Hello Dmytro,

Splice strength comparisons between vulcanized, cold cure, and mechanical splicing can be an exercise in frustration - as so much depends on the base belt and the quality of the splices done. That being said, the following rules-of-thumb for well constructed splices can be used as a guidline:

Vulcanized splices - 300% to 900% of rated PIW (the strength variance is due to belt construction and belt safety factor over the rated PIW)

Cold cure splices - 300% to 900% of rated PIW (the strength variance is due to belt construction and belt safety factor over the rated PIW)

Mechanical splices - 100% to 900% of rated PIW, with the commonly used metal fasteners mechanical splices in the 100% to 300% range and the SuperScrew splice in the upper range. Note that the mechanical splice strength is very dependant on the construction of the base fabric carcass belt.

If you want to get refinements on these rough values, contact the suppliers of the mechanical fasteners for their test results. The main problem with laboratory testing is that it tends to be s straight pull test instead of the flexing, abrasion, and scraper interaction that the splices are exposed to in service.

Hope this helps. ■

Dmytro,

This may help to clarify also. Safety factors are used to calculate the tension ratings of the belts or PIW's. In the U. S. belting has traditionally used a 10:1 safety factor so a belt that has a rating of 330 PIW was actually pull tested to 3,300 lbs. when testing a one inch wide piece of the belt.

Flexco has traditionally used a 4:1 safety factor when creating the PIW ratings that the fasteners are designed to work with. This same 330 PIW belt was actually pull tested to at least 1,320 lbs. using a mechanical fastener.

These safety factors are in place to ensure that the belt/fastener will work in the operating conditions that they are subjected to such as the extreme tension at start up, material getting caught in the system, loading, etc.

We have found that some manufacturers have begun to play with these numbers using less than a 10:1 or 4:1 rating to make their product appear to be stronger. Also, these numbers can vary depending on the design of the belt. Make sure that you are comparing apples to apples.

The 500% that you speak of regarding a vulcanized splice retention rating is relating to a two ply belt. A three ply belt will have a retention rating of 666% when vulcanized. You lose one ply's worth of strength when vulcanizing a belt. Both of these numbers relate to the 10:1 (1,000%) safety factor of the belting.

Kevin Finnegan

Flexco

1-630-971-6471 ■

THe breaking strength is determined from the operating load plus a multiple of the safety factor.

The safety factor is determined from four critical value as setforth by DIN 22101:

1. operating load = 1.00 a value you calculate as a first estimate.

2. dynamic conditions during starting and stopping multiple of operating load (ie. 40% of running fluid cplg) = 0.4 x 1.0 = 1.40

3. degradation and elongation factors including: vertical curves, tracking errors, splice accuracy and splice efficiency, ageing, idler transition, pulley bending and build-up, etc.= 1.00 as per DIN 22101, thus SF total = 2.40 for items 1+2+3

4. splice dynamic efficiency (mechanical, cold or hot vulcanized, fabric or steel cord range from 25% to 50% for good practices

Required Breaking Strength = (1 + 2 + 3) / (4) = ST or EP or NN..

Typical fabric equivalent = (2.4 /.25 = 9.60 x fabric oper. load)

Steel equivalent = (2.4/.50 = 4.80 x steel cord operating load)

THe key to applying the above criteria is the dynamic efficiency of the splice under study and variations of items 2 and 3. The dynamic efficiency is the measure of endurance of the splice cycling between low and high tensions for each cycle and how many cycles it will see during its life including the loading histograms of items 1 + 2 + 3 ■