Crude coil sheilding paint

[BillNEWAST]

GRAPHITE POWDER SEED-FLOW LUBRICANT
Manufacturer Name: VAN SICKLE PAINT
MFG.UPC: 82095995003
Ensures proper lubrication & reduces friction
Use in high-speed planters & farm equipment
Helps seed flow smoothly &...
http://www.greatplainshardware.com/p...-graphite.html

I haven't tested this stuff for conductivity, BUT it's Pure Graphite as per the makers MSDS Sheet.
Sincerely
Bill Adams

[Davor]

Interesting.
I occasionally visit some agricultural shops to buy stuff such as enological steam-activated charcoal - which is a few classes purer and better than the medicinal charcoal (yuck!). Also a washing soda. I'll pay more attention to graphite now.

[Kev]

Hi,
I've ordered some of this to try, they ship internationally

https://www.stewmac.com/shop/Electro...&xst=3&xsr=515


It's composed of predominately graphite with a little carbon black.
I believe the pure carbon black paints are not the best for Minelab PI.

Cheers
Kev.

[simonbaker]

thanks

Hi,
I've ordered some of this to try, they ship internationally

https://www.stewmac.com/shop/Electro...&xst=3&xsr=515


It's composed of predominately graphite with a little carbon black.
I believe the pure carbon black paints are not the best for Minelab PI.

Cheers
Kev.

Looks good, thanks for the link!

-SB

[Kev]

Looks good, thanks for the link!

-SB

It seems good Simon, 160 Ohms across coil from 2 thin coats, I can hardly tell I've used any from the tin.
I may give it one more coat and see if my Minelab spits it back at me.
Appears to be more carbon in it than I'd like, but all the same it's very similar to what Coiltek use.
Will report back as to how it performs in the field.

Cheers
Kev.

[Davor]

160ohm seem lowish already

[Kev]

160ohm seem lowish already

Hi Davor,
Minelab PI are very very fussy when it comes to coils and the shielding must be right if you want to build an operational coil, let alone one that surpasses stock standard.
The graphite card Minelab use has a resistance of 40 to 45 Ohms per inch, and the coil above measures 35 to 40 Ohms per inch so it's in the ballpark.

Of course from a frequency domain perspective, from which I believe you are viewing this, it would be way too low, so maybe for VLF you'd need to water this paint down a bit.

I tested the coil at a beach which is littered with volcanic rocks, and it performed superbly, super sensitive while stable, now I need to test it on the goldfields which I intend to do within the week.
The spacer on this coil between the windings and shield is a very low density foam which has a very low loss tangent, and I think this is contributing to the excellent sensitivity and
depth it is achieving. Here's hoping it will also cope with highly mineralised ground.

Cheers
Kev.

[Altra]

Hi Kev,
Looking good! You have come along ways since experimenting with battery electrolyte.
I understand your coil constuction. But I am wondering what material you are using on the final layer? The layer the shield paint is applied on?
Years ago ml used some kind of cloth tape on the large mono coils. I always worried about expansion or contraction effecting the conductivity.

[golfnut]

I have had very recent success (tonight) using graphite loaded epoxy.

I figure if your potting in epoxy, why not have the screen medium in the potting resin. No foil, mylar, sprays, just a short drain wire ~1-2".



I mixed 25g of 100um graphite with 20g of thin-ish epoxy. Thick but has flow.

Trowel application - popsicle stick works well - brush useless.



It is exposed on mine and will be my scratch cover as well. Top up if wears thru.

I had read that the conductive paint has to be potted over - in my tests earlier it is fine with conductive epoxy exposed. Tested earlier on damp grass and clover no chatter an falsing - Im quite encouraged.

It went from totally unusable on wet or damp grass/clover to close to perfect . It ground balances properly and more crisp too.

It goes on like demerera sugar or tarmac, and settles to reaonably smooth. Before full cure squeegee it with a damp jaycloth encourage it to lie down flat.

You could leave this recessed and later scratch it up and por nice shiny potting compound on top, if looks are your bag.

S

[golfnut]

There is a carbon product callled Graphene and acheives really low ohmic values.

S

[Kev]

Hi Kev,
Looking good! You have come along ways since experimenting with battery electrolyte.
I understand your coil constuction. But I am wondering what material you are using on the final layer? The layer the shield paint is applied on?
Years ago ml used some kind of cloth tape on the large mono coils. I always worried about expansion or contraction effecting the conductivity.

Hi Altra,
The closed cell foam is covered with a couple of layers of ABS dissolved in MEK, this makes a smooth contiguous surface for the shield.
Once the plastic hardened I gave it a light buff with sandpaper to ensure the paint has something to grasp hold of.

Two other features of this coil may have added to its extreme sensitivity.
1) the Litz wire was given a single wrap of plumbers Teflon thread seal tape before winding the coil. This gives greater inter-winding insulation and resistance and lowered capacitance
2) the solder joints in the coil are covered by a ferrite core from a 75 to 300 Ohm TV balun. This is to evaluate a recent Minelab patent, and it give electrical isolation of the joints too.

Originally I used to paint the shield straight on a masking tape wrap, but I believe continuity was interrupted by movement and vibration etc., just as you feared with the cloth tape.

Cheers
Kev.

[Kev]

I have had very recent success (tonight) using graphite loaded epoxy.

I figure if your potting in epoxy, why not have the screen medium in the potting resin. No foil, mylar, sprays, just a short drain wire ~1-2".


S

Hi golfnut,
Thank you for your suggestion and congratulations on finding a workable solution.
I hadn't planned on epoxying this coil, it is to be eventually sealed up in an ABS housing, it is just taped together at present.
I will though investigate your suggestion for a waterproof coil.

What resistances are you seeing with your shield?
Is it for use on a Minelab PI, VLF, or other?

The reason I used the low density closed cell foam to isolate the shield from the winding was to reduce any absorption attenuation or hindrance to the field lines.
I have noticed that embedding the coil in epoxy or having shields close to the windings causes a marked loss in sensitivity. This is predominately with Minelab PIs but for a robust truly waterproof coil, potting is the best compromise.

In line with what you mention I at one time had a coil of mine leak so that the shield had continuity with the water the detector become much quieter and may have had better responses to targets, but it died before I could fully investigate it. It maybe time to look further into it.

Cheers
Kev.

[Altra]

Hi Altra,
The closed cell foam is covered with a couple of layers of ABS dissolved in MEK, this makes a smooth contiguous surface for the shield.
Once the plastic hardened I gave it a light buff with sandpaper to ensure the paint has something to grasp hold of.

Two other features of this coil may have added to its extreme sensitivity.
1) the Litz wire was given a single wrap of plumbers Teflon thread seal tape before winding the coil. This gives greater inter-winding insulation and resistance and lowered capacitance
2) the solder joints in the coil are covered by a ferrite core from a 75 to 300 Ohm TV balun. This is to evaluate a recent Minelab patent, and it give electrical isolation of the joints too.

Originally I used to paint the shield straight on a masking tape wrap, but I believe continuity was interrupted by movement and vibration etc., just as you feared with the cloth tape.

Cheers
Kev.

Thanks, that's quite a process. I sure you will feel good when you see the first gold, making it all worth it.

[ODM]

Nice method, makes for a rigid waterproof coil of arbitrary shapes.

However, didn't the ML solder/ferrite patent have very small "component pin" sized ferrite beads, of high saturation flux material?

[Kev]

Nice method, makes for a rigid waterproof coil of arbitrary shapes.

However, didn't the ML solder/ferrite patent have very small "component pin" sized ferrite beads, of high saturation flux material?

Hi ODM,
That maybe so, but after going through all my ferrite materials junk box the ones that gave a minimal signal response were the early miniature TV balun cores, almost undetectable. All other "beads" gave responses like pieces of iron. I need to find out what material was used for the old ribbon to coax baluns and obtain some small beads of the same, but for now I am just observing. It maybe that my machine doesn't sample early enough to achieve much benefit from this anyway. Who knows at this stage there maybe some advantage having both wires running through a homogenous core?

Cheers
Kev.