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topic 4970

Conductive thread film


(2000)

I have an application where I depend on electrical conductivity between a stainless steel nut and aluminum male thread and an aluminum nut and aluminum male thread. This path is always adequate at initial installation but then it deteriorates.

I would like something that I can apply to the threads to maintain this bond. I believe the deterioration is caused by corrosion. I have the addition of a non-conductive substance like loc-tite improves the situation considerably. I would like this to be something that does not create a mess.

Nick Kreigh
- Fort Wayne, In.


First of four simultaneous responses

(2000)

Hi Nick, Is it at all possible to replace the stainless with another material? If not, and loc-tite serves your purpose for the most part, then what about this, are the aluminum parts chromated? This would allow for flow of electrical contact, while providing additional corrosion resistance to the aluminum/stainless mating surfaces.

Matthew Stiltner
plating company - Toledo, Ohio


Second of four simultaneous responses

(2000)

Nick, Many years ago, when copper prices were very high, aluminum wiring was installed in new houses (including my sister's). With time, the aluminum oxidized. As aluminum oxide is a very good insulator, the electrical contact resistance increased, in many cases causing overheating at the socket and fires. To solve the problem, you'll have to plate the aluminum surfaces with copper or some other material that either will not oxidize, or whose oxide is less insulating than aluminum.

jim treglio portrait
Jim Treglio
- Vista, California


Three of four simultaneous responses

(2000)

The Locktite is actually decreasing the current carrying capacity of the nut/bolt connection. Why not use an aluminum nut. Gets rid of a lot of problems.

The electronics folks have a white paste that they put on diodes on dissimilar metals to increase the conductivity to the frame and decrease corrosion. I would guess that it is a silver compound. It to is messy, but a little dab will do a big job. Apply it with more precision.

James Watts
- Navarre, Florida


Fourth of four simultaneous responses

(2000)

If you are looking for a clear coating to use, either a PTFE or acrylic should do the trick. Both will provide added corrosion resistance, but PTFE is not known for it's prolonged protection to normal weathering.

A dip and spin method is easy to use, but if your volume is low and not worth setting up, you may want to get the process jobbed out. We have even provided some coaters with a nylon coating for similar protection.

Brian Grochowski
- Mt. Holly, North Carolina


(2000)

Dear Nick,Coat PTFE fluoropolymer based coatings on threaded nuts ,this is the better corrosion resistance and good electrical insulation property.teflon,greblon are manufacturing this kind of materials.

kalyan dhakane
Kalyan Dhakane
Mumbai, India


(2000)

We appreciate your many helpful responses today and lately, Mr. Dhakane, but I think you read too quick this time smiley.

Mr. Kreigh is looking for a good conductor and you are describing a good insulator. They are opposites.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

Aluminum electrical conductors are still used in many applications, and corrosion is a serious concern. Corrosion inhibitors are used at the connections for aluminum wiring. You could check with electrical equipments suppliers to check out alternative products. Conductive epoxies, such as those used for some circuit board applications may also work. These would have the advantage of providing some corrosion protection, holding the joint type (like Loc-tite), and providing electrical conductivity.

larry hanke
Larry Hanke
materials testing laboratory
Minneapolis, Minnesota




(2000)

As for the Al nut to Al threads, chromating of both Al parts is likely to be adequate. However, for st. steel nut to Al threads, I wonder if chromating of Al, plus zinc plating of steel would be a better choice (unless you want to use cadmium plating on steel). Can anyone comment on the effect of current flow on galvanic corrosion in these cases?

Mandar Sunthankar
- Fort Collins, Colorado


(2000)

Mandar: Current flow will not be a factor in the corrosion as long as the electron travel along a metal-to-metal path. If the two metals are not in contact and the current flows through an electrolyte from one metal to the next, then corrosion can occur. I believe that the corroded metal will be the one from which the electrons the exit into the electrolyte.

larry hanke
Larry Hanke
materials testing laboratory
Minneapolis, Minnesota




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