Discussion Aluminum or Brass End Plugs ?

[jaguar75]

As you may already know,aluminum prices have crashed very hard.
I can buy 4" round 6160 aluminum for only $6.16 per 1-1/8" but it would need to be anodized for use in chlorinated swimming pools,which I will be submerging into an Olympic size public pool.
I can also buy 4" round 360 brass but it is $36.00 per 1-1/8" and is far superior to anodized aluminum for corrosion resistance.It is three times the weight but not that much.I like the idea of easier repair with brazing brass and the longivity.
I'm not comparing this with plastic,I'm using metal, and I am machining the end plugs myself, so what are your opinions.
_________________
John

[kazzer]

Machine the aluminum, then anodise it. Want colors?

See http://www.caswellplating.com/kits/aluminum.htm
Free Anodising Instructions

[jaguar75]

Very nice products!
I am trying to weigh the benifits of using anodized 6061 aluminum versus 360 brass.The price for 360 brass is not bad for the small amount needed for the end-plugs,anodizing is not needed,it is easliy repaired with silfloss soldering and has longivity.On the other hand,anodized aluminum is tough,nicely colored and very lightweight but how does it fare in chlorinated swimming pool water? Will I have to disassemble the end-plugs everytime I submerge in the water? Will they corrode?

[jaguar75]

The reason why I would like the use of 360 brass is that I am in the swimming pool industry (www.indeksolar.com) and have seen the corrosiveness of public swimming pool water chemistry.The problem with municipal swimming pools is that they cannot afford the high cost of water metering and so they let the total dissolved solids rise to the high point of the tds meter and it becomes corrossive,eating everything in it's path.Pools having a tds of 2600ppm is not uncommon.I once called the health department about a typical case and they closed the pool because the pool water tds was so high.When it gets very much over 700ppm it will not enable the sanitizers to oxidize and disinfect the pool water.This will cause a cryptospiridium outbreak,which can kill infants and the elderly.The one single cause for this disease is any type of diapered children using the pool.

[kazzer]

Numerous companies making aluminum fittings for swimming pools anodise their products. This alone is a good reason to choose aluminum over brass.

I'd suggest you ensure you rinse off the boat in fresh water before long term storage, and therefore contact with the chemical will be minimal.

Certainly anodising aluminum will be easier than nickel plating it.

You could also pose the question on our 'aluminum anodising forum' where we have many experienced anodisers lurking.

Originally Posted by jaguar75

The one single cause for this disease is any type of diapered children using the pool.

Do they still let diapered kids in pools? YUK!

[Aeroengineer1]

The German/European groups have been using 6061 without issues due to chlorinated water. It tends to work pretty well. It can be anodized, and if you are not going for fancy colors, you can go for a hard anodize (Type III, Class 1 for a harder coating, Class 2 for a sealed finish). With the type III anodize you can get a hardness value equal to some common steels, and hence it is very abrasion resistant, and the color tends to be a dark grey.

As to the use of brass in a wtc, there is not obvious reason to not use it except that it is a very dense metal, and hence any of it that is above the waterline will have to be accommodated for with extra ballast, and could possibly cause some surface handling instabilities.

Hope this helps.

Adam

[jaguar75]

Thanks for the brilliant reply Adam.
I have decided to use aluminum and go with the hard finish.Are there more color choices for the hard finish?
Aluminum is so affordable now that the market has gone from investment to a commodity.I think 360 brass is going to crash as well.

[kazzer]

Type III anodise is extremely difficult for an amateur to produce, and even more difficult to prove an expert has actually accomplished it. The spec differences between II & III are so close it isn't even worth messing with for your application.

I guess the question we are always asked is "Can I do 'Hard' anodising?" and the answer is, "How hard is hard? Type II is hard enough!"

You can't dye type III effectively. Don't waste your time with this. You need type II. RTFM and learn about the exclusive Caswell LCD system. This is a well proven method that you can easily do in a home workshop.

[Aeroengineer1]

I hate to break this to you Mike, but there are some very distinct differences that separate the Type II and the Type III style anodizing processes, and if the shop producing it cannot accurately produce one or the other, then it amounts to nothing more than a decorative coating that could be accomplished easier by etching and alodining and perhaps a spot of paint.

So that it is known, the primary differences between Type II and Type III are the thickness and the density of the coating. A Type II anodizing will produce very little dimension growth (about .0002" per .001" of overall coating thickness) and the coating thickness is typically much less than .001" whereas for Type III the coating thickness can be up to about .004" (though overall hardness increases only up to about .003") and dimensional growth is much greater than Type II (about .0005" per .001" of overall coating thickness). The densities of the two different types of surfaces coats are also vastly different; Type II has a specified coating density of >1000mg/ft^2 where as Type III has a specified density of 4320mg/ft^2 (I am not too sure why the units are so strange for this, but hey it is straight out of MIL-A8625F). It is this density difference that provides superior abrasion resistance for Type III over that of Type II, and due to the fact that anodizing it self actually forms an aluminum oxide, it is in a very chemically stable state (ie does not want to corrode). The reason that these will eventually corrode, given the proper adverse conditions, is that they are slightly porous, and some of the aluminum substrate can eventually be attacked. Another difference between Type II and Type III is that Type III does not take color as well as Type II. The main reason being is that it will have a dark grey undertone produced by the conversion process.

In the end, how can you tell if your part has a Type III vs a Type II finish? The main method is the dimensional change. If you really do not trust your metal finisher, you would take a measurement/s of the wall thickness of the tube before and after. A typical Type III coat is .002" thick (remember half, .001", penetrates the substrate and half, .001", is actual dimensional growth) and the tubing will have two sides that have grown measurably. The overall change in thickness should be on the order of .002" where as for Type II it should be about .0004" (most calipers cannot measure this).

In the end hard coat (Type III) is not as pretty, though it is attractive, but is a more scratch resistant finish and offers near the corrosion resistance of Type II, but Type II can be finished to nice colors.

I personally am in favor of Type III for many applications, including a current project I am doing at work that requires wear resistance. This was the coating chosen over electroless nickle and hard chrome.

Adam
The practical engineer

[nick_75au]

This is all very interesting but how much corrosion can occur in 4 hours or even 8 hours immersion then a fresh water wash fair enough if the part was a pool component constantly in the corrosive environment.

Nick

[kazzer]

Originally Posted by Aeroengineer1

I hate to break this to you Mike, --------

In the end, how can you tell if your part has a Type III vs a Type II finish? The main method is the dimensional change. If you really do not trust your metal finisher,

Adam
The practical engineer

I have heard it all before, (many, many times) but what you are proposing is that an amateur can fathom this, and physically produce it in his basement. Or send it to an anodiser at great expense for a one or two off. Simply not so practical.

The difficulty of producing this marginally superior finish (not so if you want to dye it) for this particular application doesn't warrant the extra effort of Type III. Bin there - dun that - doesn't work for the average Joe.

[kazzer]

Originally Posted by nick_75au

This is all very interesting but how much corrosion can occur in 4 hours or even 8 hours immersion then a fresh water wash fair enough if the part was a pool component constantly in the corrosive environment.

Nick

Exactly! Some are discussing how many angels can stand on a pin head here!

Read the article here on our anodising forum by NEILFJ


I repeat -- You could also pose the question on our 'aluminum anodising forum' where we have many experienced anodisers lurking.

[expfcwintergreen]

Originally Posted by nick_75au

This is all very interesting but how much corrosion can occur in 4 hours or even 8 hours immersion then a fresh water wash fair enough if the part was a pool component constantly in the corrosive environment.

Nick

Exactly, therefore why even bother with the anodizing step at all. Unless you want pretty colors, then you would need to go Type II.

If you have a metal finisher in your neighborhood, talk to them about your project, let them know what you are working on and they may toss it in the bath with another job at minimal/no cost. Anodizing is a batch process, same cost for one piece or a hundred. I farm a lot of work around to different shops and find that I can get the occasional "government" job done on the side.

[Aeroengineer1]

Like I said before, the Germans/Europeans have been using 6061 for quite a while without any problems. I guess that I could have been more specific in saying that, "if you are really concerned" you can anodize it, or for that matter alodine it (it is not pretty, but very effective for corrosion resistance, and much much easier than anodizing for the person that is going to do it at home). You can pick up alodine from Aircraft Spruce for about $30 and it will treat more aluminum than you will probably ever use in a lifetime.

As for differences in the coating types, I guess we just use good shops that have consistently provided accurate results.

[expfcwintergreen]

Adam, you are right on target as usual.