A worn roll stops production. That much everyone in a mill knows. The question is what to do about it. Over the years, two main approaches have become standard: take material off the roll surface, or put new material onto it. The first isroll grinding. The second isthermal spray coating.

　　They are not competitors. Most roll shops use both at different points in a roll's life. But the decision of which to use — and when — affects cost, lead time, roll performance and what grinding wheels you need on your machines. Here is how to think about the two technologies.

　　A simple way to picture the difference

　　Imagine a wooden tabletop that has scratches, stains and a worn patch in the middle after years of use.

roll grinding

One option is to sand it down. Remove the damaged surface until the wood underneath is clean, smooth and flat. The table becomes a little thinner, but it looks and works like new. That is.

thermal spray coating

Another option is to apply a tough, protective epoxy coating over the entire surface. The scratches and stains stay underneath, sealed away, and the new surface is harder and more durable than the original wood. The table becomes slightly thicker, and it resists future damage better than before. That is.

　　Both work. Both have their place. But they are fundamentally different operations — and the grinding wheels involved are different too.

　　Roll grinding: taking material away to restore precision

　　Roll grinding is the everyday workhorse of any roll shop. The idea is straightforward: remove the damaged surface layer — wear, cracks, oxidation, spalling — and reveal clean, sound material underneath. At the same time, restore the exact geometry the roll needs: its crown, taper, roundness and surface finish.

　　A typical roll grinding cycle happens in three stages. The roughing stage takes off the bulk of the damage and sets the basic profile, usually removing around 80% of the required stock. The semi-finishing stage smooths the surface down step by step. The polishing stage delivers the final surface roughness and makes sure it is uniform across the whole roll barrel.

　　Because grinding is a subtractive process, the roll diameter gets slightly smaller each time. A work roll can be reground many times — sometimes dozens — before it reaches its minimum usable diameter and needs to be replaced or reconditioned by other means.

The grinding wheel is the heart of the process.

For hardened steel work rolls and backup rolls, CBN wheels are the standard choice because they stay sharp, generate less heat and hold profile far longer than conventional abrasives. For tungsten carbide rolls, ceramic rolls and HVOF-coated rolls, diamond wheels are required — nothing else cuts these materials efficiently.

　　Thermal spray: adding material to build a new surface

　　Thermal spray works in the opposite direction. Instead of removing material from the roll, it applies a new layer — often only microns thick — onto the roll surface.

　　The process heats a feedstock material (powder or wire) until it is molten or semi-molten, then propels it at high speed onto the prepared roll surface. The particles flatten on impact and bond mechanically and metallurgically, building up a dense, hard coating layer.

　　Several thermal spray methods exist, each suited to different needs:

HVOF (High-Velocity Oxygen Fuel)

: The gold standard for roll applications. Produces extremely dense, well-bonded coatings with hardness levels that conventional abrasives simply cannot machine. Tungsten carbide (WC-CoCr) and chromium carbide (Cr₃C₂-NiCr) are the most common HVOF coating materials for rolls.

Plasma spray

: Reaches very high temperatures, suitable for ceramic coatings and high-melting-point materials.

Arc spray and flame spray

: Lower cost, used for less demanding applications or thicker build-up layers on large components.

repair

Thermal spray is used for two distinct purposes. The first is: when a roll is worn below its minimum diameter or has localized damage too deep for grinding alone, thermal spray can build the surface back up to the original dimension. The second is: even a brand-new roll can be thermal-sprayed with a hard coating to extend its service life far beyond what the bare steel would deliver.

thermal spray is not the final step.

Critically,The as-sprayed surface is rough — typically Ra 3.5–6.5 µm for HVOF tungsten carbide coatings. The coating must be finish-ground and polished to achieve the required dimensions and surface finish. This is where the grinding wheel comes back into the picture.

　　Why the grinding wheel matters for both

　　This is the connection that does not always get enough attention: regardless of whether you are grinding a bare steel roll or a thermal-sprayed roll, the grinding wheel determines the quality, speed and cost of the operation. And the wheel requirements can be very different.

　　For a standard work roll made of forged or hardened steel, a vitrified or resin bond CBN wheel is the proven workhorse. It removes stock fast, resists wear, and delivers the surface finish the mill needs.

　　For a thermal-sprayed roll — especially an HVOF tungsten carbide or ceramic coating — only a diamond wheel will do. The extreme hardness of these coatings (HV 1300–1500 for WC-CoCr) makes short work of conventional abrasives. Diamond grinding wheels handle these coatings efficiently and hold profile under the high forces involved. Resin bond diamond wheels are often used for cool cutting and good surface finish, while vitrified bond diamond wheels provide tight dimensional control and high productivity.

　　The same applies to carbide rolls and ceramic rolls: diamond abrasive is the essential choice, and the bond must be matched to the grinding stage and the machine.

　　Side-by-side comparison

　　Choosing the right path

　　A roll shop makes the call based on a few practical questions: How deep is the damage? Is the roll near its scrap diameter? What is the cost of downtime versus the cost of coating? Does the application justify the extra wear resistance of a thermal spray coating?

　　Neither approach replaces the other. Grinding handles daily wear. Thermal spray handles dimensional restoration and extreme durability requirements. And both demand grinding wheels that are correctly specified for the roll material and the desired finish.

　　If you are grinding steel rolls, carbide rolls, or thermal-sprayed rolls — and you are not sure whether your current wheel is giving you the best cycle time and surface quality — reach out. Tell us your roll material and your machine. We will recommend a diamond or CBN wheel that fits the job, whether the roll surface is bare steel or a hard coating we helped you think about.