Dr. O Mielenz, B. Bergmoser, Dr. S. Benito and Prof. Dr. W. Theisen, HEKO, highlight a new development in round steel chain technology that enhances wear resistance and extends service life under challenging operating conditions.
Conveyor chains have a major influence on the efficiency and cost-effectiveness of conveying processes and are subject to high mechanical stress. Accordingly, there is enormous interest in extending service life with increased operational safety and damage tolerance.
In addition to the high dynamic tensile forces acting on the chains, high wear and tear occurs in the contact area at the joints of the chain links, due to high contact pressure with relative movement to one another and the effect of the generally abrasive bulk material. This applies even more to round steel chains, where the joint contact is limited to a small area. Case-hardened steels are therefore often used. These are enriched with carbon in the edge zone through carburisation during the chain manufacturing process and, after subsequent hardening, have a high surface hardness, as well as high toughness and sufficient strength in the core. In recent decades, developments to improve the performance of round steel chains have been particularly aimed at increasing surface hardness and hardness depths while maintaining the ductility of the core. However, these developments often do not consider the fact that most chain breaks are less often due to an insufficiently ductile core than to an insufficiently ductile surface layer in the areas of the chain links in which particularly high tensile stresses are present due to operational forces.
Within a joint R&D project between HEKO and the Chair of Materials Technology at the Ruhr-University Bochum, a new approach was developed to create a highly wear resistant, dynamic, and highly resilient round link chain, which was developed and successfully validated on a laboratory scale and in industrial trials. This project was supported by the Federal Ministry for Economic Affairs and Climate Action (BMWK) based on a decision by the German Bundestag.
Development
The main idea behind this HEKO development was to provide the case-hardened edge zone of the chain links in the areas that are exposed to particularly high tensile stresses with sufficiently high ductility. At the same time, the chain joints, which are subject to increased wear, should be sufficiently wear-resistant during operation. This goal was achieved by a slight modification of the chain material chemical composition targeting grain refinement and by a newly developed case hardening and heat treatment process. The latter results in a slightly lower surface hardness of approximately 750 HV of the new chain in delivery condition, and thus, a significant increase in breaking stresses and improved fatigue strength. The particularly good wear resistance of the newly developed chain grade results from in-situ-hardening in operational use up to approximately 850 HV within the chain joints and contact areas to the sprockets that are subject to high surface pressure and greatest wear. Technical data for the new HEKO chain grade is summarised in Table 1.
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