Dear Mr. K. L. Pai

I can give definite advice on the elevating means and some suggestions on feeding and transfer. We are experts on the former.

Bucket elevator is the wrong means for elevating sticky material because it carries back much of that material.

A DSI Snake-Sandwich belt conveyor can elevate the sticky material continuously vertically using smooth surfaced rubber belts. These can be scraped clean with ordinary belt scrapers. Visit our web site to learn more about DSI Snakes. By association we also offer a completely enclosed version especially designed to elevate sticky material is tight quarters.

At the feeding side you may wish to look at feeding with a belt feeder or a screw type feeder depending on how truly stickky your material is.

For extremely sticky material the chute slopes must be extremely steep with any positive slopes being offset by negative slopes at the adjacent walls.

I hope this is of some help.

Our best wishes in your success.

Joseph A. Dos Santos. PE ■

Two key features of a reliable feed system for sticky materials are the design of the feed hopper and providing matching characteristics with an extracting device.

The first essential for this duty is to establish a reliable, controlled feed from the shovel loaders. The size of the bucket dictates the geometry of the inlet of the receiving hopper and its height from floor level. The batch volume in a bucket has to be accommodated, the wall angle steep enough to clear of product and the hopper outlet dimensions must be greater than the critical arching size for the bulk material.

Ultra High Molecular density polyethelene is usuall good for resisting the adherenc of damp products due to its hydrophobic nature. Wall friction tests should be conducted to determine the angle of surface inclination neccessary to secure slip and highlight the adhesive limit of the product on the surface. This will allow the wall angle to be determined for a given geometry of construction.

A steep wall, Vee form hopper with slightly diverging end walls to a well designed screw feeder, is probably the best form of equipment for this duty, as it allows an extended face to be presented to the loading shovel and the material extracted progressively from the outlet slot. It would be good practice to fit a dump-breaking insert across the length of the hopper inlet, to prevent high compacting loads on the hopper contents during filling.

Establishing the width of opening required to guarantee flow is more tricky. The classical method is a Jenike shear test proceedure, which demands specialist attention for conducting the procedure and interpreting the results. A vertical shear test will provide a good guide and, in combination with experience and prospects of retrofit options, can give quick and ecconomical results. See www.ajax.co.uk

Standard forms of screw feeders tend to clog with sticky products. Ordinary ribbon screws are better, but a form specially designed to resist clogging has been developed at Ajax. This is described in the book 'Guide to the design, selection and application of screw feeders', published by Professional Engineering Publications for the I.Mech.E. in UK. It is also essential to generate flow over the total area of the feed hopper outlet. This means varying the geometry of the screw along the length of the hopper outlet slot. In the case of a shovel loaded hopper, this is likely to be at least two meters long. The screw would need to be at least about 300mm diameter to provide this variable geometry. This would run slow to deliver 3 tonnes per hour, but the output is virtually directly proportional to speed at low revs, so speed is no problem but a variable speed is useful for delivery rate adjustments. The fertiliser also tend to cake, so the screw tips will require hard weld deposit and chamfering to avoid high torque loading and wear.

With good feed control the bucket elevator will have a much better chance to work properly. Close attention to detail on the transfer system from the feeder to the elevator is necessary and consideration should be given to the finish of the buckets to prevent material sticking in the buckets. If the layout allows, a cantilever screw feeder giving direct injection to the face of the bucket elevator will overcome any infeed problems. Given these, it should be practical to utilise the existing elevator.

Lyn Bates ■

In my opinion, due to the low volume of the material to be elevated, it is less complex and more effective to elevate a hopper and discharge it that build any conveyor system.

You need two or three trips of the hopper. The loads are not large, the speed is relatively low and a cable elevator system would be relatively easy to design.

Just my two cents...

Antonio Reis

www.vitrom.com ■

Dear Mr. K L Pai,

Please inform type of elevator (whether centrifugal, continuous or positive discharge), its speed, bucket type, etc.

If elevator discharge is not adequate, then one solution could be to increase speed (provided feed is not affected beyond limit). The speed should create adequate " G " effect to seperate material from the surface. For feeding purpose, how about the use of high frequency vibrating feeder with stainless steel or UHMW liner? Solution is subjective and depends upon acceptable quantum of change, severity of problem, available space etc.

Please note that the equipment you choose should specifically be easy to open, inspect and clean at any time.

Regards,

I G Mulani

Author - Book 'Engineering Science and Application Design for Belt Conveyors'

parimul@pn2.vsnl.net.in ■