m*material entering=m*material leaving

(a)  

to determine the amount of energy required to carry on the operation

(a)  

The materials being processed tend to approach a definite condition of equilibrium which is defined by the specified conditions

(a)  

to determine the rate in which operations can finish a product at a specific amount of time

(a)  

𝝆𝒃𝒖𝒍𝒌=𝒕𝒐𝒕𝒂𝒍 𝒎𝒂𝒔𝒔/𝒕𝒐𝒕𝒂𝒍 𝒗𝒐𝒍𝒖𝒎𝒆

*intrinsic characteristic of the material since it varies with the size distribution of the particle and its environment

(a)  

𝟏−𝑩𝒖𝒍𝒌𝑫𝒆𝒏𝒔𝒊𝒕𝒚/𝑷𝒂𝒓𝒕𝒊𝒄𝒍𝒆𝑫𝒆𝒏𝒔𝒊𝒕𝒚

*the amount of available spaces void spaces) of a raw material in which water or air (or other materials) can fill up with

(a)  

Nonporous materials have a density equal to its true density.

Example: diamond, block of

pure aluminium

Compare: Raw material of talc

(a)  

Porous materials have lesser mass compared to its

nonporous counterpart.

(a)  

in reality, contains

moisture (20% water)

contains air on void spaces

(a)  

Moisture is an important factor when dealing with materials

such as (a)  

Resistance of material to indentation

*can be brittle/frail and these two properties are not

synonymous with each other

(a)  

the resistance to impact; the inverse of friability

* Mechanical equipment must have support that have high (a)  

those employing a selective barrier such as screen or a filter media

(a)  

those depending on the difference of phase or

density alone,

(a)  

those depending on the fluid and particle

mechanics

(a)  

those depending on the surface, electrical, or

magnetic properties of particles

(a)  

a mechanical operation that is generally used in separating large particles into specific size fractions

(a)  

is done by passing the mixture of material in a feed moving through uniformly spaced opening of the desired size as the base

* is a method of separating particles according to size alone.

It is accomplished by passing the material over a surface provided with openings of the desired size. The equipment may take the form of stationary or moving bars, punched metal plate, or woven wire mesh.

* consists in separating a mixture of particles into two or more portions, each of with is more uniform in size of particles than is the original mixture.

simplest method for laboratory sizing consists in passing the material successively over a series of screens or sieves having progressively smaller openings.

(a)  

Applications of Screening

(a)  

to remove the coarse particles for further size reduction

(a)  

to remove the fine particles from crusher feeds to save power by preventing over grinding

(a)  

to grade the crushed products into commercial sizes

(a)  

to perform a step for a subsequent process

(a)  

It is the single piece of raw material being fed into the screen.

* raw material are then separated using the screen.

(a)  

must be well understood before designing screens

(a)  

the mean distance between two parallel tangents to the projected particle diameter

(a)  

the mean chord length of the projected particle perimeter

(a)  

the clear size between the individual wires of the screen

(a)  

w

(a)  

d

(a)  

p (distance between

midpoints of wires)

(a)  

number of screen

apertures per unit length

(a)  

The _____ the mesh number, the _____ the screen is.

(a)  

the relationship between the successive sizes of

screen openings in a series.

(a)  

for smaller apertures

(a)  

for careful work and research

(a)  

the particles that pass through the apertures (opening) of the screen

• particles are smaller than the aperture screen size

• Commonly denoted by the negative sign

(a)  

when particles tend to block the screen apertures (opening), and thus prevent screening or presence of near mesh particles that have sizes very close to the screen aperture size

(a)  

the drying of a material containing a natural amount of moisture or a material that has been dried before screening

(a)  

a category for screening fines and moist materials whose screening is very difficult without washing

(a)  

____ the undersize particles

through the screen and ______ the

oversize particles

(a)  

material to be screened is delivered to the screen surface at a continuous rate

• Particle loses its vertical component of velocity and undergoes a change in direction of travel

* essentially lets the large particles (oversize) rise to the top of the material bed while the smaller particles sift through the voids and find a way to the bottom of the screen surface (bed) to reach the screen apertures (openings)

(a)  

Stroke characteristics

(a)  

Factors Affecting the stratification

Process

(a)  

how frequent does undersize particles pass through the screen how frequent does oversize particles retain in the screen

- a function of particle size and

opening

(a)  

•Particles that have dimensions of 1.5 times the screen opening (are less important for the screening result as these will not all pass through

•Particles that have lesser than the 0 5 size of the screen opening have lesser importance since they pass through easily

(a)  

0.5𝑤<𝑑𝑝<𝑤= require several attempts before passing

through

𝑤<𝑑𝑝<1.5w= may clog many openings before leaving the screen as they are oversized material

(a)  

usually made of steel bars, discarded rails, or cast iron bars

- ideal screening surface for primary screening

(a)  

-made of metal or plastic sheets punched by dies of various

patterns

- circular, square, hexagonal, slot like

(a)  

used in finer screens

- are crimped so as to avoid distortion upon impact of feed

(a)  

with three different crimp styles in a single weave

(a)  

ideal for materials that have needle like shapes

-the percentage of openings with respect to the total screening surface is greater compared to square types

(a)  

screens offer distributed loads throughout the screen allowing for

coarser work.

(a)  

Material construction for screening surfaces

(a)  

For ____ _______additional support can be applied by reinforcing the fine screen with a coarser and stronger screen.

(a)  

carbon steel and alloy steel

(a)  

iron, bronze, copper, monel (nickel 52% 67% and copper alloy), stainless steel

(a)  

widely used for screening large percentage of coarse particles with sizes 20 to 300 mm and more

- can be stationary at an angle 20 50 or moving

(a)  

Screening factors

(a)  

moisture content feed material to be resize and reduce

(a)  

(2)Factors affecting the screening operation

(a)  

resistance of a material moving against another material

(a)  

friability

*property of materials easily broken by impact

(a)  

the particles that retain in the screen

•are larger than the screen aperture size.

•Commonly denoted by the positive (+)

sign.

(a)  

inverse of friability

(a)  

the factor that affects the screening operation that arises when particles are extremely dry

(a)  

for finer-size separations, these perforations are more preffered than the others due to lesser tendency to blind

(a)  

mass per unit volume

(a)  

the ratio of the density of a material to the density of some reference substance

For solids and liquids, the reference substance is usually water at 4 C

(a)  

Those crystalline planes which are easily broken are termed

(a)  

is the ratio of the force parallel to the surface of friction in the direction of motion required to maintain a constant velocity to the force perpendicular to the surface of friction and normal to the direction of motion.

(a)  

usually constructed about 3 to 4 ft wide with the bars from 8 to 10 ft in length

approximately 100 to 150 tons of material per square foot of area per 24 hr when the bars are spaced to give about 1 in. of clear opening

(a)  

* made of punched metal plate or woven wire mesh, usually set at an angle with the horizontal up to about 60 degrees

• suitable for intermittent small-scale operations, such as screening sand, gravel, or coal by throwing the material against the screen

(a)  

are used where large tonnages are to be treated, widely used screen equipment

is imparted to the screen surface by means of cams, eccentric shafts, unbalanced flywheels, or electromagnetic means

(a)  

high amplitude, low speed

(a)  

low amplitude, high speed

(a)  

characterized by a relatively low speed (300 or 400 oscillations per minute) in a plane essentially parallel to the screen

(a)  

a screen driven in an oscillating path by an eccentric or other mechanism attached to the sole support of the screen, usually a vertical bar extending from the top of the screen box

• it is the cheapest form of screen on the market and is used for batch screening

(a)  

boxlike container holding a number of screen cloths nested on top of one another and oscillated by an eccentric or counterweights in a nearly circular orbit

(a)  

consists of a series of decks with its own discharge spout

(a)  

are driven by an eccentric under the screen at the feed end

this type of screen is popular and widely used for screening dry chemicals down to about 300 mesh

(a)  

are revolving screens consisting of a screen cylindrical or conical in form rotated about its axis

(a)  

are revolving screens driven at relatively high speed

• they are used in the flour milling industry and for other light, dry, nonabrasive material

generally 24 to 40 in. in diameter and 5 to 8 ft long, and they are rotated at speeds that may vary from 100 to 200 RPM

(a)  

frequently employed to measure particles of dust from the atmosphere and to evaluate the effectiveness of air filters.

the size may be determined by simple measurement of a photomicrograph of known magnification

This number divided by the optical magnification of the objective and eyepiece will give the true dimension in inches or other units.

(a)  

are based on the fact that small particles of a given material fall in a fluid at a rate that is proportional to their size

These portions are evaporated to dryness, and the residues weighed.

• Other modifications have been developed, such as having one balance pan suspended in the pulp of suspended solids and weighing at intervals as the particles settle on the pan.

(a)  

also depends on the velocity of settling.

• If the material is placed in a rising stream of fluid having a fixed upward velocity, particles whose normal falling velocity is less than the velocity of the fluid will be carried upward and out of the vessel.

• If fractions obtained from a series of fluid velocities are collected and weighed, a complete size analysis may be obtained

(a)  

generally used for control and analytical work.

(a)  

evaluated by determining the percentages of materials passing or materials retained on specified testing sieves

(a)  

tyler screen standard

(a)  

steps for a screen analysis

(a)  

methods of making a scree analysis

(a)  

signifies a composite individual representative of an entire group of similar but not identical specimens.

property should be capable of multiplication by the number of specimens in the entire group to give a total value for that property.

(a)  

mass fraction retained on each screen versus average screen aperture

(a)  

mass fraction passing each screen versus particular screen aperture may be the basis for comparisons of different mixtures of the same materials, indicating changes with time or shipment.

(a)  

sample is taken to the sieve tester where it is shaken for a specific amount of time

(a)  

is that diameter which, when multiplied by the number

of particles, will give the sum of all the diameter in that group.

(a)  

that surface by which the total surface area may be obtained

(a)  

is that volume or mass from which the total volume or mass of the group may be obtained by multiplying by the number of particles.

(a)  

measured by the mass of material that can be fed per unit time to a unit area of the screen.

number of tons of material that 1 sq ft will pass per hour.

(a)  

may be defined as the ratio of the amount of material passing through a screen divided by the total amount that is small enough to pass through, with the ratio expressed as a percent.

(a)  

factors that affect the capacity of a screen

(a)  

obtained for a given capacity depends on the nature of the screening operation.

(a)