28 replies to this topic

[phildunford]

Im not sure I fully understand some of the problem of construction phil (I guess its a bit difficult to explain in words without seeing them in pics

I'll try and post some pics sometime...

Why not get out your 'Blue Peter' kit and have a go? You will either see the problem - or maybe you will make the perfect cone and show how cack-handed I am!

[Mortartube]

I think it shows you in Weingart how to make a cone case. Can't recall as I can't find mine.

[crystal palace fireworks]

The case needs to be REALLY strong as the pressure increases a great deal as the composition burns down, owing to the ever increasing surface area.

Some of the really big cones have the last increment punched to ensure compression. I have literally seen the knuckle marks in the comp. Very odd but seems to work.

You cane use standard type round (not conical) rammers of ever increasing size, but you need to work out the increments very carefully and also put the inverted case in a conical mould to stop it being distorted. Probably the easiest way to do that is make a former for the case, so your cases are all the same size and then cover one in cling film and cast a mould around it from resin, reinforced plaster (Chopped fibreglass may help to hold the plaster together) or some other castable liquid.

Could the paper layered cone casings not be coated with a fibre glass matting and glue for strength? in other words;
is the problem with cone casings one of buckling due to internal combustion pressure?

Also, would it not be possible to compress cone shaped compositions in one go (but with paper disks to seperate different comps) if one had the tooling made for a arbour press?,..in other words the one lump piece is then transfered to a paper casing seperately with the bottom attached afterwards?

[Mortartube]

In my experience with commercially made large cones, it is often the bottom disc and maybe also an increment of composition that get blown out as the disc is the weakest point. It is easier for the composition to blow out if internal pressure builds too much as the composition is a tapered plug effectively and doesn't cling to the inner sides of the case as well as it would in a parallel wound tube.

[Mumbles]

To prevent the bottom from blowing out, Weingart recommends packing the comp by hand tamping with a dowel, then a layer of saw dust being placed in before the bottom disk. I went to look some thing up in regard to this. He describes rolling must as was described above. Conical wooden former. There was something about using 1/3 circle for paper, but lancaster describes the whole circle with a slit.

[crystal palace fireworks]

The small back street chinese work shops make there cardboard hemisphers with pre-cut & patterned round discs of brown paper + paste in a few layers. which is compressed via a spinning half-moon shape drill tool come hydraulic pressing machine into a former, the same machine then trims/cuts the edges in one go,...there is a film of it on youtube somewhere.

The large commercial cone making equipment is numerous & huge,(paper mill scale),..will have to search for this another time.

For those who have adapted there 10 tonne hydraulic garage presses at home to press comps, cone shape tooling will have to made or bought,....although the spinning action is not needed (infact it would make it difficult), as was mentioned elsewhere, the cone shape paper is made by cutting a wedge in a circle, then taped in place and layered & pasted as above.

To help increase the strength of the base of the cone, a 3 or 4 prong protruding square edge from a circle of ply could be used (its like a circle with a few outside square edges) , this then slots & twists into a `L` shape cut into the casing of the base of the cone, the gap is packed with glue/sawdust or plaster (might be possible to use cone again)

Damn,..I wished I had bought that benchtop plastic moulding machine that was on Ebay a few week ago for £120.

[CCH Concepts]

Have you ever made a injection moulding mould. They thought it was a good idea to have us make them in school, took for ever. If you wanted a 100mm cone. Now imagine 50 layers of 2mm steel with ever decreasing holds perfectly in like and them filed to give a consistent edge. Long.

[crystal palace fireworks]

Have you ever made a injection moulding mould. They thought it was a good idea to have us make them in school, took for ever. If you wanted a 100mm cone. Now imagine 50 layers of 2mm steel with ever decreasing holds perfectly in like and them filed to give a consistent edge. Long.

No Ive never made an injection moulding mould, don`t think I would attempt to with the methods you describe at your school,..as you imply,..too long a process unless you have the use of a lathe or furnace etc.

[Arthur Brown]

Your school sadly but clearly have NO IDEA how injection moulding tools work, or how they are made.

Cones get taller as they burn as the flame front enlarges, like a rocket the speed of the compound has to be matched to the strength of the casing.

[CCH Concepts]

Your school sadly but clearly have NO IDEA how injection moulding tools work, or how they are made.

probably not, sounds about right they would make us do it the hard way. ow and when i say school i am talking over 10 years ago. still one of the young'uns in the forum i know, but not a teenager lol

Edited by CCH Concepts, 23 November 2009 - 10:43 PM.

[portfire]

Injection moulding at school? Do you mean Vacuum Forming

[CCH Concepts]

no, defiantly injection molding. basically done with a glorified hot glue gun and thermo-set plastic instead of glue.

[MDH]

I do not follow conventional methods with cones. Typically I fill the bottom half of the cone with a clay or sand all the way to the bottom of the opening. It prevents the bottom from blowing out.

I make the cone itself by bending a thick cardboard (think cheap, there is still wood pulp it in) sheet sideways, the same way I produce toy rocket nozzles. I cut off the uneven bottom, which can be used to make firecrackers and other small products (another philosophy of mine: waste nothing). The actual tube is treated with tartrates, carbonates, dextrin and other binders to prevent it from being corroded or eaten away by the flame. The cone thickness is usually 4mm or thicker - definitely not your standard 10 second fountain tube.

The actual cone composition is a mixture of 5:4:1 or 6:3:1 infused with a little bit of glitter or spark additive. I rarely use colour stars in cones, even commercial cones appear to have trouble making them successfully leave the tube still intact half of the time. When I'm using the fabulous calcium sulfate as a fire retardant in the cardboard I simply do not use metal powers at all (they react with it).

[CCH Concepts]

another thread we were talking about fiber glass, what do people think of a fiber glass cone. could easily be made thick enough to coup with the pressure, but theres the issue of shrapnel if it Cato's. but would defiantly be alot easier.