Conductive paint on piezos?

[Rickard]

Hi,

I have a piezo with damaged silver coating on one side. Does anyone know if conductive silver paint (often sold as "car demister repair paint") can be used to fix it? The piezo will be used in a fishfinder transducer with up to 1000 V transmit voltage.

Regards,
Rickard

[Davor]

I know some people use silver felt tip pen to fill the vias in multilayer PCBs, so it is worth a try. There is not much current flowing there.

[WM6]

Are you sure that your piezo ceramic part for sonar transducer is still intact?
It is unusual that you lost conductive paint only without other damage on piezo pad.
But if so, then paint it back as Davor say.
If there are visible damage signs you can expect low prognosis on re-use.
What shape is your piezo?

[Rickard]

Thanks guys,

The loss of coating is my fault. It was ripped off when I retreived long piezos from a fully functional Humminbird sideimaging transducer. I plan to join several elements to get a long array with very narrow beam. You can see where the damage is located in the image. I'm bit concerned since the gap in the coating has cut of the surface completely so current must pass through the repair substance to affect the entire surface. I will test with silverpaint and see what happens.

Rickard

[WM6]

Clean with ethanol first, dry and paint it back with conductive silver coating. Should be ok.

Check first if existing conductive silver coating is surface protected with some protective (not conductive) lacquer. If so, you need to remove (using very fine sand paper granulation 300 or more) some of protective lacquer from surface to establish good contact with your paint.

[ApBerg]

Hello WM6,

Where you found the long no.3 piezo's ?

Best regards.

Ap

[WM6]

Hi Ap

You can try here:

http://www.unictron.com/product_deta...s.php?p_id=153

[ApBerg]

Hello Friends,

WM6 , thanks for the link

Rickard , do you know what the material is that is around the piezo strip ? is it some sort hard 2 comp. epoxy or is it rubber, flexibele ?

Best regards.

Ap

[Rickard]

Hi Ap and thanks WM6,

The piezo is wrapped in a thin layer with cork. In the same transducer there are also two large, circular elements, they are wrapped in very soft foam tape. I was surprised by how thin the cork layer around the long piezo is. But it seems to be enough to give some space for the small dimension variations and also to absorb and stop sound transmitted in unsuitable directions.

I have also been searching for piezo elements on the web, but found nothing useful. A transducer manufacturer gave me the advice to buy complete transducers and retreive the elements. This would be the cheapest solution, albeit awkward.

Regards,
Rickard

[ApBerg]

Hello Rickard,

Thanks for the info, ... that they still use cork as sound isolation ?! in the 70 years cork sheets have been used as decoration on walls (wallpaper) , see if I can find some.

Regards,

Ap

[Rickard]

Ap,

I think the special mix between cork and rubber in the sheets is quite good. Apart from being a good insulator this material is rather stiff which is good in a towfish application where the transducer is put under pressure. The elements must have even support and stay in their positions and I think cork plus rubber sheets can provide that, at least at the depths I need to reach - down to 40 m. These sheets are sold as gasket material for car engines.

Rickard

[Rickard]

I have a related question,

I would like to remove the original solderings on the piezos because they look clumsy (one wire came loose by accident anyway) and connect the wires with conductive epoxy. Is there any chance this might work?

Rickard

[WM6]

I have a related question,

I would like to remove the original solderings on the piezos because they look clumsy (one wire came loose by accident anyway) and connect the wires with conductive epoxy. Is there any chance this might work?

Rickard

In principle it can work, but it is question of conductivity/resistance of conductive epoxy glue point and another question is how those conductive epoxy glue point is resistant on ultrasound vibrations generated by transducer (don't forget that such piezoelectric transducer are used in surface cleaning devices too).

[Rickard]

I can report the conductive silver paint has been tested now at the highest load setting without signs of any problems. But the epoxy/glue method for soldering has not been tested due to very creative prices.... There are one-component glue productes using carbon as conductor with higher resistivity than silver epoxies, but much more attractive price. Is there any experience out there from use of such glues with pzt piezos?

Rickard

[Rickard]

I can close this sequence of issues now after testing conductive carbon glue. Carbon glue does work if the wire is clamped to the piezo while the glue dries. The result is better if the joint is wet with silver paint and then covered with carbon glue. However, best result (zero resistance) is achieved with the combination silver paint secured with standard epoxy. This bond is much stronger than the silver paint plus carbon glue combination and cheap. Let's see if the bond holds up in the long run.

Rickard