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| OPENING PLASTIC BAG WITH VACUUM |  | ||
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| Posted by: paddyh ® 08/19/2010, 11:33:36 Author Profile eMail author Edit |
We are currently developing a machine to make a bag, ie cut and heat seal a bag, and then pull the bag over a product. To do this we have the open the bag using suction before we grip and pull the bag away mechanically.
However, we are experiencing problems opening the bag consistently. Sometimes both sides of the bag get pulled up to the top suction cups and bag doesn't open. or sometimes it seems that the both sides of the bag get pulled towards one vacuum cup. The bag material is HDPE 230mm wide and 0.1mm thick each side. We move the top suction cups away at an angle when we try to open the bag. We have tried different suction cups and configurations but getting inconsistent results. Any ideas. See attached JPEG.
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| : OPENING PLASTIC BAG WITH VACUUM -- paddyh | Post Reply | Top of thread | Engineering Forum |
| Posted by: Marky ® 08/19/2010, 14:17:59 Author Profile eMail author Edit |
jboggs is right...I've seen these machines they usually blow air in and the product is pushed in. This type pf machine was also it on a episode of Undercover Boss....The CEO of 7-11 was trying to pack hamburger rolls on this machine...he couldn't do it and the Cell Leader fired him. |
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| Posted by: RWOLFEJR ® 08/19/2010, 11:46:02 Author Profile eMail author Edit |
Hard to tell for sure from the picture, but it appears that the three suction cups at the bottom are directly below the ones above? If so... I'd try moving the upper or lower cups to a position in between or offset from the ones on the opposite side. This way they aren't battling for the same material...? |
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| Posted by: jboggs ® 08/19/2010, 12:59:17 Author Profile eMail author Edit |
Ditto above. Offsetting the upper and lower cups from each other was my first thought too. That way they aren't working directly against each other and you actually set up some shear load between the two layers that could loosen their adhesion. This is obviously established technology for many companies. I would expect that there are many ways to do this. Also, blowing air at the open end might help. You might contact exair.com. I think I have seen their products used for that purpose. I would be interested to see what finally works for you. |
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| Posted by: Kelly Bramble ® 08/20/2010, 08:35:30 Author Profile eMail author Edit |
I have this vision that the vacuum cups are pushing and distorting the film on contact and preventing proper contact to get a vacuum seal. When I look at the upper suction bracket I wonder what is holding the film in place during suction cup contact. Paddyh, have you tried roller wheels that contact the film and hold in place (taunt) until the vacuum gets a grip? Also, how much vacuum air flow capacity per suction cup do you have?
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| Posted by: paddyh ® 08/20/2010, 03:13:05 Author Profile eMail author Edit |
We have tried moving the cups as you suggested and added an air blow but still 1 in ~10 bags don't open. |
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| Posted by: Pinkerton ® 08/22/2010, 11:55:50 Author Profile eMail author Edit |
Instead of fixed vacuum cups, what about allowing some flexibility in their seating angle. Maybe a bellows like part at the top where it attaches to the vacuum piping so the lip will seal regardless of angle of contact. Allow the mechanism to push the bellows section flat before the vacuum comes on. Maybe larger vacuum piping and a greater "suck" so that any misalignment or leaking at the edge if the lip becomes irrelevant. Nice drawing. Dave |
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| Posted by: paddyh ® 08/23/2010, 06:21:50 Author Profile eMail author Edit |
WE are using rollers to get the bag to this point.
We cut the bag 400mm back from the pick point. We are clamping the bag while cutting. We have tried bellows cups but they seem to make things worse. Thanks for your suggestions. Will try all. |
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| Posted by: jboggs ® 08/20/2010, 08:15:53 Author Profile eMail author Edit |
Have you experimented with static charges? De-ionizing?
Also, the Exair Company includes an example of bag opening in their applications list. |
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| Posted by: Pinkerton ® 08/23/2010, 11:28:14 Author Profile eMail author Edit |
Is the cut a shear or a chop? A chop may be mooshing (technical term for molecular integration/migration) the edges together. Dave |
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| Posted by: paddyh ® 08/24/2010, 04:04:31 Author Profile eMail author Edit |
it is a shear |
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| Posted by: paddyh ® 08/24/2010, 04:17:14 Author Profile eMail author Edit |
see attached
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