRI BLUE 556. These tanks should preferably be constructed from reinforced plastic materials. Mild steel tanks lined with a suitable acid resistant material (for example glass fibre) are also not suitable.

Good solution mixing in rack application requires compressed air agitation. The tube should be preferably be made from PVC and air throughput control should be fitted with oil free filters.

OPERATING CONDITIONS:

Concentration:
It is advised to operate at the lower end of the concentration band, using extended process times to compensate, where cycle time constraints allow, alternatively for automatic lines concentration can be elevated.

Temperature:
At temperature below 15oC, passivation is slow and uneven, with spot formation and a matt appearance.

pH:

To lower the pH, use additions of nitric acid.
To increase the pH, use additions of sodium hydroxide solution.

Immersion Time:

The immersion times quoted above include the transfer time to the first rinse, as the solution carried out on the work continues to operate during such a transfer.

Agitation:

Air agitation should be moderate but, above all, uniform. Alternatively, agitation may be carried out with the working solution being circulated by means of a centrifugal pump. Immersion times will have to be increased where agitation is insufficient.

CONSUMPTION:

	ALKALINE ZINC	ACID ZINC
TRI BLUE 556	5 ml (6.4g) per m2 +	5 ml (6.4 g) per m2 +
Nitric Acid (42o Be)	8 ml (11.2g) per m2 +	5 ml. (7.0 g) per m2 +

These are average values, which will vary depending on the drag-out on the work. The nitric acid figures are given as starting point values for initial plant dosage. These should be checked and altered to suit any given installation.

TESTING AND REPLENISHMENT:

pH:
The pH should be checked frequently, at least every 4 hours during operation. Should it fall out with the desired range, it should be corrected with either nitric acid or sodium hydroxide solution.

All the above is based on our in-house experiments in totally controlled conditions and no warranty or guarantee covertly or overtly is implied hereon.

ANALYTICAL CONTROL OF WORKING BATH:

1. Take a 20 ml sample of working solution into a suitable flask and dilute to
about 150 ml. with de-ionized water.

Add 10 ml of Sodium hydroxide (20 % wt/v) solution and heat to boiling.

Add sodium peroxide in increments of 0.5 gm. until the depth of the brown
Colouration produced is stable. Simmer for 30 minutes.

All to thoroughly cool then add 20 ml. concentrated Hydrochloric acid, 10 ml of Potassium Iodide (10%) solution and 2 g. Ammonium bifluoride.

Titrate using 0.1 N. Sodium Thiosulphate until the appearance of a pale green colour.

Calculation:

Reading – 1.42 = ml./l of TRI BLUE 556

TROUGBLESHOOTING GUIDE:

DEFECT	POSSIBLE CAUSE	SOLUTION
Blue with yellow tingers	- pH too low - Immersion time too long	- Check and adjust pH - Reduce immersion time
Yellow spots	- Insufficient rinsing - Insufficient activation	- Improve rinsing - Check nitric acid - activation
Blue with green tingers	- pH too low - Concentration too low - Immersion time too short	- Check and adjust pH - Add TRI BLUE 556 at 2 ml/l - Extend immersion time

Process Sequence: Pre & Post – Treatment

• A pre-rinse in water acidified with Nitric acid is recommended.
• After acid any cyanide zinc, use a concentration of 0.2% of 42° Be acid.
• After alkali, non-cyanide zinc, use concentration of 1.0% of 42° Be acid

The final water rinse after TRI BLUE 556 is usually run at about 60° C.