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 Goldleaf 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 for 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 interface 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, Goldleaf 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.

Selecting a High Performance Overhead Stirrer

Determining needed laboratory and pilot plant overhead stirrer features and benefits is a first step in setting up your purchasing specifications.  Mixing speed, motor power, processing capacities and programmable control functions all must be considered.  Money spent in an overhead mixer will be money wasted if the model you selected cannot perform the job.  Our post on mini overhead stirrers looked at entry level models; here we will explore the features available to researchers who need more extensive performance and control parameters.

A Snapshot of Goldleaf Scientific’s R100CT Pilot Plant Overhead Stirrer

The GOLDLEAF R100CT Pilot Plant Overhead Stirrer control panel

The R100CT overhead stirrer is designed for use in chemical and biological laboratories of industrial enterprises, universities and pharmacies.  It can be used for pilot plant applications processing samples to 200 liters.

It comes with a mounting stand and a powerful silent drive 220-watt high-performance brush motor that provides up to 600 Ncm torque energy to process medium and high viscous materials (10,000 to 100,000 mPa.s).  Stirring speeds can be precisely controlled between 50 and 500 rpm with higher speeds available on order.  A soft start/stop feature keeps samples from splattering out of the beaker or flask.

Researchers will appreciate the R100CT simplicity of operation exemplified by the intuitive control panel.  An incremental encoder wheel is used to set up operating and timing from 1 minute to 99 days.  A separate LED illuminates when the timer is active.

The On/Off button has an LED indicating when the system is on.  Set the stirring speed with the speed control knob.  The adjacent Load LED will illuminate if the unit is not able to hold set motor speed due to too high torque. Under this condition the unit will automatically reduce the motor speed so that the maximum allowed motor torque is not exceeded and burnout is avoided. The unit will also shut down if the impeller is blocked.

The dual-level liquid crystal display shows all relevant systems data such as set and real values of speed, torque, time and power output.  Accessing this information is achieved by pressing the panel’s display select button to alternate between various functions.

As with all Goldleaf overhead stirrers the R100CT pilot plant stirrer self tests to protect against overload and overheating, and can be paired with a variety of stirrer impellers as described in our post on the topic.

Data Collection

At the back of the fan-cooled control operating panel is the 9-pole sub-D connector for the full duplex RS-232 interface to allow remote operation as well as the collection of speed, torque and power data.   GLP record keeping is supported by full remote access of all stirrer functions (read and write).  Its “daisy chain” feature by sub addressing allows researchers to connect up to 255 units to a single serial interface on the computer side.

Complete details on this high-level overhead stirrer can be found in the operations manual or by contacting us for further information.