Vulcanization 101

What is Vulcanization?

A vulcanized splice is the process of bonding two belt ends together through the application of Uniform Pressure and Temperature.

A fabric belt splice consists of two belt ends stepped down and held together by vulcanized rubber. The ends are shaped like matching ends of shallow steps.

A steel cord splice consists of removing the cover on the two ends to be spliced, stripping the cables, overlapping them and vulcanizing them back together.

The prime advantage of a vulcanized splice is that the hot vulcanized splice is nearly as strong as the belt itself, the splice results in longer belt life, and because of that, conveyor belt downtime is reduced.

Why is a vulcanized splice better than other methods of joining belt ends?

a) Fasteners:
One of the issues with fasteners and/or lacings is that the entire load is thrown on a very small portion of the belt. This area is exposed to moisture and the possibility of wear caused by bulk materials entering the joined ends. Sometimes, the complete conveyor system suffers from vibration and wear, in part due to those fasteners.

When belts ‘run-off’ due to misalignment or some other unforeseen reason, the odds are that a metal splice will ‘hang-up’ and pull out, or ‘hang-up’ and rip a strip off the side of your belt. If your belts have been vulcanized this likely won’t happen, because there is no irregular surface to ‘hang-up’.

This allows your maintenance personnel the time needed to correct the situation, preventing production loss, belt loss and the added maintenance cost of either replacing or repairing the belt.

90% of the actual belt strength is retained in a vulcanized joint. Only 40% of actual belt strength is retained at a metal fastener joint. In the event of a sudden overload or a plug-up somewhere on the system, it is not difficult to determine which type of splice is going to fail.

Why purchase an expensive, high tensile strength belt only to have it fail because of a metal joint that retains less than half the strength of the belt?

b) Self-cure Splicing Materials:

  • Self-curing materials are not always suitable for splicing since tensions involved often exceed adhesion capability;
    • A post-cure period of up to 24 hours can be required;
    • a certain amount of technical skill is necessary.
    • Self-curing repairs generally do not last.

Why has the vulcanizing method been discarded by many?

  • Conventional vulcanizing equipment is often deemed too heavy and time-consuming to setup.
  • Rigid platens are not suitable for worn belting sections because they bridge the low spots.
  • Mechanical pressure deflects the frames causing loss of pressure in the center of the vulcanizer.
  • Conventional equipment is too expensive.

What are the benefits of a vulcanized splice?

  • A vulcanized joint allows the belt to wrap smaller pulleys than a metal fastener.
  • Additional product material leakage and loss can occur at the area of a metal fastener but not in a vulcanized splice. Additional leakage leads to product loss, can contribute to additional build up on pulleys and create more belt maintenance work.
  • Belting can be plowed or cleaned more efficiently.
  • Where gaseous, static or dusty conditions exist, the danger of sparking is eliminated.
  • Damage to a finished product due to marking, is eliminated.
  • Bacteria build-up in the metal joint is eliminated where finished food product is being conveyed.
  • Reduces one more maintenance job: the checking and repairing worn out metal splices.

###Comparison Chart | | FASTENERS | COLD SPLICE MATERIAL | HOT SPLICE MATERIAL | |-----------------------|----------------------------------------------------|--------------------------------------------------------------------|-----------------------------| | STRENGTH | 50-80% | 80% | 80% | | DOWNTIME | 1 TO 6 HOURS | 4 TO 8 HOURS | 4 TO 8 HOURS | | EXPECTED LIFETIME | Short (25% belt life). Wears faster than the belt. | Semi-Permanent (dependent on splice conditions) | Permanent | | METAL DETECTORS | No | Yes | Yes | | MATERIAL SIFT-THROUGH | Yes | No | No | | BELT DAMAGE | Holes, punctures, open cut moisture penetration | No | No | | CONVEYOR DAMAGE | Yes: Idlers, Pulleys and belt cleaners | No | No | | AMBIENT CONDITIONS | No problems | Susceptible to moisture and dirt contamination. Belt must be dried | Overhead tarp is sufficient | | SPLICE FAILURE | No Warming | Warning Period | Long Warning Period |

What is the Almex Advantage?

  • With modern lightweight materials, vulcanizers are lighter and have greater portability for field splicing.
  • There is no need to build up worn sections when splicing and repairing a worn belt. The ALMEX Flexible Platen contours to the belt regardless of wear. This is accomplished by a laminated platen floating on the pressure bag. There is a savings in labor since there is no need to shim worn sections.
  • No guess work as to the amount of pressure required, no bolts to tighten. The ALMEX unique Pressure Bag Principle which is simple to operate, gives up to 200 p.s.i. (14 kg/cm sq.) in a matter of minutes and ensures Uniform Pressure over the entire platen area._