A Guide to Lab Stirrers and Lab Mixers

Laboratory mixing equipment – lab mixers, lab stirrers and lab homogenizers (sometimes known as high shear mixers) – are important research tools.   Which to use depends on several factors including but not limited to sample size, sample viscosity, the purpose of the mixing or stirring action and whether or not heating the sample is desired.  Here’s a brief look at lab stirring equipment to help you decide which configuration is best for your research work.

Nomenclature can be confusing at times.  What’s the difference between a mixer and stirrer and homogenizer?  Because they are often used interchangeably we will describe them by how they work.

Magnetic Hotplate Stirrers

Magnetic stirrers use a rotating coated magnet to perform stirring action in flasks and beakers.  The container is placed on the magnetic stirrer plate beneath which a motor-driven rotating magnet causes the magnet in the sample container to rotate the same way.   Hot plate magnetic stirrers allow researchers to provide a controlled amount of heat to the sample in increments to 500⁰C depending on the model.  They also control the speed of the stirring action to 1600 RPM and the mixing duration before shutdown.   Operating parameters are programmed into the magnetic stirrer with set and actual values shown on the LED display.

Most magnetic hotplate stirrers are equipped with built-in safety functions to guard against overheating, hotplate failure and other malfunctions.  Optional Pt100 temperature probes take control of the mixing function, monitor the action and shut the equipment down if inconsistencies are detected.  An RS232 interface is available on certain models to collect operating date for record keeping.

Because they are driven by magnetic power rather than a direct connection to the motor, magnetic stirrers are not efficient for high-viscosity samples.

An Overhead Stirrer for More Mixing Power

Overhead stirrers are powered by a drive motor affixed to an adjustable support stand.  Mixing tools, a.k.a. impellers, paddles and blades, are attached to a steel rod of sufficient length to immerse the tool at the required depth into the sample beaker. The upper end of the rod is inserted and tightened into the mixing motor chuck.

Overhead stirrer motors can be specified by torque power necessary to work with samples based on viscosity, and by stirring speed and duration.  Self-test features will shut the equipment down in the event of overheating or sample viscosity exceeding the unit’s limits.

Overhead stirrer controls vary depending on the model.  All have adjustable speed control (typically 500 to 2000 RPM) and basic LED displays.  Higher end mixers display set and actual parameters along with other operational details.   RS232 interfaces can be used to operate overhead stirrers by computers and collect operating data for record keeping.

Lab Homogenizers for High Speed Processing

Laboratory homogenizers take on tasks that other stirring methods can’t perform.  They are selected when the objective is thorough mixing of samples or the processing of samples for further analysis.  They are also used in medical applications such as cell disruption.

Homogenizers consist of a drive motor typically mounted on a stand for stability. The equipment is offered in several power ratings in watts and has variable speed controls that depending on the model can reach 45,000 RPM.

Mixing is accomplished by a homogenizer generator consisting of a rotor-stator assembly.  The rotor shaft is attached directly to the drive motor while the stator is at the base of a tube affixed to the drive motor housing.  Sharp teeth machined at the base of the rotor shaft interact with sharply machined slots on the companion stator.  The configuration of the homogenizer generator is selected based on the properties and volume of samples being processed.  Volumes can range from 0.1 ml to 20 liters.

Lab homogenizers draw the sample up into the generator assembly where the rotor violently propels it against the stator subjecting it to mechanical shearing and sonic energy.

Contact the mixing and stirring specialists at CAT Scientific for help in selecting the proper equipment for your lab.  Or ask us a question.

Bob Wilcox

Bob Wilcox has represented CAT Scientific’s family of homogenizers, magnetic stirrers, liquid handling and related laboratory equipment since 2002 when Staufen, Germany-based CAT Ingenieurbüro M. Zipperer GMbH established operations in North America. Bob oversees CAT Scientific laboratory apparatus sales and service organization from the company’s headquarters in Paso Robles, CA. He also is in charge of the parent company’s line of JetCat jet turbines, turboprop, and helicopter power plants for hobbyists’ radio controlled fixed wing and helicopter model aircraft. -- Earlier in Bob’s career he was involved in visual and special effects as well as camera and electronics supervisory responsibilities for the motion picture and television industry.

3 Comments

  1. Bing Liang on February 19, 2014 at 9:18 am

    Hi,

    I am looking for a lab mixer/stirrer that is able to mix high viscosity liquid. The sample volume is small (around 1 ml – 10 ml). What the most suitable product for my application? Thank you.

  2. anand on September 9, 2015 at 10:04 am

    Could you please recommend a suitable sample mixing unit without shear effect on the viscous lube oil sample which contains polymer additive to improve the viscosity index.

  3. Arrow on March 27, 2018 at 2:00 pm

    Excellent post. Very concise description of each piece of equipment. It’s good that you included that magnetic stirrers are not efficient for high viscosity samples.

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