For food manufacturers, no single piece of equipment is more critical than the mixing vessel’s agitator when it comes to product quality and consistency and operational efficiency. The right agitator design can ensure uniform mixing and heat transfer in every batch—even when challenged by large volumes, high viscosities and delicate ingredients—and streamline cleaning and maintenance demands for decades. But agitators come in a wide range of styles with differing features and many options, each engineered for a particular purpose. This guide can help you recognize the differences and how they relate to your product and process, so you are well-positioned to choose the agitator design that best fits your situation.
Factors about your product that affect agitator design decisions
As is the case when choosing your vessel design, several factors about your product mix must be considered to determine the best agitator solution for your operation. These include:
Individual ingredient characteristics - The characteristics of each of your product’s ingredients and their composition at the end of the process affect agitator design choices. Take, for example, food products with delicate, fresh-cut ingredients—such as potatoes, tomatoes, other cut vegetables and fruit—that must cook evenly and stay intact throughout the mixing process. These require a gentle lifting and folding action to keep the ingredients evenly suspended in the batch and reduce the potential for damage.
Ingredient miscibility - The extent to which your ingredients are able to form a homogenous solution by fully dissolving in each other at any concentration—i.e., their miscibility—will influence the design of your agitator. Hard-to-blend ingredients are common in creams, soups, sauces, mayonnaise and margarines, and may require agitators with high-speed propeller/high-shear or double-motion, counter-rotating capabilities.
Product weight and viscosity - Heavy and thick products require a much different agitator configuration than lighter and low-viscosity products. With common food products ranging from viscosities of 1 cP (water-like consistency) to 2 million cP (peanut butter, paste or similar consistency), this must be factored into specifications for the appropriate style mixer such as propeller, scraped-surface, high-shear, double-motion or a combination of these.
- Product variety and variability - If you will be producing only one product line, your agitator design can be completely tailored to that product. But if you will use your vessel to produce multiple products, your agitator design must be flexible enough to allow for maximum productivity across the complete range.
Factors about your operation that affect agitator design decisions
In addition to your product’s characteristics, consider these factors about your processes and facility to determine your best agitator solution option:
Production volume and utilization - Many food processors run high-volume production schedules, up to continuous 24/7 operations. Your expected utilization must be considered in your agitator specifications to ensure its long-term reliability, with particular attention to drive unit horsepower, gearbox and shaft construction, and blade and cross-member fabrication.
- Access to power - A lack of sufficient power is one of the leading reasons for agitator drive-unit failure. Drive motors wear out more quickly when they draw amperage above their rated load.
Agitator options: matching the design to your need
Once you’ve considered your unique product and operational factors, you can begin to determine the most effective agitator solution for your application:
Single-motion agitators turn continuously in one direction with variable speed capability. Equipped with either bar, sickle or sweep arms with or without scraper blades, they can be configured to work with hemispherical kettles, as well as dished-, cone- or flat-bottom vessels. The design of single-motion agitators makes them ideal for simple mixing of low-viscosity liquids or gentle-motion stirring of higher viscosity products. In hemispherical bottom kettles, the single-motion can also be inclined for specialty, hard-to-mix applications where vertical agitators are not sufficient.
Key Design Features
- Can be incorporated into hemispherical kettles, as well as dished, cone and flat-bottom tanks
- Accommodates bars, anchor or sweep designs, with or without scraper blades
- Custom designed for new or existing vessels
- Low viscosity liquids and simple heating or cooling applications, or gentle-motion mixing of higher viscosity products to keep ingredients in suspension
- High-viscosity inclined mixing
Also known as counter-rotating agitators, double-motion agitators use two concentric agitator shafts—an inner and outer shaft—that turn in opposite directions to provide thorough mixing and even distribution of heat. While some double-motion agitators use separate drives to control each shaft, others are engineered with a single motor and gear drive to power both the inner and outer shafts at the same speed. Double-motion agitators are ideal for high-viscosity products, or products with ingredients that require gentle blending or folding action.
Key Design Features
- Counter-rotating shafts powered by single motor with variable speed and controller to produce constant relative speed throughout the motor’s speed range and ensure stable batch-to-batch consistency*
- Independent gearbox option can maximize mixing flexibility as well as provide extra support in heavy-duty applications
- Standard design rating of 100,000 cP with heavy-duty design options available to accommodate product viscosities up to 2,000,000 cP
- For extreme-duty mixing applications, an idler pinion provides extra stability for the agitator drive assembly where there are constraints to using the (2) stacked motor design
- High-viscosity products or those containing ingredients where both thorough mixing and suspension of ingredients is required
*Single-motor design is an exclusive feature of Lee Industries. Other manufacturers may use two agitator drives.
Inclined agitation can be configured with either single- or double-motion agitation to meet the needs of products with fragile ingredients that may either sink or float, such as fresh-cut vegetables, fruits or meats as well as high-viscosity, heavy-duty applications. Because of its design, inclined agitation must be paired with a hemispherical kettle. With inclined agitation, the scraper blades can sweep the inside surface of the kettle, leaving no unmixed product in the vessel and putting more product in contact with the heating jacket for more consistent heating and cooking results. Moreover, the angled agitator creates a gentler lifting and folding action that keeps all ingredients evenly suspended in the batch to prevent ingredient damage.
Key Design Features
- Allows for slower speed lifting/folding to prevent damage to delicate ingredients
- Requires a hemispherical kettle
- Available in 22.5°, 30° and 45° incline configurations (45° incline is available in single-motion only)
- Can be accommodated within single- and double-motion design styles
- Products with premium, fresh or solid ingredients that require gentle bending or folding action
- High-viscosity products requiring thorough mixing (e.g., ground beef, refried beans, pie fillings)
Agitators can be configured with features or upgrades that may add additional value to your production environment, depending on your product and operational situation. These can include a tilting feature for easier cleaning and maintenance, electropolishing and finishing options to enhance sanitation, and piggy-back drives for extra flexibility and heavy-duty rating.
Regardless of the size or scope of your operation, choosing the right agitator is an important decision that affects your operation’s efficiency, quality and consistency. The better you match your agitator design to your product attributes and operational characteristics the more value you will gain.