drodrig,

Does the part have to be lead? How would eleven or twelve tonnes of some other material work? This could be a cost and ROhS issue.

--
JHG

casting individual teeth sounds like a plan. would small gaps between the teeth (where the parts nest) be a problem ? maybe solder together ? the natural nesting of the individual parts would provide some labyrinth seal ...

another day in paradise, or is paradise one day closer ?

Hi,

The material must be lead. We are looking for a property called "radiation length". The value should be as small as possible. Tungsten is the other option (actually better) but much more expensive.

Actually lead is used as standard shielding material in particle accelerator facilities.

Small gaps would not be a problem. Would the soldering be strong enough to keep all the parts together?

Cheers,

You can actually weld lead. The process is referred to as " Lead burning" There are companies who have expertise in this, although not for parts as big as yours.
B.E.

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

• http://vulcangms.com/processes/lead-lining-2/lead-burning/

Lead shielding is often assembled by stacking lead bricks so the shielding can be easily moved or transported. You give no information on any other requirements or functions, so how can we help? Is that a spiral thread you are depicting?

You could have the lead tiles set up with overlaps/interlocking features on them both for location during assembly and also to avoid any line of site gaps.

Does it need to be solid lead? What about outer shells of X material filled with very small pieces/balls... of lead?

Obviously, powdered lead or tungsten (or DU) has some health and safety issues but just throwing it out there.

Cast individual blocks that nest together. Like these:


Join them together with a molten lead "mortar".

By the way, re my lead particle idea - you don't have to leave it as loose lead - could make a type of polymer concrete or similar from it.

I think the interlocking block idea is good ... but there will probably be a price to pay on tolerances ... you could machine the final assembled rings, you could weld the pieces together

another day in paradise, or is paradise one day closer ?

Darn, someone beat me to my heavy metal polymer composite idea.

http://www.tungstenheavypowder.com/Tungsten_Heavy_...

Lead can be a real bear to machine, it has a tendency to smear on the tool. You need a " Coolmist lubrication", spray nozzle using Kerosene as the cutting fluid. From a machining point of view it is better if the lead is not pure lead, but has some Antimony, arsenic, tin, silver, or calcium in it to harden it a little.
This also helps , a little, to stop it deforming when the part is clamped in a vice or collet. Whether your application would allow any alloying elements into the lead I do not know, but they would help from a machining point of view.
B.E.

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

Bricks sounds like a good idea but there are a few things to consider.

Will the cylinder be mounted horizontally or vertically
Is it static or does it rotate/move horizontally or vertically?
If it's static- why does it have the shark teeth?

If the only purpose of the outer teeth is to allow the unit to be manipulated/moved- would it be more cost effective to use a cheaper material (i.e. if relatively thin it will not contribute significantly to radiation shielding)

Given the effectiveness of the shielding will be dictated by the thinnest section of the wall- is it worth using lead at all in the teeth- or should you just make the outer shell out of stainless steel, including the teeth- and then line the interior with lead bricks.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

Can you add a few % of antimony (Sb) to the alloy? This would increase the hardness and yield strength substantially, and probably allow the shield to be self-supporting. You still need to consider the creep strength of the alloy, which is very low since lead has such a low melting point.

Drodrig:
You have a lot of questions to answer before you can start putting some of the potentially good ideas offered above into a final solution. Is its final position as your sketches show or is it standing vertically, or what? How is it loaded, all the various possible loadings? You have to design it for these loads, not just the radiation level. How finely detailed do the teeth have to be and what do they do? Where is the liner which adds some support to the lead cylinder, inside or outside, inside, right? Is there outside support and laoding? Depending on some of your answers, I would cast rings about 6" high, to match the pitch of the toothed rings, with one tooth per cast ring. This would give you about a 6" x 6" ring which you could design some lifting equipment for. I would cast a sloped/slightly tapered lip about 1" deep on the i.d. of each ring and a matching groove on the next ring, for fit-up and assembly. The top or bottom of the basic mold cold be modified/adjusted for the left and right end variations shown in your sketch. These rings give you pieces you can practically cast and handle, I think. You need mechanical properties info. on the lead alloy you will be using.

How about making a thin walled container the shape you need and fill and vibrate lead shot into it. You may have to consider the packing factor in your attenuation calculations. Shot is easily available and the lead would be easy to recycle when you no longer need it. The container could be filled/drained in place to minimize the handling of such a big weight lowering costs even more.

Timelord

I would sand cast 20(?) interlocking rings that look like the sketch below and stack them over the inner metal sleeve. The joint overlap arrangement shown would seem to work well for a shielding function. Each individual lead ring would weigh around 1000lbs, so they could easily be handled with a small forklift. The axisymmetric profile is quite simple, so you can probably have a wood sand casting pattern made for under $1000. The price of 99.9% pure lead ingot is around $5/lb. So I imagine you could have each ring made for around $6-7K.

The only issues I can see are finding a foundry that is willing to work with lead, and disposing of 10+ tons of used lead shielding.

I think the lead acid battery manufacturers would have a reasonable handle on OH&S for both the casting and machining stages, and recycling. As to making the part, you haven't given enough details to really eliminate any alternatives, so although I like the interlocking bricks idea, how about wirewound? just wrap lead wire around a cylindrical mandrel, slightly oversize, finish to size with a bloody big soldering iron. Rolling the thread like shapes also springs to mind.

The big issue with large lead parts is that they move around under their own weight, you may want to keep the axis of symmetry vertical as you build it, and then transport it.

Needless to say this has all been solved a hundred times before, make sure you do a good literature search before embarking on any detail design.

I can't believe, given the disparity in properties and cost, that either lead or tungsten is acceptable for the thread like part.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

berkshire, interesting the lead welding; I didn't know, I'll bear it in mind

Compositepro, this is just a shield. it has this funny shape because it stops some particles that come with a defined trajectory from bouncing. No thread or mechanical function.

Kenat, very interesting the idea of filling with powder/balls, noted and I'll ask if this works. Also the polymer

Mintjulep, rb1957 (and others) ok, the idea of bricks/staggering seems to be more liked than casting

Berkshire, Our workshop has experience machining lead, I'll check with them if pure lead is better or with some other components

Itdepends, The cylinder will be in horizontal position, static. The shark teeth to stop some particles from bouncing. The material must be lead or tungsten (which is much more expensive). Maybe the teeth can be made in tungsten and bolted/welded.

btrueblood, Good point, also noted the info about the Sb. I want to run a simulation to see how the lead behaves because it's own weight.

dhengr, It stands horizontally. The loading procedure is to be defined by us. Unfortunately I work with physicists; they fix the rules and I have to build it. Of course there is some room for changes but it needs to be checked. The tolerance/precision doesn't have to be so high. The teeth are to stop particles coming in a particular path. This lead part will be held with an aluminium allow/stainless steel (non magnetic) support, just for one side, here some tentative design:

http://files.engineering.com/getfile.aspx?folder=7...
http://files.engineering.com/getfile.aspx?folder=b...

I like the idea of the tooth-ring assembly. noted!

Timlord, yes, somebody mentioned something like this, I'll check with my colleagues if this also works (vs solid lead)

tbuelna, Yes, the rings idea seems very nice. Do you think they come out of the mould with good precision to fit them together? Do we need machining afterwards? Your sketch looks very nice. About the price I thought it was cheaper, like 1$/lb. After defining the shape and the mounting/building options, we of course have also to look at the costs.

Greglocock, about health and safety I'll check with the manufacturers, but I found companies casting lead, they should know about this. The wire winding idea seems also a very nice alternative (like the housing powder/ball filling). I'll ask, because I have colleagues who built copper solenoids and have some winding experience. About literature I didn't find anything, I'll check deeper, but building such big parts of lead is not so common. I saw a lead casting company which can make parts up to "just" 100 kg.
About lead vs tungsten. They are both used in this field (particle accelerators) because of their short radiation length. Tungsten is better (for this property, but also because it is harder; it doesn't deform easily), but more expensive, so lead is preferred. Tungsten is used to make collimators.

Thank you all very much. I am really learning many things and different ideas

This shielding is to be put in an experiment of particle physics, if anyone has interest in knowing more details about the whole thing I'll be happy to explain.

• http://files.engineering.com/getfile.aspx?folder=bed19be9-7ce2-43cd-a724-4f

The boffins will probably insist on something that's simple enough to calculate the resultant shielding and related parameters. e.g. solid.

If it's built such that it's not solid (e,g. pellets, wire, bricks with any gaps), then the build may be easier than the required calculations. The boffins might not like that. But, you never know.

Good luck.

My suggestion is to wrap the inner cylinder with lead sheet. X-ray facilities have lead sheet in the walls. It is easily obtainable. Don't understand enough about the bottom and the teeth. Tungsten doesn't appear to have a very high coefficient of thermal expansion, so heating tungsten rings and sliding over the lead doesn't look too promising. Seems like there are some companies who deal with lead shielding exclusively that will have some good ideas.

Just took a look at the mounting arrangement shown in your sketch for this cylindrical lead shield. Are you really planning to support this 20,000+lb x 6.5ft long cylinder of lead using a tube frame attached at one end? If so, then that would have a big influence on the construction of the lead shield.

dodring, try (really hard) to get away from the cantilever design, else be prepared to have some real large/strong/space consuming supporting structure and strong foundations. Barrel supporting would specifically require design space within the barrel. Selfsupporting structure design could call for the single ring idea, the like of a rear pinion cassette of a racebike. Make sketches / design drafts combining in detail both your ideas for the barrel and the support designs, you'll see better.

@drodrig,
Try the following people for ideas, and casting capability: http://www.pittslittle.com/
Good luck,
Dave

Thaidavid

Hi there,

In the end it must be solid, if there are pellets or powder the properties change too much (air in between).

Thin layers is good idea, I will check

tbuelna, what influence? we can load the cylinder slowly. For mounting purposes we can fix the support on the other end or making temporary parts which allow the mounting (i.e. rings entering the cylinder)

we have to make the cantilever design because we can not put material in the open end. I've been running FEM simulations and it seems the support is not strong enough, I have to check deeper.

thaidavid40, thanks for the link. but we are based in Germany I guess it would be very expensive to look for a company outside

thanks to all

Quote (drodrig)

tbuelna, what influence? we can load the cylinder slowly.

The concern with your cantilevered support structure is probably more about stiffness rather than stress.

Only gamma (X-ray or lower energy) radiation? If any other particle-type radiation hits the alloy, you "might" get induced radiation in an alloy, but not in "pure" lead. Gamma usually don't activate what they hit at most energies.

tbuelna, you mean it will deflect too much?
I have calculated like 6-7 mm, which is actually pretty much

racookpe1978, about the radiation I don't have much knowledge; just that we must use materials with low atomic number (aluminium is the typical material to be used, it doesn't get activated so easily). I have colleagues with experience in this, there is radiation here everywhere and this is taken care

cheers,

Doesn't make sense.

If you need to stop gamma/xray type radiation, you specify very heavy, dense matter (lead (as here, concrete, steel, etc. Light weight metals are very, very inefficient at stopping that kind of radiation (high energy rays). These rays can also form also from the impact of particles into shielding: as the shielding stops the particles, the collision can result in radiation.)

To stop nuclei (neutrons, protons from an accelerator, etc.) you need lightweight (plastic, water, or very light weight metals) whose individual molecules are hit by a particle and exchange kinetic energy. The lighter the shielding molecule each particle hits, the more energy is lost in each collision.

Thus, claiming aluminum is "better" doesn't make a lot of sense if the shield is going to be made of lead forms. (Maybe lead inside the Al canisters?)

Racookpe1978,

Of course we need Lead (or Tungsten) to stop the radiation.

The point of the aluminium is the fact that it doesn't get activated with the radiation (let's say it doesn't "keep" the radiation when the radiation attacking it it is stopped). The lower the atomic number the better for this.

I even heard people use beryllium (atomic number: 4) for experiments

I am not an expert about this, I don't understand the whys, I just know what materials must be used for what other experts have told me

cheers,