---
type: process
name: "Centrifugal Casting"
category: "Forming"
subcategory: "Metal"
materials: ["Metal"]
tolerances: "Outside diameter, cast against a metal die, holds substantially tighter than the bore, which is uncontrolled and always machined; wall thickness is set by pour volume and carries the loosest tolerance of the three"
volumes: "1–10,000 parts; a single large ring is economic on a sand-lined mold"
lead_time: "2–6 weeks for a run against existing mold sizes; longer if a new permanent mold is required"
url: https://manufacturingprocesses.org/processes/forming/centrifugal-casting
---

# Centrifugal Casting

Centrifugal casting pours molten metal into a spinning mold so centrifugal force packs it against the wall and drives inclusions toward the bore.

- **Category**: [Forming](https://manufacturingprocesses.org/processes/forming.md)
- **Family**: Metal
- **Materials**: Metal
- **Typical tolerances**: Outside diameter, cast against a metal die, holds substantially tighter than the bore, which is uncontrolled and always machined; wall thickness is set by pour volume and carries the loosest tolerance of the three
- **Typical volumes**: 1–10,000 parts; a single large ring is economic on a sand-lined mold
- **Lead time**: 2–6 weeks for a run against existing mold sizes; longer if a new permanent mold is required

## Overview

Centrifugal casting pours molten metal into a mold spinning about its own axis, so centrifugal force throws the metal outward against the mold wall and holds it there while it freezes. Density does the quality control: dense metal is driven to the outside diameter while slag, oxide, and gas — all lighter than the melt — collect at the bore, where they are machined away.

The result is a hollow cylindrical part with exceptionally sound outer-wall metal, no cores, and no risers. It is the standard process for cast iron pipe, bronze bushings and bearing sleeves, cylinder liners, mill rolls, and large rings in stainless and nickel alloys, from a few inches to several feet in diameter.

Geometry is the constraint: the process only makes bodies of revolution, and the bore is set by how much metal is poured rather than by tooling, so it is always machined. Metal yield is high because there is no gating system to cut off and remelt.

## How it works

Two arrangements cover most work.

**True centrifugal casting** spins a cylindrical mold — often a water-cooled steel die, sometimes sand-lined — about a horizontal or vertical axis and pours metal into it with no central core. The bore forms itself as a free liquid surface. A horizontal axis is used for long parts such as pipe and liners; a vertical axis suits short rings, where the bore takes a slight parabolic taper because gravity competes with rotation.

**Centrifuge (semi-centrifugal) casting** arranges several conventional mold cavities around a central sprue on a spinning table, using rotation to pressurize the feed into shapes that are not themselves bodies of revolution.

The cycle:

1. **Mold prep.** The permanent mold is coated with a refractory wash or a sand lining, then preheated. Coating thickness controls how fast the shell chills, and therefore the outer-wall microstructure.
2. **Spin up.** The mold reaches speed before pouring. Speed is set by the G-force required at the mold wall rather than by rpm directly — G-factors quoted in foundry practice for horizontal work generally fall in the range of 60–100 — so a small-diameter mold spins far faster than a large one.
3. **Pour.** Metal is delivered along the length of the mold from a launder or trough. Pour rate and traverse speed set wall uniformity.
4. **Solidification under force.** Freezing runs from the outer wall inward. Because the pressure gradient continuously feeds the freezing front, no risers are needed and shrinkage porosity is pushed toward the bore rather than into the wall.
5. **Segregation.** Lower-density inclusions, oxide film, and dross migrate to the free inner surface. This is the process's defining metallurgical advantage.
6. **Extraction and machining.** The casting is stripped once solid. The bore is bored out — commonly 0.125–0.25 in (3–6 mm) of radius or more — to clear the segregated layer, and the OD is turned to size.

Bi-metal parts are made by pouring a second alloy after the first has partly frozen, which is how bronze-lined steel bushings and hard-faced rolls are produced.

## Design guidelines

### Bodies of revolution only

The economic geometry is a cylinder, sleeve, ring, or pipe. Flanges and steps on the outside diameter are possible in a stepped die; features on the bore are not, because the bore is a free liquid surface. Anything non-round is either a centrifuge casting or a different process entirely.

### Machine the bore, always

Plan on removing 0.125–0.25 in (3–6 mm) of radius from the bore, and more on large castings or less clean melts. That layer holds the inclusions and dross the process deliberately pushed there. A design that specifies an as-cast bore discards the main advantage of the process.

### Wall thickness

Keep the wall above roughly 0.25 in (6 mm) for iron and steel, with 0.375 in (10 mm) a more comfortable minimum on long castings. Uniform wall along the length is easiest; a tapered wall requires a controlled pour traverse and adds cost.

### Wall tolerance is the loosest dimension

Wall thickness is set by the volume of metal poured, not by tooling, so it carries a looser tolerance than the die-controlled outside diameter. Tolerance the OD, machine the bore concentric to it, and let the wall fall where it falls.

### Length-to-diameter ratio

Long horizontal castings need a traversing pour to keep the wall uniform, and wall control gets progressively harder as L/D rises. Short rings are easier and are usually cast on a vertical axis.

### Alloy selection

Bronze bearing alloys, gray and ductile iron, stainless, and nickel alloys all cast well centrifugally. Alloys with wide freezing ranges and strong density differences between phases segregate radially — useful when it puts the hard phase on the wear surface, a defect when it does not.

See the [surface finish chart](/charts/surface-finish-chart) for what boring and turning will deliver on the machined surfaces, and [metal melting points](/charts/metal-melting-points) for pour temperature planning.

| Feature | Recommended | Limit | Why |
| --- | --- | --- | --- |
| Geometry | Cylinder, sleeve, ring, pipe | Non-round needs centrifuge casting | Rotation only pressurizes bodies of revolution |
| Bore machining stock | 0.125–0.25 in (3–6 mm) on radius | More on large castings | Inclusions and dross segregate to the bore |
| Wall thickness, iron/steel | ≥ 0.375 in (10 mm) | 0.25 in (6 mm) | Thin walls freeze before the pour completes |
| Wall uniformity | Constant along length | Tapered walls cost more | Uniform wall needs only a steady pour traverse |
| Cast features | OD steps and flanges | None on the bore | The bore is a free liquid surface |
| Risers and gates | None required | — | Centrifugal pressure feeds the freezing front |

## Cost drivers

The distinguishing economics are yield and tooling reuse. There is no gating system and no riser, so metal yield is very high compared with static casting, where risers and runners routinely consume a third or more of the poured weight. Permanent metal molds are reused for thousands of castings, so per-part tooling cost falls quickly. Against that, machining is not optional — every bore is bored — and machine time on a large ring is significant.

Volume breakpoints: sand-lined centrifugal molds make one-off large rings economic; a permanent steel die pays back over hundreds to thousands of parts. Very high volumes of small bushings are usually better served by press-and-sinter powder metallurgy, which produces them net shape with no machining at all.

1. **Size the casting to minimize bore stock.** Every extra thousandth of radius removed is chips and spindle time.
2. **Cast the longest tube you can, then part off.** Several short bushings from one cast tube spread the setup across many parts.
3. **Use bi-metal casting where a solid part of expensive alloy is not needed.** A thin bronze bearing layer on a steel backing is a large material saving.
4. **Standardize on a few mold diameters.** Because wall thickness comes from pour volume, one die can produce a family of wall thicknesses at the same OD.
5. **Do not specify tight wall-thickness tolerance.** Wall is a pour variable, not a tooling one; tighten the OD instead.

## FAQ

### Why is centrifugal casting metal denser than sand casting?

Rotation applies a continuous pressure gradient that feeds the solidification front from the outside inward, so shrinkage porosity never forms in the wall. Lighter inclusions, oxide, and gas migrate toward the bore, which is machined away. The result is a very clean outer wall with no risers at all.

### How much stock has to be machined out of the bore?

Typically 0.125–0.25 in (3–6 mm) on radius, and more on large castings or less clean melts. That layer is exactly where the process concentrates dross and inclusions, so leaving it in place forfeits the main quality advantage.

### What shapes can be centrifugally cast?

Bodies of revolution — pipe, tube, sleeves, bushings, rings, cylinder liners, and mill rolls. Outside-diameter steps and flanges can be cast into a stepped die. The bore is formed by a free liquid surface, so it cannot carry any cast feature.

### Does centrifugal casting need cores or risers?

No. The bore forms itself from the free surface of the spinning metal, so there is no core, and centrifugal pressure feeds solidification, so there are no risers. That is why metal yield is far higher than in static sand casting.

### Can two different alloys be cast into one part?

Yes. Pouring a second alloy after the first has partially solidified produces a metallurgically bonded bi-metal wall. This is how bronze-lined steel bushings and hard-faced mill rolls are made, and it saves a substantial amount of expensive alloy.

### Centrifugal casting or machining a bushing from bar stock?

Bar stock wins for small quantities of small bushings in common alloys, since no foundry is involved. Centrifugal casting wins on large diameters where bar stock is expensive or unavailable, on bronze bearing alloys, and wherever wall soundness through the full section matters.

## Alternative processes

- [Forging](https://manufacturingprocesses.org/processes/forming/forging.md): Forging deforms solid metal under compressive load in a hammer, press or dies, so the grain flow follows the part contour and fatigue strength rises.
- [CNC Turning](https://manufacturingprocesses.org/processes/cutting/cnc-turning.md): CNC turning rotates the workpiece against a stationary tool, producing round parts with excellent concentricity and short cycle times.
- [Powder Metallurgy (Press and Sinter)](https://manufacturingprocesses.org/processes/forming/powder-metallurgy-press-and-sinter.md): Press-and-sinter powder metallurgy compacts metal powder in a rigid die and sinters it below its melting point into a finished net-shape part.
- [Metal Extrusion](https://manufacturingprocesses.org/processes/forming/metal-extrusion.md): Metal extrusion pushes heated billet through a shaped die, producing continuous aluminum or copper profile of constant cross-section.

## Related processes

- [Sand Casting](https://manufacturingprocesses.org/processes/forming/sand-casting.md): Sand casting pours molten metal into a cavity formed in bonded sand around a pattern, then breaks the mold away to release the part.
- [Investment Casting](https://manufacturingprocesses.org/processes/forming/investment-casting.md): Investment casting builds a ceramic shell around a wax pattern, melts the wax out and pours metal into the cavity, giving fine detail in almost any alloy.
- [Die Casting](https://manufacturingprocesses.org/processes/forming/die-casting.md): Die casting injects molten aluminum, zinc or magnesium into a hardened steel die under high pressure, producing thin-walled net-shape metal parts.
- [Heat Treatment](https://manufacturingprocesses.org/processes/forming/heat-treatment.md): Heat treatment cycles metal through controlled heating and cooling to change its hardness, strength, ductility or internal stress state.

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*Source: [Manufacturing Processes](https://manufacturingprocesses.org/processes/forming/centrifugal-casting)*

*Last updated: August 11, 2026*