Search Coils for Metal Detectors, page 20

Sealing Search Coil Cover To Secure Against Dirt & Moisture

Within the first year of using my metal detector, I started noticing short false signals while swinging the search coil in the air. No matter what program settings I was using, the false signals would not disappear.

The puzzle was solved easily when I finally detached the coil cover to clean it inside. As a substantial amount of dirt, sand, and small rock fragments fell out, not only the coil became lighter but also the false signals disappeared. The dirt that got inside, between the search coil and coil cover, through the gap consisted of mineralized soil and caused the false signals' appearance.

Prior to that discovery, I used either duct tape or electrical tape to prevent the coil cover from falling off during metal detecting. Now, to seal the gap and keep the coil cover secured, I used the silicone sealant because, for its water resistance and flexibility, it is the most reliable way to seal the gap against the elements. At the same time, the silicone sealant cushions movements between search coil and coil cover resulting from temperature changes and mechanical shocks.

Silicone Sealant

Silicone Sealant

Your objective is to seal hermetically the gap between the search coil and its coil cover (skid plate). First you have to make sure adhesive surfaces are dry and free of dirt, grease and dust as they would impair the silicone sealantís adhesion and curing. Put the cover on the search coil tightly and secure it with electrical tape if necessary.

Then you cut the plastic applicator nozzle with scissors at an angle to achieve a 1/8-inch hole in the end. Puncture the seal on the silicon tube with a nail. Screw the nozzle on the tube clockwise until it becomes tight. Place the nozzle on the area for sealant, then squeeze it to apply a small but constant bead of silicone filling the gap all the way around the circumference.

The first mistake one can make is applying too much silicone, this is easily done and can make a complete mess. So apply the silicone sparingly. If you miss a little bit you can always go back afterwards and fill the gap. Use a small spatula (you can cut it from the plastic bottle with scissors), paper or a cloth to remove the excess silicone. If necessary, use the washing up liquid and draw it along the bead of silicone.

While sealing, do not inhale the fumes over a long period or in a high concentration. Make sure there is adequate ventilation. If the eyes or mucous membranes come into contact with uncured silicone rubber, rinse well with water to prevent inflammation. Cured silicone rubber can be handled without any health risks.

Wait until the next day and wipe the coil clean with a damp cloth. If you want the coil to look neat, wipe off the residue with a cloth moistened in a solvent such as white spirit or ethanol, and follow safety instructions. It is best to save the remaining sealant as it always comes in useful. Do this by screwing a tight fitting screw into the nozzle, this stops the air getting to the silicone and curing it.

Clear Silicone Sealant On Standard Minelab 10.5" Search Coil

10.5 Inch Minelab Search Coil Sealed

Brown Color Silicone Sealant On Minelab 7-1/4" Search Coil

7.25 Minelab Search Coil Sealed

Since I sealed the coil covers on all my metal detectors, I have not had any problems so far. Unlike other joint fillers, silicone sealants have the best resistance to weathering and aging. Not even years of open-air weathering will change their physical properties. The outdoors silicone sealant, both clear and in different colors, is sold in any hardware store.

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