Causes of Failure of Rotary Kiln Kiln‑mouth Guard Plate

1. Thermal‑stress damage (primary cause)

The kiln‑mouth area is subject to high temperature and frequent alternating heating and cooling. Repeated thermal expansion and contraction of the guard plate generate significant thermal‑fatigue stress. Under long‑term cyclic loading, the guard plate suffers warping, cracking and deformation. Cracks tend to initiate at welded or bolted fixing positions between the guard plate and kiln shell, eventually leading to fracture and falling‑off.

2. Abrasion by material scouring

High‑temperature clinker and kiln dust scour the surface of the kiln‑mouth guard plate at high speed, causing continuous abrasive wear. Turbulent gas flow inside the kiln results in constant impact from granular materials, gradually thinning the guard plate until perforation and damage occur.

3. High‑temperature oxidation and sulfidation corrosion

Flue gas at the kiln mouth contains sulfur and alkali‑metal components. At high temperatures, oxidation, sulfidation and alkali‑induced corrosion take place on the metal guard plate. Loose oxide layers peel off continuously, reducing material strength and accelerating failure.

4. Structural and installation factors

1. Improper material selection for the guard plate, with insufficient heat‑resistance and wear‑resistance performance for service conditions.

2. Fixing bolts elongate under high temperature, become loose or fracture, resulting in displacement of the guard plate.

3. Unreasonable reserved gaps between spliced guard plates; insufficient allowance for thermal expansion causes mutual extrusion and cracking.

4. Defective welding workmanship such as blowholes and cracks, forming weak stress points.

5. Influence of process operation

1. Large fluctuations in kiln temperature and frequent kiln start‑stop operations intensify thermal shock.

2. Over‑long flame directly impinges on the kiln‑mouth guard plate, causing local over‑temperature.

3. Ring formation and falling of large clinker lumps produce mechanical impact damage to the guard plate.

6. Failure of supporting refractory materials

Premature spalling of castable or refractory bricks at the kiln mouth removes thermal‑insulation protection. Heat transfers directly to the guard plate, which causes a sharp rise in operating temperature and rapid deformation and damage.