Twisting a 160x80x3mm Rectangular hollow tube.

[Jay_]

Dear Experts,
I rarely post in this forum, but we have a project that consists of twisting the above mentioned hollow tube for a 90 degrees.
I have read that people tend to heat the tube, or to put a pipe inside of it to prevent collapsing or even sand and to pressurize it a little and then to start twisting.
My problem is that we can't heat, or put a pipe inside (since its a rectangular shape) and the section is fairly large and requires a lot of torque applied.
Some people cut the four corner of the tube and then grind diagonally along each face of the tube and then twist and then weld the cut edges. but I'm not sure than I can do that sine it's an architectural project.
Any insights??


Detailing is a hobby,

 

[r13]

The formula may help in planning the process to avoid crashing the tube. It works the best with the incorporation of suggestions received from JStephen and CANPRO.

 

[JStephen]

I had to watch that video a couple of times, and also the one after it.
They're not actually twisting the pipe. They're taking round pipe and rolling flats into it. The flat-rolling part rotates to make a spiral shape, but it's not actually rotating the pipe when it does that. IE, it's forming a twisted pattern into the pipe, but not twisting the pipe.

 

[BUGGAR]

I believe your b/t ratio is too high to preclude buckling before reaching the torsional (shear) yielding you require.

 

[Jay_]

Could you do two 80 x 80 tubes then glue them / weld them together after bending?

It's not practical since you can't actually predict the exact shape of the finished product, plus if we go this way we will have a lot of material loss.

Is this subject to any load? I don’t fancy the buckling calc on that!

Only self weight.

could you 3D print this ?

the technology isn't available in our country.

I would break form this tube

I did some calculation and the amount of torque required to do this job is dramatically high. we will need to use the press instead (Option 1)

My idea is to put it in a press

We are already preparing the procedure and logistics to do this option (option 1) it does seem quite challenging and very practical thank you!

The following idea may seem crazy but may work..

can you explain more?

this might be an option:

We actually did that yesterday and it looked so good!!

The formula may help in planning the process

thank you!

Detailing is a hobby,

 

[WARose]

They're not actually twisting the pipe. They're taking round pipe and rolling flats into it. The flat-rolling part rotates to make a spiral shape, but it's not actually rotating the pipe when it does that. IE, it's forming a twisted pattern into the pipe, but not twisting the pipe.

At the end of the day though, I'd think it would still give the OP what he is after.

 

[dik]

rectangular or square, the tube would distort during twisting.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[HTURKAK]

Dear Jay,

The Material is carbon steel st37-2, could not see the reason that you can't heat.

.

In order to keep the rectangular shape, I thought to insert rectangular plates and fill the inside of the hollow tube but it may not come out easily.
For this reason, i suggested to fill with frozen sand plates. You may cut several slices from rectangular tube with h 15mm, and fill them with soaked sand in kitchen small bags and freeze them. You may try for a 500 mm sample length. First plug one end with a plate tack welded, insert the frozen sand plates and plug with a wooden wedge the other end. You should twist before the frozen sand plates melted.

You may consider just an idea but it is worth to try.

 

[rb1957]

would wax be a good filler ?

another complexity is elastic spring-back.

Can you stress relieve after twisting ? This should help elastic spring back.
If not stress relieving, how to account for forming stresses ? what about creep ??

If the twisted tube is structural, what properties post-forming ?

If not structural, why steel ?
Why disregard 3D printing just because it's not available "in country" ?

another day in paradise, or is paradise one day closer ?

 

[EdStainless]

The roll forming of a round to square/rect is an odd process. If the roller head rotates 90deg then the pipe likely twists about 1/2 of that. The roller formers are actually very simple to do, the frame for the head needs to be strong, but it doesn't take that much force to pull a pipe through this.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[r13]

The roll forming of a round to square/rect is an odd process.

Do you think they press to form the square first, then twist to the end shape? Interesting piece of machine then.