Dear Gentlemen,

Thank you for your replies.

But wouldn't it be, by conventional wisdom, that an extra ply of fabric would add strength to the joint? Or, as the resulting joint is thicker, is this benefit negated by higher shear stresses and displacement between the plies as the joint moves through the pulleys leading to higher fatigue and perhaps premature delaminating of the joint? Would appreciate if you can confirm this.

Also, can anyone comment on the flow and curing of the tie and stock rubbers during vulcanization when attempting to do a thicker joint as mentioned?

Best regards.

Barry Chung ■

Dear Corey,

Yes, that is also my understanding of how a hot splice is normally done.

My questions are in response to a couple of recent joint failures experienced by one of our clients. When I examined the original failed joint (prior to ones above), I discovered the following.

1. Torn carcass just outside the joint area up to 180mm deep measured from the belt edge. I was told the damage was about a year old was probably caused by mechanical contact. No reinforcement fabric was visible and the edge was repaired by simply closing up using a cover strip.

2. Half of the joint (on side transversely across from 1 above) had delaminated while the remaining half suffered catastrophic fabric failure.

3. The conveyor is possibly loaded up to 40% above its design capacity based on the observed discharge rate of the wagon cars.

4. Examination of the subsequent failed joints showed the fabric at about the same transverse location as the latter half of (2) had sheared.

5. I concluded that the subsequent failures were due to a longitudinal stretch of carcass that had become weakened or damaged just prior to the catastrophic failure of the original joint. I imagined, at the time of failure, that the belt would quite probably have cupped both upstream and downstream of the joint due to the uneven distribution of stresses brought about by the delaminating of half the joint area described in (2).

While such analysis is possible posthumous, it would understandably be difficult to call simply by visually inspecting the remaining belt at site. Therefore, short of making a recommendation for a belt change and so that one remains on the safe side, would a 3-stepped joint be justified under these dodgy circumstances?

Best regards.

Barry ■

Dear Gentlemen,

Thanks for concurring with my findings on the failures. The belt width is actually 900mm. My calculations showed that the maximum running tension under the overloaded condition was at exactly 100% rating of belt and used exactly 100% of the trough area. Coincidence? Maybe not. I suspect the designers had known in advance that the belt was going to be operated at those levels but maybe underbelted to save on cost. To make matters worse, the designers actually reduced the takeup weight by 40% to keep the running tension within the rating of the belt. Smart huh! As a result, the inclined conveyor suffers frequent spillage and mistracking especially at the tail end as evidenced by the severe ply separation and edge damage observed along the entire length of one side of the belt.

I doubt increasing the splice length on the 2-stepped pattern would have help because of the dodgy integrity of that suspect longitudinal section I mentioned. Also, as Mr. Mulani has advised against doing the 3-step pattern in view of the attendant problems on the idlers, pulleys and cleaners, I think I would be compelled to advise this client to use fasteners as a temporary measure until they can decide on the change-out.

I would still welcome more opinions, apart from the ones already expressed, especially on the differences in the dynamic stresses between the 2-step and the overlapping pattern (despite the 3-step being a non-starter.)

Best regards.

Barry Chung ■