1. What air pressure is required for the conveyor and what factors determine the volumes of air ?
The pressure and volume of air is dependent on the conveyor length, capacity, belt speed and bulk density of the product.
Less air is required for a lighter conveyed product like Bagasse than would be required in the case of material like manganese, on the same belt.
Basically the air required is low pressure i.e. from a centrifugal fan delivering air at typically 5k/Pa(g).
As far as air volumes are concerned, a 200 m long conveyor transporting 1 500 m/hr of woodchips would typically use an 11 kW motor, which would deliver 0,8 m air/sec.
2. What vertical curves can be negotiated i.e. convex radius and concave radius ?
Both convex and concave radii can be negotiated by the air supported conveyor.
The calculation of vertical curve radii is generally the same as that for conventional conveyors.
3. How is the belt supported on a convex vertical curve to prevent localised wear of the trough ?
Troughing idlers are used at the apex of the convex curve since the air pressure in the plenum chamber isn't sufficient to keep the belt off the trough.
Air is diverted from the end box of the casing leading up to the curve, to the next casing after the curve, to continue the support of the belt.
4. What happens to the air once it has exited the belt / trough ?
The air is virtually at atmospheric pressure and travels towards the discharge-end of the conveyor with the movement of the belt.
The air is exhausted to atmosphere directly or through a filter.
5. What belt speeds can be designed for?
Belt speeds are not restricted by the limitations of carrying idlers and therefore, the air supported conveyor can be designed for belt speeds greater than conventional conveyors.
Installations in South Africa by Aeroconveyors run at 5 m/s.
6. Can the normal range of belts be used or is specialised belting required?
Standard conveyor belting can be used.
BAREBACK belting is preferred since the total enclosure of the belt and product leads to a greater possibility of the ambient temperature over-curing the bottom rubber cover. This leads to the rubber degenerating into a soft and sticky compound which generates a very high friction factor.
7. Surely the belt touches the trough at times, causing wear - especially if material ingresses between the belt and trough ?
At times this can occur due to high spots along the conveyor.
These high spots however are polished in a short space of operating time and the wear is negligible.
Air supported conveyors are known to have belts last 6 years and in some installations, belts are lasting 10 to12 years with a 24 hour per day duty.
8. What about spillage at loading points getting into the trough and clogging the holes or causing building up ?
There is a risk that spillage at the loading station can lead to higher wear rates in the trough. Experience and expertise are needed to ensure that the loading stations are designed to minimise such ingress.
The positive pressure in the plenum chamber prevents the holes in the trough from clogging.
9. How big are the holes in the trough and typically how many holes are required ?
Holes are spaced at intervals which ensure that sufficient overlap of the air supply is provided, to support the belt correctly.
The size of the holes varies depending on the volumes of air needed to support the belt.
Holes are typically provided in a single row along the centre of the trough for the full length of the conveyor.
10. How is the troughed belt trained ?
It is important to load the belt centrally to ensure correct alignment, as is the case with conventional conveyors, as the air-supported conveyor is self-centering.
The tracking on the return belt is exactly the same as for conventional conveyors.
11. Can the conveyor negotiate horizontal curves ?
No. Standard practice would require a break in the continuous box section and a transfer point onto a second conveyor.
12. How long can the conveyor be ?
The longest Aeroconveyors in South Africa are 369 m and 332 m.
Theoretically the conveyor length could be as per conventional conveyors however, practically speaking the length of air supported conveyors must be determined by the site conditions, the route and the application etc.
The shortest recommended conveyor would be around 10 m.
13. How many fans are needed and what power is typically drawn ?
One fan is required for a conveyor length up to approximately 350 m.
Once up to speed, centrifugal fans draw little more than their no-load rating of the motor.
14. What material are used to fabricate the conveyor structure ?
Mild steel, 3CR12 and aluminum, depending where the conveyor is to be installed and the specific requirements of the project.
15. How is belt tension maintained ?
Belt tension is considerably less than for a conventional conveyor.
Short conveyors (up to 60 or 70 m) comprise screw-type tensioners.
Longer conveyors and / or wider conveyors use gravity take-up units.
Some Aeroconveyors measuring 100 m in length and 500mm wide belts use screw take-ups.
16. Can mechanical belt fasteners be used to join the belt ?
Vulcanised splicing should always be used.
In exceptional cases, mechanical fasteners can be employed however, this should be on a breakdown basis and should be replaced by a vulcanised splice as soon as possible to prevent wear of the trough
17. How clean must the air be ?
Generally the air must be clean but conditioned air is not required.
18. How is the trough cleaned out and how often is this necessary ?
Generally there is no need to clean out the trough or plenum chamber.
In some applications however the trough can be washed out and in these cases, a drain plug is fitted to the plenum chamber.
19. What type of products can be conveyed e.g. coal, maize, etc ?
All products conveyed on conventional conveyors can be conveyed on the air-supported conveyors.
20. What limitations are imposed by particle lump size ?
Irregular lump size over 250mm is not ideal as the point load would break the air film and cause the belt to rub on the trough.
If smaller particles can be loaded prior to the lumps, then the large lump can be transported.
21. What is the maximum capacity (tph) that can be conveyed ?
The maximum conveying capacity would be basically the same as conventional conveyors for the different belt widths.
22. What happens if one of the fans trips ?
If the air supply fan trips, the belt bottoms onto the trough and the frictional resistance increases. This results in the conveyors' main drive motor tripping on overload.