Table of Contents 1.0
TITLE: Molding Preparation and Pouring .................................................................................. 2
2.0
INTRODUCTION ........................................................................................................................... 2
3.0
OBJECTIVE ................................................................................................................................... 3
4.0
APPARATUS ................................................................................................................................. 4
4.1
MATERIALS .............................................................................................................................. 4
4.2
EQUIPMENT ............................................................................................................................ 4
4.3
HAND TOOLS ........................................................................................................................... 4
5.0
EXPERIMENTAL PROCEDURE ...................................................................................................... 5
5.1
PREPARATION OF GREEN SAND MOLD ................................................................................... 5
5.2
PREPARATION OF MOLTEN METAL ......................................................................................... 7
5.3
POURING AND COOLING PROCESS ......................................................................................... 8
6.0
RESULT ........................................................................................................................................ 9
7.0
DISCUSSION............................................................................................................................... 11
8.0
CONCLUSION ............................................................................................................................. 15
9.0
REFERENCES .............................................................................................................................. 16
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1.0 TITLE: Molding Preparation and Pouring 2.0 INTRODUCTION In metalworking, casting involves pouring molten metals into a refractory mold with a cavity of the shape to be made and allowing it to solidify. When solidified the desire metal object is taken out from the refractory mold either by breaking the mold or taking the mold part. The solidified part is known as casting. Casting is more often used for making the complex shapes that would be difficult or uneconomical to make by other methods. Casting is widely used for sculpture, especially in bronze, jewellery in precious metals, and weapons and tools. Traditional technique include low-wax casting, plaster mold casting and sand casting. Sand casting is the one of the most popular and simplest type of casting and has been used for centuries. Sand casting also known as sand molded casting. Sand casting allows for smaller batches than permanent mold casting and at a very reasonable cost. Not only does this method allow manufacturers to create products at a low cost, but there are other benefits to sand casting, such as very small size operations. Generally, we can distinguish between two methods of sand casting, the first one using green sand and the second being the air set (carbon dioxide) method. Green sand molding is more wide develop than any other process. Green sand molding is replacing many of the more expensive molding methods as sand control is being applied. These expendable molds are made of wet sands that are used to make the molds shape. The names come from the fact that wet sand are used in the molding process. Green sand is not a type of sand on its own, but is rather a mixture of silica sand, bentonite (clay), coal dust and water with ratio 4:2:2:1. There are some basics process of sand casting. A sand casting or a sand molded casting is a cast part produced by forming a mold with the help of a model or pattern pressed into a sand mixture and then removed, after which molten liquid metal is poured into the cavity in the mold. The mold is then cooled until the metal has solidified. In the last stage, the casting is separated from the mold.
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Figure 1: Basic process of green sand casting.
3.0 OBJECTIVE The objective of the experiment are: 1. To investigate the principles and terminology underlying the sand casting process. 2. To investigate the defect after the metal has solidified. 3. To overcome the defect of the product.
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4.0 APPARATUS 4.1 MATERIALS i. ii. iii.
Aluminium Green sand Parting agent
4.2 EQUIPMENT i. ii. iii. iv. v. vi.
Flask Pattern Furnace Crucible Sand separator Sand muller
4.3 HAND TOOLS i. ii. iii. iv. v. vi. vii.
Aluminium plate Spure pin Parting sand Heart trowel Trowel Lifter Scriber
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5.0 EXPERIMENTAL PROCEDURE 5.1 PREPARATION OF GREEN SAND MOLD DRAG 1. A bottom board is placed. 2. The flask is placed on the bottom board, upside down with pattern at the center of the board.
Figure 5.1: The pattern was placed on the bottom board
3. Sprinkle the parting agent over the board and pattern. 4. Molding sand is poured into the drag. 5. The sand is rammed properly and uniformly by using the rammer and the jolt squeeze machine.
Figure 5.2: The sand was rammed by Jolt Squeeze Machine.
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6. The excess sand in the flask is scraped using the trowel. 7. Vent holes are made to the full depth of the flasks by using the vent wire. 8. The drag flask is rolled over exposing the pattern.
Figure 5.3: The drag was rolled over exposing the pattern.
COPE 1. The cope half of the pattern is placed over the drag pattern. 2. A sprue pin and riser pin is kept at an appropriate place. 3. The molding sand is prepared similar to the drag. 4. The pouring basin is cut near the top of the sprue.
Figure 5.4: The pouring basin was cut.
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5. The cope is separated from the drag. 6. The pattern are withdrawn using draw spikes. 7. Runners and the gates are cut in the mold. 8. Cope is placed on the drag.
Figure 5.5: The cope was placed on the drag
5.2 PREPARATION OF MOLTEN METAL 1. Heat the furnace to a temperature greater than the melting point of
aluminium. 2. Cut larger pieces of aluminium into smaller pieces and work only in small
batches in order to more evenly distribute the heat and allow all of the pieces to melt. 3. Place the pieces of aluminium into the crucible and maintain the furnace
heat until all units of aluminium have melted. 4. Use tongs to lift the crucible and pour the aluminium into prepared metal
mold while still in liquid form. This must be completed quickly to prevent the aluminium from solidifying while in the crucible.
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5.3 POURING AND COOLING PROCESS 1. The cope and drag are then combined and are ready to accept the metal. 2. The molten metal is then poured into the mold. 3. The part is allowed to sit and cool. Once cooled the casting and gating system
are removed from the mold and the sand is recycled.
Figure 5.6: The casting was cool and solidified.
4. Then the casting are cleaned by using the blower to remove the remaining of
the green sand.
Figure 5.7: The casting was blow to remove the remaining of the green sand
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6.0 RESULT
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1 3
4 5
Figure 6.0: the final products of green sand casting.
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TYPE OF DEFECT (based on figure 6.0)
1) Metallurgical defects (hot tear)
3) Material molding defects (swell)
2) Washes and flashes defects
4) Misrun defects
5) Gas defects (pin hole)
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7.0 DISCUSSION During the lab, we are required to build the mold for sand casting. The mold can be divided into two parts, known as Cope for the upper part and Drag for the lower part. We used green sand for the mold. During the lab, the process of producing the drag went smoothly. But there are some precautions that needs to be measured such as putting or spreading the parting agent onto the pattern so that the mold will not stick to the pattern. We can use any kind of powder or flour as parting agent. However, the same cannot be said for the cope. For the first attempt, our cope is broken when we lift it from the base. We found out that the cope is not solid enough. The reason for this is because we did not rammed the sand properly. Thus the cope is not compressed enough. Since the process of making the cope is divided into three stages of ramming, therefore it is essential for the first ramming to be a little longer and a little harder to make sure that the base of the cope is compressed. After taking this precautions into action, we finally managed to produce the cope for our mold. Then after the pouring and cooling process, we take a look and we analyze our products. Our products contained several defects such as shrinkage defects, pouring metal defects (misrun), metallurgical defects (hot tear), gas defects (pin hole), wash, flashes, and inclusions. For shrinkage, this can be caused by improper directional solidifications, or inadequate feeding. The solidification process will lead to volumetric contraction which must be supported by feeding. Therefore this defect can be prevented by supplying enough amount of molten metal and we can also providing proper gating system and pour at the correct temperature.
Figure 7.1: Shrinkage defects 11
Misrun occurs because of the pouring temperature is low that the metal has become solid before it can fill the entire section. The temperature of the molten metal is essential so that it can flow and fill the entire section before it is solidifies. The suitable pouring temperatures vary depends on the metal material. However, we can minimized it by proper design of casting, providing suitable gating and using the suitable temperature of the melt.
Figure 7.2: Misrun defects
Hot tears also known as hot cracking are failure in the casting that occurs as the casting cools. This happens because the metal is weak when it is hot and the residual stresses in the material can cause the casting to fail as it cools. Proper mold design prevents this type of defect.
Figure 7.3: Metallurgical defects (hot tears)
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Swell occurs when the mold wall gives way across a whole face, and is caused by an improperly rammed. This can be avoided by ram the sand properly.
Figure 7.4: Material molding defects (swell)
Washes and flashes are caused by corrosion of mold and core surfaces by metal flowing in the mold cavity. It can be also caused by lower shell strength and cracks during dewaxing. But, this can be prevented by increase the green shell strength, and improve dewax method. And can be also avoided by proper ramming, and controlling the turbulence while pouring.
Figure 7.5: Washes and flashes defects
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Pin hole is a gas defects that occurs when the gas is trapped during solidification. The gas dissolved during solidification can be caused by hydrogen or nitrogen in the initial liquid or core gas decomposed from the sand core and vented to the liquid. To reduce or eliminate core-gas related defects, detailed information is needed regarding the core gas generation, flow and venting in the core, and the metal flow and solidification behaviour in the mold. Make sure the air vent on the mold are enough for gas flow out from the mold and prevent from the gas trapped in the mold.
Figure 7.6: Gas defects (pin hole) Inclusions defined any foreign materials present in the cast metal. It can be in the form of oxides, dirt, sand or nails. The main cause of the inclusions are the impurities with the molten metal, sand and dirt from the mold are not properly cleaned, core or gating system and foreign items picked on the mold cavity while handling. But this defect can be minimized by using correct grade of mold sand and proper skimming to remove impurities. In order to produce the highest quality of a product, we can take some precautions especially during the pouring process. For example, the pouring temperature needs to be suitable according to the material used. The difference between the pouring temperature and the solidification temperature needs to be higher and this is known as the superheat. Another precaution that can be measured is the pouring rate. It has to be carefully altered and controlled during the metal casting operation. If it is too fast, It can result in turbulence and if it is too slow, it can solidify before filling the mold.
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8.0 CONCLUSION From this lab we able to investigated the principle and terminology underlying the sand casting process. Although there are several defects found at the end product which is shrinkage defects, pouring metal defects (misrun), metallurgical defects (hot tear), gas defects (pin hole), wash, flashes, and inclusion, we can minimized this defects by improving molding process. Also we can get better quality end product by controlling the pouring rate which if it is too fast, it can result in turbulence and if it is too slow, it can solidify before filling the mold. Besides that, we must consider the pouring temperature which must suitable with material used. Thus, we can conclude the experiment may be done perfectly if the above process has been taken full consideration while the process done thoroughly.
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9.0 REFERENCES
Blair, Malcolm; Stevens, Thomas L. (1995), Steel castings handbook (6th ed.)
Rao, T. V. (2003), Metal Casting: Principles and Practice, New Age International,
PN Rao , Manufacturing Technology (Foundry, Forming and Welding), Second edition.
http://www.mechanicalengineeringblog.com/tag/die-casting-defects-causes-andsolutions/
http://www-old.me.gatech.edu/jonathan.colton/me4210/casting.pdf
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