Landracing Forum
Tech Information => Technical Discussion => Topic started by: Jonny Hotnuts on April 09, 2008, 05:48:32 PM
-
Making take up tubes, the ends are chromoly and was going to use a stout mild steel tube for the body.
Is there any problems in welding the two materials?
-
:-o
Be very careful!!! You will have to preheat and then anneal with a gas torch before and after welding to help prevent the weld from cracking. Also, I found that if you weld using stainless steel or nickel rod there is less tendency for the weld to crack (this is what I've had the best luck with). Tig, Heli-Arc doesn't work as well as electric arc welding in this case and Mig won't work at all. DO NOT use a mild steel rod to join the two materials together (the weld is sure to crack either as soon as you are finished or when it is stressed from use or vibration). I have heard of people joining the two materials together using an oxi/acel torch (but a friend of mine used this technique and was killed when his home built airplane crashed :cry: ) I don't recommend it unless you are very, very good and you don't destroy your metal's physical properties. Also, braze welding is a consideration...but that should be all that it is because the strength just isn't there for highly stressed areas :wink:
Good Luck :-D
Terry
-
IS there anyway you can make a mechanical joint ??
-
Howdy, :-D
Have heard of CrMo and mild steel joints using a pre and after heat of weldment to decrease the generation of martinsite which is very brittle. The stuff that I was exposed to used Eutectic 660 or 680 (don't remember which) as filler rod using Tig. The rod has high nickel content and is super smooth to use as a filler. :roll:
The big issue seemed to be what mild steel was used was important. I seem to remember that the mild steel was probably C1030 and not C1018. As I understand it the higher content carbon was easier to attach to the CrMo (C4130 in this case). :?
Sorry I don't have any very definitive data for you, perhaps this might trigger someone else's memory because mine is kaput! :-o
Regards to All,
HB2 :-)
-
I use aeutectic 680 to join metals when I'm not sure of the alloys. Have had no problems with it.
Howard
-
I'm assuming the mild steel is for BODY mounts off the chromoly main chassis. You are wire welding it using wire that has a 70 in it's spec, right?
Every Saturday nite circle track racer welds up his car with that WIRE and we use ER70s-2 rod to weld 4130.
I may be wrong and there may be a difference but both wires tell me the TENSILE is 70,000 psi.
Common sense tells me it's plenty OK.
You're not building a spacecraft.
Hope you continue to keep your build journal; going.
-
Every year usually in the spring I weld a couple of pieces of tubing together and I put them in the press and squeeze them till something lets go.
Its a test for me to test my welds to make sure that my welds are strong.
I've tried many different kinds of rod including stainless and have found that the flagged er70s2 in a 1/16th rod works the best for me. I weld alot of mild steel tubing and alot of chrome moly tubing. Most of the mild steel is .120 wall and most of the chrome moly is .065 or .083 wall. Every year when I put these welded tubes in the press the tube that is fishmouthed usually gives up near the weld. Which should be actually the weakest spot on the material because of the leverage. This year since I seen this posting about chrome moly and mild steel welding I decided to weld a piece of chrome moly to mild steel, which I've done 1000 times and never gave it much thought. After all its all steel.But it set me to thinking that I should try the chrome moly to mild steel this year, which I did.
I used a piece of 1 5/8 .120 wall mild steel, which for you car guys would be frame rail size. I fish mouthed a piece of chrome moly thats 1 1/2 by .083 wall. welded them together with the er70s2 rod. Nothing special just an ordinary everyday weld. Put it in the press and as usual the fish mouthed piece broke near the weld. I did notice that it took a lot more pressure than it usually does with the mild steel.
I do alot of NHRA cars and their rules are chrome moly to be tig welded only. This test was to test my weld only. I am going to post some pics so that you can look and draw your own conclusions. But I would say that if you are tig welding, you could weld chrome moly to mild steel. What would help spread the load and keep the material from ripping near the weld would be a couple of gussets stitched welded and not welded solid.Or you could just build a motorcycle and don't worry about a roll cage or seatbelts or firesuit or fire system or......
Seriously though I hope this helps you guys out.
Willie Buchta
-
more pics
Willie Buchta
-
Thanks Willie!
We are just getting started on the cage for the car.
I would have a bike but I like seatbelts and firesuit and fire system and air conditioning and tunes and...
Geo
-
Willie,
Thanks for sharing the pics and the data on what you were welding. :-D
Could you please do the same type weldment (CrMo and mild steel) but with after weld heating of the welded area with a gas torch and after it cools off and gets easy to handle....then place it in the press and see what happens? :roll:
Hope things are going well for you out there. As a kid I spent a lot of time in nearby Patterson and spent weekends in Modesto cruising the streets. :-o
Thanks in advance and we all thank you for the help in sorting this out. 8-)
Regards,
HB2 :-)
-
yea harold i will but if im to do it right i will have to buy some heat stick so i can get the right temperature i will try and do that tomorrow but i can tell you now the same thing will happen thats my guess willie buchta
-
Willie, :-D
Dummy me, :| I didn't even think about some heat crayons. :lol:
I only visualized in my mind heating the entire heat affected zone to a dull red and let 'er coast back down to room temperature. :roll:
I do think that this is a great opportunity for folks to see how stuff works and that is very difficult at best to get information in any other venue but this one. And with photos yet! :evil:
Regards,
HB2 :-)
-
I don't think that on most of the stuff that we are usually welding pre heating is required. I would say if you are doing something 1/4 inch thick or more you might want to pre heat, also the size of the part has a lot to do with it. The idea behind pre heating is to get the surrounding metal hot enough so that it does not become a heat sink for the welded area. If the surrounding metal is think, large and cold it will cool the weld area to quickly and then start a crack. When we did thin walled stuff that was not to big we would bury it in a sand box an let it cool real slow. I have seen chassis builders anneal weld joints on drag cars but have never seen any testing. Willy's testing is real world and probably as good of information as we could find anywhere.
I did a couple of motorcycle frames years ago using the back bone, head piece and down tube from a Husky and then built the engine cradle, seat frame and the rear part of the frame, all from 3/4 inch x 049 4130 normialized tubing and welded it all with a gas torch. I read up in some aircraft book how to do the chrome moly with a gas torch and it was pretty easy, I was a pretty good gas welder, and I never broke either of the frames both of which I desert raced and moto-crossed for a couple of years. As I remember you use a slight carborizing flame and then when the weld pass is complete you pull the torch away from the weld puddle very slowly and watch it solidify, then let it cool in very still air. Gas welding is still recognized as an acceptable method for aircraft tube repair and fabrication.
Rex
Rex
-
Today I got around to welding the other tube together, same material, same rod, same heat. The difference was after I finished welding it, the weld cooled I took the torch and heated the chrome moly from the weld to about 1 inch out to a dull red. When that cooled I took it to the press and put the squeeze on it. As you can see from the pictures I took it out of the press a couple of times and took some pics. The first pics you'll see the metal starting to distort. The second set you'll see the cracks starting. And then the third set you'll see the metal with a good tear.As you can see in the pics the chrome moly held together longer and the mild steel distorted much more in the second test then in the first. But, I can tell you this, the first test took much more pressure to break the tubing than the second test. The first test the tubing distorted a certain amount and then just ripped. The second test the tubing bent and distorted much more before it ripped, but it took alot less pressure from the press to do it. So my conclusion other than my second weld held flawlessly, was that if you don't heat it after you weld it, its much stronger but more brittle. If you heat it after you weld it the chrome moly acts much more like mild steel would. My personal preference is mild steel. Availability, cost, easier to bend, easier to weld. If I was going to use chrome moly in a door car I wouldn't heat it after welding. But if it was a dragster or an altered or a motorcycle chasis and it was chrome moly I would heat it after I welded it. But look at the pics and make up your own mind. I hope that I have helped someone out there.
Willie Buchta
-
more pics
Willie Buchta
-
last of pics
-
Good stuff Willie, thanks. I'd like to see how you are bending/breaking it in the press. You don't need to stick a new piece in there, just the bent one. I think I would be afraid of it flying out of the press. I don't like things under compression. I had a good friend loose an eye two years ago pressing bushings into an a-arm and he had done it hundreds of times before at his parts store. I always wear a face shield now when pressing something.
I might want to try this and would like the see the successful method of using the press.
Thanks,
Sum
-
Willie,
You sir are a craftsman, scholar, and a gentleman. :-D Your kindness is only exceeded by your skill. :lol: Wow that sounds cheesy, but I think that it is true from what I have seen.
Thank you so much for doing all the work and supplying the pics. You made the best statement about the brittleness of the welded area and that was what I wanted to verify. :-o :roll:
Although the failure just outside the welded area appears to be a somewhat classic martinsitic failure, the test is fairly conclusive in my opinion. 8-) :?
I think that CrMo is one of the most overrated and misunderstood materials for use in racing. It has its place, but it also has its inherent dangers. And jsut because somebody that can spell TIG or buy a machine should not necessarily be the guy that welds up a cage or a chassis. There is a whole other discussion of using condition N vs hardened condition CrMo that is perhaps beyond this venue because of the things that you have shown us all. 8-) CrMo is bad ju ju for roll cages for all the reasons that are obvious in your testing.
I look forward to your comments and a pic like Sum has requested on how the samples fit into place in your press. 8-)
Hoping that you have a great day.Thanks again. :-)
Regards,
HB2
-
There's a couple of pics with the press, the way I press stuff. Fortunately the pump for my press is on the side, which allows me to kind of hide behind the upright. Seeing a guy with a piece of plywood and a rope with the rope dangling around his neck and the plywood dangling down in front of him when he operated this press, gave me a great idea which you will see in the second set of pics. I've devised what I think is the perfect shield. Here are the pics of the press....
Willie Buchta
-
Here are the pictures of the shield.
enjoy....
-
I think that Willie and Harold are right about using Chrome Moly for our kind of racing. It just doesn't compute, you buy a material that is much more expensive, Willie has shown what the welding problems are and what do we gain? We save a few pounds so that we can add ballist??? Don't make much sense.
The post weld heating of the weld area that Willie did probably shows that this type of joint will adsorb more energy during a crash before failing and that a similar joint that was not post heated would probaby fail in a big bang. If you use mild steel you get the same charteristics and save money and the PITA(Pain In The A$$)of having to mess with 4130.
I was pretty good friends with Doane Spencer and he built some pretty nice race car stuff and he absolutely would not use chrome moly tubing and just for the reason that Willie has shown us in his testing.
Thanks Willie!!!
Rex
-
Here are the pictures of the shield.
enjoy....
Thanks for the pictures I was having a hard time visualizing how you did it.
Well at least one of you behind the shield is good looking and sorry, but it ain't the one with the beard 8-),
Sum
-
i guess in all fairness i should do a mild steel to mild steel and i will as soon as i get a chance willie buchta
-
i guess in all fairness i should do a mild steel to mild steel and i will as soon as i get a chance willie buchta
I was going to ask that you do that, I would be greatful if you did!
Also guys, what about the differences between DOM steel and welded seam? Can someone shed a little light on the differences of these two types of tubing?
Scott
-
scott the only differance ive found between ew and dom is the thickness (im talking about 1/2 inch up tp 2 inch od) all electric welded (seamed) tubing is not what it appears to be it has a nominal wall thickness which means its made from flat plate then rolled into a tube and welded and according to mill specs .120 wall can be as thin .110 but usually is .114 to .115 ---the mininum wall thickness for nhra is .118 in mild steel so i always have to use dom --if you buy .120 dom it will pass tech for nhra --i have a sonic checker and check all my tubing--if you dont you can buy .125 wall dom ---they dont make ew in .125 although i have seen and used some .134 wall ew but its hard to find in anything other than 1 5/8 or 1 1/4 od --i think the scta rule book says nominal wall thickness so ew will be fine if your worried you could buy .120 wall dom but i dont think .004 or .005 of an inch will make any differance in a crash---i think what will make a differance is a properly designed and welded and gusseted roll cage --i build a lot of bike frames (no roll cage) and i always use dom just because i always have --also remember that the cheapest tube you can buy ( EW ) is still about .015 thicker than the most expensive (cm) parden the spelling willie buchta
-
i guess in all fairness i should do a mild steel to mild steel and i will as soon as i get a chance willie buchta
I was going to ask that you do that, I would be greatful if you did!
Also guys, what about the differences between DOM steel and welded seam? Can someone shed a little light on the differences of these two types of tubing?
Scott
DOM is welded seam tubing, after its welded it is Drawn Over a Mandrel which smooths and sizes the i.d. Essentially a cold working process that gives it higher strength also.
-
i corrected that willie buchta
-
o k guys i think this will be my last post on this subject--the tubing is dom .120 wall both pieces --a couple of things the pressure was about the same as the heated cm --the main tube was distorted a lot not as much as the heated cm but the tubing was thicker and should of distorted less which it did--the tubing ripped close to the weld which is usually the case with mild steel --my advise is no matter what you weld spend a day and do some testing i think the tubing type is probably less important than the design the welds and proper bracing and dont forget those gussets thanks willie buchta
-
more pics
willie buchta
-
Thanks Willie.
This has been a really helpful and informative session. In all my years of fabricating I haven't used an approach like that for testing myself and my results. I have tested individual projects at various times. I think from now on I may do a little more self testing.
It's postings like this series that makes these forums so valuable.
Pete
-
Howdy Willie, :-D
Thanks for all the effort and sharing the info with the rest of us! :-o
I look forward to meeting you on the salt someday and will hopefully be able to click a glass with you or break some bread. 8-)
Best Regards from the high country where it has finally rolled into spring. :lol:
HB2 :-)
-
Interesting, so after looking at the pictures the weld itself is actually sstronger than the piece of tubing? Do you guys agree? I have always thought that the weld would be the weak link.
This is assuming that the pieces of tubing that were welded together were properly prepared.
Scott
-
thanks guys just fired sheris bike up yesturday sounds like a record breaker --i have until monday to get mine to the paint shop albert the painter said he will have it painted buy wednesday that gives me 15 days to assemble plumb and wire before el mirage see you there willie buchta
-
Scott:
If the weld is done correctly that will not be where the fracture occurs. Depending on how the weld is blended into what is being welded and the quality of the material being welded the break will occur right at the junction of the weld to the material or in the material itself.
Pete
-
Scott:
If the weld is done correctly that will not be where the fracture occurs. Depending on how the weld is blended into what is being welded and the quality of the material being welded the break will occur right at the junction of the weld to the material or in the material itself.
Pete
I guess the moral to this story is when things go to hell and break at least you can say "my weld held" 8-).
Willie thanks for taking the time to do all the testing :-),
Sum
-
Great stuff here guys.
I'm new to the LSR scence, but I am a professional Metallurgical Engineer with a decent amount of welding and practical industrial/manufacturing experience. All of the welds in the photos look very good and have failed in an expected manner. As was stated above, if the weld is made properly, the strength of the weld will exceed the material immediately adjacent to the weld.
Welding rods/wire for steel are typically rated based on their tensile strength after welding. Let's say 70,000 psi tensile strength. In its as-delivered condition, the tubing will probably be slightly above this strength level for mild steel, and well above it (possibly double) for 4130 type materials.
However, when the welding occurs, there is a Heat Affected Zone (HAZ) which forms around the weld itself. This HAZ will extend into the base material differing amounts depending on how much heat in introduced during the welding or post-weld heat treatment. The base material becomes softer (and weaker) in this HAZ. For 4130 type materials, the difference between the base strength and the HAZ is greater than the difference between mild steel and its HAZ. In either case, the strength of the welded joint is limited by the strength of the material in the HAZ. That is why all "good" welds will fail near the weld seam, but not in the actual weld bead itself.
I agree that for our purposes, mild steel is the way to go. The only possible benefit to 4130 tubing would be to reduce the weight. There is no strength benefit to 4130 unless the entire frame is post-weld heat treated to restore the proper hardness and strength.
Again, what a great thread.
SteveM.
-
thanks steve i am trying to get two bikes ready for el mirage but will do some filler rod --minimal weld(low heat ) and some butt weld testing after may 18 th willie buchta greenfield mo.
-
Curious, since we are talking about the welds and the strength of the welds. When welding tubing together like this and with a good tight fit is it recommended to use filler? I don't know but I am assuming adding filler to the joint/weld would make it stronger. Is this true?
Scott
-
Curious, since we are talking about the welds and the strength of the welds. When welding tubing together like this and with a good tight fit is it recommended to use filler? I don't know but I am assuming adding filler to the joint/weld would make it stronger. Is this true?
Scott
I would say definitely use filler rod. I know with a tig it is easy to flow two pieces together on a tight fit and I do it on something that is non-structural where I want a flat weld area that I don't have to grind much. The problem is with a joint no matter how tight material is going to have to flow to fill the joint and create the weld. If you don't add filler where is that going to come from? The surrounding metal, so you have now taken some away from there and it is weaker. The fill also spreads out the surface area of the welded joint which is evident by the fact that it is breaking past the filler in a thinner section of the pieces that were joined.
At least that is my take on it.
Another thing to consider that I didn't when making the tongue on my teardrop is the effect of welding in gussets and such and just moving the weak point to a new point. If anyone is interested I posted my screw-up on my site.....
http://purplesagetradingpost.com/sumner/teardrop/teardrop14.html
........... I have been laughed at for the failure of the tongue, but felt by posting this info it might save someone else from the same problem or worst. What happened with the tongue can happen many places on our race cars or other projects. Hope no one else has the same problem,
Sum
-
Sumner,
Thanks for the reply and posting the trailer write-up, it takes a man to admit his mistakes.
I believe in most things in life you must first fail prior to heading down the path of success, it is how we learn!
Scott
-
If I may offer a simple suggestion...
I highly suggest that everyone pick up a copy of Carroll Smith's "Engineer To Win", Motorbooks Workshop, ISBN-13:978-0-87938-186-8. It should be manditory reading in my opinion. It basically a guide to materials technology and how to build a chassis that doesnt break. Actually... I would recommend his whole book series.
I believe that the biggest issue with CM, especially for structural and/or roll cages, is that it needs to be heat treated. If you dont heat treat CM, you will end up with an expensive product with pretty much the same strength as 1020... but with brittle weldments. At the very least... if the structure is not fully heat treated... it should be at the very minimum, normalized... as it is critical that the weldments be stress relieved.
Always use filler rod. As it has been suggested by others during the topic of discussion, I too have found that welding with OXWELD 32 CMS has shown the best results with CM.
-
Here's some good information that you might want to check out.
http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp
Willie Buchta
-
My experience with chrome-moly is the front engine dragster chassis I built in 1965 and tortured for 5 years (still have it) . The cage is mild steel which I had tig welded and the rest is 1 1/4" .049" wall 4130 which I gas welded . We raced on lots of rough strips in the north east , got it sideways on rough tracks and bent the rails sideways and had to heat and straighten them . None of my gas welds ever cracked . From my experience chrome-moly tubing is very user friendly . With welded triangulated tubing the ones in compression normally buckle before the tubes or welds fail in tension . The softened metal around the welds protects the welds as in Willie's tests . Compression (buckling) failures are much better than tension failures .
John
-
john im looking at my nhra rule book and it says all 4130 chromoly must be tig welded --mild steel must be welded with mig or tig only ---i think that gas welding chromoly isnt a bad idea if you know what you are doing and follow some aircraft industry standards but tig welding is the answer its easy its fast its clean just dont try it in the wind as far as your car is concerned hang it from the ceiling it would cost more to get it updated than what you could build a new one for as far as nhra is concerned ---i would like to thank every one who has posted here i hope we have learned something to make the sport safer now how about faster thanks willie buchta
-
Well, here is another metallurgist voice. A chance for this newbie to contribute technical content. I agree with what SteveM said. The welded assy should always fail in the HAZ. It is the weakest point. Cr-Mo has to be TIG or gas welded because if you try MIG or SMAW (stick), the weld cools too fast and you get brittle martensite. This is where the slow-cooling is beneficial in TIG or gas welding. You get a weld with normalized or annealed like properties. Meaning ductile. Using a more ductile filler just helps to keep the weld from being brittle.
I do agree with the general consensus of many prior replies that Cr-Mo is spending money that is not an issue for land speed racing. Weight is not the enemy like other forms of racing. So just use mild steel tubing and have easier fabrication or welding.
-
Gas welding works just fine on chrome- moly tubing but the tubing has to be "Condition N"-- normallized. As others have already said, mild steel is a better choice for most applications; its cheaper, easier to weld, and it absorbs energy in a crash by deforming plastically. Cr-Mo is more expensive, stronger, easier to find in very thin wall sizes, but it does not absorb as much crash energy as mild steel.
-
Excellent thread and many thanks to Willie for starting it and sharing the pics. :-) It should be noted the strength of the weld is also dependent on the thickness, or the amount of material of the fillet. The filler material and tubing both have a specific tensile strength. However, the thicker they are the more force it takes to deform or break. On many weld symbols the fillet thicknes is called out to guarantee enought strength is put into the weld joint. All of the fab procedures mentioned are critically important but the amount of filler is equally important.
-
When NHRA mandated a CM cage and TIG; I thought it was strictly for safety. Obviously CM is lighter but they make rules changes like that mostly for safety reasons no? There is no question 4130 is cleaner (electric arc melted, vacuum degassed) and it is much easier to weld with any method. Mild steel has inclusions and any manner of garbage in it. Who knows where it is comming from? I have found great variability in mild steel. 4130 is certified tubing. It is wonderful stuff to work with because it is predictable and always good. That is why I thought NHRA made the requirement. I don't have the NHRA book but does it define the process? I.e. post weld annealing? That is the only way to get a strong 4130 weld. After the discussion here I am lead to believe that mild steel is the most forgiving of process, fab technique, craftmanship or skill and therefore safer. Willie's testing seems to support that so I am in a quandary as to why NHRA made the rules change? This is a big disparity I wish I knew NHRA's technical or engineering reasons.
Wether a cage should be rigid and strong or yield in a crash is a continuing discussion in all racing venues. But almost everyone agrees the force must be attenuated in some manner and not imparted to the driver. The speeds in NHRA are equal to many LSR classes. Yet mild steel seems to be the choice in LSR. Is it because there is a wide range of fabrication skill allowed in LSR and due to this unpredictability, mild steel is safer? I know the NHRA cage is certified. Does that mean the welder is certified also? so many questions . . .
-
saltfever---you know its funny that you mention a certified welder --i do and have done many nhra cars that require tig and CM --so i thought that i would go down to the local welding school and take the test --when i got there and talked to the owner he explained that the test was a pass or fail (he had been in my shop and seen my welds and he said i would have no trouble passing the test )the test was very expensive and only covered thin wall round tubing of minimum and maximum size--anyway he explained the test would be a butt weld on a piece of thinwall tubing--NHRA does not allow a butt weld on CM except under very limited situations then the weld has to have a sleeve inside that goes into each tube 3 inches 6 inches total with rosette welds --any way i didnt take the test and saved myself a lot of money willie buchta -------- you dont have to be a certified welder to weld on a nhra car or a lsr car or any other kind of race car that i know of i think if it was airframe you might have to be ---------
-
You don't need a certificate to weld on an airframe if it is classified "Experimental".
-
When NHRA mandated a CM cage and TIG; I thought it was strictly for safety. Obviously CM is lighter but they make rules changes like that mostly for safety reasons no? There is no question 4130 is cleaner (electric arc melted, vacuum degassed) and it is much easier to weld with any method. Mild steel has inclusions and any manner of garbage in it. Who knows where it is comming from? I have found great variability in mild steel. 4130 is certified tubing. It is wonderful stuff to work with because it is predictable and always good. That is why I thought NHRA made the requirement. I don't have the NHRA book but does it define the process? I.e. post weld annealing? That is the only way to get a strong 4130 weld. After the discussion here I am lead to believe that mild steel is the most forgiving of process, fab technique, craftmanship or skill and therefore safer. Willie's testing seems to support that so I am in a quandary as to why NHRA made the rules change? This is a big disparity I wish I knew NHRA's technical or engineering reasons.
Wether a cage should be rigid and strong or yield in a crash is a continuing discussion in all racing venues. But almost everyone agrees the force must be attenuated in some manner and not imparted to the driver. The speeds in NHRA are equal to many LSR classes. Yet mild steel seems to be the choice in LSR. Is it because there is a wide range of fabrication skill allowed in LSR and due to this unpredictability, mild steel is safer? I know the NHRA cage is certified. Does that mean the welder is certified also? so many questions . . .
The preferred material for World of Outlaws sprint cars and Super Mods is chromemoly.
Whether mild steel or chromemoly is better at dissipating energy is a moot point because effective impact attenuation requires crumple zones that don't exist in many land speed classes.
-
The chassis & roll cage are the "crumple zones". Plastic deformation of the tubing structure absorbs energy.
-
The chassis & roll cage are the "crumple zones". Plastic deformation of the tubing structure absorbs energy.
I would hope my chassis and body would "crumple", but not sure if I want the roll cage to "crumple" much.
c ya,
Sum
-
The reason W of O and modifieds use moly is because they can use thinner therefore lighter tubing. Weight or lack thereof is everything.
Pete
-
Sum;
I don't want my roll cage to crumple either but, in a hard crash, it probably- will but only a little. Every little bit of deformation absorbs energy that would otherwise be transferred to the driver. We don't want the cage to collapse but it will deform some in a hard enough crash. Much of the energy absorption takes place as the car's body is crunched, the suspension is torn off, and various bits & pieces are shed during the event. All that kinetic energy has to be dissipated somehow.
-
A few posts up NHRA was referred to as mandating 4140 tubing . To be exactly correct NHRA relies on an SFI spec, just like safety belts, bell housing shields, rollbar padding, ad infinitem.
The SFI program was formerly the SEMA Chassis Builder program and the whole now giant SPECIALTY EQUIPMENT MARKETING ASSOCIATION- the guys with the second biggest trade show in 'Vegas -actually started with need for a chassis spec for slingshot dragsters. SFI divorced from SEMA some years back and, although not part of NHRA, has always been closely affliated.
Because of recent fatalities/crashes the SFI program has come under a lot of flack. Part of it deals with summarily dropping chassis comitteee members because they didn't agee with the SFI head and his close friend, a prominent midwest builder who IMHOP legislated rule changes without proper engineering diagnoses that were prone to causing catastrophic failures-and DID!
Oxweld 65, an old Linde number was the rod of choice for years but I UNDERSTAND it's no longer made- if anyone knows different, please post.
You'll be safe in TIG welding 4130N with ER70-S2 rod- commonly available- don't be mislead by chromoly rod -unless the whole assembly is undergoing normalizing after weldment.
-
that might of been me --what i was refering to was a sfi chassis --faster than 7.50 --the chassis has to be CM and tig welded --nhra has changed some rules lately and i havent done a nhra car sence i got cancer 4 years ago but below 7.50 the chassis can be mild steel ew-dom or seamless with a minumim of .118 wall thickness --tubing is checked with a sonic checker which i still have if anyone ever needs to use it --i will say this for the NHRA rules they are very precise and easy to understand --no wiggle room your either legal or your not --no in between ---if anyone is thinking about building a chassis and cant weld do yourself a favor and get someone to do it that knows how its not that expensive compared to the alternative willie buchta
-
Interested:
I think you'll find that Oxweld 65 and ER70-S2 are almost identical in specs. I think probably Oxweld 65 met the ER70-S2 spec before the spec was made. I know I burned a lot of it. You'll definitely know if you don't have the right rod and try to tig weld with a steel rod designed for oxy/acetylene.
Pete
-
. . . Whether mild steel or chromemoly is better at dissipating energy is a moot point because effective impact attenuation requires crumple zones that don't exist in many land speed classes.
But if one was designing-in a crumble zone, the selection (or performance) of the material is critical. If using mild steel the geometry “might” be triangulated spaces? But if 4130 it might be trapezoidal spaces? These may be bad examples but I think the kind of material dictates the shape for a crumple zone. Geometry works hand-in-hand with tensile strength and stress/strain. Agree, that LSR past-practice negated or minimized the use of crumple zones. In fact, until the Dale Earnhardt accident very little focus was given to attenuating forces on the driver. NASCAR spent millions after that. Nowadays all the major racing venues spend major dollars on design and research to lessen impact force to a driver. And that is my quandary. I constantly heard conflicting opinions, or anecdotal examples about what is the best material for a cage in LSR. That was the same scenario in NHRA for the past 50 years! Do you make it Light(4130) and strong, or heavy(1030) and ductile? Finally, 2 years ago, NHRA ended the debate and required TIG and CM. I don’t know the data they based that change on. I am sure they had very good engineering data and excellent accident analysis to come to that decision. I just wish we had a way to access that information. All the major racing venues are entertainment corporations. They face the same constraints on their business as any corporation. They must weigh, risk, and liability but at the same time keep their product attractive to their audiance. They don't make changes capriciously. They spend serious money on good engineering and careful anaylsis making safety rules decisions. Knowing that, maybe the NHRA spec is a safer way to go?
Willie, do you have the SFI spec number for a CM cage?
-
saltfever--there is no sfi number its just a spec sheet that you have to go by--the nhra cars and lsr cars have not much in common other than the speed --in lsr there are no other cars to run into there are no guard rails -grandstands-steel poles and cables-broadcasting stands-or cement walls at the end of the track--i think that engine explosions are the biggest problem for the fast guys and they dont care if they explode the engine as long as they make the next round--they just shortened the track from 1320 ft to 1000 ft i dont think that will solve any thing--if they would quit blowing up the motors i think most of there problems would be solved in that area ------- i would never build a car or bike for myself of CM , i have always thought MS was the way to go and still do --just remember before you go trying to change the rules (LOL) that the rule books are minimums and if you arnt comfortable with that then add tubes and gussets and crumple zones and even air bags if you like just some thoughts willie buchta
starting a new topic on this subject
-
Earlier in this topic it was mentioned that chrome- moly tubing was "4140". If I remember right, 4140 is used for heavy sections while 4130 is for lighter sections such as tubing.
Maybe that was only a typo.
-
Earlier in this topic it was mentioned that chrome- moly tubing was "4140". If I remember right, 4140 is used for heavy sections while 4130 is for lighter sections such as tubing.
Maybe that was only a typo.
More metallurgist information. Steel is basically classified by the first two digits and then the nominal carbon content for the last two. So for 4130, the 41 = chrome and molybdenum as the main alloying elements; and 30 = .30 weight percent carbon. 4140 is also 41 = the 41 = chrome and molybdenum as the main alloying elements; and 40 = .40 weight percent carbon. So the only difference between the two is that one is slightly higher carbon content.
Now you may also have heard of 4340 as a steel, the 43 = nickel, chrome and moly, and the 40 = .40 % carbon.
Most mild steel is like 1010, 1018 or something like that. the first 10 = plain iron, no specific alloying elements; and the second 10 or 18 = .10 or .18 % carbon.
Lower carbon is better for welding and forming. Higher carbon content is better for strength. So much for today's quick lesson.
-
Higher carbon steels are stronger but also more brittle. Better to use an alloy steel if you need strength and toughness.
Regards, Neil Tucson, AZ
-
OH DEJAVOUS,
Met 101 all over again.
next we will looking at iron carbon phase diagrams.
What a wonderful place this is....
I'm still using 4130N and heat treating very carefully....
Rick
-
Higher carbon steels are stronger but also more brittle. Better to use an alloy steel if you need strength and toughness.
Regards, Neil Tucson, AZ
Yes, the alloying elements typically add toughness while maintaining or increasing strength. All this discussion is based on solution strengthening, and not for heat treating. Solution strengthening means strtength you get in the normalized or non-heat treated condition.
BTW, nickel is better for toughness vs chrome or moly. So if you want real tough material (toughness defined as the amount of energy absorbed by the metal during failure), the 4340 is better than 4140 for example. Either 4130, 4140, or 4340 are better and tougher than a plain carbon mild steel.
Carbon content controls and defines the ultimate strength potential of the steel when heat treated, but has relatively minor effect on non-heat treated steel strength.
-
What a joy to get such wide coverage for such an important part of our LSR world!!!!!!! Thanks again Willie and to all who posted!!!!!!
-
Thought I might stir this up a bit.
When chromemoly 4130 is welded with enough heat to prevent rapid quenching of the heat effected zone, it is normalized or even annealed in the heat affected zone, if enough heat is applied. In this region the strength can be less than mild steel DOM "work hardened" tube in tension.
However, the structure may far exceed the strength of mild steel DOM tubing!
Sometimes the failure mode is from compressive stresses! Long tubes fail from buckling and high yield strength in the middle of the tube resists buckling. Yes the heat affected zone, if not brittle, has a lower yield strength. If the load is tensile the yield strength will be the limit, however if the tube is long and the load is compressive, high yield strength chromemoly tube will allow the tube to carry significantly larger compressive loads than mild steel tubes.
Akk
-
Ref: "Sometimes the failure mode is from compressive stresses! Long tubes fail from buckling and high yield strength in the middle of the tube resists buckling. Yes the heat affected zone, if not brittle, has a lower yield strength. If the load is tensile the yield strength will be the limit, however if the tube is long and the load is compressive, high yield strength chromemoly tube will allow the tube to carry significantly larger compressive loads than mild steel tubes. "
____________________
Not so! Column buckling of slender members (Euler buckling) is an elastic failure mode and is determined by the stiffness of the material and the cross-sectional geometry. Material strength has no bearing on the critical load to produce buckling.
Therefore, in the postulated situation of the 4130 tube with mild steel properties at the ends under compressive loading, one of two things may happen. If too short to fail by buckling it will fail by local crippling at the ends at a compressive stress equal to the mild steel yield strength. If long enough to fail by buckling before yielding in compression at the ends, the buckling load will be the same for either 4130 or mild steel, since the elastic properties (Young’s modulus) of the two steels are essentially the same.
The upshot being that 4130 does not offer increased buckling load performance. (However, after it has buckled, it may absorb slightly more energy as it collapses).
If the member is short enough to not be subject to buckling and the 4130 is properly heat treated after welding to enhance its strength, the direct compression failure load would be improved over the mild steel version.
-
I guess it gets down to..... how long is long? The technical description of length is "slenderness ratio". This ratio is calculated and depends on end conditions, length of tube, section modulus and end area.
There are two buckeling stress equations generally used Euler and Johnson. The Euler is for high slenderness ratio "long" tubes and is geometry driven, the equation does not include material strength. The Euler equation is for low slenderness ratio "shorter" tubes, the equation includes material yield strength.
In any case a compressively loaded tube with a length more than a few diameters can fail in compression at a stress less than yield.
Depending on end conditions (fixed "welded", pinned on one or both ends), slenderness ratio, material stiffness and yield strength, one or the other of these equations is used.
A higher yield strength tube can be longer than a lower strength tube before buckling occurs (all other things being equal). A higher yield strength tube can carry more load than a lower yield strength tube if the length is less than the length associated with the critical slenderness ratio.
The heat affected zone can reduce the yield strength of the tube material to the annealed condition say 35,000 psi. In the case where a high strength chromemoly tube is weakened on the ends, up to the critical slenderness ratio it can carry the same load in compression and tension.
For 1.25 x .135 wall 70,000 psi yield strength steel tube with welded ends, the critical slenderness ratio is 92 and the length at this ratio is 36 inches. This 4130 tube will have compressive strength equal to the tension strength of the heat affected zone with a load of 17,087 lbs.
A 1.25 x .135 wall 50000 psi yield strength tube with welded ends of the same dimensions could hold only 15680 lbs.compressively!
A 1.25 x .135 wall 35000 psi yield strength tube with welded ends of the same dimensions could only hold 12,807 lbs compressively!
A shorter tube will yield the the heat affected zone in compression and act as a hinge joint at the end of the tube. This hinge will cut the critical length by half.
The high yield tube at a length shorter than the length associated with the critical slenderness ratio, will be more resistant to buckling failure than the lower yield tube.
Unless I punched the numbers wrong Yield strength matters...so does length...
Akk
-
The Johnson formula is merely a convenient contrivance and approximation that applies only to the short and intermediate slenderness ratio range. It contains the yield strength in order to have the endpoint and tangent point of the curve located where they are postulated to belong. It is used in lieu of the more laborious but more properly founded “generalized Euler formula” or the “tangent modulus formula.” Inasmuch as Johnson was artificially created using yield strength, it is not surprising that yield strength can be said to influence the capacity. Johnson may be a useful device, but is strength really the controlling quality?
It remains that the earlier unqualified statement “if the tube is long and the load is compressive, high yield strength chromemoly tube will allow the tube to carry significantly larger compressive loads than mild steel tubes” is, in general, inaccurate and misleading.
-
309 is specifically designed for welding dissimilar metals and is most commonly used for joining stainless and mild steel. I'm not sure how well it works or cro-moly, but it has a high nickel content and is rated to 70,000 psi tenile strength. Esab has an 800 number for these kind of questions, but they will probably recomend the most expensive product they carry when there could be something more affordable that will work just fine. ex.- they recomended an ER82 filler metal to me that costs $46 pre lb. and is sold in 30lb. in its smallest quantity when 309 worked perfectly and costs $<6 per lb. and comes in 5 and 10 lb rolls.