plating, anodizing, & finishing Q&As since 1989
Problems in Blackodising
October 14, 2008
Q. WE ARE DOING BLACKODISE TO MS/EN 8 PARTS AS UNDER:
1] 5 KG SODIUM NITRITE + 10 KG CAUSTIC SODA + 10 LTR WATER
2] BOILING WITH GAS HEATING
3] ACID CLEANED COMPONENT PUT INTO HOT MIXTURE FOR 5-10 MINUTES
BUT WE ARE FACING PROBLEMS AS UNDER:
1] WE DO NOT KNOW THE STEP TO STEP PROCESS LIKE MIXTURE / TEMP / TIME
2] SOMETIMES WE GET IT RED, SOMETIMES NO BLACK, SOMETIMES POOR BLACK
3] HOW MANY KGS CAN WE DO FROM 5 KG OF MIXTURE?
4] HOW CAN WE IDENTIFY THAT NOW WE HAVE TO REPLACE THE MIXTURE?
5] INSTRUMENTS TO IMPROVE STRON BLACK + SHINING
6] WE HEARD ABOUT SEVEN TANK PROCESS? WHAT IS IT
7] BEST OPTION? CAN COLD BLACKODISE GIVE US SAME / BETTER SHINE?
8] ANY CHEMICAL ADD-ON WHICH CAN IMPROVE THE BLACKODISE ?
MANUFACTURER - AHMEDABAD, GUJARAT, India
May 13, 2013
A. UNDERSTANDING BOTH METHODS
A summary of the hot and cold blacking methods.
1. Hot blacking converts the metal surface into an iron oxide, which has no oil absorption properties. It is a glossy finish and has a black appearance when dried without oil.
2. Room Temprature blacking converts the metal surface to a copper complex, which has excellent oil absorption properties. It is a matte finish and has a dark grey appearance when dried without an oil. The oil is an important component of the process because it helps to retain the black colour and provide protection against oxidation.
- Pune, MAHARASHTRA, India
May 13, 2013
A. Thanks Ulhas.
Manish may also wish to review our FAQ "Black Oxide and Cold Blackening". In the USA (where this site is based) we use the term "black oxide" rather than "blackodising"; if people search the site for "black oxide" they will find dozens of threads addressing Manish's issues.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Functions of Sodium Nitrate & Caustic Soda in Blackodising / Blackening ProcessDecember 6, 2013
Q. Can any one guide what are the Functions of Sodium Nitrite Sodium Nitrate and Caustic Soda in Blackodising / Blackening Process?Chintan Mehta
Partner - Bhavnagar, Gujarat, India