How to Calculate Pressure Exerted by C in a Lever and Fulcrum Configuration?

[JBA]

Yes, at this point, the shear strength of the B & C 1 1/4" dia axle shafts' material and the potential for lubricant breakdown and galling between the those shafts and the plate holes without the 1/2 bearing shells are still a bit of an unknown.

I was just looking back at your last assembly picture in your post #67 and there are a couple of suggestions regarding the reinforcing of the links and their cross bar.

First, I recommend that you extend the added side plates all the way to the top of the crossbar tubing at the ends of the links.

Second, with regard to the crossbar tubing, it is really hard to calculate the possibility of load buckling of the crossbar tubing where it sits on the top steel angle; so, if it can be reasonably done at this point, adding a bit of the same type of reinforcing strips all the way across the bottom face and on the sides of that crossbar tubing might be a good idea. (those should be fully welded to the tubing along both edges)

Apart from those issues, it appears everything else we have discussed so far seems to be getting worked out.

 

[john101]

The cross bar :

When I place it on the angle it allows me to bolt it in place. If I thicken the side against the angle it moves off center.

What about doubling the cross piece with a second on on top?

_________

Thinking aloud :

I keep getting stuck in thinking about how big to make the piston and chamber.

I still like the idea of making 6x12x4 blocks.

This allows me to make

one 6x12x4 block
or two 6x12x2
or two 6x6x4
or four 6x6x2

or two 9x3x4 bricks and a 3x6x4, or two 9x3x4 and a 4.5x3x4 and a bit (ie two and one half bricks)

per pressing

if I reduce the width or length I can only make one standard brick per pressing plus other relatively useless pieces.

Therefore my current thinking is to reduce the expected Mpa to say 5, keep the original piston/chamber dimensions and stabilise the blocks with Lime (not Cement, Lime is much less energy intensive in production, costs less and, if cured properly, makes a strong bond (as well as waterproofing the bricks/blocks)).

If I do so, are all, if not most of, the structural strength concerns solved?

edit add : in post #79 is 182 100 meant to be 182.1 lbs?

edit add 2 :

another thought :

make two piston/chambers.

one 9x6x4 54 ^2" to use up to 20Mpa

one 12x6x4 for 5Mpa blocks.

edit add 3 :

I came across a couple of more web sites discussing this type of press. 20Mpa is an expected pressure. Also one states the soil volume reduces by about half.

I think I have to let go of the 12x6 size and the idea of making two bricks in one go and and go for a 10x5x7 chamber and make an add on 'chamber height reducer', to place on top of the piston, of a height to be determined by experiment.

 

[JBA]

I just looked at the #79 post and now I see that when I pasted it from Excel all of the number columns became scrambled and essentially unreadable. I can't believe I didn't catch that when I did that post. Below is a screen shot of that data in a readable form

The first table simply gives the compression pressure limits for the side links for each of the three material grades.

The purpose of the second "For All Plate ..." table was simply to show you the amount of operator handle force that would result at a handle position 4" above the horizontal and the toggle at 176° with a 725 psi (5 MPa) and a 400 psi plate pressure to give you an idea of how high the operator load would be with the handle at that position at those pressures.

At this point, I think what is important for you to see is that the first table shows that you can safely have up to 1973 psi (17.6 MPa) pressure with the Grade A material limits with your desired 72 in^2 of area; and assuming we return to using the full toggle extension with your latest design and revisions then you would only have a operator handle force of 134 lbs at 1" handle height with your current 60 in handle. So other than possibly lengthening the handle a bit I don't see that is is really necessary to reduce your compressing pressure all the way down to 5 MPa. Does this help clear things up a bit or am I missing something.

With regard to the reinforcing of the crossbar, I was not saying that your current crossbar tube will not be strong enough. I was only suggesting reinforcing it a bit if possible because I don't have any way to calculate whether or not the tubing wall might buckle or not under a 200,000 lb load.
Adding the strip on the bottom of the crossbar will definitely help, so if placing the strips on the sides is a problem then just don't add those suggested plates. Adding a strip to the top of the crossbar will not improve the buckling strength so there is no reason to do that.

Let me know what you think about all of this with regard to your above thoughts about changing your current design.

 

[john101]

yes, thank you that clears a lot up. I'll try to figure out what that means re design.

 

[john101]

"At this point, I think what is important for you to see is that the first table shows that you can safely have up to 1973 psi (17.6 MPa) pressure with the Grade A material limits with your desired 72 in^2 of area; and assuming we return to using the full toggle extension with your latest design and revisions then you would only have a operator handle force of 134 lbs at 1" handle height with your current 60 in handle. So other than possibly lengthening the handle a bit I don't see that is is really necessary to reduce your compressing pressure all the way down to 5 MPa. Does this help clear things up a bit or am I missing something."With this paragraph: If what I'm using is Grade A material (ie the weakest) I can have an area of 72in^2
safely up to 17.6Mpa. Then the operator force at 1" handle height will be 134lbs, and all materials and construction details can be as so far proposed. As far as I understand only the pins at B and C and the lugs at B (and presumably at C) are unknowns.

Is this correct?

 

[JBA]

Yes, for everything we have identified and addressed so far that is correct.

Having said that, your first test still has the potential to show us something we may have missed, but that is all a part of the process on any new machine design; and, when you get ready to test your machine I have some suggestions as to how that test sequence might proceed with a goal of doing so safely for both you and the machine.

Just as a note on the handle force, while we can reasonably predict what the handle force will be at the 1" point with the 17.6 MPa pressure, the handle force at each point of travel above that 1" point is going to be dependent upon the soil compressibility vs the force multiplication factor of the toggle, so the actual handle forces through the 89° of travel before reaching that 1" point are still going to be an unknown until your test.

Edit: PS I really want to apologize for my ridiculous error when first posting the above tables. It no doubt caused you a lot of unnecessary confusion and lost time trying to understand it, I generally try to do a much better job of checking what I post.

 

[john101]

I've thought about the errors. My opinion is that they are inevitable and in themselves instructive. Through pondering them before coming to know they are errors I learned a lot of other things. The errors are revealed and fixed. All is good.

edit add : while some may regard it as lost time, I don't. I find that the slower I can do something the less likely I'm to make a mistake which would be a real waste of effort. For example at the moment I've made a cardboard box 12x6x4 and one of 10x5x4 and have them lying around to look at. In this way I familiarise myself with the sizes in a way a drawing cannot do for me.

Part of the good reason for taking it slow has been the design of the piston/chamber. Because the stroke is about 2.8" and the compressibility of the soil according to web accounts is from 30 to 50 % the chamber cannot be more than 6.8 and might have to be (no less than) 5.6". Based on the style and format of the account I suspect the guy who wrote 30% did not apply 20Mpa. There's a photo on his page that shows a youth operating the press. Ditto the chinese video. There doesn't seem to be a great effort in making the brick. On the other hand the page stating about 50% mentioned 21Mpa in the same sentence. So, if it's about 50% with ab being 3" the stroke determines the chamber depth (?). IOW if I want a block pressed to 17.9 % it seems reasonable that I cannot get a block thicker than about 3". Though I might find it compresses less and hence get a thicker block. IOW a finished block size of 12x6x3 appears to be it. The upshot of all that seems to be that a chamber size of 12x6x7 is good allowing for adjustment by adding spacer.

This then determines the minimum height of the piston from c to the top of the rubber/spacer sandwich, the location and length of c's guide slot and the final length of bc.

 

[JBA]

As I see it, if you start with a 5.8" deep fill you would have a 48% compression with a 3" thick finished brick; but, since I think the new target compression pressure is 17.6 MPa, at that lower pressure the compression compaction percentage should be reduced and as a result you might get a thicker block from the same fill.

Theoretically speaking, if the compression effect is linear (which I seriously doubt) and 50% compression is results in a 20 MPa finished brick; then the required compression for the 17.6 MPa would be 44% so you would end up with a 3 1/4" brick for the same 5.8" fill. By that measure, a 7 1/8 " fill would give you a 4" finished brick at 17.6 MPa. So on that basis your 7" depth is right in line, but you might want to increase it to 7 1/2" or so because, as you stated, you can always add filler plates to adjust for the finished brick height

I doubt it is going to be as straight forward as the calculation predicts but it is a least a starting point.

 

[john101]

I agree.

Got a bit distracted yesterday. Had to move a huge (1 meter wide 2.5 meter diameter) tyre using only a car jack and bricks to partially tilt it upright and ultimately the car pulling it upright so I could roll it.

The next thing I'm thinking about is the construction of the piston.

This photo shows what I propose.

The top plate (here on bottom) is 3/8 inch. The angle irons are 1/4 " and the bars with the hole for c (ignore the other hole with the split) 1" thick.

edit add : or

 

[JBA]

It looks as though it should handle a heavy loading. I recommend beveling the angles' bottom edges at the angles' bottom attachment to the center post to insure a full penetration weld.
What is the length and leg width of the bar angles and the overall dimensions of the assembled base plate?
I want to try and analyse the loading stress on the welds between the center section and angles'
I don't expect any issue, and even if I find one, it can easily be addressed by adding gusset plates between the top edges of the angles and side posts.

What is the function of the four holes in the bottom angle faces?

 

[john101]

The angles are 3x3x1/4" and 4 1/4 long, all up the size of the plate will be 6x12".

The holes were just there. I got a stack of those off cuts that just happened to be the right size.

 

[JBA]

I think your first design with the angles is cleaner than the second; but, I will let you know how my analysis works out before giving a more definitive answer.

Suggestion: when you have something to add it, is better for me if you place it in a new post rather than an edit. If it is a new post I get an alert but for an edit there is no alert so it is only when I decide to return to your thread to add or review something that I discover there is something new for me to see.

 

[JBA]

I noticed something in your #95 quote of mine that looks like it could be confusing for you. I stated: "]you can safely have up to 1973 psi (17.6 MPa) pressure with the Grade A material limits".
What I should have said is " you can safely have up to a 17.6 MPa (2553 psi) compression pressure at the 1937 psi stress limit of the Grade A material"

As long as you understand you can have a 17.6 MPa press pressure then that is what is important, but I obviously didn't make that very clear.

 

[JBA]

I have run an analysis on your first design and it is going to require some reinforcing in a number of areas; but, before I get into that I would like to see what your alternative design with the 2x2x1/4 square tubing looks like as a complete assembly, including the thickness of the bottom plate, to see what the stresses might be on that design.

 

[john101]

I did a bit of gimp manipulation to make it like this.

The bottom plate is 3/8". size 6x12

The upright plate is 1/4" x4x12. (I've only shown one but both sides are mirrors of each other)

 

[john101]

 

[JBA]

Since this is the piston, on the first design, how are you planning to guide it to keep the piston face horizontal in the box?

Is that what the side plates in this last design are intended to do; or, are you planning on using the side slots for controlling it?

At this point, my main calculations are focused on supporting the horizon pressing face plate so that it will be rigid enough to deal with the high compressing pressure; and, in that respect, my calculations show that the face plate should be at the very minimum 1/2" thick (this can be by adding a 6 x12 x 1/4" thick plate on the bottom pf the existing structure.

On your latest design, since you are using the 2 x 2 sq tubing if you insert a third 2x2 sq tube between your current two side tubes to make that part of the structure into an essentially reinforced box and with the added 6x12 3/8" bottom face plate.that would would a really good rigid assembly for resisting the compressing pressure without deflecting so if you can do that, I think your last above design with that third tube added would make a really strong piston. I was intending to ask you add some side gussets to reinforce the first design but the vertical plates on the last design will serve that function.

 

[john101]

The idea is that all edges are flush with the 'case', the two c points are apart only by the thickness of the case walls and that this provides sufficient guide for the piston.

Adding the strengthenings you advise is no problem.

In this drawing I've added the rubber mat and a plate above that. ?

 

[JBA]

That looks like a really good design, during the pressing process, the links will hold the piston face parallel to the press top plate in the direction of the axle centerline but either the vertical side plates or the axle slots will need to act as a guide to keep the axle centered in the direction perpendicular to the axle centerline, otherwise, any variance in material density from one side to the other can cause the axle end of the assembly to shift sideways during the pressing process. If you were pulling up on the piston this wouldn't be a problem but since you are pushing it, the axle end can want to shift one way or the other under load.

If the side plates are used as the guides then they should extend as far down as possible to give them the best mechanical advantage and minimize their side force friction on the box walls but the plates don't need to contact the walls for their full height. They can have a recess along each edge that leaves only about 1 inch at the bottom end for wall contact.

 

[john101]

Ok, I forgot to mention the slots as guides. (Which (slots) should stop 7.5" from the lid.) Well that seems to be it for the piston. ?

I'll let the piston, when built, decide the exact size of the case and in turn the width of the cross bar.

re the case. 1/4" thick walls? Can you see a reason to reinforce that? My understanding is that soil when compressed is not going to exert much sideways force unless over compressed and shears. Though it is plastic. Most of the compression is a tighter rearrangement of the components of the soil and the displacement of water. Because there will be gaps all around (cut the rubber mat smaller so it doesn't end up acting as a seal) water will readily leak out.

As I write the above I feel I'm talking myself into thicker walls. What do you think?

 

[john101]

Roughly a question to ask a Soil Engineer:

I have a cubic foot of loose soil, composition 25% clay, 10% lime, 10% water, 55% sand, well mixed.

I place it in a cubic foot box with one side open. The walls of the box are permeable to allow water and air to escape.

Over the side that is open is placed a piston that compresses the soil in the box. The base opposite the piston is fixed, rigid, impermeable.

If the piston presses down on the soil with 20Mpa.

How thick steel must the 4 walls of the box be in order to not (permanently) deform?

 

[JBA]

I am having a hard time deciding about the walls as well since I agree that the shearing displacement force of the soil should be relatively low. At the same time, that box is going to be supporting all of mechanism weight and loads plus the operator handle loads. So I am inclined to recommend a thicker wall as well; but, I don't know specifically what the thickness should be or how I could calculate it.

The box will be setting on the ground so a bit more weight shouldn't be a factor unless you intend to transport it around a lot, so I think I would be inclined to increase it to a minimum of 3/8" plate.

 

[JBA]

With regard to your last post, I don't have any background in soil mechanics and that is the science that addresses the issue of shearing in the soil that will load the walls of the box.
I have been doing a bit of searching on the subject and much of the information is very technical and hard to draw conclusions from but the below reference that seems to indicate a general average of 30° for compacted sand and clay. If that is true then for each 100 psi of vertical pressure there will be approx 57 psi of lateral pressure which would mean that the wall pressure will be 1443 psi at a 2500 psi compacting load which, as I see it, would mean you would need reinforcing bands around the region of the rectangular compacting chamber and I haven't seen anything like that on the other machines I have viewed; but, as I stated above, I am really out of my area of knowledge with all of this.

http://www.geotechdata.info/parameter/angle-of-friction.html

I guess I would like to have a couple of days to see where the information I have found takes me before making any kind of suggestion about the box construction and the plate thickness required.

 

[john101]

What about instead of a centre tube I add spacer like indicated here in grey.
spanning between the two upright plates (only one shown here) ?

(I've also added the rubber and spacer plate.)

 

[JBA]

How thick is the piston face plate?

 

[JBA]

Edit: See the below #117 post for an update on this and the above question

This morning I decided it was time to do some more internet searching to see what hints I might find about the thickness of the box walls. From what I have seen most of the machines onlne are designed for bricks with cement in the mix that do not require the type of compression loads needed for your type of brick; however, I did locate a few views that appear to indicate that at least 5/8" or thicker plate has been used for the compression chamber wall region of the press. One example is the below site and its video immediately shows a clear view of the top edge of the chamber and, by using visual size comparison, it seems to confirm what little I saw on other locations.

https://offgridworld.com/open-source-compressed-earth-block-machine

 

[JBA]

Edit:
Update on the piston. and box

I have analyzed the stress on the walls assuming the .57 transverse load factor is correct and I have found that, based upon the 12" long side, a 1" thick mild steel plate material should work; for all sides, but nothing thinner than that and be sure to use heavy welds at the corners. The top 6" of the box in the high pressure area is all that really requires that thick of a plate, so a thinner plate can be used for the lower box section, doing that in the piston travel area will require welding the top and bottom section together with a perfectly flat inside face on the joint; but, below that point there isn't any real joining issue and you may want to do that to make the box lighter and the cutting of the the piston rod slots easier.

Since you have already assembled the piston to this point, adding the third center tube is probably not an option because for that to work the three tubes have to be in full side to side contact with welds along the top and bottom joint lines to provide the reinforcement I was looking for.

I think the spacer alternative you have suggested will work; but, I may want you to add similar spacers between the ends of the two tubes as well. Once you give me the the piston frame top plate thickness then I will have a better idea of what i think is needed.

 

[john101]

That is thick. However, it sounds like it would allay any concerns. Is it ok to layer 4 1/4" plates to get that 1" ?

The two top plates are 3/8".

Ok. 3 spacers.

BTW That image and all the other piston ones are Gimp generated. I haven't welded anything yet.

 

[john101]

Just further to the above. I don't like the idea of layering 1/4" plates. Too difficult to keep clean and rust free. Any surface rust that takes off can make it bulge inwards. I'll have a look around town. See if I can get 1" plate. The thickest I have is 3/8".

 

[JBA]

With regard to stacking plates, this does not work to increase the strength to the degree that a single thicker plate does. Simply welding the plates around the edges creates an extremely high shear stress that can crack those welds. For example, if you hold together a couple of strips of anything and bend them you will see that while bent the bottom one will extend out beyond the ends of the top one. That is the shearing effect that happens with stacked plates, and if you really grip your strips tightly in an attempt to prevent that from happening you will see that it is much harder to bend them or that you cannot keep them from slipping.

On the piston, putting inserts between the tubes will strengthen the piston plate from one side to the other but will not add bending resistance along the length of the piston; and, that is what I am concerned about. Depth of a member is the main thing that makes it resistant to bending, that is why the sq tubing works well. Since I now realize your tubes are only 1 15/16" sq, that means three of them across will only be 5 13/16" wide but using three tubes and having only 3/32" of the face plate extending over the side edges is much better than the alternative.