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Size reduction.pptx
- 1. Mr. Mhaske Shubham Balasaheb (Assistant Professor) PRCOP, Loni SIZE REDUCTION
- 2. CONTENTS Size Reduction: Objectives, Mechanisms & Laws governing size reduction, factors affecting size reduction, principles, construction, working, uses, merits and demerits of Hammer mill, ball mill, fluid energy mill, Edge runner mill & end runner mill.
- 6. What is Mesh Size? U.S. Mesh Size (or U.S. Sieve Size) is defined as the number of openings in one square inch of a screen.
- 25. THEORIES OF SIZE REDUCTION / MILLING • A number of theories have been proposed to establish a relationship between energy input andthe degreeof sizereduction produced. • Rittinger’s theory : • Bond’stheory • Kick’stheory • Walker’s theory
- 26. Rittinger’s theory Rittinger’s theory suggests that energy required in a sizereduction process is proportionalto the new surfacearea produced. where, E=energyrequired for sizereduction KR=Rittinger’s constant Si=initial specificsurfacearea Sn=final specificsurfacearea Application:It ismostapplicablein sizereducingbrittle materials undergoingfine milling.
- 27. Bond’stheory • Bond’s theory states that the energy used in crack propagation is proportional to the new crack length produced. • where, E=energyrequired for size reduction • • • KB=Bond’swork index di =initial diameter of particles dn=final diameter of particles • Application:Thislaw isusefulin roughmill sizing.Thework indexisusefulin comparing the efficiency of milling operations.
- 28. Kick’stheory • Kick’s theory states that the energy used in deforming (or fracturing) a set of particles ofequivalent shape is proportional to the ratio of change of size/diameter • where, E=energyrequired for size reduction • • • KK=Kick’s constant di =initial diameter of particles, dn=final diameter of particles • Application:Forcrushingof largeparticlesKick’stheory most useful.
- 29. Walker’s theory • Walker proposed a generalized differential form of the energy-size relationship: Where E=amount of energy(work done) required to producea change D=sizeof unit mass K=Constant n=constant For • • • • • • • • • n=1.0 Walker equation becomesKick’stheory It isusedfor coarseparticles >1 um. n=1.5 Walker equation becomesBond’s theory. Thistheory isusedwhenneither Kick’snor Rittinger’s law isapplicable. n=2.0 Walker equation becomesRittinger’s theory Usedfor fine particles<1 um size.
- 30. VARIOUS EQUIPMENTS USE IN SIZE REDUCTION
- 35. ADVANTAGESOFHAMMERMILL • It is rapid in action, and is capable of grinding many different types of materials. • They are easy to install and operate, the operation iscontinuous. • There is little contamination of the product with metal abraded from the mill as no surface move againsteach other. • The particle size of the material to be reduced can be easily controlled by changing the speed of the rotor, hammertype, shapeandsizeof the screen.
- 36. DISADVANTAGES • Heat buildup during milling is more, therefore, product degradationispossible. • Hammer mills cannot be employed to mill sticky,fibrousandhard materials. • Thescreensmayget clogged.Wearing of mill andscreenismore with abrasive materials.
- 37. BALLMILL • Theseare alsoknowsastumbling mills. • Principle: The ball mill works on the principle of impact between the rapidly moving balls and the powder material, both enclosedin a hollow cylinder. • At low speeds, the ball roll over each other and attrition (rubbing action) will be the predominate mode of action. Thus, in the ball mill, impact or attrition or both are responsible for the size reduction.
- 41. Advantages: • It canproduceveryfine powder. • Ballmill isusedfor both wet anddry grinding processes. • Toxicsubstancescanbeground, asthe cylinder is closedsystem. • Rodor barscanalsobe usedasgrinding media. • (example: Stickymaterial are sizereduced) In ball mill, • installation, operation andlabour costsare low.
- 42. Disadvantages: • Theball mill isavery noisy machine. • Ballmill isa slow process. • Soft, tacky, fibrousmaterial cannotbemilled byball mill.
- 48. ROLLERMILL
- 49. ROLLERMILL https://youtu.be/uwe_ixKCkl4 https://youtu.be/snqeuh0VISE https://youtu.be/cbCdB 0h2MMY
- 50. ROLLERMILL