How to identify 4130 CrMo bicycle frame?

[bobale]

I'm looking for a steel frame for my e-bike, and found one which is very cheap, and it says 4130 Chromoly on it. Seller, of course, claims it is CrMo. Is there any simple way of checking whether it really is 4130 steel, or it's just made out of cheap, ordinary steel?

 

[MadRhino]

Companies who spec frame material, usually build with the material that they spec :wink:

Then, if you want to be sure, you can cut a piece off it and send it to density testing.

 

[bobale]

That doesn't fall under "simple" . Would it do any good if I weigh it? It should be how much lighter than an ordinary steel frame? 20-30-40%?

 

[Thud]

That is a name brand frame...with a serial #s that the company prolly has documentation on production dates & may even be able to trace the batch # provided by the steel suplier.

Dramatic over kill for what it is. Far more important if you were making gun barrels for the government than for a bicycle.

 

[SamTexas]

Would it do any good if I weigh it? It should be how much lighter than an ordinary steel frame?

Yes it would. Weighing should be simple enough. The "slightly" harder task is to measure the actual volume of the metal used in the frame. With weight and volume you can derive the actual density. By the time you're done with this task, you'd have spent more time and/or money than the frame is worth. I'd rather just believe that it is what it says it is.

 

[dogman dan]

Looks like a good frame to me. I would trust that it's made of what they say. It's not a brand known for super cheap bikes. But no disk mount though.

If you did happen to have a cheap steel frame right next to it, and picked them both up, you'd be able to tell the good one with your eyes closed. Generally, I can spot a crap frame just by the way the welds look.

 

[Zoot Katz]

Grab a grinder and make some sparks.
http://www.capeforge.com/Spark testing.html

 

[Drunkskunk]

Its a Felt. Felt only make higher end bikes. If they say its CrMo, its CrMo.

CrMo isn't lighter than other steels, its a little stronger and a lot stiffer. They could make it lighter if thats what they were after, but thats a mountain bike frame. Likely they wanted CrMo for its strength and stiffness, so its weight will be meaningless.

If you really have reason to doubt Felt's claim of it being CrMo, then hire a metallurgist and a lawyer.

 

[John in CR]

If you like the frame and a magnet sticks to it, then that's good enough, buy it if the price is right. Cheap steel frames make fine ebikes too, and in a hardtail I doubt that even an experienced extreme rider like MadRhino could tell the difference once batteries and motor are installed.

John


PS- Zoot, thanks for that spark testing link. I'll be putting that to use.

 

[bobale]

That is a name brand frame...

Unfortunately, I don't think this actually is Felt frame as I can't find any info on the internet, and it is dirt cheap (a bit over $20 for a new one).

I'd rather just believe that it is what it says it is.

I'm going to buy it anyway as it's very cheap, but I wanted to know whether there's a simple way to tell plain steel from 4130.

It's not a brand known for super cheap bikes. But no disk mount though.

It's not, but as I said, I'm not sure this really is Felt frame. No disc mount, but V-brake will do just fine when paired with regen.

Grab a grinder and make some sparks.
http://www.capeforge.com/Spark testing.html

Thanks, that's exatly what I wanted, a simple way to test a frame material.

If you really have reason to doubt Felt's claim of it being CrMo, then hire a metallurgist and a lawyer.

I was just being curious, as it's cheap I can't complain much.

If you like the frame and a magnet sticks to it, then that's good enough, buy it if the price is right.

Indeed the price is right, and as the magnet sticks to it, it will do the job.

 

[dogman dan]

True enough, it could be anything with felt decals stuck on. Chances are it's fairly light if it's the real thing, because they could use thinner tube than a cheap steel bike. Look down the seat tube, and you might get an idea if it's thick or thin. Weld qualty looks better than really cheap bikes.

 

[SamTexas]

Grab a grinder and make some sparks.
http://www.capeforge.com/Spark testing.html

I'm betting that this method sounds a lot easier in writing than it is in practice. I have no doubt that it's meaningful to professional metal workers, but to a normal person who does metal grinding once or twice a year? Not a chance.
Exerpt from above link:

Spark testing requires some practice to correctly classify the steel. The pressure used in grinding all the pieces should be the same. The lighting should always be the same. This is not unlike heat treating when you are learning the colors. It is a technique that its better to be shown than to read about, for once you see the colors it easier to work from there. Keep in mind the lighting for one shop will be different from another and this can produce entirely different colors.

 

[Thud]

http://bikedaten.de/bikes/felt/2001/fs_250/komplettbike/

Does Felt sell 12 year old decal sets? I suppose some one could pirate a set with corel draw easy enough....& its an old frame. There is literly a TON of unsold high end bicycles that get running gear stripped off for re-use & the frames are sold off for cost.
JOhn said t right....if a magnet sticks its going to work fine.

I have high confidance its a Felt from 2001.

As for spark testing....you need a clean pc of steel to do it properly & it helps to have a clean pc of known alloy for side by side testing.

 

[bobale]

Does Felt sell 12 year old decal sets? I suppose some one could pirate a set with corel draw easy enough...

I don't think they do, but those decals are fairly simple, and could be pirated easily.

I have high confidance its a Felt from 2001.

I hope you're right.

Ok, let's just forget all those things about grinding. As I'm not an experienced metal worker, it's not going to work. But the idea is nice, and we've learnt something new, which is also nice.

I'm going to buy it, and when it arrives here I'll post more details about it. Hopefully it's just nicely welded together and droputs are strong enough for ~2KW. That's all I'm asking for.

 

[John in CR]

...Hopefully it's just nicely welded together and droputs are strong enough for ~2KW. That's all I'm asking for.

You still need torque arms or beefed up dropouts. Thickness of the axle contact is even more important than strength, because a super strong but thin dropout can cut right into the axle and allow it to spin. Take it from someone who had an axle spin failure in the 1st 10ft of his 1st hubmotored ride who used thin but strong stainless steel torque arms. Thank goodness they held the motor in place, because it was a front hubbie that snapped the alloy dropouts like toothpicks.

John

 

[bobale]

At least the frame is steel, so it'll be easy to weld on torque arm/plate to it.

 

[nechaus]

You do not need to worry, that is CrMo, Tig Welded im not sure. but it is CrMo

 

[cal3thousand]

Would it do any good if I weigh it? It should be how much lighter than an ordinary steel frame?

Yes it would. Weighing should be simple enough. The "slightly" harder task is to measure the actual volume of the metal used in the frame. With weight and volume you can derive the actual density. By the time you're done with this task, you'd have spent more time and/or money than the frame is worth. I'd rather just believe that it is what it says it is.

In that case, you could measure water displacement in a large enough bathtub.

 

[SamTexas]

In that case, you could measure water displacement in a large enough bathtub.

Not that simple. You may have to drill holes in certain questionable part of the frame to ensure that no air is trapped inside first. After that you still have vigorously shake the bike to make get rid of the bubbles.

 

[Joseph C.]

Use your knuckle and knock on it. If it sings like a bell it is cromoly. If it has a dull sound it is high-tensile steel.

Be sure to check all the tubes. Often to cut down on prices only certain parts of the frame will be cromoly with the rest just high tensile steel.

 

[Hillhater]

In that case, you could measure water displacement in a large enough bathtub.

:lol: :lol: :lol:
The difference in density between mild and CrMo steel is less than 1% ( more like 0.5% actually).
So on a 5kg frame , you are looking for a 50gm max difference , which in your "large bathtub" would be 50cc of water, ..
...or about one egg cup full !
Good luck trying to measure to that accuracy in a bathtub !

Why would anyone attempt to produce an exact replica of a frame in a substandard material...and then sell it dirt cheap ! ???

 

[flathill]

For aluminum you can quickly check for proper heat treatment using a conductivity test....
http://www.everyspec.com/MIL-STD/MIL-STD-1500-1599/download.php?spec=MIL_STD_1537C.1409.pdf
I'm guessing you might be do sometime similar to check if the 4130 is real

http://www.ndt-ed.org/GeneralResources/MaterialProperties/ET/Conductivity_Iron.pdf

 

[dogman dan]

Just to keep arguing on here, a good cromo frame will be noticeably lighter than a cheap steel frame because it will use much thinner wall tubing. You don't need a bathtub, just one frame in one hand and the cromo one in the other. You'll know with your eyes closed which is the good frame.

Good tip about the ring. I had forgotten about that, but for sure, my good steel frames do ring like a bell. Ting ting, if you tap a fingernail on em. Thunk thunk on the wallbike frame.

 

[bobale]

Thanks for the advice, I'll try that when the frame arrives.

 

[Chalo]

Just to keep arguing on here, a good cromo frame will be noticeably lighter than a cheap steel frame because it will use much thinner wall tubing. You don't need a bathtub, just one frame in one hand and the cromo one in the other. You'll know with your eyes closed which is the good frame.

Better to have your eyes open. Chromoly can be used to make as light or as heavy a frame as you can imagine. There was a period about 15 or so years ago when very heavy duty BMX bikes came into fashion. Some of those frames weighed ten pounds without forks, but that didn't mean they weren't chromoly.

For our purposes, a heavy frame is a good one as long as its details are good. Nice thick dropouts, good welds, lots of braze-ons. That's where department store bikes fail. They use enough metal in the tubes to do the job; they just get the details and workmanship wrong. If department store bikes were made from seamless chromoly, they'd still be bad. But a steel bike doesn't need to be made of chromoly to be good.

Chicago-made Schwinns were good bikes with very strong and straight frames. (Schwinn offered a lifetime warranty against frame breakage when hardly anybody else did.) But most of those bikes were made out of 1010 alloy steel-- milder, technically, than what's in a fencepost or a rebar. They were strong on the basis of good design, careful workmanship, and plenty of metal.

Even a "heavy" mild steel frame weighs only a couple of pounds more than its chromoly equivalent. For a bike that is going to pack on 30 to 100 pounds of motor, battery, and electrical gear, a couple of pounds doesn't matter. It can even help by stiffening the frame and making the loaded bike less wiggly. (Chromoly may be stronger than mild steel, but it's not any stiffer. So frame stiffness is a result of the shape and amount of steel, rather than the kind of steel.)

The moral of the story is, 4130 chromoly is a premium material that's worth looking for, but it's not the only reasonable option. It's about twice as strong as the plainest and cheapest mild steels, but only a third as strong as some of the exotic high strength steels used in bike frames. There's no reason to use a less suitable frame that is made of all chromoly instead of a more suitable frame that is partly or all 'high tensile" (mild) steel.

Chalo