Grey and ductile iron
Cast Iron Machine Bases, Beds and Columns
Grey iron is the default for a repeat machine model that needs damping. The pattern is the tooling: slow and costly to a first part, cheap per part once the run is long enough. We read your drawing and put it in front of partner foundries and machining shops in Vietnam that cast and finish iron of that size and class.
We are a sourcing service, not a foundry or a fabrication shop. You pay the fabricator you choose, nothing to us. Reply within 24 business hours.
What it is
A cast base is poured into a sand mould formed around a pattern, shaken out, fettled, aged to release casting stress and only then machined. Grey iron has flake graphite, which absorbs vibration. That is why it remains the default for grinders, precision lathes and machining centre beds and columns. Ductile iron has spheroidal graphite, is tougher and yields before it fails, and damps noticeably less. Substituting one for the other is a real engineering change, not a grade swap.
The economics are the opposite of a weldment. The pattern costs money and foundry queue time, so a first casting is usually measured in months, and a geometry change usually means a new or reworked pattern. Once the pattern exists and the volume repeats, the cost per unit falls with volume. Cast iron suits a design that is frozen and a run that is going to repeat.
Where it fits
- A repeat machine model in steady annual volume
- Grinders, precision lathes, machining centre beds and columns where damping decides surface finish
- Complex, closed shapes that are awkward to weld
- Ductile iron where the part sees shock or cyclic tensile load
Where it does not
- Prototypes and one-offs, unless the pattern cost is already accepted
- Designs still changing: each change goes through the pattern
- Very large single structures where a weldment can be split and bolted more cheaply
- A first unit needed in weeks
Process
How it is made
- Pattern built in wood, resin or metal, sized to allow for shrinkage
- Mould formed around the pattern in green sand or a chemically bonded sand
- Molten iron poured and left to solidify and cool in the mould
- Shakeout, then fettling to remove gates, risers and flash
- Stress relief or ageing before any machining begins
- Rough and finish machining of ways, pads and bores, then inspection
Standards
What governs it
EN 1561, EN 1563, EN 10204, ISO 1101, ISO 2768.
Each is explained in the standards index, including the one that is most often cited where a different one was meant. Themanufacturing technologies page shows the stages side by side with the other constructions.
Before you ask for a quote
What to put in the RFQ
Typical ranges for this construction, and what to state so two quotes can be compared. Ranges are not promises: they depend on the shop and the part.
| Item | Typical | Say in the RFQ |
|---|---|---|
| Material grade | Grey iron EN-GJL-200 to 300 (GG20 to GG30). Ductile iron such as EN-GJS-400-15 to EN 1563. | The grade and the governing section thickness together. The grade is a separately cast test bar value; a thick section of your casting will be lower. |
| Casting weight | Limited by the foundry furnace and the shop crane. Ask for the class in the RFQ rather than assuming. | Casting weight and finished weight, they are not the same number. |
| Pattern | Wood, resin or metal. The pattern is the tooling and the largest single cost on a first unit. | Whether a pattern already exists, who owns it, and the expected annual quantity. |
| Ageing and stress relief | Before any machining begins. Method varies by foundry. | Which method, and whether you want a record of it. |
| Machined geometry | Flatness commonly held in the 0.02 - 0.10 mm band over a metre on machined pads; ground or hand-scraped work goes tighter. | Flatness, parallelism and squareness per surface, with the datum scheme. |
| Documents | Chemical and mechanical test report, ultrasonic testing of thick sections where specified, dimensional report. | EN 10204 type 3.1 by name, and the NDT scope if any. |
The full checklist is in the RFQ checklist guide, and the seven things that move the price are on the home page.
Questions
How long does a first casting take?
Plan in months, not weeks. The pattern and the foundry queue come first, then casting, ageing and machining. If the first unit is urgent, a welded base is the faster route and can be revised afterwards.
Grey iron or ductile iron?
Grey iron damps better and is the default when vibration decides accuracy. Ductile iron is tougher and suits shock and cyclic tensile loads, but damps noticeably less. If you are unsure, send the load case and the guide on the two grades explains the tradeoff.
Who owns the pattern?
Agree it in the quote. Ownership, storage, how long the foundry keeps it and what happens if you move production are all negotiable and all worth writing down before the pattern is built.
What if the casting has a defect after machining?
Casting defects such as shrinkage porosity or sand inclusions often only appear once the surface is cut. Ask for the NDT scope and the acceptance criteria before the order, not after. The guide on grey iron casting defects lists what to look for.
Read next
- Ductile iron vs grey cast iron
- GG25 vs GG30 for machine beds
- Grey iron casting defects
- Casting pattern: wood vs foam
- Meehanite cast iron for machine tools
- VMC column and bed castings
- Hand scraping machine base ways