IMPORTANT TABLEMILLACTIONPRODUCT SIZEUSE FORNOT USED FORFriable materialsCUTTER MILLCUTTING20 to 80 meshFibrousCrude(animal andvegetable drug)Roller MillCOMPRESSION20 to 200 meshsoft materialAbrasive materialHammer MillImpact4 to 325 meshalmost all drugsAbrasive materialDisintegratorImpact20 to 80 meshalmost all drugssoft and stickymaterials.Ball MillAttrition andimpact20 to 200 meshBrittle drugssoft materialsFluid Energy MillAttrition andimpact1 to 30 micronssoft and stickymaterialsEdge Runner MillCrushing andshearingModerately hardand friablematerials20 to 80 meshalmost all drugssticky materials

Construction & Working A hammer mill is essentially a steel drum containing a verticalor horizontal rotating shaft or drum on which hammers aremounted. The hammers swings on the ends or fixed to the central rotor. The rotor is rotates at a high speed inside the drum whilematerial is fed into a feed hopper. The material is put into the hopper which is connected withthe drum. The material is powdered to the desired size due to fastrotation of hammers and is collected under the screen.

This are mainly operated at 2500 rpm or 1000 to 2500 rpmfor the reduction of the large sized particles. High speedrotor uses 10000 rpm speed.

ADVANTAGES OF HAMMER MILL It is rapid in action, and is capable of grinding manydifferent types of materials. They are easy to install and operate, the operationis continuous. There is little contamination of the product withmetal abraded from the mill as no surface moveagainst each other. The particle size of the material to be reduced canbe easily controlled by changing the speed of therotor, hammer type, shape and size of the screen.

DISADVANTAGES Heat buildup during milling is more,therefore, product degradation is possible. Hammer mills cannot be employed to millsticky, fibrous and hard materials. The screens may get clogged. Wearing of mill and screen is more withabrasive materials.

BALL MILL These are also knows as tumbling mills. Principle: The ball mill works on the principle ofimpact between the rapidly moving balls and thepowder material, both enclosed in a hollow cylinder. Working: At low speeds, the ball roll over each otherand attrition (rubbing action) will be thepredominate mode of action. Thus, in the ball mill,impact or attrition or both are responsible for thesize reduction.

Advantages: It can produce very fine powder. Ball mill is used for both wet and dry grindingprocesses. Toxic substances can be ground, as the cylinder isclosed system. Rod or bars can also be used as grinding media. (example: Sticky material are size reduced) In ball mill, installation, operation and labour costs are low.

Disadvantages: The ball mill is a very noisy machine. Ball mill is a slow process. Soft, fibrous material cannot be milled byball mill.




Principle Colloidal mill works on the principle of rotor-stator. The size reduction is affected due to shearing, when thematerial is passed between the narrow gap of millingsurfaces of rotor and stator. A rotor turns at highspeeds of 3000 - 20000rpm. The high levels of hydraulicshear applied to the process liquid disrupt structures inthe fluid. Higher shear rates leads to smaller droplets of 1 micron.Based on a rotor rotating at high speed and very closeto a conical stator, the particle size is done by modifyingthe gap between the rotor and the stator

Construction A colloidal mill consist of a high speed rotor and a stator with aconical milling surfaces between Which is an adjustable clearance ranging from 0.002 to 0.03inches. The rotor speed is 3000 to 20000rpm. The material to be ground should be pre milled as finely aspossible to prevent damage to the colloidal mill. Rotors and the stator may be smooth surfaced or rough surface. With the rotor and the stator there is a thin uniform film ofmaterial between them and it is subjected to the maximumamount of shear.

Colloidal Mill

A colloid mill is a machine that is used to reduce theparticle size of a solid in suspension in a liquid, or toreduce the droplet size of a liquid suspended inanother liquid.Colloid mills work on the rotor-stator principle:A rotor turns at high speeds (2000 - 18000 RPM).

Working The material is placed into the mill though the inlet hopper. It is then passed through the narrow gap between the rotor andstator and thus reduced the fine particle size. A colloid mill is a hydraulic shear producing device. The colloid mill works to reduce the size of the suspendeddroplets. The mill allows the solid particles to become so small.

Colloid mills are used in the followingindustries PharmaceuticalCosmeticPaintSoapTextilePaperFood