Casting & Working of Metals Lab Manuals LIST OF EXPERIMENTS

Transcription

1 LIST OF EXPERIMENTS PRACTICE FOR PREPRATION MOULDING SAND MIXTURES (1 session) PRACTICE FOR MAKING SAND MOLDS USING DIFFERENT PATTERNS (2 sessions) 3. PRACTICE FOR MELTING ALUMINUM AND ITS ALLOYS (2 sessions) 4. PRACTICE FOR MAKING SAND CASTINGS USING DIFFERENT PATTERNS (3 sessions) PRACTICE FOR MAKING CORES FOR SAND CASTING PROCESS (2 sessions) PRACTICE FOR MAKING PERMANENT MOLD CASTINGS(2 sessions) PRACTICE FOR MAKING SAND SAMPLES USING SAND RAMMER (1 session) TESTING OF GREEN & DRY STRENGTHS OF DIFFERENT SAND MIXTURES (2 sessions) 9. TESTING OF PERMEABILITY OF A GIVEN SAND SAMPLE USIND PERMEABILITY TESTER (1 session) 10. TESTING OF A.F.S. CLAY CONTENTS IN THE GIVEN SAND SAMPLE USING SAND WASHER (1 session) 11. Theory and Practice for using coverall fluxes, exothermic compounds, degassers and mold coats. (1 session) 12. Analysis of Casting Defects. (1 session) 13. A study on molding equipments and machines. (1 session) 14. A metallographic study of Rolled, Forged, Extruded and Cast Structures. (2 session)

2 PRACTICAL # 1 PRACTICE FOR PREPARATION OF MOLDING SAND MIXTURES Silica sand (SiO2) is used more frequently for making castings than any other moulding materials. It is relatively cheap, and has sufficiently refractoriness even for steel foundry use. A suitable bonding agent (clay or molasses) is mixed with the sand; mixture is moistened with water to develop strength and plasticity and to make the aggregate suitable for molding. A definite mulling action is always required for thorough mixing, in which sand grains, bonding agent, and water are rubbed intimately together. Different types of sand mullers are used to serve this purpose. Equipment: A. Sand Muller B. Hot Tray C. Shovel Chemicals / Materials: Sand, Molasses and Water. Procedure: Take silica sand and stack it over hot tray with the help of a shovel. Put on the fire and heat the sand for sometime. When it is sufficiently hot, throw it into the pan of muller with a shovel. Then add some amount of molasses in the sand and switch on the muller. The wheels rotation inside the muller will thoroughly mix up sand and molasses. 5. Continue adding and mixing molasses in the sand until sufficient strength and plasticity is developed in the sand-molasses mixture.

3 PRACTICAL # 2 PRACTICE FOR MAKING SAND MOLDS USING DIFFERENT PATTERNS Silica sand (SiO2) is used more commonly for making castings than any other molding materials. It is relatively cheap, and has sufficiently refractoriness even for steel foundry use. A suitable bonding agent (clay or molasses) is mixed with the sand; mixture is moistened with water to develop strength and plasticity and to make the aggregate suitable for molding. The resulting sand mixture is easily prepared and molded around various shapes to give satisfactory casting of almost any metal. The fundamentals of mold making are simple, but expert hand molding requires much skill and practice. Production line work is done today by machine molding, in which nearly all operations are automatic. The skilled molder is replaced by a relatively untrained machine operator. Equipment: A. Flask or Molding Box B. Rammer C. Riddle D. Wooden or Steel Board E. Different Patterns F. Draw spikes Chemicals / Materials: Molding Sand, Graphite Powder, Molasses

4 Procedure: 1. First of all place the wooden or steel board (bottom board) on the table or floor. 2. Place the drag-half of the flask on the bottom board and position drag-half of the pattern in it. 3. Sprinkle some amount of graphite powder in the flask and over the pattern to produce smooth surface finish. It also acts as a parting agent. 4. Now, fill the drag-half of the flask with molding sand keeping the pattern in position. 5. Ram the molding sand in the flask with the help of a rammer. 6. Continue adding and ramming the sand until it is densely packed in the flask. 7. When the flask is properly rammed, then use a metal strip to remove excess sand from the upper surface. 8. Now, place a second flat board upside down on the mold and flask, clamp it and over turn the whole. 9. Remove the first bottom board which is now on top and sprinkle some amount of graphite powder (parting powder) on the surface of mold to finish it. 10. Now, position the cope-half of the flask over drag and also the cope-half of the pattern. 11. Place two rods vertically on either sides of the pattern, at a suitable distance, to produce pouring basin and risering system. 12. Fill the cope-half with molding sand keeping the pattern and rods in position. 13. Ram the molding sand in the flask with the help of a rammer. 14. Continue adding and ramming the sand until it is densely packed in the cope. 15. When the flask is properly rammed, then use a metal strip to remove excess sand. 16. Now, remove the rods from the cope-half and as a result holes for spruce and riser will be produced. 17. Separate cope and drag portions of the flasks from each other, use draw spikes to remove the pattern from the mold. 18. Cut the in-gates in the mold and again sprinkle some amount or graphite powder over the surface of mold to finally finish it. 19. If necessary, position the cores in the cavity of the mold and close the mold again by placing cope again atop the drag. 20. The mold is ready for pouring.

5 PRACTICAL # 3 PRACTICE FOR MELTING ALUMINUM AND ITS ALLOYS Manufacture of castings is essentially a matter of heat transfer in one or another form. Heat is first added to the cold, solid metal (scrap or ingot) for melting and for superheating the molten metal until it is fluid enough to pour into a mold. Various types of furnaces are used for this purpose e.g. crucible furnace, electrical furnaces, cupola furnace etc. Heat is then extracted from the metal by mold to re-form it into a solid, cold body of desirable size and shape. The furnace which is most commonly used for melting non-ferrous metals and alloys is crucible furnace. Equipment: A. Pit Furnace B. Crucible Chemicals / Materials: Aluminum scrap, Flux and degasser Procedure: Take required amount of aluminum scrap and put it into the pit furnace crucible. Switch on the blower and turn on the gas valve. Then, put on the fire so that metal in the crucible can be melted. Continue supplying heat to the metal until it is completely liquefied and fluid enough to pour into a mold. Fluxing: Assignment Degassing: Assignment

6 PRACTICAL # 4 PRACTICE FOR MAKING SAND CASTINGS USING DIFFERENT PATTERNS The casting process is the oldest, most versatile, and the most flexible process for forming metals. Basically, it consists of introducing molten metal into a cavity or mold of desired form and allowing the metal to solidify. There is practically no limit to the size, shape, and alloy of the casting that may be made. Castings regularly produced range from tiny dental inlay of rare metals to complicated steel castings exceeding 2000 ton in weight. Almost any article may be cast with proper technique. In sand casting, a mold is produced by shaping a suitable refractory material to form a cavity of desired shape, such that a liquid metal can be introduced into this cavity. The mold cavity has to retain its shape until the molten metal has solidified and the casting is separated from the mold. There are also some other types of casting processes: e.g. permanent mold casting, die casting, plaster casting, investment casting, squeeze / semi solid casting, slush casting, shot casting etc. Equipment: A. Sand Molds with different shapes of cavities B. Crucible Chemicals / Materials: Molding Sand, Aluminum metal Procedure: 1. First of all, prepare sand for sand molding according to the procedure described in Experiment # Then, prepare a sand mold according to the procedure described in Experiment # After the preparation of sand mold, melt aluminum metal or any available aluminum alloy in a pit furnace. 4. When the metal is liquid enough to pour into the mold, put off the fire and hold the crucible with the help of a holder. 5. Place some weight on the mold and pour the molten metal into the mold through the spruce or pouring basin. 6. Continue pouring until the molten metal comes out of risers of the mold. 7. Allow the metal to solidify in the sand mold for some time. 8. When the metal in the mold is solidified, break the sand mold with the help of breakers to remove the required metal casting. 9. Finally, the casting is machined to get the finished shape.

7 PRACTICAL # 5 PRACTICE FOR MAKING CORES OF SAND CASTING PROCESS Cores are used to obtain the internal configurations of different castings. Cores are usually made of synthetic sand, although clean, natural sand containing only 1 to 2 % clay can be used. Cores may also be made of green sand used in the dried condition. Most frequently, however, they are bonded with organic agent such as linseed oil, cereals, molasses etc may be added to make the raw mixture stronger. The basic advantage of organic core binders (as compared to clays) is that they break down under the heat of metal (have collapsibility) and so can be easily removed from the casting as shakeout. Equipment: A. Core Box B. Rammer C. Chemicals / Materials: Chemicals / Materials: Moulding Sand (mixture of sand & molasses). Procedure: 1. Take a core box and fill it completely with molding sand (mixture of sand & molasses). 2. Insert iron wires for reinforcement. 3. Then ram the molding sand present in the core box with the help of a rammer. 4. Continue adding and ramming the moulding sand until the sand is densely and fully packed in the core box. 5. Then, open the core box and carefully remove the core from it. 6. Bake this core in an oven at about 230oC to develop the strength in core and to remove gases. 7. After baking, wash the core with refractory slurry to improve the casting surface finish.

8 PRACTICAL # 6 PRACTICE FOR MAKING PERMANENT MOLD CASTINGS In permanent mold casting method, molten metal is poured into metal molds and around metal cores. The metal molds are coated with a mold surface coating and preheated before being filled with molten metal. A pre-measured amount of molten metal is poured into the permanent mold under gravity. Permanent molds are made in two halves; they may be designed with vertical parting line or with horizontal line as in ordinary sand molding. The mold material is usually a good grade of cast iron, although die steel, graphite, copper, and aluminum are also being used. Cores for permanent molds can be sand, plaster, collapsible metal cores, or simply heavily tapered metal cores which are removed while the casting is still hot. Permanent mold castings have been made commercially of tin, zinc, lead, aluminum, magnesium, copper, and cast iron, and from their alloys. Higher production rates are obtained in permanent mold castings than sand casting. Equipment: A. Permanent Metal Mold B. Brushes Chemicals / Materials: Aluminum scrap, refractory wash Procedure: 1. Clean the mold by brushing or blasting with warm air. 2. Maintain it at proper casting temperature by a gas or oil flame. 3. Paint or spray the mold surface with a thin refractory wash or blacken it by depositing carbon from a reducing oil or gas flame. 4. Insert cores, if necessary and close the mold by hand or automatic action if available. 5. Pour the molten aluminum metal from the crucible into permanent mold. 6. Allow the sufficient time for the casting to solidify. 7. Then, open the metal mold and eject the casting from it automatically or by hand. 8. Finally, machine the casting to get the finished shape.

9 PRACTICAL # 7 PRACTICE OF MAKING SAND SAMPLES USING SAND RAMMER The sand rammer is a machine for preparing specimens for testing of the permeability and strength of moulding sand and is comprised mainly of a base, ram, tamping bar and lever. The machine is so constructed that the ram is brought up by the crank and is then caused to drop to strike and drive down the tamping bar at the lower end of which is fixed a tamping plate which slides into a sand tube to press the sand tube into a certain size with certain energy. Equipment: A. Sand Rammer B. Sand tube C. Sand stripping bar Chemicals / Materials: Testing sand Figure: Sand Rammer

10 Operating Procedure: Preparation of Strength Test Specimen: 1. Set the sand tube in the tube rest for about 15 mm, and holding it by hand, introduce about 140 g to 175 g of the test sand gently so that the sand surface is level. 2. Next, pull the handle toward you to force the tamping bar up, then load the sand tube having the sand charged together with the rest on the base, and introduce the ramming head quietly into the sand tube until it is held by the sand surface. 3. Then, turning the lever forward, perform ramming three times. 4. With the sand thus rammed, if the pointer provided on the tamping bar stops within the tolerable range on the scale, the compacted sand is usable as a test specimen of a standard size (height 50 mm). 5. The tolerances ±1 mm graduated above and below the base line, and if the pointer does not remain within the tolerable range, such specimen is not usable as a test specimen, so that it should be discarded. 6. Then, adjusting the quantity of sand to be introduced in the sand tube properly, repeat the foregoing procedure. 7. When a specimen of standard size is obtained, raise the ramming plate, remove the sand tube and set it over the sand stripping bar to withdraw the standard sand specimen from the sand tube. Preparation of Permeability Test Specimen: 1. Set the sand tube on the rest, and prepare the test specimen, as in the case of the strength test specimen, with about 140 g to 175 g of the test sand fed. 2. The specimen height shall comply with the standard 50 mm (tolerance ±1 mm). 3. In the case of testing the permeability of green sand, the test specimen should not be withdrawn from the sand tube but be applied to the permeability tester immediately together with the sand tube. Caution: The machine is subjected to considerable impact in use so that it should be installed in the rigid concrete base preferably in a height of mm.

11 PRACTICAL # 8 DETERMINATION OF GREEN & DRY STRENGTH OF DIFFERENT SAND MIXTURES Strength or bond strength is the property of sand whereby it offers resistance to deformation and enables the sand to hold together under pressure. Green strength is referred to the strength of moist or tempered sand whereas dry strength is strength of sand dried at 110oC. The green strength of sand is usually lower than its dry strength. Bond in moulding sand is due to the presence of binders such as clay, core gum, molasses, linseed oil etc. Universal Sand Strength Testing Machine: The Universal Sand Strength Testing Machine consists of three major parts; frame, pendulum weight and pusher arm. The pusher arm is motivated by means of a small handwheel, which, through a gearbox, rotates a pinion engaged in a rack on the quadrant. The pendulum weight swings on a ball bearing and can be moved by the pusher arm, via test specimen, from a vertical position, with a consequent increase of a load on the test specimen. A magnetic bar is moved up the calibrated scale by the pendulum weight and indicates the point at which the specimen collapses. The machine can be calibrated in g / cm3. Figure: Universal sand testing machine

12 A. Green Compression Strength: Test Procedure: 1. Place the compression heads in the lower position as shown in the figure. 2. Raise the weight arm slightly and insert an A.F.S. standard 50 mm X 50 mm test specimen between the compression heads so that the face that was uppermost in the ramming operation is facing the right-hand compression head. Care should be taken not to damage the specimen. 3. Ensure that the magnetic rider is resting against the pusher plate and that there is at least 6mm clearance between the rubber bumper and the lug on the weight arm. If this clearance is insufficient, it means that the specimen is smaller than the permitted tolerance and should be discarded. 4. Apply a load to the test specimen by turning the hand wheel at uniform rate (approximately 30 g / cm3 / sec) until the specimen collapses. 5. Record the reading shown on the lower edge of the magnetic rider, reading the scale designated Green Compression Strength. 6. Return the weight to zero by gently reversing the rotation of the hand wheel. Remove the sand from the compression heads. B. Green Shear Strength: Test Procedure: 1. Place the shear test heads in the lower position in the machine, with the head having the half round holder attached to it in the pusher arm. 2. Raise the weight arm slightly and insert an A.F.S. standard 50 mm X 50 mm test specimens between the heads. 3. Ensure that the magnetic rider is resting against the pusher arm and that there is 6mm clearance between the rubber bumper and lug on the weight arm. 4. Apply the load uniformly until the specimen shears. 5. Read the lower edge of the magnetic rider on the scale designated Green Shear Strength. 6. Return the weight to zero by reversing the rotation of the hand wheel. Remove the sand from the shear heads.

13 C. Dry Compression Strength: Test Procedure: 1. Place the compression heads in the top position of the machine. This position increases the load applied by factor of Prepare A.F.S. standard 50 mm X 50 mm test specimen in the usual way and dry in an oven at 110oC for few hours. 3. When cool, place in position between test heads and adjust clearance between rubber bumper and the lug on weight arm to approximately 13 mm using the adjusting screws in the pusher arm. 4. Apply the load as for Dry Compression until the specimen collapses. 5. Red the scale designated Dry Compression Strength according to the test heads being used. 6. Return the weight to zero by reversing the rotation of the hand wheel. Remove the sand from the compression heads. D.Dry Shear Strength: Test Procedure: 1. Place the shear heads in the top position of the machine. This position increases the load applied by factor of Prepare A.F.S. standard 50 mm X 50 mm. test specimen in the usual way and dry in an oven at 110oC for few hours. 3. When cool, place in position between test heads and adjust clearance between rubber bumper and the lug on weight arm to approximately 13 mm using the adjusting screws in the pusher arm. 4. Apply the load as for Dry Shear until the specimen shears. 5. Red the scale designated Dry Shear Strength according to the test heads being used. 6. Return the weight to zero by reversing the rotation of the hand wheel. Remove the sand from the shear heads.

14 PRACTICAL # 9 DETERMINATION OF PERMEABILITY OF GIVEN SAND SAMPLE USING PERMEABILITY TESTER Permeability is that property which allows gas and moisture to pass through the moulding sand. It is determined by measuring the rate of flow of air through A.F.S. standard rammed specimen under a standard pressure. The volume of air in cm3 / min. passing through a specimen of length 1 cm. and cross sectional area of 1 cm2 under a pressure difference of 1 cm. water gauge is called Permeability Number. Permeability Number: The volume of air passing through a sand specimen 1 sq. cm area and 1 cm. in height at a pressure of 1 gram per square centimeter in 1 min. is called the Permeability Number and is computed by the formula: P = (v x h) / (p x a x t) Where, P = Permeability Number v = Volume of air passing through the specimen (cubic centimeter or in mil) h = Height of specimen (centimeters) p = Pressure difference between upper and lower surfaces of test specimen (in centimeter of water column) a = Cross-sectional area of specimen (square centimeter) t = time (minutes) Permeability Meter: The body of the Permeability Meter is an aluminum casting of a water tank and base. Inside water tank floats a balanced air drum carefully weighed and designed to maintain constant pressure of 10 cm during its fall. The outlet from the air drum is connected to a centre post in the base via three way air valve. The centre post incorporates a pipe for measuring pressure, which is connected to the water manometer and an expandable O ring for sealing the specimen tube. It also accommodates the orifices.

15 Equipment: A. Sand Permeability Tester B. Testing sand specimens Figure: Sand Permeability Tester A. Standard Permeability Test: Test Procedure: (A.F.S Standard Time and Pressure Method) 1. Check that the open orifice is in the position in the centre 2. Prepare an A.F.S. standard specimen of sand. Before stripping from tube place in position on the centre post and seal by rotating the knurled ring anti-clockwise. 3. Check water level in the tank. Turn air valve to NENT and slowly raise drum until it is out of water. 4. Allow the air drum to descend by turning the air valve to a position midway between CLOSED and VENT. 5. Time the descend of the air drum between zero and 2000 ml mark with a stop watch and record the pressure indicated on the manometer during the descend of the drum. 6. Calculate the permeability by applying the given formula.

16 B. Dry Permeability Test: The permeability of a moulded mass of sand dried at 105oC to 110oC is called Dry Permeabilty. It is used for dried, baked or cured sand specimens. Test Procedure: 1. Place split specimen tube on pedestal, and insert steel ring in bottom of tube. 2. Tighten clamp on split specimen tube. 3. Weigh out sufficient sand to produce a test specimen of standard dimensions, and ram according to standard procedure. 4. Release clamp on specimen container, remove the tube, and place specimen on drier. The clamp is then release and the core is stripped. 5. Place core in an oven and dry at 105oC to 110oC for one hour or until dry. 6. Remove the specimen from oven, and place it in a desiccator to cool. 7. When cool, place specimen in a core permeability tube. Clamp the specimen firmly in position. 8. Place permeability tube in position in permeability meter, and determine permeability in usual way, as described above.

17 PRACTICAL # 10 DETERMINATION OF A.F.S. CLAY CONTENTS IN THE GIVEN SAND SAMPLE USING SAND WASHER Sand testing washer is used for measuring the clay contents and sand contents of general moulding sand in percentage, and comprises 1 /20HP single phase motor (steplessly adjustable between 600 and 3,000 rpm), vane shaft, beaker, siphon and timer. Equipment: A. Sand Testing washer B. Timer Chemicals / Materials: Testing sand, Caustic soda solution Operating Procedure: 1. Dry the sand for one hour at 105 ± 5oC. 2. Then allow it to stand in a desiccator for cooling, and weigh 50 g of sample accurately, put into the beaker, add 475cc of 20 to 25 oc distilled water and 25cc of caustic soda solution (with 30 g of caustic soda dissolved into 970 cc of water). 3. Place the motor slowly on the beaker, and stir sufficiently for about 10 minutes. 4. Take out the beaker, and pour water in it, to wash the sand adhering to the wall into the beaker, up to about 15 cm depth in total. 5. Stir it sufficiently, and allow it to stand for about 10 minutes and allow supernatant water to flow through siphon bringing the level down to 2.5 cm. 6. Add 20 to 25oC distilled water again up to 15 cm depth, and stir sufficiently, and allow it to stand for about 10 minutes. 7. Again allow the supernatant water to flow out by the siphon until the height from the bottom becomes 2.5 cm. Then, add water again up to 15 cm depth, stir it sufficiently and allow it to stand for 5-10 minutes. 8. Repeat the same operation until the discharged water becomes clear. 9. Filter the sand particles remaining in the beaker, using about 9 cm filter paper in a Buchner funnel, and move the sand along with filter paper to a large wash glass. 10. Dry it perfectly at 105 ± 5oC and cool in a desiccator. 11. Double the difference between the weight of washed sand particles and the weight of original sample is the percent of clay content.

18 Remarks: 1. If the distilled water is not available, ordinary water can be used. 2. It is desirable that test should be conducted twice or more for the same sample, and that the mathematical mean value of test results within deviation ±5 % should be taken as the result of the test. 3. The motor speed can be adjusted steplessly between 600 and 3,000 rpm, and therefore when it is desired to shorten the time or to change stirring eddy current, the speed can be adjusted arbitrarily (standard speed is 1,500 rpm for 50 Hz, and 1,800 rpm for 60 Hz).