Archive for the ‘MSM’ category

October 24, 2011

Fatigue

Powder Metallurgy / Introduction / Process / Methods

September 16, 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.

02-PowderManufacturing-metallurgy-particles

 

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:

 

01-powder-metallurgy-process-step by step

 

01-powder metallurgy processes-mixing-finished product

 

02-finished product 

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.

03-mechanical pulverization-milling-powder

04-crushing-shredding-conveyors-powder

 

  • 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.

03-atomization-powder metallurgy

 

  • 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.

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.

01-space-lattice-unit-cell-represenatation

 

 

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.

01-lattice-crystal structure

 

  • 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:

01-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

image


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

0I-bcc-structure-body center cubic02-bcc-structure-body center cubic

03-bcc-structure-body center cubic

 

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

02-fcc-structure-face center cubic-unit cell

0I-fcc-structure-face center cubic-unit cellHexagonal 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

0I-hcp-structure-Hexagonal close packed-unit cell

0I-hcp-structure-hexagonal close packed

0I-hcp ball-structure-Hexagonal close packed-unit cell

 

 

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

02-miller indices-crystalographic planes

 

Intercepts :   a , a , ∞

Fractional intercepts :   1 , 1 , ∞

Miller Indices :   (110)

 

2. The (111) surface

03-miller indices-crystalographic planes

 

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

04-miller indices-crystalographic planes

 

Intercepts :   ½ a , a , ∞

Fractional intercepts :   ½ , 1 , ∞

Miller Indices :   (210)

PLASTIC-2

August 23, 2011

What are Plastics?

Plastics are a material that is made up mainly of macromolecules, that can be made fluid by the action of heating and pressurizing, and that can be processed into end products with any useful shape you want to make.

01-plastic products-plastic household products-Chemical-in-Plastics-to-Cause-Breast-Cancer

Classification of Plastics

Plastics can be classified into:

1. Thermoplastics and Thermo sets
2. Amorphous Thermoplastics and Crystalline Thermoplastics
3. Commodity Plastics and Engineering Plastics

Thermoplastics Vs Thermo sets


01-thermo plastics vs thermosets-difference between thermo plastics and thermosets

Thermoplastics Elastomer

• TPE – thermoplastic elastomer
• Resemble rubber at room temperature
• Can be melt-processed like other thermoplastics
• Become elastic like rubber when cooled

Amorphous Thermoplastics Vs. Crystalline Thermoplastics

01-Amorphous thermoplastics-crystalline thermoplastics

Thermo sets Classifications

01-thermo sets-thermo sets classifications- thermo setting plastics-examples of thermo sets

Commodity Plastics Vs Engineering Plastics

01-difference between commodity plastics and engineering plastics-examples of commodity plastics, examples of engineering plastics

PLASTIC-2

August 23, 2011

What are Plastics?

Plastics are a material that is made up mainly of macromolecules, that can be made fluid by the action of heating and pressurizing, and that can be processed into end products with any useful shape you want to make.

01-plastic products-plastic household products-Chemical-in-Plastics-to-Cause-Breast-Cancer

Classification of Plastics

Plastics can be classified into:

1. Thermoplastics and Thermo sets
2. Amorphous Thermoplastics and Crystalline Thermoplastics
3. Commodity Plastics and Engineering Plastics

Thermoplastics Vs Thermo sets


01-thermo plastics vs thermosets-difference between thermo plastics and thermosets

Thermoplastics Elastomer

• TPE – thermoplastic elastomer
• Resemble rubber at room temperature
• Can be melt-processed like other thermoplastics
• Become elastic like rubber when cooled

Amorphous Thermoplastics Vs. Crystalline Thermoplastics

01-Amorphous thermoplastics-crystalline thermoplastics

Thermo sets Classifications

01-thermo sets-thermo sets classifications- thermo setting plastics-examples of thermo sets

Commodity Plastics Vs Engineering Plastics

01-difference between commodity plastics and engineering plastics-examples of commodity plastics, examples of engineering plastics

PLASTIC

August 23, 2011

Plastics are excellent materials with unique and very useful properties. You can produce just about anything you can imagine using plastics.

01-Plastics-food-containers-durable plastic products-plastic boxes

Characteristics of Plastics

01-plastics-characteristics of plastics-plastic parts-various plastic products

History Of Plastics:

1. Before Plastics—Age of the Natural Resins

  • Rubber—Tough elastic substance (light cream or dark amber
    colored) from the milky juice (sap) of rubber tree
  • Ebonite—Hard black rubber; natural rubber + sulfur
  • Gutta-Percha—Dark brown substance like natural rubber
  • Shellac—dark-brown material from lac insects

2. Bakelite—The First True Synthetic Plastics

  • Leo Hendrik Baekeland invented Bakelite from coal
  • Bakelite helped make 20th century “The Age of Electricity”

01-Reaction to produce plastics-plastic formation-industrial plastic manufacturing-plastic production methods3. Industrialization of Major Plastics

Year Type of plastics Note
1872 Celluloid (Hyatt, USA) Semi-synthetic
1910 Phenolic resin, “Bakelite” (Baekeland, USA) From coal
1931 Polymethyl methacrylate (PMMA) (Rohm and Haas, Ger-many) From coal
1935 Polyvinyl chloride (PVC) (IG Farben, Germany) From coal
1935 Polystyrene (IG Farben, Germany)

From oil

1938 Nylon 6 (IG Farben, Germany)
1939 Nylon 66 (DuPont, USA) From coal
1939 High-pressure low-density polyethylene (LDPE) (ICI, Eng-land)
1953 Polyethylene terephthalate (PET) (DuPont, USA)
1953 Low-pressure high-density polyethylene (HDPE) (Montecatini, Italy) Ziegler catalyst
1955 Medium-pressure high-density polyethylene (HDPE) (Phillips, USA) Phillips catalyst
1957 Low-pressure high-density polyethylene (HDPE) (Hoechst, Germany) Ziegler catalyst
1959 Polypropylene (Montecatini, Italy)
1977 Linear low-density polyethylene (LLDPE) (UCC, USA)
1991 Metallocene very-low-density polyethylene (VLDPE) (Exxon, USA) Metallocene cata-lyst

4. Concept of High Molecular Weight Compounds & Polymers

  • Herman Staudinger, German chemist, proposed a new theory that several thousands of reactive units bonded together in chains and form giant molecules to make up cellulose and rubber
  • In 1920, Staudinger proposed calling such materials: high molecular weight compounds, macromolecules, or polymers.

5. Nylon—The First Tailor-Made Plastics

  • 1931 – Fiber 66 was produced, later called Nylon 66 in 1938