The sand mold aluminum casting method provides some advantages over the castiron aluminum casting method. The most important of these advantages is cost. The use of sand molds in aluminum casting is quite economical compared to the use of other molds. While it is necessary to mold the copillary mold at high costs in aluminum casting, the same products can be produced at lower costs in aluminum casting in sand mold. In the sand casting method, the molding is also quite simple and the cycle of the same sand can be poured aluminum many times In the sand molding method, different metalscan be plucked. For example; aluminum casting with sand mold, bronze casting, brass casting peak casting (GG), ductile iron casting (GGG) etc. In the sand mold made of aluminum casting, it is possible to cast any material we want. The cast mold made of aluminum is not used for the casting of different metals. For example, we cannot use a cast mold made of aluminum for the casting of steel, cast iron, etc.
In the method of aluminum casting into sand mold; According to customer demand, there is no problem in casting one or a few pieces of aluminum and there is no problem in mass production. But pouring a small amount of parts in aluminum casting into the coulet mold is a rather laborious task and is not preferred. In aluminum casting, connecting and removing the cast mold is a waste of time in itself. Therefore, while the aluminum casting method to the cast mold is mostly used for mass productions, the aluminum casting method to the sand mold can be applied even for a single part.
A great advantage of aluminum casting in sand mold compared to aluminum casting in the cast mold is that parts can be poured in the desired size. It is possible to cast a part that is 1 kg and the part that is 1000 kg with the aluminum casting method into the sand mold. This is one of the great advantages of aluminum casting into sand mold. For this reason, sand is one of the reasons why aluminum casting is preferred to the mold.
There are multiple manufacturing methods to be able to produce a part. The most commonly applied yöntem is the casting method. Casting methods are divided into two as degradable die casting and permanent die casting. The permanent mold casting method can pour any number of pieces from a single mold and remove the mold and reuse it. In the perishable mold casting method, mold must be made for each part to be poured. The biggest reason for this is that we need to break the mold in order to remove the part from the mold. It is the most widely used sand casting method among the perishable mold casting methods.
Sand casting molding method is first prepared as a model of the part we want to pour. The model can be wooden, metal or plastic. Due to the fact that it is the most cost-effective and lightweight, it is most often made of wood. When making the model, it is made slightly larger than the normal part size. The biggest reason for this is that every material has a tensile share when moving from liquid to solid. When the model is made in part size without calculating the shrinkage margin, the part will be lower than the dimension tolerances after casting. After the model is prepared, the mold for casting begins to be prepared. The shape of the model is removed as the upper and lower degrees of the mold. The lower and upper degree are combined to make metal input from the upper degree. Metal takes the shape of the cavity in which it is located. We place it in the match in the areas where we want it to come out hollow in the piece. Metal fills around the spade. When the core is emptied from the part after breaking the mold, the place where the core is in the piece is hollow. The metal is filled from the hopper in the upper degree. There are two reasons why the entrance to the runner is in the form of a hunu. One is slag, dirty, and to prevent air from entering the metal mold. The second is to convert the turbulence flow created by the metal in the air into the laminar flow (smooth flow, layered flow) and to transmit it from the narrowed vertical runner to the heel part of the metal at the lower degree. The heel section allows the metal to slow down in the laminar flow, indicating the direction in which the metal will go. In the metal heel part, there are nozzle inlets between the horizontal runner and the piece. Nozzle inlets allow the metal coming from the horizontal runner to be transferred into the part in the laminar flow. Turbulent flow traps the gas in the metal and causes casting errors in the part. Therefore, in the runner design, sudden turns are avoided and the metal is advanced in the laminar flow within the runner and part. Breast inputs are also located at the lower and upper levels. The metal cools in the lower nozzle and acts as a feeder for the upper breast, allowing the metal to be filled with metal from the upper nozzle to the inside of the part.
Casting gap , recession, non-walking, gas gap and similar casting errors may occur in the part. In order to prevent these errors, additions such as feeder, gas outlet and cooler are made to the region where the casting error occurs in the runner design. With the closure of the upper and lower degree, air remains in it. As the metal fills into the part, the air uses the gas outlet to get out. In cases where the metal cannot take the exact shape of the part where the early cooling occurs before it can fill the part, the metal does not feed the part. In this case, the feeder is made to the areas where we want the part to cool later as metal and take the full shape of the part. In the feeder part, apart from the runner design, a second addition is made to the part. The coolant is the use of a solid metal higher than the melting temperature of the metal to be poured. It is placed in the area where the casting error is located while preparing the grade.
A large part of the cast parts is made into sand molds. In general, on average, 4-5 tons of sand is required for 1 ton of casting. These quantities may vary according to the type of metal to be poured, the part size and the molding method. The task of the formwork material is to form the shape of the casting cavity and to ensure that this shape protects itself until the liquid metal is poured and solidification is finished. The formwork material is divided into three main ones; sand grains providing sufficient high refractory properties, and clay and added water that are naturally present in the sand or added binder effect allows the sand grains to stick together and therefore makes the sand a suitable molding material.
Sand mold sands are divided into two groups as natural and synthetic. Natural formwork sands; they contain clay in their natural proportions and are used as is, water is added to strengthen bonding (adhesion). Its main advantage is the ability to retain the amount of moisture for a long time. The disadvantage is that its properties are very variable. Synthetic sands, on the other hand, are sands that contain low clay content as they are found in nature, so binder and water addition such as bentonite to increase their binding properties. Its advantages are more uniform grain size, higher refractoriness and good controllability. Sand is known as a mineral grain with dimensions of 0.05-2 mm. The most preferred and used sand in castings is in the composition of SiO₂ . The most important reasons why silica sand is preferred as cast sand are that it is easy to find, cheap and has high refractoriness properties. Since it shows high expansion, it has to be taken into account in dimensional tolerances. The other sand composition preferred as a second alternative is zircon sand. The main feature of zirconium sand is its high conductivity (twice that of silica) and low expansion. The disadvantage is that it is of high density (twice as high as silica). Other sands used are olivine (magnesium iron silicate-(Mg,Fe)2SiO4) and chromite (iron magnesium chromate-(Fe, Mg)Cr2O4). Chemical formula of sand Density (kg/m3), Hardness (Mohs), Color (Silica SiO2 2650 7 Yellow - Zircon ZrSiO 4 4700 7.5 Brown - Olivine (Mg,Fe)2SiO4) 3500 7 Green-yellow - Chromite (Fe, Mg)Cr2O4) 4500 5.5 black - Composition % Silica Olivine Chromite Zircon SiO₂ 98.82 41.2 1.34 33.5 MgO 0.031 49.4 8.75 - Cr2O3 - - 45.8 - ZrO2 - - - 65 Al2O3 0.049The properties expected in mold sand are numerous. Among them, the main properties that can be controlled in sand preparation are:Wet strength, dry strength, sand gas reality, moisture content, clay quantity, grain size fineness and distribution. Wet Strength; It is the strength after the temper water is added to the mold sand. It is the necessary strength for the preparation of the mold and for the liquid metal to maintain its shape from the moment it is poured. It is measured as compressive strength on the standard test sample. Factors affecting age strength; grain fineness, grain shape, type and quantity of binder, amount of moisture. Grain fineness: The smaller the grains for a given volume of sand, the larger the contact surface between the grains. Fine-grained sand has a higher wet strength. The contact surface also naturally depends on the shape of the grains of sand. Round-shaped grains cause them to be tighter and therefore more durable than sharp grainsThe amount of moisture;
Wet strength increases first with the amount of moisture and then shows a decrease. The moisture up to the point where the strength increases is called "temper water" and the moisture in the region where it falls is called "free water". Sand gas permeability; is that it allows the passage of air, gas or steam through the mold sand. It is expressed by a number related to the speed of passage of air through the sand under standard pressure, which increases as the clearance between the grains of sand increases. It is the gaps between the grains of sand that give this feature to the mold sand. The four factors that control them are;
1) grain fineness, 2) grain shape, 3) binder type and quantity, 4) moisture quantity.
1) Grain fineness, the effect of grain fineness on wet strength, the more the grains touch each other, that is, the tighter they are arranged, the strength increases. However, as a result of this strict arrangement, the gas permeability decreases
2) Grain shape : A similar situation comparison can be made here. While round grains are desired to increase wet strength, pointed and angular grains are preferred this time for gas permeability
3) Amount of binder : As the amount of binder increases, the permeability will also decrease. Sand gas permeability decreases as bonding and adhesion between grains increases
4) Moisture content : Similar to the effects of binders, gas permeability will increase as temper water increases, but sand gas permeability decreases as the amount of free water increases
Dry Strength; However, the most effective determining feature of dry strength of mold sand is the type of binder. Ca-bentonites have lower dry strength properties than Na-bentonites. As the grain fineness increases, a smoother surface will be obtained. Grain fineness is determined according to AFS standards and the grain fineness determined as AFS number (AFS no) is the number of screens per inch square inch. Therefore, as the AFS number increases, it is understood that there is finer grained sand.