Yes you could use a hanger bearing in the middle of the shaft but it is not absolutely necessary. You can run a continuous pipe if you like but I would recommend going with a heavy wall pipe and a larger shaft than what would be called for on a screw with a hanger. The other disadvantage is that there will be more wear as the flight will rub on the trough.

The hanger type is usually determined by the product being conveyed.

Download the PDF file from Martin Sprockets as per link below. Unfortunately for you it is not in metric. But it will give you all of the design procedures that you need to follow.

http://www.martinsprocket.com/2001/SecHa.pdf#H5

Good Luck

Gary Blenkhorn ■

The duty described is quite practical, but ripe for causing problems and the task of designing amd making such an item is not advised to be undertaken by non-specialists. Apart from the commercial fact that the skill and experience of suppliers is a major feature of the sale value on such individually designed detail, there are many details of both design and fabrication that will determine the suitability of the equipment and it would be imprudent to pass on guidelines that would imply that the task is straightforward. Suffice to say that an intermediate bearing would be a perennial maintenance nuicance and such aspects as auger deflection, shaft straightness, potential vibration and 'epicyclic rolling', 'run-back' at 37 degrees inclination, bottom seals and bearings and feed hopper and inlet chute design for flow reliability must be considered. My book, 'Guide to the Design, Selection and Application of Screw Feeders', available from The British Materials Handling Board, outlines many of the factors of screw equipment relating to elevators. It is unlikely that an equipment manufacturer would go further with supplying free design information. Screw conveyors are relatively simple handling devices. Screw feeders apparantly so, but there are a host of features where a specialists input can be invaluable but generally, screw elevators are strictly for the experts. ■

I would recommend that the user be very cautious about followed STU’s well-meaning advice. The notion that the screw will transfer at 95% of its swept capacity would be quite optimistic if the screw axis were horizontal, even with flights of 1/3 pitch, but is out of the question at with the screw axis inclined of 37 degrees. Also, the full pitch section presents a maximum flight face inclination of 45 degrees to the horizontal at the flight tips and 41 degrees at the flight root. Taking account of the wall friction value of STTP dust on mild steel, the spill back over the centre tube and through the casing clearance would mean that the conveyor was flooded over the full length and would not clear at the end of the run. 5 HP at 20 rpm would certainly provide plenty of torque to keep the screw happily turning round, and the material with it, but hardly be adequate to handle the capacity required with the given geometry.

This case is a good example of separating easy applications from more tricky ones that ensnares those who can’t tell the difference. I reiterate my advice, to seek export advice on applications that are not straightforward as the cost of being wrong can far outweigh the apparent economy of using standard kit. ■