Mixers

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Mixers,  depending on the application, may have sharp blades or large flat paddles. The attachments or heads are generally removable to maximize the mixer's effectiveness with different materials. Mixers are most commonly constructed out of stainless steel because of its desirable sanitary and corrosion-resistant properties. Some mixers are made from thermoplastic, titanium, steel, cast iron or aluminum. Mixers are used throughout many industries during the manufacturing or processing period. Their powerful motors and blades allow mixers to work with a wide range of materials. These machines are widely used across many industries including the cosmetic, pharmaceutical, chemical, agricultural, pulp and paper, automotive, water treatment, adhesive and sealant industries to process toothpaste, glue, petroleum products, cement, biodiesel, dry and wet chemicals, medicines, syrups, beverages such as milk, medical ointment, lotions, creams, vitamins, shampoos, detergents, toothpaste, hair dye, petroleum products, silicone, adhesives, polyurethane and many other products or ingredients.

When a mixer is used for large-scale commercial production, it is most likely an industrial mixer because these mixers can process large amounts of materials. They usually have large tanks or vats to hold the substances as they are being mixed by mixing blades, the part of the agitator that imparts force to the material being mixed. Within the category of industrial mixers there are many variations. Paddle mixers are constructed around a horizontal rotating axis with broad shearing paddles radiating from spokes around the axis. Ribbon shaped mixing blades are flat and thin and are used in static mixers. These mixers do not have any moving parts and instead use carefully designed obstructions to force the flow of material to mix and blend together. Because of the simple arrangement of stationary blades inside, static mixers are sanitary and easy to clean. High shear mixers are quite the opposite; these high-speed machines offer homogenization, emulsification, disintegration, particle size reduction and dispersion for many different solid and liquid materials. Another variation of mixers is drum mixers, gallon drums that use the drum's rotation to mix materials. Drum mixers are generally used to blend mixtures of low to medium viscosities such as cement or adhesive slurries; this particular kind of mixer is capable of mixing substances of very different particle sizes.

There are also very specific kinds of mixers that are used with certain materials or to product a certain effect. Food mixers blend, mix, fold, whip, beat or knead multiple edible ingredients in food manufacturing processes. These mixers must meet certain regulations and be completely sanitary. For a breakdown and complete blending of a material, a homogenizer is used. Homogenizers have been used for a number of years in many industries, including science and technology, food processing and in some industrial mixing processes. A pair of common products that are homogenized is milk and cream. By using a perforated screen and high velocities, emulsifiers are able are able to thoroughly mix substances that are generally unblendable. For substances with low viscosities, agitators are used. Agitators are basically process aids because their main functions are secondary to the larger process. Agitators are used mainly in liquids, as agitation is not as effective with thick, highly viscous materials. For material that requires variable lengths of mixing, batch mixers are commonly used. These mixers work with a single load of material at a time before being refilled with another. When materials need to be broken down into smaller pieces, blenders are chosen for their sharp blades and high speeds. The terms "blender" and "mixer" are frequently used interchangeably.

Mixers are an integral part of many industries. Many companies rely on their correct function because mixing is often a first step for products that require further processing. These essential machines must be reliable and durable because certain materials may take a long time to be mixed thoroughly. Improvements in the manufacturing process help mixers perform better for longer periods of time. Because the parts of a mixer can be machined and assembled with precision and with quality materials, they tend to perform better and last longer. The materials that are used to construct mixers are chosen for certain attributes such as corrosion resistance or near-frictionless surfaces. Customized mixers are available though they are not widely offered. Specialty machines are able to perform to exact specifications which allows operators to better control the mixing process without causing excess wear and tear on other general models. The engineering of the mixer also has a role. The placement of the paddles, the design of the blades or the power of the motor are important factors for the engineer to consider. Additionally, companies must determine what additional characteristics they require. For example, some mixers are used to provide significant pressure drops while others are capable of handling large particles moving at high velocities.

Ribbon Blender Image Provided by Patterson Industries

Mixer Types

• Agitators commonly mix substances with low viscosities in low-shear applications. Agitators range in size from small agitators used in laboratory applications to large industrial agitators with 10,000-gallon capacities.
  
• Batch mixers mix one load of material at a time and are refilled with one load after another.
• Blenders usually mix miscible substances possessing comparable viscosities. Because substance properties remain similar, blending can usually be accomplished with relative ease.
  
• Continuous mixers are important parts of large production lines that typically have paddle type agitators with a series of mixing stages that progressively move and blend ingredients. Materials are constantly fed in specified proportions into continuous mixers, then are mixed, conveyed to the opposite end and discharged.
  
• Dispersers are single-shaft mixers that break apart or dissolve solid particles into liquid using a high-speed, rotating saw-tooth blade. The blade provides high shear forces that break apart the ingredients of low viscosity products, such as paints.
  
• Disposable mixers are low-cost plastic spouts containing plastic mixing elements. Disposable mixers are as efficient as most metal mixers but are not appropriate for in-line use at high pressures.
  
• Drum mixers have adjustable blades in a swing-blade design that maximize liquid movement at all speeds.
  
• Emulsifiers provide high speed rotation and centrifugal force through a perforated screen to achieve emulsification. Emulsifiers are very effective where a high shear is required, as they can provide fast mechanical and hydraulic shear
• Food mixers are sanitary machines that thoroughly combine ingredients for edible products.
• High shear mixers utilize counter-current mixing, which places very high parallel forces upon substances. During counter-current mixing, the mixing pan and the mixing tools rapidly revolve in opposite directions, resulting in substance uniformity.
  
• High speed dispersion mills are continuous mixers that break down particle masses to efficiently provide fine dispersions and stable emulsions.
  
• Homogenizers are high-shear mixers that subject mixtures of varying viscosities to intense mechanical and hydraulic forces, reducing mixing time and assuring uniform blend.
  
• Horizontal mixers have three or four augers and are used for quick mechanical mixing of particular substances, especially in feed processing.
  
• In-line mixers are being used more and more in large volume operations, as they can handle an extremely large batch with much lower horsepower and with predictable batch turnover. Dynamic in-line mixers utilize a combination of pump pressure and high-speed rotating elements, while static in-line mixers have specially contoured stationary mixing elements located in a tubular housing that serves as part of the pipeline.
  
• Laboratory mixers are an integral part of any laboratory or processing environment, as they can perform a variety of functions, such as mixing, emulsifying, homogenizing, disintegrating and dissolving. Types of lab mixers include compact, dual-shaft, constant-torque and high viscosity.
  
• Industrial mixers create a uniform mixture from various combined substances on a large scale for a variety of industries.
• Mixing blades push materials around the mixer.
• Motionless mixers, also known as static mixers, inline mixers and pipeline mixers, are continuous mixers that operate inline and have no moving parts. Motionless mixers allow for the blending of two or more fluids and disperse treatment chemicals into fluid streams.
• Paddle mixers are fast mixers that use horizontal rotating shafts with fixed arms and attached paddle-shaped feet to impact the solids and throw some of them onto the second shaft, while pushing the rest toward one end of the device. The paddles on the other shaft push the solids toward the opposite end and toward the other shaft and paddle set.
• Pharmaceutical mixers are used in processing a variety of liquids, powders and crystalline solids in the pharmaceutical processing industry. Common applications that utilize pharmaceutical mixers include the mixing of medicine, such as cough syrups and the creation of tablet coatings for pills.
  
• Production mills are efficient, high-speed dispersion mills that can quickly disperse, emulsify, suspend, cook, aerate and deaerate masses of particles. Material can be put in the production mill through radial slots where they are hurled off the slot tips against the stator slots, which produces efficient wetting-out of the solid phase and the quick achievement of stable suspensions, dispersions and emulsions.
  
• Proportional mixers properly mix concentrations of water to produce working and make-up solutions for applications that include coolants, cleaners, strippers, degreasers, fertilizers and fungicides. Venturi proportional mixers use water passing over an orifice to create suction to draw the concentrate from the container and mix it with water, while water-driven mixers use water to drive a piston, which then pumps concentrate into a mixing chamber where the concentrate is mixed with water.
  
• Ribbon mixers create an extremely diverse velocity field by using a counter-transport mechanism consisting of an outside right-hand ribbon and an inside left-hand ribbon, both connected to the same horizontal shaft. Ribbon mixers provide fast blending and mixing in the vertical plane, as they can transport an entire mass of solids a short distance in both directions of the axis of the shaft while lifting a portion of the solids a short distance in each direction; however, they are slow when mixing end to end.
  
• Rotary drum mixers contain blades that spin around the axis of the drum, mixing the substances, such as concrete. Drum mixer axes may be either horizontal or inclined.
  
• Rotor stator technology includes high-speed mixers that utilize a rotor and stationary stator to produce high rotor tip speeds. The differential speed between the rotor and the stator in these mixers imparts extremely high shear and turbulent energy in the gap between the rotor and stator.
  
• Static mixers, also referred to as in-line mixers, are motionless mixers that operate continuously. Static mixers remain quite efficient and generally require very little maintenance.
  
• Vacuum mixers have either top- or bottom-mounted mixers and are used to eliminate air pulled into the material during mixing, which increases product quality.

Mixer Terms

Agglomeration - The recombination of finely dispersed particles into larger particles, typically caused by a disturbance of surface forces resulting from a change in environment.
 
Alginate - Salt found in the cell wall of brown algae. Alginates are used in food processing to stabilize certain mixtures (e.g. emulsions), to seal in moisture and to thicken texture, among other things.
 
Axial Flow - The movement of fluid from the top to the bottom of a tank.
 
Batch Mixing - Mixing process that involves the weighing and measuring of ingredients, the creation of a mixture from separate ingredients, the removal of the mixture and the cleaning of the mixer and mixing tools before the start of a new batch.
 
Brine - Mineralized water consisting of sodium chloride, metallic and/or organic contaminants. Brine solutions are utilized in food processing procedures.
 
Colloid - Fine particles of a substance that remain between the dissolution phase and the suspension phase. Colloids neither dissolve into other substances, remain suspended within the other substances nor settle out of the substances.
 
Continuous Mixing - Mixing process, involving the automatic creation of a series of mixtures, in which the mixer contains a metering mechanism, such as a pump, and measures, combines and mixes the ingredients. Because smaller amounts are mixed continuously, cleaning of the mixer and mixing tools usually remains fast and easy.
 
Density - The ratio of substance mass to substance volume, measured in g/cm3 (grams per cubic cm).
 
Dispersion - Small particles of a substance evenly distributed throughout another substance. Dispersed particles are small, but remain larger than colloids.
 
Emulsion - A suspension in which one substance is suspended within the other. They are unable to be blended or mixed but can be combined, though not dissolved (e.g. oil and vinegar).
 
Heterogeneous - Consisting of different components that may not be distributed evenly throughout a mixture. The components, while mixed together, still remain separate entities.
 
Homogenous - Consisting of identical components distributed uniformly throughout the mixture. The components no longer remain separate entities, but have become one entity, as in a solution.
 
Impeller - The part of the agitator that imparts force to the material being mixed. Examples of impellers are propellers, turbines, gates, anchors and paddles.
 
Kinetic Energy - The use of motion to create and transmit power.
 
Mechanical Seal - A device consisting of two rings, one stationary and one rotating with the agitator shaft, which is used to seal against pressure where the shaft enters the vessel. Springs or tank pressure forces the accurately machined faces of these rings together.
 
Micrometer or Micron - A unit of measurement equivalent to one-millionth of a meter.
 
Mixture - A substance containing two or more substances that may not be distributed evenly throughout and do not bond together chemically. Substances in mixtures, although combined, maintain separateness.  
 
Paddle - A two-bladed impeller whose diameter is somewhat larger than the radius of the tank.
 
Residence Time - The average time a component remains in a continuous-process mixing environment.
 
Size Reduction - The breakdown of immiscible particles in a mixture that cannot be dissolved.
 
Solution - A homogenous formation created by the dissolution of a substance or substances into another substance.  
 
Solute - In a solution, the liquid, gaseous or solid substance or substances that dissolve into a liquid or gaseous substance, called a solvent. Solutes usually consist of smaller quantities than the substance into which they are dissolved.
 
Solvent - The liquid or gaseous substance into which a liquid, gaseous or solid substance, known as a solute, is dissolved.
 
Suspension - A heterogeneous mixture in which fine particles of a solid neither dissolve into a liquid or gaseous substance nor settle out, but remain within the substance supported by buoyancy. In suspension, both substances remain separate entities.
 
Viscosity - The resistance of a fluid, whether liquid or gas, to flow easily. Fluids with high viscosity, such as molasses, flow slowly; low viscosity fluids, such as water, flow easily.