During my career, I have often been confronted with technical challenges requiring rapid and precise analysis. One of them occurred as I was handing over to my successor as site manager of a plant specialising in the manufacture of refractory bricks, to take up my new role as Product Line Manager Glass. It proved a highly instructive experience regarding the importance of rigorous control of manufacturing processes.
An Unexpected Quality Problem
Shortly after I left the position, we were confronted with a major problem: the bricks intended for an anode baking furnace for a Greenfield project showed internal cracks. These defects were undetectable to the naked eye and could only be identified by means of ultrasonic testing.
It did not take me long to identify the cause. Everything pointed to the problem being directly linked to a modification of the refractory brick production process introduced by my successor.
The Impact of a Poorly Controlled Change of Production Rate
For fear of destabilising the furnace over the weekend, when the presses were at a standstill, the new manager regularly slowed the production rate, dropping from 22 wagons per day to 18. Then, on Monday morning, he abruptly accelerated the rate to 24 wagons to compensate for this slowdown.
These weekly variations had unforeseen consequences for the furnace temperature. Indeed, the recuperation zone of the furnace supplies the dryers with hot air. The temperature drops caused by the weekend slowdowns led to a decrease in the temperature in the dryers, which then proved insufficient to ensure optimal drying of the bricks. As a result, when the bricks were loaded into the furnace, they still contained a quantity of residual water. At the start of firing, this water expanded under the effect of the heat, causing the appearance of internal micro-cavities.
Lessons to Remember
This incident highlights several fundamental elements in the management of industrial processes:
- Control of critical parameters : Every manufacturing process rests on precise thermodynamic balances. Modifying a variable without measuring its impacts can lead to irreversible defects.
- The importance of intermediate controls : Putting rigorous controls in place at each critical stage (such as the drying of the bricks) makes it possible to detect, upstream, deviations likely to generate non-conformities.
- Training and supporting successors : A change of manager requires a thorough transfer of skills to guarantee the continuity of good practices.
- Anticipating side effects : A change of production rate may seem trivial, but it can disrupt the entire production process if the interactions between the various stages are not taken into account.
Conclusion
Good control of manufacturing processes is not limited to the strict application of procedures; it also requires a fine understanding of the interactions between the various stages and appropriate controls to guarantee the quality of the final product. This incident perfectly illustrates how a seemingly minor change can have major consequences for product quality, and underlines the importance of a rigorous approach in the management of industrial operations.
Xavier Schuster
Consultant at SXE Consulting. Industrial consulting firm based in Luxembourg, 25 years of experience in operational excellence.
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