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Mortar Rack Design


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#16 Arthur Brown

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Posted 15 May 2009 - 07:03 PM

All the racks to 6 inch that I have ever seen were timber, a single row of boxed tubes. They all had a fastening on the end for stake fastening or assembling an array with side plates.

I have seen pics of steel racks with a matrix of tubes supported, but usually for larger tubes where weight of timber is greater, I've never seen a real one though.
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#17 Guest_PyroPDC_*

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Posted 21 May 2009 - 09:42 PM

thank you for all the advice so far. iv been told by my welder it will cost considerately less and weigh less if i got rid of the 50mm gap between each mortar

from what i read a gap of 1/2 the diameter of the mortar showed it was 90% less chance to damaging other mortars around it in a mortar failure) but is this just being to safe.

should i leave a gap or not (im not one for saving money over safety but iv seen so many mortar designs without any gap it cant be that bad.)

#18 Arthur Brown

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Posted 21 May 2009 - 10:34 PM

If you have an insurer I'd certainly run designs as fundamental as a mortar rack by them before you construct anything. Your insurer has the power to say yes or no to insuring you based on how you work. Uninsured is out of business.
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#19 Spyrotechnics

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Posted 22 May 2009 - 07:58 AM

I don't think you will get an insurance company to "approve" a design..

however

but is this just being to safe.

- isn't that what should be paramount in a mortar rack design?

Edited by Starsky72, 22 May 2009 - 08:00 AM.


#20 phildunford

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Posted 22 May 2009 - 08:27 AM

When you see what happens to a tube during a cato, my gut feeling is that half a tube diameter spacing will not really make things any safer. I have no experimental evidence for this however...
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#21 pyrotrev

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Posted 22 May 2009 - 12:05 PM

In the experiments I've done with 3" shells, a gap seems to make a useful improvement providing your tubes are good and strong. A tube tight up next to the one that popped got seriously damaged and if there was a shell in it I'm sure it would have been ignited. With just a 40mm gap, the tube was dented but not actually pierced.
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#22 mlepyro

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Posted 22 May 2009 - 06:17 PM

Hiya

We did extensive testing on our racks where the glass fibre tubes touch each other.

In a 6" rack, the tube with a shell in upside down would destroy the tube, and neighbouring tube, which in turn damaged the next tube, and so on... resulting in the whole rack failing almost instantly.

No shells, no danger...

In this situation us moving the tubes further apart would actually increase the danger, so there is a point between whereby damage can be done without damaging the shell enough to explode in the tube. Past this point the rack becomes safe again.

If I had the option - I'd rather all my shells explode together in a failure... to remove further risk.

We also found that our steel racks can take the force of all 8 6" tubes exploding, you could even use the rack again if you really had to, but of course you wouldn't.

Mat
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www.mlepyro.co.uk www.firebywire.co.uk

#23 Richard H

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Posted 22 May 2009 - 07:59 PM

A different perspective, thanks for adding your thoughts Mat. I find these discussions extremely interesting given recent accidents in the UK.

#24 pyrotrev

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Posted 22 May 2009 - 08:26 PM

The other thing to consider is that when using wooden racks, spacing tubes seems to somewhat reduce the likelyhood of the rack coming apart and tubes being scattered, hence it has to be a good thing. Of course a better cure for this is to use metal racks!
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#25 Guest_PyroPDC_*

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Posted 23 May 2009 - 03:45 PM

does the size of the shell make it more likely of a flowerpot damaging the mortar eg. would a 3" shell less likely damage a mortar than a 4" shell.


i think if i was making the rack out of wood, I would definitely space them. But as Steel i think i could get away with it as mat says its better off damaging all off in one go including the shell I suppose if i was really worried i could just make smaller racks so instead of 4x4 mortars with spaces I could do 3x3 mortars without spaces that way worse case only 9 would go off in one go.

Edited by PyroPDC, 23 May 2009 - 03:46 PM.


#26 Arthur Brown

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Posted 23 May 2009 - 03:57 PM

One reason why timber racks are still used is the versatility that they can offer.

I have assisted with shows at a nice venue where the firing site is a 100 yard walk through a single personnel gate. The hand cart just goes through, then you can pass the load through.

If you build racks bigger than you can lift with one hand, then you need power tools on the firing site. If you make big steel racks then you may need truck access and possibly a hiab.

If you are firing off big concrete flats like docksides big things and cranes are part of the job. If you are across the lawns at a nice hotel and they don't let the truck round then with big racks you are stuck.
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#27 mlepyro

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Posted 24 May 2009 - 10:24 AM

In our tests normal shells didn't often damage 3" tubes but most of the time did damage 4".

Metal racks are more convenient than wooden ones in my opinion. In terms of carrying them, it requires 2 people to carry any of our metal racks - but would take a minimum of 2 trips to carry the same number tubes in wooden versions.

Some disadvantages of metal racks...
1) heavy
2) you can hurt yourself with them if you trap your hands when stacking without gloves on
3) very expensive compared to wood

Mat
MLE Pyrotechnics Limited
www.mlepyro.co.uk www.firebywire.co.uk

#28 pyrotrev

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Posted 24 May 2009 - 12:37 PM

Metal racks don't really have to be much heavier than wooden ones, particularly if you make them of high strength aluminium alloy rather than steel. But cheap they are certainly not!
Trying to do something very beautiful but very dangerous very safely....

#29 mlepyro

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Posted 24 May 2009 - 05:07 PM

We blew aluminium out, not so much because of the price of material, but more because of the time it takes to weld it.

There is also something nice about them being heavy... in that they gain support from being able to freestand (not that I'd encourage that!).

Mat
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#30 Arthur Brown

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Posted 24 May 2009 - 06:24 PM

Mat
Is there a sketch or picture of the steel racks available in public webspace? The one design I've seen was like a milk crate but 6ft x 6ft x 4ft high. It had about 80 - 100 tubes inside and was a challenge to assemble form barely luggable parts.
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Keep mannequins and watermelons away from fireworks..they always get hurt..




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