Silicon Carbide Grinding Paper: Grit Sequence, PSA vs Plain Back, and Buying by the 100
Silicon carbide grinding paper is the highest-volume consumable in a metallographic prep lab, and at LabSupplies.com it is also the one most often ordered wrong — usually a correct grit in the wrong backing, or a diameter that is close to the platen rather than equal to it. Three specifications decide whether a disc fits your process: grit, diameter and backing. All three are in the listing title, and all three matter before price does.
What WP Means, and Why You Grind Wet
WP on these listings designates wet-or-dry paper: a waterproof backing and a resin bond that tolerate running under water. Metallographic grinding is a wet process in practice, because the water flushes removed material out of the abrasive and carries the heat away with it. Grind dry and two things happen at once — the paper loads with debris and stops cutting, and heat goes into the sample face as deformation the later stages then have to remove. Running wet is not a refinement; it is the reason the paper is specified this way.
Grit: Stock the Ladder, Not the Favourite
The sequence only works if every grade is available, because each step exists to erase the previous step's scratches. Missing one middle grade does not shorten the run, it breaks it. Our SiC range in 12 inch plain back covers the common ladder:
| Grit | Role in the sequence | Stocked as |
|---|---|---|
| 60 | Heavy stock removal after a rough cut | AMR0195, 10 in PSA, pack of 100 |
| 120 (zirconia cloth) | Fast planar grinding, longer life than paper | AMR0386, 12 in PSA, pack of 25 |
| 240 | First true grinding step | AMR0055, 12 in plain back, pack of 100 |
| 320 | Intermediate | AMR0045, 12 in plain back, pack of 100 |
| 400 | Intermediate | AMR0143, 3 × 11 in PSA strips, pack of 100 |
| 600 | Fine grinding, common entry to polishing | AMR0025, 12 in plain back, pack of 100 |
| 800 | Finer entry where the method asks | AMR0121, 12 in PSA, pack of 100 |
| 1200 | Finest grinding before polish | AMR0008, 14 in plain back, pack of 100 |
A note on the coarse end: for heavy planar work, a zirconia cloth outlasts SiC paper by enough to be worth the higher price per piece, because SiC breaks down fast when it is doing bulk removal. That is a different trade from the fine grades, where paper is the right answer.
PSA vs Plain Back: the Platen Decides
| PSA-backed | Plain back | |
|---|---|---|
| How it holds | Pressure-sensitive adhesive, straight onto the platen | Water seal or retaining ring |
| Best on | Automatic heads, higher loads, fast grade changes | Manual wheels with a good water film |
| Trade | Costs more per disc; adhesive residue to clean off | Can creep or lift under heavy load if the seal is poor |
If your head is automatic and running real load, PSA is the safer choice — a disc that creeps mid-step ruins the sample and the step. On a manual wheel with a clean platen and a proper water film, plain back does the same job for less. The same grit is often stocked both ways for exactly this reason: compare 800 grit PSA in 10 inch (AMR0119) with the 12 inch version (AMR0121) and pick on platen size first, backing second.
Diameter: Measure the Platen
Eight, ten, twelve and fourteen inch are all stocked, and this is one specification where close is wrong. An oversized disc overhangs and tears at the edge; an undersized one leaves an outer band of platen doing nothing while the inner band wears. Measure the platen rather than trusting the machine's nominal designation, and if your grinder takes strips rather than discs, the 3 × 11 inch PSA strip format (AMR0234) exists for belt and strip grinders.
Buying by the 100, and Why That Is the Right Unit
Every grade above is stocked in packs of 100 — 25 for the zirconia cloth — and that is not an upsell, it is the consumption rate. A disc is spent after a handful of samples, so usage tracks throughput almost linearly. The practical approach for a lab running steady volume:
- Measure before you commit. Count discs used against samples completed for two or three weeks. That number, not a supplier's estimate, is your reorder rate.
- Buy the whole ladder to the same depth. The busiest grade is usually a middle one, and it is the one that stops the line when it runs out.
- Keep one coarse grade deeper than the rest if your sectioning is rough, since planar grinding eats the coarse end fastest.
- Standardise on one diameter across grades where your platen allows it, so a shortage in one grade can be covered by the same size in another.
Most of this range carries an OEM cross-reference in the listing title — several of the SiC grades cross to LECO part numbers. If your written method names a part number, search that number directly rather than a description, then confirm grit, diameter and backing before ordering; our OEM cross-reference guide covers how to check that a cross-reference really fits.
Browse the full range in metallographic abrasives and polishing, or the wider Alpha Resources range for polishing suspensions, cloths and mounting consumables.
Frequently Asked Questions
What is the difference between PSA-backed and plain back grinding paper?
PSA-backed discs have a pressure-sensitive adhesive on the reverse and stick straight to the platen. Plain back discs have no adhesive and are held by a water seal or a retaining ring. PSA is faster to change and will not creep under load, which matters on automatic heads; plain back costs less per disc and suits manual wheels where a water film holds the paper reliably. The platen decides, not preference.
What does WP mean on silicon carbide grinding paper?
WP designates wet-or-dry paper — a waterproof backing and resin bond that tolerate running under water. Metallographic grinding is almost always done wet, because water flushes the removed material away and takes the heat with it. Grinding dry loads the abrasive with debris and puts heat into the sample, which is exactly the deformation the sequence exists to remove.
Which grits do I actually need to stock?
Stock the ladder, not the favourite. A working sequence needs a coarse planar grade, two or three intermediate grades and a fine entry into polishing — commonly 240, 320, 600, with 800 or 1200 where the method requires it, plus a 60 or 120 grade for heavy stock removal after rough sectioning. Running out of one middle grade stops the whole sequence, because skipping a grade leaves scratches polishing cannot reach.
What disc diameter should I order?
Match the platen on your grinder-polisher exactly. Eight, ten, twelve and fourteen inch are all common, and a disc that is close but not correct either overhangs the platen edge or leaves an unused outer band that wears unevenly. Measure the platen rather than relying on the machine's nominal size.
Why are grinding discs sold in packs of 100?
Because a working prep lab consumes them continuously. A disc is spent after a small number of samples, so consumption scales directly with throughput, and a pack of 100 per grit per diameter is the practical reorder unit. Buying single discs of several grades costs more per sample and guarantees a mid-run shortage on whichever grade is busiest.
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Send us your platen diameter and whether your head is manual or automatic at support@labsupplies.com and we will confirm grit, diameter and backing before you order.
Related Guides
- Building a Grind and Polish Sequence
- Alumina vs Diamond Polishing
- How to Verify an OEM Cross-Reference Before You Order
- Elemental Analyzer Wear Parts to Keep in Stock
- Lab PPE Requirements Guide
Sources and Technical References
- ASTM E3 — Standard Guide for Preparation of Metallographic Specimens, ASTM International — store.astm.org
- ASTM E112 — Standard Test Methods for Determining Average Grain Size, ASTM International — store.astm.org
— By the LabSupplies.com Technical Team