Principle, Construction, Working, Uses, Merits and Demerits of Twin Shell Blender

Twin Shell Blender

Principle

With tumble blenders, the powder cascades within a rotating vessel due to the action of gravity. Blending with a V-blender is primarily achieved through diffusion. During diffusion blending, solid particles move in a random manner on a small scale. Blender movements help particles move around and, as a result, diffuse blending takes place. Particles are diffused over freshly formed interfaces during diffusion blending. There are no segregating effects when diffuse blending is used.

Construction

V-blenders are made by connecting two hollow cylinders at an angle of 75° to 90°. Using a tank made out of two V-shaped cylinders rotating around a horizontal shaft, the components of the mix can be homogenized perfectly and quickly. At the tip of the V, the product easily enters and exits without dust accumulating. In addition to trunnion-to-vessel intensifiers, a V-blender can employ liquid addition spray pipes to add liquids to the vessel through trunnion bars. By dissolving agglomerates in the charged material or those formed during wet mixing, intensifiers can dissolve agglomerates. An illustration of a V-blend showing the intensifier bar is shown below. V-blenders are available in a range of sizes with volumes ranging from 0.25 to 100 ft3. A number of features are included, including a vacuum system, intensifier bars, spray nozzles, a heating/cooling jacket, and a motor and control system that are explosion-proof. Further, heavy-duty models with capacities of 90 - 100 kg/ft3 are available.

Working

A blender is used to blend the material. V-Blenders should be filled to a volume between 50 and 60% of their entire capacity. Tumbling occurs when the blender is rotated. The V-Blender continuously separates and recombines the material as it tumbles. Continual convergence and divergence between the material and the blender results in homogeneous mixing. A blend is usually completed in between 5 and 15 minutes depending on the properties of a material being blended.

Mixing efficiency can also be affected by blender speed. Low speeds reduce shear forces in blenders. Although higher mixing speeds provide greater shear, this can result in more dust as fines are segregated. The mixing efficiency will be greatly reduced if the critical speed is approached. Increasing the number of revolutions per minute will result in centrifugal forces exceeding the gravitational forces needed for mixing at the extreme points of the blender. Therefore, the powder must tend to move towards the outer walls of the blender casing. In general, the rotational speed decreases with the size of the blender in proportion to the peripheral speed.

Uses

• V-blenders are used in the pharmaceutical and nutraceutical industries to blend free-flowing solids.
• Usually, V-blenders are used to mix food products, coffee, milk powder, ceramic powder, pigments, pesticides and herbicides, plastic powder, animal feed, spice blends, fertilizers, baby food, cosmetics, and polyethylene.
• Up to ten ingredients can be mixed in this blender.

Merits

• By eliminating moving blades, there is minimal reduction of particle size and attrition. This makes it suitable for fragile materials.
• The material is easily charged and discharged.
• By design, blender bodies like those with sanitary butterfly discharge valves produce a near-complete discharge of product.
• Without shaft projections, contamination is prevented.
• During the feeding and discharge of products, there is no dust generated.
• A liquid can also be injected into the mix to assist mixing if temperature is controlled.
• It allows ingredients to be mixed down to 5% of the final mixture size.

Demerits

• Installation and operation of equipment require a large amount of headroom.
• These machines are not designed to blend particles of different sizes and densities, which may separate once discharged.
• There may be unwanted particle attrition and cleaning problems associated with intensifier bars.
• Several soft powders and granules cannot be mixed effectively due to the low mixing shear.

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