Slide 1

SIZE REDUCTION

PREPARED BY : AZWIN BT AHMADOBJECTIVEDefine size reduction processState the important of size reduction processExplain the forces involved in size reduction process, (compressive, impact & shear)Calculate the ratio for the size reduction operationEstimate energy requirement for size reduction by using Rittingers, Kicks & Bond lawDifferentiate and explain the disintegration method of fibrous materialsIdentify and elaborate suitable equipment for different types of foodUnderstanding screening process and identify and elaborate screening processPre-Test 2 State whether these statement are true(T) or false(F)QUESTIONANSWER1.Communition have the same meaning with size reduction2.Shear force is used for fine grinding.3.Energy use in size reduction process in unit horsepower,HP. 4. The force use in hammer mill is compressive force5. The force use in crushing rolls is impact force6. Reduction ratio , NP is the feed size over the final product size7. Kicks law is used for fine grinding8. A screen is a surface containing a number of equally size aperture9. Screening is the unit operation in which a separated into two or more fraction by passing over a tube10. Small capacity plane screens are call fractionDEFINITION OF SIZE REDUCTIONThe size reduction or comminution is a unit operation in which the average size of solid pieces of food is reduced by application of grading, compression or impact forces

THE IMPORTANT OF SIZE REDUCTIONFORCES INVOLVED IN SIZE REDUCTIONDISINTEGRATION METHODS OF FIBROUS MATERIALSCUTTING / SLICINGSliced fruits are much in demand as a desert dish. They present an attractive appearance, the portions produced being of convenient size for eating. Rotary cutting knives are usually employed, the knives being set to cut the material being presented to them often on a vibrating belt into parallel slices or of the desired thickness. In other fruit slicing operations the fruit is forced through a tube containing stationary knife edges arranged radially along the length of the tube. This type of assembly can produce decored, wedge shaped sections from firmer fruits such as pineapple.

SLICING EQUIPMENT

CUBINGCubing is the cutting of materials into cubes that usually follows a preliminary slicing operation which produces slices of the desired thickness. These slices are then fed onto a conveyer belt containing a series of studs which hold the slices in position as the belt carries them against the rotary knife assembly which cuts them into strips. The strips then pass through a further cutting zone at right to the stripping section. This produces the required cube. Dicing Is a method of food preparation in which the food item is cut into small blocks or dice.

CUBING EQUIPMENT

SHREDDINGShredding is torn into small fragments, the average size of the pieces depending on the type of machine and on residence time in the action zone.

Shredding often precedes dehydration, the increase in surface aiding the rate process. Hammer mills are commonly used as shreddersPULPINGPulping is widely used in the processing of lower grade fruits separated during grading.

The fruit, which is edible but unacceptable for whole fruit processing, may be used in jam manufacture.

A combination of pulping and sieving is used with many fruits and vegetables.

A common equipment used for pulping consists of a cylindrical perforated screen containing high speed rotating brushes.

Material is fed to the inside of the cylinder, the brushes forcing pulped material through the perforations.

EQUIPMENT FOR SIZE REDUCTIONHAMMER MILL

A hammer mill is essentially a steel drum containing a vertical or horizontal rotating shaft or drum on which hammers are mounted. The hammers are free to swing on the ends of the cross, or fixed to the central rotor. The rotor is spin at a high speed inside the drum while material is fed into a feed hopper. The material is impacted by the hammer bars and is thereby shredded and expelled through screens in the drum of a selected size.Hammer mill apple shredder for juicing.

CRUSHING ROLLSTwo or more heavy steel cylinders revolve towards each other.Particles of feed are nipped and pulled through the rolls, experiencing a compressive force with crushes them.In some machines a differential speed is maintained between rolls and shearing force also arise.

BALL MILLERA ball mill, a type of grinder, is a cylindrical device used in grinding (or mixing) materials like ores, chemicals, ceramic raw materials and paints. Ball mills rotate around a horizontal axis, partially filled with the material to be ground plus the grinding medium. Different materials are used as media, including ceramic balls, flint pebbles and stainless steel balls. An internal cascading effect reduces the material to a fine powder. Industrial ball mills can operate continuously, fed at one end and discharged at the other end. Large to medium-sized ball mills are mechanically rotated on their axis, but small ones normally consist of a cylindrical capped container that sits on two drive shafts .The grinding works on the principle of critical speed. The critical speed can be understood as that speed after which the steel balls (which are responsible for the grinding of particles) start rotating along the direction of the cylindrical device; thus causing no further grinding.

To be continue