Posted: 22 February 2005 at 7:27am | IP Logged

Global concern over use of cyanide in Zinc Plating has led to the virtual elimination and sharp reduction in the use of cyanide in zinc plating operations world wide.

In India the average plater continues to use cyanide and discharge the waste water to drains and over land and agricultural crop growing areas too.

What can be done and how can this use of cyanide be regulated and eliminated.

Please post suggestions and opinions/

Asif Nurie

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Posted: 05 March 2005 at 6:58am | IP Logged

Hello,

      Now awarness of using non cyanide zinc plating processes started among major zinc plating industries. However some platers still prefer to use cyanide zinc because they face problems in blue passivation. They do not get blue finish as in cyanide zinc plating. If you give some suggestions to get equal finish as in cyanide mostly all zinc platers will change to non cyanide zinc.

Selvaraj

Posted: 07 March 2005 at 4:18am | IP Logged

  Hello Mr Selvaraj,

True , some platers do have a problem with blue finish on Alk zinc. 

 The causes and their removal....

1) Post Plate rinse and Nitric dip. 2 rinses. 2 Percent Nitric dip.= 20 mls per liter. Replenish with 5 mls Nitric after 4 hours of work. caustic neutralisation major issue causing poor blue.

Nitric is sometimes adulterated with water so it should be titrated in the lab for strength.

2) Insufficient Conditioner in Solution.  If the deposit is dark when coming out of the bath it means there is insufficient conditioner. Adds of up to 0.5 mls per liter at one time are acceptable. The LIMIT is 1 ML per liter over a 2 or 3 day period. Once the deposit is cleared up  regular conditioner adds are 10 to 15 mls per KAH. This helps blue  chromate acquire its real blue look.

Another cause of dark deposits is lack of purifier in bath. Adds of up to 0.5 mls at a time are workable provided not more than 1 ml/lit is added over 3 working days to set a bath right. Excess adds over 1.5 ml per lit cause anodes to polarise.

Regular Purifier adds  are 20 to 25 mls per KAH.once deposit is cleared up.

3) Less brightener in Solution and poor Micro leveling. Chromate color is a function of the refraction of light rays as they bounce back from the surface of zinc , get refracted thru the chromate and hit the eye as light of a certain frequency. Blue color is the result when correct reflection takes place and max light gets back to the eye. Correct chromate thickness is the result of proper conditioning and right application.

Most rack solutions work well at:

Brightener:  225 to 270 mls per KAH

Booster. 125 to 150 mls per KAH

\barrel solutions:

Brightener.    250 to 310 mls per KAH

Booster 150   to 220 mls per KAH

If a bath appears low on Brightener , adds of up to 2 mls per liter in 24 Hours with Booster up to 0.5 mls/lit are workable . Thereafter follow recommended figures for regular addition.

If attending to a particular bath, first check the 1st point of Nitric. Then go for the deposit color from bath and use the conditioner and Purifier. Then verify the adds of Brt and Booster.

Of course the bath composition should conform to :

Metal.  11 to 14 gpl.

Caustic  125 to 135 gpl.

Spare anodes in MS baskets on Non working sides dissolve continuopusly help keep metal stable. MS baskets with Zinc in caustic soln set up an electrochemical couple which helps dissolve zinc chemically more efficiently.

Trust Zinc anodes are lead aluminium and copper free.

Correct Brightener and Booster adds help the microleveling of zinc. Which in turn help with Blue chromate. Clean bath, proper conditioner Purifier adds help. So does proper caustic neutralisation after plating.  These are the major factors that will keep your blue chromate smiling.

Let me know if there are any points that need clarification. Regards

Sincerely. Asif Nurie

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Posted: 07 March 2005 at 5:26am | IP Logged

  Hi Mr Selvaraj,

Further to the Blue Chromate mail...

Four points which seem obvious but usually get neglected ..

1) Continuous filtration is a must.  Plate , or cartridge. 4 turnovers/hour. If there is continuous filtration , good blue is certain.

2) 0.25 gp[l carbon on filter every 250 hours of plating to remove broken down additives and clean up organics. Helps blue greatly.

.3) Oil and black MUCK on solution which is a result of poor pretreatment and no anodic cleaner. This will always make the blue weep.

Poor cleaning puts muck into solution which floats or sinks, absorbs additives eats up brightener,  and co deposits with zinc making the deposit less leveled and less bright.

Anodic cleaner is required for rack plating. All Rack plated parts should be cleaned anodically once before plating in 150 gpl caustic at 12 volts for 2 to 3 minutes.

For barrel PLATING, barrel tumbling any method to ensure OIL free, Rust freee and dirt Free parts.

SOAK WITH SOME FORM OF MECHANICAL OR MANUAL CLEANING. OR JUST ALKALINE CLEAN IN SMALL PERFORATED PLASTIC BASKETS MADE FROM 5 LIT CUT JERRY CANS AND MS RIVETED HANDLE PASSING THRU INSIDE SIDES , INSIDE BOTTOM THAT SUSPENDS BASKET IN 50 CENTIGRADE 150 GPL CAUSTIC AT 12 VOLTS FOR 5-6 MINUTES. THE MS HANDLE CONTINUES INSIDE BASKET AND IS THE CONNECTOR FOR CURRENT TO PARTS. IT IS USED TO SUSPEND BASKET ON BUS BAR AND PASS CURRENT THRU PARTS.

A good sequence for barrel.

Soak in cleaner CP 585 BY CMF @ 25 gpl + caustic 50 gpl at 50 centigrade 10 min or at Room temp overnight.

If option to soak overnight , next days production parts can be left in soak  solution. overnight.

Gas burner direct on MS tank bottom has been used sucessfully FOR ECONOMY HEATING.. Its called a canteen burner used by sweet shops . NOT domestic burner. Run thrice in 8 hrs for 45 minutes . enough to keep warm  using first option of 50 centigrade 10 min.soak clean. One cylinder lasts almost  14-18 days.  GOOD FOR ANODIC TOO.

POST SOAK Rinse x 2 times 

 Pickle in 50% HCL as needed.

Rinse x 2 times

Neutralise in post soak rinse.

Anodic clean as described. . Naoh @ 150 gpl for 3 min at 50 centigrade 12 volts.

No rinsing..pl note this point.

CONDITION IN CAUSTIC DIP.. 100 gpl.  ROOM TEMP.

Plate.

If parts before loading dont make a tissue black , they are fit for alk zinc plating. This keeps tank clean. Nop Muck and path to good blue.chromate.

4) Direct adds of Caustic flake to an alk bath cause local overheating. localised steep pH rise and immediate localised additive breakdown which leads to sharp rise of inorganic impurities in bath. Result. Poor Blue.

Solution. Carbon pack. 0.25 GMS / lit 3 HRS. SAME TIME Dummy at 6 to 7 volts on large sheet for 3 hours. BOTH TOGETHER.

Then add Conditioner and Purifier. 1 ml / lit Brightener and 0.3 mls./ lit Booster.

Check Dummy for clarity . If Ok and clear start plating after making adds as above.

 Trust these points are clear. Please revert if there are queries.

Note that we have faced each and every one of the above stated issues in INDIA, and these are practical solutions to the given situations.

Some element of patience and discipline are ordained as old cyanide zinc practices die hard.

Regards.Sincerely.asif Nurie

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