Sand Casting

Sand Casting Components

Sand casting involves several components:

1. Pattern: The pattern is a replica of the final part to be produced. It’s usually made of wood, plastic, or metal and is used to create the cavity in the sand mold.
2. Mold: The mold is formed by packing specially formulated sand around the pattern. It consists of two halves, the cope (top) and the drag (bottom), that are assembled to create the cavity.
3. Core: Cores are used to create internal cavities or complex shapes that can’t be made by the pattern alone. They’re made from sand or metal and placed in the mold before closing it.
4. Pouring Cup and Sprue: These components provide a path for the molten metal to enter the mold. The pouring cup is where the metal is poured, and the sprue is a passage that directs the molten metal from the pouring cup to the cavity.
5. Risers: Risers, or feeders, are additional reservoirs of molten metal designed to compensate for shrinkage during solidification. They help prevent defects by feeding metal into the casting as it cools and solidifies.
6. Gating System: This system consists of channels, runners, and gates that control the flow of molten metal into the mold cavity.
7. Molding Flask: The flask is a frame or container that holds the sand and supports the mold during the casting process. It separates to remove the finished mold.

These components work together in the sand casting process to create the cavity into which molten metal is poured, solidified, and cooled to form the final cast part.

The History of Sand Casting

Using sand to cast metal is the oldest metal casting method and one of the most versatile. The earliest recorded use of sand casting is from around 1540.

It wasn’t until the high demand for automobiles and machines that the sand casting process would become fully automated. This increase in demand also led to technological advances in sand casting including increased molding speed and improved strength of the molds.

Is Sand Casting Right for Your Product?

Image above: A clevis manufactured via sand casting.

Sand molded castings are cost-effective but may not be the best manufacturing process for every product or part. Key things to consider are quantity, budget, production timeline, shape, dimensional accuracy, tolerances, and surface finish.

The Advantages of Sand Casting

The main advantages of this casting process include:

• Lower costs for low-volume production runs
• Suitability for fabricating large parts and components
• Ability to use ferrous or non-ferrous metals
• Shorter lead time compared to other processes

One of the most attractive features is that it has the lowest initial setup cost. The process is also easier to modify and reduces the cost of changes to the sand casting mold.

Due to these features, this method of casting is ideal for the fabrication of low- to medium-volume production runs, prototype castings, and the conversion of welded components to castings.

What Is Green Sand Casting?

Green sand casting is a type of sand casting that refers to a method involving moist sand for forming the molds.

The sand used for this process is not literally green in color. It is called “green” due to the moisture but is usually silica sand.

The moisture comes from the clay that is added to the sand. Combining bentonite clay and sand provides a stronger mold as the moisture helps the sand stick together. The sand remains uncured and “green” when the molten metal is poured into the mold.

Air set casting (no-bake casting) and resin sand molding are two other common casting processes. With air set casting, chemical binders are used to bond the molding sand. Heat is not needed for this process.

Using green sand provides cost reductions compared to other casting processes. However, each process has its advantages. For example, the air set casting method allows for a better surface finish and greater consistency compared to green sand. It is also more costly.

Resin sand molding involves a mixture of quartz sand and resin. The mixture creates a hard mold and requires no heating.

As with air set casting, resin casting increases costs and production time compared to green sand casting. However, it also produces fewer defects and a smoother finish.

What’s the Difference Between Die Casting and Sand Casting?

Sand casting is not the only metal casting solution. Die casting is also a viable option for certain parts. Compared to sand casting, die casting may reduce the need for additional tooling.

Die casting also relies on liquid metal or molten metal. Instead of forming a mold cavity in the sand, a steel mold is created in the size and shape of the product; this mold is also referred to as the “die.” The molten metal is forced into the die. After the metal cools and solidifies, the die may be reused, which allows for a quicker cycle compared to casting with sand.

Possible defects include pores, hot tearing, and surface projections. These defects are often caused by issues with the manufacturing processes. For example, porosity often occurs when the liquid metal is heated too high or the sand has a low permeability.

Raw castings may also require additional finishing. The surface finish often has a rough texture and with die casting, the finish is smoother. The die also allows for more complex shapes for parts with tight tolerances.

Sand casting is a low cost casting solution especially for low-volume runs. When creating thousands of castings, cost-effectiveness tends to decrease. With die casting, the reusable mold allows for faster production and lower costs, especially when dealing with high-volume orders.

What’s the Difference Between Sand Casting and Investment Casting?

The sand casting and investment casting processes are both used to produce metal parts by pouring molten metal into a mold. Besides that similarity, there are many differences between these two metal casting processes.

Surface Finish

Investment casting typically has a higher quality surface finish in comparison to sand castings. This is because the sand mold in sand casting can produce a more textured surface finish on the final product. Although, the surface finish created by sand casting can be adjusted via secondary machining methods.

Dimensional Accuracy

Sand casting generally doesn’t offer high dimensional accuracy compared to some other casting methods. It’s known for its versatility and cost-effectiveness rather than precision. For tighter tolerances and higher precision, processes like investment casting or die casting are often preferred.

The Molds

If you anticipate any changes to the design of the mold, then sand casting is right for you. Sand casting molds are much easier to adjust than the molds used in the investment casting process.

Our Sand Casting Process

Image above: Commercial stove burner manufactured via the sand casting process.

We offer a variety of sand casting methods and materials to suit your project, including:

• Greensand molding
• Resin sand molding
• Air set molding

Along with these processes, we offer a complete metallurgical analysis. With our state-of-the-art foundry, we can prepare metals for analysis to help reduce casting defects and process inefficiencies.

Our solutions also allow for the use of a wide range of materials including stainless steel, alloy steel, iron, aluminum, magnesium, brass, bronze, and copper. Our equipment includes magma solidification software to reduce or eliminate porosity. We also utilize a coreless induction melting furnace to increase productivity.

Our Sand Casting Equipment

• Magma Solidification Software: Using this software results in better pattern making and gating to reduce or eliminate porosity.
• Coreless Induction Melting Furnace With a fast heat-up time, this combines high productivity with maximum alloy flexibility.
• Channel Holding Furnace: The channel holding furnace combines high productivity with the economical operation and provides a continuous supply of ready-to-pour molten metal 24 hours a day.
• Automatic Sand Molding Machine: Made with mechanical automation and used for high volume casting, all molds have the same dimensions, tension, moisture content, and other properties.

The Federal Group’s Sand Casting Capabilities

Image above:  A sand casted and machined product finished with a rust preventing paint. Manufactured by The Federal Group.

Our foundry capabilities have a wide range from 1 lb to 30,000 lbs per piece. Different materials and methods can be used to achieve the ideal result for your casting products:

Green Sand Molding

Castings are made using sand molds formed containing water and organic bonding compounds (typically clay).

Resin Sand Molding / Shell Molding

Castings are made with resin sand, which is a mixture of quartz sand and resin. Also known as a hard mold, the resin sand becomes very hard and solid after mixing and burning.

No-Bake / Air Set Molding

This sand casting process involves the use of chemical binders to bond the molding sand at room temperature. Heating is not necessary for this process.

Complete Metallurgical Analysis

• Our state of the art lab is fully capable of preparing metals for analysis.
• Microscopic and Macroscopic Analyses: Sectioning, mounting, polishing, and micro etching are done to prepare the metal for analysis.
• X-Ray Diffraction Analysis: We are also capable of preserving the specimen: This is a nondestructive technique for characterizing crystalline material or minerals.
• Fully Equipped Sand Testing Lab:  Capable of testing all of the characteristics of prepared sand for casting, we have maximum control over processes. This identifies casting defects and process inefficiencies, resulting in superior products at a lower cost of operation.

Our Sand Casting Materials

Various metal material can be used for sand casting depending on the application and desired properties of the final product. We use the following materials in our sand castings:

• Alloy Steel
• Aluminum
• Brass, Bronze & Copper
• Cast Iron
• Grey, Ductile & White Iron
• Magnesium
• Stainless Steel/ Duplex 2205, 2507 & Zeron

What Is Sand Casting Used For?

Sand casting can make metal parts for every size – from small to large pieces. The dimensional accuracy and low cost benefits make sand casting a great solution for a range of products and assemblies.

In addition, sand moulding can form castings with excellent exterior and inner cores. Almost anything that is metal is possible for sand casting. Hollows can be made from moist sand containing molten metal, then cooled.

Below are a few products that are typically produced using the sand casting manufacturing process:

• Axles
• Engine blocks
• Exhaust manifolds
• Gearboxes
• Impeller housing (pictured above)
• Pistons
• Pumps
• Turbine housings

Contact Us Today for a Free Sand Casting Quote

If you’re interested in getting a quote for your upcoming sand casting project, contact The Federal Group USA today. We’re happy to talk through our manufacturing process and any other metal fabrication solutions you may be interested in.