HI, does any one know the strengths of box vs tube steel?
For example what size pipe would be comparable to 25mm box or is this question like 'how long is a price of string' ?
basically I was wondering what size and type of pipe (if anything) would be comparable to typical 75 x 50mm mild steel box to keep weight low - real low.
any help appreciated
NJ
Relative strengths
Relative strengths
SWB V6 Paj with one or two mods 
Sort of 
here's a simplified look at the strengths assuming sqaure and round are of the same size
As a beam (load across section) sqaure is marginally stronger if your load is parrall to the sides as you have the bend all of the side section, if you can do it in rectangular section with the long edge in line with the load that way you use the most weight of the metal in supporting the load... the bonus with tube isn't that its lighter (less circumferance = less metal) its that it has the same strength in any direction
Compression and tension loads... this is about cross section and weight, the box wins here becouse it has a larger amount of metal for a given size
to tell you what 75x50 is egaul to in tube you'd need to know the wall size and load direction, type of load etc.... it is possible to work out but a lot of trouble
If you keen to lose weight consider building structures and using triangulation... its why race cars use space frame chassi's
Cheers Reece
here's a simplified look at the strengths assuming sqaure and round are of the same size
As a beam (load across section) sqaure is marginally stronger if your load is parrall to the sides as you have the bend all of the side section, if you can do it in rectangular section with the long edge in line with the load that way you use the most weight of the metal in supporting the load... the bonus with tube isn't that its lighter (less circumferance = less metal) its that it has the same strength in any direction
Compression and tension loads... this is about cross section and weight, the box wins here becouse it has a larger amount of metal for a given size
to tell you what 75x50 is egaul to in tube you'd need to know the wall size and load direction, type of load etc.... it is possible to work out but a lot of trouble
If you keen to lose weight consider building structures and using triangulation... its why race cars use space frame chassi's
Cheers Reece
Short answer yes it does lose strength
Out of all the styles of bending a mandrel bend is the best in that it retains the shape of the tube around the outside of the bend, but... it does this by stretching it thinner tho
A pipe bender with its open die dosn't crush the bends it just does a piss poor job of holding the sides of the bend in shape allowing them to bolge out and the back to cave in narrowing the cross section of the tube... this narrowing weakens its structure
Tube benders use special dies made to tightly fit the tube and use rub blocks or rollers to retain the shape at the bend piont... this does allow some collapse of the back of the tube and narrowing of structure but is used becouse they are the best bender for price
Mandrel benders use an internal die as well that stops the back collapsing but they cost!!
If your building something from tube, work on the idea that bends are bad as they provide a weak piont for failure and compromise the structure of the tube... triangulate, triangles are the stongest structure you can build and don't get ideas from american sites fashion seems to be more important than good design
So what you thinking about building????
Cheers Reece
Out of all the styles of bending a mandrel bend is the best in that it retains the shape of the tube around the outside of the bend, but... it does this by stretching it thinner tho
A pipe bender with its open die dosn't crush the bends it just does a piss poor job of holding the sides of the bend in shape allowing them to bolge out and the back to cave in narrowing the cross section of the tube... this narrowing weakens its structure
Tube benders use special dies made to tightly fit the tube and use rub blocks or rollers to retain the shape at the bend piont... this does allow some collapse of the back of the tube and narrowing of structure but is used becouse they are the best bender for price
Mandrel benders use an internal die as well that stops the back collapsing but they cost!!
If your building something from tube, work on the idea that bends are bad as they provide a weak piont for failure and compromise the structure of the tube... triangulate, triangles are the stongest structure you can build and don't get ideas from american sites
fashion seems to be more important than good design
So what you thinking about building????
Cheers Reece
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gomulletgo
- Hard Yaka
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- Joined: Sat Aug 26, 2006 12:00 pm
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wow, deranged. very informative and balanced views. Me likely 
I'm not suggesting I would do this on something structural such as a roll cage but.....could weld in bends be stronger than mandrel?
the way I see it, bends are weaker, welds are weaker.....what is the lesser evil?
working on the understanding that weld in bends are the same thickness right through (I'm guessing on this one)
keep it coming guys
I'm not suggesting I would do this on something structural such as a roll cage but.....could weld in bends be stronger than mandrel?
the way I see it, bends are weaker, welds are weaker.....what is the lesser evil?
working on the understanding that weld in bends are the same thickness right through (I'm guessing on this one)
keep it coming guys
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gomulletgo
- Hard Yaka
- Posts: 320
- Joined: Sat Aug 26, 2006 12:00 pm
- Location: Amberley / North Canterbury
De-Ranged wrote:Got some bad news weld in bends are mandrel bends
As for knowing this sorta stuff
Cheers Reece
Only exhaust tube weld in bends are mandrel bent. Pipe bends appear to be cast, especially in smaller sizes.
As for strength of box vs tube, it depends entirely on the geometry and loading.
FWIW pipe is most often mild steel (grade 250), RHS and SHS (rectangle and square hollow sections) are usually higher grade.