Overhead Stirrers
Overhead stirrers are laboratory devices used to mix large-volume, viscous solutions. They typically include a stirrer, paddle, and stand. The Fisher Scientific channel offers a wide range of overhead stirrers with features such as digital displays, varied speed ranges, and advanced safety and control options.
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FAQ
An overhead stirrer is a laboratory instrument that mixes liquids using a motor-driven shaft and impeller inserted directly into the sample.
Unlike magnetic stirrers, which rely on a magnetic field and are limited to low-viscosity fluids, overhead stirrers handle high-viscosity or large-volume mixtures up to several liters.
They are ideal for polymer synthesis, emulsification, suspensions, viscous reagents, and pilot-scale formulations where precise torque and continuous mixing are required.
- Torque: Determines the stirrer’s ability to handle resistance; higher torque motors can process viscous or dense materials without speed loss.
- Speed range: Variable-speed drives (typically 50–2 000 rpm) allow optimization for low-shear blending or high-shear dispersion.
- Impeller type:
- Propeller blades provide axial flow for homogeneous liquid-liquid mixing.
- Anchor or paddle impellers suit high-viscosity pastes and gels.
- Turbine or dispersing blades create strong radial shear for emulsions.
Selecting the correct impeller geometry and torque rating ensures efficient energy transfer, consistent shear, and reproducible results across batch sizes.
Modern overhead stirrers include advanced controls and safeguards for precision and laboratory safety:
- Overload and stall protection to prevent motor damage under excessive load.
- Digital torque feedback and closed-loop speed control to maintain constant mixing speed regardless of viscosity changes.
- Soft start/stop and anti-splash acceleration to minimize sample loss.
- Sealed housings (IP-rated) for protection against spills or corrosive vapors.
- GLP/GMP-compliant logging, USB or RS-232 connectivity, and programmable profiles for traceability in regulated environments.
These features enhance reliability, user safety, and reproducibility for demanding analytical and process workflows.
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