Department of Metallurgical Engineering

Transcription

1 PRACTICAL WORKBOOK MY-406: POWDER METALLURGY Name Roll No Batch Year NED University of Engineering and Technology 1

2 PRACTICAL WORKBOOK MY-406: POWDER METALLURGY PREPARED BY: ENGR. MUHAMMAD RIZWAN (LECTURER MYD) This is to certify that this practical book contains pages. NED University of Engineering and Technology Approved by: Approved by:chairman Chairman MYD 2

3 CERTIFICATE It is Certified that Mr. / Miss Student of class Batch Bearing Roll No. has completed his/her course work in the subject of as prescribed and approved by. His/her performance is reflected by index/contents of his/her practical workbook. This overall performance of the student is Excellent/Very Good/Good (satisfactory)/not Satisfactory Course Teacher 3

4 TABLE OF CONTENTS Practical No. Practical Objective Page No. Remarks 01 To study risks, hazards and safety precautions in Powder metallurgy laboratory. 02 To determine powder properties through simple examination and testing techniques To determine apparent density and powder flow rate with the help of Hall Flowmeter. 04 Study the effect of compaction pressure on the green density of the compacted parts To produce Iron powder electrolytically Determination of split density of green compacts by Archimedes principle. 07 Perform sintering on different temperatures and study its effect on microstructure of sintered parts. 08 Determination of oil content and open pores of powder metal bearings. 09 Perform slip casting, after sintering compare its density with conventionally compacted and sintered parts. 10 Determination of Radial crushing strength of bushes manufactured through Powder metallurgy

5 PRACTICAL 1 OBJECTIVE: To study risks, hazards and safety precautions in Powder metallurgy laboratory. INSTRUCTIONS: 1. Wash your hands before entering in the lab and wear protective clothing, such as lab coats or aprons, gloves, and eye wear. Be sure that your work area should be clean and dry. 2. Never attempt to operate any equipment without prior instruction. 3. Work in the laboratory only when a lab instructor is present, and only on authorized experiments. 4. Do not bring any unnecessary items into the lab. Do not place any personal items (purses, book bags, coats, umbrellas, etc.) on the lab table or at your feet. 5. Make sure all apparatus is supported and squarely situated on the table. 6. Do not put anything in your mouth while in the lab. Never eat, chew gum, drink, taste chemicals, mouth pipette, lick labels, smoke, or store food or drink in the lab. DO NOT bring food and drink into the laboratory. POWDER HANDLING PRECAUTIONS: Certain powders of metals and metallic compounds can have harmful effects on users exposed to these powders. Powder handling requires proper safety precautions and cleanliness. Persons exposed to metallic dust can be affected by respiratory diseases or other dysfunctions. The particle size and the specific gravity of the material largely determine the deposition site for a respirated particle. Coarse particles are trapped on the precious membranes and do not reach the lungs; fine particles, however, can reach the lungs and may be dissolved into the body. However, special care is needed when using elemental powders as alloying elements (e.g. Cr, Ni, As, Cd). Contact with these metals in the powdered state should be minimized whenever possible. Another hazard with aluminum based powders and several others is their thermal instability in the presence of oxygen. Aluminum powders in a finely divided state are pyrophoric (burn in air) and potentially explosive. Aluminum powders require very little oxygen content in the atmosphere (less than 3 %), have a low ignition temperature (less than 600 C) and very low explosive limit (20-50 g/m3). Explosion and fire prevention is based on the evaluation of: Potential ignition sources (e.g. Electrostatic discharge); Dust cloud generators; Gaseous atmosphere composition. If a fire occurs in a metal powder, the fire should be approached with extreme caution. The best way to attack burning metal powder is with special dry-type fire extinguishing agents. Water should never be applied to fires of metal powders. 5

6 POWDER COMPACTION PRECAUTIONS: Never place your hand or any part of your body in compaction press. Never operate press when it is not working properly, stop working and immediately inform to your instructor. Never approach press up to its limit or beyond always keep load at least 5 tons less than its upper limit for safe operation. Clean pressing area after each job. Never try to change die or place your finger without first releasing the pressure. SINTERING PRECAUTIONS: Immediately inform to your instructor if atmospheric gas is found to be leaking. Never try to pick parts with bare hands when they are hot after sintering Do not operate the sintering furnace once sintering cycle has started. EXERCISE1 Q1. Write down the names of materials which can be carcinogenic in particulate form. Q2. Name the type of fire extinguishers/fire extinguishing techniques for different types of fires. 6

7 PRACTICAL 2 OBJECTIVE: To determine powder properties through simple examination and testing techniques. MATERIALS & APPARATUS: Copper powder, Aluminum powder, paper, Test tube, Beaker, Measuring cylinder, Weighing Balance. THEORY: Powder characterization is vital for tailoring and determining the ultimate mechanical properties of the final finished product. Hence, examination and testing of powders prior to use is thus essential. Such testing can be of a restricted nature, involving only such simple tests as microscopic examination, flow, bulk density and sieving tests etc. Simple tests can be conducted to ascertain the basic powder characteristics such as particle size and size distribution, particle shape, apparent density, and particle microstructure. Perform the following tests on the powder material provided: i) Visual test ii) Tactile test iii) Adhesion test iv) Flow test v) Packing test vi) Sedimentation test Powder properties such as particle size, density, flow and packing should be qualitatively examined and estimated through these tests and commented on in the observation section. PROCEDURE: 7

8 OBSERVATIONS: Mention the results of each test for the powdered material provided. EXERCISE2 Q1. What are important shapes of metal Powders? Also attach a figure explaining these shapes. Q2. Enlist the advanced methods for characterization of powders. 8

9 PRACTICAL 3 OBJECTIVE: To determine apparent density and powder flow rate with the help of Hall Flowmeter. MATERIALS & APPARATUS: Metal powder, Hall Flowmeter and Stop watch. THEORY: Flow rate and apparent density are two most important characteristics of metal powders. Both of these tests are performed with the help of a simple apparatus called Hall Flowmeter. These two tests are very common in Powder Metallurgy industries. These tests are very helpful in the determination of die filling capability of metal powders. Fig1: Schematic view of Hall Flowmeter. 9

10 MEASURING FLOW RATE BY HALL FLOW PROCESS: 1. Take 50 gm powder which has to be tested in a density cup. 2. Carefully fill powder into the Flowmeter funnel keeping the discharge orifice at the bottom of the funnel closed by placing a dry finger under it. 3. The stop watch should be started at the instant when powder starts coming out of the orifice after the removal of finger from the discharge orifice and stopped at the instant the last of the powder leaves the funnel. 4. The elapsed time in second shall be recorded. 5. Same procedure should be repeated three times with different samples. 6. Take the mean of reading which will be the flow rate of powder. OBSERVATION: S.No Flow Rate (sec/50gm) Average Flow Rate (secs/50gm) APPARENT DENSITY: 1. The test specimen shall consist of a volume of 25 c.c. of metal powder whose apparent density to be carried out. 2. The entire specimen should be carefully loaded into the flow meter funnel and permitted to flow through the discharge orifice into the density cup having capacity of 25c.c. 3. When the powder completely fills and overflows the periphery of the density cup, the funnel shall be rotated approx 90` in a horizontal flare so that the remaining powder falls away from the cup. 4. Using a non-magnetic spatula with the blade hold perpendicular to the top of the cup, the powder in excess will be removed this way. 5. The density cup along with the filled powder is now placed on the mass balance & the mass of powder is calculated. 6. The observed mass is now divided by the volume i.e. 25c.c to get the apparent density of the powder used. 10

11 OBSERVATION: S.No Apparent Density (gm/cm 3 ) Average Apparent Density (gm/cm 3 ) RESULT: Average flow rate of metal powder is found to be secs/50gm Average flow rate of metal powder is found to be gm/cm 3 EXERCISE3 Q1. Define and compare the following terms: Apparent density, Tap density, Bulk Density, Green Density. Q2. What is Carney funnel and why it is used? Q3. Write down the name of standard which deals with the chemical composition of Metallic powders. 11

12 PRACTICAL 4 OBJECT: Study the effect of compaction pressure on the green density of the compacted parts. APPARATUS: Metal powder, Binder, Compaction press, Vernier caliper and Weighing balance. THEORY: Compaction is an important step in powder processing as it enables the forming of loose metal powders into desired shapes with sufficient strength to withstand handling till sintering is over. This step is also a precursor to the manufacture of near net shape parts, which is an important advantage of P/M processing. Metal powders are mixed with a lubricant prior to compaction. The term compaction is used to describe consolidation of powder particles without the application of heat. Compaction is followed by sintering to make the finished parts. There are many methods of compaction and the choice is dependent on the application as well as the scale and economy of operation. In many cases, it is advantageous to cold press a mixture of the component powders because of ease of compaction. However, it may be advantageous always: for example sintering of compacts containing elemental zinc is difficult, while pre-alloyed brass powders is easily cold pressed and sintered. Generally, pre-alloyed powders are hard and cannot be readily cold pressed. Fig.2 Compaction Press 12

13 PROCEDURE: OBSERVATIONS: Specimen Compaction Pressure (Mpa) Green Density (g/cm 3 )

14 GRAPH EXPLAINING THE RELATION BETWEEN COMPACTION PRESSURE AND GREEN DENSITY OF THE PART: EXERCISE4 Q1. Write down the names of several compaction techniques used in Powder metallurgy. Q2. What are different types of lubricating techniques, write down their advantages and disadvantages? 14

15 PRACTICAL 5 OBJECT: To produce Iron powder electrolytically. APPARATUS: Power supply battery of 5 amps, Sulphuric acid, Ferrous sulphate 100 gm, Stainless steel rod and Beaker. THEORY: Electrodeposition of metals from solutions produces a variety of metal powders. Direct deposition of powder or sponge on the cathode is achieved by controlling the composition (concentration of metal and ph), temperature, and rate of circulation of the electrolyte, current density; size and type of anode and cathode and their distance from each other; quantity and type of addition agent; and removal of deposits at the cathode (brush-down interval). The shape of electrolytically produced powder particles depends on the metal deposited and the operating conditions. Electrolytic iron, copper, and silver are the most widely used powders made by this technique, but tin, chromium, beryllium, antimony, cadmium, lead, and zinc powders also have been produced by electrodeposition. In modern practice, a chloride or sulfate electrolyte is used with soluble low-carbon steel or ingot iron anodes and stainless steel cathodes. Cathodes are stripped of deposited iron. The iron deposits are pulverized subsequently in ball or hammer mills, and the powder then is annealed in hydrogen to make it softer. PROCEDURE: 15

16 OBSERVATION: gm Iron powder is produced in minutes. RESULT: The morphology of electrolytically produced Iron powder is found to be. EXERCISE 5 Q1. Write down the several shapes of powders with respect to their powder production techniques. Q2. What is Mechanical alloying and what advantage it adds to Powder metallurgy? Q3. What are Metal foams and how they are produced through Powder metallurgy? 16

17 PRACTICAL 6 OBJECT: Determination of split density of green compacts by Archimedes principle. APPARATUS: Green compacted parts, Water beaker, Weighing balance and Wire for hanging sample. THEORY: Powder Metallurgy (PM) is a high volume manufacturing technique that offers a reduction in production costs and a reduction in material waste over conventional manufacturing techniques. However, a current challenge facing the PM industry is non-uniform powder density of the compacted product as a result of die wall friction. Part density has to be carefully controlled in order to achieve a high product quality and as such, density analysis is an important technique in compaction processes. Non-uniform powder density results in decreased mechanical properties that can ultimately lead to part failure. Density analysis offers a way of evaluating the compaction process and also allows for identifying problematic areas of steep densification gradients. There are several established techniques that can be used to analyze density distributions including; Archimedes method, and ultrasonic velocity, laser ultrasonic s and X-ray radiography. Archimedes method is an inexpensive way to measure density. In this method molded green part is split into two equal parts, the density of each part is measured separately and the difference in their densities is called split density. If the value of split density is within specified limits the part may be considered as up to the mark otherwise it will be rejected. Fig3: Apparatus for split Density 17

18 PROCEDURE: EXERCISE 6 Q1. What do we mean by full density processing in Powder metallurgy? Q2. What Heat treatments can be used in Powder metallurgy to enhance the properties of final products? 18

19 PRACTICAL 7 OBJECT: Perform sintering on different temperatures and study its effect on microstructure of sintered parts. APPARATUS: Compacted samples, microscope and suitable etchant THEORY: Sintering is one of the most important steps in Powder Metallurgy processing. It is the process of consolidating either a loose aggregate of powder or a green compact of the desired composition under controlled conditions of the temperature and time. Sintering may involve: (1) single component system (e.g. pure metals and ceramics), where in shrinkage is major factor (2) multiucomponent system, involving more then one phase, where several processes like solid solution formation and liquid phase formation may also occur in addition to densification. Major variables in the sintering process are following: (1) Sintering Temperature (2) Sintering Time (3) Sintering Atmosphere Temperature is an important parameter in sintering and must be closely controlled in order to achieve the desired density and properties. Too high or too low a temperature during sintering will have adverse effects on the microstructure as well as properties. Fig4: Schematic representation of industrial sintering furnace. 19

20 PROCEDURE: CONCLUSION: 20

21 EXERCISE7 Q1. Write down the name of most common sintering atmospheres. Q2. What is sinter hardening? Q3. What is spark plasma sintering? Q4. What is Ostwald ripening and what effect it produces on sintering? Q5. What is the mechanism of sintering also draw a diagram to explain sintering mechanism? 21

22 PRACTICAL 8 OBJECT: Determination of oil content and open pores of powder metal bearings. APPARATUS: Weighing balance, Atmosphere controlled furnace and oil impregnated self lubricating bearings. THEORY: Nothing runs without bearings motors, video recorders, CD players, fans, etc. Window blinds, seat adjusters, sun roofs cannot move without bearings. The properties of self lubricating bearings are determined by the defined density of the bearing material. The resulting number of pores acts as a reservoir for the lubricant. Through linking of the pores, a canal system is produced which forms a lubricating film on the contact surface and helps to circulate the lubricant. In runningcondition, within a short time an equilibrium is established in the circulation of the lubricant. Pressing Impregnation Sintering Schematic view of preparation of Oil impregnated Powder Metallurgy bearings. To determine the oil content of bearings, First of all weigh the impregnated samples in air and then heat the samples in furnace upto sufficiently high temperature (Usually 439 to 650 o C ) to evaporate the oil and weigh sample again and again until the mass of the sample becomes constant. The weight content of oil in the sample is calculated using the equation»c m =[(m 1 -m 2 )/m 1 ]x100 The volume content of open pores in the sample is calculated using the equation» V op =[(m 1 -m 2 )/m 1 ]x100 Where; C m = Percentage mass difference before and after removal of oil. m 1 = Mass before removal of oil. m 2 = Mass after removal of oil. V op = Percentage volume of open pores 22

23 PROCEDURE: CALCULATIONS: RESULT: Oil content percentage of bearings tested is found to be Open pore volume percentage of bearing tested is found to be EXERCISE8 Q1. What do we mean by full density processing in Powder metallurgy? Q2. Write the names and properties of oils used for impregnation of bearings. 23

24 PRACTICAL 9 OBJECT: Perform slip casting, after sintering compare its density with conventionally compacted and sintered parts. APPARATUS: Any solvent for metal powder, Mould and sintering furnace. THEORY: Slip casting is frequently used for compacting metal and ceramic powder to make large and complex shapes as well as for limited productions runs. Slip is a suspension of metal and ceramic powder (finer than 5 µm) in water or other suitable liquid which is poured into an absorbent (usually plaster of paris) mould, dry and subsequently sintered. The slip to be cast is taken in the form of suspension of the metal powder in a suspending medium. The slip should have a low viscosity so that it can be readily poured. It should be stable during standing and have a low rate of setting, the slip cast shape should be readily removable from the mould, it should have a low shrinkage on drying and high strength after drying. Metal powder may be slip cast into the desired shape using a porous mould prepared from plaster of paris. Major advantages of slip casting are: Fig5: Slip casting process 1. Article can be made with shapes or in sizes that could not be possibly pressed. 2. No expensive equipment is required 3. It works best with the finest possible powders, which are the same time most suited to sintering. Consequently the finished products have excellent properties. 24

25 PROCEDURE: CONCLUSION: EXERCISE9 Q1. Explain the importance of pressureless compaction techniques Q2. What is Coolidge process and why it is used? 25

26 PRACTICAL 10 OBJECTIVE: Determination of Radial crushing strength of bushes manufactured through Powder metallurgy. MATERIALS & APPARATUS Sintered bushes and Universal Testing machine. THEORY: Radial crushing strength is one of the most important tests employed in Powder metallurgy industries. The radial crushing strength is a standard basis for analyzing the sintered properties of sintered products such as bearings. Radial crushing strength is determined by compressing the test specimens between two flat surfaces at a no load speed of 2.5 mm/min the direction of the load being normal to the longitudinal axis of the specimen. The point at which the load drops due to the first cracks is considered the crushing strength. This test is applied to plain cylindrical bearings; flanged bearings are tested by cutting off the flange and compressing the two sections separately. P KLT 2 D-T where P is the radial crushing load, kg; K is the strength constant for the grade and type specified; L is the length of the bearing, cm; T is the wall thickness of the bearing, cm; D is the outside diameter of the bearing, cm. Compressive force Compressive force Fig6: Radial crushing strength. 26

27 PROCEDURE: RESULT: Radial crushing strength of bushes is found to be EXERCISE Q1. Which Heat treatment is used to increase corrosion resistance of Ferrous Powder metallurgy components? Explain its mechanism. Q2. Write down the mechanism of manufacturing Tungsten Carbide through Powder metallurgy. 27