measuring coating thickness of small metal springs

hi, does anyone know a method to measure coating thickness of small metal springs?

Hi,

capacitive measurement.

Where the coating acts as dielectric material. The thicker the coating, the thicker the dielectric, the more the distance between electrodes, the smaller the capacitance.

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i also can imagine eddy current.



Klaus

KlausST said:

Hi,

capacitive measurement.

Where the coating acts as dielectric material. The thicker the coating, the thicker the dielectric, the more the distance between electrodes, the smaller the capacitance.

*********

i also can imagine eddy current.



Klaus

Click to expand...

thanks for the quick reply. can you tell me any standard product in market available to do what i asked?

Hi,

i know that there are tools for measuring paint finish at cars to check if the car had an accident.

But sorry i caonßt recommend a tool.


Klaus

KlausST said:

Hi,

i know that there are tools for measuring paint finish at cars to check if the car had an accident.

But sorry i caonßt recommend a tool.


Klaus

Click to expand...

In your case some research will have to be undertaken. There are commercial instruments utilizing eddy currents for measuring coating thickness on flat steel or aluminum. For other shapes you will have to modify sensor shape and take several calibration steps with gradually increasing coating thickness. You can use simpler capacitive sensors but again, the sensor contact shape must be modified to your object shape and calibrated with growing coating thickness.

Without further details, it is hard to say much. What is the coating? and how large and consistent are the springs? I feel that a capacitive method could be very difficult to archive, as the parasitic shunt capacity would swamp the value you are trying to measure.
I fancy using the cross section(or part of it) to complete the magnetic path between the jaws of a pair of soft iron tweezers, which you plunge into the coil capturing part of one turn (needs a stop for constant insertion depth?). If a low frequency energised coil on one leg, the magnetic field goes down one leg through the crossection of the wire then up the other leg into the other end of the coil. Any shunt effects would be minimal.
Frank

A destructive test procedure may be easier.

1. Cut the spring and take a single turn coil (looks like a helical spring lock washer).

2. By using a small vice press the single turn coil at its cutting side, so that helicalness disappears.

3. Measure the diameter of the coated spring wire by a digital micrometer screw gauge.

4. Take out the coating (by using emery paper or chemical or other way) and measure the diameter of the uncoated spring wire.

5. Coating thickness = [diameter(coated) - diameter(uncoated)] / 2

Digital micrometer screw gauges with 1um (0.001mm) resolution are easily available.
ebay link: **broken link removed**

ahsan_i_h said:

A destructive test procedure may be easier.

1. Cut the spring and take a single turn coil (looks like a helical spring lock washer).

2. By using a small vice press the single turn coil at its cutting side, so that helicalness disappears.

3. Measure the diameter of the coated spring wire by a digital micrometer screw gauge.

4. Take out the coating (by using emery paper or chemical or other way) and measure the diameter of the uncoated spring wire.

5. Coating thickness = [diameter(coated) - diameter(uncoated)] / 2

Digital micrometer screw gauges with 1um (0.001mm) resolution are easily available.
ebay link: **broken link removed**

Click to expand...

thank you for the information. i need to know further how to take out ONLY the coating for different coating/base material combinations. if you have any experience in this field, pls help me.

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i attached a photo for further detail. pls help.


https://drive.google.com/file/d/0B95NmAoZNKhZZFBocUQtbEZNRTg/view?usp=sharing

Can't see the photo. Placing the link in address bar brings a photo but I guess it is not spring related.

Chemically removing the coating is easy and accurate. Google search with the words "[coating name] stripper", you will get many stripping chemicals. For example NISTRIP removes nickel coating from many different base materials and SUPERSTRIP MS removes many different coating materials from steel. Reference link: http://www.pcichemicals.com/electroplating-product.php?sid=273

If chemically removing the coating is not possible, then you can try with mechanical abrasion method. Repeatedly apply abrasion on a specific area of the sample and after each time compare it's color with neighbouring area. When a clear visual difference is found with exposed color of base material then coating removing is done.

You can also burn the coating and scrape off the residual.