What is Green Sand Casting? Its Process and Advantages

Green sand casting is a particular casting method under the bigger umbrella of sand casting, which involves using the combination of sand, water, and additives to make the wet sand mold and pouring liquid metal to form the final product. The green sand casting industry involves foundries that offer the services, and such services ultimately lead to quality castings and the developments we see in the world.

It is a global industry. Geographical regions like Asia Pacific, North America, and Europe contribute the most to this growing market. Casting Market report shows that the green sand market’s value in 2023 was $110 billion and is likely to increase to $190 billion by 2030. In this article, we will explore all key aspects of green sand casting to understand its process and pros and cons.

 

What is Green Sand Casting?

The technique of casting metal using green sand is called green sand casting. The term green sand itself is also known as wet sand. While the term green is used to refer to this type of sand, the truth is that wet sand is not green. The high quantity of moisture is the reason why it is called green sand. Nevertheless, the molding sand gets dried when hot metal is poured into the sand.

It is important to note that green sand casting is different from simple sand casting because of the clay mixed with sand in the mold. The mixture of sand and bentonite clay ensures the sand sticks together, so it can be utilized on a long automated assembly line. While this is the basic definition, there are no hard-and-fast rules when it comes to its composition.

dawang_caasting

Composition of Green Sand Casting

Other than the green sand casting definition, it is important to discuss typical components of it:

  • 75% to 85% of sand
  • 5% to 11% of bentonite or kaolinite clay to bind the sand particles
  • 2% to 4% of water
  • 3% to 5% of sludge that acts as a filler
  • 1% or less anthracite is a carbonaceous additive
  • Other inorganic compounds on the basis of green sand casting foundry and purpose.

An important thing to remember about the composition of that is that there are many different ways to create it, especially by varying the proportion of clay. Tweaking these proportions has a significant impact on the surface finishing, structure’s moldability, and metal’s degassing ability.

Generally, there are no coal additives in green sand casting for non-ferrous metals because carbon monoxide does not prevent oxidation. On the other hand, there is olivine sand in green sand for aluminum to bring stability and durability.

Metal pouring temperature has a significant impact on the sand chosen for the casting process. Such wide-ranging compositions and choices of sand make it important to rely on reliable green sand-casting manufacturers.

 

Origin of Green Sand Casting

The evolution of it starts from ancient history as its origins can be traced back to ancient history. Civilizations in Egypt and China used to create clay molds to create unique objects from bronze and other metals. It started the concept of creating structures and molds.

A turning point in green sand casting’s history was during the 1540s. An Italian polymath, Vannoccio Biringuccio, published his research about using moist sand to make molds. This paved the way for the large-scale adoption of that during the Industrial Revolution. Such adoption was necessary to meet the rising demand for complex machinery and metal parts.

Moreover, modern machines, such as sand slingers and mechanical sand mixers, were introduced during the 1910s. They significantly improved the green sand processes.

Keep in mind that green casting is still an evolving process. Foundries continue to improve their green casting processes to fulfill the unique and complex requirements of the manufacturing industry.

Image from: metmuseum.org

Process of Green Sand Casting

Let’s dive deep into the process

Mold Development

A mold is created by forcing prepared sand around a set pattern held in a flask. The exact shape of these patterns can vary, but they are designed in a way that the metal can easily be poured into them.

The first step in green sand casting is to develop a green sand mold for the process. It is done by loading green sand into a mold maker and pressing a suitable pattern into the sand. A significant amount of pressure is created when then the mold is pressed into the sand so a suitable shape is obtained.

However, it is important to note that the tolerance level of green sand is not as good as some of the other types of molds, such as die cast molds and investment cast molds. Hence, further processing is often required to get the desired shape and results.

Shell core production

Cores are made from sand bonded with resins and rammed together to provide significant strength and ensure the mold cavity supports the internal structure and castings.

The next step in the green sand casting process is shell core production to refine the design. Creating a pattern on a green sand mold is not enough to fulfill unique and specific requirements.

Core creation is useful to create internal cavities that are simply not possible in a traditional mold. Generally, a core box and a sand mixture combined with resin or binder are used in this stage.

Once the cores are created, they are hardened or cured with the help of chemical procedures or extreme heating to ensure they can tolerate the molten metal being poured into them in the following stages of the procedures.

Overall, shell cores are a critical part of that because they ensure dimensional accuracy and quality finishing.

Casting Parts

Assembly of shell mold and core

After the green mold sand casting and shell core production, a final assembly line is created. The cores have to be carefully placed inside the green sand mold cavity to get the desired internal design as per the requirements.

The mold halves are properly placed and merged together to ensure there is a proper seal between them. It is also important to ensure that there is no misalignment or leakage of the molten metal during the green sand casting procedure, as it can disrupt the entire assembly line.

Melting_Furnace

Pouring and cooling

Once the green sand mold and shell core are assembled, the molten metal is created in a furnace at a suitable pouring temperature of anywhere between 1200-1400 degrees Fahrenheit.

A runner system connecting the mold cavity to the outer side of the mold is used to carefully pour the molten metal and fill the cavity as well as the core surroundings. Once the cavity is fully filled, the metal is left to cool down within the green sand mold.

The entire cooling and solidification can take either a few minutes or even several hours. It is also possible to control the time of this process through runners, risers, filters, and the addition of chills if required. Make sure the metal is allowed to fully cool down to ensure maximum dimensional accuracy and achieve the mechanical goals.

Shakeout and cleaning

While a well-designed green sand casting process is meant to ensure accuracy from the very start, minor mistakes are common, even in experienced services.

After metal solidification, the green sand mold is broken to release the casting. This process is called shakeout. Large-scale green sand casting services typically use machines in the shakeout process to vibrate and mold and break it from casting. However, it is also possible to manually break the mold.

Thorough cleaning is required to ensure there is no residual sand, scale, or any other impurities in the casting. Techniques such as shot blasting, grinding, or wire brushing can be employed to fully clean that.

Shakeout and cleaning is one of the most important parts of the process as it ensures the accuracy of the entire process. It is important to put significant resources and time towards this step and ensure the shakeout is handled by the experts accurately as per the casting’s specifications.

Inspection

No manufacturing process is complete without a comprehensive and careful inspection. It is the key to making sure all the above steps are followed correctly.

Hence, the final step in the procedure is a comprehensive inspection of the casting obtained via shakeout. A thorough inspection includes checking the casting to ensure dimensional accuracy, surface finishing, shape defects, internal mold defects, and overall imperfections.

Other than manual testing, modern methods like X-ray and ultrasonic testing are used to identify internal defects. Keep in mind that defects are common in that, but it is the severity of the defects that will determine whether the casing can be repaired or scrapped completely.

Once the inspection is done and the green sand casting is of good quality, it is now ready to be used in many different ways.

Post-Casting Sand

Once the green sand is used to create a casting, the sand is used and cannot be used again in the casting process. While it is possible to separate out the impurities from sand to reuse it, the process becomes lengthy and expensive.

Hence, the services always use new sand for each casting process and use impure sand for other purposes. Reusing the sand for other purposes is also important to reduce waste in landfills. Modern testing techniques can be employed to ensure there are no toxic substances in the sand.

Applications of Green Sand Casting

It is widely used in various industries. The parts produced by the the process have high strength and high quality properties, so they have been widely used in the railway industry. At the same time, it is also used in our common agricultural machinery industry and construction machinery industry.

Its wide tolerance of materials makes its products corrosion-resistant, and thus it can be used in the oil pipeline industry. In our daily lives, the parts are also commonly seen on our commonly used vehicles. For example, automobile exhaust system parts and ship turbine system parts, etc.

Green Sand Casting Advantages & Disadvantages

We have compared the advantages and disadvantages of various sand castings, including common processes and niche processes.

Sand Casting MethodAdvantageDisadvantage
Green Sand Casting

(most popular)

● Low cost

● Short cycle time

● Affordable molds

● High reusability

● Low surface accuracy

● Rough surface finishing

● High potential for defects

● Limited complex shapes

Resin Sand Casting (most popular)● High surface smoothness

● Good dimensional accuracy

● Suitable for complex designs

● Detailed castings and strong molds

● Higher cost

● Long production cycle

● Requires safety precautions

● Non-reusable molds

Shell Molding Casting(most popular)● High precision

● High production efficiency

● High strength

● High cost

● Not suitable for large items

Dry Sand Casting● High surface smoothness

● Suitable for complex shapes

● Good dimensional accuracy

● Less risk of defect due to moisture

● Expensive

● Long production cycle

● Requires advanced mold preparation

● High energy consumption

Wet Sand Casting● Low cost

● Suitable for mass production

● High flexibility

● Average surface quality

● Low dimensional accuracy

● Not suitable for complex parts

Vacuum Molding or V-Process● High quality surface

● High precision

● No pollution

● Higher cost

● Lower production efficiency

Conclusion

Dawang has developed sand casting products for different industries such as oil pipeline, agricultural machinery, construction machinery, automotive industry, shipping, and railway industry. It can meet the various needs of customers from product development to production and finish processing. You have the flexibility to choose between superior resin sand casting production line and shell molding casting production line for your project. Please consult us to consult for what is the best choice, Dawang will tailor the best solution to your needs.