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Up Topic Welding Industry / General Welding Discussion / Repair welding on Al trailer
- - By devo (***) Date 08-13-2007 20:14
The company I work for has an aluminum trailer with a crack in the tongue.  It was sent in to a local weldor to be repaired.  The crack is in the flange of the C-channel that makes up the tongue of the trailer.  The crack is about 24" back from the hitch.  This weldor charged $35 per hour for his "expertise".  He simply smeared some Mig weld over the crack and called it good.  A day later the weld cracked, and now it is starting to creep down the web of the channel.  I told my employer I can do a much better job with my Tig welder, not to mention I will do little things like grinding out the crack and actually getting some penetration, unlike this joker's PJP weld.  The question is, can a crack like this be repaired?  Since it has been poorly welded twice now, I assume the HAZ has gotten pretty soft.  I was thinking about doing a CJP weld on the crack, and then welding a cover plate for about 6" on either side of the crack.  Where the web meets the flange gets a little thick in cross section for my 200 amp machine, but some He gas might do the trick.  So all of you expert Aluminum repair weldors think about this one and let me know what you think.
Parent - - By Kix (****) Date 08-13-2007 20:33
I think you should of welded it in the first place.;-)  Yeah you need to fix that crack with a CJP weld and buff er out and then need to fix the reason it cracked in the first place by putting some sort of stiffener on it like you said.  Should of been an easy fix and i can't believe how many jokers are out there that have their own businesses that do this kind of work and don't go under.  Makes me want to start up a fab shop, but i allways thought you had to have a lot of luck at first to keep from going under in a couple years and i'm not a gambling man.
Parent - - By js55 (*****) Date 08-13-2007 20:50
You need to find out first what kind of Al it is before you do anything. Even good welders will crack it if you use a filler that puts you in crack sensitive ranges with Cu, Mg, Si, etc.
Maybe some of th Al guys in here can help us on common alloys for that application.
Parent - - By reddoggoose (**) Date 08-13-2007 21:18 Edited 08-13-2007 21:26
I would think that the trailer is some 5XXX alloy. A 5356 electrode should do the trick. Like Kix mentioned I would fish plate the cracked area.
Parent - - By ssbn727 (*****) Date 08-13-2007 23:33
May I also suggest to also "fish plate" both the flanges and the web of the "C" channel to add strength towards the overall weakened location where the crack propagated...

Afterwards, in strategic locations just otuside of the area where the fishplate within the web is located if possible, fit gussett(s) or, stiffener(s) within the "C" channel itself, adding even more structural strength to the channel itself.

Sounds like what you're pulling is way too much for the original design of the tongue which has therefore weakened the overall integrity of it - as a result, and the tongue area, and it's adjacent components needs some "beefing' up to withstand the loads that are being put on those components of the trailer.
Just my two cents :)

Respectfully,
Henry
Parent - - By Milton Gravitt (***) Date 08-14-2007 02:03
Maybe you can box the C-channel making it stronger if its not in a bad place to get to.
Parent - - By DaveBoyer (*****) Date 08-14-2007 04:45
As others have suggested the design was not up to the task, or it wouldn't have broken. Aditional material needs to be added. How You achive this is pretty much up to You, as the rest of Us can't see the trailer. I would suggest that the repair cover a great length of the tongue [ ending where load should be less], or You will have more cracks in the parent material in the HAZ at the ends of the repair. Some of the aluminum trailers on the market are not engineered in the slightest, just built on a "Wing and a Prayer". I know because I know someone who builds them this way. My boss has a poorly designed aluminum dump bed and lift tailgate that have always been troubble, no good way to make them better either [economically], so I patch them up as needed.
Parent - - By 803056 (*****) Date 08-14-2007 13:45 Edited 08-14-2007 13:48
Unlike steel, aluminum does not have a lower stress level (other than zero stress) where fatigue is not a factor.

To say it another way, aluminum is always going to fail by fatigue if it is subjected to any cyclic loading no matter how low the stress is.

Even if the original welds were perfect (Right!), you can expect fatigue to cause cracking. Even once the frame is repaired, it will crack elsewhere. The aluminum frame has a finite fatigue life after which the battle against cracks is on going, never to be won. 

Fish plates, cover plates, call them what you may, will only transfer to load to another area that is near it's endurance limit and the cracks will initiate in the new area where the stresses are highest.

I'm not saying you are wasting time, effort, and money, just be aware that aluminum is going to crack at some point in time once the fatigue limit has been reached.

The other responses regarding knowing the alloy, proper selection of filler metal, etc. are all true. However, don't overlook the importance of proper cleaning and joint preparation. Most of the problems I've seen with aluminum go back to cleaning and preparation.

Another item to consider, finishing of the welds. Avoid notches like the plague. Grind any CJP groove welds flush. Concave fillet welds perform better than convex fillets, etc. Any porosity detected should be excavated and rewelded. Any welds ground to improve the surface contour should be lightly tapped with a wire brush. The tapping will reveal the porosity as slight rounded depressions. You have to look close to see the, but its effort well spent. You can "pop" the depressions with a sharp scribe if they at due to porosity (and they will be!). Intersecting welds (x, y, and z axis) can result in stresses that easily exceed the tensile strength of the weld. Intersecting welds are  prime location to examine closely for cracks.

Good luck - Al
Parent - - By devo (***) Date 08-14-2007 14:42
Thank you all for the great responses.  In the book "Welding Fabrication and Repair" by Frank Marlow there is a good chapter on repairing borken truck frames.  It describes all of the reinforcing methods that have been described on this thread.  It suggests bolting a plate tight against the web of the C-channel and welding stiffeners along the flanges.  As long as the bolt holes aren't too large and they are drilled in the neutral axis of the member, it shouldn't weaken the channel too much, right?  I am trying to figure out how to do as little welding as possible.  This trailer was not designed by an engineer, and it appears to have been welded by someone who mostly knew what they were doing.  While I agree with the comment about the trailer being underdesigned for the loads it is experiencing, the crack is on the TOP flange, not the bottom one, which is where I would expect it to be.  I work for a whitewater rafting company where this trailer is driven on sketchy West Virginia roads with me and my fellow raft guides riding in the back of a stake bed truck which is pulling the trailer.  I don't want to be in the truck if this trailer fails on the road, and buying a new one is out of the question, so I am trying to convince my owner to let me fix it.  And I only charge him $20/hr!
Parent - - By DaveBoyer (*****) Date 08-15-2007 04:00
The middle of the web [neutral axis] in theory is loaded only in shear IF the load is a force parallel to the web. That will be the safest place to drill if You are using bolted repairs. I am unfamiliar with the book You have, but You are most likely better off folowing that advice than disregarding it. Might the crack have started from side loading, like if someone jacknifed it backing up? If it is built from 6061-T651, a common extrusion alloy and heat treatment, it is unlikely to bend [permanantly] much before failure.
Parent - By Bob Garner (***) Date 08-15-2007 16:25
If this material is the tapered flange type C channel, it is likely 6061 T6 alloy.
Parent - - By ssbn727 (*****) Date 08-15-2007 18:09
Hi Al!
first of all , No Ofense there Devo but, sometimes we overlook the fact that this gentleman named "Devo" may not be privvy to all of the nomenclature we tend to unknowingly share with him in this thread.

So my question to Devo would be: Do you understand all of the acronyms, terms, that are being used in this thread  wiht the ultimate goal of passing along suggestions that will help you repair your trailer???

Respectfully,
Henry
Parent - By devo (***) Date 08-15-2007 20:42
I appreciate your concern Henry.  While I am  relative novice when it comes to welding (6 months rebuilding coal mining equipment and another year of repair work/odd jobs), I have taken a couple of courses from Lincoln Electric and I have acquired a decent library from which I have gained a lot of good info.  Just for fun sometimes I like to try and read the research supplements in the welding journal, but usually they just make my eyes cross.  So far, everything posted on this thread has been making sense to me, but I am never afraid to admit when I am clueless.  I have found that once I admit my ignorance, a great wealth of knowledge will come my way.  I even used trigonometry on a recent welding project!  Never thought that would happen.  So thanks for the advice and keep it coming.
Parent - By Sourdough (****) Date 08-15-2007 16:42
Reddog and Henry have a very good point........why did it crack in the first place?

Fishplate or start over if you ask me..........
Parent - - By js55 (*****) Date 08-15-2007 17:19
rdg,
I wantd to respond to your post here because it got me to thinking. Uh oh.
Anyway, the 5XXX makes a lot of sense, necesary for one such as myself with limited Al application diversity experience. Though of course nothing is for certain, but: it certainly wouldn't be 1XXX, not strong enough, nor 2XXX, precip hardening for a trailer?, nor 3XXX, still generally not strong enough, I say generally as an estimate, nor 4XXX, used mostly for fillers, possibly 6XXX, though this is mostly used for extrusion/tubing, etc, nor 7XXX, again a precip alloy. So 5XXX is the logical assumption. But I believe it was Henry that recently posted about the meaning behind the word assume.
However, good post. 5XXX seems the most logical choice once one cures himself of cerebral rectumitis.
Parent - By reddoggoose (**) Date 08-16-2007 02:41
Whether 6XXX or 5XXX, a 5356 should readily weld either one. However, you are right, there are people out there who do the weirdest things.
Parent - - By DaveBoyer (*****) Date 08-16-2007 03:23
5xxx might be the best material,[I don't know, I havn't reasearched it] but the guy I mentioned who builds by the "Wing & a Prayer" method uses 6061-T6 0r T651, probably due to availability, and I am pretty sure they were welded with 4043, at least the ones His brother built for Him. Don't get the idea that I endorse His product, choices or methods.
Parent - - By js55 (*****) Date 08-16-2007 12:39
Dave,
Avaialbility and price is probablyan important issue for him. I would guess. And thats not to say there wouldbe anything wrong with that choice. I don't know enough to argue it. But I would support dbg's contention that 5XXX is a better choic, or at least more likely, for structural like trailers, due to solid solution strengthening with Mg as opposed to the precipitation strengthening of 6061(of Mg2Si), which would rely on precip heat treatments to acheive comparable HAZ efficiencies. If memory serves, 5XXX achieves higher %'s of joint efficiency without PWHT than 6XXX(shootin from the hip without checkin the data). But, I would certainly welcome opposing or varying thoughts on alternative materials and the reasoning behind the choices. Services and their requirements are unique.
And I would agree with rdg, that the 5 Mg 5356, the workhorse alloy, is a commonly accepted filler for both 5XXX's and 6XXX's. Though with some 6XXX's the 5 Mg may contirbute to increased Mg2Si intergranularly.
Parent - - By DaveBoyer (*****) Date 08-17-2007 04:23
I know there is 5xxx channel, I recently built a job from it. However I just looked at the stock list from Hadco, an aluminum supplier in My area, and ALL the extruded shapes they stock are 6xxx. In aluminum yacht building the hull & deck plating is generally 5083 & 5086, but the internal stringers are  generally 6061, probably due to availability.
Parent - By Tommyjoking (****) Date 08-17-2007 07:50 Edited 08-17-2007 09:36
5356 whould be the safest/best choice IMHO considering its  a trailer and the likely metals its built from.  A lot of good info here but bottom line is fix  it.....remove the bs weld cut out the crack and weld it up right, fishplate it at least an inch beyond the length of the crack....all aluminum trailers fail with time...its just a shorter life span then with steel.  IF you want to beef it up box the channel (as previously said) and perhaps add a triangular gusset at the nose/tounge.  If you keep using it it will develop other problems eventually its just the nature of the beast in its enviorment....they all get shored up numorous times before they find the scrapyard.

my measily $.02 
Tommy
Up Topic Welding Industry / General Welding Discussion / Repair welding on Al trailer

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