Fireworks Mortar Workshop
Types Of Mortars Available For Fireworks Displays..
HDPE: High-density polyethylene is increasingly the preferred type of mortar for launching fireworks in the west since it's high density polymer construction gives it a very high strength to weight ratio, makes it very pliable in longer lengths, and also makes it very safe to use with fireworks.
If a shell explodes prematurely inside an HDPE mortar, the HDPE would absorb much of the shock "flower-potting" rather than exploding and creating shrapnel. The durability of HDPE also means it can be used many times with little wear.
Blue PVC pipes which are prevalent in Thailand are extremely brittle and cannot withstand the explosive force created by the burst charge of a shell. If a shell fails to leave a PVC mortar due to incorrect loading or faulty fusing, the burst charge would shatter the PVC into extremely sharp, highly dangerous shrapnel.
Cardboard tubes are the type generally supplied to consumers, and most small shell kits and single shot mortars come with a cardboard tube, but they are not suitable for reuse or displays.
Fibreglass Mortars are the standard in Thailand and most of Asia, they are relatively easy to get hold of, extremely strong and safe to use and although not as well known by Western Pyro's, they have been tested and approved by the NFPA (National Fire Protection Agency) and AFSL (American Firework Standards Laboratory) for use in firework displays.
Steel pipes are mainly used to launch very large shells, i.e., around 12" and up, but the drawback of extreme weight and high initial cost means that they are not widely used.
Mortar Type Comparisons
| Weight | Cost | Strength | No: of Fragments If Over-stressed |
Danger of Fragments |
|
| HDPE | Low | Modest | Moderate | Few | Low |
| Fibreglass | V. Low | Low | High | Few | Low |
| Cardboard | Low | Low | V. Low | Few | Mid |
| Paper | Low | Modest | Low | Few | Low |
| PVC | Low | Modest | Low | Many | High |
| Steel | High | High | High | Few | High |
Diameter
The inside diameter of the Mortar needs to be slightly larger than the outside diameter of your re-loadable shells, but only very slightly. If a shell can be fit into a tube without force, then it's a good fit, but if the shell fits too loosely, the lowered force generated by the lift charge may prevent the shell from reaching a safe height before the burst charge fires.
For most of the consumer fireworks at 1.75" (44.5mm) in diameter, Mortars with an inside diameter of 1 7/8" (47.6mm) are used as this is exactly the size necessary to launch these shells. Common sizes for HDPE mortars are:
-
2"IPS-DR11 with an inside diameter of ~1.9". This is fine for all ~1.75" shells and is size most commonly used in the US. Generally this is not for use with ~1.5" or smaller shells.
- 2"IPS-DR9 with an inside diameter of ~1.8". Will work for most 1.75" shells, however some 1.75" canister shells wont fit. For those shells that do fit, using DR9 mortars will provide louder lift and higher breaks than DR11. SDR9 can be used for ~1.5" shells, but is not recommended for smaller shells.
In case the only diameter of mortar available is a little too wide, a possible remedy is to slightly increase the diameter of the shell itself. Unwrap the fuse of the shell, and take it out of the string loop at the top and gently bend it back so it's out of the way. Use several 6" long strips of duct tape torn in half lengthwise to wrap around the middle of the ball of the shell, keeping track of how many you put on. Insert the shell into the tube occasionally to make sure it still fits and stop adding tape when it barely fits. Put the same number of tape strips on each shell you plan to launch. >top
Length
The length of the mortar tube is fairly important since it allows the lift charge to work correctly and ensures that the shell is traveling in the right direction, as with a long barreled rifles, and reaches the correct altitude before the main effects detonate. The table below shows approximate mortar lengths for single-break shells, for multi-break shells extra length is probably a good idea. although in general snugness of fit is a more important concern
| SHELL SIZE | MORTAR HEIGHT | WALL THICKNESS | PLUG HEIGHT |
| 2" | 360 mm - (14") | 2.5 mm | 10 mm |
| 2.5" | 400 mm - (15 3/4") | 2.8 mm | 15 mm |
| 3" | 450 mm - (17 3/4") | 3.0 mm | 20 mm |
| 4" | 550 mm - (21 1/2") | 3.0 mm | 30 mm |
| 5" | 800 mm - (31 1/2") | 3.5 mm | 30 mm |
| 6" | 900 mm - (35 1/2") | 4.0 mm | 35 mm |
| 7" | 1000 mm - (39 1/3") | 4.2 mm | 50 mm |
| 8" | 1100 mm - (43 1/3") | 4.5 mm | 60 mm |
| 10" | 1200 mm - (47 1/3") | 5 mm | 70 mm |
| 12" | 1300 mm - (51") | 6 mm | 80 mm |
| 16" | 1600 mm - (63") | 10 mm | 100 mm |
Mines - Mortars for mines should be 6-10" long. Shorter mortars result in lower and "fatter" spreads of the stars and material, longer mortars result in taller and skinnier spreads of stars. Shorter than 6", and the mine may be too wide and low for safety. Many mines have shorter fuses than aerials, so they won't be able to reach the top of a mortar tube longer than 10". >top
Plugging Mortars
All mortars need to be fitted with a plug in the bottom to prevent lift charge gases from escaping. As can be seen in the above table, the plug height increases in relation to the size of the shell's being fired.
The plug is usually made of hard wood cut into a circular shape, which is done by using a hole saw for smaller mortars or a sturdy router to cut out lager plugs.
The drilled plugs should fit tightly into the tube with little or no free space around the edges. A continuous bead of Liquid Nails adhesive is used to to create an airtight seal around the inside, before finally securing the plug with nails or staples fitted at 120 degree angles. > Top
The Fireworks Company Thailand accepts no responsibility whatsoever for any injuries or accidents that occur as a result of attempting any of the displays or projects mentioned in this site, or as a result of use or misuse of any pyrotechnic products purchased from us. We highly recommend the use of professional display service for anything other than consumer 1.4G Fireworks with shells 1.75" or less in diameter.