Conveyor material backflushing

[turnyourbassdown]

Hello,
I was recently given a project to assess what needs to be done about a raw material (limestone and gypsum) conveyor "backflushing" (12 degree incline). By backflushing I mean the following: material rides too high on the belt and it moves backwards and causes spillage off to the sides. It is not possible to reduce the angle of incline.

Belt speed estimate: 685 feet / minute (3.5 m/s, 7.8 mph)
material size: 1-3" diameter
belt width: 48"

I am not sure how to calculate the maximum allowable speed of conveyor belts, I assume it varies with material type and density. If the belt speed is increased, material depth is decreased while tons/hour stays the same.

Does anyone have any other suggestions on how to prevent the material from falling back down the incline? Since we can't reduce the angle of the conveyor, and the current chain drive system is already problematic at current RPM, I am searching for alternatives.

Also, if anyone knows how to calculate conveyor volumetric utilization %, that would be useful.

Your help is greatly appreciated.

L

 

[tc002]

Firstly, you might try adding side skirting to the top to reduce side overflow and secondly you might try adding cross ribs or flights to form pockets. If you do add flights you'll have to modify the discharge cleaner into a beater and you'll have to increase the drive mechanism horsepower.
As far as capacity is concerned the web is full of conveyor design information, but to make it easier just contact a conveyor manufacturer and more than likely he'll do all the calcullations for you.

 

[PBroad]

There is an association of conveyor equipment manufacturers association that sets industry standards> I suggest that you contact them.

Is it possible for you to crush finer or use a ribbed belt? I normally use conveyors for crushed rock upto 20 degree with no "roll back". If you have side spillage I guess the belt is packed. Can you go to a deeper trough angle 9say 35deg rather than 20, or install side skirting?

Speeding the belt up should help. This will compensate for roll back and move the ore ahead before it moves back more than one idler spacing?

CEMA home page is at

http://www.cemanet.org/

 

[FOETS]

Turnyourbassdown
firstly give the designer a good slap as these are tough to fix once built; without starting again.

Skirting is an option but if you already have a problem with the drive its also going to add more load.
Most options will add more strain to your drive so get that sorted first.

You can look at the idler spacing. ie. putting in more will smooth out the ride and cause less disturbance to your material - ie. keep it sitting on the belt without the wavy motion. Once again more load.
Cheers

 

[macmil]

The actual way the material is spilling needs to be Identifed. If the convetor belt is sagging between rollers, deflecting and allow material to fall off the sides of the belt, then consider adding troughing idlers in between the existing idlers in the spill area.; as mentioned above perhaps go to 35° idlers if they are currently 20°. One possibility is that someone 'chintzes' on the belt and it's too flexible for the load.

 

[polleke]

Hello Turnyourbassdown,

we have belts with a 17 degree incline, running at 4.5 m/sec
beltwidth of 1800mm transporting coal, ironore and olivinesand. No problems with backflushing. We have no sideskirts.
Troughangle is 40 degree, idlerspacing 1000mm.
As mentioned before: keep the belt on the right tension, no sagging. Only with heavy rainfall backflush with coal may occur. This is simply solved by mounting beltcoverplating.
What type of belt do you use?
We have Trellex/scholtzflexcord st1600 10+5 and Contitech steelcord belts. No special surface finish.