Use hydraulic motor for very slow rotation, or is there a better way? 2

[minfarm]

Hello,

I have a bin with a unload system in that I am trying to improve. This system has two screw conveyers that go out from the center of the bin. (see photo for more detail) While these screw conveyers are spinning, I would like to power rotate them around the bin.

I have calculated that I will need approximately 400 ft-lb's of torque. The biggest problem that I see is trying to get the rotation slow enough. I only need it to rotate about once every three hours. This would put the horsepower requirements as fractional.

Would it work to use a hydraulic motor, under sufficient pressure to apply the 400 ft-lb's, or would that cause problems because it would be turning so slow? Also, if I did drive it hydraulically some way, what type of pump setup would I need for the very low flow rate?

Any help will be greatly appreciated!

 

[zdas04]

Speeds like that are really difficult to achieve with a direct drive of any sort. Your load requirements are low enough to belt drive, and you could likely do it in a two or three stage belt system. That would let you rotate your motor at a slow speed, but not so slow that you are worried about it stalling and surging. 0.006 rpm would be a really tough problem with direct drive, but with sheaves it is a cake walk.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[hydroman247]

Some sort of reduction gearing would make this a fairly simple job. You could then use a small electric motor which would probably be easier and cheaper than a hydraulic system.

 

[minfarm]

Thank you for the suggestions.

Something that I did not mention that makes this more difficult is that all of the drive components will be under about 15' of grain. Attached is a better picture of what it looks like.

I believe installing a belt drive reduction would be nearly impossible. Grain would need to be kept out of the belts and pulleys and also the large size would carry the burden of all the grain on top of it that is displaced.

I have done a little checking into driving it with an electric motor and gear reduction but I was not able to find a gear reducer that would be slow enough and be able to handle the amount of torque that I need. Would any of you be able to steer me in right direction of what to look for? The largest reduction gear reducer that I could find was a 900:1 but we are still at almost 2 RPM which is a long way from .006 RPM. That one also could not handle anywhere near the torque that I need.

Thanks again for the help!

 

[zdas04]

Any way to run a drive rod out of the space (either towards a crawl space or towards a roof)? That would let you get the drive system out of the mess and explosive atmosphere. If you can go up, then (using pulleys or chains) the bull wheel can be any size you need. With gear drive you are limited to the specific ratios you can purchase, but with belts/chains you are only limited by your imagination. In Oil & Gas we regularly drive downhole pumps with drive belts that are driving many times the torque you are talking about here, so I don't think that (with sheaves) you need to feel limited by torque limitations.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[minfarm]

That is a very good idea. Yes, I believe that I could go horizontally out the side of the bin. I will think about that a bit.

Thank you!

 

[zdas04]

Horizontally requires a cellar for the bull wheel. It can be done, but the logistics get messy if the wheel ends up 10-15 ft diameter.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Compositepro]

What is wrong with the way it works now? Obviously these augers were designed to work themselves around the bin. Trying to rotate these around from the center will not work under 15 ft of corn. The augers appear to have drive wheels at their tips and centers. These wheels would mostly be slipping but should provide some drive to move around the bin. Perhaps you should contact the manufacturer to find out what to fix or adjust.

 

[berkshire]

That type of flat bottom bin discharger will self feed, until the grain gets to half the height of the diameter, without moving the screws around the bin.
Are you concerned that the screws will move too fast at the bottom of the discharge ?
B.E.

You are judged not by what you know, but by what you can do.

 

[minfarm]

When we installed this bin unload system about fifteen years ago, it was installed on a trial type basis for our application. We have fought with it ever since. The augers were designed to propel themselves around the bin, not by the spacing wheels at the center and end but by the biting action of the auger flight into the grain (so I was told by a rep. who works for the company that manufactures the augers). In our experience the augers will rotate around the bin for several days on their own but then as fines build up underneath them (this is my hypothesis) the drag becomes to great for the augers to overcome and they stop rotating around the bin. At this point we start drawing grain from the top of the bin instead of from the bottom. We then have to unload the bin and clean the fines out, then we start all over again.

I have spoken with a representative of the company who sold them to us and essential he told me this system was obsolete and we should scrap it. We do not want to scrap it, we just want it to work all the time. That is why I am pursing some type of positive drive system for the rotation.

Compositepro, may I ask why you say it will not work to drive it from the center under 15' of grain? After the bin has been cleaned out we have had it work now with up to 20' of grain on the top.

berkshire, I have never heard the half height of the diameter rule. On this unload system I haven't noticed much of a difference with how full or empty the bin, it seems to be more a function of time as to when they quit rotating. Once they quit rotating around, the grain level has to get down so the augers are exposed before they begin to rotate again. It does stand to reason that the more grain there is on top of the augers the more pressure that there is to prevent their rotation.

Thanks for all of your help!

 

[MikeHalloran]

I'm thinking that any attempt to yaw the augers by driving the center assembly/gearbox will add bending stress for which the augers may not have been designed, and it's fully reversed stress too, which is worse.

Could you put radial pins on the spacing wheels and corresponding pockets in the bin floor, turning the augers into a crude crownwheel drive? Or conversely, circles of pins on the floor and pockets in the wheels?

If you think that would yaw the augers too fast, you could put planetary reducers (like modern bus wheel hubs) inside the wheels, at considerable cost in complexity.





Mike Halloran
Pembroke Pines, FL, USA

 

[minfarm]

Mike, a major hurdle with putting any type of positive drive on the outside of the auger is the bin floor. It is a raised steel perforated floor. The other major issue you already mentioned is that the augers are turning way to fast. They would destroy most drive grippers or whatever you put out there in short order. Trying to reduce the speed with planetary reducers would be complex as you mentioned and this planetary would also need to be able to push through 15' or so of grain depth. This would also add a considerable amount of load to the existing drive and gearing.

I believe you are correct in saying that driving the center gearbox will add stress to the augers, but I do not think it will be substantial enough to cause damage. Anyway, I am will to take that risk by trying it. Most of the time this system works the way it is, it seems it just needs a little help the rest of the time.

Thanks!

 

[berkshire]

Minfarm,
I used to work as a designer in the feed milling industry, that half height rule was based on the angle of repose of the grain, which for corn was usually somewhere around 35*. We had tried and discarded that rotating auger design in the 1960s, and came to the conclusion that for a flat bottomed bin, a full live bottom was the only way to go. We also used to recommend to customers that a conical bottom worked far better if they had the vertical space to install them . Your bin looks like a low cost bin of the type sold to farmers who stored for long periods and only drew from the bins one or twice a year.
B.E.

You are judged not by what you know, but by what you can do.

 

[minfarm]

You are correct in assuming this bin was initially built for long term storage. We installed this unload system in it later to use for continuous cooling of grain out of a grain dryer. When the unload is working properly it is a first in first out type system whereas a typical farm bin unloads last in first out as does a typical conical or hopper bottom bin.

What is a full live bottom type unload?

 

[berkshire]

They look like this, conical bottom bins filled from the top are also first in first out.
see attachment.
B.E.

You are judged not by what you know, but by what you can do.

 

[ScottyUK]

For very high ratio reduction drives, try the Cyclodrive by Sumitomo. Not certain they can seal them to food grade standards but no harm asking.

 

[lukin1977]

a quick idea.
what about a pinion at the end of the conveyor shaft and a rack around the botton of the bin?
coupling between shaft and pinion could be done with some sort of friction coupling so the pinion wont spin fast

 

[lukin1977]

another option
Spin the mechanism from center as you plan but instead of doing it at a constant very low speed, do it a little faster but in time intervals. You can use a torque limiter electric clutch if you dont want to start/stop the electric motor
Anyhow, I think an hydraulic motor is not the best option here

 

[minfarm]

Sorry for the slow response. I was out of town on a family get-a-way.

Thanks for the link, berkshire. I don't believe the full live bottom type of unload would be practical in my application.

ScottyUK, I have the Sumitomo representative's contact information for my area and will get in touch with him. They sound like the exact drive that I need.

lukin1977, see posts 11 and 12 about driving around the outside perimeter. You do have a good idea on starting and stopping the drive to get my low speed. I will see if one of the Sumitomo drives will get me slow enough. If not I may, look at starting and stopping to reduce the speed enough.

Thanks to you all!

 

[hydtools]

A late suggestion, a rotary actuator by Helac Corporation.

http://www.helac.com/products-services/rotary-actuators/

They are limited to 360 degree rotation or less. Perhaps run back and forth 0 to 180 to 0.

Ted