Mixing is ubiquitous in industrial, academic, and industrial laboratories. The choice of overhead or magnetic stirring to achieve uniform mixing is based on the scale and viscosity of the medium being stirred.

Commercial labs often “scale down” large manufacturing processes that involve mixing combinations of water, organic solvents, and soluble and insoluble materials to create solutions, suspensions, slurries, syrups, pastes, and creams; others work with inherently viscous materials such as polymers.

Then there is the whole other world of small-scale chemistry, biology, and analytical laboratory operations associated with basic research, or in support of production or manufacturing research and development.

These two scenarios closely approximate the domains of overhead mechanical stirrers and magnetic stirrers, respectively. Or as Charles Villano, sales and marketing manager at Kinematica (Bohemia, NY), says, “Overhead stirrers are used when sample viscosity and/or size are issues, or when there exists a concern for significant changes in viscosity.”

Overhead units are common in the food, material science, cement, adhesives, polymers, and energy industries.

Basic overhead stirrers consist of a drive mechanism or motor, controller, drive shaft, and stirring fixture or panel. Stirrer configurations include propellers, either x-shaped, anchor shaped, or flat panels, each appropriate for specific applications. Materials of construction are often critical as samples may be acidic, basic, or otherwise corrosive. For example, stainless steel or glass rods are common in the food industry, as are inert materials such as Teflon.

Data- and documentation-hungry labs have demanded feature-rich overhead stirrers, and manufacturers have met the challenge. Most stirrers today sport digital panels that display stirring element rotation and applied torque; many connect to computers, which log this information, via RS232 or USB ports. Torque applied to mix a sample is directly proportional to the sample’s viscosity.

These amenities are useful for unattended or automated operations, particularly when viscosity differences indicate endpoints. Mr. Villano estimates that about 20 percent (and growing) of overhead stirrer applications are integrated into processes via computer control.

Sizing an overhead stirrer for a specific application is part art, part science. “You can buy a 50-watt motor that says it can mix two liters, but if your material is viscous it may only handle 500 mL,” Mr. Villano explains.

While technologically more complex than overhead stirrers, magnetic stirrers are easier to use and set up and possess greater functionality. Magnetic stirrers use a drive magnet that causes a magnetically susceptible stir bar to rotate inside a flask or beaker. The stir bar core is coated with either glass or Teflon for easy cleaning. Most magnetic stirrers incorporate a heating element that operates independently of the stirrer.

“Stirrer-hotplates are definitely more convenient than overhead stirrers,” Mr. Villano observes, “but they’re mostly for smaller-volume organic chemistry labs or aqueousbased processes.”

Buyers also have the choice between round- or rectangular-bottomed stirrer-hotplates.

Round stirrer-hotplates more closely match the bottoms of Erlenmeyer flasks and beakers, which are round, and therefore take up less room. “Heat transfer is also better with round models,” says Refika Bilgic, managing director at IKA (Wilmington, NC). “But rectangular models can accommodate more labware.”


Helix 250 Orbital Shaker

  • New AccuStop feature ensures that when the shaker is paused, the platform/tray will stop in the Home Location
  • Allows users to increase the quality of experimental data, reduce lab experimentation time, and ensure sensitive experiments are carried out identically, every time
  • Users can now program the Helix 250 via RS232 connection

LabStrong
www.labstrong.com


PRO Lab Plus Series

  • Series includes VSN-5 nutating mixer, the VSM-3 Vortex mixer, the VSR-50 variable speed rocker, the VSOS-4P digital programmable orbital shaker, as well as the HPS-7 hot plate stirrers
  • Features a variety of available accessories for an array of applications
  • can be integrated into your current lab procedures with ease

PRO Scientific
www.proscientific.com


MIR-S100C Compact Orbital Shaker

  • Designed specifically for use in high humidity and/or elevated CO2 concentration conditions
  • Incorporates antibacterial copper alloy stainless steel for the shaker section, with a small window that can be used for spraying disinfectant inside
  • Revolution speed is adjustable from 40 to 200 rpm and the timer can be set for up to 99.9 hours or continuous operation

SANYO
www.sanyo.com


CM250 Mini Orbital Shaker

  • Digital LED display and easy programming sequence make setting speed and time simple
  • Can be adjusted to speeds from 50 to 250 rpm, and has an orbit of 20mm
  • Features a small footprint and is cold room compatible for applications that require refrigeration

Scie-Plas Ltd.
www.scie-plas.com