Every day we encounter countless straps, belts, ropes and cordage, almost without noticing them. They are subject to constant loading and must fulfill certain quality characteristics to be able to perform their safety functions reliably (for example, safety belts, climbing ropes, and conveyor belts). Real-world conditions require complex test arrangements, special specimen grips, and reliable results— requirements that are fully met by ZwickRoell’s product portfolio.
Rope testing requires a certain amount of expertise. Untwisting of the rope on clamping should be avoided as far as possible or kept to a minimum.
The specimen is inserted ergonomically, quickly, and carefully via a winding principle. Specimen material is clamped only on the ends making this principle ideal for very sensitive surfaces. The specimen is automatically centered via a centering ring Tensile stress on the specimen is reduced via frictional contact with the load reduction roller. The ends are clamped mechanically via a screw (with force amplification if required), a wedge, or a hydraulic gripping unit.
Applying gage marks to the surface of braided or twisted specimens can also be tricky. In view of the energy released when the rope breaks, a non-contact-measuring optical long-travel measuring system is essential because the crosshead travel reference value for the strain cannot be precisely defined. ZwickRoell’s range of capstan grips and rope grips, together with a non-contact long-travel measuring system, provide the ideal solution.
Safety belt manufacturers and original equipment manufacturers use ZwickRoell testing systems to determine the strength of the safety belts they produce (with and without buckle). The tensile test requires special specimen grips and impact-resistant safety housing.
In a different test, the actuation force of the safely belt (unloaded and with tensile load) is determined. In this test, the specimen is rolled in the roller grip and is held in place by itself. Since a conventional clamping method is not used, this system is also recommended for clamping-sensitive specimen. Via the rolling of the rollers the specimen material is clamped independently due to the frictional contact.
Alternatively, capstan grips are also used with straps and belts. Specimens are clamped quickly and easily. These grips are also used for materials that are thin and sensitive to clamping forces and to prevent jaw breaks or to prevent specimen slipping during tensile tests. The force reduction curve reduces the tensile strength before end clamping. The specimen is held securely preventing jaw breaks, and the test is performed according to the standard. The specimen should break in the free clamping length and not in the deflectors. An optical travel measuring system must be used for strain measurement, because a high degree of energy is released at break and the crosshead travel reference value for the strain cannot be precisely defined.
The adhesion test determines the ply adhesion between constitutive elements of items such as conveyor belts. The material specimen is prepared in accordance with DIN EN ISO 252. At one end of the specimen (cut lengthwise) the first layer is removed and clamped in the specimen grips. The standard specifies two test methods, A and B, for determining the adhesive strength between the plies and between the covers and casings of conveyor belts; the basic test conditions conform to ISO 36. The test is applicable to all types of conveyor belts, with the exception of belts with steel cord reinforcement and textile-reinforced belts with a full thickness tensile strength of less than 160 N/mm.
The applied standard, DIN EN ISO 283, specifies a test method in determining the breaking strength, strain at break, and the force by strain of conveyor belts at full belt thickness. A specimen cut from the thickness of the conveyor belt is elongated until it breaks using a tensile testing machine. High and individual gripping forces are required to hold the specimen. Hydraulic grips with suitable jaw inserts are used for this purpose. An extension measuring system is required for measurement accuracy. A mechanical measuring system should be used only when the risk of damage at specimen break does not exist.