So I told you some things in
another post about working at the canning factory to earn money for school, and one of the things I talked about there was the palletizer.
The palletizer, which I described back in that other post (and really, go read it if you haven't), was a machine with a big magnet that would pick up a pallet-sized square of cans from a shaker table, and swivel over and stack it on a pallet. The operator's job included putting a sheet of cardboard on top of each layer as it was stacked, and then wrapping the whole pallet with a giant roll of clear plastic wrap when it was done. Hit the button, and the chains started rolling, pulling the pallet down to the end of the short track. There it waited for the lift truck (forklift) to take it away to one of the warehouses, while you-the-operator pulled another big wooden pallet off the stack and put it into the working end of the track and started over.
I'm pretty sure we brightstacked fourteen layers high. Funny what sticks in your mind.
Anyhow, what I was going to tell you about was what happened when the shaker table didn't get the cans into a perfect honeycomb pattern.
When everything worked right, the shaker table filled up row by staggered row, each can fitting neatly into the spaces left by the previous row, and when the table filled up enough for a row to hit the switch, everything was perfect and ready for the huge square magnet thingie to come pick it up. That was usually how it was.
We pause this entry for a link to a photograph of a Whallon britestacker! When I found
this photo, I confess I let out an oddly affectionate "Heeeeeey, there's my big green beast!" (It's at the bottom of
this page of equipment if you want to read more about it.) It's not set up quite like ours were, though. For one thing, the pallet track is arranged differently. In that picture, it's horizontal; in the warehouse it would have been rotated ninety degrees, coming out straight at the viewer about where that bolted plate is, two thirds of the way to the right. The control panel is that thing on a green pedestal to the far left, freestanding; ours looked different, and would have been on the far right and back a little bit.
In that picture, the magnet on the long arm is down on the shaker table. It's resting on a pallet, and I have no idea what dang fool put that there, because you never would. So in place of that wooden pallet, imagine a layer of bright (unlabeled) one-pound cans of beans.
See where the arm from the magnet attaches to that beam and cylinder structure over to the right? When the magnet picks up a load of cans, it rises to full height, sliding up that beam part. Then it swivels ninety degrees, stops, and begins to descend. If you've done your job right, there's a pallet underneath it, with a layer of cardboard ready for those cans to go on. If there's no pallet underneath, your life is going to be really un-fun and your supervisor is going to be seriously pissed off. But there's another way for it to go wrong, even if your pallet is right where it should be and properly covered with cardboard. If the pattern of cans on the shaker table has a gap in it, it's probably because one of the cans came off the line sideways or fell over. Your magnet might pick up that sideways can, and this is either an annoyance or a problem.
It's an annoyance if it just picks the can up firmly, because it goes ahead with its process, rising up, stopping with a jerk, swiveling ninety degrees, stopping with a jerk, and then descending until the load of cans makes positive contact with the cardboard and whatever's under it (pallet, or cans, depending on how far you've gotten on those fourteen layers). (If it was fourteen. Now I'm second-guessing myself. Somebody will have to remind me, if anybody knows.) Anyhow, you've now got a layer of cans there with a hole in it and a sideways can, and you have to stand that can up and fill in the pattern where things are missing, and do it quickly before the palletizer brings the next load of cans. That's an annoyance.
The problem would be if the sideways can gets partly dislodged when the machine jerks at the end of its rise, and hangs by one edge of the rim, sort of diagonally, as the magnet arm swivels into position over the pallet and stops with another jerk. On a bad day, that second jerk will be enough to free the precariously caught can from the magnet. If you're lucky, it will hit the cardboard below it and roll off.
If you're not lucky, it will roll a few inches, positioning itself where the magnet and its load of cans will come down square on it. Remember how I said the magnet uses positive contact and pressure to determine when to let go of its load? Well, when it's pressing on a whole nice square of cardboard-and-cans, that's fine, but when it's pressing the whole weight on one sideways can of beans, something's probably going to explode.
It's only one can of beans, but it's fresh out of the cooker and still boiling. You do not want that exploding on you. Not on your face, not on your arms, not on your clothes where boiling water and crushed vegetables will stick to you and burn longer.
That is a problem.
If you're quick and it's near the edge and the pallet is only a few layers tall so there's more time before the magnet load comes down, you can grab that can and get it out of there. If there's not much room and you're an old hand, you can grab a spare can and essentially shoot pool at the problem can, knocking them both off the pallet if you're good at it and lucky. If you can't do either, you run over to the control panel and stop the arm. They get cranky when you shut down the line, though, so you do anything you can not to have to.
More often than not, if there's a missing can along the edge, it's just missing, and you can reach up and add a can to the pattern as the magnet's coming down. (Don't judge the distance wrong, though. That's how I got an unhappy thumb knuckle. Not so good. Not so bad as the guy on the day shift though. I think he had a can fall in the middle of the pattern, and it was already stacked kinda high, so he misjudged the time there was to grab it.)
Anyhow, if a fallen can gets squashed, you hear the noise of it popping and the spray of water and beans, and then you hear the noise of all the cans falling as the magnet lets go, because the squashed can gave the signal but the load isn't close enough to the pallet to land real well. And that's a big mess, and shutting the line down, and all that.
So that's today's story. Next time maybe I'll tell you about bowling for rats.