Convexing a Steel Plate

What will the tank hold? Working pressure? What tools do you have? Sounds like heat, bend, cut to finished size and stress relieve.

But then, what do I know?

Meant to hold hot water (80C) up to 6 atmospheric pressure.

Tools I have next to nothing just hammer, cold-chisel, some cutting tools and was thinking of heat too but....idea.

Don't forget to install a pressure relief valve. Just in case the pressure goes wrong. You will definitely need to weld the parts together and some insulation should be in place too.

Weld it or let a welder who knows how, weld it together.

6 bar? "DON'T DO IT, ETHEL!"

This sounds as though it ought to be a proper pressure vessel designed and tested in accordance with some code, and not some home-brew job!

Buy yourself a proper hot water heater, it'll be glass lined and hydrostatically pressure tested up to 150 psi if memory serves. It'll have a sacrificial anode to prevent corrosion and it will have a proper pressure relief valve, and it will be insulated too. if the idea is for hot water storage, there is no reason to actually connect it to the gas or electrical supply, but you could to help keep that water hot for extended periods.

5 mm? Wish you luck.

Hydraulic presses use quite some more force to shape this mass.

If you can bring the temperature close to the elastic phase temperature it will work.

But this setup will be even more dangerous if air gets in the water. Like you said IF the welds are fair, but they will be stressed to elongation.

A flat 5 mm sheet steel plate at the ends, can have already quite some pressure, without changing its plane shape.

Of course it all depends on the applied pressure in the vessel.

Those caps are not THAT expensive either.

What shape the edges would take up at the end of inflating?

GA from me and thanx for the hint!

Personally this is the only suggestion I would take side with as it is not only the least dangerous method to use but also the best one given my humble setup.

I used to do welding and boiler-making in my younger years but as I was told 'it is always better ask somebody if you unsure of what you're doing.'

I had a reasonable idea before this posting but I had this urge on the back of my mind to check in case there's a better one.

Do your caps need to be steel? You can hammer a brass sheet into a fine sand bed to make your shape then braze it together. Be careful though, if you have to deform it too much, you will need to anneal it by heating it (forget the temp, but google can tell you annealing temp of your brass).

If you need steel, find a local blacksmith who has a swage block. A good smith may be able to do it without the block, but it makes it easier.

Drew

maybe you could use a thicker plate and simply do a flat end ?

or maybe shape to conical ? but 5mm plate is quite hard to bend if you only have a hammer and some heating equipment.

5mm is a bit heavy for this, but you might give it a try:

Heat the center. The steel will try to expand, but the cool steel around it prevents this. When it cools, it will try to shrink. This will warp the steel around it.

You may need to do this in a number of areas starting near the OD and working your way in.

Why can not a suitable 'Dish End' be used?

A hydraulic jack and patience - saw it done all the time in İndia. Some of the workers got quite good at it. A little slow and for smaller sizes such as this it is normally easier to buy a dished end.

I would weld a slightly larger version over the end of a steel pipe.

Set it in a hot blacksmiths forge with forced air (make a simple one if you don't have one), heat the middle of the with an extra gas torch (not acetylene, just gas, but a big one,) get it cherry red, hit the middle of the dish with a big ball pein hammer and form as well as you can, use a metal template to help get the right shape......

Cut out when cool and weld to the tank.....

First and foremost, I would buy one already made as this will reduce the risk of an explosive tank failure.

Now as to how it is done commercially? there are two methods, the most common is hydroforming, where a form is machined out of a large block of steel, the plate to be formed is sandwiched under force between the form and another plate with a series of hydraulic ports drilled in it. the hydraulic ports are connected to a very high pressure hydraulic pump which forces the plate into the form.

Prior to this method becoming common, large plates were spun to shape. In this operation the plate is clamped in a lathe or Bullard type VTL (depending on the size of the workpiece) against a form, often made from wood. the toolpost has a heavy duty roller on a pivot that is pressed down onto the workpiece while it is turning and slowly advanced along the profile of the from the inside to the outside.

here is a company that does metal spinning.

http://www.hialeahmetalspinning.com/metal-spinning.html

I think this is beyond the OP's capabilities. It takes a tourch, or some form of heat, to spin steel.

I agree. Hence my comment that first and foremost he should consider purchasing one ready made, or barring that contracting with someone who had the wherewithal to manufacture the part in question.

this is the dish end work but as you said that you are having the heating and hamming tools only,as i understand that you need the both covers like the air compressor tank side covers, so , you just have to heat the center till elastic point and if you have the hydraulic cylinder and a 20cm high and one 3quarter dia ring ,just put this plate on that and apply the pressure from upper side,or you can use the hammer with a smaller ring but it will never give you the good looking shape. there is one other way (if you can afford). you have to hold tis sheet in the center and use 2 tapper rolls one on the upper side of plate and the other on the bottom side,with the required degree taper make the guides and hydraulic cylinders to push the rollers opposite to each others.apply the heat on the other side of roller bases(to soften the material and to save the force),just take out the rolls at every step till edge,i hope it will work, regards

Buy one! İf you follow some of the directions given here it will be a mess and probably somewhat dangerous. A flat plate end can be used with stiffeners but must be of adequate (calculated) thickness and stiffeners designed correctly. Not to mention it will be e bit funny looking when complete. İf it is an air tank İ expect you are aware of the necessary precautions - that can be real danger!

Cut an equal pipe size saddle on each end and then split a piece of the same size pipe and using the saddle as a guide layout and cut two ends and weld them to the pipe. This will give you a curved end but it will not be a true dished head. You can layout an orange peel cap on each end of the pipe and cut it off and reverse fit it to get a convex end. The first suggestion above makes a very strong end that has a very nice appearance. The second suggestion takes allot more time to execute but if done correctly it will be the strongest end short of just installing a correctly sized weld cap on each end of the pipe. Be careful to not cross over from pipe fitting to tank fitting when you do this and violate the ASME code by building a pressure vessel without a stamp.

"Any suggestion how to do it without the right machine setup?"

Big hammer.....