By Richard Hepworth, President, Trelleborg’s marine systems operation
The Thermo-Gravimetric Analysis (TGA) test, adopted by many high quality fender manufacturers, determines whether fenders have been produced using a technically superior rubber formulation that includes little or no recycled rubber and only reinforcing fillers like carbon black.
Reinforcing fillers improve the mechanical properties of rubber. However, contrary to the belief of some across the industry, non-reinforcing fillers such as white calcium carbonate (CaCO3), actually reduces the lifespan of a fender, especially when used in larger quantities. CaCO3 is not a substitute for the carbon black used in high quality fenders.
Considerable research has been carried out over the years on the use of CaCO3 in rubber formulations. It is added to rubber to lower costs, improve processing and impart a lighter color. However, CaCO3 provides very little reinforcement to the rubber. Naturally obtained CaCO3 (ground CaCO3) has poor polymer-filler interaction due to its coarse particle size and its large surface area. Therefore, the rubber compound has poor adhesion and tear resistance.
Some manufacturers make use of large quantities of CaCO3 in the compound formulation of fenders to achieve lower cost. However, while more CaCO3 in a rubber formula may have its advantages in the processing of the compound and lower cost, it negatively impacts the primary aging properties over time, leading to a lower lifespan of the fender.
But, chemical testing is not enough. Full scale testing on prototypes and finished products should also be performed in the manufacturing facility to guarantee that the fenders meet lifecycle and performance specifications. This needs to be verified by testing a randomly chosen fender either at an independent facility, or, by using an independent testing jig.
Although deployed at a manufacturer’s facility using their own test frame, an Independent test rig provides a witness (third party or consultant) with real-time independent testing data captured and shown on an external display. Results are also printed in real-time providing witnesses with direct access to the data. What’s more, load cell and deflection measuring devices can be calibrated on the spot or by an external party independently, outside of the control of the fender manufacturer. Meanwhile test data obtained from the rig can be compared with that reported by manufacturers using their own measuring devices.
It’s vital that the industry understands that the substitution of carbon black with non-reinforcing fillers, such as CaCO3, means that equipment will need to be replaced earlier, and in the long term, result in heavier investment, not to mention the higher risks of failure during service life. Port owners and specifiers also need to educate themselves on the testing methods that can guarantee that the performance of their fenders meet specifications.
For more on Trelleborg’s research into the importance of ingredient selection, mixing and the manufacturing process in marine fenders, please refer to the ‘Guaranteeing Fender Performance’ and ‘Rubber Fenders: Mixing it Up’ whitepapers.