Quick Answer
Choosing a cast-iron cutting blade comes down to five decisions: the tool type (diamond grit, abrasive wheel, or carbide), the bore (must match your spindle), the grit (speed vs finish), the bond (gray vs ductile), and dry or wet. For a foundry deburring line cutting sprues and gates off gray or ductile castings, the usual answer is a medium-coarse, hard-bond, dry-capable diamond grit blade — because on an automated line diamond holds its diameter and outlasts a resin abrasive wheel many times over. This guide walks each decision so you can spec the blade — or write an accurate RFQ — without guessing.
First: Diamond, Abrasive, or Carbide?
Before grit and bond, decide the tool. Three things cut cast iron, and the right one depends on volume and the line:
- Resin abrasive cut-off wheel — cheapest per piece, contains no diamond. It wears down continuously, so its diameter and cut depth drift, forcing frequent compensation and changeovers. Fine for occasional or low-volume cutting.
- Diamond grit blade — diamond grit bonded to a steel edge. Higher unit cost, but it holds its diameter and lasts hundreds to thousands of cuts. The right tool for automated, continuous deburring lines.
- Carbide-tipped (TCT) cold-saw blade — used for controlled sawing of more machinable irons, but gray iron's abrasive, sandy structure wears the carbide and the impact of cutting a sprue can chip teeth. Better for clean bar/section sawing than rough foundry cut-off.
| Tool | Unit cost | Diameter stability | Life | Best for |
|---|---|---|---|---|
| Resin abrasive wheel | Lowest | Poor (wears down) | Short | Occasional / low volume |
| Diamond grit blade | Highest | Excellent (holds OD) | Very long | Automated / continuous lines |
| Carbide-tipped (TCT) | Medium | Good | Medium (gray iron wears teeth) | Clean bar / section sawing |
For repetitive sprue, gate, and riser removal on a line, the choice is usually diamond grit vs abrasive wheel — and the rest of this guide assumes a diamond grit blade.
Bore & OD — the Gating Dimensions
Two dimensions gate the order before grit or bond even matter:
- Bore — the hole that mounts on your machine spindle. It must match exactly; a wrong bore scraps the blade. Common bores are 25.4mm (1"), 30mm, and 32mm, often with reducer rings. This is the one number you cannot guess — measure the spindle.
- Outer diameter (OD) — set by the machine and the cut depth you need. Foundry deburring lines commonly run 300-400mm. A larger OD gives more cut depth but also raises the peripheral speed at a given RPM, so the blade's max safe RPM must match the machine.
Get these two right first. Everything else is performance tuning; these two are fit-or-fail.
Grit: Speed vs Finish
On a grit-edge blade the grit size (mesh) is the headline spec, and it trades speed against finish:
- Coarse (≈30/40) — fast, aggressive, with a rough face. Right for sprue and gate cut-off where a downstream grinder does the finishing.
- Medium (≈50/60) — slower but gives a cleaner break, better for thinner or smaller castings where chipping matters.
Most foundry cut-off uses the coarser end, because surface finish is the grinding station's job, not the cut-off blade's. Pick finer only when the break quality itself matters.
Bond: Gray vs Ductile Iron
Bond hardness follows the inverse rule: the more abrasive the material, the harder the bond needs to be, so the diamond is not stripped out too fast. That makes the iron type a real spec driver:
- Gray iron — brittle and abrasive ('sandy'). A harder bond resists wear and keeps the blade round.
- Ductile (nodular) iron — tougher. The grit and bond are re-tuned for the tougher matrix, balancing wear resistance against keeping the diamond exposed and cutting.
Tell your supplier which iron you pour. Gray vs ductile genuinely changes the blade — it is not a marketing distinction.
Edge Type & Dry vs Wet
Two edge constructions, plus the cooling mode:
- Segmented grit edge with cooling slots — for thick cross-sections and dry running. The slots clear chips and keep the cut cool, which protects the core and limits graphitization. This is the foundry default.
- Continuous grit edge — for thinner or smaller castings where a cleaner break and less chipping matter.
- Dry vs wet — foundry lines usually run dry, so the blade is built to shed heat (cooling slots, tensioned core). If the machine floods coolant, the bond is specified differently. Confirm your machine's mode before ordering.
Diamond vs Abrasive: Line Economics
Why pay more for diamond? On a line, unit price is the wrong lens. A resin abrasive wheel is cheap but wears down every cut — its diameter shrinks, the cut depth and position drift, and the operator compensates or changes it constantly. A diamond grit blade costs more up front but holds its diameter and cuts hundreds to thousands of feeders between changes. On a machine meant to run continuously, the figures that matter are changeover frequency and cut consistency — not the price of a single blade — and that is where diamond wins. For specific pricing on either, ask your supplier with your volume and spec in hand.
RFQ Checklist
To get an accurate spec and quote without back-and-forth, send:
- Casting material — gray iron or ductile (nodular) iron
- What you cut — sprue, gate, runner, riser; approximate cross-section
- Machine bore (the hard number) and blade OD
- Dry or flood coolant; line speed or spindle RPM if known
- Volume or target cuts per blade, if you have it
- Edge preference (segmented grit edge vs continuous), if any
Zhonghuan builds the cast-iron grit-edge blade for exactly this job — gray and ductile, vacuum-brazed, specified to your machine and witness-cut on your casting before volume; see our cast-iron and foundry diamond blade program, and the science of why diamond works here in why a diamond blade cuts cast iron but not steel. And the honest line: cast iron is where a diamond grit blade is right — for steel, the answer is CBN or an abrasive wheel, not diamond.
