What Are Double Arm Mixers Used For?

Double arm mixers are used for mixing high viscosity or high solids material including adhesives, butyl rubber, candy nugget, carbon fiber materials, ceramics, chewing gum, composites, sealants, and silicone rubber.

What Are Some Of The Other Names For A Double Arm Mixer?
Double arm mixers, also known as sigma blade mixes, mixer/extruders, kneaders, masticators or Mogul mixer.

What Is The Mixing Mechanism In A Double Arm Mixer?
The mixing mechanisms of a double arm mixer is a pair of blades called sigma or Z-blades for their shape, Naben blades, fishtail blades or dispersion blades. Double arm mixer blades are typically tangential, rotating at different speeds. Double arm mixer blades may also be overlapping, rotating at the same speed. Double arm mixers can drilled and cored to pass heating fluid through the blades to pre-heat them.

How Are HIgh Viscosity Or High Solids Products Discharged From A Double Arm Mixer?
Double arm mixers can discharge product in three ways based on the flow characteristics of the product and need to maintain fixed or non-fixed connections.

• Bottom Dump Discharge: Low viscosity or free flowing products can be discharged from a double arm mixer from bomb-bay doors or flush bottom ball valves.
• Tilt Discharge: Medium viscosity or moderate flowing products may be discharged from a double arm mixer by tiling the mixing bowl.
• Extruder Discharge: High viscosity or poor flowing products may be discharged from a double arm mixer by an extruder screw also known as an auger screw.

What Are The Units To Describe Viscosity?
When considering a double arm mixer, viscosity must be considered. 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 is 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 viscometer also known as a Rheometer.

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

• Newtonian liquids include water and most solvents. Agitation or other stressors do not change the viscosity of a Newtonian liquid.
  
  
• Non-Newtonian liquids are more complex. Non-Newtonian liquids will change their viscosity with agitation or stress in a double arm mixer.
  
  
  • Thixotropic Liquids: The most common non-Newtonian liquids are Thixotropic liquids. These are also known as shear thinning liquids. The viscosity of these liquids is reduced when mixed in a double arm mixer. Ketchup is a Thixotropic liquid which thins when shaken which is necessary to get it to flow from the bottle.
  • Dilatant Liquids: Dilatant liquids are shear thickening which is an important consideration for a sigma blame mixer because blade speed may need to be reduced, and larger drive motors installed. The water-starch experiment often done in high-schools is an example. The low viscosity starch slurry thickens and 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: Pseudo-plastic liquids increase in viscosity but only for a short time when the stress is applied. An example of pseudo-plastic liquid is Mayonnaise.
  • Rheopexy Liquids: Lastly, we have the rare Rheopexy liquids which increase in viscosity over time with stress or mixing. Examples are printer inks and gypsum pastes.

What Other Issues Should Be Considered When Designing A Double Arm Mixer?
Some of the process issues to consider when designing a double arm mixer are how to load solids and liquid into the double arm mixer, the need to purge with inert gases, the ability to generate a vacuum or pressure inside the double arm mixer or heating or cooling the double arm mixer.

Looking For A New Double Arm Mixer?
Paul O. Abbe® offers a variety of customizable double arm 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!