Rolling plate: orientation

[BrianR]

I am to the point in my Dix 43 construction that i need to have the radius chine sections rolled. It seems to me that having the " grain ' run the same direction in these radius chine segments as the topsides and bottom plating would be a good thing. But-it may turn out to be less wasteful of material to cut and roll the segments the other way! So, I'm trying to figure out if there is a strong engineering reason for one over the other...Does it make any difference, structurally, which direction aluminum ( or steel, for that matter) plate is rolled? When manufactured, the cold rolling does impart a "grain " direction running the long way down a sheet. But if one cuts a section off of a long sheet and rolls with the grain parallel to the plate rolls, versus having the grain perpendicular to the 3 rolls is it better or worse. I am not implying that I want to mix the directions, and I know that one direction may be slightly " easier" to roll than the other, but does it really matter, ultimately? Hope this is not too confusing, it's late...

Cheers
Brian

[KevinMorin]

Brian, I believe that most sheet has a "cup" or 'lay' to the sheet when sheared in the 5x20 6x20 size ranges because sheets, thinner than .365"/3.8"/9.25mm, are in some mills taken up in huge rolls off the thickness forming roll line. This allows the material to cool in a more controlled manner but also leaves the outside edges to cool more rapidly by a small amount.

When re-rolled off the coil and sheared to sell 20' or 26' long that entire piece may have a "cup"- that is; if stood on edge, length-wise, the sheet will exhibit a tendency to a slight curve in the 5' or 6' direction (vertical while standing) and some tendency to curl along the length in the same direction of the cup. This observation is from standing a five or six hundred sheets on edge to find this 'lay' of the sheet. I used this fact to help make the sides of small skiffs- 250-300 of them in the 16' to 25' range- easier to build as we didn't frame any of the skiffs for tack up so the cup was worthwhile to find and cut in our 'favor'.

However, since the metal is completely homogeneous I don't think there is an actual "grain" but there is definitely a cooling induced shape to a sheet, in my experience. I have never seen any rolling, bending, shearing or forming differences related to grain but I have seen sheets form the easy way - with the cooling curvature and the hard way against the cooling curvature. In both cases the forming overcame the slight cupping tendency and there were no ill effects.

I have not rolled aluminum sheet to plank/plate/panel a rounded form sailing hull so all my experiences are limited to rolling for other purposes; like deck equipment and fish pumps' chambers. I cannot see any reason to use the plate in a less than optimal use fit of the parts. I'd use the sheets to the most cost effective orientation as there is no 'grain' consideration that I've seen in sheet aluminum.

[Assassin]

There is a grain in all metals, and any working of metal distorts this grain, so if it is rolled in any way shape or form the grain and the molecular structure are distorted. The only way to restore the grain is annealing, but on any formed panel it will distort it anyway, so will serve no useful purpose.

Just cut to the best way for saving material if it is to be rolled, shaped, or formed.

[BrianR]

After installing 34 rolled plate sections on my sailboat, I can now claim to be the proud owner of a new skill: unrolling plate! To unroll a bit of alloy plate, place the ends on a sturdy flat surface such as a concrete slab, convex curve up. Make sure the area around the plate is clear of debris, and that the air above the plate to a height of approx. 7 feet is clear as well. Now, launch yourself upward, drawing the knees up slightly. Aim your feet at the center of the curved section below you as you reach the apex of your flight. As your descent velocity increases, unbend your knees to increase the power stroke, thus providing enough force upon impact with the 6mm aluminum plate to cause a very slight "unroll". Repeat this sequence vigorously, occasionally pausing to check the curve with your desired radius gage. With practice, quite precise work can be achieved using little more than ones entire body as the tool!

Happily,
Brian

[nofacey]

LOL - I think we need a video of this technique being applied, Brian.

[Conall]

Hey Brian,

I've been working with my 12 year old daughter lately on her science class, and we've been talking about kinetic and potential energy. A picture of you and your technique would surly help her understand these concepts much better.

Conall