Fiberglass

[Pin Head]

Hi all, Will fiberglass cloth and resin hinder the performance of a spiral wound coil? And has any body tried using carbon fiber cloth instead of glass cloth and will it act like a shield?

[Nupi]

If it is based on polyester resin, it not hinder the performance.
With carbon fiber cloth I think so, but have not tried it myself.

[Qiaozhi]

Hi all, Will fiberglass cloth and resin hinder the performance of a spiral wound coil? And has any body tried using carbon fiber cloth instead of glass cloth and will it act like a shield?

I have made a quick test:
A carbon fibre sheet (approximately 11"x7", from a Caterham car) is easily detected by a VLF, but you might get away with it for a PI, as long as the sample delay is not too short.

[Koala]

be carefull with polyester resin as if mixed correctly gets quite hot.

I don't have much luck with polyester resin and vlf coils but no problems with epoxy resin and fiberglass.



You could seal the spiral wrap a protected layer over top before applying the resin and fiberglass. I have not tried on a PI detector.

[Pin Head]

I was not going to use the carbon fiber just wonder if any body has been playing with it as a shield it seams like carbon would work like graphite. Seams strange that carbon can be detected with a VLF. Will a VLF pick up heavy amounts of graphite? But I guess they are both minerals not unlike a high mineral content soil.

[Pin Head]

Not to be dumb but what is a Caterham car?

[Koala]

A few have experimented with carbon fiber but unable to get a reliable connection. I looked into trying but cost was too great.


For Caterham car google is your friend. Very famous brand of sports car in the UK

[Pin Head]

I am from US our sport cars are junk do know of the car you are speaking of.

[baum7154]

If you look at the CHANCE PI COIL thread it shows a few of my 8" fast coils used for detecting small gold. My chance detector samples down to 8us and there is no problem with the 2 layers or more of polyester resin and fiberglass I have used to armor the coils. I have heard that polyester resin will absorb moisture but the can of it I have says it is suitable for marine applications. There are quite a few pictures in the thread, one with a graphite shield layer in place before the fiberglass was put on. I always put a layer of cloth self-adhesive hospital tape over the coil and profile forming foam before glassing to insure that the air space in the coil is not flooded with resin. Flooding the air spaces slows the coil down.

Have not tried carbon fiber matt or fabric. Does anyone know the resistance per square inch of carbon fiber? If it is in the range of 2K ohms or more it might be a good shield for PI, but if it is less than that I think it will adversely affect sensitivity. The one I shielded with graphite at a resistance of 1200 to 1500 ohms per running inch exhibits some loss of sensitivity.

Regards,

Dan

[baum7154]

Did a little research on carbon fiber and it looks like it generally has about 100 ohms per inch. This might explain why the CF Fabric was so easily detected by the VLF detector. In my experience this is far too low a resistance to be used on a coil shield for a PI Detector. The research also indicated a negative resistance property of carbon fiber that was cured in resin at a very high pressure leading to a new branch of structural electronic devices.

Dan

[Pin Head]

Yes I have seen your thread and at one time I printed the pics of it (if it is the thread I am thinking of)but my pics got thrown away and I have been unable to find the thread again. I thought it was in the chance PI thread but must have over looked it. So once you build the coil you put the graphite on next? I thought there should be a certain amount of space between the coil and the shield. I will have to find the pics again because I seam to be missing something. I made a spiral coil of 22ga. cheap speaker wire from radio shack. According to several coil calculators I used it should have took around 30 turns with a 5" center. Well after I made it it only had 200uH @ 0.5 ohms. I had to splice back on to it and add another 5 or 6 turns witch made it 304uH @ 0.7ohms. I added about 3 1/2 ft of coax that I got from a old depth find transducer not even sure what coax it may be because their is no numbers on it. It is about 1/8" diameter with a very dense ground and no foil shield. With coax and cheap mic connector it measure at PCB 308 uH @ 0.8 ohms. Not looking for gold nuggets where I live, (close to St.Louis Missouri U.S.A) and the only beaches I get around are river and lake beaches when I can, mostly go to city parks and find maybe a couple hundred dollars of modern day coins a year and maybe some rings on something. Haven't really tried this coil outside yet and not sure if I even need a shield. It seams to work fine so for with out one. I was going to glass it in first for armor as you say and then take it out and try it and if needed add a shield.

[Pin Head]

Just looked through the chance pi coil thread again and although that is a mighty fine looking coil that is not the pics I was looking for. The pics I am trying to find was of a flat spiral wound with speaker wire, just can't seam to find it again.

[baum7154]

Just looked through the chance pi coil thread again and although that is a mighty fine looking coil that is not the pics I was looking for. The pics I am trying to find was of a flat spiral wound with speaker wire, just can't seam to find it again.

I assume you searched SPIRAL WOUND COIL. TEPCO is a contributor on this forum and I know he has posted on the spiral wound coils. You might do a search on his posts. The spiral coil is quite fast if built with thick insulated wire. It's geometry makes it difficult to shield without losing much of it's speed because it is so broad and flat. For best results the graphite shielding should be spaced at least 1/4" off of the windings with polyethylene foam sheet, I'd probably go 3/8". Then the fiberglass armor can be applied but you can glass it first, try it out, then if needed graphite and spacer, and glass it again. The penalty is more weight in doing it this way.

Good Luck!

Dan

[Pin Head]

Thanks for the info. searched SPIRAL WOUND COIL & post by tepco and still have not found it. I am new to this forum and not sure if I am using the search correctly but I will find it again. What are you or they getting polyethylene foam sheet is that just packing stuff? And you said I can glass it first and try it and then if needed graphite and spacer, and glass it again. Should that not be space it then graphite and then glass it again?

[baum7154]

Yes you can do it either way i.e. spacer, no shield, glass or glass it then if needed spacer, shield, then glass again. I would be inclined to just try it out without any glass or shield first and then add spacer, shield, and glass if needed.

Yes the white, pink, or black, semirigid, but resilient common foam you see in packing is typically polyethylene and is use 1/4" to 5/16" sheets of it from electronic equipment packaging. For the round sections I use 3/8" backer rod used for crack filling before caulk application. This can be had from Home Depot or Lowes, etc.

If I run across the spiral coil thread I'll forward it to you here.

Dan