Vulcanization vs Fastening – some common misconceptions
Every splicing method has its limitations, and it is essential to get the facts before deciding how best to splice a belt. Some of the most common misconceptions include:
‘Mechanical fasteners cannot be used with higher-tension belts’ (ie more than 800 PIW). Synthetic belts and improved fastener designs have resulted in mechanical fasteners that are compatible with belt tension ratings of up to 350kN/m (2,000 PIW).
‘With mechanical fasteners, sift-through of carried materials is a problem’. To prevent leakage and sift-through, vulcanized belts are ideal. However, when all things are considered, mechanical fastening may be preferable. If the splice is done properly, sift-through should not present a problem. Solid-plate splices can be sift-proof and, if filler materials are used with a hinged fastener, only minimal sifting should occur.
‘Mechanical fasteners are noisy, incompatible with belt cleaners and scrapers, and generally damaging to the belt’. If mechanical splices are properly installed, maintained and countersunk by skiving the belt, there should be no problem with noise or damage to the belt or belt cleaners.
‘All belts can be vulcanized’. Old and/or worn fabric belts are not well suited to vulcanization because the belt layers are weaker and will become brittle when heat is applied. Older rubber belts are also poor candidates for vulcanizing, as the bondable properties of rubber deteriorate over time. Finally, vulcanizing requires additional belt length, so operations with little take-up simply may not have enough belt to vulcanize.
‘You can vulcanize any time, anywhere’. Only clean, dry and relatively warm conditions are suitable for vulcanizing. Chemical residues, excessive moisture and extreme temperatures can interfere with the curing of adhesives and cause nicks and/or bubbles. These conditions, in turn, weaken the strength of the splice. In addition, vulcanizing can be extremely difficult in areas that are not easily accessible.
‘Vulcanization does not mean a lot of downtime’. Vulcanization actually requires the shutdown of the belt for a substantial amount of time – much longer than a mechanical splice would require. Not only do the chemicals take several hours to cure, but a vulcanized splice is also at the mercy of the vulcanizer’s schedule.
‘Vulcanization does not compromise belt strength’. Vulcanizing actually robs the belt of an entire ply of strength – even more if not done properly. Mechanical fastening, on the other hand, does not compromise the belt’s integrity.‘Inspecting a vulcanized splice is easy’. The early signs of adhesion breakdown in a vulcanized splice are nearly invisible to the naked eye. Often, operators are not even aware that a vulcanized splice is experiencing problems until it fails – a catastrophic event that requires the immediate shutdown of the line.