Blended powders can be incorporated in a variety of products including pharmaceutical tablets, vitamins, supplements, mineral blends, and even various foods like energy bars. Applications also include plastics, metal powders, chemicals, pigments, cosmetics, food, pyrotechnics, and others.

Many of these formulations involve the fine blending of as many as 40-50 components, including powders and trace ingredients (<1%) that are vastly dissimilar in size and density. In some cases, this requires multiple “key blends” and frequent testing in a time-consuming and costly process.

To resolve this, manufacturers require high-volume precision blending of formulations on equipment that provides exceptional batch-to-batch consistency and repeatable results.

Among the available options is tumble blending equipment that can be engineered to meet the requirements of the application to rapidly produce a more precise, homogenous blend containing all necessary components and trace elements in the specified amounts.

To examine the benefits of tumble blenders and dryers, we discuss the advantages and benefits of this approach with Gregg Muench, vice president of business development, GEMCO. The company, which began producing tumble blenders for mixing gunpowder for the war effort since its founding in 1916, still manufactures tumble blending and vacuum tumble drying equipment today.

Q: Tumble blending equipment has been used to blend powdered ingredients for more than a century. Why is this approach still so popular today?

A: Tumble blending is a very low-impact processing technique for handling abrasive or sensitive solids. This allows for a gentle repeatable pattern that not only maintains a superior blending design, but also preserves the product’s physical characteristics.

Although there are different types of vessel shapes, including the double cone and V shape, the blending is achieved by rotating the vessel and allowing the material bed to fall away from the vessel’s walls.

Tumble blenders are engineered to create a repeatable pattern in which the entire bulk material moves to form a homogenous mixture. The blender moves at a precise speed, with the vessel wall at a precise angle, so that the material cascades over itself. There is no additional force from paddles, plows, or spiral ribbons – just gravity.  

While this occurs, micro mixing (if needed) simultaneously proceeds via agitator blades located in the mixing zone center of the vessel, where fine processing in the material transpires. Together, macro and micro mixing evenly expose each particle to six times more active blending per revolution than traditional mixers.

At that point, it just becomes a matter of scale. Tumbler blenders can range in capacity from ½ to more than 400 cu ft for larger production models.

Q: How does tumble blending compare to traditional mixing equipment that uses blades or paddles?

A: Traditional equipment such as plow, ribbon, and paddle mixers use blades or paddles to push material and so are limited to moving the material within the confines of their active area. The mechanics force the material bed outward, leaving dead spots inside the vessel where material moves more slowly or remains stationary.

Also, because these units are stationary, they have one stationary port at the bottom of the machine. This port has a long neck, which isolates the material from any processing force during mixing. Operators often need to empty the discharge area and manually reintroduce it back into the top of the mixer. This means some portions of the mix will receive more additive than others. In fact, such mixers cannot accommodate blends with 7% or less of any one ingredient.

Another issue lies in the positioning of the intensifier bars or fluidization zones. These intensifier bars should ideally be located in the mixing zone, where every particle passes through. Many times, however, traditional mixers have their intensifier bars in dead zones. When this happens, the material will not be fluidized properly, and active ingredients will not be incorporated throughout the batch.

Traditional mixers also tend to waste expensive additives. Because additives being added to the vessel initially contact only a very small portion of the material, they get quickly absorbed into the material bed. The typical response is to add more additives to achieve the desired mix concentration, which drives up the cost.

Q: One of the industry challenges is thoroughly blending in trace amounts of solid or liquid ingredients into a larger batch. How is this accomplished with tumble blenders?

A: It is more difficult to create precise blends with trace ingredients (<1%) that are dissimilar in size and density.

However, properly blending in trace ingredients can be critical for pharmaceutical manufacturers, for example, so they can meet the regulatory requirements of the United States Pharmacopeia (USP), National Formulary (NF), or FDA.

To do this, they must achieve results within blend uniformity requirements for every batch, whether the formula is predominantly active ingredients and several excipient ingredients, or predominantly excipient ingredients with very small amounts of active ingredient.

Although nutraceuticals and supplements are not strictly regulated like pharmaceuticals, these types of products still must substantiate any label claims such as specific RDA or FDA allowances, vitamin percentages, or active components.

When tumble blending equipment is engineered to meet the requirements of the application, the equipment can rapidly produce a more precise, homogenous blend containing all necessary components and trace elements in the specified amounts.

Such blending can not only eliminate the need for key blends, but also produce a better distribution of active ingredients.

In one example, a large nutraceutical manufacturer in Nevada was blending approximately 40 components in 1000-kilo batches in a 6-7-step process with multiple key blends. Through onsite analysis of the manufacturer’s process, including examination of the physical characteristics of the powders used, it was determined that all of the components could be mixed in one step using both macro and micro mixing.

By eliminating the need for key blends and all intermediate testing, the customer estimated the new equipment saved them about $875,000 a year.

Q: Can Tumble blenders be used for drying as well?

A: Tumble blenders can include vacuum tumble drying, if required.

Powder movement is a critical element that is necessary to eliminate both overheating and the burning of particles. The constant movement and flow path allow the powder to achieve a consistent drying temperature throughout the entire batch. This helps eliminate cold spots and wet powder. The smooth tumbling lets powder lay on the heated surfaces only long enough to allow heat transfer to the particles, driving energy efficiencies. Gentle product movement stops particle degradation as well.

Vacuum tumble dryers allow for precise control over the drying process and repeatable low moisture end points. Dynamic vacuum tumble drying dries pharmaceutical powder energetically as it rotates inside the vessel. This dries the powder faster, more evenly, with less labor, and is particularly helpful in reducing residual organic solvents. Even with all this said, the tumbling action is the gentlest of all the dryers.

Traditionally, manufacturers use tray dryers, where wet material is laid in thin layers on multiple racks of heated trays. However, this can lead to uneven drying as heat is applied. Also, volatile material may be trapped on bottom layer particles as a crust forms on the top layer of material. As the inner materials are insulated from the inert atmospheric drying process, they remain unstable.

Tumble drying can also be used to blend in an active ingredient with a carrier, such as alcohol, which is sprayed on the particles. As the powder tumbles in the blender, the cold powder moves out to the heated walls of the blender. The heat vaporizes the alcohol while it is drying.

Q: How precisely can tumble drying be controlled?

A: The level of control of vacuum tumble dryers is directly related to the number of sensors used to monitor temperature, pressure, humidity, vapor pressures, vapor pressures, etc.

To keep equipment operating, sensors are also used to determine when filters are clogged to initiate a blowback to clear the obstruction and keep the equipment operating without intervention. In more advanced models, all this information is shared in real-time to the end user as well.

The sophistication of the controls allows for intelligent determining of the end point of the drying process. Most drying equipment is designed to run for a specified, set time that may have no relation to achieving the drying levels required. Sensors can be used to monitor when the material is dry. This takes the potential for error from humans involved in the process out of the equation. It can also speed processing time if the material is dry sooner than expected.

GEMCO has installed thousands of powder blending and drying units in 37 countries around the world. For more information, call 800-654-3626 or visit okgemco.com.

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