42 replies to this topic

[Frozentech]

I've just pressed my first BP cakes in a similar way, I havent got a huge press though I've used a 10 inch "G-Clamp" in a bench vice with a long steel tube for a lever.

It doesn't get up to the same sort of pressures as a hydraulic jack, but seems to compress the BP quite well into a homogenous block that can be pushed out of the tube once the pressure has been released.

I used a piece of 15mm marine ply as a blast shield which had the disadvantage of not allowing me to see the pressing as I pressed.

Having read the article above about blast shields I have a coupel of questions:
Anyone know an easy source of lexan in the uk?

Anyone actually had or heard of a BP cake ignitting becasue of the pressure?

Edit:

here's a link to a pic of my first pressings http://www.damian-fe...yro/bpcakes.jpg

Here's a possibility... use two layers this thickness and it will withstand most anything an amateur pyrotechnician would be likely to work with:

http://cgi.ebay.co.u...1QQcmdZViewItem

[r.burgy]

im having a problem with corning my lift powder.the bp is good quality.if i rice it ---it works great,but if i press and corn it ---it barely lifts.when i press it as per passfire i corn immediatlyand it more less crumbles.
im corning in a bowl with a stick.is it possible that its not pressed enough?also the the grains are alot smaller.perhaps this is the problem.sorry if this is posted elsewhere,all that i found was the method---no help
anybody have this problem???
thanks

[Frozentech]

im having a problem with corning my lift powder.the bp is good quality.if i rice it ---it works great,but if i press and corn it ---it barely lifts.when i press it as per passfire i corn immediatlyand it more less crumbles.
im corning in a bowl with a stick.is it possible that its not pressed enough?also the the grains are alot smaller.perhaps this is the problem.sorry if this is posted elsewhere,all that i found was the method---no help
anybody have this problem???
thanks

You don't say how much pressure you are using to press the pucks with, nor your die size and volume of the charge, so it's hard to tell what exactly the problem is.

The only reason that Passfire mentions corning immediately after pressing is for use in a corning machine.

I press mine in small increments ( 4 heaping tablespoons ) in a 3" die, to 8,000 PSIG ( never bothered to work out the actual force on the powder ), and let them dry for at least 24-36 hours in low humidity for "immediate corning", otherwise let them dry for 5 or more days for complete hardening. They will 'clink' together like china when dry.

I very much doubt you will be able to use a bowl and a wood stick to break them up, unless the bowl is a large steel one, and the stick is a baseball bat ! I put the pucks between layers of newspaper on a concrete floor and crush them with a stainless steel rolling pin. It takes all my weight bearing down to do it. I screen the crushed BP after each 'crush' to seperate all the 10-20 mesh grains that I use for lift. It can take an hour to corn 200 grams by hand this way, but it sure works good !

[Phoenix]

To give you some idea of the pressure you need, I used to use a 1-1/2 ton jack with a 40mm die, and now use a 5 tonne jack on a 70mm die. The different "ton(ne)s", BTW, are intentional.

I press the powder very slightly dampened - not enough that any water would runs out when it's in the press, but enough to help it hold together a little. Whilst the pressure I use probably doesn't produce grains as dense and as commercial BP (which is intended for use in firearms), I have found it to quite adequate for fireworks (including roman candles).

[r.burgy]

To give you some idea of the pressure you need, I used to use a 1-1/2 ton jack with a 40mm die, and now use a 5 tonne jack on a 70mm die. The different "ton(ne)s", BTW, are intentional.

I press the powder very slightly dampened - not enough that any water would runs out when it's in the press, but enough to help it hold together a little. Whilst the pressure I use probably doesn't produce grains as dense and as commercial BP (which is intended for use in firearms), I have found it to quite adequate for fireworks (including roman candles).

with the info you guys gave me makes alot better sense.my bottle jack is 12 tons. more than enough for my 3 in. die.ill try again and let dry for days before crushing.i think this will make an immense difference. as always thank you very much.

[alany]

I press my pucks completely dry now days.

I used to a true-believer in the dampened powder method. I still am, I did the experiments to prove to myself that dampened powder is a bit faster. However I've since been able to make much faster meal powder using better charcoals, with which the difference after dampening is not significant enough to worry about.

Pressing them dry also means you can corn immediately, which is kind of handy.

I don't use much lift, I am more of a rocket guy, so I use only a 2" comet pump to press my BP. I just press the hell out of it as hard as the press can muster. Then I let it dwell for a few minutes before tightening up the press one last time. I then press-out the puck using an ejection sleve.

About the only problem with this method is BP sometimes flows up the side of the pump and jams it easily. I have to press it out and clean the bore walls. Under enormous pressures after sufficient milling the Sulfur seems to be all the binder you need.

[Phoenix]

That's reminded me of a few thing's I hadn't mentioned; I actually corn mine whilst it's still damp(ish) straight out of the press. I haven't had too much trouble with it breaking up into powder. I usually aim for mostly 4-6mm grains, as that is what I use most of, and then break it into smaller sizes once it's dry, if I need more finer material.

The dwell time that Alan mentioned is definitely important - pump the jack as hard as you dare, and then leave it for a few minutes and give it a few more pumps - the powder will probably compress some more after a while.

One other thing, which is probably more relevant to pressing comets, is that if you let the pressure off suddenly the comet or puck is more likely to crack. Obviously in the case of a BP puck you're going to smash it up anyway, but a sudden release of pressure may contribute some weakness to the grains. This is just me waffling really, but it can?t hurt to let the pressure down gradually anyway.

[EnigmaticBiker]

I've been meaning to mention this for months.

Last year I made some corned BP with 0.5% dextrin (I wanted to use the fines to roll stars).

Ball milled for 5 hours with 4% water and corned using two thick dowels inside a PVC pipe; Compressed using a screw jack until the pipe distorted slightly .

The resulting "puck" was then dried over silica gel. It was almost glassy in appearance and a blow with a wooden pickaxe handle only chipped it!

The resulting 10-30 mesh grains were then used in a few replica rip-raps, which when lit went with a series of cracks as per usual.

On examining one after, it felt full, the larger grains hadn't burnt?! Amazing, despite being propelled across the garden by the force, half the BP was still there. Only the finer grains had gone.

[ProfHawking]

I would like to ask peoples opinions on BP density and pressing techniques.
I had a basic press for a while, but I broke it last year and havent had chance to fix it until now. I have some lovely thick aluminium plates, instead of the wood ones that snapped. I could never get much pressure without snapping the wood, but now i can, i want to fine tune it.

What are the recommended densities people use? Dan Williams notes down 1.7g/cm³, is this the standard, or does anyone aim for something else?
And if that is the case i just want to check that my calculations are correct;
My powder die has an internal diameter of 7cm, so an area of 38.48cm² ...
That would mean then for a standard load of 100g of powder to get to 1.7g/cm³, i need a volume of 58.82cm³.
This gives me a thickness of the puck to be Height=Volume/Area, 58.82/38.48 = 1.53cm (edit - Right way round now i hope!)
Have I worked that work out correctly?

So the next question is about moisture. Again, the standard seems to be 4% weight of water to the dry powder. Does adding more than this then allowing extra drying time have any adverse effects?
Just re-read through the passfire article, and its suggesting 10% there. Thats quite a difference. I think i'll try one of each maybe

Edited by ProfHawking, 25 May 2007 - 06:50 PM.

[Bonny]

What are the recommended densities people use? Dan Williams notes down 1.7g/cm³, is this the standard, or does anyone aim for something else?
And if that is the case i just want to check that my calculations are correct;
My powder die has an internal diameter of 7cm, so an area of 38.48cm² ...
That would mean then for a standard load of 100g of powder to get to 1.7g/cm³, i need a volume of 58.8cm³.
This gives me a thickness of the puck to be 38.48/58.8 = 0.65cm
Have I worked that work out correctly?

So the next question is about moisture. Again, the standard seems to be 4% weight of water to the dry powder. Does adding more than this then allowing extra drying time have any adverse effects?
[/quote]
I've never bothered to calculate the density of my lift powder...but I might now as I am curious. I press about 150g-200g pucks in a pc of 3"ID ABS pipe re-enforced with hose clamps. My press uses a 12 ton bottle jack and I max it out, followed by another pump on the handle about 10 minutes later. I use about 8% water, as I read somewhere that old powder mills used 8-12%. I do get a few drops of water coming out, but my lift seems to perform well once sieved to 10-20 mesh. I do this out of the city on weekends, so I usually allow at least 1 week to dry.

[mike_smith919]

Hi all,

I was reading this thread and was wondering how people make their die's?

Also, I have seen mention of a corning machine?! Can someone please explain how this works?

Cheers,

Mike.

[Bonny]

Hi all,

I was reading this thread and was wondering how people make their die's?

Also, I have seen mention of a corning machine?! Can someone please explain how this works?

Cheers,

Mike.

A lot of people make their dies out of a pc of ABS or PVC pipe re-enforced with hose clamps, and plastic pistons, made from solid PVC, UHMW (polyethylene), or nylon. The powder is pressed between the pisons.

As for the corning machine there are several methods. One of which turns like a ball mill, but the jar has a screen (probably around 4 mesh) mounted on part of one side (not end). The pcs of BP pucks are crushed by large wood/ceramic/ (maybe brass) balls and the powder falls through the screen once it is small enough.
There are also corning machines that crush the BP between rollers.

[Arthur Brown]

Commercial BP is pressed into cakes about 12 inches square and half an inch thick. The pressed BP is placed on an alloy plate then a plate is put on top, more BP then another plate, and so on.... The stack of plates with powder is pressed as one in a huge press and the flat slabs of pressed powder are removed. The pressed PB is then passed between rollers to break it into pieces of ever finer size. The graded powder is then sorted by size.