In a competitive market, everything used in the construction of food processing machinery must be justified in the terms of commercial advantage. Stainless steels provide the advantages of aesthetic appearance, extended machine life and reliability, reduced cost of ownership and improved processing. Two examples show the range of grades required in this sector.
Extruders are used for preparing some food products. Two shafts with intermeshed screws are rotated in a barrel forcing the mixture of ingredients through a die whilst also cooking it. The requirements for this machine are transmission of high torque and corrosion resistance. High torque demands high strength, coupled with moderate ductility and toughness. 17-4 PH (1.4542) provides these properties along with a moderate corrosion resistance. It replaced previous non-stainless engineering steels such as En 19 and En 30B giving much longer life.
Salt is commonly used in processed food. Although concentration in the cooking solution is low, boiling and evaporation can lead to higher concentrations in some parts of the process. For these components, the standard austenitic grade 316L (1.4404) is not good enough. The duplex grades 2205 (1.4462) and 2507 (1.4410) with their superior resistance to pitting and crevice corrosion are used.