51089

Need 0.001" zinc plating on MS screws, even the heads  

January 29, 2009

We require 25 microns ( 0.001" ) zinc plating on iron screws.
In a trial lot working on 7 volts with acid zinc barrel plating for 4 hours on 6 kg screws ( taking 75 - 80 amp current ) we got reading of 27 microns on a small 1" square plate got plated along with screws. Laboratory also confirms 27 microns on plate.
Will the round head of screw will also contain the same microns or not ?

Asheesh Kumar
Plating shop - New Delhi, India

I have been thinking about this a little bit...

If I think about it in theory...

6 kg of screws... maybe 16 dm2 per kg... but you should definitely check your exact surface area as with screws it might be a much higher surface area than the above number.

For Acid Zinc...

um per minute = i * 0.285

where i = current density in ASD (amperes per square decimeter)

You have 80 amps with 96 dm2 so you have around 0.8 ASD.

So you get 0.2375 um per minute.

25 um / 0.2375 um per minute = 105 minute plating time

HOWEVER... the heads might be a low current density area and there might take longer to get the 25 um minimum.

The "plate" you have in the barrel load possibly has a lower current density than the threads and sharp edges of your screws. And I am not sure that the "plate" is a good reflection of the current density that your parts receive.

To be absolutely certain... I recommend to measure the "head" with an X-Ray if this is possible (maybe these screws are too small). If the screws are too small... you might put in a larger screw that can be measured by X-Ray as this screw might be more reflective of the "true" current density that your small screws receive.

I hope I have been more helpful than confusing... : )

Thomas E. Kidd
- Budapest, Hungary

For very heavy thicknesses, electroplating is hardly the finish of choice. On the high current density areas, the deposit will not be very ductile; it will flake off producing "stardust," as some platers call it. In addition, it will be in the electroplating line a long, long time. A far better choice would be mechanical plating, which has better economics over about 0.0005" to 0.0007".

Tom Rochester Plating Systems & Technologies, Inc.   Jackson, MI, USA