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Hi All,
Charles provided a link to a couple of shielding paints that can be used for coil shielding. Those paints are the electrodag and the aquadag. Now, both appear to work ok but they are both quite expensive.
Wouldn't it be nice to find a paint that would work and cost a whole lot less? Well, that may be possible. There are some paints out there that will work. They just do not have the real low resistance of the ones mentioned above. Is the resistance low enough to work? For that answer I went searching for some info I found posted By George Payne some time back regarding the shielding. Here is what he said:
"Sometimes there are very simple answers why some manufacturers use paint and others use foil or paper for the loop faraday shield. Usually it is related to ease of construction or cost, not necessarily to performance. Each technique has its advantages and disadvantages. And, you may only determine what those factors are by trial and error. My background has been in using paint shields. This process can be a little tricky if you don’t know what to avoid. For example. It’s best to have a very smooth surface on which to place the paint. Painting a shield on an irregular surface can cause excessive noise in the detector. If fact early Discovery loops had only the bottom cover painted in order to avoid too many surfaces that were not smooth. However, after some problems were worked out all their loops were 100%shielded. Making an electrical connection to a paint shield is difficult too. When I was with Teknetics we experimented with many correction methods before settling on one process that produced consistent results. A poor connection was prone to breaking loose or producing very high detector noise. Generally its best to have some distance between the shield and the coils. However, I have seen many designs were the shield is place directly on the wire. A foil shield for example. The conductivity of the shield must be low enough to not interfere with the detector operation. My personal experience has suggested that resistances around 10K ohms per square or optimum. However, the resistance can vary quite a bit without effecting detector operation. When this value drops below 1k then you can have pickup problems."
Here is the link to that info:
http://jb-ms.com/Baron/gb.htm
Getting back to the shielding paint, I found a paint that is really quite cheap. The cost does vary depending upon where you purchase it and can range probably somewhere between about $8 and $14 a quart. Also it comes in different varieties and not all have been evaluated, but the spray paint has. Anyway, the paint is made by Van Sickle and goes by the name of EZ Slide. It comes in three different varieties inlcuding regular oil base, a combustible version, and waterborne mixture. They vary in the carrier of the graphite, more than the mix itself. I believe the waterborne and the combustible are new and were designed because of the limitations of shipping the oil base. Finally, this paint comes in a spray can which is very similar to the oil base in nature. This sells for about $5 a can.
Last but not least, for those who want to try to make their own mixture or want to thicken the existing one, they sell a high quality graphite powder for a little more than $4 a lb.
One place to purchase this paint is where I bought mine and that is P & R Supply. Here is the link to the page with the EZ Slide info:
http://pandrsupply.com/SearchResult.aspx?CategoryID=24
Just tell them Reg sent you. No, I don't get a discount if other people buy from them but they were extremely helpful and willing to send out as little as one can, so I told them I would try to steer business their way. Also, they were curious to know if the paint would work for the shielding application.
One last note, if you do not like how this stuff works for shielding, then you can use it for its original intended use and that is to provide a very slippery surface. This paint is intended to be used as a coating on various surfaces to keep things from sticking. Good examples would be the bottom of a lawn mower, on a snowblower, maybe on a show shovel, etc, etc. Heck, I am even thinking about coating the undercarriage of my ATV or my vehicle to keep dirt from sticking and to reduce drag. Who knows, I might even pick up a mile per gallon. They say it works on power boats also.
Now, one final note, I found the resistance of this paint to vary with the number and thickness of coatings. Using the spray I found a single coat can be as high as 5K or so and 3 coats can be down less then 300 ohms. BTW, it is messy so it should be used outside and proper precautions taken.
Have fun. This stuff is great and has a lot of different uses. The beauty is, it is cheap.
One last note, my first shielding attempt using the spray worked just fine. I had three coats on the bottom half of the coil housing and 1 good coat on the top. I may try just one good coat on both next time.
Reg
Charles provided a link to a couple of shielding paints that can be used for coil shielding. Those paints are the electrodag and the aquadag. Now, both appear to work ok but they are both quite expensive.
Wouldn't it be nice to find a paint that would work and cost a whole lot less? Well, that may be possible. There are some paints out there that will work. They just do not have the real low resistance of the ones mentioned above. Is the resistance low enough to work? For that answer I went searching for some info I found posted By George Payne some time back regarding the shielding. Here is what he said:
"Sometimes there are very simple answers why some manufacturers use paint and others use foil or paper for the loop faraday shield. Usually it is related to ease of construction or cost, not necessarily to performance. Each technique has its advantages and disadvantages. And, you may only determine what those factors are by trial and error. My background has been in using paint shields. This process can be a little tricky if you don’t know what to avoid. For example. It’s best to have a very smooth surface on which to place the paint. Painting a shield on an irregular surface can cause excessive noise in the detector. If fact early Discovery loops had only the bottom cover painted in order to avoid too many surfaces that were not smooth. However, after some problems were worked out all their loops were 100%shielded. Making an electrical connection to a paint shield is difficult too. When I was with Teknetics we experimented with many correction methods before settling on one process that produced consistent results. A poor connection was prone to breaking loose or producing very high detector noise. Generally its best to have some distance between the shield and the coils. However, I have seen many designs were the shield is place directly on the wire. A foil shield for example. The conductivity of the shield must be low enough to not interfere with the detector operation. My personal experience has suggested that resistances around 10K ohms per square or optimum. However, the resistance can vary quite a bit without effecting detector operation. When this value drops below 1k then you can have pickup problems."
Here is the link to that info:
http://jb-ms.com/Baron/gb.htm
Getting back to the shielding paint, I found a paint that is really quite cheap. The cost does vary depending upon where you purchase it and can range probably somewhere between about $8 and $14 a quart. Also it comes in different varieties and not all have been evaluated, but the spray paint has. Anyway, the paint is made by Van Sickle and goes by the name of EZ Slide. It comes in three different varieties inlcuding regular oil base, a combustible version, and waterborne mixture. They vary in the carrier of the graphite, more than the mix itself. I believe the waterborne and the combustible are new and were designed because of the limitations of shipping the oil base. Finally, this paint comes in a spray can which is very similar to the oil base in nature. This sells for about $5 a can.
Last but not least, for those who want to try to make their own mixture or want to thicken the existing one, they sell a high quality graphite powder for a little more than $4 a lb.
One place to purchase this paint is where I bought mine and that is P & R Supply. Here is the link to the page with the EZ Slide info:
http://pandrsupply.com/SearchResult.aspx?CategoryID=24
Just tell them Reg sent you. No, I don't get a discount if other people buy from them but they were extremely helpful and willing to send out as little as one can, so I told them I would try to steer business their way. Also, they were curious to know if the paint would work for the shielding application.
One last note, if you do not like how this stuff works for shielding, then you can use it for its original intended use and that is to provide a very slippery surface. This paint is intended to be used as a coating on various surfaces to keep things from sticking. Good examples would be the bottom of a lawn mower, on a snowblower, maybe on a show shovel, etc, etc. Heck, I am even thinking about coating the undercarriage of my ATV or my vehicle to keep dirt from sticking and to reduce drag. Who knows, I might even pick up a mile per gallon. They say it works on power boats also.
Now, one final note, I found the resistance of this paint to vary with the number and thickness of coatings. Using the spray I found a single coat can be as high as 5K or so and 3 coats can be down less then 300 ohms. BTW, it is messy so it should be used outside and proper precautions taken.
Have fun. This stuff is great and has a lot of different uses. The beauty is, it is cheap.
One last note, my first shielding attempt using the spray worked just fine. I had three coats on the bottom half of the coil housing and 1 good coat on the top. I may try just one good coat on both next time.
Reg
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