Build big lead part

[drodrig]

Hi everyone,

I was assigned with the task of designing a big part made of lead. Cylindrical, around 2 meters long and 1 meter diameter, 300 mm wall thickness. Here some pictures:

http://files.engineering.com/getfil...606-ad09-5bf2280c482c&file=04_lead_barrel.png

http://files.engineering.com/getfil...e74-a30e-5290ce7fb2a1&file=01_lead_barrel.png

One can see there are also some "shark teeth" (name given by my colleague), these funny outer cylindrical angles.

The aim of this part is being an active shield for radiation (high energy particles). There will be a cylindrical aluminium alloy or stainless steal support inside to hold it. The total weight is about 11-12 metric tons.

The main problem is how to manufacture such big part.

I came up with two ideas.

One is making small parts like tiles with can be bolted to the inner support. These will be easy to manufacture, and not so heavy in order to install them.

The other option is casting; melting the lead on a mould (using the support as part of the mould would be ideal).

Apart from the lead we can also use tungsten for the teeth section since it is not so soft.

What do you think? How would you build this part?

thanks
regards,

 

[dvd]

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.

 

[tbuelna]

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.

 

[RolMec]

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.

 

[thaidavid40]

@drodrig,
Try the following people for ideas, and casting capability:

http://www.pittslittle.com/

Good luck,
Dave

Thaidavid

 

[drodrig]

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

 

[tbuelna]

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

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

 

[racookpe1978]

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.

 

[drodrig]

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,

 

[racookpe1978]

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?)

 

[drodrig]

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,