Screw conveyor HP requirements 1

[rwelk]

I have seen a few forums related to this topic, but I always seem to get ridiculously small HP numbers.

If i have a conveyor 4"OD, 8'LG., i get an approx. volume of 0.7 cuft. I have a material density of 45lb/cuft.

Torque = (0.7 * 45 ) * 2" (moment arm)

Torque = 5.2 lb-ft

my conveyor rotates at 20 rpm

P = 20 * (2 * PI / 60) * 5.2 = 11 lb *ft/s = 0.02HP

This does not seem like a reasonable answer in any sense. I'm also wondering if anyone knows the thrust force this would create. Can I simply take a component of the radial force, using the flight angle?

Any help would be appreciated,

Cheers

 

[ruble3]

look at this site - if you still get the same number then you must be correct- when you get on look under Engineering manuls, then Horsepower- calc's are there for screw conveyors

 

[rwelk]

Ruble3, what site is that? No link showed up in your posting.

 

[smckennz]

Hi rwelk
I cannot understand your calcs (i.e. they do not make sense)
Have a look at any number of design articles on screw conveyors. They will tell you how to calculate.
Then take my advice and double the horsepower requirement on small sizes such as theirs - even if they have already doubled it in their calcs.
The big issue (an the one you have not included) is friction - especially in smaller sizes.
Its a very inexact science. In your case I would not give you an estimate of power without knowing the material, depth of fill and the sizing.
An outfit called Jacmor used to do some good work but you still needed double the HP in smaller sizes.

Cheers

Steve

 

[ruble3]

sorry rwelk- try this;

http://www.conveyoreng.com/engman/DesignStep4.htm

 

[rwelk]

Just to clear up my initial thread to try to keep anyone else from being confused. Keep in mind I am not sure if what i've done is correct. My big problem I believe is finding the force.

Torque = Force * radius
Power = angular velocity * Torque

my material is ash, the density is approx. 45lbs/cuft.


I am looking into every tip I have been given, but would like to continue getting as many as possible.

Thanks to everyone who's helped me out so far.

Cheers

 

[PeterCharles]

The traditional way is first to establish the size and rotational speed of the screw conveyor you need from throughput (te/hr), density (kg/m3) and % filling. The latter is based on experience but figures can be found in assorted materials handling reference books.

The absorbed power of the screw conveyor is then calculated from te/hr, length, rotational speed and assorted factors according to size of the conveyor and type of bearings used. Again, the necessary information can be found in materials handling reference books.

With the power and speed established it is straightforward to establish the torque at the machine shaft.

Remember none of this is an EXACT science. Most data is held by equipment manufacturers who regard it as commercially confidential to themselves. They had to find out the hard way and are not keen to give away their knowledge to competitors.

 

[engaggie]

Go to the CEMA (Conveyor Equipment Manufacturers Association) website and look under publications for CEMA Standard No. 350, Screw Conveyors. It costs $50. It is a good source of info for the vast majority of applications. Otherwise, most screw conveyor companys still have cataloges with most of the same type of info.

It sounds like your material is bottom ash from maybe a wood or coal fired boiler. For the most part is a pretty beign material, other than very abrasive. I have speced and purchased quite a few screw conveyors for a variety of other materials over the years and have not had any failures.

Check out the "materials handling equipment engineering" site in this website.