Useful tube for DIY mortar?

[deer]

I got a cardboard core from plastic wrap spool and was wondering if it might be good idea save it for when I get into mortars or just use for whatever else?

 

The tube is 20" long, has I.D. exactly 3" and 5/8" wall thickness (seems parallel wound, but feels dense). I assume it could be used with 3" shells?

 

As a beginner (still trying to get my first rockets to fly), what difficulty level mortars and this size are? I mean if I still be doing just bigger rockets year or two later it's probably just a waste keeping this tube exclusively for mortar use.

 

How suitable it is for such conversion? Do you just glue and screw it to board, or dedicated mortar tubes have reinforcements and mounting terminals? I see commercial ones just being plugged up with wood. The economy wouldn't be big (in my case mostly shipping prices), but still it would be nice to have it at hand if it's suitable, instead of having to hunt it down.

 

Picture of said tube:

[Arthur]

From the picture it looks rather like my card 3" mortars, which came from shrink wrap!

 

I have a source of resin so my tubes are plugged with about 2" of polyester resin (50% DRY sharp sand for filler) -just gaffer tape over the bottom and pour the resin in carefully. A paper coffee cup full does several. You can plug paper tubes by just pouring resin in. You CANNOT plug plastic tubes this way.

 

First time you use a tube use it from a good distance 50+ metres as a start

[nater]

Mortars require some type of solid plug which can resist the force of the shell lifting. Typically they are plugged with wood discs between 1/2 the ID of the mortar to 1 ID tall. You will also find mortars which are plugged with resin or were cast in one piece. Some single shot Chinese devices use rammed clay to form the plug, but this is not very durable in the long run.

 

Single mortars are often buried in the ground or sand buckets for safe firing. Depending on local laws and the AHJ (Fire Chief who approves a shoot) you might find mortars secured on the ground to single posts. Consumer sized mortars (~ 2" ID and smaller) come with a plastic or wood base and are intended to stand up on firm, level ground. It is a good idea to brace them with a rock, brick or something so they cannot tip over.

 

I would make a wood plug and screw it in to the mortar. I don't use a lot of resin, but Arthur's method sounds easy too. For firing, I would secure it to firm ground by strapping it to a stake.

 

3" shells are not too difficult to make. I would say they are an "advanced-beginner" project. Do you have a local club where you can get hands on instruction?

[pyrokid]

I'd like to add to the consensus opinion that that tube is worth saving. 3" shells are a lot of fun.

 

Something that many beginners might not consider is that smaller isn't always better with shell building. It can be quite difficult to get proper performance out of 1.75" shells, and many find that it is easier to start with 3 inch shells.

[ddewees]

Press a rocket motor out of it (in to it? ).

http://i1149.photobucket.com/albums/o588/SaltLakeAreaPyros/20150411_193505_zps9yasxqrd.jpg

Edited April 21, 2015 by ddewees

[rogeryermaw]

I was wondering the same. I have similar tubes I have been saving from work in case they were useful. Average # of shots such a tube is good for?

[FlaMtnBkr]

They can be used a lot. Especially if you coat/reinforce them to protect the paper and keep it from unraveling.

 

There is a way to make a very durable coating on the inside and one guy claims to have tubes 25 years old. Obviously you can't leave them outdoors.

 

If you want to treat them:

 

-glue down any loose paper

 

-rinse inside with saturated solution of calcium chloride. Allow to stand and dry as much as possible. Very hygroscopic so will remain damp (this is wanted)

 

-pour in a 25% solution of sodium silicate and rotate to cover everything and pour out and save for next tube. Most liquid silicate is 40% and about like syrup so will need to be diluted a little with water.

 

- This will form calcium silicate which is very durable. When dry rinse with water because there will also be residual sodium chloride.

 

-coat outside with linseed oil and turpentine or appropriate solvent 3:1. Can add 15% lampblack to make tubes black.

 

-let dry for at least 2 weeks for any residual water to evaporate.

 

I got this from someone else and have coated inside but not outside with oil. I used wood glue on outside and ends and they are still holding up years later.

 

I use a wood plug 1 ID glued in with wood glue and then 4 wood screws thru tube into plug.

[schroedinger]

For these i just drive some bolts through the wall about 1" over ground. Cover the botttom with paper tape and plaster (a cut off funnel sitting in the top of the tube really helps to not hit the walls.

After they are dry flush them with sodium silicate. No linseed oil on the outside, the oil is more expensive than a new mortar.

[deer]

Wow, thanks for all the detailed advices. The outside should be fine since it still has layers of plastic wrapping on it (unless they burn off).

I guess I should get a 3" shell then to see how well it fits. Still, all the shells I've seen in the pictures are much longer compared to their diameter, is L=20" enough for ID=3"? What problems or effects can this produce?

 

P.S. What exactly does a 3" shell mean - I'm assuming one that freely fits 3" ID mortar (incl. fuse and all of it's essential parts - lift charge, ropes and layers wrapped around shell casing)?

 

Once again, thanks for the tips.

[nater]

You are right that a 3" shell is sized to fit in a 3" mortar. Typically they are built using a 2.5" former for cylinder shells or similar size chipboard hemis for ball shells. Shells are then finished with paste wraps and spiking (for cylinders)

 

Each break in a cylinder shell is usually filled so it is as tall as it is wide. Different breaks can be stacked on top of each other as the shell is built which makes some shells get pretty tall. With the pattern of the spiking, the resemble salamis and you might hear a builder referring to his or her shell as such. I have seen shells tall enough the stick out of the mortar and they still function as intended.

[deer]

-rinse inside with saturated solution of calcium chloride. Allow to stand and dry as much as possible. Very hygroscopic so will remain damp (this is wanted)

 

Finally have some time to do that mortar, but got confused by this step. Do I do whatever it takes to dry it completely or some moisture is required to successfully apply sodium silicate?

 

I mean I could leave it for a day or two to stand freely, so it looks dry but still feels cold and soft to touch. Alternatively I could put it next to heater for a week or more to make it completely dry and hard and then proceed with next coat.

Edited November 7, 2015 by deer

[stix]

The tube has to be damp for the reaction to take place.

 

This link is possibly where the original info (on the web) regarding treating cardboard tubes comes from. As indicated, the treatment has been used and known of for years.

http://www.pyropage.com/Misc/cardboard.html

 

Treating Cardboard Mortars

 

One of the problems faced by pyrotechnicians is getting a reasonable life span out of their cardboard mortars. Myke Stanbridge documented this treatment which he claims will make cardboard tubes last 25 years or more. I'll report back in 2022 on whether it worked that well for me! Perhaps the cheapest, easiest and most effective treatment for paper mortar tubes is the following:

Clean out any debris, cobwebs, etc. Use PVA adhesive to stick down any 'flapping' edges.

 

Rinse each tube internally with a strong solution of calcium chloride in water. Allow your tubes to stand until they are just damp. Calcium chloride is rather hygroscopic and will not dry past remaining damp.

 

Using a 25% w/w solution of sodium silicate in water rinse each tube internally. Pour out the excess into your bucket and let the tubes dry open end up. There is a chemical reaction that produces tough insoluble calcium silicate in the structure of the paper. This hardens and binds the surface making it resistant to damage by abrasion and alkaline residues.

 

When dried give the tube a fresh water rinse to remove residual sodium chloride produced in the reaction and let dry open end up in a warm location.

 

Coat your tubes externally with a mixture of spirits of turpentine 1 part (pine spirit NOT mineral turps) and boiled linseed oil 3 parts. Add 15% lampblack to the mixture if you want black tubes. Leave the tubes to dry for about two weeks, open end up... Omit this step if the tubes are for immediate use or will form elements of a boxed mortar block...

Note: I'm still using tubes prepared like this around 25 years ago, and they still function perfectly! The method of treatment is very quick and cheap once you've got set up... You can treat a hundred tubes in an hour or so for around 10 cents per tube. Painting costs around a dollar per tube and is not as effective... Regards, Myke.

 

This page most recently updated on April 23, 1997

 

I found this a few years back and was intending to try the method for strengthening and fireproofing cardboard tubes for sugar rockets. I haven't got around to it yet. It looks like the tube will and needs to remain damp - which is what you want, then it's coated with the sodium silicate solution and the reaction takes place.

 

It will be good to see someone make this work successfully and report back. Good luck with it deer.

Edited November 8, 2015 by stix

[stix]

It will be good to see someone make this work successfully and report back.

 

You know what deer, I reckon I may join you on this quest, and we can compare notes - you may already have this sorted so it would be good to get some tips. I've got a free weekend coming up, and a possibly suitable tube, calcium chloride crystals and sodium silicate solution.

 

The cardboard tube I have is similar to yours and Arthur's (ex shrink-wrap tube), except that it's smaller: ID 2" (51mm), Wall Thickness 3/16th (5mm) and 20 inches long. I was going to use it for a large sugar rocket but I can't see that happening easily.

 

I did have the idea of using sugar rockets to launch a shell, but that seems like a lot of effort. I've been thinking why go to all that effort when a small mortar would get the job done?. I've got plenty of 1/4" cut stars that demand to be tested with small can shells, which will take a lot of learning anyway.

 

At the moment I'm drying in the oven sodium silicate solution from a pottery supplier to test the percentage of solids - that way I can adjust to make it 25% solids, because you don't want it too thick.

 

I do like the "Old School" approach of using cardboard tubes.

 

 

Cheers.

Edited November 10, 2015 by stix

[Arthur]

Realistically professional GRP mortars are not silly money. While I like the DIY ethos I'm cautious of the cheap bodge job especially where anyone may get hurt. Start with card mortars repurposed from industrial tubes but when I paid for commercial plugs they came out at £3 each which came close to the cost of a Chinese professional mortar complete.

[stix]

Realistically professional GRP mortars are not silly money. While I like the DIY ethos I'm cautious of the cheap bodge job especially where anyone may get hurt. Start with card mortars repurposed from industrial tubes but when I paid for commercial plugs they came out at £3 each which came close to the cost of a Chinese professional mortar complete.

 

Are you saying that I shouldn't try to use the tube I have, and buy some "professional" Chinese made tubes?

 

No can do. I'll be persevering with what I have.

 

After drying the SSS in the oven, I now know that it's ss 45/65 water. I can now crush to powder or adjust the original solution. That's a job for tomorrow or the next few days

 

Cheers.

Edited November 10, 2015 by stix

[Arthur]

The tube you have looks OK but the cost of making it fire resistant and plugged starts to approach the cost of a professional tube.

 

If a Chinese GRP tube and the unplugged shrink wrap tube were the same price, I'd get the Chinese one. But If I couldn't get a GRP tube I'd get one or more paper shrink wrap tubes.

[Col]

The SIO2/Na2O ratio of the silicate would be worth posting if its listed on the bottle. It can range from less than 2 to more than 3.5, if someone uses a silicate with a different ratio to yours it may produce a different result.

If the cardboard tubes are free.and available locally you wont have any postage costs, not to mention recycling is more environmentally friendly. The cost of treating them wouldnt be much, maybe £7 per 100 tubes.

[Arthur]

My "cost" for recycling thick wall paper tubes was the turned wooden plug. If you can turn your own wooden plug or pour your own with resin then card tubes are cheaper.

BUT commercially they sit in store for a long while then get pulled out and used (in the UK) in the wet november season, and no matter how you care for them being wet for a month doesn't help, hence my move to GRP or some yellow gas pipe off cuts.

[deer]

Reporting back. Overall, I took a very basic approach, which might result in sub-par results, so take this all with a grain of salt.

 

First I put 100g KCl in 300g of room temperature water (~20°C) - this should result in nearly saturated solution. Put the tube in bucket at and angle and while I was slowly rotating the tube, kept pouring the solution. Did this several times flipping the tube until the inside and ends were soaked.

 

First conclusion - way too moist. Don't let one end sit in the solution at bottom of bucket - put some brick or anything in there. The ends get soft, spongy and expand irregularly. Pour only enough solution to cover the inside. Do the next pour only after waiting for the first to be well absorbed, otherwise deeper layers cant keep up and the surface becomes fragile.

 

Next day I mixed 2/3 sodium silicate with 1/3 of water and let it run trough middle of tube several times. Also in the same bucket. Same problem - ends of tube swelled up and now it seems to be drying that way.

 

TL;DR; - If you coat the tube in bucket, have a brick or anything at the bottom, so the tube doesn't sit in solution.

[ivars21]

http://www.amateurpyro.com/forums/topic/7748-cardboard-tube-mortars/

I used waterglass with some good success, they are still holding strong. Wooden end plugs cut with jigsaw and screwed with 3 screws from each side. Each mortar has been used 5+ times and still looks like I just made it, just some residue inside.

[Mumbles]

Did you really mean to say KCl? For this method to work properly, you do need to use calcium chloride, not potassium.

[deer]

Well damn me.. I really did use KCl. That's what you get for not paying attention.

Kinda got fixated on the fact that I already have KCl. Also in my language they are way too similar (Kalcijs and Kālijs).

 

I wonder if it's still salvageable.

Edited November 11, 2015 by deer

[Mumbles]

I've give them a good rinse with water and give it a shot. Ideally you use the calcium solution first, so it can penetrate deeper. I bet you'll still get some protection. Maybe not 25 years, but it should be better than nothing.

[stix]

Thanks for posting the tip deer.

 

...First conclusion - way too moist. Don't let one end sit in the solution at bottom of bucket - put some brick or anything in there. The ends get soft, spongy and expand irregularly. Pour only enough solution to cover the inside. Do the next pour only after waiting for the first to be well absorbed, otherwise deeper layers cant keep up and the surface becomes fragile.

This has prompted me to seal the exposed cut face/edge of both ends with Sodium Silicate Solution - in theory this should stop the calcium chloride from penetrating and swelling the edge of the tube? I'll soon find out.

 

Col quoted:

The SIO2/Na2O ratio of the silicate would be worth posting if its listed on the bottle. It can range from less than 2 to more than 3.5, if someone uses a silicate with a different ratio to yours it may produce a different result.

Col, unfortunately it doesn't say on the container what the ratio is - I guess I could ask the ceramics supplier if this works out successfully.

 

...Well damn me.. I really did use KCl. That's what you get for not paying attention.

Kinda got fixated on the fact that I already have KCl. Also in my language they are way too similar (Kalcijs and Kālijs).

 

I wonder if it's still salvageable.

Well I hope it still works out for you.

 

----

 

I'm just about to start the CaCl₂ coating now, - and now that I am, I'm wondering how long to saturate the tube for. Too much penetration could cause the tube to never dry out after the final sodium silicate layer is applied, not enough and the surface may become fragile as deer suggested.

 

What I'm going to do is seal one edge by stretching 2 layers of nitrile gloves over the end (like a prophylactic) and secure with rubber bands. Then pour in the calcium chloride, secure the other end in the same manner, and using my hands swish back and forwards for a few minutes then pour out the residual fluid. I'm aiming for about 1-2mm? of penetration into the cardboard - it should be enough but it's just a guess.

 

I'll report on my progress in about an hour.

Edited November 15, 2015 by stix

[stix]

Results may vary.

 

 

I don't know when it should be flushed with water. It seems to me that the "reaction" has taken place. The crust is hard and secure.

Edited November 15, 2015 by stix