Comparison of Brass and Bronze Centrifugal Castings vs. Sand Castings
Which to Choose for Your Application
Brass and bronze are two common copper alloys used in casting. Each has unique properties and benefits for different industrial uses.
The casting methods for these alloys, like centrifugal casting and sand casting, significantly affect the final product. They influence the product’s physical properties, grain structure, and performance. This article explores the key differences between brass and bronze centrifugal castings. It focuses on centrifugal and sand castings. We will examine each type’s grain structure, physical properties, and common uses.
1. Casting Methods: Centrifugal vs. Sand Casting
Centrifugal Casting:
At Johnson Centrifugal, we pour molten metal into a spinning mold. This creates a force that pushes the metal against the mold walls. This method is commonly used for producing cylindrical parts, such as pipes, bearings, and bushings. The centrifugal force results in a dense outer layer and a more uniform microstructure. The casting process is more automated, which can lead to improved consistency and fewer defects.
Sand Casting:
Sand casting is the most traditional casting method, where a pattern of the desired part is placed into a sand mold. Molten metal is poured into the mold cavity, and once it cools and solidifies, the mold is broken away to reveal the cast part. This method is more versatile and can produce complex shapes, but it tends to have less precision and more surface roughness than centrifugal casting.
2. Grain Structure Differences
The grain structure of a cast alloy plays a critical role in determining its mechanical properties, including strength, ductility, and resistance to wear.
Centrifugal Castings:
In centrifugal casting, the molten metal is rapidly drawn toward the outer walls of the mold by centrifugal force. This results in a finer, more uniform grain structure near the surface of the casting, with a denser material profile.
The outer layer of centrifugal castings typically has a well-ordered grain structure with less porosity. The grain structure may become coarser as the casting cools toward the inner core.
In some cases, the inner core of a centrifugal casting can exhibit dendritic (tree-like) grain patterns. However, the transition zone between the inner and outer sections is generally more gradual, reducing internal defects. Johnson Centrifugal uses this improved grain structure to create parts for critical military, industrial, oil and gas, and infrastructure applications.
Sand Castings:
Sand castings often display a more irregular and coarse grain structure compared to centrifugal castings. Due to slower cooling rates and less directional solidification, sand castings typically experience more segregation of alloying elements, leading to a less uniform grain size. The cooling rate is slower on the outer surfaces, resulting in a larger, less homogeneous grain structure throughout the casting. The central region may also show more porosity and defects, particularly when compared to centrifugal castings, which can affect the material’s strength and fatigue resistance.
3. Mechanical/Physical Properties
The mechanical properties of brass and bronze castings depend heavily on the alloy composition and the casting process used. For both centrifugal and sand casting methods, the following general trends can be observed:
Tensile Strength and Hardness:
Centrifugal casting typically produces castings with higher tensile strength and hardness compared to sand casting. This is due to the more controlled cooling process and finer grain structure, which reduces the likelihood of defects like porosity and internal voids. As a result, centrifugal castings often show improved mechanical properties such as greater tensile strength and higher fatigue resistance.
Ductility and Toughness:
While centrifugal castings are generally stronger, sand castings tend to exhibit higher ductility because of the coarser grain structure. The slower cooling in sand casting can allow for more homogeneous phase distribution in alloys like bronze, which can enhance toughness. However, this advantage in ductility comes at the expense of other mechanical properties like strength and fatigue resistance.
Porosity:
One of the primary disadvantages of sand castings is the potential for increased porosity. The slower cooling process can lead to gas entrapment, which results in voids and bubbles within the casting. This reduces the overall strength and integrity of the material, making it less suitable for high-stress applications. In contrast, centrifugal casting, due to its rapid cooling and high pressure, produces much less porosity, resulting in a denser, stronger material.
Corrosion Resistance:
Both centrifugal and sand castings made from brass and bronze exhibit excellent resistance to corrosion, particularly in environments where exposure to water or salt is common. However, the denser, finer grain structure of centrifugal castings often results in better long-term durability and resistance to environmental stress, making these castings more suitable for critical applications like marine components, industrial fittings, and machinery exposed to harsh conditions.
4. Applications and Suitability
Centrifugal Castings:
Typical Applications: Bearings, bushings, pipes, fittings, rings, gears, and cylinders.
Suitability: Johnson Centrifugal castings are ideal for producing high-performance components that require high strength, minimal porosity, and consistent physical properties. It is especially useful for parts that must withstand high wear, such as bearings and bushings, where uniformity and durability are critical.
Sand Castings:
Typical Applications: Large parts such as engine blocks, pump housings, decorative items, and marine components.
Suitability: Sand casting is more suitable for producing complex and large geometries, often in lower volumes. It is a more cost-effective process for producing fewer demanding components, where the castings’ aesthetic qualities and mechanical properties are less critical. The ability to use complex molds and the flexibility in casting shapes make sand casting popular for prototype development and small to medium production runs.
Conclusion
Brass and bronze castings produced by centrifugal casting and sand casting each offer distinct advantages and are best suited for different applications. Centrifugal castings at JCTexcel in creating dense, high-strength, and precise parts with finer grain structures, making it ideal for components that require excellent mechanical properties, such as bearings, bushings, and pipes. On the other hand, sand casting is a more flexible and cost-effective method, offering the ability to cast intricate and large shapes at the expense of precision and mechanical strength.
If your application has these elevated Mechanical/Physical requirements, centrifugal castings from Johnson Centrifugal Technology are the ideal fit. We have been providing our customers with solutions for over 100 years.
For help with a component part project, please access our Request a Quote Form or call 262-377-9440.
Posted by
Isaac Brummer Project Engineer / Estimator
Johnson Centrifugal Technology
ibrummer@jct-usa.com