Metal casting is one of the oldest technology through which tools, machinery, shields, and wheels were made. Within the broader metal casting scope, sand casting is one of the most popular metal casting methods in many foundries.
This article will demonstrate the fundamentals of sand-casting methods and each step of the sand casting process. It will also highlight the famous sands used in this method and how to distinguish the best sand for casting. So, take your time and read the following passages carefully. We hope this article will be the best guide for sand casting.
What Is Sand Casting?
Sand casting, recognized as one of the most ancient metal casting methods, is widely employed across industries due to its adaptability and cost-effectiveness. Sand casting is a metal casting process that utilizes a non-reusable sand mold to form different shapes of metal products. It is the easiest metal casting method. However, every foundry must deal with more precautionary and quality control steps. This metal casting method works with all types of metals and creates metal products from ounces to tonnes of weight.
Tooling for sand casting is simple. It is possible to create sand molds with fine exterior detail and interior cores of any shape. However, complex bodies would be difficult to process with sand casting. Other casting methods like investment casting method could be considered.
Overall, sand casting is beneficial for large parts with low-volume production, as it’s capable of creating large, complex parts or those that require a core. This method offers quick start-up and completion times, making it faster than many other casting techniques.
The sand casting method is prevalent in a wide range of applications. The popular products from sand castings are pistons and valves, engine blocks, cams, bearings, bearing balls, hydraulic pumps and housings, agricultural equipment, automotive equipment, lever arms and pulleys, and electrical equipment appliances parts, railroad equipment, petrochemical engineering equipment, construction machinery.
Although based on different complexity, the type of metal casting may vary. The popular industries it serves are medical, agricultural, automotive, defense, marine, mining, power plants, etc.
Sand casting is the most used metal casting method in every industry, as we have already known it. Because of its wide range of benefits, this method is prevalent in every sector where metal is concerned. Sand casting provides the following advantages over other metal casting methods.
- Sand casting is highly versatile for working with all types of metals. It can produce metal products of every size.
- It can create relatively complex parts in a budgeted option.
- This metal casting method creates relatively precise metal castings. However, later requires additional machining to minimize the dimensional tolerances.
- Sand casting is undoubtedly the best-budget option for precision metal casting. Investment casting, shell mold casting is comparatively more expensive than sand casting.
- This metal casting method is the fastest in the world. Both tooling and formulation require less time than other metal casting methods.
- Sand molds are recyclable but not reusable for casting. These are easy to recycle and can do multiple production cycles.
- Casting sands typically can withstand extremely high melting points.
Although sand casting offers many benefits, it still has some drawbacks. Depending on the different factors of the required applications, several cons of sand casting may appear.
- The sand casting method produces higher porosity defects in the castings than other metal casting methods. Therefore, it would be best if you decide the porosity level of your metal casting applications.
- Another casting defect often found in sand casting is surface inclusion. In the casting process, the molten metal picks up loose sand from the molds. As a result, it creates surface inclusions in the form of sand grains.
- We know that sand casting requires less tooling cost. However, on the other hand, it ultimately increases the labor cost as the process is manual.
- Sand casting requires special cleaning and additional machining to minimize the dimensional tolerances.
- This casting method is not suitable for large order quantities. In those cases, reusable permanent molds are prevalent in most foundries.
What is Sand Casting Process?
The sand casting method is easy to operate and requires less tooling. But it follows consecutive production steps where operator skill is concerned for better quality. We have summarized the complete sand casting method in the following seven steps.
First Step: Mold Creation
Mold-making is the most critical step, which ensures the precision of the final casting dimension. A container filled with specialized sand includes the pattern of the original object. In this case, a casting pattern replicates the actual product. It can be made of wax or other materials. However, the sand mold container’s top and bottom halves are called cope and drag, respectively.
Second Step: Mold Preparation
After the sand mold is ready, the operator prepares to pour the molten metal. In this case, lubrication on the surface of the cavity is necessary. Each metal type differentiates the lubricate type. Later, the operator closes the two halves of the container and clamps them together. Clamping is also a critical step where proper precautions are taken for defect-free metal casting.
Third Step: Pouring Molten Metal
The gating system is one of the essential terms in this step. The operator pours the molten metal through these gates. In this case, gating refers to the gap between the casting cavity and the mold outside.
Fourth Step: Cooling
After pouring metal into the casting cavity, the operator puts the container into the cooling chamber. In this case, an appropriate cooling temperature is necessary to minimize the shrinkage defects of the casting. When the liquid metal turns into solid metal and comes to a moderate temperature, it is now ready to be removed.
Fifth Step: Remove The Cast From The Mold
At this stage, the operator breaks the sand mold and removes the casting from the mold. In Dawang casting, the expert operator uses a vibrating machine that gently removes the sand from the casting. Finally, the hot blasting method removes the remaining sand and the oxide layer which was stuck on the surface of the casting.
Sixth Step: Machining
It is important to note that sand castings have higher dimensional tolerances. At this stage, proper machining is necessary to make it precise. Some excess material might be attached to the surface, which needs to be removed to get the original shape of the castings.
Seventh Step: Finishing
After trimming and other machining stages, the casting goes to the finishing stage. The finishing stage includes polishing, painting or powder coating. The type of finishing depends on the casting materials and application.
What Are The Different Types of Sand Used in Sand Casting?
Sand is the primary ingredient of the sand casting method. It is not the regular sand that you see every day. Three different types of sand are famous for sand casting in every casting foundry. “Types of Sand Used in Casting” is a definitive guide on the sands used in casting.
- Green sand: Green sand consists of sands (75-85%), bentonite clay (5-11%), water (2-4%), and other materials (3-5%).
- Sodium-silicate or Water glass: Sodium silicate mainly consists of metasilicate. It is ideal for fire protection. Besides, this sand is also popular in the textile industry, lumber handling, and silica gel production.
- Resin sand: Resin sand is a mixture of quartz sand and resin. It provides good fluidity and accessible compaction properties.
How to Choose The Best Sand for Casting?
Choosing the appropriate sand is crucial for the sand casting method. The variations of sand for casting depend on the type of metal chosen. We know that different sand for casting behaves differently with various metals. For this reason, we should know how to select the best sand for casting. The following six points are the most crucial factors you should consider while choosing the best sand for casting.
- Temperature refractoriness: The most critical factor you should consider is the ability of the sand that withstand the high molten temperature of the liquid metal.
- Gas permeability: The ability of sand to allow gas to pass through the sand. During the casting process, some gas may dissolve in the liquid metal. However, when it starts solidification, this gas tries to come out of the mold. In that case, the gas permeability of the sand is the most crucial factor to consider.
- Fluidity: The sand’s ability to compress to a compact density allows the molten liquid to pack around the pattern.
- Contractibility: Collapsibility or contractibility refers to the ability of the sand to collapse after solidification.
- Adhesiveness: The ability of the sand allows the sand particles to stick to other materials.
- Strength: The ability of the sand allows the sand particles to stick to each other.
The sand casting method is one of the best-budgeted options for average complex metal casting shapes. The sand casting method will be best if your application does not require highly high-precision metal parts. Read more on what sand casting service Dawang Casting can provide for your project today!
Don’t hesitate to contact us if you have any questions. We have a team of professionals who can provide the finest recommendations for your business.