metallic substrate

Making the Coating Stick to the Metal – What We've Learned

We get failed converters sent back. Cut 'em open. The metal honeycomb looks fine. The coating looks fine. But they ain't stuck together. The washcoat is flaking off like dead skin.

You can have the best metal in the world. You can have the best coating formula. If they don't get along, you got nothing.

Here's how we match 'em.

The Problem – Metal and Ceramic Don't Like Each Other Naturally

The honeycomb is metal. The washcoat is ceramic. Metal expands when hot. Ceramic expands less. That difference – thermal expansion mismatch – is the enemy.

If the coating is too stiff and the metal moves too much, the coating cracks. Flakes off. Then your catalyst is gone.

If the metal surface is too smooth, the coating can't grab. Too rough, it pools in the valleys and leaves the peaks bare.

So you gotta pick the right dance partner.

Surface Roughness – Grip Matters

The washcoat needs something to hold onto. A mirror finish is too slick. Coating slides right off.

We control the roughness of the foil before coating. For automotive, we shoot for Ra around 1-2 microns. Smooth enough to not trap junk, rough enough for the washcoat to key in.

Too rough? The washcoat fills the valleys and the peaks are bare. Uneven coverage. Bad.

We learned this when a supplier sent us foil with a rough mill finish. The coating looked thick but flaked off in big sheets. Switched to our spec, problem gone.

Material Choice – Aluminum vs. Stainless

Aluminum expands a lot. Stainless expands less. The coating's thermal expansion needs to match the metal.

For aluminum substrates, we use a washcoat with higher thermal expansion – more alumina, less silica. For stainless, a lower expansion formula.

Put an aluminum‑matched coating on stainless? It'll crack. Put a stainless‑matched coating on aluminum? It'll peel.

We keep two different washcoat recipes. One for each metal.

Foil Thickness – Thin vs. Thick

Thin foil heats up fast. Good for light‑off. But it also cools fast. The coating sees rapid temperature changes.

Thick foil heats slower, cools slower. The coating has an easier life.

So for thin foil (0.05 mm), we use a more flexible washcoat – one that can take thermal shock. For thick foil (0.08 mm and up), we use a harder, more durable coating.

Match the coating's thermal shock resistance to the foil's thickness.

Cell Density – Don't Plug the Holes

High cell density (600 cpsi) means tiny cells. The coating has to flow into those little channels without blocking them.

If the coating is too thick, it bridges across the cell openings. Plugs. Too thin, it runs off the walls and pools at the bottom.

We adjust the coating goo for the cell size. For 600 cpsi, thinner mix, slower dip, more air blow. For 200 cpsi, thicker mix, less blow.

You can't use the same coating process for every substrate. It's like painting a radiator – you need thin paint for tight fins.

The Tape Test – Does It Stick?

We test every batch. Simple. Press a piece of tape on the coated substrate. Pull it off.

Tape comes back clean? Good. White powder on the tape? Bad.

For high‑temperature jobs, we also do a thermal shock test. Heat to 500°C, dunk in water. Look for flaking.

Good match survives. Bad match flakes.

Real Example – Generator Substrate

A generator customer kept losing coating on their 400 cpsi stainless. Coating peeled after a few hundred hours.

We checked the coating. It was made for aluminum – too high expansion. Switched to our stainless‑matched recipe. No more peeling.

Real Example – Marine

Marine, salt air, high humidity. The aluminum substrate corroded under the coating. Coating lifted.

We switched to stainless 316L. Same coating. It stayed put because the metal didn't rot.

The match isn't just thermal. It's chemical too.

The Process – Dip, Blow, Dry, Fire

The process matters as much as the materials.

Dip time. Blow pressure. Drying speed. Firing temp.

Dry too fast, the washcoat cracks. Cracks grow during firing. Flakes later.

Fire too hot, the washcoat gets brittle. Won't flex with the metal.

We dial in the process for each substrate. Thin foil gets a slower drying ramp than thick foil. Less thermal shock.

How We Match – Step by Step

Customer brings a new substrate. Here's what we do.

What metal? Thickness? Cell density? How hot will it run?

Pick the washcoat – high expansion for aluminum, low for stainless.

Run test coupons. Coat 'em, fire 'em, tape test. Thermal cycle 'em. Look for cracks.

Cut the coupons open. Look at the cross‑section. Coating even? Any voids? Stuck to the foil?

Then we run a full batch.

What We've Seen Go Wrong

Smooth foil – coating slides off. Fix: scuff the foil.

Wrong expansion – cracks. Fix: change washcoat.

Too much coating – plugs cells. Fix: thinner mix, more blow.

Too little coating – low activity. Fix: thicker mix.

Wrong firing temp – brittle coating. Fix: adjust furnace.

Each one took time to figure out. Now we have a checklist.

Matching the metal and the coating ain't complicated. But you gotta pay attention.

Surface roughness. Material expansion. Foil thickness. Cell density. Coating thickness. Drying and firing.

Get any of these wrong, and the coating will peel, crack, or plug.

We match 'em every day. Learned what works.

If you have a substrate and need a coating that sticks, send us a sample. We'll run tests and give you a recipe.

That's what we do. No flakes, no cracks, no comebacks. Just a coating that lasts.