How iron castings are made in Indian foundries
Iron castings are usually poured into green-sand moulds, made by hand, on jolt-squeeze machines or on automatic moulding lines. Cores of resin-bonded sand form the internal passages of pump and valve bodies. Iron is melted in cupolas or induction furnaces; TERI's 2012 profile of the Kolhapur foundry cluster recorded a shift from coke-fired cupolas to induction furnaces, partly because induction melting suits SG iron. Ductile (SG) iron is made by treating the melt with magnesium so the graphite forms spheres instead of flakes, then inoculating it just before pouring.
After knockout the castings are fettled: risers and gates cut off, sand removed by shot blasting, parting lines ground. Many foundries machine the castings in-house or through job shops, then paint or prime them. Small defects found at fettling are sometimes repaired by welding or filled with putty and painted over, which is why the inspection looks closely at painted surfaces and asks for the foundry's repair rules.
DC-MSME lists completed common facility centres for the Foundry Industry Cluster in Ahmedabad and the Pump and Foundry Cluster in Rajkot. TERI counted about 300 foundry units across Kolhapur and Sangli districts in 2012, mainly making SG and grey iron castings for the automotive industry.
What we check on iron castings
| Check | How it is checked | What fails |
|---|---|---|
| Cast dimensions | Sampled castings measured against the drawing; untoleranced cast dimensions judged against the ISO 8062-3 tolerance grade the drawing names | Wall thickness, flange or boss positions outside the grade; core shift giving uneven walls |
| Machined features | Bores, faces, hole positions and threads measured against their tolerances, or ISO 2768 where the drawing cites it; machining allowance left on as-cast faces checked | Bores out of tolerance; a machined face that does not clean up |
| Surface defects | Every face of sampled castings examined after shot blasting and before painting where possible; machined faces checked for exposed porosity | Blowholes, shrinkage, sand or slag inclusions, cold shuts above the agreed limit |
| NDT | Dye-penetrant or magnetic-particle testing done by the foundry's certified technician on castings we select, witnessed; procedure and technician certificate checked | Linear indications or cracks the specification does not allow |
| Hardness | Brinell hardness (ISO 6506-1 method) witnessed on the foundry's calibrated tester at the agreed position | Hardness outside the grade's range, or hard spots that will not machine |
| Grade and microstructure | Certificate checked for grade, tensile results from test bars of the same heat and, for ductile iron, the nodularity report; heat numbers traced to cast marks | No test bar results; nodularity report from another heat or below the agreed level |
| Pressure or leak test | For pump and valve bodies, the foundry's hydrostatic or air test witnessed at the specified pressure and hold time | Weeping through porosity; gauge out of calibration |
| Coating and marking | Primer or paint thickness by gauge; cast-on marks, part number and heat code | Paint over unrepaired defects; marks missing or illegible |
Grey iron, ductile iron and what the certificate should show
Grey iron has graphite flakes. It machines and damps vibration well but is brittle. EN 1561 names grades by minimum tensile strength, such as EN-GJL-250, and ASTM A48 names them by class, such as Class 30. Ductile iron, with spheroidal graphite, is much tougher. EN 1563 names grades by tensile strength and elongation, such as EN-GJS-500-7, and ASTM A536 by three numbers, such as 65-45-12 (tensile and yield in ksi, elongation in per cent).
The difference between the two sits inside the metal, so a visual inspection cannot tell them apart. Proof comes from three records: tensile results from test bars poured from the same heat; a nodularity figure from a polished sample, assessed by comparison charts or image analysis (ISO 945-4 sets a method); and hardness. A buyer who orders 3.1 certificates should expect these per heat, with the heat code cast on the parts or stamped next to them. Where results are in doubt, we cut or pull spare castings or separately cast bars and seal them for an accredited lab through lab testing coordination. See EN 10204 certificates for what a 3.1 must contain.
Common defects in iron castings
| Defect | Why it matters | Class |
|---|---|---|
| Crack or cold shut through a load-bearing section | Part can fail in service | Critical |
| Leak in a pressure-retaining body | Pump or valve fails its pressure duty | Critical |
| Wrong grade (grey iron supplied as ductile) | Brittle part where toughness was specified | Critical |
| Porosity or shrinkage exposed on a sealing or bearing face | Leaks, poor seating, short bearing life | Major |
| Core shift or mould mismatch beyond the tolerance grade | Thin walls; machining does not clean up | Major |
| Undisclosed weld repair or putty under paint | Hidden weakness; repair not approved | Major |
| Hard spots or chill at edges | Breaks cutting tools at the buyer's machine shop | Major |
| Rough fettling, sand left in cavities, uneven paint | Appearance and cleanliness | Minor |
For manhole covers and gratings sold in Europe, the load class (A 15 to F 900) and EN 124 marking must match the product and its test evidence; a cover marked D 400 without a test behind it is a critical finding.
Packing, transit and your purchase order
Unpainted machined faces rust within days in humid ports. Ask for rust-preventive oil or VCI film on machined faces and bores, and plugs in threaded holes. Heavy castings should be bolted or blocked onto pallets or skids so they cannot shift; small castings packed in layers with separators so faces do not knock together. Wooden packaging must be ISPM 15 treated and marked (see ISPM 15). The inspector checks gross weights against the packing list and that the load is spread and lashed in the container.
Under EU CBAM, heading 7325 (other cast articles of iron or steel) is not on the Annex I list as of October 2026; castings classified as parts of machines fall under the machine's heading.
Put these in your purchase order:
- Drawing and revision, with the ISO 8062-3 tolerance grade and machining allowances.
- Material standard and grade, and EN 10204 certificate type (usually 3.1).
- Test bars per heat, hardness range and position, and nodularity minimum for ductile iron.
- Surface acceptance criteria for cast and machined faces, and whether weld repair is allowed.
- NDT method, extent and acceptance level, and pressure test details for pressure parts.
- Heat code marking, paint system and rust protection; pallet and crate specification.
Castings for vehicles are covered on engine and transmission components. Book an inspection anywhere in India.
Sources
- DC-MSME: Completed Common Facility Centres under MSE-CDP (updated 20.03.2024)
- TERI (2012), Cluster Profile Report: Kolhapur Foundry Industry, for SIDBI
- ISO 8062-3:2023, general tolerances and machining allowances for castings (iso.org)
- ISO 945-4:2019, Microstructure of cast irons: nodularity in spheroidal graphite cast irons (Standard Norge listing)
- ISO 6506-1:2014, Brinell hardness test, test method (Standard Norge listing)
- EN 1563:2018, Founding: spheroidal graphite cast irons (Standard Norge listing)
- ASTM A536, Standard Specification for Ductile Iron Castings
- EN 124-1:2015, Gully tops and manhole tops (Standard Norge listing)