Removing Stainless Screws from Aluminium Rig?

[Guest]

What's tefgel Mr Wolf?

[PaulR 3]

Tef-Gel.

 

1. The function of Tef-Gel in eliminating dissimilar metal corrosion is the elimination of electrolytes from entering the interface of the metallic surfaces. Tef-Gel paste contains 40% PTFE powder and 0% volatile solvents, no silicones or petroleum solvents to evaporate, which would leave voids for electrolytes to be drawn into creating a galvanic cell. When both surfaces are coated and mated with Tef-Gel there are no voids for electrolytes (saltwater) to be drawn in by capillary action over extended periods of time.

 

EXAMPLE:

 

A. Bolt with nut or lock nut. Bolt into tapped aluminum, steel, stainless steel, inconel.

Use mascara brush, bottle brush, or toothbrush to apply a thin coat of Tef-Gel to both the threaded hole and the bolt threads and tighten. (Torque requirements may have to be altered according to application of thread lubricants).

 

B. Bedding surfaces: A closely mating surface (10 mils .010 or closer) can be protected from capillary action by applying a thin coat of Tef-Gel with brush, toothbrush, or plastic scraper and assembling the parts and cleaning excess product with mineral spirits or WD-40.

 

Tef-Gel does not electrically insulate hardware. The PTFE (40%) is ultra fine powder that will extrude out of the contact area and into the voids of the surrounding areas.

 

Tef-Gel applied between electrical contacts and connectors does not increase the resistance of the connections even at hundreds of amps, maintaining the integrity of EMI shielding.

 

2. The function of Tef-Gel in eliminating seizing galling and friction welding of stainless steel, inconel, and other nickel alloys.

 

EXAMPLE:

 

Tef-Gel applied to both mating surfaces of nuts and bolts or threaded holes and bolts leaves a layer of 40% solid PTFE within the thread interface, which works as friction barrier. Tef-Gel, which contains 0% volatile solvents, will no evaporate, cold flow, or dry out, giving protection many years later when hardware must be dissembled.

 

Cage Code: 05SA2

NSN: 8030-01-450-4009

HMIS Rating 100B

 

Tef-Gel is a registered trademark of Ultra Safety Systems, Inc.

[wheels 543]

Just like the Tefgel, keeping the two surfaces apart and water out can be down with several products. I have had good results using Locktite and it has the added advantage of locking the thread, but at the same time, allowing it to be removed with a little effort later on. Lanocote seems to work well at least so far, but i have not pulled something apart 20yrs later to really see. I used to use Rescue-Steel, but now i use Nickel antisieze. It has the big advantage of allowing dissimilar metals, especially when one is SST, to thread without thread damage. The compound never hardens, so it always remains to keep the materials protected.

Another material is a non-solvent urathane adhesive/sealant. You use them as the bedding compound anyway and so it is right there for the threads. I slodge a liberal amount on, screw the thread home and wipe the excess off using a bit of WD40 to clean it or best is Turps. Everythng is then sealed, bedded and sound and i have removed the threads later with no issues.

[Guest]

I use Duralac for SS into Ali. It is a messy yellow liquid that sets.

It works by the same priciple as Tefgel.

[Gappy 9]

yip and durlac is one of the most toxic products you can buy not many people I know use it know becuase of this Tefgel is great use it all the time

[wheels 543]

Gappy, it is toxic, but not that bad in the actual mixed state you get it in. Duralac is just Barium Chromate. Which happens to be a very commonly used compound, even as a paint colour. It is a natural at being an electrolytic isolator and is used in many paints as a corrosion inhibitor. In it's powder form, it is nasty stuff if inhaled, but once it is captivated in a mixture, it is not so bad. Although you should not handle it, just like many other chemicals that we should ot handle.

[MrWolf 0]

We especially use Tefgel on any fastenings that are likely to need removal.

 

Duralac sort of sets, and we use that on the more permanent fasteners. You can still remove duralac'd in screws but you need to apply more duralac before you put the screw back in, where as tefgel you can take out the replace the screw a few times.

[smithy09 50]

Use a hammer, make sure your screw driver is old. Put the screw driver in the slot like you were going do undo them and give the top a good wack, this loosens the crud most times. But heat is good too.

I'll second that. On Jap motorcycles right through the 70s and 80s they used what we called "butter bolts" pozi drive machine screws that seized into the alloy engine cases. Impact drivers just ripped the heads off, so then you had to drill and tap. An old mechanic showed me how to do it. He took a punch (flat end pin punch) and rested it on the end of the screw, then whacked it. Then he used a screw driver or possibly an impact driver. The whack actually stretches the threads slightly and breaks the "weld" between the alloy and stainless.

Interesting thread with all this stuff available to insulate stainless from alloy. I always used silicone but thos looks heaps better.

[wheels 543]

Yeah a good wack and the screws can nearly be undown with your fingers. But it's a slightly different reason why they sieze in there. The white corrosion is a different beast again. If you can get them after smacking them one, then great. But sometimes the corrosion is so bad, that techneque won't work.

[ScottiE 174]

I've used heat then a good whack with a hole punch then product similar to WD-40 (can't think of it at the mo - will edit later) and then finished off with another good whack. I think the idea is to get a couple of minute cracks in the white stuff after heating it to open a little more, then the WD-40 gets into contact with more surface.

Always been nervous about impact drivers but if you're doing it often enough you get to know how much torque it'll take to twist off a screw head. But one problem with screws is that if they're quite old and been under tension (which is often the case) then they can be susceptable to stress corrosion cracking especially is the thread ends very close to the head. In the case of a screw in a mast - If they're tapped into a mast wall then they won't be under very much tension at all (the thread would have stripped out of the ali on install). But with an engine block machine screws are usually torqued into place (and have a much longer thread embed to achieve the tension the designer wants) to eliminate fatigue failure and that's where you can have a few issues.

 

While where on the subject - where can I get some decent sized molybdenum rivets - the largest size at burnsco isn't quite big enough and I need to put my goose neck back on the boat. Only need 6 or 8 (plus one or two to cover the usual collateral drop in the piss!)

[ScottiE 174]

sorry - I guess I meant monel - was thinking aboout somut else at the same time.

[wheels 543]

Monel, you want to try the fastenings suppliers like Blacks Fastners or Mico or similar. For very small amounts, a Chandler may have them, but you are paying heaps more.

Where you can, the use of Monel is far better than SSt and even Titanium screws and bolts are available if you can find them and they don't corrode. And yes they are expensive, but the cost has come down huge amounts now that technology has improved in making the things.

[Guest]

I get the impression many here don't actually know what one is or have never used a impact driver.

 

Don't know about stripping threads when you 1st screw them in Scottie but I suppose there has been a few dickhead mast builders in the game over the years. Why a good sparmaker would go out of their way, as you would have to do, to strip them I have no idea.

[wheels 543]

Yes many over tighten screws. You only need to be firm. Another reason to use a bedding compound.

A good thread type to use in alloy is a coarse thread, not fine. So either a UNC or Imperial thread is best to use. The really fine metric threads don't have enough grab and you can easily strip the thread out.

[ScottiE 174]

sorry - I may not have explained myself too well. I was trying to explain that the reason for some mechanic's approach the removal of old set screws in alli blocks is because often those screws were torqued in. As a consequence they are more susceptable to the heads twisting off as they may have been compromised. The last thing you want to do to 25yr old pride n' joy block is loose a screw in the bloody thing (whereas a 25yr old GBE rig has no place in the marine envrionment in the 1st place!) Screws in spars are probably almost exclusively subjected to shear, don't need to be/aren't torqued up and as a consequence are not quite as susceptable (though the do have their own unique set of issues).

(I got tangled up explaining thread embeddment length needed to achieve tensioning - sorry KM)

[Guest]

You're still on the CC list Scottie, Xmas card before you think I'm sending a Credit card:)

 

We never torqued in screws like that don't know anyone who did so in theory a good whack should break the screw/corrosion seal and it's fingers to get the screw out. The theory usually was right. We used impact drivers all the time to remove screws. Like most things start gentle and work up to 'up fecking piece of crap come out or I'll fecking hurt you big time'. Sharing the tops off was very unusual, mind you screws were better back then knot to sometimes soft sh*t that is most these days.

[Guest]

ScottiE

For Big monel rivets try eddie at nordic marketing : http://sailutions.co.nz/ , barrys point rd, takapuna.