When Do You Need A Magnetic Mixer?

When Do You Need a Magnetic Mixer? 

Let’s say you want to mix the green acid from the Batman movies with the lava from Dante’s Peak at a fixed pressure of 250 PSI. Why you would want to attempt this endeavor is totally besides the point, but whatever. Let’s just say someone is paying big bucks for it.



Untitled design I may have stolen this idea from a Captain Planet episode.

So you put all your material in your vat, stick in a motor and start mixing. What is probably going to happen? Well, first let’s assume you’ve bought a tank, shaft, and propeller that won’t melt like a teenybopper at a Ricky Martin concert when you put your mixture in. If you don’t burn or corrode the seals around the turning shaft that is moving the mixing blade, you’ll probably blow the motor straight to the moon or at least into a low orbit.

Yeah, ok, this is an extreme case. But if you’re reading this, then you’re probably thinking, "This is extreme, but I actually need to mix something like this.” If that’s you, and you are having problems with the what you're using for your mixing equipment, I think I have an option for you that will make your life a whole lot easier and less dangerous.

You need a magnetic mixer.


Double Mechanical Seals Are So 2013

For those of you who are in this line of work, you might think, “Eh, a double mechanical seal will work just fine.” And it might, but it will cost you more money in the long run. Let me explain.

For those of you who are new to the mixing or mechanical engineering world, a double mechanical seal is very close to what it sounds like. Two seals with a mechanical mechanism inside that help it keep pressure, heat, or acid in the place where they are supposed to be.



Meech seal So, the real thing is much more complicated than I make it sound. Source: www.chetraseal.com

What you usually have is a tank. Into that tank you insert a shaft with a propeller on it. In order to seal the tank to keep it pressurized, you have to use some type of seal around the shaft. The problem is, one seal is not strong enough to hold the pressure in. So you get a second seal that you put on the shaft above the first seal. Then the problem becomes that even those two seals might not be enough to keep the pressure in. So then you rig up a way to push a liquid between the two seals so that you have pressure on both sides of the first seal that pushes back against the seal keeping the pressure in the tank.

Great idea. Ingenious idea. Really top-notch stuff.

Until your seals fail.

And because the shaft is turning in order to mix your highly corrosive, heated, and pressurized material, your seals will fail because the shaft turns in the seal creating friction. It’s only a matter of time before that bad boy breaks. Then you have to replace the seals. And if the seals break in a dramatic enough fashion, you might have to replace your motor or your tank. And if what your mixing is really dangerous and you spill 55 gallons worth of it, you’ll have to call the EPA. All sorts of fun stuff that a magnetic mixer can take care of.


How It Works

So how does a magnetic coupled mixer work? Well, remember those magnets that you played with in elementary school and how if you put the “N” side of the magnet together with the other “N” side of another magnet, they would push each other away? OK, well, take those magnets and make them out of neodymium. Magnets made of neodymium are the strongest in the world, and they are permanently magnetic unlike those lame magnets you teacher had that lost their magnetism because Grady who is a year ahead of you put the magnets in the box so that they were repelling each other the entire year they were in storage and so now they don’t work. Totally not bitter.

Anyway, put one of those magnets around the rotating shaft and put that in a close container. Then put a magnet on the outside of that container so that the “N” of the magnet on the inside is close to the “N” side of the magnet on the outside. When the outside magnet turns, it is going to “chase” the magnet on the inside. Because the magnet on the inside is in a closed container, it cannot weeble, wabble or fall down. It can only spin in circles. So the outside magnet spins and that spins the magnet on the inside that is attached to the rotating shaft. Because the magnets don’t have to be physically touching each other, you can have a barrier between them, like a stainless steel tank.

That means that you don’t have to put a hole in your tank for the mixing shaft. That means you don’t have to have a seal for the shaft. That means no seals on your mixing tank have movable parts, and that means no seals on your tanks will be constantly under the force of friction wearing them down.

Now you might be thinking, “Well, that’s sounds really cool, but it’s really expensive.” Well, what if I told you a magnetic mixer is about 10% more expensive than a double mechanical sealed mixer? And then what if I told you the money that you’d save on the maintenance of a magnetic mixer would more than cover the cost of the extra money up front? Well, it’s true.

You also might be thinking, “Yeah, but I have to mix stuff over 176 degrees Fahrenheit and that’s when neodymium loses its magnetic pull.” Correct you are, sir, but samarium cobalt magnets can handle up to 350 degrees. Boom! Roasted.

The long and the short of it is, if you are mixing anything under high pressure, high temperature, or highly corrosive, you should really consider a magnetic mixer. Not only will it save you the hassle of having to design a double mechanical seal for your mixer, it will save you money in the long run.

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