Monday, September 28, 2015

Waterjetting 37b - How safe is it?

We began looking into the use of water jets to deal with energetic materials (a group that includes, but is not limited to, explosives) at the beginning of the 1980's. One of the earliest questions dealt with the need to find the jet pressures at which the explosive materials would react to the impact of the water.

We produced a short video of that initial work, and with apologies for the degradation that occurs with time and the transfer of the material through different media, here is what I believe was the second report we made, after we had been told that just showing that jets could remove material without reaction was not sufficient.


Figure 1. Looking for the initiation of explosive.

Mrs. Vicki Snelson did the initial commentary with Dr. Paul Worsey developing the technology that we used to see how the explosive was reacting.

Part of the problem, we discovered, was the the jet could start the explosive burning (deflagration) without causing it to detonate, but that the succeeding flow of water would wash that burning material away from the surface. Looking at the surface afterwards did not, as a result, show any reaction signs, and we could not always fully see the contact area. As a result the design was changed, so that the explosive could be held in a small chamber flooded with inert gas. The driving system was changed, so that only water entered the chamber, and so we could determine, by examining the chemical composition of the gases in the chamber after the test, if any reaction had, in fact taken place. Paul explains the modifications.


Figure 2. The first modifications to the test equipment.

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Sunday, September 13, 2015

Waterjetting 37a - Removing Explosives

One of the major efforts carried out at the High Pressure Waterjet Lab at Missouri S&T during my tenure related to removing explosives and other energetic materials from different casings. The casings ranged in size from very small anti-personnel mines to the large rocket motors that carry objects into space. The first part of that program dealt with the factors relating to the removal of explosives from warheads. Initially we had to show that this was relatively safe, and we initially thought that we were done when we showed that the explosive did not react as we went up to and beyond the pressures needed to wash the explosives from the case.

"Oh, no!" we were told, "That is not enough, we need to know how safe it is!" Which meant we had to determine, for each explosive we were likely to find, the waterjet pressure at which it reacted. (i.e. went BANG!) This meant that we had to fire water jets at pressures that ultimately reached 10 million psi (at which point all the explosives tested got seriously annoyed) to cover the field of response.

Once that safety level had been established then we could determine the pressures required to wash out the munitions, and from that design a tool to carry out the washout. We called the first one, WOMBAT, and here is a short video showing it in being used to clean out a SPARROW warhead.

Figure 1. Description of a Washout

The program examined a number of different approaches for different munitions, and we worked with Wilkes University in PA to build a full scale washout facility for shells, that was installed at the Navy facility in Crane, IN - but I'll show that, and movies of the development of a capability to cut into sealed munitions, in later posts.

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Sunday, September 6, 2015

Waterjetting 36d - Going through more complex walls.

This is a short post illustrating an early stage in our development of a light-weight tool that could be carried into building rubble, after a collapse, and drill down through it to provide access for tools to search, without the danders of destabilizing the pile.

We illustrated the lack of vibration by placing a full glass of water on top of the first concrete block to be drilled. As Mr. Dorle, the graduate student who built the equipment explains, the tool cut through all material it is likely to encounter, while using a pump available at the local hardware store, and in a total envelope that fits into the back of a pickup.


Figure 1. Mr. Dorle describing his design for a waterjet cutting tool.

in later work the tool was made even simpler, since the rotary mechanism was the heaviest and most difficult to move with the lance it proved possible to remove it, and I'll post a video of one of those demonstrations shortly.

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Sunday, August 30, 2015

Waterjetting 36c - Cutting walls

This is just a short video from back in the days when 1/2-inch tapes were still our way of recording, but before we reached the higher quality resolution of today.

We had a problem in that the basement of our building was partially covered with dirt, and concrete window wells held that back from the windows used to light light into the rooms. It would have been prohibitively expensive for us to pay to remove the concrete conventionally, but it turned out that with the construction of a set of simple tools (there were no really good high-pressure swivels available at the time - hence the orbiting action of the nozzle as it moved over the slot) we were able to cut the walls relatively simply and quickly.


Figure 1. Cutting the window well protecting the wall. (Over 30 years ago)

In this first video segment I mis-spoke when I spoke of the nozzle as rotating, it was actually being moved over the wall in an oval pattern, as will be more evident in the second segment (below the fold).

As noted in the video the support platform for the rig is a simple platform shop lifter and the rig is held on the platform with a couple of G-clamps. There is relatively little reaction force and so the rig can be made very simply out of available tools. The lesson we learned very early on was that the rebounding water carried the removed cement and aggregate particles, so that PPE was important, and keeping folk back even more so.

After the window wells were removed we had to cut an entrance through the main wall of the building - about 14-inches thick.


Figure 2. Cutting the main wall behind the window well.

Note that it was not necessary to remove the glass in the window until after the walls had been cut, and it was time to remove both window and wall.

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Wednesday, August 26, 2015

Waterjetting 36b - Katrina anniversary and the power of water

When I began to write these posts, I wrote about the difference between overall jet force and the focussed effects of a very high-pressure but small diameter jet. At the time I made reference to the relatively low pressure, but huge flow rate effects when Katrina hit New Orleans.

I specifically wrote about the damage to the Lower Ninth Ward when the levee collapsed and a wall of water, carrying a barge, suddenly flooded into the neighborhood. Though there was little water pressure, perhaps 20 or 30 psi, the volume of flow and the fact that it applied that pressure over the full face of a building, resulted in sufficient force to destroy the buildings and leave only the concrete slab, if that.

I was part of a survey group that went through the area after the Hurricane and made several hours of video which I summarized in a short review. On the occasion of the anniversary it is, perhaps appropriate to put this up. This comes with the sound, as I recorded it at the time. It begins in the Lower Ninth Ward, and then goes back to the start of the trip.


After visiting one of the smaller breaches in the city, we drove down the Delta to the point where the boats went out to service the rigs, and where the hurricane had come ashore as a more powerful force. Yet it was the water damage that was prevalent, as can be seen from those buildings that had survived because they were on stilts and thus out of the storm water.

We then returned to the Lower Ninth Ward, mainly near the breach. This is where the barge went through the breach, obviously at some speed, since it was carried beyond the main channel of the flow and then dropped onto the school bus as the flood waters passed further into the ward.

As I mentioned there are hundreds of photos and hours of video that we shot, but this gives some sense of the disaster.

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Friday, August 21, 2015

Waterjetting 36a - Jet stripping of tires

Stripping tires to recover the rubber has been one of the topics that has come up on a number of occasions, and through a number of different tests we have been able to demonstrate that water jets can remove the material in a range of sizes depending on the desired output.

The work has ranged from cutting steel-corded truck tires, for subsequent rubber stripping, through to the simplest removal of rubber to separate the cords and to then separate the rubber from the water and use that as a subsequent feed stock for a variety of uses. The control on the marketability of the product comes through a guarantee of the size range of the product, and while this can be achieved in part through secondary processing, it is an advantage if the rubber can be controlled in a certain fine-particle size range. Which is why, in this movie, you will see the nozzle assembly rotate as such a high speed.


Figure 1. Short video of a jet stripping rubber from a tire.

As the video notes, by changing the jet pressure between 10,000 and 13,000 psi one can control whether one is just removing the rubber, also removing the fiber cords, or going all the way through the tire and also removing the rubber material behind the cord.

The economics of the operation also involve the tire size, the speed of the operation, which is controlled by the relative rotation speed of the tire, relative to that of the jets, and the resulting product size of the crumb rubber that is removed - as well as its cleanliness. Those are subjects that are much more job specific than we need to get into at this stage, since the object of the video was rather just to show that, without a huge investment in equipment, it is possible to recover the rubber.

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Monday, August 10, 2015

Waterjetting 35e - A low cost version of the soil sucker

Posting will run just a little slow for a few weeks, as I run-through and catalogue the some 200 hours of video that I have amassed over the decades showing our waterjet research. There are a number of different review reports that I will insert over the next few weeks, as I find the good copies and then convert them from the earlier form into a digitized version. But I ask for your patience as I do this, since the conversion has to be done in real time.

To end the current thought over the removal of material through the addition of vacuum to a waterjet soil dislodging system, here is a short segment that shows us uncovering some inert mines. As it was part of a Humanitarian Demining Effort we had to make the system as inexpensive and simple as possible.

The pump therefore is one that you can buy at the local hardware store - operating at about 2 gpm and 1,000 psi and we have used a simple Shop Vac to provide the suction. The rest of the parts also came from the store, apart from the very small fractional hp electric motors that we used to turn the head and traverse the head over the ground. The excavation unit was, as you can see, mounted on a camera tripod. The idea being that if the mine reacted then the part destroyed would be so simple and inexpensive that it could be replaced within a few minutes for relatively little money.


Video of a small unit being used to uncover inert mines and other objects.

Mines are relatively sensitive things and so we had to be sure that the very low thrusts that the jet would exert in disaggregating the soil would not set the mine off. This required a combination of pressure, jet size and rotation speed considerations. The effectiveness of the combination selected is shown by the pebble sticking out of the side of the excavation which is not disturbed, although with only a little finger pressure it could be lifted out of the side wall.

We would then cut the mine apart, through the fuze, using an abrasive laden jet and in another post I will show the pictures of how we cut detonators apart and other sensitive explosive-laden materials, without their reaction, as well as showing pictures of what happens when we got a waterjet to ignite explosive.

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