Vulcanization is a complex procedure that, if done correctly by an expert, can offer a smooth splice with minimal risk of snagging, tearing and other harmful wear to the belt. There are several types of vulcanized splice, including stepped splices, finger splices and overlap splices, and two types of vulcanizing processes, hot and cold. Each process requires unique tools and an intimate knowledge of the rubber bonding process.
For both hot and cold vulcanization, the belt must be disassembled and each belt end prepared according to that particular belt’s splicing recommendation. Proper belt preparation is crucial to ensure the finished splice will hold to its published tensile ratings.
With hot vulcanization, splices are heated and cured under pressure with a vulcanizing press. This process takes several hours. If a belt is re-tensioned and used before the splice is bonded and completely cooled, the splice will be ineffective and may come apart completely, causing additional downtime.
Cold vulcanization does not employ a vulcanizing press, but instead uses a bonding agent that causes a chemical reaction to splice the two belt ends together.
When vulcanizing, several factors must be considered to ensure a high-quality splice. First, an expert who is skilled and trained in the procedure and who has a thorough knowledge of solvents, bonding materials and other cover and fill materials must perform a vulcanized splice.
Secondly, the process requires a specific temperature, compression and equipment dwell time, in addition to a virtually moisture-free work area.
Thirdly, some types of belt may not allow for vulcanization. If the belt is old, dirty or unevenly worn, vulcanization is not a good option because it will not always cure evenly, which can result in a weaker splice.
Vulcanized splicing of a 600mm wide belt could take between six and 11 hours, depending on working conditions. Wider belts may take longer. And because vulcanization often requires time for a specialized vulcanizing crew and equipment to be brought on site, operations can be shut down for half a day or more.
To summarize, vulcanized splicing can be used where:
- The belt is clean and free of contaminating agents, such as oil, sand and material fines
- The belt is compatible with the adhesive of choice
- The belt is new or without excessive wear
- The procedure is performed by a trusted, certified vulcanizer
- The work environment is at an optimal temperature and moisture level
- There is easy access to the area that needs splicing and plenty of room to work
- There is enough downtime available to allow for a properly installed vulcanized splice.