Gravity Sand Casting

1. Gravity Sand Casting Process

The process of gravity sand casting involves creating a mold from sand that is shaped to contain molten metal. Unlike pressure-driven casting methods (like die casting or lost wax casting), gravity sand casting relies solely on the force of gravity to fill the mold.

a. Pattern Creation

• Pattern Design: A pattern is created to match the part to be cast. Patterns are typically made from non-ferrous metals, steel, or other materials that can withstand the heat of the molten metal.

• Pattern Material: The pattern is typically made from aluminum, brass, or stainless steel for better durability. These materials are chosen because they can be used to create accurate patterns and withstand the high temperature of molten metal.

• Pattern Coating: For more precise patterns, they can be coated with a refractory material to improve surface finish and reduce defects in the casting.

b. Sand Molding

• Molding Sand Preparation: The sand is mixed with a binder (typically clay, water, and other additives) to make it cohesive enough to form a stable mold. The mixture is often called “green sand,” and it can be reused multiple times for different molds.

• Mold Box Assembly: The sand is packed around the pattern in a mold box. The mold box is typically divided into two parts: the cope (top half) and the drag (bottom half). These two parts form the full mold when combined.

• Compaction and Setting: The sand mixture is tightly packed around the pattern using mechanical vibration, manual ramming, or pressure, ensuring that the mold holds its shape once the pattern is removed.

• Pattern Removal: After the mold has hardened, the pattern is removed, leaving a cavity in the sand that replicates the desired shape of the casting.

c. Pouring the Molten Metal

• Metal Melting: The metal to be cast is melted in a furnace until it reaches the appropriate pouring temperature, typically ranging from 1,200°C (2,192°F) for aluminum to 1,600°C (2,912°F) for steel, depending on the material.

• Pouring the Metal: The molten metal is poured into the sand mold using gravity, typically from a ladle or pouring basin. Gravity casting relies solely on the weight of the molten metal to flow into the mold cavity, which may include intricate geometries, hollow sections, or complex shapes.

• Filling the Mold: The metal flows into the mold, filling the cavity and taking the shape of the mold. The mold material is designed to withstand the heat of the molten metal without deforming.

d. Cooling and Solidification

• Cooling Time: The molten metal gradually cools and solidifies inside the mold. Cooling rates depend on the metal type, mold material, and casting thickness. Slow cooling helps prevent defects such as cracks and warping.

• Solidification: As the molten metal cools, it solidifies in the mold cavity, creating a casting. The cooling rate can be controlled in some cases by modifying the sand mixture or adding metal chills to specific areas of the mold.

e. Mold Removal and Cleaning

• Mold Breaking: Once the casting has cooled and solidified, the sand mold is broken apart to reveal the casting. In gravity sand casting, the mold is usually broken manually or with mechanical tools to ensure easy removal of the casting.

• Cleaning and Finishing: The casting is then cleaned to remove sand, scale, and any other debris from the surface. This can be done with abrasives, mechanical cleaning tools, or chemical treatments.

• Post-Casting Machining: The casting may undergo additional machining to meet exact specifications, such as trimming excess metal, drilling holes, or adding threads. Gravity sand casting typically requires less post-processing than other methods, but this depends on the required tolerances.

2. Applications of Gravity Sand Casting

Gravity sand casting is used in a variety of industries and applications, particularly when high production volumes are not necessary, and parts with complex geometries or large sizes are needed. Below are the main professional applications of gravity sand casting:

a. Automotive Industry

• Engine Components: Gravity sand casting is widely used to produce engine blocks, cylinder heads, and other parts that require good strength and thermal stability. These parts typically need to withstand high temperatures, pressure, and mechanical stress.

• Transmission and Drivetrain Parts: Components such as gears, clutch housings, and crankshafts are often produced via gravity sand casting. These parts require high mechanical strength and durability, making gravity sand casting an ideal choice.

• Suspension and Steering Components: Castings for suspension arms, control arms, and steering knuckles are often made using gravity sand casting to provide the required strength and precision for critical automotive applications.

b. Power Generation

• Steam and Gas Turbine Components: Gravity sand casting is used to make components like turbine blades, rotors, and casings for power generation turbines. These parts require high precision and strength to withstand high-pressure steam or gas flows.

• Valve Bodies and Pump Components: Castings for valves, pumps, and other critical power generation equipment are made using gravity sand casting, as the process provides the strength and durability needed for long-term, reliable operation in power plants.

c. Marine Industry

• Propeller and Shaft Components: Components like propellers, shafts, and rudder housings are made using gravity sand casting. These parts need to be resistant to corrosion, wear, and mechanical stress, which gravity sand casting can provide.

• Pump Bodies and Valve Parts: Gravity sand casting is used for creating pump housings, valve bodies, and other critical parts that must withstand seawater corrosion and high pressure.

d. Industrial Equipment

• Machine Tool Parts: Gravity sand casting is used to produce heavy-duty machine tool components, such as beds, bases, and frames, which need to be strong and precise.

• Construction Machinery Parts: Large castings for heavy construction equipment like excavators, bulldozers, and cranes are often made using gravity sand casting. The process can produce large, robust components required for high-stress environments.

e. Heavy Machinery and Infrastructure

• Foundry and Casting Equipment: Components used in the casting industry itself, such as furnace parts, molds, and mold components, are produced using gravity sand casting due to the durability and high temperature resistance required.

• Large Casting Components: Gravity sand casting is often employed to produce large and heavy parts such as steel mill rolls, bearing housings, and gears, where the casting needs to be both precise and strong.

f. Custom and Low-Volume Production

• Prototype Castings: Gravity sand casting is used for prototype development in industries such as automotive, aerospace, and industrial machinery, where custom parts need to be tested and evaluated before full-scale production.

• Custom Metal Products: For low-volume or custom casting needs, such as small-run specialized parts, gravity sand casting is ideal due to its flexibility and the relatively low cost of the process compared to other casting methods.

3. Advantages of Gravity Sand Casting

• Cost-Effective: Gravity sand casting is one of the most cost-effective casting methods, especially for small to medium-sized production runs. It is suitable for a wide range of materials, including ferrous and non-ferrous alloys.

• Flexibility: It can be used to produce castings with complex geometries, large sizes, and thin walls. The process allows for high flexibility in design and customization of parts.

• Large Part Production: Gravity sand casting is ideal for producing large, heavy, and complex parts, making it widely used in industries like aerospace, automotive, and power generation.

• Good Surface Finish: While it may not produce the mirror-like finishes of investment casting, gravity sand casting can achieve a reasonable surface finish, especially with the use of fine sand mixtures and careful mold handling.

• Reusable Molds: The sand molds can often be reused multiple times, lowering the overall cost per casting.

Materials we can do but not limited to:

Carbon steels, alloy steels, stainless steels and duplex steels.