Ribbon Blender

Ribbon blenders have been the workhorses for blending applications and are very common in the chemical, pharmaceutical, and food industries.

Construction and Operation

A ribbon blender consists of a U-shaped horizontal trough containing a double helical ribbon agitator that rotates within. The agitator's shaft is positioned in the center of the trough and has welded spokes on which the helical ribbons (also known as spirals) are welded. Since the ribbon agitator consists of a set of inner and outer helical ribbons, it is referred to as a “double" helical ribbon agitator. The gap between the ribbon’s outer edge and the internal wall of the container ranges from 3 to 6 mm depending on the application.

The ribbon agitator is powered by a drive system comprised of a motor, gearbox, and couplings. Ribbon blenders are generally powered by 10 HP to 15 HP motor for 1000 kg of product mass to be blended. The specific power may range from 3 to 12 kW/m3 depending on the products to be blended.

The agitator shaft exits the blender container at either end through the end plates bolted or welded to the container. The area where the shaft exits the container is provided with a sealing arrangement to ensure that material does not travel from the container to the outside and vice-versa. The blender assembly along with the drive system components viz. motor, gearbox, couplings and bearing supports is mounted on a supporting frame.

The charging of material in the blender is generally through nozzles or feed-hoppers mounted on the top cover of the blender. The inlet cover also provides maintenance and cleaning access to the inside of the blender. An external jacket can also be provided on the blender container for applications which require heating or cooling of product material.

The materials to be blended are loaded into the blender, typically filling it to between 40 and 70 percent of the total volume of the container. This is generally up to the level of the outer ribbon’s tip. The ribbon agitator is designed to operate at a peripheral speed (also known as tip speed) of approximately 100 metres / minute, depending on the application and the size of the equipment. A spray pipe for adding liquids can be mounted above the ribbons. For materials that tend to form agglomerates during mixing, high-speed choppers can be provided for disintegration of the agglomerates. Figure 2 shows an assembly of a 3000 liters working capacity ribbon blender.

During the blending operation, the outer ribbons of the agitator move the material from the ends to the centre while the inner ribbons move the material from the centre to ends. Radial movement is achieved because of the rotational motion of the ribbons. The difference in the peripheral speeds of the outer and inner ribbons results in axial movement of the material along the horizontal axis of the blender. As a result of the radial and the counter-current axial movement, homogenous blending is achieved in short time. Blending is generally achieved within 15 to 20 minutes of start-up with a 90 to 95 percent or better homogeneity. The particle size and its bulk density have the strongest influence on the mixing efficiency of the ribbon blender. Ingredients with similar particle size and bulk densities tend to mix faster as compared to ingredients with variation in these attributes

After blending, the material is discharged from a discharge valve located at the bottom of the trough. The discharge can be fitted with any of various valves, viz. slide-gate, butterfly, and flush bottom, spherical and other types depending on the application. The operation of the valves can be manual or pneumatically actuated. Ribbon blenders can be designed for multiple discharge ports.

 

Applications of Ribbon Blenders

 

Ribbon blenders can be designed to operate in both batch and continuous modes. Batch type blenders can be built up to capacities of 50 m3. The ribbon blender’s versatility for blending solids combined with its ability to perform heating, cooling, coating, and other processes make it a very popular blender. The following are the applications of the Ribbon Blender:

  • Blending large volumes of dry solids.
  • Dry powder to wet phase mixing.
  • Mixing of bulk drugs, chemicals, and cosmetic powders.
  • Dry Blending of capsule formulations.
  • Lubrication of dry granules in large quantity.
  • Heating, cooling, and drying of materials.
  • Coating solid particles with small amounts of liquids to produce formulations.

 

Materials commonly blended in the ribbon blender are as follows:

 

Abrasives

Engineered plastic resins

Pesticides and herbicides

Animal feeds

Epoxy resins

Pet foods

Bakery premixes

Eye shadow

Pharmaceuticals

Bird seeds

Face powders

Pigments Cake Mixes

Fertilizers

Plastic powders

Carbon black

Fire retardants

Polyethylene

Chemicals

Gypsum

PVC compounding

Cleaning compounds

Instant breakfast cereals

Spice blends

Dietary supplements

Instant drink blends

Talcum powders

Dried food products

Laundry detergents

   

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