The maximum angle at the loading point is the same maximum angle that the product can be elevated without rolling back. The most critical element of any loading pont is the design of the feed chute that will feed onto a conveyor at the specified angle. ■

Hi there..

As Gary has indicated, a lot depends on the chute design. The idea is to get the flow of material reaching the belt to be at the same velocity as the belt itself.

However, beware steep loading angles, especially for material with a shape that can roll.

When starting to feed or at the end of material supply, the burden depth is not sufficient to lock the material, and you often get roll-back, which causes spillage.

(See also previous thread on this topic)

Cheers

LSL Tekpro ■

The lower the loading angle the better. Lower angles allow for a better transition of the material from the trajectory above to the loading at the belt. As previously stated the transfer chute should deliver the material to the loaded belt as closely as possible to the speed and direction of that belt. Too high of a loading angle makes hat more difficult as the chute flow angle will have a more abrupt angle change with the loaded belt.

Our sandwich belt high angle conveyors can elevate materials continuously at angle to 90 degrees (vertical). We load onto the lower belt as a conventional conveyor before it than joins the top belt to form the sandwich. For favorable loading we typically limit the angle at bottom belt loading to 10 degrees maximum.

Joe Dos Santos ■

We offer a granular flow code "ROCKY" where you can solve the angle by configuring the flow rate and rock density, rock shape, belt speed, chute geometry and wall liner properties, skirtboard geometry and wall liner propertes, Idler trough geometry and material properties and moisture. Within each of 11 or more variables to the above, there are multiple variants and techniques to enhance the outcome.

Note: there are too many dimensional and mineral properties to give a simple answer. Just look at the website, its subwindows and simulations.

http://www.conveyor-dynamics.com/rocky.htm ■

Originally Posted by nordell

We offer a granular flow code "ROCKY" ............................................ there are multiple variants and techniques to enhance the outcome

http://www.conveyor-dynamics.com/rocky.htm

Larry, after the analysis can you offer a numerical safety factor against slide-back?

Joe Dos Santos ■

Joe,

Depends on how you define safety factor and what design parameters can be controlled. ■

Originally Posted by nordell

Joe,

Depends on how you define safety factor .......

Larry, that is a good question. If this were a static situation it would be the ratio (coefficient of friction of material on belt surface)/ (tangent of the slope angle). For the moving material and belt the ratio is similar but the numerator would be some dynamic coefficient of friction. Our inability to quantify this hints at the problem. Economic considerations always tend to push conventional conveying angles to the edge of slide back failure.

Joe Dos Santos ■

There was a dreaded 22 degree loading direction mentioned in belt manufacturers' literature until recently (2009) which maximisd belt wear. Shouldn't this be considered towards optimising performance: although it is not mentioned in the literature nowadays? i.e.is 22 deg still relevant today? ■

Originally Posted by louispanjang

There was a dreaded 22 degree loading direction mentioned in belt manufacturers' literature until recently (2009) which maximisd belt wear. Shouldn't this be considered towards optimising performance: although it is not mentioned in the literature nowadays? i.e.is 22 deg still relevant today?

Indeed, even for angles where catastrophic slide-back does not occur there is the issue of material movement that scuffs the belt surface, obviously much worse at the loading point. The distance, from loading, over which material settles is increased with increased loading angle. The fact is that there is no scientific basis for the recommended incline angles at open troughed belt conveyors, by CEMA or any other standard. The only instance that I know of, where a scientific (statistical) approach was taken to determine the correct incline angle at a specific site with a performance history, was at Sasol in South Africa. There they came up with 12 degrees as their maximum recommended angle for any coal handling conveyor. As I have mentioned in previous posts, after they executed one new project according to the new criteria the costs were so increased that they abandoned that criteria and went back to the cheaper set-of-the-pants higher incline criteria.

Joe Dos Santos ■

Joe,

I disagree with your claim there is not scientific solution to loading station criteria. ROCKY and similar codes have shown proper chute designs are possible that are derived from DEM analysis which can adminster proper granular particle contact properties and shapes.

Maybe you should try a proper code and enjoy the more accurate solution to chute geometry and stable loading at the appropriate incline. In 1994, we redesigned the 6600 t/h Palabora chute that stopped surge and roll-back spillage, centralized the primary crushed rock onto the belt, stopped excessive belt wear, minimized noise and stopped excessive impact idler replacement.

Then, I am sure you already know this well published Palabora story and the subsequent designers who visited and copied this approach. So, why the claim that there is no scientific solution? I can offer you a 2 week trial to see for yourself. Visit our website:

http://www.conveyor-dynamics.com/rocky.htm

We have many other success stories of chute designs at all tonnages (24,000 t/h) and speeds (8 m/s), with wet (sticky clay) and dry materials, with many shapes and loading configurations. ■

Originally Posted by nordell

Joe,

I disagree with your claim there is not scientific solution to loading station criteria ................

Larry,

I must admit that I have not dabbled in the the bulk flow simulations. My question/statement about safety, scientific determination or quantifying of a safety factor is more general, not only at the loading point but the incline angle as well. When you perform such a transfer analysis or determine the slope angle for a troughed belt conveyor we can, by experiment or simulation determine when proper flow and transfer occurs and when proper flow and transfer does not occur. We can determine an angle where material does not slide back and an angle where material slides back. How close do we push the former to the latter? How do we quantify the margin of safety?

Joe Dos Santos ■

Originally Posted by ppquintal

What is the maximum recommended angle for a belt conveyor at loading point?

See attached file.

Regards

The angle depends on the product characteristics, the transfer chute design, the belt speed etc.. For aerated cement a negative angle might be recommendable. But, with a proper transfer chute design and a slow moving belt a horizontal transfer might work. For other material one can go to 13 deg.

Holger Lieberwirth ■

CEMA Standard 550 lists maximum incline limits that conventional trough conveyors can safely convey various bulk materials. These maximum angles generally range from 10-30 degrees depending on the bulk material. Recent developments in steep angle conveying increase this incline angle thereby enhancing the flexible path that standard belt conveyors can now negotiate. ■

The shape of the trough also is of significant importance in evaluating the potential conveyor transport incline angle.

Pipe conveyors and like shapes glove the material and generate an inter-particle consolidation pressure within the material stream and higher contact stress between product and belt. Higher product consolidation and belt contact pressure or stress allow greater incline angles. The transition from loading point to pipe shape equivalent must also be considered.

Mr. Dos Santos has proven this with the various sandwich conveyor concepts.

Now simulation codes such as ROCKY can further demonstrate all of theses behaviors from chute loading, skirt consolidation, and transition to final cross-sectional form. ■