Hi all,
Just been doing some testing on my brand spanking new card mortar tubes from Essex Tubes. Upon inserting a 3" shell upside down into 3" tube, I was hoping to test my racks. However, rather than the tube rupruting, the plug actually blew out of the bottom, causing my rack to pretty much blow apart at the bottom.
Is this common for card tubes? I must say I was surprised when it did it, as I had hoped it would be part of the manufacturer's tests to ensure the plugs wouldn't blow out???
It makes it quite hard for me to design racks to withstand a shell malfunction, when the strongest part of the tube doesn't seem to hold!
Many thanks for anyone's thoughts/input.
Mark
Card Mortars - Plugs?
Started by FaithlessRock, Jun 27 2010 05:04 PM
5 replies to this topic
#1
FaithlessRock
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#2
rocketpro
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Posted 27 June 2010 - 05:18 PM
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Edited by rocketpro, 06 August 2010 - 09:33 AM.
Who tests the tester.
#3
phildunford
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Posted 28 June 2010 - 08:14 AM
As it's pretty much a requirement of many insurers to undertake this kind of destructive testing of racks, I would find this a bit worrying. In a way, I suppose it's a failure of the system in the least destructive way, but it would suggest the plug fixing is not very good. Was it glued and nailed?
Teaching moft plainly, and withall moft exactly, the composing of all manner of fire-works for tryumph and recreation (John Bate 1635)
thegreenman
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#4
Mortartube
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Posted 28 June 2010 - 10:03 AM
In my experience it's the most common type of failure, although if used correctly it is a rarity. The older the tube the more likely this is in normal use as the plug takes ther brunt of the lifting force.
You should limit your card mortars to a particular number of firings before replacing them, this can only be established by keeping a record of how many firings you have made and regular inspection of the tubes. You will probably see the holes where the nails go through begin to elongate a bit before the plug blows out in normal use.
You should limit your card mortars to a particular number of firings before replacing them, this can only be established by keeping a record of how many firings you have made and regular inspection of the tubes. You will probably see the holes where the nails go through begin to elongate a bit before the plug blows out in normal use.
Organisation is a wonderful trait in others
#5
FaithlessRock
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Posted 28 June 2010 - 10:52 AM
The plugs are both nailed and gued, so I'm a bit worried too!
The good thing is it did at least contain the explosion within the tube and the neighbouring tubes remained intact, even though the rack didn't.
I think I need to modify the racks so that the horizontal along the bottom does not come up higher than the top of the plugs. That way the tube will blow as it did but not take out the rack with it!
The good thing is it did at least contain the explosion within the tube and the neighbouring tubes remained intact, even though the rack didn't.
I think I need to modify the racks so that the horizontal along the bottom does not come up higher than the top of the plugs. That way the tube will blow as it did but not take out the rack with it!
#6
BrightStar
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Posted 29 June 2010 - 07:52 PM
A few quick tips...
When I've had card mortars fail, it's often because the layers of the cardboard become 'delaminated', reducing the hold of the glue and allowing the plug to come loose. Short staples / screws help a bit but tend to bend downwards when this happens, losing their grip.
One thing that does help is to put a long bolt or length of studding through the entire diameter of the tube and the base, from one side to the other. It's also worth using quite long plugs - pretty much as long as the mortar ID.
Re the racks, one technique is to use good strong planks for the top side rails but chipboard or MDF for the lower side rails. The chipboard tends to blow out in chunks next to the gun, leaving the rest of the rack intact, rather than splitting along its entire length... With substantial end-pieces (sometimes reinforced with an extra layer of plywood in case of splitting), you should be able to keep the rack reasonably well together (except perhaps with large salutes...).
When I've had card mortars fail, it's often because the layers of the cardboard become 'delaminated', reducing the hold of the glue and allowing the plug to come loose. Short staples / screws help a bit but tend to bend downwards when this happens, losing their grip.
One thing that does help is to put a long bolt or length of studding through the entire diameter of the tube and the base, from one side to the other. It's also worth using quite long plugs - pretty much as long as the mortar ID.
Re the racks, one technique is to use good strong planks for the top side rails but chipboard or MDF for the lower side rails. The chipboard tends to blow out in chunks next to the gun, leaving the rest of the rack intact, rather than splitting along its entire length... With substantial end-pieces (sometimes reinforced with an extra layer of plywood in case of splitting), you should be able to keep the rack reasonably well together (except perhaps with large salutes...).
Edited by BrightStar, 29 June 2010 - 07:52 PM.
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