For generations, most people have been making use of sand casting for various purposes. Today, this process is frequently used for manufacturing cast parts. Manufacturers find it very valuable due to its cost-effectiveness, versatility, capability to withstand high temperatures, as well as other great features. Here, we are going to explain the process of sand casting and when to use it for your casting project.
What Is Sand Casting?
Casting is often used by manufacturers in creating their products which are mostly composed of metal parts and elements. Casting is the process in which molten metal or metal alloys are poured into a customized mold that is made of sand. The inner cavity will be filled, which allows the metal to cool down. After the metal has been solidified, the manufacturer will then remove the mold from the cast part, and what’s left is the precise replica of the molded part.
Among the various methods for making metal molds, sand molding is popularly used by a lot of industries. Sand casting, also referred to as sand molding, is a process of transforming molten metal alloys to produce various metal products by making use of sand molds. This process is highly customizable, making it easier for manufacturers to produce metal parts of different sizes, from small components that require small amounts of alloy, to large components that weigh several tons.
This process also allows the manufacturer to produce a wide variety of products by using almost any kind of metal alloy material. Hence, sand casting is the best method of creating molds with complicated shapes.
What Are the Different Types of Sand and Sand Mixtures?
The most common type of sand being used in sand casting is silica-based sand, but there are still other types of sand that can be used. Silica sands and other sand varieties are mostly preferred since they are composed of small grains that are tightly packed together, giving you a smooth surface without any flaws and inconsistencies.
The perfect sand to be used for the molding process should have consistent structural integrity. Even if it is under extreme mechanical stress, it should be porous enough so that steam and gasses can get out of the mold during the casting process. Its moisture content should also be well balanced. If the sand’s moisture content is low, it can crack or break apart, destroying the mold. On the contrary, if the sand has excessive moisture, then the steam and gas in the mold will not be able to escape properly.
The major factors that can help in determining whether the sand can perform well as a casting mold are the shape and size of the sand grains. Additionally, you should also consider the refractory strength of the sand or its resistance to excessive heat. It is also important to consider its reuse and conditioning abilities as well as its breakage caused by an outside force.
Generally, the different types of sand mixtures are classified based on the binder that keeps the sand together. Sodium silicate, green sand, and resin sand are just some of the most common types of sand mixtures.
How is the Sand Casting Process Performed?
Sand casting is quite a simple process. However, it takes time, accuracy, and preparation. The following are the essential steps of the sand casting process:
Before you start with your casting process, it is important that you prepare all the supplies that you need including your workspace. The most crucial element is the kind of sand and binder that you want to use. Aside from deciding what is the best type of sand to use, you should also build the shape for your mold.
When creating a mold, make sure that it is easy to remove around the metal component once you are done with the casting process. While it cannot affect most projects, it could restrict the complexity of your casings. Manufacturers should prepare all the tools needed for the molding process. This includes the following:
- The mold of the component.
- A sufficient amount of molding sand.
- A ladle for pouring the molten metal into the mold.
- An oven or a kiln for melting the metal alloy.
- A mallet or a hammer, or any other tools that can be used for cracking the sand mold.
- An adequate amount of any type of meltable metal alloy
The amount of metal alloy and sand that you need will likely depend on the size of your mold. After you have prepared all the essential materials, then it’s time to prepare your workspace. When done, you can now start with your casting process.
Fill the Form
After gathering all the components and casting forms, you can now start making your molds by using sand. The sand will be poured over the object forms so that a negative impression will be created. After it has been removed, you will now have a mold for your metal alloy. Examine everything to make sure that the mold is entirely clean and free from any debris which could likely influence the shape of your sand impression.
While the sand is being poured, it is very important to ensure that all the areas, shapes, and ridges are filled up. This can help prevent any gaps in the mold. Unfortunately, if there are any gaps that are not filled, then it can likely destroy the shape of your casting since the molten metal will flow into these gaps. Also, make sure to have a thick layer of sand so that it can withstand burning or cracking once they are exposed to the molten metal substance.
After you have poured and packed the sand, let it stay for a while until it solidifies. The solidification process will likely take longer or shorter, depending on the size of your mold.
Remove the Mold
After a while, when your sand mold is all set, then you need to take it from the form. Keep in mind that you have to be careful in doing this process since it requires accuracy. The packed sand should be hard so that it can sustain its form. But at the same time, it can crack from any outside force or impact. However, if the mold is unwieldy or large then you might need to get some assistance from others.
The first thing to do is to check the sand and ensure that it is hard enough, so it won’t move. If it’s not set enough, then it might crack or fall apart if you try to extract it from the mold. In order to extract the mold, you need to tap the bottom half, also referred to as the drag, using a mallet or hammer. This can loosen it up from the inside so that you can gradually flip it and put it in a safe area. Do the same process on the other top half of the mold, also referred to as the cope.
Assemble the Mold
After removing the mold successfully, it’s time to assemble it. However, before putting it together, be sure that the inner part is cleaned and packed so that it can be filled with molten metal effectively. If it contains any debris or loose sand, then it could create a negative impact on your casting. It is important these are gently cleaned so that you can get the smoothest surface possible. Lining up the impressions is also crucial to guarantee an even and flawless casting. The cope and the drag must be aligned and bonded together tightly.
Pour the Molten Metal
Now that the sand mold is ready for casting, you can now start melting down the metal alloy. You have to be careful in filling the mold with molten metal since it is very dangerous. Necessary safety precautions must be observed at all times during the process. The person who pours the metal should wear protective gear such as boots, face shield, long sleeve coat that is heat resistant, eye protection, as well as heat resistant gloves.
The working area should be cleared of any hazards and obstructions that could cause slipping, tripping, or any possible accidents. Always ensure that the mold is in a level and stable position to guarantee proper setting. The ladle will be filled with molten metal and poured into the mold carefully. When pouring the molten alloy into the sand mold, try to avoid any spills onto the outer surfaces. Accuracy is important since numerous pouring can result in different cooling levels, causing imperfections in the casing. Pressure should not be applied during the pouring process. Gravity plays a significant role in pouring down the molten metal into the mold.
Crack the Mold
After the metal has completely cooled down and solidified, it is time to crack the mold. The cooling time usually varied depending on the alloy being used as well as the size of the item. Use a mallet, hammer, or any other tool that can’t cause damage to the component inside. When the sand mold is cracked open, you can now retrieve the metal object. Work carefully in order to prevent damaging the object during the cracking process.
Cool Down the Molded Object
Although it is already solidified, most likely the metal object will still be hot. That is why you should not touch it without using any protection. You can cool it down by placing the metal object in a container filled with cool water. If the object is very large, simply pour down water over the metal object. Once the metal has completely cooled down and can be handled, check for any imperfections and make some adjustments if needed. SEI Castings manufactures various types of aluminum die-cast products. For more information, give us a call at (408) 374-1031.