There are three popular shapes of tumble blenders: the V-Blender, the double cone, and the slant cone. Tumble blenders rely upon the action of gravity to cause the powder to cascade within a rotating vessel. The V-Blender (also known as a twin shell blender) is one of the most commonly used tumbling blenders. The blending performance of this type of blender has shadowed many of the members in the blender family. They offer both short blending times and efficient blending.
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The V-Blender is made of two hollow cylindrical shells joined at an angle of 75° to 90°. The blender container is mounted on trunnions to allow it to tumble. As the V-blender tumbles, the material continuously splits and recombines, with the mixing occurring as the material free-falls randomly inside the vessel. The repetitive converging and diverging motion of material combined with increased frictional contact between the material and the vessel’s long, straight sides result in gentle yet homogenous blending. Figure 1 shows a V-Blender.
The primary mechanism of blending in a V-Blender is diffusion. Diffusion blending is characterized by small scale random motion of solid particles. Blender movements increase the mobility of the individual particles and thus promote diffusive blending. Diffusion blending occurs where the particles are distributed over a freshly developed interface. In the absence of segregating effects, the diffusive blending will in time lead to a high degree of homogeneity. V-Blenders are therefore preferred when precise blend formulations are required. They are also well suited for applications where some ingredients may be as low as five percent of the total blend size. Normal blend times are typically in the range of 5 to 15 minutes depending on the properties of material to be blended.
The charging of material into the V-Blender is through either of the two ends or through the apex port. Studies on V-blenders have demonstrated that for solid powders which have similar size and shape, there is no mechanism to move the powders across the line of symmetry of the blender. For such materials, care must then be taken to load each side of the blender equally to ensure the desired homogeneity of blends.
Blending efficiency is affected by the volume of the material loaded into the blender. The recommended fill-up volume for the V-Blender is 50 to 60% of the total blender volume. For example, if the fill of material in the blender is increased from 50% of the total volume to 70% of the total volume, the time taken for homogenous blending may be doubled.
Blender speed may also be a key to mixing efficiency. At lower blender speeds, the shear forces are low. Though higher blending speeds provide more shear, it can lead to greater dusting resulting in segregation of fines. This means that the fines become air-borne and settle on top of the powder bed once the blender has been stopped. There is also a critical speed which, if approached will diminish blending efficiency considerably. As the revolutions per minute increase, the centrifugal forces at the extreme points of the blender will exceed the gravitation forces required for blending. Consequently the powder shall tend to gravitate to the outer walls of the blender shell. As the size of the blender increases, the rotational speed decreases usually in proportion to the peripheral speed of the blender extreme. V-Blenders are designed to operate at 50% to 80% of the critical speed.
Discharge from the V-blender is normally through the apex port which is fitted with a discharge valve.
Advantages of Using V-Blender
Disadvantages of V-Blender
A V-Blender can be provided with high-speed intensifier bars (or lump breakers) running through trunnions into the vessel, along with spray pipes for liquid addition. The intensifiers may be provided for disintegration of agglomerates in the charge material or those formed during wet mixing. Figure 2 is a schematic drawing of the V-Blender with the intensifier bar.
Provision of the intensifier bars makes the V-Blender adaptable for more applications. These include:
Provision of intensifier bars may have the following disadvantages:
V-Blenders designs are most often used for the dry blending of free flowing solids. This blender is often used for pharmaceuticals, but the mixing action’s slight shear limits the blender’s use for some very soft powders or granules. V-Blenders are generally used for the following:
A blender a very important piece of equipment for the pharmaceutical, chemical and food industries. In the pharmaceutical industry, medicine is manufactured by mixing various combinations of drugs and chemicals. Each one of them also has different chemical compositions and reactions and mixing may be done either in a dry or wet state depending on these factors. There are various types of blenders available and each of them has its purpose. We shall have a look at the types of blenders depending on their use in the manufacturing process.
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Principle of a Blender – It works on the principle of producing a wave as the material gets tumbled. The shear plane first makes the wave in the top one-fourth of the product load and then subsequent mixing is done.
The Advantages of a Blender are –
Double Cone Blenders – These blenders are typically used for mixing dry granules, powder, and abrasive heavy material. It is shaped in a cone form and has multi-shear deflector plates which help in easy blending. There are paddle-shaped baffles available which can also be fitted on the shaft if better blending is required. The canonical shape of the blender enables homogenous mixing of bulk material and an easy discharge
Double Cone BlenderPrinciple of a Double Cone Blender– They are most often used for dry blending of any free flow solids. These solids could be of different densities and get intermixed as the double cone rotates. Normal Cycle times are set as and when required and the butterfly valve at one end is provided for material discharge and the other end for material charging and cleaning.
The Advantages of a Double Cone Blender are–
Octagonal Blender – This a slow tumbling machine that helps perform the mixing function along with the lubrication of dry powders and granules. The advantage of this octagonal blender is that it can blend the finest of particles while rotating and does not degrade the particle structure.
Principle of an Octagonal Blender – This blender has removable baffles mounted on a rectangular shell and is supplied with a bin charging system and can also be designed for vacuum charging. The material that is required to be mixed is charged either from the bin or manually or through the vacuum charger. Once the port is locked positively, the blender is set with a preset timer. Once the blending is done, the product is discharged into the process containers through the butterfly valve.
Octagonal BlenderThe Advantages of an Octagonal Blender are
Importance of Various Types of Blenders – Blenders plays a crucial role in manufacturing processes. There are different types of blenders in the market each one suiting its purpose. The correct choice depends on the ease of operation, maintenance without any compromise on the quality of output. The octagonal blender is designed to process a larger volume with less power consumption. The space occupied is less and useful for smaller particle blending. A double cone blender is apt for mixing 2 to 5 type ingredients. The double cone design is effective in eliminating any dead spot and is simple to load and unload and clean. However the functionalities of these blenders are irreplaceable.
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