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Old 01-11-2010, 08:21 PM   #1
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Aluminum Frame for a Liner?

I'm thinking about aluminum. Would it be crazy to use aluminum to build the frame? I got the idea after seeing a gorgeous aluminum trailer that was built for a friend's boat. The boat weighs about 8000 pounds. The I-beam is probably 7-8 inches deep.
I'm just thinking about options. I've seen plenty of steel frames, and even that fancy stainless frame, but I'm curious if anyone has used all-aluminum, or if it would be a bad idea? I want to really use my trailer and want modern weight-adding things like tanks and brakes. The old pipe frame, as much as I appreciate the idea, probably isn't something I should consider replicating...

Thoughts?

Rae
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Old 01-11-2010, 08:30 PM   #2
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Along with the aluminum frame, you could probably come up with some kind of aluminum floor, like Airstream did with some Argosy Minuets in the '70's.
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Old 01-11-2010, 08:38 PM   #3
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A friend has an all aluminum car trailer for his street rod. I don't know why a frame couldn't be made for your trailer.
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Old 01-11-2010, 08:56 PM   #4
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Rae, I considered this with my Liner. It was very cost prohibitive and the weight savings it very little, maybe a couple hundred pounds. You must use much more material to make up the structural integrity aluminum. I went with a standard steel "ladder" frame. My Liner fully outfitted comes in at 3500 lbs.
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Old 01-11-2010, 09:11 PM   #5
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Rae,

You could certainly make a frame out of aluminum. But, you'd be better off to rivet it or bolt it together, rather than weld. If you weld it, you ruin the heat treat and weaken it.

As Old Trucks said, it is a lot more pricey than steel. But it would make a really cool frame. I could help you design it if you wanted. It would be a little harder to make than a steel one, but not totally unreal.

You could just do a steel one, welded up, and get it powdercoated silver

best of luck,
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Old 01-11-2010, 10:27 PM   #6
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VINSTREAM VINTAGE AIRSTREAM TRAILER CUSTOM DESIGN RESTORATION SALE

The first and only non rot floor and no rust frame!!!!! Need I say more!

Todd
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Old 01-11-2010, 10:28 PM   #7
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Jim,

I know my featherlite car hauler is all welded. They only both the tongue coupler to the frame rails and the axles. Do I have to worry about the welds cracking?
You would think you could use this same technology on the airstream.

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Old 01-12-2010, 03:41 AM   #8
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VINSTREAM VINTAGE AIRSTREAM TRAILER CUSTOM DESIGN RESTORATION SALE

The first and only non rot floor and no rust frame!!!!! Need I say more!

Todd
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Old 01-12-2010, 05:03 AM   #9
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Rae,

You could certainly make a frame out of aluminum. But, you'd be better off to rivet it or bolt it together, rather than weld. If you weld it, you ruin the heat treat and weaken it.
SF,

Jim's point is something to consider. As a rule of thumb when aluminum is joined by welding there is strength loss. resulting from the heat input. Below is part of a rather lengthy report I wrote on the topic a while back discussing aluminum behavior. It will help you fall asleep.

Aluminum

Aluminum weldments are heat treated to increase strength in the weld, or heat affected zones after welding has been performed, not to relieve stresses. Stresses in aluminum weldments are a result of heat related distortion, not temper changes. Some aluminum alloys change temper when welded, some do not. The resulting temper change typically returns the temper to it’s original state which is weaker, not stronger. Aluminum characteristics, and how aluminum behaves when welded are discussed in the following paragraphs.


Aluminum Characteristics

Aluminum alloys can be divided into two primary groups: Non-Heat–Treatable (NHT) consisting of alloy families 1XXX, 3XXX, 4XXX, and 5XXX. Heat-Treatable (HT) consisting of alloy families 2XXX, 6XXX, and 7XXX.
Let’s look at the differences between NHT and HT alloys.
NHT alloys cannot be strengthened by heat treatment. They can only be strengthened by cold working. After cold working, the alloy is given the designation of an F temper (as-fabricated). Alloys are then often given a subsequent annealing heat treatment, after which they are classified as an O temper (annealed). Many alloys are sold in this condition. Thus the correct designation for a plate of 5083 which was annealed after rolling is 5083 – O. One of the attractive properties of these alloys is that they can be significantly increased in strength if they are cold worked after annealing. So when we brake, bend, or form NHT alloys they gain strength.
With HT alloys the scenario is somewhat different. HT Alloys are heat-treated by initially heating the material to approximately 1000°F (540°C), holding the temperature for a short time, and then quenched in water. This operation is intended to dissolve all the alloying additions in solution and hold them there at room temperature. Some HT alloys also “age” at room temperatures, which can lead to additional strength increase over time. This is very important when forming this type of material. Case in point, I’ve actually seen instances where we received an order of a certain HT alloy. A portion of the material was worked (bent, formed, broken) shortly after receipt. Several weeks later when the other portion of the same material was worked, it fractured, and broke.
Most HT alloys are given additional heat treatment when produced to obtain high mechanical properties. This heat treatment consists of holding the material at approximately 400°F for a few hours. During this time, the alloying additions that were dissolved in the prior heat treatment precipitate in a controlled manner, which strengthens the alloy. Material in this condition is designated as T6 temper (artificially aged), the most common heat-treated alloy temper. Most of us are probably familiar with 6061-T6.
The aluminum tempering designation system is more complex than this, but this covers the basics.

Aluminum Behavior When Welded
When aluminum is joined by welding material properties are changed. This is typically exhibited as a loss of strength in the weld, or areas adjacent to the weld.
In NHT alloys such as 5052-H32 the physical alteration occurs in the Heat Affected Zone (HAZ). The HAZ is the area of the base material adjacent to the weld. This damage is usually limited to re-crystallization and grain growth, which creates minimal strength loss in the base material. The weak area in the case of 5052-H32 is the weld itself.
In HT alloys such as 6061-T6 the loss of strength is observed in the HAZ, due to the dissolution, or coarsening of the strengthening precipitates. Arc welding of HT alloys constitutes an additional heat treatment for the HAZ. As such some alloys experience an additional solution heat treatment, while others over-age in the HAZ.
This results in a loss of material properties, especially if the as-welded properties are compared to T6 properties. For example, the minimum specified tensile strength in ASTM B209 for 6061–T6 is 40,000 psi. In the post welded state we routinely see measured tensile strengths drop to the 26,000 psi range. Very significant! The weld/HAZ strength can be restored to T6 properties if the weldment is re-heated treated (i.e., solution treatment at 1000˚F, with a 400˚F quench/age). This practice is commonly performed on small structures such as bike frames, etc.
So when we look at this scenario we see that the weld joint strength is typically weaker, which does not indicate a built in “Stress” issue. In reality it means we have somewhat ductile condition as along as the material alloy and welding electrode alloys are matched for the specific application.
Hot cracking of aluminum welds is not a “stress” issue, it’s an alloy selection issue. When we discuss aluminum alloys we usually refer to “weldable” or “non-weldable”. What we really mean is can the material be welded without hot cracking. Hot cracking in aluminum weldments is typically a function of base material and weld material chemistries, not stress. Some alloys such as 6061can be welded without filler metals, but they will almost always crack. To prevent cracking when welding 6061 it is necessary to use filler materials high in silicon, or magnesium.


Regards,

Kevin
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Old 01-12-2010, 07:49 AM   #10
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Ok, so that makes sense about the no-weld/ bolt-rivet instead attachment.
The boat trailer I looked at was fastened this way as well. It was a "military-grade" trailer.

I'm certainly interested in pursuing this idea- if I can afford it. I'm not sure what something like this would cost. It could be something of interest to other Airstreamers...a test pilot of sorts.

I was thinking last night- between sleep, that the area where the springs/shocks come into the frame would be a stress area and maybe that requires a doubling-up of the frame? The other stress point I'd think would be on the tongue where the anti-sway control runs into the A frame? (My lingo is awful- I know! I'm still in the "thingy/ whatchamacallit" stage )...

My other questions: Is there concern over condensation between the floor and bellypan? How about road salt?

And ... I really wanted to put down a wood floor- could I still do that? I have a neat idea with the floor. It could just float on top- doesn't have to be structural- if that helps...

Rae
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Old 01-12-2010, 07:50 AM   #11
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Vinstream-- very cool. Have you put this one all together? I'd love to see it!
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Old 01-12-2010, 08:00 AM   #12
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Originally Posted by Kevin245 View Post
SF,

Jim's point is something to consider. As a rule of thumb when aluminum is joined by welding there is strength loss. resulting from the heat input. Below is part of a rather lengthy report I wrote on the topic a while back discussing aluminum behavior. It will help you fall asleep.

Aluminum

Aluminum weldments are heat treated to increase strength in the weld, or heat affected zones after welding has been performed, not to relieve stresses. Stresses in aluminum weldments are a result of heat related distortion, not temper changes. Some aluminum alloys change temper when welded, some do not. The resulting temper change typically returns the temper to it’s original state which is weaker, not stronger. Aluminum characteristics, and how aluminum behaves when welded are discussed in the following paragraphs.


Aluminum Characteristics

Aluminum alloys can be divided into two primary groups: Non-Heat–Treatable (NHT) consisting of alloy families 1XXX, 3XXX, 4XXX, and 5XXX. Heat-Treatable (HT) consisting of alloy families 2XXX, 6XXX, and 7XXX.
Let’s look at the differences between NHT and HT alloys.
NHT alloys cannot be strengthened by heat treatment. They can only be strengthened by cold working. After cold working, the alloy is given the designation of an F temper (as-fabricated). Alloys are then often given a subsequent annealing heat treatment, after which they are classified as an O temper (annealed). Many alloys are sold in this condition. Thus the correct designation for a plate of 5083 which was annealed after rolling is 5083 – O. One of the attractive properties of these alloys is that they can be significantly increased in strength if they are cold worked after annealing. So when we brake, bend, or form NHT alloys they gain strength.
With HT alloys the scenario is somewhat different. HT Alloys are heat-treated by initially heating the material to approximately 1000°F (540°C), holding the temperature for a short time, and then quenched in water. This operation is intended to dissolve all the alloying additions in solution and hold them there at room temperature. Some HT alloys also “age” at room temperatures, which can lead to additional strength increase over time. This is very important when forming this type of material. Case in point, I’ve actually seen instances where we received an order of a certain HT alloy. A portion of the material was worked (bent, formed, broken) shortly after receipt. Several weeks later when the other portion of the same material was worked, it fractured, and broke.
Most HT alloys are given additional heat treatment when produced to obtain high mechanical properties. This heat treatment consists of holding the material at approximately 400°F for a few hours. During this time, the alloying additions that were dissolved in the prior heat treatment precipitate in a controlled manner, which strengthens the alloy. Material in this condition is designated as T6 temper (artificially aged), the most common heat-treated alloy temper. Most of us are probably familiar with 6061-T6.
The aluminum tempering designation system is more complex than this, but this covers the basics.

Aluminum Behavior When Welded
When aluminum is joined by welding material properties are changed. This is typically exhibited as a loss of strength in the weld, or areas adjacent to the weld.
In NHT alloys such as 5052-H32 the physical alteration occurs in the Heat Affected Zone (HAZ). The HAZ is the area of the base material adjacent to the weld. This damage is usually limited to re-crystallization and grain growth, which creates minimal strength loss in the base material. The weak area in the case of 5052-H32 is the weld itself.
In HT alloys such as 6061-T6 the loss of strength is observed in the HAZ, due to the dissolution, or coarsening of the strengthening precipitates. Arc welding of HT alloys constitutes an additional heat treatment for the HAZ. As such some alloys experience an additional solution heat treatment, while others over-age in the HAZ.
This results in a loss of material properties, especially if the as-welded properties are compared to T6 properties. For example, the minimum specified tensile strength in ASTM B209 for 6061–T6 is 40,000 psi. In the post welded state we routinely see measured tensile strengths drop to the 26,000 psi range. Very significant! The weld/HAZ strength can be restored to T6 properties if the weldment is re-heated treated (i.e., solution treatment at 1000˚F, with a 400˚F quench/age). This practice is commonly performed on small structures such as bike frames, etc.
So when we look at this scenario we see that the weld joint strength is typically weaker, which does not indicate a built in “Stress” issue. In reality it means we have somewhat ductile condition as along as the material alloy and welding electrode alloys are matched for the specific application.
Hot cracking of aluminum welds is not a “stress” issue, it’s an alloy selection issue. When we discuss aluminum alloys we usually refer to “weldable” or “non-weldable”. What we really mean is can the material be welded without hot cracking. Hot cracking in aluminum weldments is typically a function of base material and weld material chemistries, not stress. Some alloys such as 6061can be welded without filler metals, but they will almost always crack. To prevent cracking when welding 6061 it is necessary to use filler materials high in silicon, or magnesium.


Regards,

Kevin
Excellent post.

Kip
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Old 01-12-2010, 11:35 AM   #13
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I'd be inclined to stick w/ steel for this application. If you're worried about corrosion, have the frame flame-sprayed w/ zinc or painted like a steel boat hull w/ a two part epoxy paint. There are also some one-part moisture-cured polyurethanes that work really well on steel.

Issues w/ aluminum frames:

  1. Pick your alloy carefully; many aren't really suitable for a marine environment - which is what you have in the winter time in the snow states.
  2. If you weld the aluminum frame, remember that the strength of the welded areas will be that of the annealed alloy.
  3. If you use bolts, they should be stainless to reduce corrosion.
  4. The frame on the AS is a conductive member; bolted joints can cause high resistance connections, ground loops and other electrical problems.
  5. You'll need a taller frame to insure adequate stiffness; this may interfere w/ ride height or axle mounting.
Aluminum frames can be made to work - but it's much more of an engineering project than a steel frame. You may wish to spend your time and money on something that will have a greater impact on your enjoyment of the AS...

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Old 01-12-2010, 01:18 PM   #14
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Featherlite and Pro-Tech

These are two mfg's out here in PNW area that specialize in aluminum fabrication. I have seen all kinds of stuff put out by Pro-Tech-just look at virtually every semi-tractor you see...look for a black and aluminum colored name tag-aluminum is the way to go with an aluminum floor, too-you may want wood, but aluminum wont rot.
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