Tubular Belt Conveyor

[jakegordonII]

We are operating a tubular belt conveyor about 400 meters lenght between feed and discharge end. Three weeks ago, we changed the tube (belt). Much problems the first week with the tube turning radially and tripping the sensors. After a break-in preiod the belt was put on line and ran fine. Now, two weeks later we have similar failure which shuts down the belt and entire plant. After manual twisting we can resume normal operations.

We do not understand the basic cause.

any ideas.??

 

[PeterCharles]

Did you buy the replacement belt from the supplier of the tube (normally referred to as pipe) belt conveyor??

 

[jakegordonII]

We bought it from the belt supplier. Also, since my initial thread we have had a root cause analysis session with both the belt supplier and the conveyor supplier. During this review, it was commented that a certain "run in" time was normal.

 

[Ross0684]

Firstly, let me say that I have had no experience with tubular belts, but some of the paramaters that affect flat belts "may" apply.
Belt tension is always a critical consideration in that it allows the crowning on head and tail pulleys to have the desired effect i.e. applying variable tension across the width of the belt (edges even tension, higher tension in centre)which makes the belt "track" hopefully to the centre of the pulleys.
I am not sure whether this applies in your case.

Another phenomena I have seen is that wide belts being cut from a wide slab of belt(say 1200 mm from a 1500 mm slab), with one edge of the belt being the original side of the slab, but the other edge being towards the middle of the original slab, results in a variable pre-tension of the belt, to the extent that if the belt is laid out flat on the floor there is a linear curvature in the belt- there is then no chance of tracking the belt without applying un-realistic tensions to the belt which in turn creates problems with over loading of other components plus increasing the drive motor requirements(hope all that made sense!).
Cutting the same belt from the same slab, but cutting centrally about the centre line of the slab resulted in near perfect tracking performance.
Hope this may be of help.
Ross

 

[jakegordonII]

Thanks Ross, and following some more discussions from the RCA session we may have closure. In the interest of win-win I will share what we learned. It is dissapointing that this scenario and solution where not discussed prior to job planning and execution.

The tubular belt is flat at both ends (feeding and discharging) and is rolled into the tube the remaining length of the conveyor which can be hundreds of meters long.

Best way to explain is to take a sheet of A4 paper and roll it into a tube with a 1 cm overlap. Now, as this tube travels the length and is guided by sets of six rollers equally spaced around the circumfrance with varying distance between the sets of rollers. Overall, there are hundreds of sets of these six rollers.

Pardon the non-technical analagy, but this works best to explain.....

Between the sets of rollers, the belt wants to "open up" kind of like when you watch a national geographic film about a snake eating something.

As the belt tries to "open up" you can compare this to the rolled sheet of A4 paper and you will note the sliding action between the underside of the overlap portion against the outside of the overlapped portion.

On a new belt this natural sliding may not be sufficient due to extra coeffecient of friction due to new belt.

The inability of the belt to slide then transfers into an overall turning or rotation force which can lead to the entire belt rolling clockwise or counterclockwise (I am not sure which way) which is what we were seeing.

During the breakin period it was suggested to add talc powder to act as kind of a lubricant to help let the belt slide between the sets of rollers.

When we added talc to the belt we say an immediate reduction in the amperage loading which validates the theory as well as appears to have helped us to run through the break in period.

thanks for your help and best of luck.

 

[Ross0684]

Good news for once!
Yes talc has always been a good stand-by to reduce friction as you have discovered-especially on flat belt conveyors where there can be an initial high friction surface on the top of the conveyor bed( mill scale-paint-surface rust etc).

In addition, most belts have different friction characteristics between the top surface(product side) and bottom surface, for obvious reasons!

Also, one can get caught out with new belts as in recent times there have been big advances in technology to achieve higher top surface chacteristics which is not visually apparent.


And again, as it seems you may have just been through, a conveyor can run fine for years, you make a seemingly simple change and all hell breaks loose!!

Many thanks in advising what steps were taken to get a result-we all can learn from other peoples heartaches

Ross