The wear that operations cause themselves

When a furnace is inspected, thermal causes are almost always looked for first: thermal shock, infiltration, chemical attack. That is correct — and it regularly overlooks the simplest cause.

Part of the damage is impact damage. It looks different from thermal wear, and it occurs in different places.

How to tell the difference

• Thermal wear takes back surface. The face moves evenly to the rear, edges become rounded, the transition is soft.
• Mechanical wear takes out pieces. The fracture surface is fresh, sharp-edged and stands out in colour because it has not yet seen the furnace atmosphere.
• Mechanical wear has a direction. Several break-outs on one line or at one height point to a tool or a charging path, not to the flame.

The three points of attack

First the sill and the door area. This is where tools go in and out, where material is scraped off, where something is propped up. It is the place with the highest mechanical load and at the same time the one with the greatest thermal shock.

Second, the impact zone during charging. Where scrap, ingots or fuel land, no material lasts if the drop height is not limited. Often a sacrificial layer or a different charging sequence helps more than a higher-grade brick.

Third, cleaning. Build-up and slag are knocked off, and with every blow a little lining comes away too. That is unavoidable — what is avoidable is doing it with the wrong tool or too late, once the build-up has set hard.

What can be changed without material

• Shorten the cleaning interval instead of sharpening the tool. A young build-up comes away with less force.
• Define contact points and places to set things down, so that not every shift loads a different spot.
• Treat the sill as a wear part: its own quality, its own interval, planned replacement instead of repair after break-out.
• Note every impact damage with a date. Only over several entries does it become clear whether the problem is one spot or one way of working.

None of these points costs material. They cost agreement — and they are the only part of wear that does not depend on physics but on a decision.

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