tight radius bends in conduit

Nice work, from another fan of EMT, the duct tape of metalworking.

Got structural integrity figs for that type of bend, Don?

And shouldn't that last sentence read "Bondo and paint are the amateur weldor's friends!"?

- - - - - - - - - - - - - - - - - - Heart Attacks: God's revenge for eating his little animal friends --

Nice job Don. Another method which works, and doesn't wrinkle the metal, is to heat the area almost red or just till it starts being red, and spray water on it. Do this a few times and the bend is very controllable. I learned about this method in welding class. I saw it being done at Lockheed Shipyard in Seattle before it closed. They were using huge torches to heat 3 inch thick steel pie shaped sections. These were being curved so they could be welded into a 1 half spherical shape. It eventually was welded to the hull under the prow of a ship. I'm sure you've seen an empty ship riding way out of the water and there is this bulbous thing sticking out of the hull. Also, we were shown a movie of the men who bent the legs to the Space Needle using the same method. After seeing this I had to try it for myself and have bent and straightened both mild steel and stainless steel. Eric

Not very strong with wrinkles, but if the gullets are filled with MIG weld the bend is stiffer than the straight tube it was part of.

Well, I didn't want to admit that,but.... :

I'll try that. Thanks!

Do you have it packed tightly with sand when you bend it?

D>

I have also used this method for tightening cross braces... works great!

Mark

Could you provide a few more details? I am assuming you spray a small quantity of water on the inside of the curve to be bent, correct?

Jerry

Don, You will find that the wrinkle bends whould be limited to 15 degrees each. To do a 90 you should have six wrinkles. I first stumbled on to this procedure in an old Union Carbide gas welding textbook. The procedure works with any size pipe and if you follow the 15 degree rule there is no appreciable reduction in cross sectional area so fluids are not restricted. On really big pipe a com-a-long is needed to maintain bending force as you heat the pie section. As you mention cooling off after each heat is necessary so that you can locate the wrinkle accurately. Randy

procedure works

restricted.

I have a "Copper and Brass Pipe and Tube Bending Handbook", published in 1954 by the Copper & Brass Research Association, that has 8 pages of text, tables, and photos devoted to the subject of wrinkle bending. Maybe I'll scan them and post to my personal page...

I never thought of that. It sounds like it could be a great way in some situations. Eric

Greetings Jerry, What happens is that the heated metal expands. Since the hot metal is plastic it will move as far as it can, which is where the metal is too cool to deform. Then when the hot area is cooled the space between the molecules shrinks and the metal contracts. If left to cool slowly the displaced metal will move back into it's original shape. But rapid cooling prevents this so instead the metal shrinks. So rapid cooling is important. The metal you are shrinking must be able to go through these hot and cold cycles without damage. So mild steel is a good candidate for this process. It takes practice but not that much and once mastered it can be real useful. Another place this method is used is with removing dents from sheet metal, as in auto bodies. Big dents in an auto body stretch the metal and to avoid using bondo to fill the depression heat shrinking the area is sometimes used to fix these dents. I've done it with a torch and a wet rag. Sheet metal is so thin that a wet rag can cool the area fast enough. ERS

Silly question - don't the tight bends in EMT make it a bitch to pull wire through it?

It is very important to understand that you do not cool the red area. If you have spray mist or wet rags you cool the area surrounding the red section keeping as large a temperature gradient as possible. The larger the temperature difference the larger the forces are on the plastic red area. You chase the perimeter of the red until it disappears. At that point there is no more plastic movement . In our local area a huge pipe bender is being set up that will heat by induction using massive amounts of electrical power and at the same time water spray mist is applied. This is for large pipe over two feet diameter from what I understand. Or.... you can build a 3000 ton horizontal press that pushes the pipe. We built one for a customer over a year ago,. Randy

I'd be interested. Karl

Randy, When I learned this water was applied to the red area. And stuff shrank right up. This is what I was taught: The red area, as it cools, draws the metal in toward the cooled area. I will try your method however, because it always pays to know as much as possible. Thanks, Eric

published

bending.

OK. I've scanned the entire bending handbook (30 pages) in jpg. I'll upload it as time allows then post a link. It covers hand, machine, and wrinkle bending.

Each scan is about 300K though (scanned at 150 dpi) so it's going to take me a while to upload on a dialup..

If you can picture the shrinkage action the only upsetting that happens is the red metal. The cool metal surrounding it is preventing the red from expanding so it upsets/swells. When you cool that area around the red the cooling metal fights the expanding red area increasing the upsetting. Once the whole area is black the metal is cooling and contracting but the shrinkage effect is lost.. I have bent one inch plate heating it to a red on one side and spraying air /water mist at the same time on the other side. It will take a kink out right fast. Randy

Randy, I did exactly that method on the back blade for my tractor. My neighbor was dubious, but it worked great. Eric