POWDER METALLURGY Powder Metallurgy or PM is a process of producing components or materials from powders made of metal. Different geometries can be obtained by this process. This may also include non metal powders.
IRON METAL POWDER PM or Powder Metallurgy can drastically reduce the metal removal process to obtain a desired structure, which reduce the yield loss while manufacturing and cut down cost. Powders are generally compressed by applying heat to obtain a specific geometry followed by sintering to achieve a solid part. Many unique materials can be made which is impossible to mold or melt. For example tungsten carbide used for cutting and is used to make other metals in many industries and around 50,000 tonnes per year is made by powder metallurgy. Some other products are:
Automotive parts Sintered Filter (http://catalystrecoveryfilter.com/ , http://sparger.in/ , sintered disc for sensor protection etc) Porous oil impregnated bearing Diamond tool Electrical contact
Steps for Powdered Metallurgy: 1. Powder Manufacturing 2. Blending
3. Compaction 4. Sintering 5. Sizing
Powder Manufacturing Metal used in manufacturing of powder are SS316L, Titanium, SS304, FeCrAl, 904L, Nickel and many more. The two most common processes used in manufacturing of PM are: a. Sponge Iron Process b. Atomization Sponge Iron Process A magnetite (Fe3O4) ore with lime and coke are placed in a silicon carbide retort. The retort is heated in a kiln thereafter where a slag and a sponge iron cake are formed due to reduction process. The iron cake is then crushed and annealed after separating from the slag. The powder obtained is very irregular in shape containing internal pores which looks like a sponge.
SPONGE IRON PARTICLE SHAPE
Gas Atomization A hot liquid metal stream is passed from a orifice at high velocity to generate turbulence and just before the molten liquid stream exit the orifice a gas is injected which creates this turbulence (gas expands due to heating and creates turbulence).
"POWDER METALLURGY SCIENCE" SECOND EDITION, R.M. GERMAN, MPIF- VERTICAL GAS ATOMIZER. The liquid stream is then collected in a collection volume filled with gas where further turbulence is created. With the help of a cyclonic separation, air and powder stream the PM particles are separated. The particles obtained are non porous, smaller, have more breadth in size and are cleaner allowing better compaction. Particles have a pear or spherical structure with an oxide layer over them. Water Atomization It is a technique in which atomized water at high stream is introduced on a molten liquid metal stream which converts the liquid metal stream into drops and cools down the metal powder before it reaches the collection bottom.
"POWDER METALLURGY SCIENCE" SECOND EDITION, R.M. GERMAN, MPIF-WATER ATOMIZATION PROCESS. Milling and chemical are some other techniques to obtain PM metal particles. PM metal particles characteristics: i. Metal Powder Size After manufacturing of metal powder different sizes are obtained with the help of screens which is made up of wire mesh. The screens separate the metal powder depending upon the sizes.
ii.
Metal Powder Shape
The flow characteristic and powder density depends on the shape of the metal powder. Different techniques results in appearance of metal powder.
Water atomization produces irregular shapes with no internal porosity. Gas atomization produces spherical shapes with no internal porosity. Oxide reduction gives irregular shape with substantial amount of internal porosity.
Milling and other mechanical techniques gives variety of shapes. Chemical techniques produce a range of shapes from spherical to angular.
“ATOMIZATION - THE PRODUCTION OF METAL POWDERS" A. LAWLEY, MPIF -THE IMAGES ARE OBTAINED FROM DIFFERENT PROCESSES SUCH AS FIG. 1-SPONGE IRON PROCESS, FIG.2-ELECTROLYTIC PROCESS FOR COPPER PARTICLES, FIG. 3-MECHANICAL PROCESS FOR ALUMINUM, FIG. 4-IRON WATER ATOMIZATION & FIG. 5-NICKEL GAS ATOMIZATION. Metal Powder Compaction It is a process of compressing the metal powder in a vertically oriented tool by applying pressure from top to bottom using a external force in this case a punch tool. After getting the desired shape or structure the compacted shape is ejected from the die cavity. This is the most cost effective manufacturing from rest of the process. The compacted metal powder density is directly proportional to the pressure applied. Commonly used pressure in the metal powder compaction is from 10 to 50 tonnes per square inch or 150 MPa to 700 MPa. Around 15 to 30 metal parts can be obtained by this process. i.
Die Press
Die press Technology Die Press technology can be achieved by hydraulic presses, mechanical and servo-electrical techniques, on a larger scale hydraulic presses are commonly used. The steps involved in a production cycle are:
A known volume of feedstock is filled in a die cavity. Pressure is applied from the top and bottom by using punches for compressing, this generally reduces the density gradient level within compact. Compacted metal is ejected using the pressure applied by the lower punch. The metal powder product is removed from the top using the fill shoe.
Major advantage of this technique is this, that it can make complex geometries. The dimensions which can be achieved are: Area less than 0.65 square centimeter and larger than 160 square centimeter and from 2.54 centimeter to 20 centimeter in length are possible.
Isostatic Pressing and Compaction The metal powder is placed in a mold and then a external pressure is applied by using a gas or fluid as a source. The compacted product is then sintered in a furnace which bonds or fuses the metal particles and increases the strength of the material. This technique is used to make different structure and products very little scrap metal is generated from this process. The material produced through this process is very precise. The product ranges from 0.2 millimeter for axial dimension and 0.5 millimeter for radial dimensions. This technique is more costly and applicable to small production quantities. Amount of pressure needed for compaction are 2000 psi to 10000 psi for non metals and 15000 psi to 40000 psi for most of the metals, approximately. a. Hot Isostatic Pressing Heat is applied to the metal powder from 480 degree Celsius to 1230 degree Celsius by compressing and sintering the part simultaneously. An inert gas such as Argon is used to prevent any chemical reactions during operation. b. Cold isostatic pressing In this technique a fluid is used to pressurize the mold at room temperature. This is followed by sintering the metal powder. A liquid is used as a medium to distribute the pressure uniformly. Industries where the powdered metallurgy is used are: Automotive products Fluid technology Bearings Mechatronics Filter Applications (Refer www.catalystrecoveryfilter.com & www.sparger.in for more details) Industrial porous metal content Read the next step, sintering by clicking the link http://catalystrecoveryfilter.com/free-resources/apiresearch-papers/ scroll through the articles to view sintering process.