Ribbon Mixers
The property of ribbon mixers that differentiates them from other forms of mixers is the design of their mixing blades, which have the shape of helical ribbons that move different forms of materials from the middle of the mixer to the walls and back again. Helical blades are chosen for ribbon mixers because they provide the versatility to mix dry and damp powders, pastes, slurries, and liquids. The helical design has a slow rotational speed that efficiently mixes ingredients.
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Structure of Ribbon Mixers
The simple structure of ribbon mixers adds to their efficiency. The two basic types of ribbon mixers are horizontal and vertical with horizontal ribbon mixers being used the most. The components of a ribbon mixer include a trough, ribbon or helical agitator, a direct drive motor, feed inlet or inlets, a discharge valve, and a control panel. Each of the different parts has exceptional durability and resilience in order to withstand constant use.
Trough
The trough is the main structural piece of a ribbon mixer. It has a tub-like construction that is completely sealed to avoid leaks. Troughs come in different designs regarding how ingredients are added. In some configurations, ribbon mixers are directly fed and are part of an assembly or production process. Inlet valves are positioned along the top of the trough with some troughs having lids. Discharge valves are placed in the bottom of the trough in the middle or on one end and are tightly sealed to prevent leakage.
The shaft, which is sealed on both ends and connected to the direct motor, extends along the full length of the trough. It has a helical ribbon attached to it using spokes. The position of the ribbon and shaft is carefully calculated such that the blades of the ribbon do not touch the sides of the trough but are close enough to avoid the build-up of ingredients. In general, horizontal ribbon mixer troughs are U shaped, which allows for easy access and cleaning.
Although the U shape of troughs is the most common, there are variations in the shapes of troughs, which include cylindrical, fully cylindrical, semi-cylindrical, and cone-shaped. The variations in the shape of troughs are in accordance with the applications for which a ribbon mixer is used.
Agitator
The agitator or ribbon is the key feature of ribbon mixers. It includes the shaft and helical blades that are attached to the shaft with spokes. The slow rotation of the agitator moves the ingredients back and forth and up and down. As with troughs, there are different agitator designs, each of which completes the mixing process in a unique way. One version of ribbon mixers has inner and outer ribbons that move the ingredients in different directions. The inner ribbons move the ingredients from the center of the trough to the end of the trough while the outer ribbons move the ingredients back to the center of the trough. The back-and-forth motion gently combines and blends the ingredients to form a homogeneous mixture.
Agitators take several forms and have different designs. Some of the variations include enhanced paddles and plow agitators. In addition to the ribbons, these designs have flat pieces of metal attached to the shaft by spokes and are designed to alter the traditional mixing pattern of ordinary ribbon mixers. While the inclusion of paddles creates another form of mixing pattern, the ribbons on ribbon mixers vary as well and include single, double, triple, and hybrid types. Of the different types of ribbons, double ribbon versions are the most popular and widely used.
Drive Systems
For many years, the drive motors for ribbon mixers had belts and chains that turned the shaft of the mixing blades. The slow speed of the mixing process made the chains and belts a perfect choice. The downside of the method was the deterioration of the belts and chains, which necessitated changing the belts and chains frequently. In addition, mixing and blending were halted causing a slowdown in production.
The landscape of ribbon mixers was changed forever with the introduction of variable speed drives (VSDs) or variable frequency drives (VFDs), which are direct-drive electric motors that are attached directly to the shaft. VSD motors can run continually and require far less maintenance than belt or chain drives. They allow for more precision control and are able to endure the stressful constant use required by mixing.
Feed Inlet
The feed inlet is where ingredients are introduced into a ribbon blender. They can take the form of a nozzle, hopper, or powder inlet and are positioned on the top of a ribbon mixer. Feed inlets take several forms that include hatches, lids, and sealed openings. As with any opening into a ribbon mixer, feed inlets are tightly sealed to avoid leakage. On the interior of the mixer, feed inlets conform with the configuration of the trough such that they do not interfere with the mixing process. Lids are normally locked, so they won’t pop open during mixing.
There are several seals on ribbon mixers to prevent ingredients from moving outside the mixer. Aside from seals on the feed inlets, there are seals on both ends of the shaft, the discharge valve, and the lid. As with the other openings of a ribbon mixer, the seals are positioned such that they do not interfere with the mixing.
Discharge Valve
The discharge valve is an opening through which the contents of a ribbon mixer are removed. As the ingredients move back and forth in the trough, they are forced toward the discharge valve, which is generally located at the bottom of the trough at one end. When the valve is opened, the contents of the mixer drain out of the mixer through the discharge valve. The forms and types of discharge valves vary in accordance with the design of ribbon mixers. Plug valves are the most popular and widely used. They have gaskets and openings that match the interior of the trough and provide a perfect seal.
The types and kinds of discharge valves are endless and include a wide array of valve types. The most common forms of discharge valves are paddle gates, knife gates, butterfly valves, spherical, and universal flanges. Each type has its benefits with some forms not providing a complete seal allowing leakage.
Control Panel
Control panels for ribbon blenders can take different forms from simple on and off buttons to a set of interactive controls. As the controls become more sophisticated and technological, they allow users to change the characteristics and parameters of the mixing process. Control panels, as with all forms of machinery, allow users to adjust settings, change timing, and alter feed protocols to match the requirements of the assembly and packaging processes.
The key feature of control panels is the ability to input the settings for the mixing process and do other things instead of standing with the mixer to oversee mixing. In the computer age, control panels can have an interface such that the mixing process can be controlled by desktop or laptop computers.
Conclusion
Ribbon mixer manufacturers outline the capabilities of their equipment and supply customers with detailed information regarding the operation of ribbon mixers. They work diligently with users to ensure users have the right ribbon mixer for their application. An understanding of the components of a ribbon mixer can assist users in their understanding of the capabilities of ribbon mixers such that users can converse authoritatively with manufacturers.