One of the most used laboratory tests to evaluate the quality of a compound / O-ring is the elongation and tensile strength test. The test requires a standard specimen / O-ring to be “stretched” until it breaks. At that moment, the percentage of elongation that it has undergone and the effort necessary to break it are calculated.
The elongation is therefore measured as a percentage (so the percentage value of how much it has stretched) while the tensile strength is measured in MPa or N/mm2 or PSI.
There are various reference standards for the elongation test (they vary according to the type of material) but the most used in our market are ASTM D 412C and DIN 53504.
Have you ever wondered what this test is for? Why is it done? How can we use the test in “real life”?
There can be countless answers given the many applications where elastomer products are used.
Here we will analyze some related to the O-rings:
Evaluate the molding quality of the O-ring
All produced O-rings have weak points and strong points. Usually where the junction point of the material is present during vulcanization (present both with compression molding and injection molding), a weaker point could be present. Furthermore, in the event that the vulcanization of the product has not been completed correctly during the molding cycle, there could be anomalous values of elongation (too high) and tensile strength (too low).
Test the capacity of the O-rings: withstand sudden strong stretching
There are applications where the O-ring must resist strong and rapid elongation and ensure an equally fast springback. This is the case of the assembly of the O-rings in an automatic way (usually o’rings of small diameter). In this case, automatic pliers widen the O-rings very quickly and then release them over the component that will house the gasket. If the molding process is not correct there is a risk of breaking the o’rings every time they are enlarged.
Test the ability to withstand a constant load
Sometimes the O-ring is used as a transmission belt. In this case, the load and elongation are constant and in some cases even very sustained.
Do you need to evaluate the correct elongation or tensile values of your O-Ring?
If you need to find more information about the values indicated above, please get in touch with us, our technical staff will be able to offer the best answer to your questions.