How to Make a Heat Sealer

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Well, finally, as promised, here's my how-to.

Q. What's a heat sealer?

A. Also known as an impulse sealer, a heat sealer uses a resistive heating element to seal and/or cut thin plastic bags or sheets. Rather than using continous heat, which would turn the bag into a gooey-edged mess, it uses a timed impulse of heat - hence "impulse" sealer.

This instructable reveals to you many secrets that certain people do not want you to know! I have already received several death threats from one of the major recloseable bag companies. Please enjoy this instructable, which might be my last....

Step 1: Why Would I Want a HEAT SEALER, Anyway?

Using a proper heat sealer, you can do a much more than making toothpaste packets!

Click on the pics below to find your reason. If you do not see it, then perhaps playing with Dremel tools and electricity is reason enough.

And dare I say, you can even store your beads with it?!

Step 2: So HOW Do You MAKE THIS THING?

The parts:
Some of the things you will need are:

Structual Pieces:
1. Some plexiglass or wood, approx 1/4" thick and about a foot in length. I always have some plexiglass around, so that's what I used, but hardwood would probably be better.
2. Four nails
3. A Dremel tool or router, and preferably a routing table.
4. Routing bit and side-cutting bit (or perhaps a thick cutting disk would suffice).
5. A drill and drill bit the same size as your nails
6. Coarse sandpaper
7. For plexiglass: some acetone and a dropper bottle, or some epoxy.
For wood: wood glue? I dunno much about wood-working.

Electrical Part:
There are literally an infinite number of ways to skin this cat. I can't describe them all, so I'll tell you exactly how I made it, using a laptop power supply, 19.5V and 3.16 amps.

If you have the power supply and the tools/supplies to make the structural parts, and you can solder smd parts and read a schematic, I can provide you with the exact circuit components I used. The kit would include all of the following items.

1. Nichrome wire (this comes in a plethora of specs and sizes. After much experimentation and for several reasons, I have settled on Kanthal A1, 27 gauge.) 2 yards of it. More than enough for a couple of screwups.
2. A power mosfet that can handle 9amps!
3. A PIC microcontroller, custom programmed to provide the pulse and to be user-programmable on the fly so that it can be instantly adjusted for a myriad of wire length, power supply, and bag thickness combinations, using only a single button!
4. A bicolor LED, red/green.
5. A 78L05 voltage regulator to power the PIC
6. A couple of caps and a few resistors
7. Some SIP headers, male and female
8. Some protoboard
9. 30AWG kynar wire, about 3 feet.

Step 3: The Science

So, what's going on here? Well, ohm's law is a good place to start. I began by taking a look at my available power source... a 19.5v, 3.16A powerbrick for a laptop. My particular nichrome wire has a resistance of 4.4 ohms per foot. So in making a 12" heat sealer, I use just over a foot length of nichrome wire.

19.5V/4.4 ohms is... 4.4 amps! This draws too much current! Well, yes, and no. The rating on a laptop psu is the constant current rating. A peak rating is typically 2-3 times as high. Because the pulse is going to last under 1 second, it's all good. So let's get started.

Click on each pic below and read the highlighted captions.



Step 4: Ok, Now What?

Ok, so take the blade and sand the cutting edge flat as you can. Use coarse sandpaper. Take your time. This part is important.

Then you can make the base. Basically, I just used some scrap pieces of plexiglass and bonded them to the four corners of the base. The ones at the base are the hinge. The pair up front are guides, to keep the blade squared up.

Also, notice I put all the electronics right onto the blade. The base is just a base. This way, I can take the blade out and use it alone. This allows partial cuts, by using just the tip, or you can combine two cuts for a larger bag.

You might think "why not just leave off the guide rails." Don't do that. The guide rails are necessary, and I can't bother to explain why, at this time.

Step 5: Now Make the Circuit

Here's the schemmy. If you want to really DIY, you can forego the PIC and power it with a 555 timer and potentiometer setup.



Step 6: Ok, Now String Up the Wire

So you put a single nail in the front. Wrap one end of the wire around this nail and then twist it a few times. Then put the nail in. Then, holding the other end in a crescent wrench, or wrapped around a stick a few times, pull it taught across the edge of the blade and then wrap it around the other two nails in a figure eight. Make sure you don't pull towards your eye, in case the wire breaks while you are doing this!

There are two reasons I prefer 27AWG for this (whereas 26AWg or larger is typical). 1. It heats up very fast, even with a laptop supply. 2. It cools down very fast. 3. It is easier to get decent tension on the wire even using this crude method. Tension is important, because the wire stretches when heated. If there's not enough tension, the wire will "walk" during the impulse. 4. It's big enough to do the job. Mine will seal 4 mil bags. I use 2 mil for everything in the pics.

Step 7: Now Set Up the PIC for Use

Click the video link to see a demo. For my particular setup, it takes about a half second impulse for get a good seal on up to 4 mil bags.
http://s18.photobucket.com/albums/b103/klee27x/?action=view&current=bfd9110a.pbr

Now here's a video of it in action. Mind you, in this vid, I am still experimenting with 26AWG KA1, so the impulse is much, much longer than it is, now, and it doesn't work quite as good.
http://s18.photobucket.com/albums/b103/klee27x/?action=view&current=83ed7b18.pbr

Step 8: Now for Some Tips and Tricks

The best bags for heatsealing are polyethylene or polypropylene bags. The more they stretch when pulled, the better. The bags can make a big difference in how strong a seal you get. The bags I use are polyethylene, 2 mil thick, 9x12" bags made by Uline. They work alot better than a seemingly similar polyethylene bag I was using before!

Here is a pic of 4 different ways to use your heat sealer.

But how good can these seals hold? See on.

Step 9: Water Tight Resealable Closure With PACKING TAPE? Are You Serious?!?!

Here's how to make a recloseable seal that is OJ-tight. Click on the pics below to see the step-by-step.

Step 10: I Want One!

Well, the longest part by a long shot was to obtain the wire and to program the pic. The rest was relative child's play. I always buy in bulk, because I never know what I might want to make next, but in this case, I have way more nichrome and mosfets than I'll ever know what to do with. The minimum order from the specialty shop I found for wire was 2000 feet! So I have the parts to make several of the control circuits for this project, and will be putting together some kits for my fellow enthusiasts.

I'll be giving away kits on my favorite electronics forum, http://dutchforce.com/. Check the Trade Forum under the "Want its," section. They should be avail in the next few days. If there's any demand, I might try selling some on ebay!

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    104 Discussions

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    VictorB203

    Question 9 months ago

    I am really new in electronics, please someone could helpme with a detailed explanation of the PIC controller.

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    ScottW237

    Question 9 months ago on Step 2

    What PIC Controller did you use and how did you program it. Also you mentioned the Time would this be used instead of a PIC Controller

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    Brandonoutdoors

    2 years ago

    I need a device similar to this one but hand-held for welding long runs of 8 mil pond liners. Industrial welder a are very expensive so I need a DIY solution

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    Brandonoutdoors

    2 years ago

    Could this be made to weld 8mil poly

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    razordu30

    2 years ago

    If anyone is trying to find wire in smaller bulk, I'd suggest vaping supplies. Nichrome wire is usually pretty cheap there, and in many different sizes and lengths.

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    amiir

    2 years ago

    acetone is not good for welding plaxiglass! you should use Chloroform (CHCI3) its the only liquid that could weld plaxiglass in best way!

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    JessicaC151

    2 years ago

    I would like to make one these but it would be in a design. I am about to try to look into how to attach the wires. I know a few people in electronics and i am going to show the to them to help explain. I do not know if my idea is possible but i will find out. Thanks for this information. You broke it down very well.

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    asdfa2

    3 years ago

    If you have a kitchen food vacuum sealer try using that first, it has a heating element built in for sealing the bags after the air is vacuumed out

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    Mikechristeson

    3 years ago

    I want to make a 36" weld on 6 mil Visqueen and it needs to be 5 mil or greater. Can your impulse sealer be adapted for this?

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    bgroicahn

    8 years ago on Step 5

     An incandescent light dimmer though a GFI breaker would be just a useable and a lot easier to make.

    10 replies
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    klee27xbgroicahn

    Reply 8 years ago on Step 5

    That would miss the point. This isn't a foam cutter. The PIC doesn't do PWM power control. It is just a fancy way to provide a user-adjustable full-power timed pulse with a single button. (Actually 2 timers... there's an adjustable delay BEFORE the pulse starts, too, in case you want it. For instance, you might want a half second or so to readjust your hands after pushing the button, if you're sealing a bag in a way that you can't use one hand.)

    You have to melt the plastic. The idea is to get the wire up to temp AS FAST AS POSSIBLE, then immediately cut power. So you could use an on/off switch, if you have good timing. But a light dimmer would do nothing to help for a heat sealer. Sure, you could set the power to the point where it would only just be able to reach the melting temp of the bag, but then it'd just take LONGER to actually reach that temp, and you'd still have to turn it off and wait for it to cool down before opening the heat sealer.

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    neffkklee27x

    Reply 3 years ago on Introduction

    Thanks, klee27x. That's all I needed---full power on for a certain time. Could not find that anywhere. Theory of operation should be covered in the intro, especially for something so simple.

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    bhushan1572klee27x

    Reply 7 years ago on Step 5

    Dear klee27x,
    please let me know if the current to be passed through is AC or DC.

    I have tried for both AC and DC in one of my designs where i have a grid system to pass the current through. Please answer my few quries :

    10 Ni wires in series total resistance 25 Ohms with : (each piece : width 1mm, 18inch long, 2.5 Ohms )
    1. Do we have information regarding plastic bag thickness and temperature needed to seal it and corresponding current required?

    2. I am able to seal it with naked wire but when put behind a teflon tape(standard one used in impulse sealers), then it does not seal at all. to solve this problem, should I pass more current or should I heat it for longer duration.

    I have a very simple circuit designed for the pulse.
    I am not using any transformer as AC supply is 240 V, current being passed is around 10 Amp for this 25 Ohm series strip. if any one is interested.. i will post the full design details.

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    Hi bhushan1572, I´m interested in see the details of you circuit for the pulse, seem quite more simple. I´ll would be very grateful. I´m making an automatic bag sealer and once if finish it i will post my instructable. My e-mail is francisco.g.h@live.com.mx

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    Hello, thanks for your interest. I have actually completed and successfully implemented the circuit.
    As mentioned earlier, I took 10 Ni wires of 2.5ohms/18inch in a grid based structure. We have 230 V AC supply at home. I prepared a timer - RC circuit through a relay where in i used a switch.
    Once the switch is turned ON, the capacitor starts charging, within 3 seconds the capacitor is charged and the relay is cut-off (reverse action through a NOT gate to a transistor).
    So actually I am passing around 9.2 A AC current through the NI grid for 3 secs. This heats up suffieciently to seal up the bags.
    The said design as attached is used for packaging 25 bags in 6 seconds.
    This is faster than an automated machine.
    Please find attached images for the actual design

    current delivery circuit.JPGNi Grid.JPG
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    klee27xbhushan1572

    Reply 4 years ago on Introduction

    That's awesome. But I wouldn't call that my circuit at all. This looks to be 100% bhushan! I'm glad you found my instructable helpful.

    hi bhushan,
    I came across this instructable when trying to concept some thing you seem to have done. I'm actually trying to build a batch packing machine. I think ill use your plans. Just a couple of things though. How have you been using this and any problems yet?

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    I'm still using it. I had to rebuild it after a couple years, though. The wire had melted into the plastic enough to cause trouble. When I refurbished it, I put teflon tape UNDER where the wire sits. (On commercial sealers, the tape goes over the wire; mine is not powerful enough for that). My GF and her roommate also have been using a copy of the improved version for almost 3 years, now.

    Note, my plans include a schematic using a PIC microcontroller. Without the firmware, it will not actually do anything. You might prefer to use a "monostable 555" circuit. Try google.

    The hardest part is finding the exact right wire to work for your power supply and length of sealer.

    I believe most commercial sealers use an SSR to trip mains current. So they can use thicker heating elements for a stronger seal. If you are need something robust, you might consider going that route. It's not much different, except you should be more careful if you are unfamiliar with working with mains AC.

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    klee27xbhushan1572

    Reply 7 years ago on Step 5

    1. No.
    2. Dunno what your timing circuit is, but it shouldn't be too hard to increase the pulse to see what happens? Or just trip it twice, quickly?

    Be careful!

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    klee27xklee27x

    Reply 8 years ago on Step 5

    Well, to be fair, a light dimmer would be useful if you were running a very low resistance filament from AC power, and you had to reduce the current draw (to prevent overloading your outlet and/or circuit breaker). But timing the pulse would still need to be done with a separate method.