Nova-tech Bel-Art Magnetic Stirring Bars Selection & Use Bedienungsanleitung PDF herunterladen

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-shape made of a metallic alloy or

a ceramic which rotates powered by a drive motor. 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 spinout.

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 (page 377) 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, are Bel-Art Products Spinfinity

magnetic stirring bars, page 374.

Spinfinity

magnetic stirring bars use ALNICO magnets encapsulated in plastic for increased

durability in granular slurries.

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370

Magnetic Stirring Bar

(Centered over drive magnet)

Slowly Increasing Speed

Until Optimum

Speed is Reached

Beaker

Surface Plate

Achieving Best Results with Magnetic Stirring

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1 2 3 4

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MAGNETIC STIRRING BAR SELECTION & USEMagnetic stirring is used in a number of common laboratory procedures, yet the importance of selecting the be

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A Magnetic Stirring Bar for Every Application371All Spinbar®and other Teflon®PTFE Coated Magnetic Stirring Bars are Manufactured in a

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)#0. (Flea) magnetic stirring bars are designed for stirring small volumes in vessels such as vials, tubes and gradient makers. Availablein a

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70%69/)-"!09+!112)00)-'!01 are completely encapsulated inPyrex®glass. Glass stirring bars are useful for high temperatureap

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Nova-tech Bel-Art Magnetic Stirring Bars Selection & Use Bedienungsanleitung

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