How long and how fast (in RPM) do you need to apply centrifugal forces to compact Hollow Spun Pile? 4

[jose_learningItAll]

Hello everyone, concrete compacting by spinning (or applying centrifugal force) is a relatively new/recent method to be used in the world of concrete construction.

Does anyone know how to determine the rotation speed (in RPM) and how long to apply the rotation (in any Time units, preferably seconds or minutes)?
I have done a bit of searching, but to no avail. It seems like there isn't much study regarding this topic yet.

If anyone can help by directly answering, or even refer to a paper/journal/codes/standards containing information about Spun Pile Centrifugal Force Speed and Duration, I'd greatly appreciate it.

Good day to all of you.

 

[robyengIT]

concrete compaction by spinning is not new/recent procedure, it is quite old (in Italy sine 1930 approx).
Any way :
1 - poles for street lighting : top diam approx 150 mm bottom diam approx 350 mm - spinning speed (of the mould, not of the wheels of the spinning machine) 300 - 350 RPM spinning time 15 - 20 minutes

2 - giant piles : OD diam 1800 - 2000 mm length 40 metres wall thickness 160 mm. Loading speed 60 RPM loading time 30 - 45 minutes final spinning speed (of the mould) 150 RPM spinning time (at 150 RPM) 30 minutes

doc for both 1 and 2 and video for 1 (lighting poles) :

http://www.pisaniengineer.com

- Curriculum Vitae

Ready for further info

PS : the important thing is to reach an RPM so that to have, on the OD, a centrifugal force of approx "15*g" where g = mean gravity force on earth (9.80 m/s^2)

 

[robyengIT]

some photos (summary)

 

[Ron]

@robyengIT...nice teaching!

 

[jose_learningItAll]

@robyengIT

Thank you very much for the quick replies and answers good sir. Also thank you for the teachings, documents, and photos that you shared.

Yes, I just looked up a bit about precast concrete and worldwide-wise it is even said that precast concrete got invented in 1905 in England. This is indeed a bit surprising to me, since through my coursework in university it is often mentioned that precast concrete is a "New" and highly-Innovative way of using concrete in construction.

I have checked out your CV and other documents that have the word "spun" in their title. Although I don't speak Italian, I can see some mentions of time (tempo) and rotation speed (velocita) for the concrete compacting process.

I'll try to read and understand more from the documents you shared, but since it is rather challenging for me (mainly to translate the language), I'd really appreciate if you can answer another question.

(Correct me if I got it wrong As you said the important thing is to reach a certain centrifugal force level on the outer diameter of the mould. But for the giant pile for example, it is initially spun at a lower speed (60 RPM), and then later on spun at a higher speed (150 RPM), is there any reason to not spin it at a high speed (150 RPM) from the start?

Thank you for reading up to this point, and if anybody else answers I will appreciate it just as much.

 

[dik]

Thanks, Roby

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[robyengIT]

60 RPM is the loading speed. The giant pile is 40 metres long and is loaded with concrete by two conveyor belts, that is each cantilevered 22 metres. The initial position of the two belts is all in (into the rotating mould, where the steel cage is already placed). While loading, the belts (mounted on wheels) are moving back until the concrete loading is complete. Then the rotating speed is increasing step by step till the final speed (150 RPM). This because the total quantity of concrete is approx 80 metric tons and you can't load all at once, so you need time and concrete load always balanced. You should consider that the total weight of the rotating mass (steel mould + steel cage + concrete) is approx 120 metric tons at a rim speed of approx 100 km/hr : is very dangerous.
In the doc I told you, there are the drwgs of mould, spinning machine and conveyor belt : if you don't find, let me know so that I can post the links and, may be, I can arrange a doc just for concrete spinning (in english)
PS : attached a simplified flow chart

 

[robyengIT]

here the flow chart

 

[jose_learningItAll]

@robyengIT

Thank you, I have looked at the flowchart, also with the other files in the same zipped file you named with code CV08.
I have seen the photos too, so you don't need to arrange another doc for that (thanks for the offer!).
At first, I didn't really understand about the conveyor belt and how the concrete was pour (step "C - Spinning" in the flowchart), but now I think I understand better, thanks to your explanation.

If I may confirm, the main focus is to maintain concrete load balance until all is loaded? (1)

Let's say the system/factory I use right now is quite different, it is not as automatic as I have seen in yours.
It is used to manufacture hollow spun driven piles (for foundation), and all the concrete is poured/loaded into the mold (bottom side mold) before spinning is started at all.
After concrete is fully loaded, the top side of the mold is placed, and then both sides are locked to each other, and then it is finally moved onto the spinning machine.
In this situation, would it be the best to spin it at the highest speed immediately, and how long? (2)

Say there are piles with outer diameter of 300 mm, and others with 600 mm.
How long (spinning time) and how fast (rotation speeds, either in multiple increasing steps or directly to highest speed) should I use? (3)

I do hope these questions won't be a bother.

 

[robyengIT]

(1) for giant pile : yes
(2) I guess you didn't watched my video, showing exactly your description. Starting from zero RPM we increased the speed slowly but continuously, so to reach approx 70-100 RPM of the mould and we leaved a bit at that speed untill, watching through the mould, we could see the light all through (my poles were conical - 1.5 - 2 % and prestressed). After that we could speed up faster till the final RPM. Spinning time at full speed approx 20 minutes

video :

https://mega.nz/#!9FVi1ATK!E7a2UUij4gOONX6EMeBdxUUdZZWLyeK5eoum4TCkEro

 

[robyengIT]

here the photos of the factory shown in the video (Jordan Electricity Authority - Amman)

 

[jose_learningItAll]

You are right, I haven't watched this one, the one I watch was the giant pile video. Sorry for that.

I see, I think my factory doesn't check watching through the mold, but we also spin it slowly at first (around 4-5 minutes) then speed up in total of 4 steps (increasing speed).
I guess the point is to make sure we can see through the "hollow" part (see through the center of the mold) before increasing speed.

Our products are fine so far, but I want to know If we can decrease the spinning time, to the lowest possible while still achieving strength and quality needed.
This is so the production line can be optimized, producing/manufacturing as many as possible in a day.

Maybe I'm being a bit too idealistic being a fresh graduate, I wanted to do a throughout experiment about this, but it is hard to get funding, and it requires using the machine also (stopping actual production process).
Since the factory is doing fine, nobody has thought that it could be improved further, and not bother finding out.

Maybe someday I'll get such funding, but for now we do it the same, also similar to your factory (JEA).
Thank you so much sir and I wish you good health.

 

[robyengIT]

spinning time depends on the quantity of water of the mix : spinning should take it out as much as possible in a minimum time. I guess that the qty of water is under control, so you could start reducing the time (i.e., 1 minute), for just one pole a day, and then for 2 minutes and so on. After that you further reduce the water of the mix (more difficult for you because one mix can affect more than one pole). After that, may be, you can reduce time of curing (with steam I guess) : in Jordan we used saturated steam at 10 atm (that is temperature approx 160 - 170 °C)

 

[jose_learningItAll]

That's a really good idea.
I'll try to propose that to my superior in duty.

It's true that it will have to be done one by one, observing the effects of one variable at a time.

Thanks!

 

[EdStainless]

Rotating slowly while loading helps spread the material and start the process. It also helps to assure that there is less trapped air. These factors can shorten the overall cycle.
Though the cycle needs to be long enough to reach a cure level that will be self supporting.
(I have experience centrifugal casting metals which is very similar)

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P.E. Metallurgy, consulting work welcomed