25 replies to this topic

[NUKE]

Hi. I was thinking about constructing aluminium mortar tubes for 2.5" and 4" shells.

What i want to ask is: Are they really safe? I know that they use it in firework industries, but are those tubes safe?

Also, do the use anything else than simple aluminium? Or are they created with a special design?

Thanks a lot:)

[Arthur Brown]

In the UK metal mortars are NOT used, probably not specifically illegal, but totally uninsurable. So not for professional use.

In the USA some people do use metal mortars especially for multibreak shells. The Maltese use lots of metal mortars.

However! There are NO professionally made metal mortars so you must make your own or get them made, and then come all the questions about the alloy and the fabrication techniques needed for a reliably robust mortar.

Aluminium may be too soft some high performance aluminium alloys may suit your needs, but they need special manufacturing techniques

Cast Iron is a killer, if it breaks it becomes shrapnel.

A ductile drawn seamless steel tube may well be technically acceptable, BUT you will need to be totally sure that the tube is a known good alloy and well plugged and welded.

In reality paper is cheap and if it fails it shreds into confetti and makes mess not damage
GRP is easy to buy and if it fails it usually makes big pieces that don't fly far.
HDPE should be good as it can take some overload by stretching before it bursts but you may have to put your own plugs in which must be done carefully.

DIY metal tubes are in my opinion a certain NO NO.

[phildunford]

In the UK metal mortars are NOT used,

Not quite true - I know at least one professional display operator who uses them and swears by them.

However if only for weight and cost I would personally avoid them...

GRP must now be the most popular by far but they are only good for 20 shots according to the Chinese makers - although most people seem to think they will last for ever.

[PyroCreationZ]

Not quite true - I know at least one professional display operator who uses them and swears by them.

However if only for weight and cost I would personally avoid them...

GRP must now be the most popular by far but they are only good for 20 shots according to the Chinese makers - although most people seem to think they will last for ever.

GRP is the same as fiberglass I assume?
20? I've heard people in USA who have used them hundreds of shots and they were still usable though losing a bit of strength over time.
I certainly won't throw mine out after 20 shots... I also understand they don't last forever and inspection after every use is a must.

As for metal tubes, yes they are used even by professionals but I think I've once read about them and they're not made out of aluminum due to their "weakness" (not sure though).
From what I've read I understand they are made out of steel casted into a mold so they wouldn't contain a weld (resulting in a strong, solid pipe).
These would last longer but they also weigh much more then fiberglass/GRP.

Edited by PyroCreationZ, 26 June 2010 - 09:42 PM.

[digger]

From what I've read I understand they are made out of steel casted into a mold so they wouldn't contain a weld (resulting in a strong, solid pipe).
These would last longer but they also weigh much more then fiberglass/GRP.

Cast steel is not as strong as forged steel, cold drawn seamless is stronger by far than cast. Weld efficiencies of 1 are possible.

The problem with aluminium is fatigue. The life span of aluminium will be short with failure unpredictable (without fancy modeling). Steel will also eventually fail from fatigue, but the number of cycles will probably be more than a mortar will ever experience.

This is not an endorsement of steel mortars in any way.

Do the maths for yourself and make your choice.

[NUKE]

Thank you very much for your replies. I also dont like metal tubes but is it okay to have a 4" tube from paper?

Fiberglass tubes are too expensive to find here...

[phildunford]

Paper tubes are common in 2 3 & 4 inch, less so in larger sizes. The ones Brocks used to supply with their shells, they claimed to be good for 10 shots. I'm certainly happy firing these sizes from paper.

As far as fibreglass go, I'm just reporting what the Chinese Manufacturers say about their life. They may well be covering their backs in case of failure. Generally by the time tubes get to firers, they have passed though several companies and original information is not available, but I have the figure of 20 from an importer who buys direct from the Chinese maker.

Certainly every tube should be carefully examined before you fire from it - even brand new ones...

[Potassium chlorate]

In Sweden professionals use metal mortars, though not of aluminium but steel. But some consider them dangerous, since they might break from a powerful burst, in which case the damage will be much worse than if a fiber glass or HDPE mortar breaks. They're also very heavy to handle.

But - if you own land of your own, you might fix a metal mortar in the ground permanently and just protect the muzzle of it with a bucket or something.

[NUKE]

nah...i dont

By the way, i have worked in a pyrotechnics company for a week and i was told that one day an iron 5" metal exploded and the guy ended in hospital and now has kinetic problems...The interesting is that the company that used such mortars was the one that made the 2004 Olympics fireworks but i think the accident happened before that...

[Potassium chlorate]

I think you better buy HDPE or fiberglass. They aren't that expensive and can be used over and over again.

[Arthur Brown]

Navies of the world use metal guns on warships! But the wall thickness approaches the bore at the breech. Also they are a high performance steel alloy. (Oh and they are heavy too!)

From a friend who has some steel mortars :-
3" - 19lbs -10 Kilos
4" - 25lbs -12 kilos
5" - 38lbs -18 K
6" - 45lbs -20 kilos

So a simgle mortar will weigh much more than you thought and a rack will need a crane!!

A 3" GRP mortar will weigh about 2 kilos!

I've seen a GRP mortar that burst -it remained as big orange pieces
I've seen a small alloy tube that was blown up from inside and basically it turned into tiny pieces of shrapnel and these passed through a bean tin like the pellets from a shotgun. I'm glad I was 50 metres away.

[digger]

A 3" GRP mortar will weigh about 2 kilos!

I put one of the thicker ones on the scales, it came in under 1kg.

[NUKE]

May i ask you something else...What is the standard diameters of tubes? Is there any chart?

For example i thought that 2.5" tubes should have an inner diameter of 63.5mm but i know found that are 58.5mm

I am a bit comfused...Beacause then i dont know what shells to use since i know that for example 2.5" shells are 57.2mm and are too big...

U know what i mean...

[Potassium chlorate]

That will work. A 2.5" needs extremely little pasting.

Edited by Pyroswede, 28 June 2010 - 02:47 PM.

[Arthur Brown]

OK weight! A three inch steel tube weighs about 10 kilos a three inch GRP tube weighs about 1 kilo by Digger's technology. So that's 9 kilos in favour of GRP.