copper barrel material usage

[ausdan]

G'day fella's

I need to move from the thinking stage to the making stage of a replacement boiler for my 5" don young HUNSLET.

The question at this time, based on conversation with a proficient boiler maker some time last year.
Was that for the rolling a barrel over a former, he would use the calculation circumference plus 1.5 x the thickness of material.

I need make a barrel at 6" OD using 3mm sheet and plan to cut the sheet copper at 152.4 + 4.5 = 156.9 rounded up to 157mm

Does this seem similar to any other person who have maybe produce a copper barrel or two?

cheers
Dan

[redmog]

Circumference not Diameter.

No - I calculate it to be 483.3mm.
Unless I have misunderstood.
6" = 152.4mm diameter
152.4mm x 3.142 ( pi ) = 478.8mm
478.8mm + 1.5thickness is
478.8mm + 4.5mm = 483.34mm.
So if you cut the 3mm sheet to be 483 mm wide
It should roll up to be 6" OD.. ish.. ish

Chris

[ausdan]

Yeah, you were right, I was too worried about the factor on the end and messed it up

ask twice and cut once ;D

[AndrewP]

Dan
The copper tube I have seasoning under the bench for my Hunslet boiler is 6" bore 10 gauge so about 6 1/4" OD - makes a slight difference! I checked and Don calls for 6".

It's not clear to me whether that formula relates to bore or od but I suspect bore.

Cheers, Andy

[GWRdriver]

I should have my references in front of me when I quote something like this, I don't, but I've never let that stop me before so here goes anyway . . . The rolling allowance for metal is typically figured on the length of the "neutral axis" . . an imaginary line that falls somewhere between the inner and outer surfaces. The location of the neutral axis varies with the metal but for copper it isn't dead center, it's nearer one surface than the other, perhaps 1/3rd the thickness IIRC. If you Google "neutral axis metal forming" (or some combination of the terms) I'll wager you'll come up with the information. For the thicknesses we use it's probably a bit of hair splitting but I used the neutral axis to figure a number of wrappers and flanges and it always seems to come out right near spot on.

PS - Heres a decent representation:
www.custompartnet.com/wu/sheet-metal-forming

[ron]

If it's of any help the Hunslet boiler I bought from Western Steam has a rolled boiler tube, it is approx 160mm OD [6.25"] and measures exactly 500mm circumference.
Ron

[grahamo]

GWRdrivers comment is correct.

The length is calculated along the neatral axis. In practice the outside material is stretched and the inside is shrunk in the rolling process. each material is slightly different, (I recall a figure of 2/3rds for steel from my apprenticeship).

An interesting and useful effect is that if you calculate for a 90 degree bend in steel, the minimum bend radius is reckoned to be the thickness of the steel. do the calcs at 90 degrees and the pattern length lost is within a nats whisker of 2 thickness of metal. meaning that to form a piece of angle or a box for example we worked by transfering inside measurments direct to the pattern.

Graham

[steam4ian]

G'day Arch

Why don't you use DN150 Type A Cu tube?

It is good for a test pressure at 20deg C of 278 psi and a safe working pressure at 175 degC of 126 psi.

You may have to ring around plumbing or fire protection engineering houses to get some but it will save rolling. You may also need to sweet talk your boiler inspector but calculations are calculations.
See www.cranecopper.com.au/downloads/wCRN8316_AS1432_Copper_Tube.pdf for details. The derating for temperature calcs are on page 6 of the brochure.

Regards
Ian

[ausdan]

thanks for the reply, looks like the formula is more of a standard, I thought it may be particular to our use.

Ian,
I did question some commercial places quite some time ago, they were keen to sell a 6mtr length, though I needed about 450mm.

Boiler inspector, wise, maybe you could sweet talk him, as I have taken my plans to your club for Bill C to go over them ;D.

We have a new steel boiler code inspector, but not copper