Roller mill

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Roller mill

Roller mills are also known as reduction mills. Roller mills are mills that use cylindrical rollers, either in opposing pairs or against flat plates, to crush or grind various materials, such as grain, ore, gravel, plastic, and others.

Roller mills consist of two to five smooth five rollers operating at different speeds, thus the size reduction is effected by the a combination of compression and shearing action.

The particle size reduction is mainly occurred by the pressure between the two or more rollers present in the mill.

By the attrition of the rollers the reduction in the size takes place and shows free flow properties. 1,2

Different roller mill

HISTORY

The invention of the rolling mill is attributed from Leonardo da Vinci. Earliest rolling mills were slitting mills, which were introduced from what is now Belgium to England in 1590. These passed flat bars between rolls to form a plate of iron, which was then passed between grooved rolls (slitters) to produce rods of iron. Later this began to be rerolled and tinned to make tin plate.

The slitting mill was adapted to producing hoops (for barrels) and iron with a half-round or other sections by means that were the subject of two patents in 1679.

Some of the earliest literature on rolling mills can be traced back to Christopher Polhem in 1761 in Patriotista Testamente, where he mentions History of the is wanted to tilt only one bar with a hammer.

Thomas Blockley of England in 1759 for the polishing and rolling of metals got the pantent. Another patent was granted in 1766 to Richard Ford of England for the first tandem mill. A tandem mill is one in which the metal is rolled in successive stands, Ford's tandem mill was for hot rolling of wire rods.

Rolling mills for lead seem to have existed by the late 17th century. Copper and brass were also rolled by the late 18th century.

The first rail rolling mill was established by John Birkenshaw in 1820. With the advancement of technology in rolling mills the size of rolling mills grew rapidly along with the size products being rolled. Further evolution of the rolling mill came with the introduction of Three-high mills in 1853 used for rolling heavy sections. 4

DESCRIPTION:

This are mills which are used to cut the large sized particles into the small sized particles with the help of the forced or pressure applied between the two rollers. It mainly works on the compression of the rollers.

BASIC PARTS, CONSTRUCTION, PRINCIPLE AND WORKING OF ROLLER MILL

Basic parts

The basic components in the roller mill are as follows:

  • The feed hopper chute which delivers the materials into the mill
  • The grinding or crushing mechanism applied by the rollers
  • The discharge chute which throws out the reduced particle size material

Construction

  • It consists of two cylindrical rollers made of stone or metal, which are mounted horizontally.
  • These rollers are capable of rotation on their longitudinal axis.
  • These rollers may be from a few centimeters up to a meter in diameter.
  • Generally one of the roller is driven directly while the second one runs freely. 1,2

Roller mill

Principle and working of the roller mill

Principle:

The material is crushed by the application of the pressure. The mill works on the principle of compression of the material by applying the pressure on it.

Working:

While working the motor drives the hanger of the grinding roller to rotate through pulley and centre bearing. The roller, which is hung by bearing and pendulum shaft, will roll along the inner circle of the roll ring while the hanger is rotating. The materials which are used to be crushed is fed from the hopper into the gap between the two rollers. Due to the rotation of these rollers, the material is crushed. The gap between the rollers can be adjusted to control the degree of the size reduction. A dust removal blower will generate negative pressure at the inlet and outlet of the grinder to prevent dust and radiating the heat in the machine. 1,2

Roller mill

Types:

RMS roller

  • RMS is used in particle reduction industry over 25 years and used to build the best products in the in the pharmaceutical industries.
  • This machines are designed with performance safety and reliability.
  • Ease of Maintenance
  • Easy of rolls changing and convenient in operation.
  • Which in turn reduces cost and minimizes down time. 3,5

RMS roller mill

Monster Mill MM3 3-Roller Mill

  • It is fabricate or supply with base, hopper, and corded electric drill.
  • Fully adjustable mill.
  • Three six-inch steel rollers form two gaps, a preliminary fixed gap of approximately 0.060 and a fully adjustable secondary gap. 3,5
  • The MM3 has a gap spacing adjustment range of 0.065.

Monster Mill MM3 3-Roller Mill

Rollers used in roller mill

PHARMACEUTICAL APPLICATIONS:

  • The roller mill is used for crushing and cracking of seeds before extract of fixed oil from the same.
  • It is also used to crush the soft tissues to help in the penetration of the solvents during the extraction process.
  • Roller mill is an dust tight design for the chemical and pharmaceutical industry.
  • The roller mill allows crushing with a narrow particle size distribution. The narrow particle size spectrum is achieved by means of a continuous compressive shear action between two corrugated rollers with a defined roller gap.
  • Suitable for grinding ointment, paste, paints, printer's Ink etc.in the pharmaceutical, plastic industry.
  • Mostly used in pharmaceutical, chemical, food, cement, tobacco and mineral industries.
  • Rolling mill machinery is used for dry material, agglomeration, granulation systems and rolling mill operations.
  • It is used in wide variety of materials within the food, chemical & mineral industries. System capacities range from 10 kg to 100 metric tons per hour.
  • It can also used pharmaceutically in finely disperse, mix, refine or homogenize viscous materials. As a result minimal particle size milling down to submicron level occurs.
  • Wide range of industries uses roller mill for paints, inks, thick film pastes, adhesives, coatings, ceramics, cosmetics, food, and pharmaceuticals. 3,5

OTHER APPLICATIONS

  • Specialized for the high production of superfine pyrophyllite powder making in glass fiber industry.
  • Specialized for the high production of gangue powder making in coal industry.
  • Specialized for the high production of various of chemical raw material powder making in the chemical industry.
  • Roll Mill finds its application in the fields of toners, lubricants, plastics pharmaceuticals. It is useful for high speed granulating, pulverizing, mixing chemicals, pharmaceuticals, dyestuff, colors, ceramics, food products, cosmetics, pesticides, fertilizers, plastics, spices, bakeries, resins, insecticides etc. 3,5

ADVANTAGES:

  • Energy efficient
  • Uniform particle-size distribution
  • Little noise
  • Dust generation.

DISADVANTAGES:

  • If the temperature of the work piece is not uniform the flow of the material will occur more in the warmer parts and less in the cooler.
  • If the temperature difference is great enough cracking and tearing can occur.
  • Roll deflection
  • Maintaining a uniform gap between the rolls is difficult because the rolls deflect under the load required to deform the work piece.
  • Little or no effect on fiber materials.

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.
  3. http://www.feedmachinery.com/glossary/equipment/roller_mills.
  4. http://en.wikipedia.org/wiki/Rolling_(metalworking).
  5. http://www.directindustry.com/prod/neuhaus-neotec/roller-mills-pharmaceutical-industry-3759.

About the Author

Saraswathi.B's picture
Author: Saraswathi.B

Assistant Professor in St. johns college of pharmacy

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