Flange Radius for Copper Boilers

Hi David,

I assume this is for your Simplex? Martin Evans usually showed quite a tight radius for the flanged plates. A gentler more generous radius wont create any problems and IMHO is advantageous. You can bash annealed copper to whatever radius you want. With hardwood formers that I use I get a 3/32" radius on the inside. With steel or cast formers you can get it tighter.

Martin Evans also has a flange length shorter than I use, plus greater spacing of the firebox stays. We can perhaps discuss these details and a few other matters re the boiler via PM.

Cheers,

Julian

Hi Julian,

Yes, thank you!

David

If you look in a zeus book the formula is there. there are published formula for all aspects of boiler design and a lot can be changed from the original drawings in most cases.

Fizzy,

Don't leave me hanging, what does the "zeus book" say? I don't have that book.

David

David. RDG sell the book. It is cheap and very useful with lots of data. Latest version does not have BA in though.

Brian

The formula in Zeus is to calculate the length of material required for a given bend angle. Basically, internal rad + two fifths material thickness X angle.

Regards Ian.

A good rule of thumb is, don't make the inside radius less than the thickness of the copper being flanged. All flanging causes local thinning on the bend, the greater the radius the less effect this has. The safety margins designed into our boilers is such that this is of no consequence, but it is wise to be aware of it. Don't ask me how much it thins as I am not cleverer enough to work it out, but I am sure that someone on this forum has the knowledge and the ability to do so.

For the curious. You can download a 1976 PDF copy of Zeus. Google Zeus PDF.

For copper sheet, is the radius something like 1.5 to twice the thickness?

Steve

Thank you to everyone that has responded!

To be clear, I was not looking for the length of material to create a bend. I am looking for the dimension of the radius at the bend based on material thickness.

David

IIRC a formula for bend radius for mallable sheet for boiler plate forming is 1.5 to 2-times the plate thickness. As mentioned by someone for model boilers, you can go tighter but then the danger exists of cracking if the copper is not sufficiently annealed. Rather go for a greater radius then less to be safe.

A quick google leads to a lot of info. Not that I know a lot about this subject. The alco site says minimum radius for bar and flat bar is the thickness of the bar. The Rime site says 'Each material to be worked also has its own conversion factor. For example, the minimum bending radius of aluminium is determined by multiplying the sheet thickness by a factor of 2. If copper has to be bent a factor of 1.5 must be used. For steel the factor is 1. In this case the minimum radius equals the respective sheet thickness.' It also mentions about bending across or with the grain. **LINK**

What John says sounds good to me.

Edited By Steven Vine on 22/04/2016 15:10:30

Bending Aluminium, you must be very careful here as the acceptable bend radius depends upon the grade of Aluminium being used, its temper, its thickness and whether you are bending across or with the grain. Stronger the material larger the bend radius. Typically the Aluminium Association suggests you can use 2 x thickness (2t) for 6082-T6 sheet up 1.2 mm thick. However do that at your peril, if you bend across the grain you may get away with it at 1.0 mm thick but 3t is required to achieve consistent results in all directions at that thickness and 4t from 1.2 to 1.6 mm. Of course heat treating changes all that, but introduces a whole new set of problems.

Regards

Dave

As my thread title suggests, I am interested only in copper, specifically copper for model locomotive boilers. Thank you to everyone that has replied!

David

Hi Dave,

There again there is copper and then there is copper. The grade and temper as supplied has a big bearing on how tight it can be bent. If the sheet is supplied as "fully annealed" then you can go pretty tight, but run the risk of cracking at a later stage when silver soldering it all together. If it is supplied "half hard" or "hard temper" then it gets much worse. Most people prefer to anneal before bending and might need to do it several times for a circular flanged plate. If it gets hard - anneal again! Copper work hardens so even if it is supplied fully annealled it most probably will need annealing again during the forming process. Just don't go berserk with a 4lb hammer and you should be OK.

Thanks John. Yes, I understand about annealing. I expect to this many times during the process of forming the plates. The copper plate I have is from a boiler kit from Blackgates. It should be just the perfect thing!

Thanks for more info!

Edited By David Wasson on 23/04/2016 18:05:28

Hi there folks

You don't actually NEED a flange at all. What you NEED is a flow of silver solder RIGHT THROUGH THE JOINT. The problem is keeping the plates in position while soldering and this is where the flange is useful. Once again the 'legislators' got in on the act and - as with our Australian cousins who made up an otherwise excellent system of specification many years ago. As the designer of a number of copper boilers, always under the eyes of the late Alec Farmer, I did as i was encouraged. The original boiler for my 5" gauge American "Washington" proved to be very efficient, but I have yet to learn if an Oz builder has had the same results as THEIR modification was to reduce the number of tubes and extend all internal flanges by 'quite a lot' and adding considerable cost of solder used with the excess going "right through the joint. As to the flange radius I suggest 1/8 inches (3mm) on any scale.

See "You Tube" "Walton Park Trains" for a "Washington" in action.

David Piddington

Hi David,

It is great to see you on here again.

I think many of us will refer you to Jack Austen-Walton's 5"g 'Twin Sisters' original boiler design, which had no flanges to the plates although to be silver soldered, and was regarded as 'dangerous'.

The Australian boiler code does throw up a number of differences, which have been discussed at some length on another forum particularly with regard to one LBSC boiler design ('Doris' and the changes required to get it to suit the Aussie Code for a 'home made' boiler, yet they will accept a UK made commercial boiler made to the original design, albeit with proper bushes etc lacking on the original design. A commercial Uk boiler is accepted with girder crown stays and LBSC stay spacing, but a home made build requires rod stays for the crown, and larger flue tube spacing, and allows a wider spacing of firebox stays!

None of this is relevant to David's query!

Cheers,

Julian

Thank you both David and Julian,

Yes, I understand what you mean about not needing a flange at all, but, it does allow for a larger surface area of the the silver solder to adhere to, rather than just the edge of the plate thickness. I am going with the 1/8" radius on the inside of the flange.

Julian, I have started reading the thread of Doris "versus" the Aussie code. It is an amazing thread that just goes on and on. It seems some folks do not understand the difference between stay diameter, and stay spacing. These are completely different issues.

So, the next question would be, what is the recommended flange width for 1/8" copper? My boiler material kit was purchased from Blackgates. The plates as supplied, are not very much oversize to make a flange that is very wide. What can I get away with for flange width and still have a decent joint with silver solder?

Thanks,

David

Hi David W,

I was going to email you on this, but a 3/8" flange beyond the radius is quite ok. the overall dimension of 1/2" on Super Simplex is prefectly ok allowing for the 1/8" on the smokebox tubeplate material and backhead same. I would use the same for the inner firebox flanged plates.

If the flanges ended up as 5/16" I wouldnt worry, but some of Martin Evans' earlier designs are a bit mean.

Cheers,

Julian