Equipment for mixing and Double cone blender, V- cone blender

1) Planetary Mixers

 

In a planetary mixer, the mixing blade tips (or the beater) rotates in a planetary motion within the mixing bowl, thus named so. This mixer is used for mixing dry and wet powders, light pastes, gels, and doughs. This mixer is mostly used in food and bakery industries due to its simple construction, operation, and lower cost.

 

Principle

 

In a planetary mixer, the blades tear the mass apart and shearing action is applied between the moving blade and fixed wall. The mixing blade reaches every spot of the mixing bowl by moving in two directions, i.e., around its own axis and around the central axis. Convective action is also achieved because the blade has sloping plates which makes the powder move in upward direction.

 

Construction

 

 planetary mixer consists of a stationary stainless-steel vessel. They can be detached from its position either by raising the blade above the or by lowering the vessel below the blades. The mixing blade is attached the vessel top, whereas the mixing shaft is moved with the help of an electric motor which connects the shaft to the planetary gear.

 

Initially the blade moves slowly to allow the pre-mixing of ingredients, but later at the final Planetary stage the speed is increased to provide active Gear mixing to the material. The stationary vessel and the blade mounted on its top provide a Vessel kneading action and shearing effect to the material being mixed due to the narrow Blade clearance present between the blade and the vessel wall. Thus, to provide thorough mixing high shear can be applied.

 

Working

 

In a planetary mixer, the agitator undergoes a planetary motion. It rotates around its own axis as well as around the central axis, thus reaches all corners of the mixing bowl. The mixing blade is so shaped that it passes closely over the side and bottom of the mixing bowl, production volume thus creating no dead spaces. The blades tear the mass apart and shearing action is applied between the moving blade and fixed wall.

Convective action is also achieved because the blade has sloping plates which makes the powder move in upward direction. Planetary mixer is variable speed driven, so controllable pitch propellers initially for pre-mixing the blade moves slowly and finally for active mixing it moves at a high speed. angle of attack Thus, high pitch angle shearing force can be applied for mixing.

 

 Uses

Planetary mixer has the following uses:

1)Different industrial mixing  like pharmaceutical, food, and cosmetic industries use a single planetary mixer for mixing high shear mixers the light and medium viscosity products.

2) Rubber, chemicals, and other allied industries use a double planetary mixer for the mixing process.

3 For the manufacture of sustained release products and ointments, steam jacketed bowls are used for mixing.

4) The kneading action requires spiral mixer faster speed for wet granulation and low speed is required for dry blending.

 

 Merits

Planetary mixer has the following merits:

l) It works at varying speeds.

2) It is more useful for wet granulation and is advantageous over sigma mixers.

 

Demerits

 

Planetary mixer has the following demerits:

 

1) It requires high power.

2) It is useful for batch purpose due to the limitation of size.

 3) Mechanical heat is built up within the powder mix.

 

 

 

2) Propellers

Propellers are mechanical devices used for mixing the liquid materials with the help of blades or impellers. Propellers mix the liquids to prepare true solutions and emulsions.

 Principle

 

Propellers work on the principle of shearing force. They are a high-speed axial flow impeller used for mixing low viscosity liquids. They are installed in mixers having shafts mounted to a motor by an inferior coupling held by set screw propellers, allowing the motor and drive assembly to vibrate caused by mixing.

 Construction

 

Propellers consist of angled blades to circulate the fluid in axial as well as radial direction. If the stirrer is mounted centrally, the centrifugal force generated by the propeller blades causes the liquid to back up around the sides of the vessel and create a depression at the shaft; this is the vortex. On increasing the rotation speed, air feed material is sucked into the fluid by the vortex, causing frothing and oxidation.

 

However, vortex formation can be prevented by an off-centre mounting. Another method is by fitting the vessel with vertical baffles, which remove the rotating fluid from its circular spiral hooks path and bring fixed pitch propeller it in the centre of the vessel, where the vortex formation would otherwise occur.

The ratio of the propeller stirrer diameter to that of the vessel is The stirrer operates at speeds of 1-20rps. The propeller stirrer depends on wide range  axial and radial flow patterns, which does not occur in case of viscous fluid. For an efficient working the fluid should flow fast towards the propeller, which occurs only in case of mobile fluid.

 

 Working

 

Propellers rotate at high speed of up to 8000rpm, giving a suitable pattern of flow to the liquids.

When the liquids are mixed, either vortex is formed in the dispersion, or the air gets entrapped in the liquid. This can be avoided by making the follow changes in the position of the propeller shaft:

 

l)      Offset from the center,

 

2)                Mounting at an angle,

 

3)               Entering the side of the vessel,

 

4)                Using push pull propeller, or

 

5)                 Using baffles,

 

 

The propellers are not suitable when considerable shear force is needed, e.g., in the preparation of emulsion.

 

Uses

Propellers have the following uses:

l) These are most widely used for liquids

2) Multi-vitamins, propellers.

 

Merits

Propellers have the following merits:

1)        They require less power for operating.

2)    Their speed of rotation is very high, i.e., up to 8000rpm.

3)    They do not take much time to carry out the process of mixing.

4)    Their diameter is much smaller than paddle and turbine mixers.

 

Demerits

Propellers have the following demerits:

1) They are not suitable for those liquids which contain viscosity greater than 5 Pascal/second, e.g., glycerin, castor oil, etc.

2) As there is little shear, they are not suitable in emulsification.

 

 

For basic notes

In order to obtain the following types of products mixing technologies, usually the process of mixing is opted equipment for mixing:

1) True solution: These solutions are formed when two or more miscible liquids are mixed with dough mixer each other.

 

2) Emulsions: these are formed when two immiscible liquids are mixed together with the additions paddle mixers of an emulsifying solid liquid  agent.

 

3) Solutions: these are dough hook mixing paddle formed when any solute (solid) is dissolved in a solvent (vehicle).

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ribbon blender and sigma blade mixer

Equipment for mixing and Double cone blender, V- cone blender