How to Shop for an Overhead Lab Stirrer

Researchers involved in R&D lab work and pilot plant production activities along with their purchasing departments may find it necessary to evaluate the need for and importance of options available when selecting overhead stirrers.  This post is designed to help you shop for an overhead lab stirrer. Among the points covered are

• stirring speed
• stirring vessel capacity
• stirring tool configurations
• sample viscosity
• safety features
• and other important considerations

But first it might be useful for you to answer the question

Do you Really Need and Overhead Lab Stirrer?

For pilot plant and low-production operations you probably do.  But another option may be open to you in the form of magnetic stirrers including hotplate magnetic stirrers.  If you are familiar with the difference skip ahead.  Otherwise here’s a brief intro to magnetic stirrers.

The big difference is that while overhead lab stirrers use a motor-driven stirring impeller, magnetic stirrers utilize a coated bar magnet placed at the bottom of the stirring vessel – typically beakers or flasks.

The container sits on a stationary flat plate beneath which a motor powered, speed controllable magnet rotates.  This causes the bar magnet to rotate and perform the stirring action.  Hotplate magnetic stirrers function by providing a temperature controlled heat to the plate.

Because there is no mechanical connection between the motor-powered rotating magnet and the bar magnet in the container, these stirrers are not satisfactory when used with high-viscosity samples, or those where viscosity may increase during the mixing and stirring operations.

For more on this see our post on magnetic stirrers.

Specifying Considerations for an Overhead Lab Stirrer

Benchtop overhead lab and pilot-plant stirrers are not equipped with hotplates.

Unlike magnetic stirrers they are able to process larger volume samples and samples with viscosities that either are too high or become too high for a magnetic stirrer to handle.

Overhead stirrers – sometimes referred to as overhead mixers – offered by CAT Scientific are precision instruments featuring microprocessor control that allows researchers to control speed in stepless increments.  As promised above here is a brief list of features you should consider when shopping for an overhead stirrer.

• Auto shutdown.  We list this first because it an essential feature that protects your investment in an over head stirrer if an increase in sample viscosity overloads the drive motor and causes it to overheat.  High-end models will automatically lower the stirring speed should the torque taken by the motor shaft means it cannot hold the programmed speed.
• Soft start-stop.  Avoids sample splashing.
• Sample size.  This will help determine the power of the stirrer motor.  Typical capacities are 35, 100, 150 and 200 liters.
• Stirring speed.This varies by model.  Examples in RPM are 50-500, 30-2000, 40-2,000 and 20-700.  Higher speeds are available on order for some models.
• Stirring time.Program when the stirrer should shut off.
• Torque energy. This is measured as Ncm (Newton centimeter).  The higher the torque energy the more torque it can apply to the sample.
• Sample viscosity.  Viscosity may change during stirring so specify an overhead stirrer capable of handing the maximum viscosity expected.
• An RS232 interfaceThis enables connections to computers that (1) can be programmed to operate the overhead stirrer and (2) collect performance data for record keeping.
• Intuitive controls.  These can be as simple as on-off switch and speed control dial with an LCD speed indicator to highly sophisticated self-diagnostic controls that alert the cause of a shut down.
• A 2-year repair or replacement warranty.

A related item to consider when shopping for an overhead lab stirrer is selecting the configuration of the various tools that can be used to perform the stirring operation.  Their configuration is important as they relate to how stirring is performed and to the viscosity of the samples.  We invite you to check this out by viewing our post on selecting overhead stirrer impellers.

Automating Multiple Overhead Stirrer and Other Lab Operations

Researchers may find themselves responsible for monitoring and controlling several instruments such as magnetic and overhead stirrers.  To assist in this, CAT Scientific offers its “Shake and Stir” computer controlled system.  For information on this see our post on automating overhead stirrer operations.

For more advice on this important topic please see our article on selecting overhead stirrers.  If you have special concerns or needs regarding the use of an over head stirrer do not hesitate to send us a question.