High shear and low shear mixing granulators are used for manufacturing of tablets in pharmaceutical industries & we are familiar that tablets are manufactured by wet granulation,dry granulation and direct compression process.
When we are going to manufacture tablets by using a wet granulation process then we may use either low shear mixing granulators or high shear mixing granulators for mixing and kneading or wetting step.
An example of a shear mixing granulator is the rapid mixing granulator or RMG & if you are not familiar with rapid mixing granulators then you must read the complete article given in the following
In this article, we will discuss what are the low shear mixing granulators and which type of equipment are used as low-shear granulators for manufacturing tablets, capsules, and dry powder suspensions by using the wet granulation process.
What Is Low Shear Mixing Granulator
A common question comes to mind, what is the meaning of a low-shear mixing granulator? As the name indicates ‘low shear’ means these are the equipment which exerts less force or pressure during the mixing and kneading stages & those equipment which exerts higher pressure or force during the mixing and granulation process are known as high shear mixing granulators.
Why low-shear Mixing Granulator
Low-shear mixing granulators are used for the manufacturing of those products where we need to protect our granules from breaking.
Due to the low shear or less force exerted over the granules, there are fewer chances of break down of granules into small particles, so we get good quality granules for those products which are difficult to handle in the high shear mixing granulators because in the high shear a higher pressure or force is applied which results in breakage of granules into small particles and this results in production of more fine during the process of drying leading towards the issues of flow during tablet compression or capsules and dry powder suspension filling.
Examples Of Low Shear Mixing Granulator
The most commonly used low-shear mixing equipment for wet granulation are
- Ribbon mixer
- Plough mixer
Ribbon Mixer
A ribbon mixer is one of the most commonly used low-shear mixing granulator for the manufacturing of tablets, capsules or dry powder suspension by using the wet granulation process. Ribbon mixer is also known as spiral mixer or sigma mixer.
It is known as a ribbon mixer or spiral mixer as the mixing blades installed inside the mixing bowl or mixing chamber are like the sigma or spiral shape.
Components of the Ribbon Mixer
In conventional type of sigma mixers or ribbon mixers, the following main components are available.
- Mixing Bowl
- Mixing Blades
- The lid of the Bowl
- Motor
- Rotating Knob
Mixing Bowl
The mixing bowl is the main component of a ribbon mixer or spiral mixer and it is a simple tub-like bowl which is made up of stainless steel grade 316 L.
The materials which we want to granulate are added in the mixing bowl and are mixed with the help of mixing blades for a defined time.
Mixing Blades
The mixing blades in the Sigma mixer are like a spiral shape. These mixing blades are installed in the mixing bowl with the help of a rod.
The mixing blades of a spiral mixer rotate around its axis and perform the mixing action for the excipients & APIs which are used for the mixing or kneading process.
These mixing blades are used for the mixing of materials before kneading to ensure uniform mixing and during the wetting stage, these mixing blades also ensure the uniform spreadability of the binder solution.
Motor
A motor is installed with a Sigma mixer which is used to rotate the mixing blades through the gearbox to perform the mixing action of the materials or excipients present in the mixing bowl or mixing chamber.
Lid Of Mixing Bowl
The mixing bowl is covered with a lid made of stainless steel grade 316L and it is used to cover the mixing bowl during the process of mixing and kneading to avoid the loss of the material during the mixing process and to ensure the operator safety during the process of mixing and kneading.
Rotating Knob
A rotating knob or a handle is used to tilt the mixing bowl to remove the wet mass in a container.
When our kneading process is completed inside the mixing bowl the rotating rod or handle is used to tilt the bowl and the material is removed & collected into the SS containers.
Working Of Sigma Mixer
The working of Sigma mixer or ribbon mixer is very simple, we add the material to be mixed and granulated into the mixing bowl of the Sigma mixer and mix for a defined period of time.
When mixing is completed then we add the binder solution & usually the binder solution is added by the manual method meaning we remove the lid of the mixing chamber and pour the binder over the mixing powders while the blades of Sigma mixer are in motion.
The powders are converted into wet mass and we remove the wet mass with the help of scoops or by tilting the mixing bowl.
Advancement
With advancements in technology, the hopper for binder solution addition is also provided in an advanced type of sigma mixer and two or three choppers are also installed on the sides of the mixing chamber.
Plough mixer
A Plough mixer is another type of low-share mixing granulator which is used for the manufacturing of tablets by using a wet granulation process.A Plough mixer is also used for the purpose of mixing and kneading.
Working Of Plough Mixer
A plough mixer resembles the sigma mixer or ribbon mixer but the main difference is that the mixing blades in plough mixers are like the groves of plough.
The mixing groves are used to mix the powders & to break down the large lumps produced during the kneading step.
The components of the plough mixer are the same as the ribbon or sigma mixer meaning it has the mixing bowl, mixing blades ,lid of bowl, motor and turning handle or rotating knob.
The materials to be mixed are added to the bowl of the plough mixer and are mixed for the defined period of time then manual addition of the binder is done.A wet mass is formed during the granulation process and after completion of the kneading step, the wet mass is removed from mixing bowl by turning the rotating knob.
Advantages Of Low Shear
- These are simple equipment and the cost is not very high.
- The granules produced are of good quality with less ratio of fine.
Disadvantages Of Low Shear
- In low-shear mixing granulators,, more solvent is used for the kneading step as compared to the high-shear mixing granulators.
- The binder spreadability is not as uniform as in the case of high-shear mixing granulators.
- For conventional types of low shear mixing granulators, the binder addition is done by manual pouring.
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