Calculate bending radius of a cone

[Ebo1000]

I have a fabrication problem on site that I am at total loss with, can anyone help?

We have a cone top economiser that we have to cut a hole into to allow a welder in to plug a tube. The shutdown team have bought a new plate section and have asked the design office to provide a rolling radius. I have only have experience of developing and rolling full cones many moons back, where the cut and profiled plate would be placed in the rolls and rolled until the ends meet but I cannot think there was ever a calculation done to provide a radius. I guess the bend radius is perpendicular to the slant rather than a radius about the centreline.

Is there a formula or a way of drafting out a solution?

 

[Don56]

The radius is constantly changing as the diameter of the cone increases or decreases.

 

[SnTMan]

Ebo1000, most practical thing may be get the large and small diameters & surface length, do a development, have a chunk formed on a press brake. More hits = smoother surface. Trim to fit. Carefully.

Oh, and save your slug

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[racookpe1978]

You're looking to make a replacement panel, not the whole thing.

Will it overlap (fillet weld) or be an exact replacement (butt weld)?

To begin make two plywood (1/4 ot 5/16 will be thick enough) templates at the exact size you want. (Layout the cut plate on the existing tank first with chalk or paint marker). Then roll the new plate slowly as many times as need to get the two tempaletes to fit the upper and lower curves.

Warning: Mark carefully the inside and outside wall radii for the templates: You'll probably template to the OD, so roll so that the template duplicates the OD, not the ID of the new plate.
You'll have to roll 3% past the desired bend to allow for strain relief when it is out of the rollers.

 

[Ebo1000]

Thanks for the replies all.

@Don56 Yes the radius is changing but this is when viewed side on. The rolling radius should be perpendicular to the sloping side; if that makes sense. If you Google images the rolling of a cone you will see that the cone is rolled at an inclined plain and inclined centreline.

@SnTMan & @racookpe The plan is to cut the slug out and then butt weld the new plate into place. I have done the development and then superimposed the new plate into place. this has given me the largest insert possible with arc lengths of 297 top and 612. I have projected a line back to the centreline perpendicular to the slope as mentioned above and this gives me (I think) a rolling radius of 645mm. See attached file below (needs rotating into landscape)

Our Mech Eng is bringing a representative of the rolling company in to discuss the job this morning (uk time) and ideally I would like a partial roll and then offer it up but I guess this will not be practical. My last resort is to measure across the chord of the curve on my 3D model and get them to roll to this dimension. The problem is compounded by the shutdown team only buying a small 1000mm X 500mm plate so no room for error.

Cheers Ian

 

[racookpe1978]

CAUTION!!!!

Make absolutely sure the rolling company understands the arc-length (as-rolled) length and radius and centerline offset (if any) at top and bottom of the new rolled panel are the final dimensions.

He (she ?) WILL need about 4-6 inch extra on both rolled ends for the center-roller-tangent to end-roller-tangent straight lengths. You should expect to see these cut-off metal costs (which will have to be cut and finished for a bevel prep before welding) with his material cost estimate.

 

[SnTMan]

...WILL need about 4-6 inch extra on both rolled ends...

...a small 1000mm X 500mm plate so no room for error.

Might be a good argument for a brake-formed part

The problem with sloppy work is that the supply FAR EXCEEDS the demand