MSM_ Unit-IV.pptxMSM _ UNIT - V.pptx material science and metullargy
- 1. UNIT –IV Powder Metallurgy Powder Metallurgy: Basic processes- Methods of producing metal powders- milling atomization- Granulation-Reduction-Electrolytic Deposition. Compacting methods – Sintering - Methods of manufacturing sintered parts. Sintering Secondary operations-Sizing, coining, machining -Factors determining the use of powder metallurgy-Application of this process.
- 5. Methods of producing metal powders
- 6. Production of Metal Powders Metallic powders possessing different properties can be produced easily. The most commonly used powders are copper-base and iron-base materials. But titanium, chromium, nickel, and stainless steel metal powders are also used. In the majority of powders, the size of the particle varies from several microns to 0.5 mm. The most common particle size of powders falls into a range of 10 to 40 microns. The chemical and physical properties of metals depend upon the size and shape of the powder particles.
- 7. various methods of manufacturing powders. The commonly used powder making processes are given Atomization Chemical reduction Granulation Electrolytic process Crushing Milling Condensation of metal vapours Hydride and carbonyl processes
- 9. ATOMIZATION In this process, the molten metal is forced through an orifice and as it emerges, a high pressure stream of gas or liquid impinges on it causing it to atomize into fine particles. The inert gas is then employed in order to improve the purity of the powder. It is used mostly for low melting point metals such as tin, zinc, lead, aluminium, cadmium etc., because of the corrosive action of the metal on the orifice (or nozzle) at high temperatures. Alloy powders are also produced by this method.
- 10. ATOMIZATION
- 13. CHEMICAL REDUCTION In this process, the compounds of metals such as iron oxides are reduced with CO or H2 at temperatures below the melting point of the metal in an atmosphere controlled furnace. The reduced product is then crushed and ground. Iron powder is produced in this way Fe3O4 + 4C = 3Fe + 4CO Fe3O4 + 4CO = 3Fe + 4CO2 Copper powder is also produced by the same procedure by heating copper oxide in a stream of hydrogen. Cu2 + H2 = 2Cu + H2O Powders of W, Mo, Ni and CO can easily be produced or manufactured by reduction process because it is convenient, economical and flexible technique and perhaps the largest volume of metallurgy powders is made by the process of oxide reduction.
- 14. It involves chemical reaction generally a halide or oxide. This may be carried out SOLID STATE: Reduction of iron oxide with carbon and tungsten oxide with hydrogen. THE FORMATION OF SPONGE IRON By Hoganas process: The batch does not move in the process . Quite pure iron ore (fe304) used with carbon and limestone. Contain in cylindrical ceramic container(silicon carbide). Total reduction time is 24 hours and 1200 *C . Limestone used to uncontaminated the sulphur from iron ore. so that pure iron can be obtain.
- 15. TUNGESTON POWDER The ore of tungsten is wolfermite(FeWO4) and scheelite(CaWO4) The ore is mixed in Hcl to form tungestic acid. Tungestic acid is mixed in ammonia to form APT (ammonium paratungastate) APT calcined to give blue oxide. Blue oxide and caustic soda are mixed to give tungsten ppt as Wo3. At 850*c reduction take place and the hydrogen used should be 99.4% pure to give high quality powder.
- 17. GRANULATION The granulation process combines one or more powder particles and forms a granule that will allow tableting to be within required limits. It is the process of collecting particles together by creating bonds between them. Bonds are formed by compression or by using a binding agent.
- 18. TYPES OF GRANULATION Wet granulation In wet granulation, granules are formed by the addition of a granulation liquid onto a powder bed which is under the influence of an impeller (in a high-shear granulator), screws (in a twin screw granulator) or air (in a fluidized bed granulator). The agitation resulting in the system along with the wetting of the components within the formulation results in the aggregation of the primary powder particles to produce wet granules. Dry granulation The dry granulation process is used to form granules without a liquid solution because the product granulated may be sensitive to moisture and heat. Forming granules without moisture requires compacting and densifying the powders. In this process the primary powder particles are aggregated under high pressure. A swaying granulator or a roll compactor can be used for the dry granulation.
- 19. GRANULATION
- 21. In this method, an electrolytic cell is set up as shown in figure. The desired metal is made to act as anode. Anode slowly dissolves and gets deposited on the cathode from where the deposit is removed, washed and dried.
- 22. CRUSHING Process of passing the metal powders against two rollers so that the metal powders are crushed to required size. Crushing requires equipments such as stamp, hammers, and jaw crushers.
- 23. MILLING
- 24. COMPACTING Powder compaction is the process of compacting metal powder in a die through the application of high pressures. Typically the tools are held in the vertical orientation with the punch tool forming the bottom of the cavity. The powder is then compacted into a shape and then ejected from the die cavity.
- 25. COMPACTING / PRESSING OF METAL POWDERS. Pressing the powders into desired part shape as closely as possible to final dimensions Powders are compacted using high pressure. Degree of pressure required depends upon • Required density of final product • Ease with which powder particles will weld together. Compacting processes are Die pressing Roll pressing Extrusion