A Different Twist on the Archimedes' Screw

I think friction between the cylinder and the product has only a minimal contribution to why this works. I believe the rotating scoops buried in the product at the bottom are the dominant cause of actually pushing the product up.

Proof of my supposition would be found by spinning just that scoop while keeping the cylinder stationery.

I think you're right that the scoop effect is a big part of it. The surprise (to the OP and myself) is that just turning the cylinder without turning the screw works.

The scoop might work for a short lift, but, for a high lift high friction between the cylinder and product, and, low friction between the screw and product is essential.

Listen again to the explanation starting at four minutes. It's the scoops that push the product up the spiral. The cylinder does move the scoops.

If friction between the product and the cylinder caused movement then more product would be ground into dust. Low to no dust production is one of the salient points of this elevator.

The scoops shown:

appear to be perfectly vertical. A vertical surface can provide no lifting force. The scoops can't have much of a lip, if any, because that would interfere with the spiral. Thus the scoops can push product into the spiral, but can't lift it.

The only lifting forces must be provided by the spiral and the product itself. Either a rough or possibly a finely fluted surface on the inside of the tube may help keep the product moving, but again can not exert a lifting force. I repeat: The only lifting forces must be provided by the spiral and the product itself.

You are correct that the wrapped inclined plane (screw) remains stationary but translates some of the rotational motion of the product into the vertical motion of the product. The rotational motion of the product is created by the rotating scoops and not friction between the cylinder wall and the product.

"The rotational motion of the product is created by the rotating scoops and not friction between the cylinder wall and the product.'

Do you have a basis for that statement? Do you have any information on the properties of the interior surface of the cylinder? I certainly don't, beyond speculation.

You ask if I have a basis for my statement. I originally did not have any reference to my concept of how this elegant machine worked. I offered a simple modification experiment somebody could perform to see if I was correct. Then I listened more attentively to the video and noticed at around 4:10 minutes the presenter states "... the buckets underneath force the particles to go somewhere." The presenter agreed with a pivotal part of my analysis.

I also noticed Mr. Olds making multiple comments that this elevator made little to no dust so it was excellent for lifting grain. He also stated that the clearance between the screw and cylinder was not critical. These two statements by Mr. Olds told me that low friction between the product and any surface was a salient point of this elevator.

You asked for a basis, that is my basis. Now, what is your basis for ignoring these points?

My basis is physics! In order to lift anything, an upward vertical force slightly greater than the weight of the object being lifted is required. To lift a column of product, the total upward vertical force must be slightly greater than the total weight of the column of product.

The scoops act as inclined planes with a rather low slope, so they can indeed exert relatively large forces pushing product into the bottom of the tube, and the product entering the tube can push on the product already in the tube, forcing that product upward, but there has to be a limit. As the column grows, its weight increases, resulting in an outward force on the material being "scooped". At some point, that outward force will prevent entry of new product, and the scoop alone will fail.

Furthermore, if the scoop alone did the lifting, then there would be no need for the screw. Friction with the cylinder must keep the material rotating, and the screw translates part of the rotary motion into vertical motion.

I too watched the entire video a couple more times, and selected parts several additional times. I was especially amazed as the presenter assembled the (presumably plastic) tube over the screw, to see that there is a rather large gap between the OD of the screw and the ID of the tube. This gap does allow product particles to pass without being crushed or significantly abraded, and I'm sure makes the tube last much longer than it would in a rotating screw conveyer.

GA

This article includes descriptions of "lifts" 4 inches in diameter and 23 foot high, and 6 inches diameter and 35 foot high: imagine the forces near the bottom of those columns if all the product was being forced up from the bottom.

Touche. I stand corrected.

The section about variable screw pitch being used for long lifts completely disproves my perspective. The cylinder walls do provide product motion.

That is a very nice and in-depth paper on this elevator design. Peter Olds has come up with a real gem.

Thanks! That article is a great find!

I still find it amazing that a "boundary layer of material" essentially forms a seal between the cylinder and the screw.

Just because the inward pressure of the scoops has a limit, everything has a limit, it doesn't mean it cannot be the dominant force pushing material along the inclined plane of the screw to the top. I'm certain this elevator has a limit that depends on many factors like product adhesion, compressibility, malleability, density, and other aspects not presented. I suspect that once the drag between the cylinder wall and product motion approaches the remaining force from the scoops that product abrasion occurs. The drag effect does contribute to product motion along the inclined plane.

I already admitted that I misspoke when I said the scoops provide lift, the screw's inclined plane provides a lift of a product moving across the plane. So please drop that argument.

Consider this final analysis along the cylinder wall and screw section. It appears to me in the transparent cylinder demonstrator that the cylinder wall surface area and the screw surface area are similar if not the screw area is larger. The pressure provided by the product on these similar each of these areas will produce normal forces to stall or move forward the product. The added force from the scoops is what keeps the product moving.

Most of the time you see the Archimedes Spiral mounted at a slant and used to pump water uphill. For pumping liquid, it would not work if the outer cylinder were rotated instead of the screw. The screw traps liquid so that it cannot run back down, and must be the rotating part.

For pumping dry material vertically, it is the static friction that makes it work, which is non-existent for liquids. If the screw is rotated, it is friction between the material being pumped and the screw. If the cylinder is rotated, it is between the material and the cylinder.

I think you were right in your first post: it's the friction between the cylinder and the product which drives the product up the screw. In both cases the screw should be as smooth as possible.

This scheme has been around for decades. I once worked for a company that made potato elevators this way.

Just got off the elevator...

Surely there must be a limit to how high this type of elevator can lift the material. For no specific reason, it seems to me that the rotating screw could lift it farther than the rotating tube.

I remember watching screw-in-tube grain elevators as a child, where I helped shovel the grain from a truck into the entry hopper to feed the screw. As I recall, these were always inclined around 30° above horizontal. I suspect there is some relationship between the pitch of the screw and the maximum angle of inclination.

I never thought about this before, but I think the rotating screw would work best with a somewhat rough surface on the screw and a very smooth surface in the tube, while I suspect that the rotating tube would work best if the screw has a very smooth surface and the tube has a rougher surface, or possibly a spirally grooved surface.

Well it seems to me that you have the weight of the screw vs the weight of the cylinder because the work of lifting the product would be equal, then the drag associated with turning either the screw or the cylinder....it seems to me that the cylinder could be made lighter than the screw because of the stresses and architecture involved...what about if the screw and cylinder were joined, what efficiencies could be gained or lost...of course these efficiencies might vary according to the weight and form of the product being transported...like sand vs gravel vs plastic balls...even air

https://empoweringpumps.com/screw-pump-basics/

https://www.vacuumscienceworld.com/blog/working-with-screw-pumps

Very interesting. Here the friction between the wall and the material lifted is the criteria, being rough is better for better efficiency. What would happen to the efficiency, if there is a screw attached to the inner wall, in the same direction as the central screw? Next question, what if this attached screw is in the opposite direction?

My above write-up is incomplete and confusing. So let me elaborate further:

Imagine that there are two screws, one inner with the central spindle and another attached to the outer wall. The inner screw diameter and the id of the outer screw diameter just have running clearance.

Case1: Both the screws are in the same direction enabling the lift. Think it should improve efficiency.

Case2: Outer screw in the opposite direction. Is the outer would try to bring the bean from top to bottom or stay stagnant as a thick wall?

Good answer question.

If the outer spiral had the same sense as the inner it would just screw the product down in the outer section.

But if the outer screw had the opposite sense it might be more efficient. I suspect that there may be more damage to the product but for some (eg. sand) that wouldn't matter.

The outer screw does not need to be the same slope or pitch as the inner one. Ultimately the outer "thread" might just provide better traction between the outer cylinder and product.

Worth investigating further.