3 replies to this topic

[icarus]

Ref - History of shaped charge effect the first 100 years author Donald Kennedy

status- unclassified  general distribution

 

Dr Munroes experiments in 1888 pressing letters into a gun cotten cube then exploding it in close proximity to a steel sheet resulting in the letters being clearly imprinted into the steel sheet was the start of research into shaped charges .

 

In order to demonstrate this in a school or public lecture the ideal explosive is a stoimetricmix of hydrogen and oxygen  this is easily acheived by electrolysis  of  dilute sodium carbonate solution  This works better than electrolysis of water as the sodium carbonate in solution results in an increased conduction and current flow at low safe voltages . The steel sheet is replaced by a flat layer of plasticine on a thermostatically controlled heated mat .As the temperature of the plasticine is increased it becomes softer so by varying the temperature of the plasticine we can change the amount of force nessecary to imprint upon the surface. A flattened leaf is placed on the surface. The surface is then covered with strong detergent solution or bubble mixture. The hydrogen/oxygen mix from the electrolysis unit output pipe end is pressed gently into the bubblemix so that the whole surface is covered with a layer of bubbles-our explosive. The explosive charge is fired by a lit taper . This results in a loud satisfying bang  that delights the audience .By careful "tweaking" of the plasticine density clear  explosive formed prints of the leaf or a coin can be stamped into the plasticine.

Plaster of paris or dental plaster can be used to take a mould of the prints to form a more permanent record of the results .

 

Hydrogen oxygen bubbles can be fired on your hand without damage this may have potential for stage special effects???   

[cooperman435]

I love the methods devised to show principals like this!

It’s fantastic when you’ve an imagination to be able to reduce down the power required to demonstrate something like this so perfectly but so relatively safely

[icarus]

It does a good job of demonstrating the principle in a safe way and the loud bangs of the exploding hydrogen/oxygen  mixture  excite the young audiences  interest . I want them to see that science is interesting, challenging and exciting.  LIke many teaching aids from a theoretical view this method is flawed . The imprint produced is nothing more than block printing caused by the pressure wave pressing the leaf into the soft plasticene and is not due to the munroe effect .  I was taught by tutors and lecturers  whose explanation of what was happening was partially  bullshi*  .The Bohr model of the atom and water boiling at 100C with no mention of pressure volume temperature relationships or why the temp remained at 100C whilst it bolled .to name just 2 of many. 

 The most important thing was that it fed and sustained an interest in science, so now i carry on the bullshi* tradition excused by a noble motive! 

The paper i quoted from is interesting reading

Munroe demonstrated the shaped charge effect blasting a hole through a safe with a quantity of explosive that had  had no effect when placed as a blob against the safe .Althogh the effect carries his name he was not the originator .The original work was by german scientists Von Baader in 1792, Von Foersters in 1883 which lead to an american patent in 1886 by Gustav Bloems  The enhancement of the effect from vaporisation of a metal support cone was around 1933 and Germany was using shaped charges in many war-time weapons  from hand grenades through to mistel  a 2M diameter shaped charge nosecone containing 3500KG of explosive mounted onto a plane to be dropped onto the target .

 

Record what you see without bias Not what -you expected to see!  . When you come across an anomally try and repeat it. 

Dont believe everything you are told- it will limit your questioningof what you see 

 

I recently produced what I claimed was an enormous magnetron  built from 8 magnetrons with a large accompanying  power supply .I switched it on whilst it was surrounded by engineers you could hear the psu humming  I approached it with a large fluorescent tube in my hands this illuminated brightly "Cor  its chucking out so much microwave radiation I can feel my eyeballs heating up "  I exclaimed -seconds later the room was empty !! .  It was a great hoax the power supply had a battery operated buzzer in it  and the massive magnetron concealed a small tesla coil with a spike output whose reatively harmless high voltage field illuminated the fluorescent lamp i held      .For some strange reason I have not been invited back there??????

[Rob.L.]

"I recently produced what I claimed was an enormous magnetron  built from 8 magnetrons with a large accompanying  power supply .I switched it on whilst it was surrounded by engineers you could hear the psu humming  I approached it with a large fluorescent tube in my hands this illuminated brightly "Cor  its chucking out so much microwave radiation I can feel my eyeballs heating up "  I exclaimed -seconds later the room was empty !! .  It was a great hoax the power supply had a battery operated buzzer in it  and the massive magnetron concealed a small tesla coil with a spike output whose reatively harmless high voltage field illuminated the fluorescent lamp i held      .For some strange reason I have not been invited back there??????" Quote from Icarus's post.

 

That is so funny it is unreal, I have recently done two microwave stripdowns and a CRT TV stripdown with my eldest son incorporating capacitor safety. A bit off topic i know steve but do you do any more high voltage stuff? I have some pretty serious HV stuff and plan on a large tesla coil in the future. If you like it may be good to have a general science area or something?