Suctions cups for lifting single sheets with forklift
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  1. #1
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    Default Suctions cups for lifting single sheets with forklift

    I have the issue of trying to load single sheets of metal off of a pallet and on to a plasma table (or just somewhere else to get to where we need it) so I built this monstrosity:

    (The cage is off of the forklift because I have to get into the engine a lot until I finish all of the repairs and the cage is very heavy to take on and off. I will put it back on once I get a pallet rack set up and have cause to lift anything above four feet.)

    There are eight suction cup assemblies. Each assembly is made from a regular 8" suction cup for material handling that had a little thumb pump and handle on it. I took the handle and pump off, and bolted them to the steel frame you see in the picture. I ran a tee from the suction cup that goes to a vacuum gauge (one per cup, very, very helpful) and to another tee which leads to a diaphragm pump and release solenoid (one per cup).

    You can audibly tell if all of the pumps are pulling a good vacuum, and the gauges all read 18 in Hg or better. It is impossible to activate the release valve while the pumps are on, so chances of accidental dumping are low.

    Each suction cup is floating so that when you set the frame down on the metal each one sits flush on the plate. Currently the pumps are powered from the forklift, but I think I'm going to get a battery and remote so you can drop it off to move regular pallets and pick it back up more easily. I ran out of vacuum hose so the gauges are mounted on each pump. As soon as more hose arrives I will put all 8 gauges where the forklift operator can see them. I will likely also add some mirrors around the edges so you can clearly see where the edges of the sheet will line up, so that getting on and off the forklift is minimized, and messing with the sheet after placement is minimized.

    Some possible questions and/or concerns:

    Why not magnets?
    -Magnets don't work on stainless or aluminum, and can pick up more than one sheet.

    What if a suction cup comes loose?
    -Each suction cup is independent so you still have 7 holding the load, which is well within the safety margin on this.

    What if you lose power?
    -The suction cups use diaphragm pumps, which have a built in check valve. Since the pumps can't bypass when off, it takes over three minutes for the sheet to be at risk of dropping.

    What if you need to pick up scratched/dirty metal
    -This works perfectly fine on plywood, drywall, and OSB, so it would have to be pretty bad metal. But you can know for sure by looking at the vacuum gauges and being sure there are no leaks.

    The pump current consumption is around 5-6A depending on how much air they are moving. Total cost was just over $600, but I had a fair amount of steel left over. The tubing the forks slide into is pretty tight, but you can just suction the whole thing to the concrete floor and back up.

    I've picked up a sheet of 5' x 10' 10 gauge steel, bounced it as hard as the hydraulics would let me, and jumped around on it and can't get anything to budge. I picked up 20 gauge SS and tried to bend it from under the suction cup and could not.

    Like any load, you should still keep it as low as reasonable and never be under it.

    I'm not sure if I was thorough or scatterbrained, but I used paragraphs, so at least I tried. Kind of.

  2. #2
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    You did very nice sir.

    Good write up, good pix, and a pretty good looking design.

    You seem to have addressed all the issues as well.

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    Looks good, the only suggestion i would have is you may want to add some kinda pivot - chain to the forklift so you have a little freedom rotationally and in x and y, like this a few slightly raised simple sheet stops on the plasma table and you can pull the sheet slightly to the stops and lower it straight down with no dragging - scratching on the used plasma - laser bed bars. Makes a massive reduction in scratching on aluminium parts being able to simply drop the sheet vertically straight onto the bed with no sliding into alignment.

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    Quote Originally Posted by Monarchist View Post
    The amazing part is that you accomplished all this usefulness in California.

    And have not (yet) been tagged with a "known to cause cancer in.." label.

    Good on yah!
    That will be forthcoming when the right(wrong?) person sees it!!

  7. #5
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    I agree with Adama on hanging it on some chains
    Also I would recommend the cups between springs
    Like the picture
    slides_group_mid2.jpg

    That way you can also lift thin sheets when they are not laying straight

    Peter

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  9. #6
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    Nice.
    You might want to calculate the load it can theoretically hold just so you know when you are running out of safety factor.

  10. #7
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    Quote Originally Posted by Miguels244 View Post
    Nice.
    You might want to calculate the load it can theoretically hold just so you know when you are running out of safety factor.
    Yes the notion of not standing under it might not be the dangerous spot. Equally even a 10x5 of 1/8" plates not exactly enough to crush you, but my experience of large thin plates falling flat they tend to glide side ways on the air cushion and the edges are the nasty sharp bit!

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    Quote Originally Posted by adama View Post
    Looks good, the only suggestion i would have is you may want to add some kinda pivot - chain to the forklift so you have a little freedom rotationally and in x and y, like this a few slightly raised simple sheet stops on the plasma table and you can pull the sheet slightly to the stops and lower it straight down with no dragging - scratching on the used plasma - laser bed bars. Makes a massive reduction in scratching on aluminium parts being able to simply drop the sheet vertically straight onto the bed with no sliding into alignment.
    The forklift I have has sideshift and an automatic transmission, so I can line up X and Y as precisely as I can see (hence the desire for mirrors). As for pivoting just cranking the wheel one way gives me tons of control, and getting a sheet where I want it is very easy. Chains would be great for a spotter to do the final alignment with, but I tend to work odd hours so a spotter isn't often available.

    Quote Originally Posted by Peter from Holland View Post
    I agree with Adama on hanging it on some chains
    Also I would recommend the cups between springs
    Like the picture
    slides_group_mid2.jpg

    That way you can also lift thin sheets when they are not laying straight

    Peter
    This is one suction cup assembly:



    The lower plate the cups are bolted to have four half inch bolts welded to it. The nuts are left purposefully loose, which allows each cup to move up or down about one inch and pivot significantly to pick up a distorted sheet. Once you lift the forks all of the suction cups hang from the same height and the sheet is held flat, regardless of if you have the sheet off to the side (springed cups would hang lower on one side if the cups were offset)


    Quote Originally Posted by Miguels244 View Post
    Nice.
    You might want to calculate the load it can theoretically hold just so you know when you are running out of safety factor.
    The theoretical separation force required is 3700 pounds. A little bit less because there is a soft spot in the middle of the cups that I'm sure will just deflect, but when you pull down on the cups substantially the vacuum increases th further down you pull it. (The valves in the pump can hold a much higher vacuum than the pump itself can produce. The actual load rating for the cups as I bought them is 125 pounds, but that's mostly because of the handle and pump it comes with, as the cups themselves are built much better. I am totally comfortable with using it for 1000 pounds, but for anything thicker than 1/4" I am going to put a pair of safety straps on it just to protect the machine I am loading, and then remove them with the plate 1/2" off of the bed.

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    Quote Originally Posted by adama View Post
    Yes the notion of not standing under it might not be the dangerous spot. Equally even a 10x5 of 1/8" plates not exactly enough to crush you, but my experience of large thin plates falling flat they tend to glide side ways on the air cushion and the edges are the nasty sharp bit!
    This is an especially large concern with this because if a sheet fails, it will likely fail at one side first, then fall at an angle. I did try dropping a sheet of 10 gauge from 18" above the pallet and there didn't seem to be any effect from the air cushion. I expect that will only happen with aluminum and thin sheets, which are luckily much lighter and won't even separate without power. (You can just squish the cups to the sheet without using the pumps and it is still very difficult to get off)

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    ^ I have personally witnessed it with a 1/2" sheet of 316 and a circa 6x12' sheet at that, fell over from standing near upright, then about 4" off the floor went about 6' diagonally across the shop, have seen a lot of flat sheets do it when handling them - laying them down on guillotine beds too.

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  15. #11
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    Quote Originally Posted by adama View Post
    ^ I have personally witnessed it with a 1/2" sheet of 316 and a circa 6x12' sheet at that, fell over from standing near upright, then about 4" off the floor went about 6' diagonally across the shop, have seen a lot of flat sheets do it when handling them - laying them down on guillotine beds too.
    From upright it doesn't even need an air cushion to kick out. The center of mass is going to try to go straight down, so unless you have one end very solidly stuck to the ground it will try to kick out one side half of the length of the sheet. The air cushion definitely helps reduce the friction towards the end though.

    A sheet will always try to rotate around it's center, so a vertical falling sheet is far more dangerous than a flat falling sheet.

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    The above three posts make me pucker.
    I've seen some scary stuff, but not a sheet of 8 gage steel out of control floating on the ground effect.
    Damn


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