Centrifugal casting is a manufacturing process in which molten metal is poured into a mold that spins at high speed, typically between 200 and 1,000 rpm. The rotation generates centrifugal force that pushes the liquid metal outward against the mold walls, where it solidifies into a dense, uniform part. The technique is widely used to produce pipes, cylinder liners, flywheels, and other round or cylindrical components, and it yields parts with physical properties up to 30% better than conventional gravity-poured castings.
How the Process Works
The basic sequence is straightforward. A cylindrical mold is mounted on a machine and brought up to speed. Molten metal is then poured inside, and centrifugal force flings it against the mold wall with tremendous pressure. Because the metal is denser than any impurities mixed into the melt, those lighter oxides and inclusions migrate inward toward the center of rotation during cooling. Once the part solidifies, the inner surface (where the impurities collected) can simply be machined away, leaving clean, high-quality metal throughout the finished wall.
Engineers use a value called the G-factor to determine whether the mold is spinning fast enough. The G-factor compares the centrifugal force acting on the metal to its own weight. For horizontal casting, a G-factor between 60 and 80 is the practical target. If the value drops too low, the molten metal won’t stay pressed against the mold wall as it passes over the top of the rotation. Instead, it “rains” down inside the cavity, ruining the casting.
One notable feature of the process is that it doesn’t need the channels and gates used in traditional casting to feed metal into a mold. The metal is poured directly into the spinning cavity, which reduces waste and simplifies cleanup.
Three Types of Centrifugal Casting
True centrifugal casting is the most common form. It uses a hollow cylindrical mold rotating on either a horizontal or vertical axis. No inner core is needed because the centrifugal force naturally holds the metal against the outer wall, leaving a hollow center. The result is a seamless tube or cylinder. This is how most cast iron pipes, engine cylinder liners, and large industrial tubes are made.
Semi-centrifugal casting fills the entire mold with metal rather than leaving a hollow center. Metal enters through a central sprue, and the spinning action pushes it outward to fill the cavity completely. The finished parts are still rotationally symmetric (wheel-shaped or disk-shaped), but they’re solid rather than hollow. If a central hole is needed, a sand core is placed in the mold beforehand. Flywheels and gear blanks are typical products.
Centrifuge casting (sometimes called centrifuging) extends the benefits of rotation to parts that aren’t symmetrical at all. Multiple mold cavities are arranged around the circumference of a spinning platform, connected to a central sprue by radial channels. The spinning forces metal outward into each cavity simultaneously. This approach is useful for producing batches of smaller, irregularly shaped parts that still benefit from the improved density and reduced porosity that centrifugal force provides.
Horizontal vs. Vertical Machines
The choice between a horizontal and vertical spinning axis depends mostly on the shape of the part. Horizontal machines are the go-to for long cylindrical parts where the length is significantly greater than the diameter, like pipes and tube stock. Vertical machines handle shorter, wider parts where the height is typically less than twice the width, such as rings, flanges, and bushings. Gravity affects the metal differently in each orientation: horizontal casting produces a uniform wall along the length, while vertical casting can produce a slightly thicker wall at the bottom due to gravity pulling downward during solidification.
Why Centrifugal Parts Are Stronger
The high forces involved produce a noticeably denser, finer-grained metal structure compared to parts made by simply pouring metal into a stationary mold. Tensile strength, yield strength, and elongation (the metal’s ability to stretch before breaking) all improve by as much as 30%. Common defects found in static castings, including internal shrinkage cavities, gas porosity, and trapped non-metallic particles, are far less likely to occur. The centrifugal force essentially squeezes gas bubbles and lightweight contaminants out of the structural wall and toward the bore, where they’re removed during machining.
This self-purifying effect is one of the main reasons the process is chosen for high-stress, safety-critical components. Engine cylinder liners and sleeve valves for piston engines, for example, are parts that could not be reliably manufactured any other way. The structural uniformity and balance of a centrifugally cast part also matter for rotating components like railway wheels and machine fittings, where even small inconsistencies in grain structure can cause vibration or premature failure.
Compatible Materials
Virtually any material that can be melted and poured can be centrifugally cast. The most common choices are ferrous metals: carbon steel, stainless steel, and cast iron (including the cement-lined cast iron pipes used in water systems). For high-temperature or corrosive environments, nickel alloys and cobalt alloys are frequently centrifugally cast into components like furnace rolls and chemical processing equipment. Copper alloys, including copper-nickel and aluminum bronze, are popular for offshore and marine applications because of their natural resistance to saltwater corrosion. Even non-metallic materials like glass fiber reinforced resin and concrete have been centrifugally cast for specialty pipe products.
Size and Shape Limits
The process does have geometric constraints. True centrifugal casting works best for round, cylindrical, or tubular shapes. Complex external geometry, internal features, and non-circular cross sections generally can’t be produced this way (though centrifuge casting addresses some of those limitations for smaller parts). Current equipment can handle parts up to about 3 meters in diameter and 15 meters in length, with wall thicknesses ranging from 2.5 mm to 125 mm. The spinning equipment itself is a significant capital investment, which means centrifugal casting is most cost-effective for medium to high production volumes or for parts where the quality improvement justifies the tooling cost.
Common Products
The process dates back to 1852, when Alfred Krupp used it to cast steel railway wheel tires. Today the list of products is broad: water and sewer pipes, industrial rollers, pressure vessel shells, bearing sleeves, ring blanks for forging, petrochemical reactor tubes, and engine components. A common everyday example is ductile iron pipe with a cement mortar lining on the interior, used in municipal water systems worldwide. In aerospace and power generation, centrifugally cast nickel and cobalt alloy tubes handle extreme temperatures that would degrade parts made by other methods.