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topic 60823

Precision Etching for 316L watch parts

August 16, 2018

Q. My situation:
I work for a watch case manufacturer that currently outsources the acid etching of it's case backs and various parts. This is both costly and time consuming as the partner we do this with is across border.

We are looking to integrate this process into our manufacturing process but since none of us is a chemist, we've met some road blocks and getting the correct information isn't easy.

First, here are the results we currently obtain from our supplier and are looking for:

i.) Clear, clean and well defined lettering and logos etched to a depth of 0.1mm (0.08 - 0.12 is the range)

ii.) A homogeneous, light grey, etched surface (not dissimilar to a fine sandblast or microbead)

iii.) We will etch designs on a flat horizontal or slightly angled surface.

Second, a few comments on the supposed means our supplier arrives at these results and the solutions we would like to explore:

a.) We suppose that our current supplier is using a UV light/photosensitive resist setup to achieve current results.

b.) We purchased a masteretch conveyor style etching machine which sprays the etchant/acid on the parts as they run through the machine. The 4 inputs we have are: Acid strength/concentration, Conveyor speed (time), Spray strength and acid temperature.

60823

Before going to the acid machine we spray the parts with a blue etch resist and cure for 30 minutes in an oven (parts are previously cleaned in trichlorethylene). We then laser engrave the design to reveal the steel where we want to etch. We want to do this instead of UV photoresist as we already have the laser machines in-house.

c.) We use Ferric Chloride (FeCl3) at 40% and 46%

d.) We've tried a 5 minute cycle time (longer and the resist is gone, less and the etch isn't deep).

e.) 45 - 49 °C acid temp

Finally, Our problems are as follows:

1.) We are unable to etch beyond 0.03-0.04mm in depth (46% allows for slightly deeper etches 0.04 instead of 0.03 after 5 minutes).
2.) The resist (we have tried numerous) is not well adapted as it either peels off during the process or cracks when we laser engrave.
3.) The etched surface is pitted and not homogenous.
4.) initial tests showed that FeCl3 worked well with 304L but it seems we are not able to replicate the same results with 316L (1.4404 and 1.4435).

Any help on this matter would be greatly appreciated.

Best,

Philippe

Philippe Meyer
Director - Geneva, Switzerland



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