What Are Kneader Mixers Used For?

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

What Are Some Of The Other Names For A Kneader Mixer?
Kneader mixers, are also known as sigma blade mixers, Z-blade mixers, double arm mixers, masticators, or Mogul mixers.

What Is The Mixing Mechanism In A Kneader Mixer?
Mixing is accomplished in a kneader mixer by two blades of the sigma or Z-blade style or Naben or fishtail blades or dispersion blade design. Kneader mixer blades are often of the tangential design which allows them to rotate at different speeds. Overlapping blades are sometimes us in kneader mixers and in this case the blades rotate at the same speed. Kneader mixers blades may be drilled or cored to allow heating fluid into the blades to pre-heat the mixer.

How Are High Viscosity Or High Solids Products Discharged From A Kneader Mixer?
Kneader mixers can discharge products in three ways based on the flow characteristics of the product. The need for fixed or permanent connection is possible only with the bottom discharge and mixer/extruder design.

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

What Are The Units To Describe Viscosity?
When considering a kneader mixer, and important consideration is the liquid viscosity. Liquid viscosity or resistance to change in flow is described in terms of Poise or Centipoise (Cps). Some industries use the unit of Stokes. Krebs is common in the paint industry. Another viscosity measurement terms is Pascal-second (Pa·s) equivalent to newton-second per square meter (N·s m–2). Viscosity can be determine by various viscometers or Rheometers.

What Other Technical Terms Describe Liquids Viscosity And How Do These Relate To A Kneader Mixer?
To describe how stress applied to a liquid and the changes its flow characteristics there are a number of rheological terms used. Rheological terminology falls into two categories: Newtonian liquids and non-Newtonian liquids.

• Newtonian liquids include water and most solvents. Mixing does not change the viscosity of a Newtonian liquid.
  
  
• Non-Newtonian liquids will increase or decrease in viscosity with stress. Non-Newtonian liquids will change their viscosity when agitated, pumped or otherwise stressed in a kneader.
  • Thixotropic Liquids: A common Non-Newtonian liquids are the Thixotropic liquids. These are also called shear thinning liquids. The viscosity of these liquids is lowered when mixed in a kneader mixer. Catchup is a Thixotropic liquid which thins when shaken as we all know is necessary to get the catchup 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 Kneader Mixer?
Other process issues involved in the design of a kneader mixer is how solids and liquids will be introduced into the kneader mixer. Other considerations are creating vacuum or pressure inside the kneader mixer, heating and cooling the kneader mixer and purging with inert gases.

Looking For A New Kneader Mixer?
Paul O. Abbe® offers a variety of customizable kneader 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!