Scenario
Commercial pizza ovens operate at sustained high temperatures to bake pizzas quickly and efficiently. During normal operation, oven walls and internal components (shafts, metal conveyors belts, pizza pans, support frames) are subjected to frequent and rapid temperature changes from startup, shutdown, door openings, product loading and unloading, and uneven heat distribution driven by airflow behavior
Cause
Thermal Stress develops when components experience rapid, non-uniform heating and cooling. Hot zones expand while cooler zones lag behind, creating thermal gradients within the same component. These gradients are strongly influenced by airflow dynamics inside the oven. If metal components are heated beyond their elastic limit, they may undergo plastic deformation, leading to permanent changes in shape and size.
Key contributors include:
- Turbulent airflow patterns creating localized hot and cold spots, and thermal gradients
- Dead zones with limited circulation allowing heat to stagnate or dissipate unevenly.
- Fan performance degradation (wear, imbalance, fouling) altering designed airflow paths
- Damper position, leakage, or control drift causing uneven heat distribution
- Rapid heat-up and cool-down cycles during production changes
- Material CTE mismatch relative to operating temperature range
- Mechanical constraints preventing free thermal expansion
- Exposure to cleaning chemicals, moisture, or food residues that promote corrosion during thermal cycling
Impact
Over repeated thermal cycles, these combined thermal and flow-induced stress accumulate and can lead to:
- Thermal bowing and warpage of shafts, conveyor frames, belts, and pans
- Permanent deformation affecting alignment, belt tracking, and clearances
- Thermal cracking initiating at high-gradient regions and stress concentrators
- Stress corrosion cracking (SCC) where thermal stress overlaps with corrosive exposure
- Reduced component life, increased maintenance, and degraded bake uniformity
This article is the first in a multi-part series on thermal stress–related shaft failures.
The articles that follow will focus on identifying thermally induced shaft damage, the inspection methods that reveal early warning signs, and the targeted maintenance actions that can interrupt the failure progression before it escalates into permanent deformation or fracture.
Tagline: Thermal failures don’t start with cracks, they start with airflow, constraints, and maintenance blind spots.
Join us on our YouTube channel for the free lecture: Thermal Expansion & Shaft Failure — Explained! 🔥 LS-005
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