40 replies to this topic

[dr thrust]

digger, would you care to elaborate on the design of your rammers so we can all benefit from your knowhow, i to would like to try them

Edited by chris m, 02 June 2009 - 05:19 PM.

[digger]

digger, would you care to elaborate on the design of your rammers so we can all benefit from your knowhow, i to would like to try them

I will put up a drawing on the rocket tools thread tomorrow night when I get a chance. They are nothing special they are just effectively weaker than the shell with a path for the gasses to escape.

[digger]

iv bolted the press to the floor and the 1/2 inch think 300mm by 300mm just a bit of scrap metal i found lieing around (do you think its a bit of a over kill being 1/2" thick ? whats the minium i can get away with ?

what are clam shells (could you post a pic of these as sounds intresting)

Look at this post

Nothing wrong with overkill on safety. 300mm x 300mm could be a bit small though depending on a number of factors.

Edited by digger, 02 June 2009 - 07:22 PM.

[starseeker]

thank you all for your help on this subject. i decided though i may only use 2 ton to do my bp at the moment, I seem to outgrow everything i buy. so i decided to get a 10 ton press with a gauge

came today, though I have to fit a blast shield, I'm still nervous like hell with that amount of pressure on the bp. But ill get used to it.

I remember the 1st time I used my ball mill with bp just thinking of the chances of it self igniting. Now i don't even give it a second thought

Would you let us know where you obtained your press from and how much?

[Bonny]

my original idea of using 1/2" think mild steel blast shield is to heavy for my press so i have decided to use lexon plastic but im unsure on the thickness.

thickest I have found so far is 12mm does anyone think this would be to thin for the job?

12mm Should be fine. I use 1/2" (12.7mm (?)) lexan on mine. If you are still worried about it, you could always double up on the 12mm or maybe put a steel grid over top of teh shield as extra re-enforcement.

[pyrotechnist]

If your device is going to explode under the pressure no amount of lexan will save your hands, your stuffed. It is the same with these blast walls around firework huts, they will do jack when a large quantity goes off cleaning the area cleaner than a baby's bottom. I just dont see how a piece of plastic will stop metal shrapnel, pieces of the press and gasses from hitting you. The safest method will be to control it via remote at a safe distance though not many of us can do such a thing.

Edited by pyrotechnist, 21 June 2009 - 01:49 PM.

[digger]

If your device is going to explode under the pressure no amount of lexan will save your hands, your stuffed. It is the same with these blast walls around firework huts, they will do jack when a large quantity goes off cleaning the area cleaner than a baby's bottom. I just dont see how a piece of plastic will stop metal shrapnel, pieces of the press and gasses from hitting you. The safest method will be to control it via remote at a safe distance though not many of us can do such a thing.

mmmm There are design codes especially designed for explosive environments. They work perfectly well. It is very possible to design blast shields to protect yourself. Clearly the shield will only protect you from the incident for which it was designed. Hence the reason why large quantities are not used (unless designed for), blast walls, frangible ends etc etc.

Where I work we have many buildings designed to ATEX zone 1 and many vessels designed to ATEX zone 0. The safety measures employed will definitely stop a vessel rupturing or a building being blown up (although I may not want to be at ground zero if there was an explosion).

[Pretty green flames]

my original idea of using 1/2" think mild steel blast shield is to heavy for my press so i have decided to use lexon plastic but im unsure on the thickness.

thickest I have found so far is 12mm does anyone think this would be to thin for the job?

Could aswell use a thick wooden (Oak, beech) shield with a vertical slot cut in the middle for monitoring the pressing procedure, then put, on the inside, a nice thick layer of lexan over the wood as to prevent any stuff coming in through the slot. May sound a bit overkill, but I'd rather have this between me and a cake of powder beeing pressed.

[pyrotechnist]

Do you work at a pyro company digger? I just don't see how a shield will protect someone from the forces of a super confined blast like a firework under that much pressure, what about the hydraulic rupturing from the blast to? I remember seeing video of ISO containers being filled with pyro material and the blasts where immense, one was also covered in earth but the end result looks like no earth was used nor was a container put there. Its good to have some protection but no one can guarantee there lifes on it.

[Richard H]

Safety screens can and do work. The screen serves to slow and deflect the fragments of an explosion. it redirects flame and gases away from the operator, who will be themselves wearing PPE. There is a vast difference between an ISO container and a cardboard tube in a press. There have been countless accidents involving presses. Operators have been saved thanks to the presence of safety screens and protective barriers. A brief search of EIDAS will return many examples.

[digger]

Do you work at a pyro company digger? I just don't see how a shield will protect someone from the forces of a super confined blast like a firework under that much pressure, what about the hydraulic rupturing from the blast to? I remember seeing video of ISO containers being filled with pyro material and the blasts where immense, one was also covered in earth but the end result looks like no earth was used nor was a container put there. Its good to have some protection but no one can guarantee there lifes on it.

Yep I have seen the videos. It has to be said though they are for slightly higher quantities of material between 5000KG and 20000KG NEQ. Don't forget the waterfall composition is basically flash powder!!

In this instance we are talking of less than 100 grams

Yes you have to account for a confined material

If you want to calculate the worst case explosion from this it is possible if you know the energy contained in the composition and estimated burn time (we are talking BP so deflagration not detonation) and you know the material properties of the containment so you can calculate the bursting pressure. From this you can calculate the worst case momentum for the case or fragments and check to see if the energy from these is capable of penetrating your shield (again knowing the material properties of your shield material).

Don't forget if the case bursting pressure is far higher than the relief pressure on the safety valve on the press then there is a good chance the net effect will be to eject the rammer and not burst the case.

Sounds simple eh, well maybe not, it would be a pretty involved calculation in which you would have to take account of all sorts of possibilities. Or you could just model it on an FEM DEM package (which we have at work).

To answer your question no I do not work in the pyro industry in my day job. I am a chemical engineer so we deal will chemical plant, however we deal with explosive mixtures of chemicals and the quantities are far higher than you will be experimenting with in your shed. I have witnessed a hydrogen explosion in a pilot plant reactor. There was a loud bump followed by a rumble as the excess pressure was ejected to a safe place (Still an unnerving experience though).

[Arthur Brown]

The release of those container vids was extreme. The vids are extreme! effectively each of them is a firework with 5+ tonnes NEQ over confined with steel.

You should not be working with that much compound, you couldn't lift 5000kilos in one hand, not even nearly!

A blast screen may not stop a blast, but it should stop the blast hitting you by deflecting it away from you