page contains a pretty detailed and somewhat lengthy explanation
of what RF Heat Sealing is and where our SealGuard Buffers come
in. I tried to keep it pretty straightforward, but there is a
lot of it.
If you're not
up for the whole thing, you can skip around with the bookmark
links below, or just figure you need the Buffers anyway, why
bother reading this stuff, and just skip this whole page. Or
you could print it out, and read it at your leisure. You don't
need to know the theory to be able to use our Buffers, but I
thought a lot of people would like a little explanation of the
When you need
to fabricate an item from two or more pieces of plastic, you
need a way of welding them together. When you need to weld sheet
materials together in an overlapping fashion, the preferred method
is Heat Sealing.
In Heat Sealing,
the two or more pieces of sheet plastic to be welded together
are placed in a Heat Sealing Machine. The Machine looks like
a large punch press with Heat Sealing Die where the punching
die would usually be.
The Heat Sealing
Die generally consists of a solid, flat lower platen on which
the materials to be sealed are placed. The Heat Sealing Die is
above the lower platen. The Heat Sealing Die consists of one
or more bars, usually brass, which are shaped in the fashion
in which the seal is desired. For example, if you want a straight
seal, you use a straight bar. If you want a seal in a circular
shape, you use a die with a circular bar.
When the plastic
is in place and the machine is activated, the die comes down
to the platen holding the material to be sealed, and the die
is energized - either with Heat Energy or with Radio Frequency
Energy. This heats the material and, along with the downward
pressure that the head of the press is exerting, seals the material
together in the desired shape. After the seal is completed (the
time necessary to seal is set by a timer on the machine; generally
it's a few seconds or so), the machine moves the die back up,
and the sealed product can be removed and new material can be
put the platen on to be sealed.
Keep in mind
that I've described a very plain vanilla Heat Sealing Machine.
There's a thousand variations -
with turntables to allow the use of different operators to
lay out the material to be sealed, and to remove the finished
which seal on belts which are themselves the Buffer material
(most people use our HiSeal®).
which allow multi-step sealing operations, either with a belt
of Buffer or a turntable carrying
the item from sealing station to sealing station.
which integrate RF Heat Sealing with other manufacturing operations
like insertion, cutting or punching, again usually on a belt
of Buffer to carry the item from
station to station.
And many others;
your mileage may vary.
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Ok, so far,
so good, but where does this Radio Frequency stuff come in? You
may recall a little while ago, I mentioned that the die required
energy to heat the plastic sheets to seal them together (it also
uses pressure on the heated plastic). That makes sense; something's got
to weld this plastic together. I said that either Heat energy
or Radio Frequency (RF) energy could be used. Well, Heat energy
is pretty much self-explanatory - you just melt the
plastic together as if you left on a radiator too long.
But RF sealing
takes a little more explaining. Do you know how a Microwave Oven
works? When you turn it on, it beams RF energy throughout the
interior of the Oven.
You may know
that Radio Waves have a frequency. (If this is too elementary
for you, I'm sorry, but I want everyone to get it). When you
change your radio from one station to another, you're changing
the frequency selection of the tuner, so that it receives radio
waves of a slightly different frequency.
RF energy in
your Microwave Oven is similar to the RF energy that your radio
station puts out, except that it's a lot more powerful (because
your food is right next to the transmitter; actually, your radio
station puts out a ton more power, but by the time it gets to
you it's pretty diffused). Also, the Microwave Oven is emitting
RF energy on a completely different frequency.
of the RF energy in your Microwave Oven is such that it excites
the Water Molecules in the food that's in the Oven. The water
molecules start moving around a lot faster. You may recall from
high school physics that when molecules get moving faster, they
create heat. Well, that's what happens to the food in
your Microwave - the fast moving Water Molecules heat it up from
was a nice lengthy explanation, and now you understand your Microwave
Oven a whole lot better, but what's this all got to do with welding
pieces of plastic together? I'm glad you asked, because here
comes the payoff (finally!). Certain kinds of plastic have polar
molecules. That means that they can be excited by RF energy,
just like water molecules are excited by a Microwave Oven's RF
energy. An RF Heat Sealer is just like a Microwave Oven, except
it isn't enclosed, and the RF energy is tuned to a different
frequency, one that excites the Plastic Molecules instead of
exciting Water Molecules.
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They both accomplish
the same thing, to get the plastic hot enough to weld together,
but just as your Microwave heats a lot faster than your regular
Oven, an RF Heat Sealer heats the material more quickly than
a plain Heat Sealer. It takes less time to make a seal, so your
production rate goes way up. In addition, (again just like a
Microwave Oven) plastic heated with RF energy cools down more
quickly than if it was conventionally heated, meaning it will
be safer to handle, come off the machine more quickly, and keep
its shape better immediately after the sealing.
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Now we get
to the fun part, at least for me, because this is where what
we sell comes into the picture. One other difference between
sealing using conventional heat and sealing using RF is that
when you seal with RF, you need a Buffer beneath
the material that you're sealing.
it or not, the purpose of the Buffer is to require you
to use more RF energy to seal! As you seal, you are
melting your plastic and reducing the thickness, because the
die is pressing down on nearly molten plastic. The RF energy
is busy exciting your plastic, but like any electrical field,
it is looking to complete the circuit in the easiest way possible.
The nearest Ground is the bottom platen of your sealing die.
Without a Buffer, as soon as the plastic is thin enough in one
place, all the RF energy your machine generates would flood through
that one weak spot to the bottom platen, and burn a hole in the
product that you're sealing.
When you use
a Buffer, even as the sealing area of your product thins, the
Buffer provides you with substantial electrical resistance to
the RF energy, keeping it diffused throughout the surface of
the sealing die, and not allowing it to break through one part
of your product and concentrate in that one spot. It increases
the window between incomplete sealing (too little power) and
burn-through (too much power).
also does other things:
- It can give
you the right balance between sticking and releasing the material
that you seal.
- It can serve
as a landing place for the sealing die that's softer than the
steel of the bottom platen.
- It can cushion
the plastic you're sealing to absorb inconsistencies in the
got you here, let's spend another minute on that first item.
A balance between sticking and releasing? The single most common
Buffer problem that people have is sticking, the plastic
material adhering to the Buffer and not coming away easily (and
we have special Buffers to eliminate
Sticking that no one else has). But too much release is
bad too, especially if you're using a multi-step sealing process.
You don't just want your product sliding all over the place;
you want to be able to achieve a good registration from step
A certain amount
of sticking is also helpful in that too much release can cause
your product to stick to the sealing die instead of staying down
on the Buffer where it belongs.
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The most common
is PVC (vinyl), but we have customers sealing Urethane, PETG,
some kinds of Nylon, some kinds of Styrene, and Polyolefins with
EVA. There are others, but some of them can get pretty exotic.
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Lots more than
you might think. RF Heat Sealing is a technology with very wide
applications. Some common ones are:
- Dust Filters
- Pocket protectors
- Tarps, Tents
- All sorts
- Sheet Protectors
- Shower Curtains
tops, doors, and sun visors
- Seat Cushions
I could go
on and on . . . (In fact, I already have!). Sorry if I inadvertently
left out your product.
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For more information
about our SealGuard Buffers, click here.
To receive our informative Free Information
Kit, click here.
acknowledge the assistance of Art Livingston of Heat Seal Services
in putting together this page. Most of the facts are his, any
errors are mine.