Author Topic: Bending a casting  (Read 5716 times)

Offline RonGinger

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Bending a casting
« on: May 08, 2016, 10:49:50 PM »
I need to make a couple of new builders plates for a locomotive we are restoring. It is an 1895 Baldwin, 2ft gauge  0-4-0  that originally ran in a paper mill. We are doing a total ground up restoration, with a new boiler. We want to make a new builders plate for the side of the smoke box. Its about 10" diameter and will be about 1/4" thick.

The problem is it must be bent to the smokebox curve, about a 30" diameter. Can we just set this up in the press and bend it? Should we just any particular brass? Is it worrth heating it before we bend it? How hot?

Offline 10KPete

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Re: Bending a casting
« Reply #1 on: May 09, 2016, 12:07:39 AM »
Any true brass will make that gentle radius cold. Do not heat as brass is hot short and unless you have the temp right it will
crumble.

If you have a choice for the alloy get what's called '360' as it's highly ductile.

Pete
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Offline crueby

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Re: Bending a casting
« Reply #2 on: May 09, 2016, 12:13:49 AM »
Pete, what does the term "hot short" mean? Have not heard that before.

For bar stock, heating to a dull red then cooling to anneal it helps bending, but I have no experience with cast brass so don't know if that behaves differently, how hardened if any it is after casting. Alloy 360 does bend a decent amount when annealed. You may need to have the form set to overbend slightly to allow a bit of springback.


Offline derekwarner

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Re: Bending a casting
« Reply #3 on: May 09, 2016, 02:29:07 AM »
A 10" diameter x 1/4" thick flat cast red brass/bronze disc being bent to the form of a 15" radius is a big ask  :hammerbash:

The original from 1895 would I suspect have been as cast from a pattern of the required diameter.....such material castings from this period are prior to any form of vacuum degassing so would be of extremely course granular structure & somewhat brittle

The material would also exhibit a very low tensile strength and yield point, both of which are not conducive to any bending action

Lettering/numerals cast in the flat plane would grossly distort and tear when bent to the 15" radius ......

Heating brass to annealing temperature is to relax a work hardened molecular layered structure.... :Director:    and not intended or sufficient to alter the course granular as cast structure

You could consider replicating the original by producing a 15" radiused pattern & sand cast the requirements ......just like the original :ThumbsUp:

Derek
« Last Edit: May 09, 2016, 02:42:56 AM by derekwarner_decoy »
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Offline b.lindsey

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Re: Bending a casting
« Reply #4 on: May 09, 2016, 02:44:14 AM »
I can't add to the discussion Ron, but am sure interested to see how you end up going about it. If you do bend a disk of say 360 brass, will the lettering/ numbering be done first or afterward.

Bill

Offline 10KPete

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Re: Bending a casting
« Reply #5 on: May 09, 2016, 03:29:11 AM »
Pete, what does the term "hot short" mean? Have not heard that before.

Metals that are 'hot short' are metals that get brittle and tend to crack or crumble when they are heated beyond a certain point.
Austinetic stainless steels and bronze are common examples. They can be annealed for bending, and they work harden. But if
they are heated to bend them, like getting up to a red temp, they will crack and crumble. Most bronzes can be heated to bend
but can not be heated to the point they turn red or they crack and crumble.

For bar stock, heating to a dull red then cooling to anneal it helps bending, but I have no experience with cast brass so don't know if that behaves differently, how hardened if any it is after casting. Alloy 360 does bend a decent amount when annealed. You may need to have the form set to overbend slightly to allow a bit of springback.

Yellow brasses, like 360, whether wrought or cast will anneal and bend well. Red brasses will do the same but less so with the cast
reds being the worst. The higher copper content makes these brasses red and the cast varieties can have lead and zinc which make
them closer to bronzes.

My experience with these metals comes from building flintlock rifles with brass casting furniture, and cast and wrought boat parts.

Hope this helps,
Pete
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Offline 10KPete

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Re: Bending a casting
« Reply #6 on: May 09, 2016, 03:41:15 AM »
A 10" diameter x 1/4" thick flat cast red brass/bronze disc being bent to the form of a 15" radius is a big ask  :hammerbash:

The original from 1895 would I suspect have been as cast from a pattern of the required diameter.....such material castings from this period are prior to any form of vacuum degassing so would be of extremely course granular structure & somewhat brittle

The material would also exhibit a very low tensile strength and yield point, both of which are not conducive to any bending action

Lettering/numerals cast in the flat plane would grossly distort and tear when bent to the 15" radius ......

Heating brass to annealing temperature is to relax a work hardened molecular layered structure.... :Director:    and not intended or sufficient to alter the course granular as cast structure

You could consider replicating the original by producing a 15" radiused pattern & sand cast the requirements ......just like the original :ThumbsUp:

Derek

In my experience, 1/4" thick on a 15" radius is not a problem for a yellow brass. Since Ron is making new plates he can specify
yellow brass. No special de-gassing will be required. Graphics should not cause difficulties in that gentle bend.

Cast yellow brass doesn't, in my experiences, exhibit reduced physical properties compared to annealed wrought yellow brass.

The simple difference between cast brass and wrought brass is that wrought brass is rolled after casting, usually a continuous
process these days

All based on my own experiences so take it for what it's worth to you,
Pete
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Offline Jasonb

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Re: Bending a casting
« Reply #7 on: May 09, 2016, 08:09:20 AM »
Does it have to be cast? Could it be CNC cut from one of teh bending brasses like CZ108 and then simply pressed over a wooden former with suitable cope. Or even bend first and CNC with a 4th axis to cut the face leaving the letters proud as if cast.

Offline 10KPete

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Re: Bending a casting
« Reply #8 on: May 09, 2016, 08:15:33 AM »
Jason, these days that just might be the way to go. Good idea!!

Pete
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Offline Jasonb

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Re: Bending a casting
« Reply #9 on: May 09, 2016, 10:15:36 AM »
It was Dave Otto's avitar that made me think of it, he posted somewhere about doing it. A lot of the nameplates here that look cast are actually done by CNC so with the right choice of a bending brass and a press or rolls it should be possible.

Cut well they look as good as cast http://www.steamplates.co.uk/

Offline kvom

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Re: Bending a casting
« Reply #10 on: May 09, 2016, 12:39:19 PM »
Does it have to be cast? Could it be CNC cut from one of teh bending brasses like CZ108 and then simply pressed over a wooden former with suitable cope. Or even bend first and CNC with a 4th axis to cut the face leaving the letters proud as if cast.

That would be my choice too.

Offline RonGinger

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Re: Bending a casting
« Reply #11 on: May 09, 2016, 12:46:13 PM »
Thanks for all the info.

I will be CNC cutting the pattern, and I could cut the brass part instead. I have done that for a few smaller labels I have made like boiler inspection tags. I only have 3 axis so I would still be bending the final part.

We have a tag that replaced the original when the loco was rebuilt in 1926. We will place that in the museum display and make a new tag like the original. A smaller tag will be placed under that to indicate our rebuild.

I have considered cutting the pattern from very thin ply, then laminating that into the curved shape. We dont think our foundry will like working with that and some kind of backer block.

I think I will push ahead with the flat pattern and see how it bends. If it breaks we can always toss it in the pot and try another approach.

Offline jschoenly

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Re: Bending a casting
« Reply #12 on: May 09, 2016, 02:19:54 PM »
My little lost wax castings in Everdur Bronze bend quite nicely.  Totally different scale there, but I would think it should still bend pretty well.  Do you know if the original plates were cast in brass or bronze? 
Jared
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Offline Alan Haisley

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Re: Bending a casting
« Reply #13 on: May 09, 2016, 02:21:38 PM »
Ron,
Can you move the Y axis from the mill to a rotary table? The programming is just math and so should be doable.
Or maybe it's time to add that fourth axis  >:D
Alan
Near Raleigh, NC, USA

Offline Maryak

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Re: Bending a casting
« Reply #14 on: May 10, 2016, 02:35:55 AM »
The little I have had to do with cast brass is

It don't bend, it breaks! ( Especially if it's heated to bend it).

Regards
Bob
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Offline Mcgyver

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Re: Bending a casting
« Reply #15 on: May 10, 2016, 04:46:46 PM »
There is a whole specialty foundry genre for plaques - memorials, historic sites, medallions on buildings and so on.  I been through one before.  I don't know that there'd be any ability to cast a curved one, but they have such slick processes for the casting it would be worth asking....and checking out the cost before making a pattern etc for a flat one.  You send them the artwork and the casting comes back....have it done in an alloy that can be annealed and then head to the brake press (I'd make short 'gentle' die, maybe from AL and bump the annealed bronze).