In my last post on shaped charges, I was asked in the comments about explosive welding. Why not?
Explosive welding is also known as explosive cladding. It is a process by which a cladding material is explosively bonded to a backing material.
Why do it? Besides that blowing shit up is cool as fuck.
Cladding is a process in which a layer of some material with desirable properties is laid over and bonded to a structural substrate.
People are often familiar with this as hardfacing. A steel member, like an auger blade, die, teeth on an excavator, etc., is welded over with a hard, wear-resistant surface material.
Cladding is often done for corrosion resistance. I was first introduced to is with alkalizer units in a refinery, which use almost pure sulfuric or hydrofluoric acid. The tank is lined with tantalum. Tantalum is very expensive, so it is clad onto steel which makes up the structural component of the pressure vessel.
Cladding is much thicker than plating, which is put on as an electrochemical process. Platings are thin and do contain porosity. For very harsh chemical environments, platings are insufficient to protect the substrate material. This is where cladding comes in.
Quite often cladding is applied with a welder. God only knows how many miles of hardface cladding I put on with SMAW when I was learning to weld. Just facing conveyor rollers for a cement plant building up hours with a torch.
But there are times when that cannot be done. The metals cannot be welded together for a variety or reasons. Sometimes the two metals form brittle intermetallics, such as aluminum and steel. With tantalum, the melting temperature of tantalum is higher than the vaporization temperature of steel, so tantalum cannot be welded to the steel with fusion welding.
Explosive welding is a solid-state process that bonds the materials together mechanically. There is no alloying of the two metals.
The metal to be clad is called the flyer plate. It is placed over the base plate with small plastic pucks that give it a standoff distance.
The flyer plate is backed with explosives, and a detonator is placed in one corner. The shockwave drives the flyer plate into the base plate, starting at that corner and radiating outward.
This is very similar to how a shaped charge works. When the metal plates impact at thousands of meters per second, that same thin shear layer forms, and any surface impurities, oxides, and contaminates squirt out from between the plates as a jet.
The material softened by the impact but not squirted out as a jet ripple against one another and lock mechanically with what looks like ocean waves and hook together like Velcro.
The clad plate can then be assembled into a structure.
This process allows very dissimilar metals to be permanently bonded together without issues associated with the fusion welding of dissimilar metals.
The downside is you can only do large flat sheets. It’s not a process that is conducive to complex geometries.
Usually, explosives are used for blowing things apart, but every once in a while they can be used to blow things together.
Also, because blowing shit up is cool as fuck.
Yes, the clad plate can be roll formed like other plates.
To make a tank, the plates are aligned and butt-welded together. The steel backing plate can be welded to other steel backing plates on the back and the cladding is welded to other cladding on the front.
The welding is done a little more shallow to prevent the weldpool from penetrating through one layer into the next.
I should also add, this is where advanced knowledge of explosives it key.
Explosive welding is best done with low velocity explosives like ANFO, where shaped charges are best made with high velocity explosives like RDX and PETN.
The speed of the detonation and shockwave affects the thickness of that shear jetting layer.
A high velocity explosive will create a larger jet, great for armor piercing.
A low velocity explosive will create enough jet to clean the plates but will bond the together.
If you tried to explosive welding two plates with Comp B or Semtex,you won’t get a good plate but a huge shape charge.
5 thoughts on “On blowing shit together – updated”
Cool as fuck, thanks J.Kb
Thanks for making my job way more boring and unfun…….. glad my hobbies involve lots of boom..( commercial fireworks and machine guns)
And of course now I have questions about making the Ta-clad steel plate into a tank… 🙂
I think you answered my question at the end, but can then do further prossesing of the plate like rolling? Obviously you can shape it into tanks etc.
IIRC, our current “silver” coins are made via this process.
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