Hygiene at the chain

For critical hygiene areas such as food production or clean rooms, Ketten Wälder has developed conveyor and stop chains made from special NiRo steel, which is highly corrosion-resistant even without coating.

Absolute avoidance of foreign body contamination, cleaning up to sterilization under high temperatures and sometimes alkaline conditions – the requirements for systems in sensitive production environments such as the food or chemical industry are very high. On the one hand, it is necessary to protect consumers and prevent contamination; on the other hand, in times of tight cost calculations, the durability and cleanability of the materials used also play an important role. For surfaces in contact with products, EHEDG therefore recommends stainless steel. But there are also now sturdy chains made from special non-rusting steel for lifting and conveying equipment, which exhibit high corrosion resistance even when uncoated and are simultaneously very load-bearing. These so-called Cromox chains from the Bavarian chain manufacturer Wälder GmbH are used, among other things, as lifting devices in cleanrooms or in conveying systems for the food processing industry.

Hygiene chains: Acid-resistant and smoothly polished

These are manufactured by Wälder GmbH from Bad Endorf. "We only use 1.4404 or 1.4462 steel for this, as these grades are characterized by high chemical resistance and favorable mechanical properties," explains Franz Wälder, managing director of the specialized company. The high chromium content in the alloys, combined with nickel and molybdenum, provides very high resistance to rust or acids. Both materials are only minimally attacked even by 10 percent sulfuric acid at 20°C, and 50 percent acetic or tartaric acid causes no surface corrosion at this temperature. The 1.4404 steel has a strength of 500 to 700 N/mm² and a breaking force of 50 kN at 8 mm diameter. The more robust 1.4462 duplex steel has a reduced nickel content and instead contains nitrogen as an additional austenite former. Its strength ranges from 650 to 880 N/mm², with a breaking force of 63 kN at the same diameter. Overall, the Cromox chains meet the quality class 5 or the safety factor 1:2, thus fulfilling the highest requirements.

The chain links are welded with high precision in-house by Wälder, ensuring smooth surfaces without hollows that could serve as points of attack for dirt or corrosion. To ensure that the finished chain has no weak points, it is calibrated afterward, and each individual link is checked for its load capacity and quality of workmanship. Even in random tests with loads exceeding the maximum, the links must not break at the welds. The metal is then treated specifically depending on the application; for the food industry, an electro-polishing process is usually performed. This process smooths the surface, making it easier to run over guide rollers. Above all, it prevents dirt or production residues from settling and facilitates cleaning.

No danger from flaking rust or paint

Particularly because of these properties, the chains are increasingly used directly in hygiene-critical production areas, as Carlo Weber, sales manager of the lifting equipment manufacturer Kurschildgen GmbH, explains: "Where cleanliness is required, Cromox chains are practically indispensable." The company uses them, among other things, as lifting chains for load handling in food and chemical production, up to cleanrooms. Standard chains could not be used here because they either rust or are coated for rust protection. In both cases, particles could loosen from the metal and contaminate the environment. 1.4404 steel, on the other hand, is resistant to corrosion even without coating, so there is no such contamination risk. Additionally, the often aggressive cleaning agents used in these industries can quickly corrode conventional steel. "Cromox, on the other hand, lasts about 50 to 60 percent longer," says Weber. The slightly lower load capacity of NiRo steels compared to special high-performance alloys, such as quality class 8, is not significant. For hygienically safe working conditions, smaller packages can simply be used if necessary.