Waterjetting 37e - Using Cavitation to disintegrate rock

In most mines the main objective is to recover as much of the valuable minerals contained within the host (or gangue rock) while minimizing cost. When miners have to go underground and haul the ore to the surface before the minerals are recovered then there is a considerable expense both in hauling all the rock, including the large otherwise valueless host rock, to the surface, and then crushing it to a small size so as to liberate and separate the valuable components.

The work at MS&T, for a number of years, has looked at ways in which rock can be disintegrated, as it is mined, so that the different components are separated as they are freed from the vein. While this work has progressed significantly since it started, this video (of poor quality for which I apologize, but it was what was available at the time) describes where we started the work.

Figure 1. Tom Fort explains the work on cavitation disintegration of rock

  The work was carried on in a number of ways after that, some of which has been described in an earlier post.

Perhaps most relevant to the video at the top of the piece, we were able to develop a more continuous mining process where the material would be mined from the solid in the mine, rather with small hand samples in the lab. While the technology could be easily developed from existing machines now used for hydro-demolition, a more telling picture is to show, by running the product from a test on a sample of dolomite hosting a vein of galena, where the product was run over a Wilfey table.

Figure 2. Mined sample run on a Wilfey table.

The result shows that clear fragmentation of the galena particles and their liberation so that they form a separate (silver) stream on the table from the darker dolomite particles that lie closer to the riffles. It is not quite as easy to see the larger particles of galena which were also separated, but would be more easily recovered perhaps with a screen, since they are not quite as easily streamed from the dolomite.

Waterjetting 37d - Underground Drilling with Waterjets

The last post showed some of the experiments that we carried out as we developed a tool for drilling "around corners", demonstrating the ability of a high-pressure water jetting system to turn from a vertical well bore and drill out a lateral well within a turning radius of about 9 inches. This was not our earliest work on drilling, and that earlier effort had been directed to the reaming of geothermal wells.

The earlier project was also funded initially by Sandia Labs, although in this case the objective was slightly different. Overall we set out to show that one could go down a vertical well bore, some 9-inches in diameter, and ream a cavity 6-feet across down in the "hot dry rock" of a geothermal deposit.

When we began we weren't sure that we could drill in stressed rock, or what those effects on drilling rate would be. So we were fortunate to get some help from Doe Run and work in one of their mines, as the following video shows.

Figure 1. Early video on Underground Waterjet Drilling

  It was this series of tests that showed how relatively quiet water jets could be in drilling, unlike the competition at the time. Below the fold I will add the second part of this program, where we demonstrated the technique we planned on using for the reaming program.

Figure 2. Reaming a Geothermal Well Demonstration

Although this program moved on to focus on other aspects of the problem (we also demonstrated that this was practical in cutting granite, which led on to the Stonehenge and Millennium Arch projects) it was not until we were tasked with reaming large scale rocket motors, some years later, that we returned to this program, and developed the tools further.

Waterjetting 37c - A Drilling Diversion

I was asked some questions about waterjet drilling of holes the other day, and it is amusing to remember where it all started, more than 30-years ago. My apologies again for the quality of the video, which has been transferred from 16 mm film, to half-inch tape and thence via a DVD to its current form, losing a little in each transition.

Figure 1. The Cygnet Project part 1.

Perhaps one of the more memorable parts of this was that we arrived on site on the Monday, and spent the afternoon setting up. Since there really wasn't that much to the rig we were done quite quickly, and were then faced with an hour before the end of the day. The overall object was to drill a hole 50-ft long, and we had arranged the camera crew to come for the filming on Thursday, so that we could work out all the snags first. But we had a pleasant surprise.

We put our first test nozzle on the lance, and started drilling - it drilled the full length with no problems, we added a second length - same result, and third . . . and then the fourth and within the hour we had achieved the goal for the week. (And run out of drill lengths).

We had the same sort of experience some years later in trials I helped with that were run by the University of Queensland in Australia, although this time we were self-propelling the drill head, so that when we ran out of the outer rigid frame we attached a length of hose, and it kept on drilling, until we had run through that also. Problem was that the drill was then pulling itself forward without any advance rate control, and if it went too fast it did not drill a large enough hole for some of the following structure (we had backward pointing jets for propulsion and hole cleaning).

So somewhere I have a photo of three of us holding the hose back to slow the advance as the drill moved forward, so that it would maintain the 15-cm diameter IIRC. And again we accomplished the goal well before we had expected, and without the need for a lot of sophistication in the design.

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.

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.

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.

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.