TENSILE TESTS ON RUBBER FROM 5 TO 500 KG ACCORDING TO ISO 37
IN THIS CASE STUDY, WE ANALYSE A PARTICULAR NEED FOR TENSILE TESTING ON RUBBER AND POLYMERS, MET WITH A COMPACT, VERSATILE AND UNIVERSAL EASYDUR SOLUTION
Nowadays, the concepts of sustainability, circular economy and recycling are prominent in many sectors. One example is the customer depicted of this case study, an Italian manufacturer of recycled rubber rollers with various testing needs for the processed materials, from tensile tests to compression tests.
WHAT CHARACTERISTICS MUST THE SPECIMEN OF A TENSILE TEST HAVE?
The request submitted to us involves material characterisation operations carried out on ISO 1798 TYPE 1 standard specimens (some examples in the photos), die-cut with special standardised tools. The analysis of the material properties is carried out by means of tensile tests on dog-bone specimens and compression tests on round profiles of various diameters and thicknesses.
As already mentioned, the product is recycled rubber or, to be more precise, a mixture of EPDM and SBR obtained from the transformation of tyres into rollers of various thicknesses by means of a process involving a machine comparable to an autoclave with a 60-metre line, capable of processing 4 tonnes per hour (about 500 tyres), a very considerable production volume.
These substances are commonly used for manufacturing sports equipment, but also in the industrial sector (belts, hoses) while plastic + rubber agglomerates are used for acoustic insulation.
Already from the beginning, it can be seen that the main requirement of the technical solution to be found for the customer is flexibility. Not only are two types of tests required (static tensile test + compression test), but the production also includes different types of mixtures, result of continuous research and experimentation, with a considerable amount of prototypes to be tested and data to be sent and stored.
These requirements, combined with the low loads involved, immediately led us to suggest DYNO, our Universal Machine for Tensile, Compression, Bending, Shear and Peeling Tests. The model recommended in this situation is the two-column benchtop version, here in customised configuration with 3 load cells (5, 50 and 500 kg) and capable of performing tests with up to 10 kN (1,000 kg). We are talking about the “little brother” of the 3MZ and AURA series (with loads up to 50 kN and 200 tons respectively), designed to perform tests with particularly low loads, therefore ideal for the characterisation of materials such as plastics, rubbers, polymers and composites, which during the tests show high percentage elongation levels.
Dyno is also available in a single-column version, with a maximum load of 5 kN (500 kg).
UNIVERSAL TENSILE TESTING MACHINE OPERATION
DYNO can perform all kinds of mechanical tests, such as tensile, compression, bending/shear and peeling tests, depending on the mechanical configuration chosen.
Each scenario provides for a different machine operation: thanks to the fully customisable test recipes, it is possible to select a tensile test to breaking point, with instantaneous stop at the breaking moment and indication of the specimen breaking point load, or a controlled elongation test. The applied force is calculated and displayed in real time on the tensile test chart, for each fraction of a second.
Moreover, thanks to its very high load and cell position detection accuracy, DYNO can measure the thickness of the specimen, returning the value in mm, applying a zero load, or a slight controllable load, for example to straighten curved samples. The large surface area of the load cells makes it possible to obtain values that are not influenced by the consistency of the mixture (the classic gauge could penetrate, distorting the result).
THE IMPORTANCE OF SOFTWARE FOR UNIVERSAL TESTING MACHINES
Since the materials produced are varied and have different physical properties, having available several programs immediately retrievable at each tensile test is a must. This is where another DYNO function comes into play, made possible by EasyQs, the intuitive software developed by Easydur.
We are talking about the ability to set and save, using a practical and large touch screen, all the information about the samples tested in special recipes. This makes it possible to complete the test with just a few steps, and quickly obtain data and charts to forward or file.
In this case, the customer wanted to be able to set geographical information concerning the location of the tests, together with time information, from the year to the actual time (including seconds). Some standards require four tests with subsequent calculation of average values, an operation that using the Easydur software can be completed automatically, speeding up the issue of reports.