## 4. Constructional and Functional Aspects of Chains
### Requirements and Dimensioning
* Calibration--the application of force to the entire chain during production to control link dimensions. * Elastic limit--the maximum force that can be applied to the chain without causing permanent deformation. * Setting force--the force used to hold the specimen under tension while the gauge length is marked or a strain gauge is installed. The standard applies to chains with link diameters ranging from 14 mm to 30 mm. In terms of mechanical performance, ISO 610 specifies three strength grades: B, C, and D.  
Figure 7 illustrates the dimensions of the chain and its individual link as specified in ISO 610 [106], including link width (b), inner width (a), link length (l\({}_{1}\)), pitch (p), wire/rod diameter (d), and total chain length (l). The figure also includes the weld width (d\({}_{1}\)) and weld length (e). The weld protrusion (c) is defined as the difference between the weld diameter and the base wire/rod diameter of the link. Chains covered by this standard are manufactured in nominal diameters ranging from 14 to 30 mm, with dimensional tolerances between \(\pm\)0.4 mm and \(\pm\)0.9 mm. The chains must be fabricated from steel with appropriate mechanical properties and weldability to ensure durability and resistance to dynamic loads after undergoing heat treatment. For grades C and D, alloy steel is required, containing elements such as nickel, chromium, and molybdenum to enhance strength and wear resistance. It is crucial to maintain a balance between tensile strength and other mechanical properties to avoid excessive brittleness. Figure 7: Chain (**a**) and link (**b**) dimensions according to ISO 610 [106]. The steel should possess a fine-grained microstructure to achieve an austenitic grain size as defined by ISO 643. The choice of chemical composition remains at the discretion of the manufacturer, who is responsible for ensuring that the final product meets the required strength parameters. The chain manufacturing process includes heat treatment, in which the links are heated above the critical Ac\({}_{3}\) temperature of the steel. Upon completion, any welding splatter must be removed and the welds properly smoothed. Each link must be free from surface defects, such as cracks, notches, or other irregularities that could compromise durability. Any defective elements must be rejected or repaired accordingly. By default, chains are delivered in an unfinished, uncoated condition unless otherwise agreed. However, optional anti-corrosion coatings, polishing, or color markings may be applied to facilitate quality class identification. Identification markings must be placed on the flat sides of the links, away from the weld, with a concave profile and without sharp edges or excessive depth. The mechanical performance of the chain is strictly related to its strength grade. The minimum breaking force is defined as follows: 190-890 kN for grade B, 250-1130 kN for grade C, and 310-1410 kN for grade D. The ratio of proof force to breaking force is typically 80%; however, for the largest link diameters (26 and 30 mm) in grades C and D, this may be reduced to 75%. The elongation under proof force is 1.4%, 1.6%, and 1.9%, respectively, while the minimum total elongation at break must not fall below 12%. All chains must undergo a proof load test of at least 90% of the specified proof force. If this requirement is met during the calibration stage, a separate proof load test is not necessary. After testing, each chain must be subjected to thorough visual inspection, and any damaged links must be replaced. Samples for mechanical testing are randomly selected based on pre-defined batch lengths. Dimensional tests are conducted on randomly chosen links to verify compliance with the specified length, width, and dimensional tolerances. Mechanical tests include tensile, bending, fatigue, and impact testing, all carried out in accordance with applicable standards.