What is Sand Casting? A Complete Guide

Sand casting is a casting-based manufacturing process that is used to make different kinds of simple and complex components. It has been around since ancient times, and it is still used today because it is a low-cost option and very fast to set up.

Sand Casting Vs Other Types Of Casting

Methods like die casting use metal molds and high pressure to give a good finish, but it’s an expensive process. Investment casting can deliver a more detailed finish, but it costs far more as well.

On the other hand, sand casting stands out as the best option because it can be used for complex shapes and offers less expensive tooling.

How Sand Casting Works: The Core Process

Before the casting process begins, several materials such as sand, molten metal, and other casting tools are brought together. The sand serves as the main molding material, and it is important to pick the right type of sand to get good cast parts.

Создание узора:

The pattern is a model of the part. It’s made from wood, plastic, or metal. This model is pressed into molding sand to form the shape.

Patterns must be designed to allow for shrinkage and machining. Some are split in two for easy mold removal.

Core making:

The cores are used to make hollow sections. They are placed inside the mold before pouring the molten metal. They are usually made of special sand that is mixed with binders, which help the core to hold its shape under the intense heat. After casting is done, the core breaks apart and is removed.

Mold preparation:

Inside the bottom and top halves of the mold, the sand is pressed around the pattern. These are called the cope (top) and drag (bottom). Once the sand is firm, the pattern is removed. This leaves a cavity shaped like the part.

Some molds use special coatings for a better surface finish. Others add metal or sand inserts to shape fine details. The sand must be packed tightly to improve the mold’s strength.

Gating & risers:

Molten metal enters through gates. These are tunnels cut into the mold. Metal flows from the gate into the main cavity. Risers are added above the part. They hold extra metal to feed the part as it cools and shrinks. Poor gating can lead to different kinds of defects.

Melting & pouring:

The metal is heated in a furnace. It melts and is poured into the mold. The metal must be clean and hot enough to fill every corner.

Pouring must be steady. If it’s too fast, it can lead to splashes, and if it’s too slow, the metal hardens too soon. Foundries train workers or use machines to get this step right.

Cooling & shakeout:

The metal cools inside the mold. After it hardens, the sand is broken away. This is called a shakeout. Leftover metal from gates and risers is cut off.

The part is cleaned using grinders or blasting. Inspectors usually check the part for flaws. If needed, it goes through machining to meet final specs.

Sand recycling:

Used sand can be cleaned and reused in order to save money and reduce waste. The sand goes through machines that shake, sift, and heat it. This removes dust, binders, and metal pieces. Most foundries are known to recycle over 90% of their sand.

Types of Sand Used for Sand Casting

There are different kinds of sand used in sand casting, and each one has unique properties.

Resin Sand:

This type of sand uses synthetic binders to hold its shape. This helps to make the molds stronger and gives parts a better finish. It is used where the part quality matters more because it is quite expensive and harder to reuse.

Dry Sand:

Dry sand is just like green sand, except that it is baked in an oven to make it harder and remove moisture. It is ideal for large parts that need precise details, but it also takes more time to prepare and cool. 

Sodium Silicate or Water Glass:

This uses sodium silicate as a binder and hardens using carbon dioxide gas. Molds and cores made this way are very strong, and they can hold up well to high temperatures. After casting, they break down easily, which makes shakeout and clean up faster. 

Green Sand:

Green sand is made from silica sand, water, clay, and other types of additives. It is the most common type of sand used in factories. It’s called green because it’s wet. It’s also very cheap and easy to reuse.

Defect Types & Prevention

Casting defects can lead to different kinds of issues. Knowing these problems makes it easier to fix them.

Common defects:

• Gas Porosity: These are tiny holes in the cast product that are caused by trapped gases or steam in the mold. These holes could be open holes, pin holes, or blowholes.
• Shrinkage: This is a severe defect that affects the casting quality. It is caused by gaps or cracks where the metal pulls away as it cools down. It usually occurs when there isn’t enough extra metal.
• Veining: These are thin, raised lines on the surface of the part. It happens when the sand expands or cracks during the pouring process.
• Metal Penetration: This happens when the molten metal leaks into the sand, making the surface of the part very hard to clean.

To prevent issues like this, chills can be used to cool thick areas fast and prevent shrinkage. Vents, which are small holes in the mold, can be made to let gases escape during the pouring process and reduce the chances of gas porosity.

Better gating systems can also be built to control how the metal flows into the mold.

Advanced & Modern Techniques

Some modern tools and methods help make the sand casting process much faster and accurate.

New software now helps factories to test designs before they cast metal. It shows them how the metal will flow and cool. Some also track heat during the pouring process using sensors in real-time. With this, time is saved and parts are more accurate.

Digital designs of sand molds can be used to make the actual mold with 3D printers. This helps to skip the pattern-making process.  It’s good for testing new parts and works well with complex shapes. There’s also ablation casting, which uses special molds that cool quickly and break away fast. It also helps to make products much stronger.

Pros & Cons of Sand Casting

As with all manufacturing processes, there are good sides to it and also trade-offs that come along.

Преимущества:

• The process is very flexible. Shape molds can be made by hand or heavy machinery.
• You can apply easy fixes if something goes wrong because it’s simple to adjust the pattern or mold.
• It works well with big molds and other shapes that can be tricky for other methods to cast
• It can be done in basic setups with limited space or equipment.
• It’s a simple process for workers to learn, and it can be used effectively in both small and large factories.

Challenges:

• During large productions, wood or plastic patterns can wear down over time.
• Fine textures or sharp edges are hard to reproduce due to the size of sand grains.
• Parts often need more trimming, grinding, or machining to meet the final requirements.
• If the core is placed improperly, it can lead to failed parts.

Applications & Market Landscape

Sand casting fits in many industries, due to the fact that it works with different metals. These metals offer their own benefits and purpose.

Common alloys:

• Iron and Steel: These metals are very strong and durable. They can also handle very high temperatures, making them ideal for parts that last a long time.
• Алюминий: This is much lighter in weight and is easier to shape or machine. It’s not as strong as steel, but it can still handle moderate pressure.
• Bronze and Brass: These alloys are made from copper. They are also very tough and don’t rust easily. They are both good in salty or wet scenarios where parts move against each other.
• Other Metals: Some other metals, like zinc, are easy to cast and work well for small parts. Magnesium is also light and works well when weight needs to be low. These metals are chosen for special jobs because of their unique features.

Industry scale

The sand casting market is very large. Reports show that the market was worth $345.5 billion in 2023, and it is expected to grow to $584.5 billion by 2031, at a yearly growth of about 7.8%.

Major sectors

Sand casting is used in many major industries that require strong, custom parts made at lower costs.

• Transportation: Car manufacturers use sand casting to make large, tough parts like engine blocks, gear housing, and brake systems.
• Aviation Industry: Aircraft usually need parts that are both strong and light. Sand casting can help make things like brackets from aluminum and other alloys. These parts also need to meet tight safety and weight rules.
• Power & Utilities: Power plants and wind farms use cast parts in turbine systems, valves, and generators. These parts usually face high heat or pressure, which can be made with the right kind of metal.
• Строительство: Heavy machinery and pumps used in building need strong metal parts to function well. Sand casting can be used here to make things like hooks, frames, and pump bodies.

Environmental & Economic Considerations

Although sand casting is easy, it can still affect the environment. That’s why many factories now work to reduce waste and improve how the process runs.

Sand casting still burns fuel to melt metals, which in turn, releases heat and smoke into the air. If this isn’t properly controlled, it pollutes the air and harms workers. To tackle this, some factories now use cleaner fuels and also track emissions to abide by safety rules. Better airflow systems are also used to track harmful fumes.

It also helps local manufacturing. Small workshops can take on custom jobs without needing expensive machines. The process is less affected by supply chain delays. Also, Patterns and sand are easy to source or reuse. Since molds are destroyed after each use, it frees up space and cuts down on costs for storage.

Вывод

People have been pouring metal into sand for centuries, and not just because it’s old. It still works. It’s rough around the edges, sure, but it gets the job done without fuss. Big part, small order, odd shape? Sand casting doesn’t mind.

If you need parts that hold up and don’t cost a fortune, свяжитесь с нами and we’ll make it happen.