My first thoughts are that, if you have to ask, you should'nt be doing it but if you want to have a go - see 'Guide to the design, specification and application of screw feeders', published by The British Materials Handling Board. ■

Sometimes these things just have to be said... :-)) ■

You could also buy the screw conveyor publications from here :

http://www.cemanet.org/publications/index.html

But most of the real knowledge is NOT in published books, but resides within companies who MAKE screw conveyors and feeders. This is their commercial lifeblood so is unlikely to be issued to competitors. At some point you will have to make your own way in the world as others have had to before you. ■

The book on screw feeders is only available in hard copy at £ 50 plus £ 8 o/sea post and packing. I can arrange for a copy to be sent by the British Materials Handling Board if you forward your full postal address to lynflow@btinternet.com.

The batch discharge accuracy of a screw feeder is determinate on many factors of the screw geometry, speed and nature of the bulk material. In the first instance the screw should be delivering material at a consistent rate and in a consistant condition. This is mainly dependent on the design of the inlet section of the feeder, where mass flow is a great asset for any products that tend to vary in density. In general, a two speed discharge is desirable for accurate batch dispensation, with the bulk of the quantity, say 90%, being fed in roughly half the total time and the remaining period dispensing at a lower rate to give a more precise teminal quantity.

The main vaiables at the discharge point relate to the cyclic form of the screw, which tends to deliver in surges, according to the rotation of the screw, and the state of the bulk material. If the bulk material is cohesive there will be a tendency for the material to hold together and fall off in erratic clumps. On the other hand the repose surface of a free flowing material will avalanche at low feed rates and inhibit a sharp cut-off unless a quick-acting valve is fitted. The techniques available to overcome these phenomena are therefore different and a close knowledge of the design and material are required to secure optimum results.

The degree af attention merited ultimately relates to the importance of the results required. Short cuts are at the expense of predictability. ■

Really no point in spending that kind of money on a book. Any reputable conveyor company will have everything you need in their catalog, complete design criteria. You just need to study the data and go from there.

I hold patents on several screw feeders, if I can help, let me know.

Ted Key ■

Found this -

http://v3.espacenet.com/results?IA=T...ARCH&=&=&=&=&= ■