Rip Prevention, Detection, Mitigation
Some Comments:
1. Ounce of Prevention - chute design is the greatest single protective device - proper DEM modeling is the key that can register the impact and shear work. One design will stand out among the many as the best for the given material conveyed.
2. Beyond Prevention - Detection: Detect defect via instruments at the loading station from:
a) Sense tearing agent with local micro switches and wiring that trip with motion
b) Tear in the belt with internal belt rip sensors from various sources,
c) Spillage detection from sensors recording light flow under belt loading zone
d) Sensing internal rip from change in belt width vibration signature
3. Mitigation - How to minimize the damage:
a) Repulse the ripping agent by using a special transverse reinforcement breaker fabric of polymer or steel - usually measured by their repulsion force in special factory testing
b) Apply the rip sensor antennas in the belt at the appropriate spacing - risk vs. benefit ■
Annunciation
Annunciation: report on type of rips, tears, punctures which can include surveyor of new and aging belt to compare/monitor degrees of damage over time. ■
Annunciation & Answers
Annunciation: report on type of rips, tears, punctures which can include surveyor of new and aging belt to compare/monitor degrees of damage over time.
There are no standards. Some belt suppliers can offer magnitude of repulsion and likelyhood of rejection after penetration.
You need to know what you are protecting against and design accordingly.
Regarding diameter of rip protection cords, is dependent if the rip protection may also be acting as a impact breaker to keep the rubber between steel cords from separating from the cords. This happens with large rock impacts. Tranverse fabric absorbs the shock. Nylon is better at absorbing impact energy, but it has limitation that steel can overcome. ■
Re: Rip Protection In Steel Cord Belts
Thank you very much Mr.Nordell
Since there are no standards, how to select the best technically offered belt if we receive more than 10 quotations? ( Other than considering the reputation of the suppliers! )
Thanks & Regards, ■
Re: Rip Protection In Steel Cord Belts
Hello Sganesh
Ask yourself why will the belt be ripped and avoid such things. The rip protection then becomes far less necessary.
The belts rip because:
- Liners and their bolts near the belt wear, and instead of being held by at least 2 bolts, they become held by only one. The liner then rotates downwards into the belt, and it will then have a 50% chance of cutting into the belt depending on the positon of the remaining bolt.
- Enclosed chute so that if a long piece of steel comes through, it can get trapped in the chute and cut the belt.. so.. keep the chute open!
- Use of non belt-friendly idler frames
- Not designed for impact per lump to be less than 900 Joules
- Ensure that even if overloaded with lumps, the lumps cannot get trapped
I design my chutes as though they are for use in a scrapyard, and rarely have rips, but even so the last one I had was due to a worn liner rotating down into the belt. More bolts required in future and better liner moitoring.
Cheers
LSL Tekpro ■
Re: Rip Protection In Steel Cord Belts
Dear Experts,
How can I be sure that the chutes are "not designed for impact per lump to be less than 900 Joules"?
Thanks & Regards, ■
Re: Rip Protection In Steel Cord Belts
Hi Sganesh..
To ensure that you don't exceed 900 joules impact you have to calculate the impact velocity of a typical lump hitting the belt. The energy thereof is calculated from E=1/2 x m x V^2.
If it falls directly onto the belt it is m x g x h
To predict the exit velocity, measure the sliding angle of an element of material on a plate of the chute liner material. From that, calculate the value of mu, the coefficient of friction of the material on the chute. You can then calculate the effective force component of gravity acting on an element of material down the chute, less the friction component up the chute.
Knowing the effective force on the element down the chute you can calculate its acceleraion.
From Newton's equation of motion V^2=U^2 + 2fs you can calculate the final speed, and therefore find the energy component vertical to the belt.
The calculations get a bit more complicated if you have a dead box, or a radius in the chute, in which case you also have to include for the effect of centrifugal force which increases the friction component up the chute considerably.
Cheers
LSL Tekpro ■
Re: Rip Protection In Steel Cord Belts
Dear Mr Ganesh,
Have you considered the possibility of employing Impact Bars in lieu of Impact idlers to minimise the risk of belt rip ? By doing away with the gap between idlers in the loading zone, you would be virtually eliminating the possibility of foreign matter like tramp iron etc. from cutting through the belt and then jamming itself between idler gaps to cut the rest of the belt.
As for prevention measures within the belt, two clear options exist -
a) Sensor loop based rip detection, and
b) Rip-trip breaker
The first named involves higher one-time expense but considerably lower replacement costs. With proper maintenance of the electronic controls, this system is considered to be the more effective of the two alternatives.
The second option carries not only a higher product cost (due to the special breaker employed) but provides a electro-mechanical resistance which depends as much on the type of breaker provided as on the reliability & sensitivity of the relay that is intended to switch off the drive upon sustained increased amperage due to resistance offered by the weft members of the breaker. This arrangement is rarely full-proof although the breaker admittedly offers considerable resistance to complete penetration of the belt by the cutting object.
Regards
BoL ■
Re: Rip Protection In Steel Cord Belts
There's a coincidence Bol..
I have just returned to my office from a local coal mine.
At this coal mine they have just thrown out impact pads at the primary tip due to belt damage, and replaced them with spring mounted rubber disc garland idlers.
The list of mines where the impact pads are being thrown out is getting longer and longer.....
Cheers
LSL Tekpro ■
Rip Protection in Steel Cord Belts
Dear Experts,
Rip Protection Cords are there in Steel Cord belts to protect long slitting of conveyors if the belt come into contact of sharp foreign objects.
My doubts :
1. Are all steel cord belts manufactured with rip protection ? Should we specifically mention
to suppliers?
2. Is there any standards present for the rip protection cords? How these cord diameters
and the pitches of these rip protection cords are determined? These cords play vital
role not only in protecting the conveyor, but also in the manufacturing cost of the
conveyor. ( Less Pitches, Higher Diameter , Better Material lead to higher
cost. So to commercially evaluate among the manufacturers there should be some
standards )
Request your answers please!
Thanks and regards, ■