A single or double srew feeder can be calculated with our free of charge calculation program.

To avoid to much wear you should take a horizontal speed of the product of no more than 0.6 m/s or less, depending on the product properties.

Send an e-mail to sales@jh.n and we will give you the details were to download this program.

You can also calculate it directly on our website www.jh.nl (section bulk conveyors - calculation program)

kind regards,

Jur Lommerts

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Jansen & Heuning Bulk Handling Systems

www.jh.nl ■

My company is working on its own feeder using polyethylene screws.

My screw feeder team might by able to help with feed rates.

Contact me through my email address and I might be able to send something to you. ■

More information about the supply hopper and purpose of the equipment would be needed to advise on design and why a twin screw is selected in the first instance. (Usually this is to provide a large extraction channel to avoid arching, but they are sometimes specified to provide a high discharge capacity, counter 'air retarded' flow, save hopper headroom, provide a more even discharge, and various other reasons). My book - 'Guide to the Design, Selection and Application of Screw Feeders' may give some useful guidelines. Particularly important is the configuration of the screw geometry in the exposed section of the hopper according to the flow regime that it is required to support by its extraction profile. I would only emphasise at this stage that feeders are totally different machines to screw conveyors, therefore conveyor calculations are not an adequate basis to design screw feeders. Optimisation of their design requires consideration of the hopper, with its associated supply and subsequent transit, as an intigrated system. That is the domain of specialists because there are too many factors to take into account to disperse unqualified generic information. ■

The answer is not that simple, but here are some ideas.

The fill factor of the screw is going to be less than 50% of its diamter.

The feedrate is going to depend on a number of factors.

The bulk density of the material (if you are using weight as a performance measure)

The size of the material (large size means lower weight)

The RPM of the screw

The diameter of the screw

The pitch (distance between flights)

The degree to which the screw is inclined (elevated)

If you know the area of the diameter of the pipe than divide it by two to get the area then multiply the area by the pitch length to determine the volume of material conveyed per (1) revolution. Then multiply the volume of material being conveyed by the number of revolutions.

I am assuming that the screw is level with the ground. Any elevations to the screw would lower the amount of material between the flights because some of it would might fall back into the next flight.

IF the pitch of the screw is 100 mm and the diamter is 100mm

than we could calcualte the area so that:

(100 x 100 x .7854)/2 = 3927 square mm

then we calculate the volume of on flight (this will not provide an accurate number because it does not take the angle of the flight into account, but does give an approximation of performance).

3927 x 100 (pitch) = 392,700 cubic millimeters per revolution

392,700 X 10 (rpm) = 3,927,000 cubic millimeters per minute

Bulk density

volume x (weight per individual cubic measure) = kg/minute

multiply by 60 to get hourly

The company that you are purchasing the screw feeder from should know those numbers if you are buying new. Knowledge is what you a buying in addition to the feeder. If they don't know those numbers than find another screw feeder company to buy from. They obviously don't understand the technology they sell.

If you are bought a used screw feeder you might have given up knowledge to save money, but you end up spending time on this to learn it that could have been spent on more profitable ventures for your company and it might have ended up costing you just as much.

Good luck. I hope my answer has provide you with many new directions in thought for you on future purchases. ■

If you are serious about wanting to design a screw feeder I would suggest that the first step is to decide on the flow regime that the feeder is to generate in the hopper. see - 'Educational Resources for Particulate Technology Vol 1, No. 1,Art 3 (1999 Jan)'. Then establish the critical arching size that the hopper outlet has to exceed - See 'storage and flow of solids. Bul 123. Univ. of Utah. 1964. Then, measure the contact friction of the bulk solid on material as the flight construction to establish the helical efficiency of the screw. Balance your findings with the site constraints and demands for capacity with the hopper form selected to finalise the orifice size and shape to be served. This will indicate the screw size and geometric form for the extraction pattern required as in 'Guide to the design, selection and application of screw feeders', Bates.L. British Materials Handling Board, 2000. Measure the bulk material shear strength and determine the overpressure acting on the orifice to find the torque needed to turn the screw from time consoldiated conditions, as per 'Bulk solids, storage, flow and handling', Arnold, et al, TUNRA. 1982, and, according to the screw speed necessary to deliver the output, this will fix the power needed for the infeed portion of the screws. The remaining power can be roughly calculated as a conveying screw under virtual full cross setional loading from CEMA 350. Check that the delivery pattern is suitable for the receiving process. If you are with me so far, the rest is fairly standard mechanical design, provided the material is not cohesive to stick in the flight corners or dilated to flush through the hopper, etc for the various operating hazards common with bulk materials. Good luck. ■

Done properly, (that's actually making and testing a feeder as well as the paper exercise), I would have thought that there's enough for three PhD's here. ■

The diameter of the screw will also determine your power needs. A larger diameter screw will be pushing more material and have a higher rotational weight than a screw have of its size.

Did tell us what the diameter is? ■

In simple language, the output of two screws in parallel will be roughly double, in volumetric terms, the output of one that is of identical construction. However, the total power will be more than double because the wider outlet offers more over-pressure from the hopper contents. Precisely how much more, and how this will effect the density of the material being discharged, is a much more complicated situation and cannot be assessed without a great deal more infomation on the lines described earlier. A crude, practical solution may be to allow 50% more power per screw, but that is a suck-it-and-see solution that I personally would not adopt if it were an important application. ■