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### Design of Screw Conveyor

September 8, 2011

The size of screw conveyor depends on two factors

1. The capacity of the conveyor

2. The lump size of the material to be conveyed (Maximum dimensions of the particle)

Usually there are three ranges of lump sizes which are considered for selection of screw size. These are:

· A mixture of lumps and fines in which not more than 10% are lumps ranging from maximum size to one half of the maximum, and 90% are lumps smaller than one half of the maximum size.

· A mixture of lump and fines in which not more than 25% are lumps ranging from the maximum size to one half of the maximum, and 75% are lumps smaller than one half of the maximum size.

· A mixture of lump only in which 95% or more are lumps ranging from maximum size to one half of the maximum size and 5% or less are lumps less than one tenth of the maximum size.

The allowable size of a lump in a screw conveyor is a function of the radial clearance between the outside diameter of the central pipe and the radius of the inside of the screw trough, as well as the proportion of the lumps in the mixture.

The lump size of the material affects the selection of screw diameter which should be at least 12 times larger than the lump size of a sized material and four times larger than the largest lumps of an un-sized material.

Example, if screw diameter is 250mm means radial clearance is 105mm, & Maximum lump size is 60mm of 10% lumps.

Capacity of Screw Conveyor:

The capacity of a screw conveyor depends on the screw diameter, screw pitch, speed of the screw and the loading efficiency of the cross sectional area of the screw. The capacity of a screw conveyor with a continuous screw:

Q = V. ρ

Q = 60. (π/4).D2.S.n.ψ.ρ.C

Where,

Q = capacity of a screw conveyor

V = Volumetric capacity in m3/Hr

ρ = Bulk density of the material, kg/m3

D = Nominal diameter of Screw in m

S = Screw pitch in m

N = RPM of screw

C = Factor to take into account the inclination of the conveyor

Screw Pitch:

Commonly the screw pitch is taken equal to the diameter of the screw D. However it may range 0.75 – 1.0 times the diameter of the screw.

Screw Diameter:

 Nominal Size D Trough height from center of screw shaft to upper edge of the trough Trough width C Thickness of Tough Tubular shaft (d1 * Thickness) Outside diameter of solid shaft Coupling diameter of shaft Heavy Duty Medium Duty Light Duty 100 63 120 – 2 1.6 33.7*2.5 30 25 125 75 145 – 2 1.6 33.7*2.5 30 25 160 90 180 5 3.15 1.6 42.4*2.5 35 40 200 112 220 5 3.15 2 48.3*3.5 40 40 250 140 270 5 3.15 2 60.3*4 50 50 315 180 335 5 3.15 – 76.1*5 60 50 400 224 420 5 3.15 – 76.1*5 60 75 500 280 530 5 3.15 – 88.9*5 70 75

RPM of Screw:

The usual range of RPM of screw is 10 to 165. It depends on the diameter of screw and the type of material (Max RPM of screw conveyor is 165)

The value of loading efficiency should be taken large for materials which are free flowing and non abrasive, while for materials which are not free flowing and or abrasive in nature, the value should be taken low:

Ψ = 0.12 to 0.15 for abrasive material

= 0.25 to 0.3 for mildly abrasive material

= 0.4 to 0.45 for non abrasive free flowing materials

Inclination Factor:

The inclination factor C is determined by the angle of screw conveyor with the horizontal.

 Angle of screw with the horizontal 0° 5° 10° 15° 20° Value of factor C 1 0.9 0.8 0.7 0.65

Types of screw flight:

The screw of the conveyor may be right hand or left hand, the right hand type being the usual design. The threads of the screw may be single, double or triple.

The flight of the screws may be made in either of the two ways:

1. As Helicoids

2. As Sectional flight

Helicoids Flight:

They are formed from a flat bar or strip into a continues helix. The threads are thinner at the outer edge and thicker at the inner edge.

Sectional flights:

Sectional flights are formed from a flat disc and the thickness of the thread is uniform throughout. A continuous helix is made by joining a number of sectional flights together on a piece of pipe and butt welded them. Various styles of screw flights are in use, depending on the service required.

Some of the typical configurations are:

1. Short pitch or continuous flight:

If the conveyor is required to handle dry granular or powdered materials that do not pack, this style of flight may be selected. It is of regular construction and recommended for inclined conveyors having a slope of 20 or more, including vertical conveyors. This style is extensively used as feeder screw.

2. Ribbon flight:

If the conveyor is to handle lumpy, clinging, sticky, gummy or viscous substances, this type flight may be selected. It consists of continuous helical flight formed from steel bar and secured to the pipe by supporting lugs.

3. Cut flight:

In this type of flight screws have notches cut in the periphery of the flight. These notches supplement the conveying with moderate mixing action. They are recommended for conveyors required to handle light, fine, granular or flaky materials.

4. Cut and folded flights:

This type of flight is characterized by notches as in cut flight, together with folded segments. This type of flight creates agitation and aeration resulting in better mixing. This type of flight is used to handle light or medium weight materials having fine, granular or flaky materials.

5. Some screw conveyors have cut flight with paddles mounted at regular intervals. The paddles counteract the flow of material past the flight resulting in greater agitation and mixing.

6. Sometimes screws are made of stainless steel to suit special requirements, like the sanitation requirements for handling food, drugs and other hygienic materials.

### TUTORIAL EXAMPLE-2

August 23, 2011

Drawing 1: Practice The isometric View given in diagram.

Drawing 2: Draw the Above diagrams in any popular mechanical software.

Drawing 3: practice the 2D drawing

Drawing 4: Chair

### TUTORIAL-2

August 23, 2011

This site provides great tutorials / lessons for the student of AutoCAD. These lessons are designed to be as compatible with as many versions of AutoCAD as possible. They are based on AutoCAD 2010, but can be easily adapted to other versions. For better understanding of CAD use this complete post.

### CRYSTAL SYSTEM

August 23, 2011

Crystalline Materials:

• A crystalline material is one in which the atoms are situated in a repeating (or) periodic array over large atomic distances.

Non Crystalline Materials:

• Materials that do not crystallize are called non-crystalline (or) Amorphous materials

Space Lattice:

• Lattice is the regular geometrical arrangement of points in crystal space.

• The atoms arrange themselves in distinct pattern in space is called a Space Lattice.
• Atoms in crystalline materials are arranged in a regular 3 – Dimensional repeating pattern known as Lattice Structure.
• They are divided by network of lines in to equal volumes, the points of intersection are known as Lattice Points.

Unit Cell:

• It is the smallest portion of the lattice which repeated in all directions.
• 3D visualization of 14 Space Lattices are known as Bravai’s Space Lattice.
• If a unit cell contains lattice points only at it’s corners, then it is called Primitive Unit Cell (or) Simple Unit Cell.
• Three edge length x,y, & z and three interaxial angles α, β, & γ are termed as Lattice Parameters.

Crystal System:

• It is a scheme by which crystal structures are classified according to unit cell geometry.

Types of Crystal Systems:

• Cubic
• Tetragonal
• Hexagonal
• Orthorhombic
• Rhombohedral
• Monoclinic
• Triclinic

Crystal Systems

Simple Crystal Structure:

Body Centered Cubic Structure (BCC)

• Unit cell contains 2 atoms
• Lattice Constant a= 4r / √3, where r is atomic radius
• Atomic packing factor APF = 0.68
• Metals are Vanadium, Molybdenum, Titanium, Tungsten

Face Centered Cubic (FCC)

• Unit cell contains 4 atoms
• Lattice Constant a= 4r / √2, where r is atomic radius
• Atomic packing factor APF = 0.72
• FCC structures can be plastic deformed at severe rates
• Metals are Copper, Aluminum, Phosphorous, Nickel, Cobalt etc

Hexagonal Closed Packed Structure (HCP)

• Unit cell contains 3 atoms
• Axial ratio c/a, where ‘c’ is Distance between base planes, ‘a’ is Width of Hexagon
• Axial Ratio varies from 1.58 for Beryllium to 1.88 for Cadmium (Therefore  a=2.9787, c=5.617)
• Atomic packing factor APF = 0.74
• Metals are Zinc, Cadmium, Beryllium, Magnesium etc

Crystallographic Planes and Directions

The Layers of atoms in the planes along which atoms are arranged is known as “Atomic” (or) “Crystallographic planes”.

Miller Indices:

Miller Indices is a system of notation that denotes the orientation of the faces of a crystal and the planes and directions of atoms within that crystal.

Miller Indices for Planes:

1. The (110) surface

Intercepts :   a , a , ∞

Fractional intercepts :   1 , 1 , ∞

Miller Indices :   (110)

2. The (111) surface

Intercepts :   a , a , a

Fractional intercepts :   1 , 1 , 1

Miller Indices :   (111)

The (100), (110) and (111) surfaces considered above are the so-called low index surfaces of a cubic crystal system.

3. The (210) surface

Intercepts :   ½ a , a , ∞

Fractional intercepts :   ½ , 1 , ∞

Miller Indices :   (210)

### X RAY DIFFRACTION

August 23, 2011

It’s useful for studying Crystal structure

This method have the details about

• Grain size (or) Crystal size
• Orientation of the crystal
• Cold worked, Distorted and Internally stressed crystals
• Re-Crystallization
• Preferred orientation etc

Methods of Examining and Measuring the condition of Crystal Structure

1. The Laue back reflection method
2. The Rotating Crystal method
3. The DeBye- Scherrer (or) Powder method:

The Laue back Reflection method:

It’s applicable to single crystals (or) poly-Crystalline masses.

When a beam of Mono chromatic (i.e. of Single Wavelength) X-Ray is directed as a narrow pencil at a specimen of a metal diffraction takes place at certain of the crystallographic planes.

The Rotating Crystal method:

It’s a useful method for determining angles and positions of planes.

Crystallographic planes are brought in to reflecting positions by rotating a crystal (Specimen) about one of it’s axis while simultaneously radially it with a beam of mono chromatic x-Rays.

If crystal orientation planes are known, the angles and directions can be calculated.

The DeBye- Scherrer (or) Powder method:

The narrow pencil of monochromatic X-Rays is diffracted from the powder and recorded by the photographic film as a series of lines of varying armature.

By the Bragg Equation:

nλ=2d Sinθ

Where,

λ– Wave length of X-ray

d- Spacing of the atomic planes

θ – Angle of reflection

### X RAY DIFFRACTION

August 23, 2011

It’s useful for studying Crystal structure

This method have the details about

• Grain size (or) Crystal size
• Orientation of the crystal
• Cold worked, Distorted and Internally stressed crystals
• Re-Crystallization
• Preferred orientation etc

Methods of Examining and Measuring the condition of Crystal Structure

1. The Laue back reflection method
2. The Rotating Crystal method
3. The DeBye- Scherrer (or) Powder method:

The Laue back Reflection method:

It’s applicable to single crystals (or) poly-Crystalline masses.

When a beam of Mono chromatic (i.e. of Single Wavelength) X-Ray is directed as a narrow pencil at a specimen of a metal diffraction takes place at certain of the crystallographic planes.

The Rotating Crystal method:

It’s a useful method for determining angles and positions of planes.

Crystallographic planes are brought in to reflecting positions by rotating a crystal (Specimen) about one of it’s axis while simultaneously radially it with a beam of mono chromatic x-Rays.

If crystal orientation planes are known, the angles and directions can be calculated.

The DeBye- Scherrer (or) Powder method:

The narrow pencil of monochromatic X-Rays is diffracted from the powder and recorded by the photographic film as a series of lines of varying armature.

By the Bragg Equation:

nλ=2d Sinθ

Where,

λ– Wave length of X-ray

d- Spacing of the atomic planes

θ – Angle of reflection

### METALLURGY

August 23, 2011

Definition:

The Process of producing components from metallic powder parts made by powder metallurgy may contain non-metallic constituents to improve the bonding qualities and properties.

Number and variety of products made by powder metallurgy are continuously increasing:

1. Tungsten Filaments for Lamps
2. Contact Point relays
3. Self lubricating bearings
4. Cemented carbides for cutting tools etc.

Characters of Metal Powders:

• Shape:

It is influenced by the way it’s made. The shape may be spherical (atomization) (Electrolysis) flat or angular (Mechanical crushing). The particle shape influences the flow characteristics of powders.

• Particle Size (Fineness) and size distribution:

Particle Size and Distribution are important factors which controls the porosity, Compressibility and amount of shrinkage. Proper particle size and size distribution are determined by passing the powder through a standard sieves ranging from 45 to 150 micrometer mesh.

• Flowability:

The ability of the powders to flow readily and conform to the mould cavity. The flow rate helps to determine to possible production rate.

• Compressibility:

It’s defines as the volume of initial powder (Powder loosely filled in cavity) to the volume of compact part. Depends on particle shape & size distribution.

• Apparent Density:

The Apparent density depends on particle size is defined as the ratio of volume to weight of loosely filled mixture.

• Green strength:

It refer to strength of a compact part prior to sintering. It depends on compressibility and helps to handle the parts during the mass production.

• Purity:

Impurities affects sintering & Compacting Oxides & Gaseous impurities can be removed from the part during sintering by the use of a reducing atmosphere.

• Sintering ability:

It is the ability which promotes bonding of particles by the application of heat.

Powder Metallurgy Process steps:

Manufacture of Metal Powders:

Methods:

• Mechanical pulverization:

Machining, Drilling or Grinding of metals is used to convert them to powders.

• Machining:

It Produces coarse particles (Flack form) especially Magnesium powders.

• Milling or Grinding:

It suitable for brittle materials.

• Shorting:

The process of dropping molten metal through a Sieve or small orifice in to water. This produces Spherical particles or larger size. Commonly used for metals of low melting point.

• Atomizing:

In this molten metal is forced through a nozzle, and a stream of compressed air, stream or Inert gas is directed on it break up into five particles. Powders obtained in irregular in shapes. Atomization commonly used for aluminium, Zinc, Tin, Cadmium and other metals of low melting point.

• Electrolytic deposition:

It’s used mainly for producing iron and copper powders. These are dense structure with low apparent density. It consists of depositing metal on cathode plate by conventional electrolysis processes. The Cathode paltes are removed and the deposited powder is scraped off. The powder is wasted, dried, screened & oversized particles are milled or ground for fineness. The powder is further subjected to heat treatment to remove the work hardening effect.

• Chemical reduction:

It’s used for producing iron, Copper, Tungsten, Molybdenum, Nickel & Cobalt powder process consists of reducing the metal oxides by means of carbon monoxide or Hydrogen. After reduction, the powder is usually ground & Sized.

Forming to shape:

1. The process of mixing the powders is called Blending.
2. The Loose powders are formed in to shape by compacting.