12 replies to this topic

[Atom Fireworks]

Hi peeps,

I have not done much research into this however i am yet to find actual proof of mortar tube degredation. Basically having set up my own small display company I am looking at safety, obviously this is the main priority.

What I want to know is after how many shells, or how long a tube is used does it become unsafe and at risk from the lift rupturiong the tube and resulting in a shell on the ground.

I know we have safety distances in place to lessen the chance of anyone being injured in such an event, however I want to know when my tubes are due for renwal.

Is there any data out there thats been carried out to determine this? There are obviously loads and loads of variables ect.. but as a base line i was thinking of buying two tubes from the same supplier of the same size. Keeping one brand new and firing X ammount of shells from the other. Then testing them both via a three point bend test with a fast head speed. ( i word for a materials testing company Exova) so i have access to the kit and the expertese.

From these tests we can determin or hopefully determine a % decrease of flexural strength along a lateral plain, it opens up a massive can of worms with reards to where on the tube the samples are taken from and testing the base of the tube where the wall is bonded ect........ I dont have the time to be going into massive detail with it just after an idea of how much strength they loose over X ammount of shells.

You also get influences from the residue so i could have some FTIR tests done to determing that degridation aswell however only if I have the time and the info isnt allready out there?

What do you guys think?

Jay

[a_bab]

Depending on the cardboard quality, 10-100 shells are said to be the max recomended number for a cardboard mortar. As the time passes, some of the paper unwraps inside. This could be a problem (there's a case of a truck full of cardboard mortars, that caught fire because of a glowing ember + air draft cased by the truck moving)

Better invest in some HDPE mortars as they will last much longer.

[Atom Fireworks]

Depending on the cardboard quality, 10-100 shells are said to be the max recomended number for a cardboard mortar. As the time passes, some of the paper unwraps inside. This could be a problem (there's a case of a truck full of cardboard mortars, that caught fire because of a glowing ember + air draft cased by the truck moving)

Better invest in some HDPE mortars as they will last much longer.

Sorry I meant GRP tubes, should have made it clearer oops. Ime not a fan of card tubes anyhow and HDPE is abit on the heavy side.

Jay

[Atom Fireworks]

I thought they would last a while but you are definatley right, massivly varies on how much care has been taken of them and where they have been stored.

[Arthur Brown]

Trucking and storage probably cause more damage than firing shells in typical small businesses. In fixed show installs (Disney etc) obviously it's different.

[Karl]

It's one of those questions with a million variables all which would differ the outcome.

I know what the tell-tale sign that cardboard tubes need replacing but what about GRP?

[scjb]

Some work on this has been published in the Journal of Pyrotechnics (first one that came up on my search was Fischer's "A Practical Performance Testing Protocol for Fireworks Mortar Tubes" (JPyro, Issue 20, 2004, pp51-54)). Might be worth a pop over to www.jpyro.com and having a look through the archive.

[Atom Fireworks]

It's one of those questions with a million variables all which would differ the outcome.

I know what the tell-tale sign that cardboard tubes need replacing but what about GRP?

I asked our GRP expert here at work what would be a good way to get an idea of the condition of the tube. He reckons simply look for cracking or " spider webbing", basically white lines appearing in the tube, thats probably the easiest way to check however obviously its not so easy to to see this on the inner wall covered in black residue!

Jay

[Mumbles]

There are two things we tend to look for with GRP mortars. The first is obviously internal or external fraying of the mortars. This is generally a good hint they are nearing the end of their lives. The other thing I look for is fading of the color of the mortar. This is generally due to UV light if they are stored out doors, though they will fade naturally over time it seems. Faded mortars seem more prone to failing. Most of the mortars I've seen fail are due to poorly constructed shells, or shells of an inappropriate mass. It's rare that I've seen one fail due to mortar fatigue even with repeated firings.

With HDPE I keep on eye on the plug. Make sure it's not cracked, and the screws are not being torn out of the plastic. I've been told they are a bit less robust with regard to repeated firings. I guess it makes sense being black and thicker that they'd hold on to heat a little better. I've only seen one or two fail with normal use, and that was generally a cracked plug. This just results in a low break usually. With steel guns, well I've only seen those fail due to shell catastrophe.

[Malcolm Smith]

You also get influences from the residue so I could have some FTIR tests done to determine that degradation as well however only if I have the time and the info isn't already out there?

How many wash out the residues as I do?

I've had several fibreglass mortars leaking water from porus areas after less than 20 shots.

I've seen crazing and delamination

Yes, they are lighter than HDPE, but look at their wall thickness.

This from Vulcan:- The usage life of mortar glass mortar tubes depend on how they are maintained and used, and how often they are being used. They can last a few years but you do need to keep a regular check on them to make sure they are still in good condition. Usage can range from average of 12 times to over 20 times.

And if the manufacturers specify 12 - 20 shots, what defence will you be able to offer to the H&SE in the event of an accident if you have not serial numbered your tubes and logged their use?


I have no faith in the longevity of this semi-brittle material after exposure to the percussive extension force of shell lifts, especially in the larger sizes.

[Atom Fireworks]

How many wash out the residues as I do?

I've had several fibreglass mortars leaking water from porus areas after less than 20 shots.

I've seen crazing and delamination

Yes, they are lighter than HDPE, but look at their wall thickness.

This from Vulcan:- The usage life of mortar glass mortar tubes depend on how they are maintained and used, and how often they are being used. They can last a few years but you do need to keep a regular check on them to make sure they are still in good condition. Usage can range from average of 12 times to over 20 times.

And if the manufacturers specify 12 - 20 shots, what defence will you be able to offer to the H&SE in the event of an accident if you have not serial numbered your tubes and logged their use?


I have no faith in the longevity of this semi-brittle material after exposure to the percussive extension force of shell lifts, especially in the larger sizes.

I totally agree with you malcome, i would myself prefer HDPE not only because its allot more durable but also in the event on a flower put it will not come apart into lots of smaller projectiles, it will remain as mostly 1 object although torn open ect.... its just the weight issue, when you consider not just a couple of racks but on larger shows where you may have 50 racks it becomes and issue transporting the weight.



Jay

[Karl Mitchell-Shead]

Trouble is there is so much variety in quality of tubes out there and unlimited varying factors for example Tube wall thickness, bung depth, lip or no lip, type of resin used, type of glass fibre, winding technique, the list goes on and on. Pyroquip tubes are thick, heavy duty and clearly meant to last, MLE tubes seem thinner, lighter and not so hardy. I reckon you'll have to tun a load of tests for each batch or type you own?