Cutter mill

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Cutter Mills are used to cut the large sized particles into small fine sized particles with the help of knifes present in the cutting mill chamber.

With the help of the knifes present reduction of the particles takes place.

About two or more knifes (stationary or rotating knives) are present or used in the cutter mill for the successive cutting of the materials.

A cutter mills can cut in two directions, sometimes known as conventional or climb milling.

Conventional milling (left): The cut is so light at the beginning that does not cut, but slides across the surface of the material, until sufficient pressure is built up and suddenly bites and begins to cut.

Climb milling (right): The materials are disposed behind the cutter for size reduction. 1,2

Different types of knives used in cutter mill

HISTORY

The history of cutter mill is intimately bound up with that of milling machines. There is a continue of development between the earliest milling cutters by the Jacques de Vaucanson from about 1760s or 1770s and from the 1810s to 1850s (Whitney, North, Johnson, Nasmyth, and others).

The cutters were futhur developed as the geometry that could take successive sharpenings without losing the form of the cut by Joseph R. Brown of Brown & Sharpe in the 1860s.

De Vries (1910) reported, "This revolution in the science of cutter mills took place in the States about the year 1870, and became generally known in Europe during the Exhibition in Vienna in 1873.

When the Worlds Exhibition at Philadelphia in 1876, exhibited to European experts a universal and many-sided application of the coarse pitched cutter mill which exceeded even the most sanguine expectations, the most far-seeing engineers were then convinced of the immense advantages which the application of the new type opened up for the metal working industry, and from that time onwards the American type advanced, slowly at first, but later on with rapid strides".

Woodbury provides a patents for various advances in cutter mill design, including irregular spacing of teeth (1867), forms of inserted teeth (1872), spiral groove for breaking up the cut (1881), and others. He also provides a citation on how the introduction of vertical mills brought about wider use of the end mill and fly cutter types.

Scientific study by Holz and De Leeuw of the Cincinnati Milling Machine Company made the teeth even coarser and did for milling cutters what F.W. Taylor had done for single-point cutters with his famous scientific cutting studies. 3,4

BASIC PARTS, CONSTRUCTION, PRINCIPLE AND WORKING OF THE CUTTER MILL

Basic parts

  • It consists of feed hopper which is used to transfer the material into the chamber (horizontal or cylindrical).
  • The sharp rotary knife cutter has a horizontal rotor with two to 12 knives spaced uniformly for the cutting of the particles by applying attrition or impact.
  • The discharge chute which is used to discharge the fine sized particles.

Construction

  • This consist of two types of knives which are fitted in the mill.
  • These are stationary knives and the rotating knives. The stationary knives are fixed in the casing whereas the rotating knives are attached to the rotor.
  • The upper part of the casing also contains a hopper inlet, whereas the lower part has a screen of desired aperture size.
  • The rotary knife cutter has the horizontal rotor with two to 12 knives spaced uniformly on its periphery turning from 200 to 900 rpm and the cylindrical casing has several stationary knives.
  • The bottom of the casing holds a screen that controls the size of the material discharged from the milling zone. 1,2

Cutting mill

Principle:

The size reduction of the materials is done by the cutting with the help of the sharp knives which provides shearing action rather than attrition or impact. With the help of the shearing action provided by the knives present in the mill shows fines sizes particles output through the discharge chute. 1,2

Working:

  • The material to be cut is put into the hopper of the mill.
  • The fed size should be less than 1 inch thick and should not exceed the length of the cutting knife.
  • For the size less than the 80 mesh the pneumatic product collecting system is required. Under the best operating conditions the size limit of a rotary cutter is 80 mesh.
  • Due to the rotation of the rotor, the material comes very close between stationary knives and the rotating knives. It cuts down the material into the small pieces.
  • Screen retains the material in the mill until the desired degree of size reduction has been affected. The product is collected which comes out of the sieve. 1,2

Cutting mill

PHARMACEUTICAL APPLICATIONS:

  • Cutting mills are used for the tough materials.
  • It is also used for the fibrous materials.
  • The mill is used to obtain a coarse degree of the size reduction of the soft materials such as roots, peels or wood before extraction.
  • Cutting mills are suitable for the grinding of soft, medium-hard, elastic and heterogeneous mixes of products. It is used successfully for a great variety of materials.
  • Examples: Aluminum slag, animal feed, bones, cables, cardboard, electronic components, feed pellets, foils, food, leather, lignite, material mixtures, non-ferrous metals, paper, PET preforms, pharmaceutical products, plant materials, plastic toys, plastics, polymers, refuse derived fuels, resins, rubber, spices, straw, textiles, waste, wood.
  • It is used for coarse materials for crushing. It output produced is 85 kg/h.
  • Mill is generally used for low energy applications, granulation of pharmaceutical powders prior to tableting.
  • It is also used for sample preparations in the pharmaceutical industries. 1-4

OTHER APPLICATIONS

  • The mill can also be used to crush the following materials
  • Examples: Rubber, leather, paper, cardboard, tissues, plastics, wood, non-metallic waste, coal, animal feeds, maize, grain, confectionery, malt, farinaceous products, spices, dried meat, bones, horn, dragees, tablets, leaves, fibers, peat, roots, tobacco, cork, straw or film.
  • The cutter mill can also be used in the pharmaceutical or animal feed industries, in dental, medicinal and metallurgical technology, in veterinary institutes and for RoHS testing.

ADVANTAGES:

  • Cutter mill produces ultra fine particles and yields narrow size distribution.
  • It is simple to install and operate.
  • The speed can be rapidly changed by the rotating knives.
  • The mill efficiency and ease of manufacture, allowing easier local construction.
  • Moreover, maintenance is easy and inexpensive. 3,4

DISADVANTAGES:

  • It is not easy to clean.
  • Wet preparation of the materials cannot be seived due to clogging of the materials take place.
  • Speed should be controlled.
  • Feed thickness should be not more than the thickness of the cutting knives. 3,4

REFERENCES

  1. Lieberman, Herbert A, Lachman, Leon (2009), Industrial pharmacy: Pharmaceutical dosage form-milling. Banglore, Pune. ISBN: 978-81-239-1679-8.
  2. Mehta RM, Pharmaceutics-I: Size reduction (1996), Page no: 90-91.
  3. http://en.wikipedia.org/wiki/Milling_cutter.
  4. http://www.f-t.co.kr/Files/201102/Cutting%2520Mills.pdf

About the Author

Saraswathi.B's picture
Author: Saraswathi.B

Assistant Professor in St. johns college of pharmacy

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