What Are Sigma Blade Mixers Used For?

Sigma blade mixers are used for mixing high viscosity or high solids material including rubber, butyl rubber, Silicone, Adhesives, Sealants, Composites, carbon fiber materials, Ceramics, Clay, Chewing gum base, and Candy nugget.

What Are Some Of The Other Names For A Sigma Blade Mixers?
Sigma Blade Mixers, also known as double arm mixes, mixer/extruders, kneaders, masticators or Mogul mixer.

What Is The Mixing Mechanism In A Sigma Blade Mixer?
The mixing mechanisms of a sigma blade mixer is a pair of blades called sigma blades or Z-Blades for their shape, dispersion blades, Naben blades or fishtail blades. Sigma blade mixer blades are usually tangential, running at different speeds or overlapping blades running at the same speed. Sigma blade mixers can also have cored blades to allow heating fluid to pass through the center of the blade to assist in pre-heating the sigma blade mixer.

How Are High Viscosity Or High Solids Products Discharged From A Sigma Blade Mixer?
The discharge mechanisms of a sigma blade mixers are based on the flow characteristics of the product and need to maintain fixed or non-fixed connections. Free flowing or low viscosity products can be discharged from a sigma blade mixer via bomb-bay doors or flush bottom ball valves. Medium flowing or medium viscosity products may be discharge from a sigma blade mixer by tiling he bowl. Poor flowing or high viscosity products may be discharged from a sigma blade mixer by an auger screw also known as an extruder screw.

What Are The Units To Describe Viscosity?
When considering a sigma blade mixers, viscosity is important. In the process industry liquid viscosity or resistance to change in shape or flow is most commonly described in terms of Poise or Centipoise (Cps). Other industries prefer Stokes, Krebs most often used in the paint industry, or Pascal-second (Pa·s) equivalent to newton-second per square meter (N·s m–2). Viscosity can be measured with a spindle type Rheometer or viscometer.

What Other Technical Terms Describe Liquids Viscosity And How Do These To Relate To A Sigma Blade Mixer?
Rheological terms are used to describe how the stress applied to a liquid changes its deformation or flow characteristics. Describing the viscosity or thickness of a liquid is described by rheological properties which have two broad categories: Newtonian and non-Newtonian liquids.

• Newtonian liquids include water and most solvents. Stress, or agitation does not change the viscosity of a Newtonian liquid.
  
  
• Non-Newtonian liquids are more interesting. Non-Newtonian liquids change viscosity with stress or agitation as in a sigma blade mixer.
  • The most common is Thixotropic liquids or shear thinning liquids. The viscosity of these liquids is reduced when being mixed in a sigma blade mixer. We all know shaking ketchup is necessary to get it to flow because it is thixotropic.
  • Dilatant liquids are shear thickening which is an important consideration for a sigma blame mixer because blade speed may need to be reduced and/or more power applied to mix the product. The water-starch experiment you may have done in school is an example. The low viscosity starch slurry does not splash when an object is dropped into it because the viscosity spikes rapidly with the stress of the object hitting it.
  • Pseudo-plastic liquids increase in viscosity but only momentarily when the stress is applied. Mayonnaise is an example.
  • Lastly, we have the very rare Rheopexy liquids which increase in viscosity over time with stress or mixing.

What Other Issues Should Be Considered When Designing A Sigma Blade Mixer?
Some of the process issues to consider when designing a sigma blade mixer are how to introduce solids and liquid into the sigma blade mixer, the need to gas purge or gas blanket the contents of the sigma blade mixer, the ability to create a vacuum or pressure inside the sigma blade mixer or heating or cooling the sigma blade mixer to control product temperature.

Looking For A New Sigma Blade Mixer?
Paul O. Abbe® offers a variety of customizable sigma blade mixers for solids and pastes of all viscosities and built for your process requirements.

Browse Paul O. Abbe's full line of Mixing Equipment today!