INTRODUCTION TO AN MULTI-MILL and CONE MILL (CO-MILL):
Both Multi-mill and Cone-mill are widely used as Size Reduction equipments, not just in Pharmaceutical Or Nutraceuticals Or Herbal medicine production, but also in Food and Chemicals manufacturing plants. In fact, some of the most popularly observed equipments used in manufacturing organizations include Multimills, Co-Mills and Vibrosifters.
We have discussed in the earlier blogpost (Micronizer/Air Jet Mill) that yield of a chemical reaction or bonding between two molecules becomes better when the particles of the participating material are of smaller and uniform size. Therefore, whether it is the dried API or Flakes Or at times even the Granules obtained from the Granulator are taken for Multimilling Or Co-Milling.
COMPARATIVE STUDY BETWEEN A MULTI-MILL and A CONE MILL (CO-MILL):
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Both Multimill and Co-Mill are often used for coarse milling. Which means, unlike the Micronizer (or AJM), Multimill or Co-Mill can yield the coarse (not so fine) material with an average size of not lesser than 500 microns Or 500 micrometers (35 mesh). However, there are a few specifics of both these equipments, which decides their preference over others, and can be listed as under:
# Multimills are used for size reduction by chopping, shredding, hammering and pulverizing. Whereas, Cone-Mill Or Co-mills are slightly gentle on the material to be grinded.
# Multimill has a set of static and high speed rotating blades and hammers. Co-Mill has a pair of blades in a V shape that simply pushes the material on the peripheral V shaped mesh.
# Since the blades and hammers in a Multimill are designed to cover a specific sweep diamater, the outer Or peripheral mesh Or screen is vertical cylindrical in nature. Whereas, incase of a Co-Mill, the outer screen Or mesh is in a V shaped Cap, as the blades are fabricated to form a V (as shown in the pic above).
# Multimill can handle slightly hard, wet and lumpy materials also, whereas, Co-Mills are advised to be used with dry and not extremely hard materials. Otherwise, there can be chances of chocking of the mesh.
GMP COMPLIANCE OF MULTI-MILL and CONE MILL (CO-MILL):
Both Multimill and Co-Mill can be totally GMP/ cGMP compliant. Because of their simple and economic construction, they are usually made out of corrosion resistant material viz. SS316 for contact parts and SS304 or equivalent material for Non Contact Parts. If need be, the superior materials such as Hastelloy C22 Or C 276 can also be selected.
OTHER ADVANTAGES OF MULTI-MILL and CONE MILL (CO-MILL):
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# Simple Construction: Both these equipments has a set of blades mounted on a central shaft which is directly (or in some cases through a pully drive) attached to an AC Motor. The blades assembly is covered with a pot made out of a mesh or screen which retains the larger size particles and allows the smaller size particles to pass through. The entire assembly along with the drive is supported by a metal stand with castor wheels for easy movement. All these features make both these equipments user friendly.
# Low Cost: Unless constructed with corrosion resistant material like Hastelloy C22 Or C276, both Multimill and Co-Mill are extremely economic, hence are usually purchased by manufacturing units even when their need is not so urgent.
# Possibility of automation: If need be, both Multimill and Co-Mill can be operated through an HMI-PLC. Both these can be integrated in an assembly line and can be automated viz. milling after granulation followed by sieving, Or milling followed by micronizer followed by packaging etc.
# Flameproof Construction: A flameproof motor can be used if need be and so can be the operating and control panel.
# Mobility, Lightweight and Less Floorspace utilization: Both Multimill and Co-Mill comes with a stand with castor wheels and hence can be relocated as and when needed. Both of them are vertically designed and hence requires minimum floor space.
# Low Maintenance: Because of the simple constructions, the chances of breakdown and occasions of maintenance are minimum.
CHALLENGES WITH MULTI-MILL and CONE MILL (CO-MILL):
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Usually the challenging instances with Multimill and Cone-Mill are associated more with the nature of the material handled than the equipment itself. Some of the common challenges can be listed as under:
# Frequent Choking of the Mesh/ Jamming of the Blades: This can take place at times and is usually linked with a particular type of material to be grinded. There could be various reasons behind chocking such as mesh being too fine (say less than 500 micron), material being sticky Or hygroscopic in nature, Or material is too hard etc.
# Material Getting Hot Or Temperature of the output material going much higher than the feed material: This is usually associated with motor consuming more current. The most common reason behind this would be the resistance offered by the material to the blades. This may be because of overloading the equipment (by the user) with the feed material or because of the reasons discussed in earlier point.
# Equipment making strange and loud noise: If the material is overloaded or offering too much resistance to the rotating parts, chances are that they may create a loud noise. There can be chances of friction between some of the metal parts Or wear & tear of some of the parts.
# CIP or SIP incase of integration in Containment Zone: Sometimes milling equipments needs to be integrated in an Isolator along with other equipments. In such cases cleaning and washing of the equipments can become bit of a challenge.
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