A Critical Review of Wear Mechanisms in Chilled Cast Iron for Food Processing Applications

Chilled cast iron is the dominant material used in food processing equipment throughout sub-Saharan Africa and South Asia, particularly for staple food milling. Its duplex structure consists of a hard white iron surface layer ranging from 400 to 600 HBW and a tough grey iron core between 150 and 250 HBW, providing an effective combination of abrasive resistance and fracture toughness at low cost. Recent studies using magnetic separation, scanning electron microscopy, and atomic absorption spectrophotometry have demonstrated that cast iron grinding discs release metallic wear particles up to 1.7 grams per 10 kilograms of milled grain, with mean diameters of 43 micrometres and measurable levels of chromium, lead, and cadmium. Despite these contamination figures and related health concerns, major knowledge gaps persist regarding how microstructural evolution influences wear rate progression, which wear mechanisms dominate under different food processing conditions, and how particle characteristics relate to processing parameters. This review offers an integrated perspective linking tribological degradation, microstructural design, and public health consequences through methodical evaluation of published work. As a consolidation, it compiles and quantifies particle release data, identifies transitions between wear mechanisms under food-relevant conditions, and suggests approaches for reconciling the opposing demands of wear resistance and food safety. The review also proposes a quantitative wear model, provides a consolidated repository on contamination, assesses alloying strategies including vanadium additions up to 1.2 percent, and presents a decision-making protocol for manufacturers, moving the discipline from descriptive observation towards prescriptive engineering practice.

Keywords: Abrasive wear; Chilled cast iron; Food processing; Food safety; Metallic contamination; Microstructure.