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Lesson 1.5ShapeChapter 1 · Casting

Centrifugal casting

Metal flung against the wall of a spinning mold

Centrifugal casting pours molten metal into a mold that spins fast, so the metal is flung against the wall and freezes into a tube or ring. Water and sewer pipes, engine cylinder liners and bearing rings are made this way. Spinning packs the metal tightly, so the walls come out dense and strong.

Centrifugal casting: a real photo
Photo: Anna Frodesiak, CC0, via Wikimedia Commons
Metal poured into a spinning mold is flung against its wall and forms a tubeHorizontal centrifugal casting of a pipe: lengthwise cut (left) and end view (right)Lengthwise cutEnd viewSteel mold, spinning fastMolten metal pressedagainst the wallDrive rollersPouringspoutInner surface gathersimpurities; machined offTube pulled outCentrifugal forcethrows metal outward12345Molten metalSteel mold, rollers, spout
Centrifugal casting · lengthwise cut and end viewThe left view cuts the spinning mold lengthwise, the right view looks at its end; circled numbers match the steps below.

How it works

  1. Spin the mold. A steel or iron mold, often lined with a thin coating, sits on drive rollers and spins, typically at a few hundred to a few thousand revolutions per minute.

  2. Pour. Molten metal runs in through a spout from a ladle. No core is needed for the hole: the bore forms by itself.

  3. Let the spin shape it. Centrifugal force (the outward push you feel on a merry-go-round) throws the metal against the wall, where it spreads into an even layer. The amount poured sets the wall thickness.

  4. Solidify from the outside in. The metal freezes first against the cool mold. Lighter impurities and gas bubbles drift inward to the bore, which is machined away later.

  5. Stop and extract. The mold stops, and the hot tube is pulled out. It is then cleaned, machined or lined, as with cement-lined water pipe.

Key facts

Materials
Cast iron and ductile iron, steels and stainless steels, bronze and brass, nickel alloys
Typical parts
Pipes, cylinder liners, bushings, bearing rings, rolls for steel mills, flanges
Part size
From small bushings a few centimeters wide to pipes over 1 m wide and about 6 m long
Precision
Outside diameter about ±0.5 to ±2 mm; the bore is usually machined
Surface finish
Outer surface fairly smooth (Ra about 3 to 12 µm); bore rougher before machining
Batch size it suits
From single large rolls to millions of pipes a year
Tooling and machine cost
Molds are simple; machines from tens of thousands to millions of dollars for pipe plants
Speed
A few minutes per casting; a pipe line can make a pipe every minute or two

Strengths and limits

Strengths

  • Dense, strong walls with few gas holes
  • No core needed for the bore
  • Little waste: no sprues or risers
  • Can cast two metals in layers, like a hard outer shell on a tough core

Limits

  • Only round, hollow shapes around the spin axis
  • The bore is rough and dirty and usually needs machining
  • Wall thickness and length are limited by the machine
  • Some alloys separate by weight during spinning

Where it's used

  • Water and sewageDuctile-iron water mains and sewer pipes
  • AutomotiveCylinder liners, brake drums
  • Oil, gas and chemicalsHeat-resistant furnace tubes, pump sleeves
  • Steel industryRolls for rolling mills
  • MachineryBronze bushings, bearing rings, gear blanks

How to recognize it

  • A perfectly round, hollow part with an even wall all the way around.
  • An outer surface that copies the mold, often with a fine, uniform texture.
  • A machined bore, since the as-cast inside is rough.
  • No parting line and no cut-off sprue or riser stubs.

Compare with

Sand casting1.1would need a core and risers to make the same tube, and gives a less dense wall.Permanent mold casting1.3also a metal mold, but it stands still and gravity does the filling.Extrusion3.3pushes hot solid metal through a die to make tubes; better finish, but only in lengths of one cross-section.

Watch it

Shubham Kola · An animated explanation of the spinning-mold principle

MetalTek International · Pouring into a horizontal spinning mold, then pulling out the tube

MetalTek International · A vertical machine casting rings and short cylinders

McWane Ductile · Water-cooled molds turning out ductile iron pipe at scale

See real photos

Remember

  • Spin, not gravity or pressure, pushes the metal into shape.
  • The hole forms by itself, so no core is needed.
  • Best for dense, round, hollow parts such as pipes and rings.

More in Casting

All 100 processes
1.1ShortSand castingMetal poured into a cavity packed in sand; the sand is broken awayOpen the lesson1.2Investment casting (lost wax)Wax copy coated in ceramic, melted out, then filled with metalOpen the lesson1.3Permanent mold castingMetal poured by gravity into a reusable steel moldOpen the lesson1.4Die castingMetal shot into a steel die at high pressureOpen the lesson1.6Lost foam castingMetal poured onto a foam copy buried in loose sandOpen the lesson1.7Semi-solid casting (thixomolding and rheocasting)A half-solid metal slush injected into a steel dieOpen the lesson1.8Single-crystal casting (turbine blades)Slow freezing from one end grows the part as one crystalOpen the lesson

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