Belt splicing: vulcanized or mechanical?

Pit & Quarry, Dec, 2003 by Neil Schmidgall

Neil Because the ends of a conveyor belt must be joined together to create a continuous belt, even the most properly specified belt is only as good as its splice. That's why operators must use the utmost care when employing either of two common splicing methods--vulcanizing or mechanical fasteners. Is there a clear choice between these two methods? Consider this simple rule: For the permanent splicing of a conveyor belt, vulcanizing is most often the best choice. However, when a belt must be rejoined frequently, mechanical fasteners may be preferred. Beyond these basics, it's important to understand the ups and downs of each splicing method.

Vulcanizing

Vulcanizing is either a hot or cold procedure. Using the hot method, the layers of the belt are stripped in a "stair-step" manner, overlapped with glue and rubber, and fabricated together using a heated press. The cold method laps the belt's layers with glue, which then cures at room temperature. As these definitions indicate, vulcanizing is more costly and time consuming, especially in emergency repair situations. Also, longer take-up travel must be provided (multiply 2.5 x belt width for belt consumed in a fabric belt splice). Yet, the vulcanizing method delivers many advantages:

* Greater splice strength and reliability.

* Longer belt life and less maintenance.

* Smoother operation--no interference with belt cleaners, idler rolls or skirting.

* Leak proof--prevents material sifting through the splice.

Mechanical fasteners

The mechanical alternative involves connecting rows of metal fasteners that are attached to each belt end. Obviously, mechanical fasteners are less expensive than vulcanization and more easily applied. It is the preferred method for making in-the-field repairs, such as adding belt length and patching holes or tears. But material leakage through mechanical fasteners is inevitable, eventually causing clean-up problems and potential damage to conveyor components.

Other disadvantages to using mechanical fasteners (as noted by CEMA) is belt damage caused by the following:

* Exposure of cut belt ends to moisture and materials.

* A rough surface that creates catch points for belt cleaners and belt system supports.

* Heat retention in the metal fasteners that leads to carcass degradation.

Notably, the most important step in mechanical fastener use is to recess the top and bottom splices pieces, removing both top and bottom covers down to the carcass. While not an endangerment to belt strength or integrity, the recess is needed to keep the fasteners from interfering with potential catch points.

Don't skimp on splicing

Avoid cost cutting where splicing is concerned, as splice failures can result in equipment damage and employee injury. If a vulcanized splice is chosen, make sure that the splicer follows the belt manufacturer's specifications concerning techniques, curing times and splicing materials. For mechanical splices, understand that there are many types of fasteners. As belt manufacturers will tell you, "One size does not fit all." In other words, don't use one type of fastener for all belts just to cut down on inventory. Always use the splicing material or fasteners that have been designed specifically for that belt. Don't skimp on splicing. Invest in the time and training required to achieve optimum splice wear life.

Author Neil Schmidgall is president of Morris, Minn.-based Superior Industries, a manufacturer of conveyor systems and components. A portion of the above is excerpted from his technical paper entitled, "Basic Conveyor Design and Maintenance."