Steel Tube Bending Info Wanted
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  1. #1
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    Default Steel Tube Bending Info Wanted

    Trying to bend 7/8" DOM tube with 0.065 wall to a 2" radius. Should be possible, but yes it is tight. I could change to another tube alloy. Is there a chart showing minimum bend radius by alloy? Comparing say DOM, Seamless, ERW? Is there a way to anneal this DOM tube? Tube is cracking on the outside radius when bent with Woods metal. Collapses unacceptably with no filler. Don't have a mandrel bender but not seeing how that would be better than Woods metal. It's a Parker bender.

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    Very often, the bend should be 3X the diameter, less than, you will have problems

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    This is very dependent on the tooling involved. Hossfeld shows dies all the way down to 1.75" centerline radius for 7/8" OD tube, and recommends a minimum of 0.065" wall thickness, so it is possible. I don't have the 7/8" tooling, but I do have their die to bend 1" on a 2.25" CLR (similar ratio of CLR to OD to what you're doing). It is pretty aggressive with the amount of pinch in the tooling, meaning the die shortens the tube in height as it bends to keep the inside wall from collapsing. I would estimate the bend area of a 1" tube ends up somewhere between 7/8" and 15/16" high after bending.

    What is unacceptable distortion for your application? Are you getting wrinkles and/or collapsing without the Woods metal, or just more change in profile than you would like?

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    No wrinkles or collapsing, just more change in profile than I'd like, that is without Woods metal. 0.875 tube collapses to about 0.780 at the bend. I pushed a 3/4 tube inside as a sleeve. This helped it now collapses to 0.820. With Woods metal it tears on the outside. I see commercially available product with much tighter bends so it's possible somehow. Look at railing components for example. I could change alloy, a softer product or annealed might not tear with the Woods metal. Surprised I can't find a table showing minimum radius for various alloys.

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    I worked in a tank shop where they used DRY sand with great success bending for davits to hold flanges when unbolted. Filled pipe with one capped by welding a disc on the end. After filling and tamping enthusiastically they welded the other end closed. Bending was done on a welding table with stop clips and a solid piece of the required diameter welded to the table. A chain com-a-long did the pulling around as they used a rosebud torch on the pipe. If you are not sure if your sand is dry enough then drill a 1/16th hole somewhere.

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    When you fill the tube, that prevents the short side from shrinking while bending so the long side has to stretch more than when the short side can shrink, that's why it's tearing.
    A mandrel bender with all the correct tooling might give you what you want, or it might take softer tubing plus a mandrel bender. At the extremes bending seems like as much art as science, and 2X dia rad. is considered extreme by the average shop. Lots of experience makes it go better, that's why it seems like art,.HREW 1018 would be softer than DOM, but would not look as nice plus you'd have to deal with the weld seam, not confident it would bend any better.

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    Try using W-FLT. It's 1010 DOM then annealed dead soft. It takes bending well even that tight. I know it's available in Ø7/8 x .065 wall. Used it a lot on manifold tubes for hydraulic cylinders.

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    Quote Originally Posted by R. Dan View Post
    Try using W-FLT. It's 1010 DOM then annealed dead soft. It takes bending well even that tight. I know it's available in Ø7/8 x .065 wall. Used it a lot on manifold tubes for hydraulic cylinders.
    Can you elaborate on that? I tried googling W-FLT and got nothing about steel tubing,
    C

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    Quote Originally Posted by Mud View Post
    Can you elaborate on that? I tried googling W-FLT and got nothing about steel tubing,
    C
    Welded hydraulic fluid line. It's formed, welded, cold drawn over a mandrel and then annealed in a hydrogen/nitrogen atmosphere. Here's some info:

    Fluid Line Services - Steel Hydraulic Fluidline Tubing

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    Try SAE J525 Hydraulic Tubing.

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    tight radius and thin wall is double wammy. Grease liberally your counter bender, and then add more just because you missed a spot. If it is stepping out of round on the inside radius reduce counterbender angle, if it is flattening across the top increase counterbend angle. If you can run the seem on inside of bend, running it centerline helps consistency more, inside holds shape better. You are going to have oval, how much is acceptable is up to you.

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    I think that W-FLT is J525. That looks very promising, J524 seamless maybe even better. Couldn’t I anneal my A513 DOM and get the same thing? I’d need a recipe though. Anyway thanks to R Dan for the info and link. The link is to the mill. You wouldn’t happen to have a retail source for a small quantity so I can try it out.


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    Quote Originally Posted by adh2000 View Post
    No wrinkles or collapsing, just more change in profile than I'd like, that is without Woods metal. 0.875 tube collapses to about 0.780 at the bend. I pushed a 3/4 tube inside as a sleeve. This helped it now collapses to 0.820. With Woods metal it tears on the outside. I see commercially available product with much tighter bends so it's possible somehow. Look at railing components for example. I could change alloy, a softer product or annealed might not tear with the Woods metal. Surprised I can't find a table showing minimum radius for various alloys.
    Attached is a photo of a test bend of 1" x 0.065" ERW with Hossfeld tooling. No mandrel or filling of the tube. It measures 0.975" high and 0.950" wide in the bent area. 0.120" wall tube collapses the same 0.050" in width on my JD2 3" CLR tooling, but doesn't lose any height.

    Sent from my Pixel 2 XL using Tapatalk

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    counterbender needs grease and is not riding center. the draw die can leave a finger print/not a scar, the scar and stretch at end shows counter die holding pipe, not supporting pipe. I think counterbender is a smidge to tight, the bump at end- now to many variables to work out angles of counterbender, which drastically change if it is tight or loose.
    open bending is hard to get good look, once acceptable repeatability and predictability is easy.

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    Quote Originally Posted by adh2000 View Post
    I think that W-FLT is J525. That looks very promising, J524 seamless maybe even better. Couldn’t I anneal my A513 DOM and get the same thing? I’d need a recipe though. Anyway thanks to R Dan for the info and link. The link is to the mill. You wouldn’t happen to have a retail source for a small quantity so I can try it out.


    Sent from my iPhone using Tapatalk
    Fluid line tubing is J525. As for sources; we bought it in bundles from Ryerson I think, when we were doing our own bending and fab because we used a lot of it. Eventually we farmed it all out to a tubing fabricator. I think that may be your best bet - a good tube shop will get it right and is likely to have a mandrel bender which IMO is the way to go when it comes to bending tube. There are shops all over the place out there who do this.

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    This who fabricated our tubes; at least they were before I retired 4 years ago: Home | Rising Star Hydraulics | Watertown, SD

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    Got a stick of J525 in today. Bent like a dream, no cracks no kinks. Really nice material for bending.


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