SUPER FAST SRHS BRIGHT CHROME PROCESS - 311

Super  Fast  SHRT  Bight  Chrome - 311  Process  is  a  specially developed  Bright Chrome Process, Applied over to Nickel. It  has all the Advantages over conventional Chromium Plating Process and Suitable for Decorative and Hard Chromium with Following Features.

1. High Cathode Current Efficiency of 16 %.

2. Auto regulation of the Catalyst.

3. Improved  Corrosion  Resistance  and Hardness  of  the  Chrome   deposits. 

4. High throwing power with less Etching Effect.

5. Interruption  of Current  for short period does not affect the  Brightness.

6. Higher Conductivity of  the Bath, Allow to work at wide operating current density range, up to 35 amp/sq. Dm.  

 Bath Make up                                                    Decorative          Hard  

Super fast bright chrome

Salt - 311 gm/litre.                                                   210-270          235-285  

Working Conditions  

Density in *  Be                                                      16-21            18-22

Temperature in *C                                                   42-52            45-55

Cathode .c.d in amp/sq.dm.                                     15-25            20-35

Anode c.d. in amp/sq.dm.                                         6-10            10-15

Voltage                                                                    5-08             6-09

Agitation                                                            ---  Cathode movement

Rate of Deposition at 20 Amp/
Sq.dm. Per minute in micron                                      0.20             0.23  

Maintenance  

Chromic acid in gm/litre                                             205-260          230-275  

Sulphate content in gm/litre                                       1.15-1.45        1.30-1.55  

Consumption 

Bright chrome salt - 311 per  
10000 am/hr in kg.*                                                  1.09-1.19        1.10-1.14  

Note :- Evaporation/mist and drag out losses are considered here  but vary according to working set up and maintenance.

Regular addition of super fast bight chrome salt - 311 should  be made to maintain the bath in proper condition. After any addition of  the  salts,  the solution should be  throughly  stirred.  The addition  as  per  consumption  level  mentioned  above  will  be generally sufficient to maintain the bath in  balance  conditions but when working at higher temperature of above 55* c, there  are enough  chances of loss of catalyst content. This will result  in lower rate of deposition, due to less cathode efficiency. At such occasion  add5 to 10 gm/lit of super fast catalyst - 312  as  per the sulphate content require.in order to keep the bath continuously  at  a fixed composition, it is  necessary  only  to maintain  the  temperature  and chromic acid concentration  at  a specified  value.  It is necessary to stir  the  solution  before start of the work and allow the sediment to settle at bottom. This process the sulphate content is autometically self regulated to a value, which is necessary as per practical consideration and is  affacted only by the concentration of the salt - 311 and  the working temerature.

It  is  important  that  the drag-in of  acid  redicals  such  as chloride,  sulphate  and  nickel be held to a  minimum  level  by proper  rinsing operation  prior  to  chrome  plating.  The  bath solution should be periodically analysed for sulphate and chromic acid  content and be corrected to a required level by addition of chrome  salt  -  311 and/or chrome catalyst -  321.  If  sulphate content  is  higher, it is to be reduced by  addition  of  bright chrome  reducer - 305, for each 1.0 gm/litre of  sulphate  to  be lower,  2.0 to 2.3 gm/litre of 305 should be added.  If  sulphate content  is  low,  it is to be increased by  addition  of  chrome catalyst  -  312. To increase 0.10 gm/lit of sulphate,  add  2.0, gm/lit of 312. 

Tin-lead (8 % tin ) anodes are recommanded for this process.  New anodes  should be worked at maximum voltage (8 to 9) and  current for  one  hour to ensure the formation of chocolate film  on  the anode. The presence of a chocolate brown film on the  anode  is necessary  to ensure that the trivalent chromium produced during the electrolysis is re-oxidesed correctly at the anode surfaces. If an anode develops an yellow film it should be brushed down  to the  metal  surface  and  rekept on the  busbar   with  a  proper electric contact. 

Preparation of bath solution :- 

1. Thoroughly clean the  plating tank with deionized or distilled water.

2. Fill  the  tank  about two-third full with chloride free  d.m. water or distilled water and heat to 55-60*c.

3. Add  required  amount  of  bright chrome salt - 311  in  small portions  with vigorous  stirring. Keep hoeing up  to  prevent it  from caking on the bottom of the tank. Measure the density of  the  bath  solution  if lower than the recommanded  value, stir further to get the required value.  

4. Place the anodes and dummy cathodes. Electrolyse  the solution at 6 volt for few hours and then use the bath for production.

Equipments :

Tank   :

Mild steel  tank  lined with pvc/frp or tin lead  or  antimonial lead alloy (92 % lead) is suitable.

Heaters   :

Tantalum or tin lead alloy or fused silica  cased  heaters can be used for heating the solution.

Exhaust   :

Suitable exhaust system with scrubbing facilities should  be installed for safer working and to keep the environment  clean. This  is  necessary  when  working for hard chrome plating.

Anodes  :

Anodes to be used are tin lead alloy with 6 to 8% tin content. Round anodes are normally preferred compared  to flat type. The anode cross-section should be sufficient to carry   the required current without over heating.

Effluent treatment :

Detoxification  of  chromic effluent is done by means  of  sodium Bisulphate  at  ph value below 2.5. To reduce 1.0 kg  of  chromic acid normally 1.56 kg of sodium Bisulphite plus 1.0 to 1.6 kg  of Sulphuric  Acid  (C.P.  98%) are  Requied.  After  reduction  of Hexavalent Chromium, it is to be made alkaline to ph 8.0 or to be mixed with basic effluent.

 Storage and handling  :

A separate dry floor storage area should be allocated for  supper fast chrome  salt - 311. It is a strong oxidizing  agent  and  on contact  with organic solvents and reducing materials  may  cause fire. While handling it is recommended that appropriate protective clothing,  including  gloves,  an  apron  and approved  chemical resistant goggles be worn. 

Safety precautions

Plating solutions and products containing chromic acid are harmful

To  health.  On contact with skin cause  primary  irritation  and ulceration. Breathing chromate dust can cause nasal and pulmonary irritation as well as Born Chogenic Carcinoma. Therefore following precautions must be taken while working.

1.    Prevent contact with skin, eyes, and clothing.

2.    Avoid  breathing mist from the solution or  dust  from  the products.

3.    Wear protective clothing, rubber gloves, aprons, goggles.

4.    Wear fresh clothing daily.

5.    Wash thoroughly before  taking food or drink or smoking  and at the end of work period take hot water shower.   

6.    During working add  required quantity of mist  controller 307  or  307 (l) or 308 or 308 (spl), to control  the  mist coming  out of the bath surface.

First aid :

In case of skin or eye contact, wash well with continuous stream of  water  for  at least  10  minutes.  If necessary consult a physician. If inhaled move the exposed individual to fresh  air. Get medical attention.