The DSI Snake Sandwich High Angle Conveyor can in fact handle bulk materials and convey them at the highest of angles.
A sandwich belt conveyor uses two conveyor belts, face-to-face, to gently but firmly contain the product being carried, hence making steep incline and even vertical-lift runs easily achievable. Snakes are available in widely ranging profiles of C and S-Shape. In any case, a long bottom belt approach is possible to the sandwich entrance, and discharge may be on the high incline or may be after the extension of the carrying belt beyond the mouth of the sandwich.
DSI Snake Sandwich conveyors offer the following advantages:
Unlimited conveying capacity
A system suitable for the most rugged mine applications, yet gentle on sensitive and friable materials.
High availability and low operating and maintenance costs.
Smooth surfaced belts allow continuous belt cleaning by scrapers and plows. This also facilitates intermediate material discharge by belt plows, as appropriate, before and/or beyond the sandwiched part of the Snake profile.
All conventional conveyor hardware insures economy and fast delivery of replacement parts.
Dos Santos-design sandwich belt conveyors have been proven in more than eighty successful conveyor systems installed by his previous employers throughout the world over the past eighteen years. Dos Santos’expertise will continue to advance the state of the art and assure our clients of the finest conveyor systems available today.
I invite you to visit our web site at www.dossantosintl.com for more information on our DSI Snake Sandwich conveyor. It is the most reliable and economical solution to your steep angle and vertical high angle conveyor requirements.
The safe conveying inclination for bulk material ultimately depends upon the stability of the inclined surface of the bulk material. Whereas a fine particulate solid may exist in a wide range of flow conditions, from fluidity to a cohesive mass depending on the degree of dilatation, a coarse product quickly settles to a condition that will sustain a surface repose inclination according to the circumstances of its formation. The inclined elevation of fine products therefore requires special attention to settle the product as much as practical before moving onto the slope.
With coarse products the particle shape and proportion of fines are also important variables and the amount of water present can be a most sensitive parameter, so the stability of an inclined surface may vary according to the weather.
The given repose angle of the material in question will be whilst the mass is resting on a static support, whereas on an inclined conveyor there will be a degree of disturbance by belt flexure and deflection by passing over rollers so, unless a simulation is made of these operating conditions or prior experience of the specific material is available, it would be prudent to allow a very generous safety allowance on the figure of 32 degrees repose angle and 10 degrees would seem to be a reasonable figure for a belt conveyor.
The maximum incline angle for a troughed belt conveyor is neither well known nor is there a desire to know this value. This is a case where the truth will not set you free, it will restrict you. I have on this forum previously recounted the work by Sasol (Synfuel company in South Africa) in this regard.
Sasol considered itself a very conservative company employing 100% redundancy of their conveying paths. Thus two conveying paths were required and used to each destination. In their coal conveying angles they typically used non-conservative inclines of 15 degrees to 17 degrees. At these angles they suffered repeated slide-back of the coal load. In response to this Sasol decided to address this problem. They formed a committee to study the issue and to return a recommendation for the maximum conveying angle. After much study the committee returned their recommendation. For the Sasol coal conveying applications the incline angle should never exceed 12 degrees. Faithfully, for their next project they followed the recommendation keeping the incline conveying angles below the 12 degrees maximum. The costs for this project were significantly higher than for previous such projects with the higher conveying angles. Indeed after only one implementation of the new max angle criteria Sasol returned to using the previous high conveying angles.
Dos Santos International
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How much is the maximum slope angle of belt conveyor for handling of concentrate copper?
Properties of material:
Density ~ 1.8 t/m3
Grain size 0.04 ~ 0.06 mm
Repose angle ~ 32’
Material Moisture < 9 %
The biggest issue with conveying material on an incline is that conveyors tend to be designed with deficient loading systems. The skirt length is generally too short and the skirt width generally too wide.
The skirt length needs to be at least as long as the acceleration length at the loading point, and the skirt width should be around 60% of the belt width. This means that when the material comes out of the skirts, it is travelling at the belt speed and once out of the skirts, the material will surcharge and take up the "correct" profile on the belt. The reason skirt length and width are compromised is to cut costs.
With a correct loading zone, the maximum incline cannot exceed the angle of repose (AOR) of the material. Any steeper, and the material will simply tumble back on itself. The whole problem with AOR is that it is for the specific sample used for testing. The actual AOR can vary considerably, so you need to apply a safety factor. This is further complicated by the rhythmic motion over conveyor idlers. This will disturb the material and cause the AOR to be further reduced.
This is why you can see factors that will range from 0.8 through to 0.5. It all depends on how variable the characteristics of the material can be and the allowable sag. For example material that has a fine grain size will tend to settle more than material that is large simply because less energy is required to initiate any movement. Lower allowable sag will see less settling and so allow for a slightly steeper incline. You also need to consider windage with fine grain size. The material may not roll over itself when static or moving slowly but may be blown back at speed.
Unless you have the facilities to carry out testing, you are best to go with the figures you will get from various published sources.
Of course, there is another overriding consideration and that is the need or requirement for a walkway alongside the conveyor. Believe it or not, but this ends up being a governing factor in many conveyors.
Quote Originally Posted by sganesh View Post
The dynamic angle of surcharge is more valid than the angle of repose,
Originally Posted by designer
How is this measured..................................................?
You mimic the action of skirts. The material is held between two vertical plates and then the plates are removed. The ultimate width and height of the material are measured. You can do this in a rectangular box where the sides can be removed. You place a known volume of material in the box and then remove the sides.
The best approximation is one where the material forms an arc. the crossectional area is known based on the volume and from this you work out the radius and the angle of the material at the edges.
The more sag you allow, the more this surcharge will be destroyed as the material goes over each idler set. On long overland conveyors where sag can be greater, material can almost level out by the time it gets to the discharge end. Where belt edge distance is marginal, I have seen instances where you have spillage off the side of the belt.