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Request help sizing a cartridge heater.

I want to build a plastic clamshell heat sealer, for volume production use. I have a hand-sealer, but it is too slow and you have to make several welds to adequately seal the clamshell we are using.

I intend to use a PID controller (as a thermostat) and two cartridge heaters. I'm going to machine a steel block, to fit where it needs to over the clamshell seal points, and be drilled to accept a cartridge heater.

Hopefully, I have explained that well enough. I left out the part about servo motors to suck in and eject the package.

My question: How do I know what size heater cartridge to get? Is there a web resource that explains this?

And the related question is: Do I purchase a heater that is about the same length of my fixture (see below)? Or, just a smaller, possibly hotter heater that would be easier to drill a home for?

My instinct tells me to get something a bit more than I need heat-wise, and let the PID regulate it from there (with a thermocouple).

I haven't designed the fixture yet, but I'm envisioning it will need be approximately 4-inches on each "business" side, capable of 2 or 3 welds each, with each weld roughly 3/8" long x 1/8" wide (or thereabouts).

For ease-of-build, I had planned to make all the welds at once. So try to envision some bar stock with little protrusions where the welds will be placed. At present, I am not planning to engage a machine shop...

Thanks everyone!!

Reply to
mpm
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mpm prodded the keyboard with:

Whilst I can understand your idea, I would go down the road of using an impulse heater and not bother trying to fit cartridge heaters. An aluminium block machined with fingers as you have described, and used to apply pressure to plastic against the impulse heater element, which would need to be protected under a Teflon membrane. The aluminium block also needs a Teflon membrane between it and the plastic otherwise you will end up with a sticky mess. A safety advantage would be that everything would be at a low voltage, usually

24 volts, isolated from the mains supply.

The other alternative would be ultrasonic welding, but that might not be suitable for your application.

HTH.

--
Best Regards: 
                      Baron.
Reply to
Baron

Thanks Baron. I will look into inpulse heaters. I forgot to mention in my original post that I already ordered some high temperature fiberglas/teflon tape (like the kind used to cover the heater wire element in poly-bag sealers).

I also agree that ultrasonic welding might be out of the price range. I did search eBay and AliExpress, but nothing jumped out at me.

After more research today, I am discovering that a big part of the success or failure of this homebrew will rest on the actual geometry of the weld tip that comes into contact with the plastic.

Reply to
mpm

If you machine an aluminium block instead of steel, it will be more thermally conductive (and easier to machine) though it may wear faster. If it wears out they you could put some inserts made of something harder at just the points where it wears.

Reply to
Chris Jones

The PID arrived today. Great price!

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(Auber Instruments) I'm probably going to switch back to aluminum for the very reasons you've stated. I started working on the 3D model today. Important: drill clean through to the other side. (otherwise, removing a cartridge for maintenance/replacement could be a huge PITA!) :) The teflon tape arrived today too.

Reply to
mpm

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