Nauta Conical Screw Mixer to be delivered by year’s end

Almost all chemical industries rely on mixing, yet it remains one of the oldest and least understood processes in process engineering. Mixing occurs across all three phases: liquid, gas, and solid. In diverse fields like agriculture, food, pharmaceuticals, and cosmetics, mixing reduces non-uniformities in properties such as concentration, color, texture, and taste. Therefore, we focus primarily on the solid-solid mixing process. Mixing particles and powders presents more challenges than fluid mixing, and quantitative measurements of dry solids mixing help control this process. To achieve a homogeneous mixture and assess its quality, we must identify and test discriminating parameters. The ideal mixing process produces a uniform mixture quickly and with minimal energy consumption. Furthermore, the mixing mechanism significantly influences mixing efficiency. Researchers have identified three mechanisms in solids mixing: convection, diffusion, and shear.

Shear mixing occurs as particles interact within layers in a slip zone formed by shear stresses. This type of mixing typically happens at both high and low speeds.

Industries such as pharmaceuticals, nutraceuticals, fine chemicals, cosmetics, and personal care rely on high shear mixers. These mixers operate at exceptionally high velocities and are essential when conventional rotor-stator mills fail to achieve homogenization. High-shear mixers excel in applications like submicron homogenizing, high-shear wet milling, and suspension micronization. With their high velocity, these mixers deliver more shear energy than those with standard agitation. When mixed at high shear, a significant boost in shear power provides the energy needed for challenging emulsifications and homogenizations. Additionally, high-shear mixers often complete tasks faster, which saves time and reduces energy requirements, leading to higher yields.

Low shear mixing, on the other hand, blends products without reducing particle size, making it ideal for easily combined materials. A simple example is stirring cream into coffee; this low-shear process effortlessly integrates the cream without altering particle size.

A low-shear mixing process can easily be translated to blending a product without reducing particle size in your mixing process. Mixing at low shear is a great option when you need to mix products that are easily combined. Next time you stir your coffee and notice how easily the cream mixes with the coffee, you can brag about your low-shear mixing skills.

n diffusion mixing, particles move and mix across a sloping surface, where gravity and particle inertia create a natural flow. As particles roll down the slope, they spread out and intermingle randomly, creating a gradual mixing effect. Diffusion is especially effective when particles are small and lightweight, allowing them to travel further across the surface. However, diffusion mixing is relatively slow and may not achieve a completely homogeneous blend on its own, particularly for larger or denser particles. Despite this, it can be a helpful preliminary step before applying other mixing techniques, as it begins the blending process by spreading particles evenly across the surface.

Convection mixing involves moving larger sections, or “packets,” of powder within the entire mass of material. This is typically achieved by mechanical agitation or rotating containers, which shifts bulk amounts of powder to different areas, promoting uniform distribution. For free-flowing powders, convection mixing proves especially valuable. Since both diffusion and shear mixing often cause particles to separate by size, convection helps maintain consistency by continuously redistributing the powder. This process works well for powders that need a thorough, even blend without the risk of segregation, as it targets large portions of material and actively prevents particle clustering. Convection mixing is highly efficient and can often achieve homogeneity faster than diffusion alone.

Delft Solids Solutions operates a testing facility that simulates a range of industrial powder processing methods, including the Solids Mixing Process. In our facility, we use specific equipment to replicate both diffusion and high-shear mixing processes.

For diffusion mixing, we employ a cube mixer with two distinct mixing units. The first unit is constructed of stainless steel, offering a 3.5-liter capacity. The second unit is an acrylic glass cube, allowing a larger 8-liter capacity, which enables us to test different mixing volumes and observe diffusion mixing behaviors under varied conditions.

For high-shear mixing tests, we utilize a Diosna high-shear mixer, adjustable for volumes ranging from 1 to 4 liters. This equipment enables us to achieve intense shear forces, crucial for high-shear applications where a uniform blend and particle size reduction are necessary. Our facility’s mixing equipment provides flexibility in simulating various industrial mixing needs, supporting effective powder processing and quality testing.

We’re eagerly anticipating the arrival of our new Nauta conical screw mixer, a highly efficient convective mixer designed for precise mixing without product distortion. This mixer operates gently yet delivers exceptional mixing accuracy. Its screw rotates at an average speed of 70 rpm, with the arm moving between 1 and 2 rpm. The screw’s speed varies from 0.5 to 2 m/s, making it ideal for all ATEX zones.

The convective mixing process in this mixer relies on a rotating, free-hanging screw that lifts the product from the bottom of the vessel to the top. The orbital arm moves the screw along the conical vessel wall, creating shear forces that enhance the mixing effect. Our lab-scale Nauta mixer will have a capacity ranging from 5 to 30 liters of dry solids, accommodating diverse testing needs.

To support our work with heat-sensitive and fragile powders, this unit includes heating and cooling options. We expect its arrival between Christmas and New Year’s, aiming to have it fully operational by early 2022.