Filling of projectiles...

[Twodeaddogs]

Hi all
This is probably a bone question but will someone please explain how projectiles are filled? Is the explosive filling poured as a liquid or is it pushed in as a putty...I see from some of the drawings on this forum that some shellcases are filled with cordite tied in bundles.Was this British practise only or common around the world?
regards
Twodeaddogs

 

[Chris 42 RQ]

Filling of Projectiles

As regards filling of High Explosive projectiles commonly with RDX/TNT most of these are usually filled by means of "pouring" in the high explosive at temperitures where it becomes a liquid, this is I believe a very critical operation for obvious reasons and is usually done remotely, also as the filling cools and contracts a "feed" of the hot liquid has to be maintained to the projectile to make sure there are no "voids" in the material and when all is cooled this "feed" has to be broken off and that can be "RISKY" to say the least.

Cordite in Artillery cases and items usually above 30mm have the charges in "silk" or similar material bags to protect the charge from possible pollutants and also makes filling easier.
Silk is very easily consumed usually leaving no residue (an important factor with BL guns especially.

Chris :tinysmile_shy_t:

 

[pzgr40]

Hi 2deaddogs, there is no such thing a s a bony questuion, just bony awnsers:tinysmile_twink_t2:

Filling of explosives was done in different ways:
*casting: mostly with TNT. TNT melts at 81,5 degr. celcius. It is mixed with a few percent was to make it less sensitive. Steam is used to make the TNT liquid.
*pressing: explosives are pressed from powder into a shape and either packed in a cartboar/steel/aluminium container which is glued to the inside of a projectile body, either it is pressed in the projectile body straigt away.

Most often explosive charges are half poured (cheap mass explosives) with packed charge (penthrite for instance) placed /glued in the center. As other stuff like smoke boxes, tubes (hollow charge) and seperation discs/cloth are placed into the charge, they can be quite complicated (especially the German WW2 types)

Tying up bundles of powder is common practice throughout the world, it makes placing the powder in the shellcase (in the factory) much easier. and prevents the powder from freely moving in the shellcase.

Added are some German WW2 pictures of pouring explosives and manufacturing and bundling of powdersticks.

regards, DJH

 

[TimG]

The explosive filling of the projectile is probably one of the most time consuming and critical phases of ammunition manufacture. One of the problems is that most explosives contract substantially between the molten and solid phase. In the case of TNT the contraction is in the region of 10%. The American and European approach to the problem is to overfill the projectile then machine a pocket for the fuze/exploder. This process was/is deemed too dangerous by UK Ordnance factories. The British approach is to use a single or multiple pour with a former that replicates the shape of fuze/exploder. The problems associated with this method are that unless carefully controlled there is a liability for cavities to form around the exploder. The TNT is normally kept at a temperature just above melting point to the point where it is cloudy with suspended TNT crystals. In modern production the cooling is controlled to the point where the projectiles have little thermal body warmers to promote slow cooling. In the case of RDX/TNT mixes more care is needed to prevent the mix separating, resulting in non homogenous mix, furthermore it tends to crust over and it is necessary to break the crust between pours.

Cavitation causes all manner of problems at the lower end of the scale there is insufficient explosive around the exploder to permit propagation of the detonation. Also, the projectile will be travelling up the bore of the barrel with an acceleration in excess of 50,000G, which is guaranteed to take up any slack in the filling by compression of the cavities again leading to insufficient main charge in intimate contact with the exploder. Thats if your lucky. If you have ever used a bicycle pump you cant have failed to notice how hot the pump gets. Although this is in part due to friction between the piston and the pump the majority is caused by adiabatic process. In simple terms if the pressure is increased, the temperature increases, so with the cavities violently collapsing one can get a very substantial release of thermal energy sufficient to cause detonation in the main charge. This invariably occurs before it leaves the barrel causing great alarm and despondency amongst the gun crew. Another scenario is that when the cavities collapse you have explosive striking explosive or something hard with an acceleration of 50,000G, which is enough to upset the most insensitive of explosives resulting in a detonation in the bore.

The filling itself takes time but so does the cooling. The cooling period for 25pdr was 55 mins, 4.7 - 2.5 hours, 5.25 - 3 hours.

In the case of bombs the casing is partially filled and then biscuits (these are pieces of explosive block) are added until you get a semi-molten mass then more molten explosive is poured in etc., etc. The process taking multiple pours and a considerable amount of time. Furthermore, in the case of a 4,000lb Cookie the cooling time was 30 hours. Its easy to see that the filling of ordnance causes a significant bottleneck unless you cater for it, which goes someway to explain why Chorley (an ROF filling factory) was one of the largest ordnance factories in Europe and employed (WW2) in excess of 25,000 staff.

Tim. G.

 

[pzgr40]

Hi Tim, you are absloutely right. cavities and base seperation (the complete charge shrinking so much that it lies "loose" in the projectile body) are a big problem, especially with long projectiles like for instance the 175 mm HE M437 projectile. Quite a few prematures have occured with the 175 mm projectiles, up to the moment a special X-ray technic was developed to find these errors.


Accession Number : ADA016110
Title : Detection of Base Separation in 175mm Artillery Shell by Gamma-Ray Transmission.

Descriptive Note : Technical rept.,​

Corporate Author : PICATINNY ARSENAL DOVER N J
Personal Author(s) : McCahill,J. ; Jentsch,A. ; Watters,S. ; Helf,S.

Report Date : SEP 1975
Pagination or Media Count : 25
Abstract : The feasibility of gamma-ray transmission to inspect for base separation between the steel shell and the high explosive casting in 175 mm projectiles was explored. The method consists of passing the section of the projectile containing the metal base-explosive interface across a highly collimated beam of cobalt-60 gamma rays and measuring changes in transmission with a scintillation detector. It is demonstrated both theoretically and experimentally that a 30-mil (0.030 in.) gap can be detected using rigidly controlled laboratory conditions with a mock projectile and an artifically induced separation. This technique was also tested with 100 fully loaded projectiles.
Descriptors : *NONDESTRUCTIVE TESTING, *PROJECTILES, *GAMMA RAYS, EXPLOSIVES, FEASIBILITY STUDIES, SEPARATION, PROJECTILE CASES.​

Subject Categories : TEST FACILITIES, EQUIPMENT AND METEORS
AMMUNITION AND EXPLOSIVES

Distribution Statement : APPROVED FOR PUBLIC RELEASE​

Regards Derk H.​

 

[Twodeaddogs]

thanks for the excellent replies, lads.I gather that the persons in the pictures are wearing anti-static clothing....I presume the filling of small-arms cartridges is much less tricky?!
regards
TDD:tinysmile_classes_t

 

[pzgr40]

Here an example of how complicated the build up of an explosive charge can be. This 80 cm shell is probably too complicated to be cast with explosives, so it's build up in layers.
Regards, DJH