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Old 04-03-2022, 01:12 AM
A Guy In Town A Guy In Town is offline
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Default Compressed Air to Shape Metal?

I am a rank amateur at this stuff, but I like to think OUTSIDE of the box.

So imagine a thick round metal plate, perhaps 1/2" thick x 28" diameter. Around the edge are one-inch threaded studs, spaced evenly. Placed over this, a steel ring 28" OD x 26" ID x 1/2" thick with holes that align to the studs.

This plate is mounted on a spindle, such as a lathe. In the center, is a small hole drilled completely through. At the back end of the hole is an air fitting that allows a hose to be connected to the plate, and it allows for rotation of the plate at a slow RPM without twisting the hose, perhaps 60 RPM. This fitting is perhaps 1/2" in diameter.

Now a flat disk is cut from 16 gauge cold roll steel. The disk is 28" diameter with holes around the perimeter so that this disk slips over the threaded studs.

The 16 gauge disk is slipped over the studs. Then the steel ring is slipped over the studs and bolted down to pinch the edge of the disk, to close off the gap between the plate and the ring.

Now the assembly is rotated at a slow speed. 100 PSI of air pressure is introduced to the back of the material.

As the disk is rotated, the flame from a rosebud acetylene torch is directed at the center of the disk, heating the metal. As the metal absorbs the heat, the torch is moved along the radius of the disk, applying heat evenly in a spiral fashion to the outside of the disk nearest the ring.

I have NEVER tried this, but it is my contention that the disk would take on a uniform bowl shape as the air pressure forces the softer heated metal to expand as it fills the air chamber between the disk and the plate.

Using some method to control the speed at which the flame moves from the center of the disk to the outer perimeter, I BELIEVE the disk would be formed into an even, smooth bowl shape, in the same way that a glass blower forces glass to expand using air pressure.

The disk could never be allowed to reach "white hot" temperatures, as this would probably blow a hole through the disk. however, a visible dark to medium red glow of a ring of heat could be directed along the radius to cause the disk to bulge out via the 100 PSI of air pressure contained in the chamber behind the disk where the air inlet is applying a constant 100 PSI of pressure.

I do not know if such a machine even exists, or if someone is already doing this. I would love to build a prototype of this machine, and test it!

Any comments or suggestions? Criticisms? I can take it. I am a big boy. Is this "insane" or would this work?

Joe



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Old 04-03-2022, 04:02 AM
cvairwerks cvairwerks is offline
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Joe: It's done all the time with fluid and no heat....hydroforming. One danger with using air or steam for the fluid, is the problem with any rupture. Liquids don't have the violent expansion with the sudden release of pressure like air and steam do. A typical liquid failure is going to simply spray the liquid as the pressure drops. Gaseous pressure failures are generally violent and very often end up creating shrapnel.

There are a number of videos out there on diy hydroforming using pressure washers, hydraulic pumps and even grease guns.
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Last edited by cvairwerks; 04-03-2022 at 04:15 AM.
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Old 04-03-2022, 07:24 AM
Gareth Davies Gareth Davies is offline
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It could be done on a spinning machine for a lot less money than that rig would cost to build. It’s an interesting theory and would probably work fine but I personally wouldn’t pursue it.
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Old 04-03-2022, 07:38 AM
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Brings to mind an "anvil shoot".
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Old 04-03-2022, 08:39 AM
A Guy In Town A Guy In Town is offline
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Quote:
Originally Posted by cvairwerks View Post
Joe: It's done all the time with fluid and no heat....hydroforming. One danger with using air or steam for the fluid, is the problem with any rupture. Liquids don't have the violent expansion with the sudden release of pressure like air and steam do. A typical liquid failure is going to simply spray the liquid as the pressure drops. Gaseous pressure failures are generally violent and very often end up creating shrapnel.

There are a number of videos out there on diy hydroforming using pressure washers, hydraulic pumps and even grease guns.
So a sheet of 16 gauge steel will form and stretch into a bowl shape (more of a satellite dish shape) using liquid pressure? I didn't think that would be possible, but then it does make sense ... pounds per square inch, I guess

DISCLAIMER: I am not an engineer, and I do not play one on TV

I know that you can produce pressure using liquid (hydraulics, for example), but how is the pressure maintained? Assuming the liquid does not expand, it must then have a feed of liquid under pressure that is ready to fill the cavity at the same PSI, as the metal expands, right?

My original GUESS-timate of 100 PSI was just a number. I believe this could be done with far less pressure, using AIR, because metal that is heated to red or bright red, or orange SHOULD stretch and bend rather easily.

Suppose the air chamber only had 10 or 20 PSI. The rotating disk of heated steel WOULD expand, wouldn't it? Since it is not paper thin metal, I cannot imagine that the "bubble" would burst. It would only bulge at the rate that the softened metal could be stretched by the air pressure, and the stretch would occur at the band of "hottest metal" on the face of the disk.

I AM NOT DOUBTING YOU, and THANK YOU, for explaining this. I have heard the term "Hydro-Forming" many times, but never knew exactly what that meant. There is probably a Hydro-Forming company near me in bowling Green, or certainly in Nashville.

So ... I have a metal art project I want to do. And I want to form the disks myself, both to SAVE MONEY over paying some company to do this, and also to let me experiment with "A little more ... a little less" until I get it right. My other option was to use a sheet of some tough plastic, but I want this to be all metal, in fact, stainless steel.

I will go in search of these videos, now that I know the proper name for the process.

I just thought that the 16 gauge steel would expand under relative control, much like the process of blowing glass. As I said, I am not an engineer! I have blown up and burnt down many a thing over the years, as I experiment with ideas. A few of them have worked out just fine.

Moral of this story: Mom was right! I should have gone to college to become a Mechanical Engineer.

Joe



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Old 04-03-2022, 08:50 AM
A Guy In Town A Guy In Town is offline
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Quote:
Originally Posted by Gareth Davies View Post
It could be done on a spinning machine for a lot less money than that rig would cost to build. It’s an interesting theory and would probably work fine but I personally wouldn’t pursue it.

Yes ... SPINNING. That was the original direction I was looking to go, but those machines are 'Spensive, Lucy!

Beyond that, AFAIK, a spinning machine ONLY produces round dishes and cannot create other shapes. I guess that is where real skill comes in, with English wheels and Planishing Hammers, etc. I have been thinking of buying one of those to experiment with it a bit.

I can weld, and make the most basic things using oxy/acetylene to bend metal, etc. But I have never taken the time to learn how to FORM metal, such as turning sheet metal into a motorcycle gas tank and such. That is a special skill in itself, and one that requires the patience of Job.

I really RESPECT you guys (and gals!) who know how to do this stuff THE RIGHT WAY. My one semester of high school "metal shop" consisted mostly of making a chisel, and trying to avoid the guys who were making KNIVES and zip guns. I went to a rough high school.

Joe



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Old 04-03-2022, 08:51 AM
A Guy In Town A Guy In Town is offline
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Quote:
Originally Posted by drivejunk View Post
Brings to mind an "anvil shoot".
I saw the video of the guy who took his ear protection off with a .50 Cal bullet! Talk about CLOSE!

Joe



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Old 04-03-2022, 08:58 AM
A Guy In Town A Guy In Town is offline
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I even thought about using a hydraulic press, with a positive and negative mold that would give me the curve I seek.

I searched for a satellite dish company that might have a "boneyard" of old dishes they would sell for the cost of scrap metal. I could then cut them to the various diameters using my CNC plasma table. However, I really want this to be stainless steel, since it will be out there in the elements for YEARS without TLC.

Joe



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Old 04-03-2022, 10:06 AM
DarkLightning DarkLightning is offline
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Dish companies use what is called an offset Cassegrainian reflector. if you have a lathe with enough swing, you could spin the whole parabolic reflector and then cut out the portion you need. The reason they are offset is to reduce the signal blockage caused by placing the feed antenna in the middle. If you can build a bigger parabolic reflector, the loss from blockage becomes negligible. Paraboloids of revolution can be spun on a lathe; you just need the correct form. Alternatively, people switch back and forth from cable to dish. Maybe you can help someone clean their roof line free of clutter?

Or do you have a different use in mind? I ask because as I mentioned, those dishes are only a section of a parabola.
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Old 04-03-2022, 12:22 PM
crystallographic crystallographic is offline
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Default Hydro - fluid - explosive forming

"Fluid pressure" forming.
("Hydro forming" is a traditional forming method of using hydraulic presses - last 85 + years.)

Fluid forming is now more commercially done - last 25 years. See companies with that term used in their names.
Internal pressure generated with various fluids to expand from within.

Different from "explosive" forming, using water, electrodes and stored electricity - but also is a contained expansive process - last 50+ years.
DuPont developed sheet explosives for outdoor bas-relief explosive forming, over 12 foot long concrete molds.
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