HARD CHROME PLATING PROCESS CRODA NF-T

HARD CHROME PLATING PROCESS CRODA NF-T
PHYSICAL PROPERTIES: CRODA NF-T: Red powder
DESCRIPTION:
CRODA NF-T is a fluoride-free high efficiency and performance non corrosive hard
chrome process, with a current efficiency of appr. 25%.
It is used to substitute traditional hard-chrome plating processes.
CRODA NF-T can be used in all installations which are usually used for traditional
sulphuric based chrome baths.
Due to its high current efficiency the production costs are proportionally 30% below
traditional chrome baths.
ADVANTAGES:
1. High plating efficiency. (1 micron/min. at 60A/dm²)
2. Free of fluorides and non corrosive.
3. Micro cracked deposits, reaching 1.000 cracks cm/line.
4. Bright, levelled and hard deposits. (1.000 - 1.500 HV)
5. Possibility of chrome multi-coat, for example chromium without micro cracks with
a excellent corrosion resistance.
6. Good metal distribution.
7. Easy control and maintenance.
EQUIPMENT:
Tanks:
Steel tanks with chromic acid resistant coating. PVC or PTFT.
Heating:
Teflon or Teflon - electric heater.
Anodes:
Lead - Tin anodes ( 93% Pb - 7% Sn )
Anode - Cathode Ratio:
minimum 2 : 1
V. Kunz Rev 1.1 25.09.2002 1/3

MAKE-UP OF 100 L:
Chromic acid 25 kg
Sulphuric acid 96 % 0,2 - 0,4 kg
(depending on quality of Chromic acid)
CRODA NF-T 1,5 kg
Half fill the tank with clean warm water (40 - 50° C) then add the chromic acid slowly
and carefully, stirring well. When the chromic acid has been completely dissolved,
water, sulphuric acid and CRODA NF-T should be added to make up the solution to
working level and correct density. Stir thoroughly, to ensure that it is mixed well.
WORKING CONDITIONS:
MAINTENANCE:
Cathode current density 20 - 90 A/dm²
Anode current density 15 - 25 A/dm²
Voltage 9 - 18 V
Specific Gravity (15° C) 21° Be
Temperature 55 - 60° C
15 g CRODA NF - T per 1 kg Chromic acid
Controls may be done by checking the specific gravity of the bath and the sulphate
content. Nevertheless it’s recommended to do complete analysis periodically in order
to assure its good performance.
Analysis methods are available.
If sulphate content is too low, sulphuric acid may be added in proportions of 10 ml/
100 litres of bath solution. If sulphate content is too high, barium carbonate can be
added to the chrome solution with the proportion of 15 g/100 litres to reduce sulphates
in 0,075 g/l. Content of 3-valent Chrome is admitted until 3 g/l.
GENERAL INFORMATION:
By running the bath the anodes are normally covered by a dark brown, chocolate
coloured film. Anodes should be worked at 0.8 to 1 ampere per cm of anode length for
10 minutes to ensure the formation of the correct anode film. The surface of the
anodes should not be allowed to become covered with a thick hard scale. The anodes
should be regularly cleaned, the frequency depending on the rate of formation of scale.
The optimum results will be achieved by running a anode current density of minimum
20 A/dm².
V. Kunz Rev 1.1 25.09.2002 2/3

CONTAMINANTS:
Impurities which affect all hard chromium plating solutions will also effect the
CRODA NF-T process. The common ones, like iron and trivalent chrome, will always
reduce the conductivity, and where thick deposits are being plated may contribute to
roughness.
Cationic impurities may be removed by the usual methods of cationic exchange resins
or electro-dialysis with membranes.
ETCHING OF STEEL PARTS:
The etching solution is made to the same formula as the chrome solution and should be
contained in a separate tank. In this operation the positive cable is connected to the
work rod. The etch should be used at the same temperature as the plating solution and
at a current density of 25 - 40 A/dm² for 1 minute. Long etching should be avoided.
Cast iron should not be etched, but should be degreased and struck at full plating
voltage in the plating tank. Components which have not been etched should be
immersed in the plating solution and the current applied only after they have attained
the temperature of the bath. To prevent excessive build up of iron in the solution,
articles should, preferable, be etched in a separate tank.
CHROMIUM PLATING:
The articles should be removed from the etching tank and immediately hung in the
chrome depositing solution with the current already switched on. They should gas
vigorously and the current be maintained according to the surface area of the articles.
The articles may be inspected during deposition but must be swilled in warm drag-out
solution at 55° C, not cold water, before replacing in the plating tank. Following a
lengthy withdrawal of the work it must be reverse etched in the chromium plating bath
for about 10 sec before deposition is resumed. After removing the articles from the
chrome bath they are rinsed in the drag out tank, where they receive a first swill,
followed by running cold water rinses and finally used a hot water rinse. The solution
in the drag out tank can be used to compensate the evaporation losses.
SAFETY PRECAUTIONS: see Material Safety Data Sheet.
GUARANTEE:
Above instructions and recommendations are the result of intensive testing and shop
experiences. They are for your information, only.
Our guarantee extends to the continuous quality of our products as they leave our
factory and not to their usage in the field, which is a factor beyond the control of a
supplier.
V. Kunz Rev 1.1 25.09.2002 3/3