by Marjorie Steele, Editor for IQS
The fact that my Kitchenaid Mixer has three different mixing attachments is a mystery to my husband, who never bakes. To him they are strange – possibly tortuous. When I got tired of taking the dough hook (which I use least often) off each time he did the dishes, we had a brief lesson in mixing viscosities and how different blades perform best for different substances. In my own house, I am the mixing expert.
In the process manufacturing community, the mixing experts are the mixing equipment manufacturers, and they understand how different blades, speeds, mixer configurations and bowl shapes interact with different types of substances during the mixing process. There are nearly as many different types of mixing as there are products to be mixed – from industrial slurry adhesives to milk homogenization to bologna meat mixing, industrial mixers work differently to achieve smooth blending.
While my Kitchenaid has only three blade attachments for three different levels of viscosity (wire whisk for beating, enameled paddle for mixing, dough hook for kneading), industrial mixers have many configurations for the entire spectrum of liquid, amorphous and friable solid viscosities. Here are a few main categories, including categories which have recently been added to our directory pages:
Agitators – A common example is the central agitating blade in a top-loading washing machine. It remains stationary on its center axis, agitating water and clothes with its paddle as it turns. Agitators in food and industrial product processing may have similar configurations, or they may be removable agitating rods which are placed into a substance only long enough to properly agitate it. Agitators are used in liquids, as agitation is not as effective with thick, highly viscous materials.
Ribbon Blenders – While blenders and mixers are basically synonymous, this type of blender is used in specific dry mixing of free-flowing bulk solids. Usually housed in a semi-cylinder, ribbon blenders have long, ribbon-like paddles which circle around a central axis, shearing through friable materials as the axis turns. Grains, pharmaceutical powders, powdered food ingredients like flour and many other solids are de-lumped or combined in this blender.
Paddle Mixers – Same configuration as ribbon blenders, but with paddle-shaped blades protruding from the axis instead of shearing ribbons. Also used to mix dry friables, but is also used in wet-dry mixing, slurry mixing and other high viscosity liquid mixing applications.
Static Mixers – AKA inline mixers, these smart pieces of equipment have no moving parts. Carefully designed ribbon-like obstructions are placed inside a cylinder through which liquids flow. As the liquid flows through, the obstructions inside cut the flow of the liquid, forcing it to mix and blend together. Inline mixers may be attached to flow tubes to enhance a liquid’s homogeneity without requiring power or servicing to moving parts.
Emulsifiers – These may be inline, like static mixers, or a separate machine; both types are used in the blending of immiscible liquids such as oil and water or cream and milk. In inline and centrifugal emulsifiers, pressure is applied to the liquid-liquid mixture as it is forced through very small filters which break up larger molecules into smaller. In the case of milk and cream, cream is composed of large fat molecules which separate from milk due to the huge difference in molecule size; emulsification breaks cream molecules down so they are similar in size to milk molecules. Emulsification is sometimes achieved by adding emulsifying agents, by centrifugal force or by fast shearing.
Homogenizers – Can be synonymous with certain types of emulsifiers. Homogenizers combine heterogeneous liquid-liquid mixtures by subjecting the mixture to extreme force and pressure, resulting in a breakdown and complete blending of the material. Most homogenizers have vertical axis shearing blades which blend within a closed container at very high speeds.
Drum Mixers – This is a broad category of mixers, and may include portable drum mixers which may be used for in-container mixing. Other drum mixers have their own container which materials must be poured into. Drum mixers are generally used to blend mixtures of low to medium viscosities such as cement or adhesive slurries; this particular mixer is capable of mixing substances of very different particle sizes, such as gravel and cement slurry or ice cream and fruit.