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What is special about ERW Steel???
CAD Monkey - 19/5/07 at 01:34 PM

Thought I'd ask here as a specific thread:

Can someone explain why ERW is better than non ERW steel please?

Thanks in advance.

Stewart

big_wasa - 19/5/07 at 01:37 PM

Electric Resistance Weld (ERW)

It means its got a welded seam.

"Why is it Better" Depending on the aplication, its not.

If you mean is it better than RHS rectangular hollow section ? then its often the same thing.

[Edited on 19/5/07 by big_wasa]

ecosse - 19/5/07 at 01:40 PM

Who said it was better?
If by non ERW do you mean CDS, then generally CDS is heavier because of the wall thickness but also stronger and more expensive.
ERW is mostly thinwall tube and is cheap to make and buy.
Does that help any?

Cheers
Alex

omega 24 v6 - 19/5/07 at 01:42 PM

quote:

What is special about ERW Steel???


you can build chassis from it that's why its special

CAD Monkey - 19/5/07 at 01:52 PM

Thanks for the help guys, I ask because on the Haynes Roadster forums we were talking about steel suppliers and one of the guys said "make sure you get ERW". And it's confused me as to why it's better than non ERW for chassis building

http://www.haynes.co.uk/forums/showthread.php?t=152

ecosse - 19/5/07 at 01:53 PM

quote:
Originally posted by omega 24 v6
quote:

What is special about ERW Steel???


you can build chassis from it that's why its special


Talking about chassis, how is your 442 coming along?
Cheers
Alex

MikeRJ - 19/5/07 at 02:38 PM

quote:
Originally posted by CAD Monkey
Thanks for the help guys, I ask because on the Haynes Roadster forums we were talking about steel suppliers and one of the guys said "make sure you get ERW". And it's confused me as to why it's better than non ERW for chassis building

http://www.haynes.co.uk/forums/showthread.php?t=152


There is nothing "special" about ERW, except that box section with the wall thickness that is desirable for building chassis (i.e. 16 gauge/1.6mm) will almost certainly be ERW. Sections formed by drawing over a mandrel will usually be much thicker and more expensive.

CAD Monkey - 19/5/07 at 02:59 PM

So that's it then? Just cost and therefore weight? I did wonder why some of the suppliers said they only supplied 2.0mm wall thickness - I take it these must not have been ERW, but the stronger weightier stuff...

omega 24 v6 - 19/5/07 at 03:33 PM

quote:

Talking about chassis, how is your 442 coming along?


Well very slowly would be an understatement
BUT i am progressing at times.

Doug68 - 19/5/07 at 04:14 PM

ERW means Electric Resistance Welded.
What this means is that the edges are forced together in the manufacturing process and an electric current is passed through to heat and weld the edges together.

ERW is the cheapest way of forming tube, in the piping industry it would rarely be considered to have a joint quality factor greater than 0.85 where seamless tube has a factor of 1.

Why I think people may be going on about ERW is that the tube they use all happens to be ERW, and there's nothing special at all about the process.

Of more importance for our application is the grade of the material, regular low carbon steel tube can have tensile strength in the range 250MPa to 450PMa typically what most people use is (here in Australia at least) 350MPa material.

Typically the bright finished material you might find is the weaker grade material as it is made for use in furniture etc where easy bending is a manufacturing requirement. Not what you want in a car frame.

Here in Australia the GR350 material has a rougher finish and is pretty much all painted blue.

I've not kept up with the UK steel grades but your supplier should be able to tell you what grade the material is that he has to supply. Hopefully someone here can inform us on the UK grading system.

Some people may not think the whole grade issue matters that much, and in daily driving it probably doesn't but when you're going through a hedge backwards the extra strength could well come in handy

speedyxjs - 19/5/07 at 05:20 PM

quote:
Originally posted by CAD Monkey
So that's it then? Just cost and therefore weight? I did wonder why some of the suppliers said they only supplied 2.0mm wall thickness - I take it these must not have been ERW, but the stronger weightier stuff...


Im using 25mm square by 2.5 thick rhs and 20 square by 2 thick because im using a bigger engine than the book and i would prefer to carry some extra weight and have a stronger car

cymtriks - 19/5/07 at 08:22 PM

Just occasionally you get non welded tube. This looks like ERW but has no weld, it's just wrapped into a shaped and the ends left butting together.

This kind of tube is usually used were the application is decorative or where there is some other reason not to weld up the joint.

This kind of tube is not appropriate for an significant loading.

TheGecko - 20/5/07 at 02:04 PM

quote:
Originally posted by speedyxjs
Im using 25mm square by 2.5 thick rhs and 20 square by 2 thick because im using a bigger engine than the book and i would prefer to carry some extra weight and have a stronger car
Speedyxjs, have you actually bought tube yet or started to build? If not, you might want to consider staying with 1.6mm wall but going up in tube size - ie 30 or 35mm. Going up in wall thickness will gain you plenty of extra weight and not much extra strength. From a recent discussion on another board, here's some comparative numbers: 

code:
Section     kg/m    Bending  Torsion 

25x25x1.6    1.12    0.78      1.54 

25x25x2.5    1.64    1.08      2.07 

30x30x1.6    1.38    1.16      2.32 

35x35x1.6    1.63    1.62      3.26 

50x50x1.6    2.38    3.44      7.03


You can see immediately that by going to 30x30x1.6 you can more strength than the 25x25x2.5 for less weight. Or, 35x35x1.6 - the same weight as the 2.5 and around 50% stronger.

Anyway, just some numbers to contemplate. Best of luck with your build.

Dominic

flak monkey - 20/5/07 at 02:14 PM

You are confusing strength and stiffness.

Going up in wall thickness will increase the STRENGTH of any given tube, but have very little effect on the stiffness.

Going up in tube size and keeping the same wall thickness increases the bending STIFFNESS but has no effect on the strength.

They are two very distinct and different things. Which many people confuse.

David

TheGecko - 20/5/07 at 11:56 PM

quote:
Originally posted by flak monkey
You are confusing strength and stiffness.

Going up in wall thickness will increase the STRENGTH of any given tube, but have very little effect on the stiffness.

Going up in tube size and keeping the same wall thickness increases the bending STIFFNESS but has no effect on the strength.

They are two very distinct and different things. Which many people confuse.

David

Flak,

You're absolutely right, strength and stiffness are two different things and, for steel tubing, strength is pretty much just a factor of cross-sectional area so going up in thickness will increase strength quite quickly. Going up in size will increase strength slightly (there is more metal) but, as you rightly point out, the main gains then are in stiffness. It was after midnight here when I posted that so I'll apologise for the loose use of terminology.

The question really is - is the outright strength of the tubes an issue in a Locost chassis or is stiffness much more of an issue? Has anyone's chassis ever fallen apart because a tube failed due to lack of tensile strength? Not a suspension tube, but a chassis tube? Insufficient beam & torsion stiffness are much more common chassis problems and those WILL respond to tubes with more stiffness.

All of that said, if speedyxjs is actually going to use a Jag V12, a Locost chassis is probably not up to the job making this conversation somewhat moot.

So, I apologise for misusing the word "strength" in a vernacular sense rather than the more correct term "stiffness". However, I think the original intent of the message stands - extra stiffness is a commonly sought quality is a Locost chassis and will be better gained with an increase in tube size rather than thickness.

Dominic

CAD Monkey - 21/5/07 at 11:28 AM

Thanks for the replies chaps, I guess I'll be going for ERW 25x25 1.6 as I intend to use a 2.0 Zetec.

Thanks again!