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Introduction of Sand Casting Raw Materials
The basic raw materials for making sand molds are foundry sand and molding sand binder. The most commonly used foundry sand is siliceous sand. When the high temperature performance of silica sand cannot meet the requirements, special sands such as zircon sand, chromite sand and corundum sand are used. In order to make the sand mold and core have a certain strength and not deform or damage during handling, molding and pouring of liquid metal, a molding sand binder is generally added in the casting to bond the loose sand particles to become molding sand. The most widely used molding sand binder is clay, and various drying oils or semi-drying oils, water-soluble silicates or phosphates, and various synthetic resins can also be used as molding sand binders. The outer sand mold used in sand casting is divided into three types: clay wet sand mold, clay dry sand mold and chemical hardened sand mold according to the binder used in the molding sand and the way of building its strength.
clay wet sand
Clay and an appropriate amount of water are used as the main binder of the molding sand, and the sand mold is directly formed and poured in the wet state after it is made. Wet casting has a long history and is widely used. The strength of green sand depends on the clay slurry made by mixing clay and water in a certain proportion. Once the molding sand is mixed, it has a certain strength. After being pounded into a sand mold, it can meet the requirements of molding and pouring. Therefore, the amount of clay and moisture in the molding sand are very important process factors.
A casting method that uses molding sand and core sand as molding materials to make a mold and fills the mold with liquid metal under gravity to produce castings. Steel, iron and most non-ferrous alloy castings can be obtained by sand casting. Because the molding materials used in sand casting are cheap and easy to obtain, the casting mold is simple to manufacture, and can be adapted to the single-piece production, batch production and mass production of castings, and has been the basic process in casting production for a long time.
The mold used in sand casting is generally composed of an outer sand mold and a core. In order to improve the surface quality of castings, a layer of paint is often applied to the surface of the sand mold and core. The main components of the coating are powdery materials and binders with high refractoriness and high chemical stability at high temperature. In addition, carriers (water or other solvents) for easy application and various additives are added.
The advantages of clay wet sand casting are:
&#;Clay is rich in resources and cheap.
&#; Most of the used clay wet sand can be recycled and reused after proper sand treatment.
&#; The cycle of making the mold is short and the work efficiency is high.
&#;The mixed molding sand can be used for a long time.
&#; After the sand mold is pounded, it can still tolerate a small amount of deformation without damage, which is very beneficial to drafting and core lowering.
The disadvantages are:
&#;When mixing sand, the viscous clay slurry should be coated on the surface of the sand grains, and a high-power sand mixing equipment with a kneading effect should be used, otherwise it is impossible to obtain molding sand of good quality.
&#;Because the molding sand has a very high strength after mixing, the molding sand is not easy to flow during molding, and it is difficult to pound it. It is laborious and requires certain skills when molding by hand. When molding with a machine, the equipment is complicated and huge.
&#; The rigidity of the mold is not high, and the dimensional accuracy of the casting is poor.
&#; Castings are prone to defects such as sand flushing, sand inclusion, and pores.
Clay dry sand mold The wet moisture of the molding sand used in the manufacture of this sand mold is slightly higher than that of the wet molding sand.
Clay Sand Cores Simple cores made from clay sand.
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Metal casting is a 7,000-year-old process used in both manufacturing and fine art. During metal casting, molten metal is transferred from a crucible into a mold to create a positive metal cast object. The metal and mold are cooled, and the metal object is removed and finished. Traditional metal casting techniques include lost-wax casting, plaster mold casting, die casting, and sand casting, to name a few. These metal casting processes may be completed in a foundry or a jewelry studio.
Metal casting processes have been known for thousands of years, and have been widely used for creating sculptures, jewelry, transportation, weapons, and tools. The first known cast object is a copper frog that dates back to BCE, found in present-day Iraq. During the Bronze Age, metal casting exploded in popularity. Bronze was a much easier and stronger alloy to work with, compared to gold and was cast into tools and weapons using stone molds. During the Shang Dynasty in China, single-use sand molds were first utilized for casting metals. Around BCE, India was among the first ancient civilizations to cast silver and copper coins for currency. Later, around 500 BCE, the Zhou Dynasty introduced iron casting. Throughout history, the Middle East and West Africa both commonly utilized lost wax casting. Many years later, metal casting technology boomed in the 20th century, developing processes that most modern methods are based on.
Throughout history, metal casting has been used to make tools, weapons, and religious objects. Casting is an inexpensive way to create complex shapes and designs and to easily create multiples of the same object. The metal casting process has broad uses across manufacturing, especially in the development of technology and transportation industries. Castings can range in size from a few grams, like a cast ring, to thousands of pounds, like a diesel engine. Cast shapes vary in complexity from something quite simple to incredibly intricate.
While transportation and heavy equipment make up the majority of castings produced worldwide, metal casting is an incredibly versatile process. You will likely find components of metal casting in the following objects:
Metal casting comes in two main categories: processes with reusable molds and processes with expendable molds. In both processes, the caster melts the metal material in a crucible, pours it into a mold, then removes the mold material or the casting once the metal has cooled and solidified.
Expendable mold casting is a method that utilizes single-use or temporary molds. These molds are typically made from resin-bonded sand, ceramic shell, plaster investments, or foam. Making your own expendable mold is an inexpensive and relatively fast process. It works best for small-volume manufacturing.
Non-expendable molds are reusable and permanent molds for metal casting. They are stronger and better suited to withstand the hot temperatures of molten metal than others. Permanent molds are often made of metals like steel or cast iron because of their high strength, low porosity, and resistance to heat. Non-expendable molds are ideal for creating multiples of the same cast metal object.
The basic metal casting process involves creating a pattern and a mold, then pouring molten metal into the mold. You will then extract the solid metal casting and finish your piece. This process is customizable for different types of metal casting, along with shapes, sizes, and more.
Before you make your mold, you must create a pattern to determine the mold&#;s shape. The pattern can be a 3-dimensional model of your final cast. It may be shaped in wax, sand, plastic, or even wood. Some casters use molds made of plaster or silicone, which are materials that could not withstand a molten metal cast, but allow the caster to mass create wax multiples to use in expendable mold casting. When you are shaping your pattern, make sure you account for any anticipated shrinkage when the metal cools. Patterns may also be gated with sprues to allow the molten metal to flow into the mold.
After you have created a pattern, it is time to make your mold. As we mentioned above, you may choose to make a reusable mold, which is typically made from metal, or a single-use mold, which may be made from sand, plaster, or ceramic shell. Each of these methods for making molds are optimized for different casting metals and various levels of pattern complexity. If you are working with a wax or plastic pattern, you can burn out the pattern inside of a kiln.
All metal castings are produced from either ferrous or non-ferrous alloys. Alloys are a mixture of elements that provide the best mechanical properties for the final cast&#;s use. Ferrous alloys include steel, malleable iron, and gray iron. Non-ferrous alloys that are most commonly used in casting are aluminum, bronze, and copper. If you are working with precious metals in a jewelry studio, you may work with silver, copper, gold, and platinum.
Melting processes vary between alloys because each alloy will have a different melting temperature. Essentially, melting consists of placing the solid alloy in a crucible and heating it over an open flame or inside of a furnace.
Pour the molten metal into the mold cavity. If it is a small casting, you may simply pour from the crucible where the metal was heated directly into the mold. A larger casting may require a small team to support heating the metal inside of a furnace, and transferring the metal into a larger crucible or ladle before being poured into the mold.
Make sure to follow all recommended safety guidance when pouring molten metal. Make sure you wear protective clothing, including natural fiber clothing, long pants and sleeves, insulated gloves, and safety goggles. Work in a well-ventilated space to avoid any risks from dangerous fumes. Make sure you have a chemical fire extinguisher nearby and keep your walkway between the furnace and the mold clear. Allow the mold to solidify before moving onto the next step.
When the metal has cooled and solidified, you can remove it from the mold. If you cast into a single-use mold, you can break away the mold from the casting. If you used a plaster investment, you will want to quench the plaster in water after the metal has solidified. The water will help break away the mold. For reusable molds, you may use ejector pins to extract your casting.
File and polish your solid metal cast! This may involve cleaning your cast metal object, like scrubbing away excess mold material in water, breaking off the casting gates with clippers for small objects, or even an angle grinder for large pieces.
Whether you want to cast a small ring or a complex piece of metal for a car engine, the possibilities in metal casting are endless. The type of metal casting you choose to pursue will depend on your vision for the final product. If you are interested in pursuing jewelry, you will want to work with precious metals such as gold, silver, and platinum. If more industrial projects pique your interest, your casting may range from smaller aluminum tiles to a cast-iron skillet. Once you nail down your goals, you can explore options to educate yourself. A local metal arts guild provides members with community, educational resources, and more. We always recommend beginners start in an in-person class to cover safety requirements, gain access to a studio, and learn metal casting from a professional.
The Crucible offers metal casting classes in both our Foundry and Jewelry Departments. Our Foundry offers students an opportunity to create their own sand molds and ceramic shell molds. We offer a fully-equipped wax room where you can shape and detail your patterns for lost wax casting. You can pour aluminum, bronze, and even iron in our foundry classes. In our Jewelry classes, you can make your own unique small pendants, rings, and more to be cast in silver and bronze. Our jewelry classes allow you to learn the full metal casting process from creating a wax pattern to pouring molten metal, then finishing your piece.
You can set up your own home foundry and casting station, with safety at the foremost importance. Make sure you wear protective clothing, including natural fiber clothing, long pants and sleeves, insulated gloves, and safety goggles. Work in a well-ventilated space to avoid any risks from dangerous fumes. Make sure you have a chemical fire extinguisher nearby and keep your walkway between the furnace and the mold clear.
The main types of metal casting utilize either expendable or non-expendable molds. Expendable mold casting utilizes a single-use mold made from resin-bonded sand, ceramic shell, plaster investment, or foam. Common types of metal casting that utilize expendable molds are lost wax casting, investment casting, and sand casting. Non-expendable molds are reusable and permanent molds and made from cast iron or steel. Non-expendable molds are used in die casting and slush casting.
To cast metal, you will need your safety equipment, a well-ventilated workspace, a mold, a crucible, tongs, and a furnace, a torch, or a kiln.
Aluminum is an easy material for metal casting because it is inexpensive, widely available, and melts quickly with a propane torch or in an electric kiln.
These are different types of molds for different projects. First, determine if you will make an expendable or non-expendable mold. Ceramic shell molds are made from dipping a wax model in multiple layers of ceramic shell slurry before burning out the wax and casting the metal inside. Sand cast molds are built inside of a wooden frame and are shaped using an impression or a model or the design is carved directly into the sand. Plaster investment molds also use some sort of frame, made from either wood or metal. The wax model is placed inside of the frame, investment is poured over the model, and the mold is left to set.
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