Slowing the wear clock: AR plate vs chromium-carbide overlay vs ceramic

Every fan that moves dust runs on a wear clock. The wheel and the scroll will erode — that is not the question. The question is whether the wear lands on a hard, replaceable surface, or on the parent metal of an impeller you will eventually scrap. Get that decision right and you change a liner; get it wrong and you change the fan. And the decision is almost always made on the wrong number.

The wrong number is hardness. The right one is a wear test.

Buyers compare wear protection by Rockwell hardness because it is the figure on every datasheet. But overlay hardness depends on how many passes were laid and how much the deposit was diluted by the base metal — quote a single HRC and you have told the reader almost nothing. The honest comparator is the ASTM G65 dry-sand abrasion test: material lost, in mm³, under a standard rubbing load. Lower volume loss wins. Ask for the G65 figure next to every hardness claim, and ask how many overlay passes the quoted HRC assumes.

The same discipline kills a common and expensive myth. 304/316 stainless buys you almost nothing against abrasion. It sits around 124–147 HBW — barely above mild steel. Stainless solves corrosion; it is not a wear material. If your dust extraction or pneumatic conveying duty is erosive rather than wet-corrosive, specifying stainless "for durability" is money spent on the wrong problem. For wear you need AR plate, an overlay, or ceramic.

Three methods, three homes

There is no single best surface — there is a best match to the abrasion severity, the geometry, and the temperature.

Method	Typical hardness	Where it fits
AR plate (AR400/450/500 class)	~400–500 HBW	Moderate abrasion where the whole wheel or liner can be one weldable, formable material. Wears uniformly; easy to repair in the field.
Hardfacing overlay (chromium-carbide, CCO)	55–59 HRC single up to ~63 HRC multi-layer	Severe abrasion — fly-ash, cement, aggressive conveyed solids. A hard skin on a tough backing. Longest practical life on harsh duty.
Ceramic lining (alumina / SiC tile)	—	Extreme fine-particle erosion where temperature and impact allow. Longest life, highest cost, brittle.

Two details decide more jobs than the hardness spec does. First, chromium-carbide overlay cannot be oxy-cut or conventionally machined — it is plasma- or abrasive-cut and formed before overlay where possible, so it is applied where it will stay, not shaped afterwards. Complex-carbide grades push to 61–64 HRC but carry a service-temperature ceiling (around 450 °C); tungsten-carbide applied by PTA covers the most severe small zones, such as blade leading edges.

Second, the ceramic trap. A bonded ceramic tile is limited by its epoxy or rubber bond line — roughly 150–300 °C — not by the 1,000 °C-plus rating of the ceramic itself. If ceramic is quoted, the number that matters is the bond-line temperature limit. Always ask whether your duty sits inside it.

Three questions to ask before you buy a dusty-duty fan

• Where does the wear land? On parent metal, or on a replaceable plate or liner — and at what wear point is replacement triggered? (Our practice works to 20% blade-thickness erosion as the change-out trigger.)
• What is the ASTM G65 volume-loss number behind the hardness claim — and how many overlay passes does the quoted HRC assume?
• If ceramic is offered, what is the bond-line temperature limit, and is the duty inside it?

How we build it

Jitamitra runs chromium-carbide hardfacing by FCAW at 55–60 HRC as the standing treatment for fly-ash erosion, using the high-chromium EFeCr-A consumable family (AWS A5.13/A5.21), and carries wear plates and impeller wear protection as preferred base scope on the radial families that take the dirtiest duty. Because any overlay adds mass to a spinning wheel, every overlaid impeller is re-balanced as a mandatory step — a hard surface is worthless if it introduces vibration. Welding and overlay are controlled to an internal procedure with recorded grade, pass count and coverage, and 100% visual inspection of critical impeller welds.

Wear protection is engineered against your stated dust loading and its nature — abrasive, sticky, hot, fine or coarse. State them in the RFQ and the wear package comes back sized to the duty, not guessed from a hardness number.

Talk to us about wear protection →

Jitamitra Electro Engineering · Fan-engineering notes, written for the engineer.