Vulcanization is the process of curing raw rubber by combining the rubber with additives in the presence of heat and pressure (“hot” vulcanization). Bonding of the belt ends with adhesives is known in the belting trade as “cold”vulcanization.
Vulcanization is generally the preferred method of belt splicing, due to the superior strength, longer service-life and cleaner operation it offers. Vulcanized splices are really the only option for the long-term performance of high-tension steel-cord belting. Operations that require frequent additions or removal of sections of belting, such as extendable underground belts or conveyors with limited take-up capabilities that require shortening of the belt to maintain tension, are not suitable for vulcanized splices.
Due to their superior strength, vulcanized splices allow the application of maximum belt tension, resulting in better pulley-to-belt traction. A vulcanized splice has no internal weaving, braiding, sewing, welding or other mechanical link. The splice is solely dependent on rubber adhesion to the carcass or steel cords, as the tensile members of the splice, textile plies or steel cords, do not touch each other. Adhesion is obtained through use of an intermediary rubber or rubber-like material called tie gum, installation gum, or cement.
Step-by-step procedures for vulcanized splices vary between manufacturers. In general, there are three steps:
There are two types of vulcanization: hot and cold. In hot vulcanization, the layers of a belt are stripped in a stair-step or finger fashion and overlapped with glue and rubber. A heated press or “cooker” then applies heat and pressure to “vulcanize” the belt into an endless loop. In cold vulcanization (technically called chemical bonding), the belt’s layers are joined with an adhesive or bonding agent that cures at room temperature. Vulcanization, particularly hot vulcanization, is usually performed by outside contractors who have the specialized equipment and expertise to perform the required procedure.
See Also: Vulcanized Conveyor Belt Splices Part 2 | Part 3.