Magnetic Stirring Bar Selection & Use

Magnetic Stirring Bar Selection & Use

Magnetic stirring is used in a number of common laboratory procedures, yet the importance of selecting the best stirring bar for each particular application is often overlooked. The drive magnet, vessel shape, viscosity and abrasiveness of the materials should all be considered when choosing the size, shape and materials (coating and magnet) of the magnetic stirring bar in order to achieve effective, efficient stirring results.

First, let’s discuss magnetism. On the most basic level, we know that opposite poles attract. A magnetic stirrer has a drive magnet, generally a bar or U-shaped made of a metallic alloy or a ceramic which rotates powered by a drive motor.

Magnetic Stirring Bar

Magnetic Stirring Bar

The magnetic poles of the drive magnet are typically about two inches apart in bench top models, and can be up to six inches apart in larger units used to mix 50 gallons of liquid solution. For optimum magnetic coupling the distance between the magnetic poles of the drive magnet and the length of the stirring bar should be equal. Bars too long or too short in proportion to the drive magnet will not have optimum coupling which is important to reduce spin-out.

Once a magnetic stirring bar has been placed in a container with solution, it should be positioned directly over the center of the drive magnet. The stirring speed should be increased slowly, until the desired vortex pattern is achieved. Should the magnetic stirring bar lose its coupling with the drive magnet because of the speed of the drive magnet, viscosity of the fluid, or an improperly selected stirring bar length, it is said to have ‘spun-out’.

Vertical distance between the drive magnet and the stirring bar should be kept to a minimum for the best coupling and stirring efficiency. Therefore, the containing vessel should be as thin as practical.

The selection of the shape of the magnetic stirring bar also influences the resulting vortex in that multi-sided shapes may be more efficient in moving solutions and certain shapes have been designed to provide a tailored fit in specialty vessels such as test tubes, cuvettes and spectrophotometer cells.

Magnetic stirring bars are generally made of ALNICO (an alloy of aluminum, nickel, iron and cobalt) magnets encapsulated in an FDA approved PTFE coating. In addition, magnetic stirring bars also use high energy magnetic materials, such as Samarium Cobalt which increases strength of coupling with a drive magnet and helps to reduce spinout when mixing viscous solutions or mixing at high speeds.

Newer to the market, the HSMAG magnetic stirring bars, use ALNICO magnets encapsulated in plastic for increased durability in granular slurries.

Use for General Stirring Applications Use for High Temperature Stirring Applications Use for Viscous Solutions High Speed Stirring Applications Use for Abrasive Slurries Extended Stirring Applications
Brand / Type Spinbar Teflon PTFE Spinbar Pyrex Glass Spinbar Rare Earth Samarium Cobalt Spinfinity
Magnetic Type Alnico Alnico Samarium Cobalt Alnico
Covering Teflon PTFE Clear Pyrex Glass Teflon PTFE Plastic
Features / Benefits Wide selection of shapes and sizes to fit vessels of all types; Individual shapes create different vortexes for efficient and effective stirring Heated stirring applications up to 274°C (525°F) Reliable Magnetic Coupling – Superior magnetic energy reduces frequency of spinout in the most vigorous applications Durable – Last 2.5 to 3 times longer under conditions known to traditionally cause material breakdown
FDA grade Teflon PTFE low friction coating is durable and inert Glass casing has zero absorption and porosity FDA Grade Teflon PTFE low friction coating is durable and inert Outer shell made from FDA approved materials
Color selection for color-coding work processes Distinct Color – Green color lets you quickly identify Spinbar Rare Earth Samarium Cobalt Distinct Color – Quickly identify the Spinfinity difference by its purple color

 

The Article from link source: Bel-Art – SP Scienceware website belart.com

 

 

Round Tapered Spinbar Teflon Magnetic Stir Bar

Spinbar Teflon Round Tapered Magnetic Stir Bar

Round Tapered Spinbar Teflon Magnetic Stir Bar without Pivot Ring, PTFE Round Spinbar Magnetic Stirrer Bar with Tapered Ends, Round Spinbar PTFE Magnetic Alnico Stirring Bar with Tapered Ends Tapered Magnetic Stir Bar Teflon PTFE is offered by HSMAG. A lab stirrer mixes substances for a variety of academic, research, or industrial applications such as solutions in […]

Teflon Oval Egg Shaped Magnetic Stir Bar

Teflon Oval Egg Shaped Magnetic Stir Bar

Egg shaped Magnetic Stir Bars PTFE, Teflon Oval Magnetic Stirrer Mixer Stirring Bar Rod Bead With Pivot Ring, Egg Shaped Magnetic Stirrers, Stir Bars and Rods in Round Bottom Flask Egg shaped magnetic stir bar is supplied by hsmag. It features ALNICO V magnetic cores which provide powerful and durable stirring instruments.  A stir bar (also known as […]

Giant Teflon Magnetic Stirbar

Giant Teflon Magnetic Stirbar

Giant Teflon Magnetic Stirbar, PTFE Stirrer Bar Giant, Teflon Magnetic Stir Bar, Lab Equipment Giant  Stirring Bars, Magnetic Stirrer PTFE Magnetic Stirbar Giant have three type: Plain, Pivot Ring, Triangle For use in very large containers. Super-Strong magnetic stir bars generate over three times the torque of conventional stirring bars. Significantly enhance stirrer performance and applications versatility. high quality mangnetic stir bars are molded […]

PTFE Stirrer Bar Plain Economy

PTFE Stirrer Bar Plain Economy

PTFE Stirrer Bar Plain Economy, Teflon Magnetic Stir Bar, Lab Equipment Plain Economy Stirring Bars, Plain Magnetic Stirrer Bar Economical PTFE PTFE Stirrer Bar – This Plain economy stir bar features an ALNICO V magnetic core which is one of the most powerful permanent magnet alloys available.  A stir bar (also known as a flea, spin bar, stirring bar or stirbar) is a […]

Economy Magnetic Square Stirbar Teflon Coated

Economy Magnetic Square Stirbar Teflon Coated

Economy Magnetic Square Stirbar Teflon Coated, Stir Bars Spin Bars, Stir Bar Economy PTFE Square, PTFE Teflon Magnetic Square-Rectangle Shaped Stirring Stir Bar Lab Equipment Economical square stirring bar is very effective stirrer, especially at low speeds, Rectangular magnetic stirring bars with high stirring power, particularly at slow speed. shaped magnetic stir bars are PTFE coated and provide excellent chemical resistance […]

PTFE Disc-shaped Magnetic Stirring Bar

Magnetic Stirring Bar PTFE Disc-shaped

Magnetic Stirring Bar, PTFE, Disc-shaped Teflon Magnetic Stir Bar, PTFE Disc Stirbar, Disc PTFE Teflon Stirring Magnets, Disc Teflon Magnetic Stirring Bars For use in tubes, PTFE Disc Stirbar for use in tubes.  A stir bar (also known as a flea, spin bar, stirring bar or stirbar) is a magnetic bar used to stir a liquid mixture or solution, usually in a […]

Triangular Magnetic Stir Bar, PTFE

Triangular Magnetic Stir Bar, PTFE

Triangular Magnetic Stir Bar with PTFE Teflon Coating, Triangular Magnetic Stirring Bar, PTFE Teflon Stirrer Bars & Rods, Labware Spinwedge Stirring Bar, PTFE Triangular Magnetic Stir Bar, Particulary effective for dissolving solids and mixing sediments because of the scraper like action on the base of the container. Triangular cross-section magnetic stirring bar efficiently churns up settled substrates to ensure complete mixing. Made of […]

Teflon Coated Star Shape Magnetic Stir Bars

Teflon Coated Star Shape Magnetic Stir Bars

Teflon Coated Star Shape Magnetic Stir Bars, PTFE Teflon Star-shaped Spinstar Magnetic Stirring Bar, Hub Magnetic Stir Bar Beaker Bar PTFE Very stable stirrer, especially at low speeds, The star-shaped Spinstar Magnetic Stirring Bar creates a deep vortex at relatively slow speeds. The PTFE Teflon® coating is inert and ideal for stirring aggressive chemical solutions. Designed for stirring inside […]