Centrifugal casting
Selecting centrifugal casting geometry, allowing for bore cleanup and machining, and specifying alloy, condition and inspection for the finished component.
Tags: processes, shaping, casting
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A hypothetical centrifugal blank with 210 mm OD and 150 mm bore, finished to 200 mm OD and 160 mm bore, has 5 mm radial cleanup on each surface. At equal 300 mm lengths the ideal finished-volume yield is 66.7%. The blank fails a 6 mm radial bore cleanup requirement even when the nominal finished wall fits.
In true centrifugal casting, a rotating mold forms a hollow casting with a free-surface bore and no central core. Foseco: centrifugal casting
Identify the route and geometry
| Route | Defining arrangement | Handoff implication |
|---|---|---|
| True centrifugal casting | Metal forms a hollow body around the rotation axis; the bore is a free surface. | Define the finished bore and required cleanup stock separately from the die-defined outside. |
| Semi-centrifugal casting | A central sprue feeds a rotationally symmetric, filled shape, such as a wheel. | Identify the hub and any core or later bore operation. |
| Centrifuging | A central sprue and radial runners feed cavities away from the rotation axis. | Individual parts need not be rotationally symmetric; include runner removal in the route. |
Foseco classifies these variants and identifies poured quantity as a wall-thickness control, without establishing a universal wall tolerance. Foseco: process variants
MetalTek describes horizontal casting for long tubes and vertical casting for rings and cylinders, with ferrous and non-ferrous production. It also offers vacuum centrifugal casting for identified high-performance alloys. Vacuum is a separately specified processing capability, not an inherent feature of every centrifugal casting. Confirm the actual alloy, orientation, atmosphere and available equipment with the foundry. MetalTek: process and capabilities
Solidification and bore cleanup
MetalTek's November 24, 2020 process article explains outside-to-inside solidification, feeding from liquid metal at the bore and migration of lower-density constituents toward the inside diameter. The intended quality benefit depends on retaining appropriate solidification and feeding conditions. The same article explicitly states that the process alone does not guarantee a superior product. Treat broad descriptions such as “defect-free” as capability claims requiring part-specific acceptance, rather than a substitute for inspection. MetalTek: advantages and limitations
The bore's inner layer can contain inclusions and porosity and require machining. Foseco also identifies a possible parabolic bore in vertical casting, and density separation as a limitation for susceptible alloys such as lead-bronze. Foseco: machining and alloy limitations
For quoting, provide a finished-part model and an agreed rough-casting envelope. Establish where the machining datum will come from, how much stock must remain after heat treatment, and which surfaces are inspected before and after removal. Do not count the inner cleanup layer as usable finished wall. A nominal average bore does not establish the minimum cleanup allowance along the full length.
Tooling, scale and secondary operations
MetalTek's 2020 discussion notes that vertical-casting bore shape affects cast weight and machining cost. It also describes casting several shorter parts in one horizontal length and subsequently cutting them apart. Irregular outside contours can require more expensive shaped tooling. Small bores can present speed and equipment limitations; a published example is not a transferable machine setting. MetalTek: geometry and cost limits
Compare routes through the accepted finished part: die availability, casting quantity, end cropping and cutoffs, heat treatment, bore and outside machining, inspection and rejection allowance. Ask whether the quotation is for an as-cast blank, a rough-machined component or a finished component. The same casting weight can support very different finished yields.
Near-net geometry can be application-specific. MetalTek's undated valve-cage case describes combining sand-core technology with centrifugal casting and arranging the final bore pass to open the windows. This supports asking about a hybrid design; it does not establish that arbitrary internal windows can be cast without cores or machining. MetalTek: near-net centrifugal valve cages
Original allowance calculation
Assume an invented, uniform cylindrical blank with 210 mm outside diameter, 150 mm bore and 300 mm length. The finished part requires 200 mm outside diameter and 160 mm bore at the same length. Ignore end cropping, shrinkage, out-of-roundness, taper and machining losses beyond these ideal cylinders.
| Quantity | Calculation | Result |
|---|---|---|
| Blank wall | (210 − 150) / 2 | 30 mm |
| Finished wall | (200 − 160) / 2 | 20 mm |
| Outside radial removal | (210 − 200) / 2 | 5 mm |
| Bore radial removal | (160 − 150) / 2 | 5 mm |
| Blank volume | π/4 × (210² − 150²) × 300 | 5.089 L |
| Finished volume | π/4 × (200² − 160²) × 300 | 3.393 L |
The nominal 1.696 L removal excludes cropping, pouring losses and rejects. Qualify the required bore cleanup before ordering stock.
Specify material and acceptance
ASTM A451/A451M-20 is a scoped example, not a universal centrifugal-casting specification. ASTM's publisher page identifies it as active, last updated August 7, 2020, for centrifugally cast austenitic alloy steel pipe in high-temperature, corrosive or nuclear pressure service. Its public abstract covers heat treatment, inner/outer machining, chemistry, tensile and hydrostatic testing; its scope excludes the identified alloys containing more than 0.20% carbon covered by A297/A297M. Use the purchased applicable edition and ordered grade for detailed requirements. ASTM: A451/A451M-20 scope and abstract
Do not replace the cast grade and specified condition with a superficially similar wrought-alloy name. Define chemistry, heat treatment, mechanical requirements and the sampling location/condition. A separately tested coupon does not automatically describe every location in a thick casting.
MetalTek's October 12, 2022 inspection overview separates chemistry, finish, dimensions, mechanical properties and casting soundness, and discusses combining examination methods according to the customer requirement. These are distinct acceptance questions. MetalTek: inspection methods and limitations
A useful release package specifies four groups of information:
- Finished geometry: drawing/model revision, datums, bore/OD, minimum wall, length, local features and surface requirements.
- Material route: cast grade, governing specification/edition, heat treatment and any atmosphere or hybrid-core requirement.
- Manufacturing envelope: agreed rough shape, machining/cleanup stock, cutoff plan and stage of supply.
- Acceptance: dimensional checks, chemistry/mechanical evidence, examination coverage and acceptance levels, pressure/leak tests where required, and traceability.
The Foseco and MetalTek capability/case pages have no separately verified technical issue date. The dated articles and ASTM public summary support the bounded discussion above; they do not supply a universal spin speed, pouring temperature or inspection plan. The allowance example is original.