Automated plastic bag cutter/sealer ( need some help)

Discussion in 'The Projects Forum' started by LETITROLL, Apr 23, 2014.

  1. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    HI everyone .

    Am currently working on a project with some friends , but i have some small issues .

    So the idea is to create a machine that have on top a roll of side-sealed plastic witch will be pulled down by a rotating mechanism , and next sealed and cut ; And all of this will be done using a programmable logic controller .

    I have already installed the mechanism that will pull the plastic , and also got a small mechanism from a HP inkjet printer .

    Now what am trying to do is use the printer mechanism for cutting and sealing at the same time , any ideas on how to do that ??


    Here is two pictures of the parts am using right now ( attached bellow ):
     
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  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    I'm pretty sure the sealer and cutter is done by a heated bar. Not a sliding cutter and heater. The bar 'clamps' the bag material, and has a rubber and metal component to it. Both parts of the clamp are heated, the bare metal doing the cutting and the rubber part the sealing.

    You-tube has some video and as always Google is your friend. :) https://www.google.com/search?q=pla...la:en-US:official&client=firefox-a&channel=sb
     
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  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    How are you going to handle the FILLING of the bag, during automated cutting and sealing? :eek:
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    A heated profiled knife pressed through the substrate, against a silicone/ Teflon roll is generically termed 'side weld'. A heated ribbon pressed against the substrate sandwiched between Teflon, is often termed 'bottom seal'. The two are often combined in form filling.
     
  5. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    I am not planning to fill the bags just sealing and cutting at least .

    The idea i had initially is installing a blade for the cut and a rolling element bearing on the print head .
    The roller should carry a heating element enrolled on it witch will be preheated , then moving freely (while still hot) with the cutter , this way the print head will do the heating and the cutting at the same time on one move or two moves .

    What do you think of this ?
     
    Last edited: Apr 23, 2014
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Why not take a leaf out of the home freezer bag sealer and cutter?
    The one we have has a hot wire cutter and sealer in one operation.
    Very similar in design to the hot wire foam cutter I just built.
    Uses Nichrome wire and a low voltage transformer, SCR or Triac regulated.
    The bagging machines that fill Nuts and chips etc use this method although they have two operations for a separate point of seal and cut.
    Max.
     
    Last edited: Apr 23, 2014
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  7. #12

    Expert

    Nov 30, 2010
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    The hot thing (whatever you use) accumulates a lot of crud. Do not expect it to stay clean for very long.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    This isnt how it's done in industry, but since you've decided on using a printer, why not mount a friggin laser beam to its head? (Austin powers reference)... but seriously. A CO2 laser might cut and seal simultaneously. Or a tightly controlled torch flame held just the precise distance away, at a precise speed, so that toward the outside of the flame its just hot enough to seal both edges and at the center its just hot enough to blow through the plastic.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The nichrome wire stays suprisingly clean on the bagger, I don't recall ever cleaning it!.
    Incidentally, this guy also lists small quantities on ebay. http://jacobs-online.biz/nichrome_wire.htm
    Max.
     
  10. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Ok guys i don't know if a friggin lazer is a safe choice , i decided to use a hot wire knife just like maxheadroom has suggested , this is the most economical and simple way to achieve the operation of cutting and sealing at the same time , i just need to know what type of wire to use for the job .

    As for the wire installation , can i install somehow the wire on the print head or use a different mechanism ?? can i achieve a nice cutting with wire on print head ?
     
    Last edited: Apr 24, 2014
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  11. MaxHeadRoom

    Expert

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    That Utube video is for a foam cutter, but if you do not have access to a freezer bag type sealer/cutter, I would recommend going to an appliance store and check one out as to how the seal and cut is.
    Mine has a silicone rubber cushion strip that is on the opposite side to the wire cutter.
    If you need to have this as an automated process then obviously some adaption is necessary to advance the bag material a measured distance and then the seal clamp and time out would be necessary and then a method of take away and repeat the next advance, this is where the mechanics of the design would come in, I think the actual seal and cut should be easy to reproduce.
    For the cost, I would use actual Nichrome wire, although some have used stainless and guitar strings etc, the cost difference is minimal if any.
    Mine uses Nichrome 60 @24gauge.
    Max.
     
    Last edited: Apr 24, 2014
  12. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Ok i see , i will get that tool and see how i can use it on the build .

    But on another POV , don't you think i can use the print head with the nichrome wire on it and use it to seal and cut ? i mean when the wire passes from the side of the plastic it will go heating and cutting , or this will not work ?? .
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I am still not clear on how you intend using the print head as part of the operation?
    I would think you need a transport mechanism for the plastic, after a certain amount of product or plastic has advanced, a clamp head would bring the wire cutter against the plastic, turn on wire power for a time and then unclamp and power off, the cut portion would need to be taken away, and the next advanced, and repeated.
    Max.
     
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  14. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Ok thanks for the assistance and all other members , i will struggle with this until done , and next move to the electrical part .
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    If you are not filling the bags, then the entire purpose of the machine is to process tube stock into bags of X length, where each bag is sealed at one end and open at the other?

    I just contact the bag supplier and order bags in the hundreds or thousands, pre-cut. Cost of pennies each. They already have the machine you are trying to make. ;)

    The cost difference bewteen buying a roll of tube stock, and buying it cut into bags of your desired length is very small. Why spend a lot fo time and money making a machine to save maybe 1 cent per bag? :eek:

    The only reason I can see someone would want to mess with bag sealing is AFTER you put your gizmo in it. The one operation you need to do in-house.
     
  16. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Really depends on the strength of seal your looking for. Seal beads have seen plenty of analysis. Many types of plastics are filmed, and the same types can often be very different in performance, depending on how they were machined. With blown film (polyethylene), the ration of blow to the haul sets the molecular chain direction, which directly affects the properties of the substrate. Process temperature profiles directly affect the molecular linking properties. These plus other factors contribute to further 'machinability' of the substrate, such as cutting/sealing. Sealing blades typically have a profile that offer control in forming the bead. 'Slit sealing' will often see the profile incorporated into the blade, where the bead is formed while sliding over the heated profile.

    No reason that a heated sealing blade couldn't be mounted on your print head carriage. The challange would be in supporting the substrate so that the blade's profile could do it's work.

    Then again, the previously mentioned 'bottom seal' could be easily employed, with either a mechanical perforator, or embedded hot knife, for separation.
     
  17. #12

    Expert

    Nov 30, 2010
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    Maybe I shouldn't describe the machines I saw in 1968. The world is probably a lot different now. :D
     
  18. LETITROLL

    Thread Starter Member

    Oct 9, 2013
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    Originally this was not my idea , it was a colleague that insisted on doing it , and finally he was doing nothing on the project , i was working alone making it .

    I also thought it is not a very interesting project , since this is already existing , but i decided to make it just to apply some PLC stuff i learned , maybe later i can develop it and make it do something else besides cutting and sealing , something like LOGO printing ???

    If you have some ideas that will add some value to this project as long as its not very complicated , i will be glad to know it .
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It would certainly give some exercise in PLC programming and machine control.
    If you use the rollers shown earlier for a transport mechanism, you would need to somehow duplicate the manual type by having a hinged cutting head that either carries the Nichrome wire or the silicone pressure pad which could be made from a small bar covered with the industrial heat shrink which has a heavier wall size.
    If making it fully automatic, the trick will be in making sure the material advances the measured amount.
    As to the electrics for the wire, most of the home built foam cutters use a 'Dimmer' on the primary of the L.V. transformer, I prefer to put the controller on the secondary side.
    Either a simple Triac or SCR based circuit will work.
    Max.
     
  20. LETITROLL

    Thread Starter Member

    Oct 9, 2013
    218
    2

    Hi again max .

    I have a few things to say about the cutting sealing mechanisms .

    So since the machine is positioned vertically , i thought about moving the NICHROM wire horizontally through the pulled down plastic , for that i had the idea of using a roller rails based mechanism on the sides of the machine.

    So what do you think about this , would i have a precise operation ?


    Here is a simple drawing of the system :
     
    Last edited: May 6, 2014
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