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Vulcanized Conveyor Belt Splices Part 2

In hot vulcanization, a special press applies both heat and pressure to the splice to cure the intermediary and cover materials into a high-strength joint. The press applies pressure consistently across all surfaces. Pressure can range from 34 to 1200 kilopascal (5 pounds per square inch to 175 per square inch), depending on the belt. Cooking temperatures range from 120 to 200 degrees Celsius (250 to 400 degrees Fahrenheit), depending on belt type and rubber compound. The time required to cure will depend on belt thickness and compound: belt manufacturers normally include time and temperature tables in splicing manuals. Although the equipment is automated, the process may require constant human attention to achieve the best results. Portable vulcanizing presses for curing the splice are available in sizes to match various belt widths. Small fabric belt splices can often be cured in a single setup. Larger fabric belt splices can be cured in two, three or more settings of the vulcanizing press without problems. With steel-cord belts and finger splices, it is important that the press be large enough to cure the splice in a single setup to avoid undesirable rubber flow and cord displacement.

When the vulcanization procedure, or “cook”, is completed, the resulting splice should be inspected for any visible defects that might indicate a weakness. It is common practice to grind or buff away any surplus rubber from the splice to improve the performance of the joint as it passes through belt cleaners and other conveyor components.

Cold Vulcanization (Chemical Bonding)

In cold vulcanization, the belt is joined using adhesives of bonding agents that will fuse the ends of the belt together to form a continuous loop.

In cold splicing, the joint is not cured in a press. The belt ends are carefully laid together in proper alignment with the adhesive, and full contact is achieved with hand rollers, pressure rollers, or hammering in a prescribed pattern. The bond can often be improved by simply putting weights on the belt during the cure interval. Most cold vulcanization cements require at least four hours for a usable cure and 24 hours for a full cure. Best results are achieved by following the manufacturer’s recommendations. The belting manufacturer is the best source of information on proper vulcanization techniques and materials.

Splice Pattern

Vulcanized splices require the cutting away of layers of rubber covers and fabric carcass to let the belt ends be overlapped and joined. In general, the geometry of a splice can be the same whether the joint will be vulcanized hot or cold.

Bias spices are most common, as the angle increases the length of the bonding surface and reduces stress on the splice as it wraps around the conveyor’s pulleys. The bias angle also serves to reduce the chance of tearing open and leading edge of the splice. This bias angle is generally 22 degrees; most vulcanizing presses are manufactured with this bias angle built in.

A splice design that is seeing increasing acceptance, particularly with high-tension fabric belts, is the finger splice. This design involves cutting the two ends of the belt into a number of narrow triangular “fingers.” The fingers—each typically 30 or 50 millimeters (1-3/16 or 2 inches) wide at the base and between 850 to 1200 millimeters (33 to 48 inches) in length depending on belting specifications—are interlaced, and then the hot vulcanization is preformed. Finger splices must be preformed in a single “cook.”

Each side of the belt is cut with &ldquote;fingers&rdquote; that intertwine, almost like 2 claws coming together so each one's fingers alternate with the other.
Used on high-tension belting, a finger splice can provide the best mix of splice strength and life.

For all splice designs, it is important that the overlapped areas and any materials added to the joint be properly installed to minimize damage to the finished splice from belt-cleaning systems or other components.


See Also: Vulcanized Conveyor Belt Splices Part 1 | Part 3.

Topics: Basics of Belt Conveyor Systems

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