| Author |
Message |
Emery Leraand (142.59.137.29)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 07, 2003 - 5:06 pm: | |
I am told by a repair shop that the siding on the new MCI coaches is aluminum. We have pretty well decided on either aluminum or flat stainless and are looking for opinions on why one or the other is desirable. Obvious that the stainless weighs more and also that it is likely to cost more. Probably need a heavier gauge of aluminum for dent resistance. Our old coach does not require a structural skin so looks, cost and ease of working with the material are prime considerations. 54 inches from drip rail to the top of the bay doors and we don't want a midpoint joint if possible. 42 year old original stainless is still sound, but dented and not available as a direct replacement.
Emery
1958 MCI |
Skorpio (Skorpio) (24.92.193.195)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 07, 2003 - 5:41 pm: | |
If the goal is to have shiny metal, forget the aluminum unless you want to buy the big gallon size cans of Never-dul every couple of months. The basic rule with stainless is the more nickel and chrome in it the more shiny it is (and the more it costs, sort of). Good flatware is 18/8 or even 18/10 which is 18% Chromium and 8 or 10% Nickel, and has really good luster. 18/8 is also known as type 304 stainless. Aluminum would need to be about twice as thick to have the same dent resistance. A good quality stainless will probably cost you about twice as much as aluminum. |
Prather (63.184.209.102)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 08, 2003 - 9:49 am: | |
Just saw on TV that they can clear powder coat AL now. Takes care of the loss of shine problem and is much more durable that anodized coating. Don't know what the cost would be. |
Skorpio (Skorpio) (24.92.193.195)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 08, 2003 - 11:57 am: | |
Yes but it doesn't look like polished aluminum, Problem with aluminum is that it is an instant oxidizer, and aside from magnesium its probably the most chemically unstable metal you could actually use structurally. Aluminum has to be coated with something or it will react, and it actually coats itself with aluminum oxide as soon as you cut it. Basically if you clean aluminum with a solvent so that a coating sticks to it, it doesn't shine much anymore. Powder coating only keeps the surface consistent it doesn't lock in the shininess.
From a metallurgy perspective aluminum has some great properties and some horrible ones. We know the good ones; light weight, easy to form, shape, good casting properties, excellent electrical and heat transfer properties, on the down side it has high dielectric qualities (reacts and creates an electrical current and corrodes when it touches another metal, especially zinc and copper), highly reactive (powdered aluminum is the main ingredient in fireworks and solid rocket fuel), when in a chain reactive state the reactions are violent (if you get aluminum burning it is almost impossible to put out, it will suck oxygen out of anything, burns underwater), It flows (meaning aluminum acts like a very slow flowing liquid, kinda like silly putty, electric companies that use electric wire for distribution have to go around every few years and remove the slack from the wires).
When you make things out of aluminum the basic rule is to make components completely out of aluminum and with as much structural bulk as possible and isolate it from any direct contact with dissimilar metals. So if you were making bay doors for example, ideally you would want to make the frames for the doors also out of aluminum and use aluminum fasteners or weld it to the frame. If using fasteners the contact area should be as large as is practical (airliners have formed countersinks to increase the fastener contact area to lessen the flowing properties of the metal). Gaskets should be used around stainless latches so the aluminum doesn't create a dialectic union with the stainless. Aluminum when polished has one of the highest reflectivities of any metal except maybe silver (maybe) but dulls quickly as the aluminum oxide layer gets more than a few angstroms thick. Like I stated earlier, with the exception of magnesium, there isn't a structural metal that oxidizes faster. Look where the chemical symbol AL is on the periodic chart sometime, next to magnesium (road flares) and sodium (burns if you get it wet) and close neighbors to lithium, potassium and phosphorous all of which are scary in their pure form.
Don't get me wrong aluminum is a great material, you just need to understand its properties when you use it if you want something lasting from it, particularly in any application when it is expected to weather the elements. |
Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 08, 2003 - 4:54 pm: | |
Several years ago, I had the aluminum wheels for my sand rail clear powder coated. Due to running in the sand all the time, it was impossible to keep them looking good because of the sand blasting effect.
The powder coating company polished the wheels and then immediately powder coated them. They definitely did not have the same shine as just the freshly polished wheels, but they did look very good and the powder coating lasted for several years. Apparently the sand blasting did not affect the coating very much.
Richard |
FAST FRED (209.26.115.225)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 09, 2003 - 5:45 am: | |
"Don't get me wrong aluminum is a great material, you just need to understand its properties when you use it if you want something lasting from it, particularly in any application when it is expected to weather the elements"
Most items that were properly designed & built of aluminum seem to be able to do amazing things.
It has been common practice for 40 years to NOT paint aluminum cruising yachts (except to antifoul the bottom) and I have seen a few after circumnavigations that were structurally brand new.
Sure they could have used a scotch brite pad to get out some scuff marks from piling & docking encounters, but otherwise , no paint , no anodizing , no powder coating and not a bit of difference from 5 or 10 years earlier when new.
Yes special techniques are used to solve problems , mostly by just welding everything on , not using bolts.
The real hassles come when anyone is foolish enough to use SS below the water ( or anyplace where it can be oxygen deprived).
The SS with out O2 goes nuts and suffers from crevace corrosion , and departs in very short order , no matter the grade of SS.
Coaches , happily are not stuck perminantly in an electrolite like seawater ,
"The Great Disolver".
But any coach will surely last longer ( even the rust prone tube framed Eagles) if a method is used to disolve the road salts.
Salt Away (from the boat store)& power wash or if painting is to follow Chlorid power wash will go a long way to keep what ever the coach is made from , from disolving.
A coating if some type protection is nice too.
Cheap insurance,
FAST FRED |
Skorpio (Skorpio) (24.92.193.195)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 09, 2003 - 10:27 am: | |
Yes with aluminum, corrosion resistance is all about mass, keep the aluminum oxide penetration percentage to minimal levels, and minimal surface areas for the job to be done.
I didn't know about the seawater/stainless thing is it because of the alloy crystallization? That would seem strange since the only common denominator to all grades of stainless is Iron and Carbon (Stainless Steel is a very loose term). How does that work for food service applications where they use SS tubing for water based liquids? Just curious I was thinking when I got around to building a [bus, coach, RV, motorhome, what ever is the proper phrase today] I would use SS for plumbing to minimize plastic leaching and not have corrosion problems associated with drained copper when empty or not pumped up (Copper corrodes if there is air bubbles in the water).
And I was bracing myself for some error in my summation of how aluminum is used in aircraft from you Fred ;) |
FAST FRED (209.26.115.230)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 09, 2003 - 4:06 pm: | |
Most water in common use has mucho air entrained, so SS has no crevace corrosion problems , as it likes the air.
I do keep my hard copper water lines full , using "drinkable " (non poisonous ) antifreez when needed ,
But have a summer cottage that was plumbed with brass water pipe in the early 50's and had stood empty of water all winter for 50 years.
I removed some of the piping for a remodel & the stuff looked in great condition.
The well is soft , so I dont know what would happen with hard water.
The hospitals have glass piping for removing goodies , not sure if you could use it for supply .
But you would have to paint it black to keep all light out , or suffer green slime in the drinks!
Flush rivets on aircraft are for their low drag heads , not much difference on holding in most text's.
FAST FRED |
|