Mixer Basics- Step 5: The Motor

When we talk motors, it is easy to think "bigger is better." However, that's not always true, especially when you don't want to put more money into the mixer than you need to.
When thinking about what kind of motor you need, you need to consider your shear and flow needs ("shear" meaning breaking down the chemicals in your mixture and "flow" meaning the rate at which the mixture moves about the container). Shear and flow are inversely related, so if you decrease your shear, you will increase your flow.
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If you want shear, you are going to want speed. As the blade spins quickly, the energy from the blade is transferred into the mixture and breaks down the chemical bonds of the elements in the mixture. At the same time you need to be aware of the size of your mixing impeller. To get a large impeller to spin at the same speed as a small impeller, you'll need a lot more power. For example, to turn a 5 inch impeller in water at 1750 RPMs, you'd need a 0.5 HP motor. To turn a 10 inch impeller at the same speed would require a 13 HP motor. That's an increase of 2600%.

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Flow takes less power to achieve than shear. Flow increases exponentially with impeller size. For example if you have a 5HP motor turning a 5 inch impeller at 1000 RPMs, you would get a bulk fluid velocity of 6.7 feet per minute. If you keep the other variables the same and increase the impeller size to 10, you would get a bulk fluid velocity of 38 feet per minute. If you increase the blade size to fifteen you would get a bulk fluid velocity of 104.9.

Expo Increase of Bulk

You also need to consider the mechanics of the motor. We sell direct drive motors and geared motors. A direct drive motor has no gears and grips the shaft going down into your mixture directly. All the power of the motor is then transferred as directly as possible into the mixture which is better for speed and shear. A geared motor has gears. Those gears are used to create torque which is better for turning a large blade to achieve a high flow.

Once you have decided what kind of horsepower you are going to need from your motor, you can start looking at what kind of power supply you'll want to use to run your mixer.