Waterjetting 1d – Not quite that simple!

By Dr. David A. Summers, Curators’ Professor at Missouri University of Science & Technology

KMT Waterjet Systems Weekly Waterjet Blog

KMT Waterjet Systems Weekly Waterjet Blog

When I first began the research on the applications of high-pressure water that was to be one of the major parts of my professional life, I must confess to a certain naïve innocence in regard to other folk’s work. One assumed that other folk had made similar mistakes to mine and then corrected them, so that when different systems were compared that the early, obvious, mistakes had not been made.

One of the first times I found that this wasn’t the case was when we were asked to go and demonstrate that high-pressure waterjet technology could economically cut granite, in quarries located in the heart of the Granite industry, in Elberton, Georgia. We were working with Georgia Institute of Technology (Georgia Tech) at the time and were asked if we could, at very short notice, go down to a couple of quarries and run a demonstration.

Back during my graduate studies I had found that Russian claims were true that said that it was possible, with a 10,000 psi jet pressure to cut through a rock with a compressive strength of 30,000 psi. (I’ll tell you how later)

9-inch thick block of granite drilled through by a 10,000 psi waterjet

Figure 1. 9-inch thick block of granite drilled through by a 10,000 psi waterjet at Leeds University. It took over 30 minutes. (Summers, D.A., Disintegration of Rock by High Pressure Jets, Ph.D. Thesis, Mining Engineering, University of Leeds, U.K., 1968.)

Knowing this, and having a suitable pump at The University of Missouri-Rolla (now Missouri University of Science and Technology), our group ran some tests at the RMERC (Rock Mechanics and Explosives Research Center) to get the angles right between the two jets that we were to use, and then, about a week later, we went down to Elberton and set up a system in the quarry.

Starting to cut a 1-inch wide slot in granite

Figure 2. Starting to cut a 1-inch wide slot in granite, pressure 14,000 psi, 90 rpm, linear cutting speed around 9 ft/min, areal cutting rate around 20 sq. ft./hour.( Raether, R.J., Robison, R.G., Summers, D.A., “Use of High Pressure Water Jets for Cutting Granite,” 2nd US Water Jet Conference, Rolla, MO., April, 1983, pp. 203 – 209.)

The trials demonstrated that high-pressure water could cut granite at commercial rates, we cut a slot some 11 ft long and about 2-ft deep, and, after a couple of days of work, we went home. Georgia Tech then went to one of our competitors who set up to run a similar test. We had been done in 2 days, it took them two weeks to cut a slot about 2 ft long and 6-ft deep. They were running a jet system at 45,000 psi, roughly 3 times the pressure of our system. Why did they do so badly?

Well it turned out that they connected their pumps to the nozzle through a very narrow length of high-pressure tubing, and we calculated (as later did they) that of the 45,000 psi being supplied at the pump, some 35,000 psi had been lost in overcoming friction between the pump and the nozzle, As a result they were trying to cut the granite with jets at a pressure of 10,000 psi effective pressure, and it was much slower than our system which retained most of the 14,000 psi from the pump to the nozzle. (Hilaris, J.A., Bortz, S.A., “Quarrying Granite and Marble using High Pressure Water Jet,” paper D3, 5th International Symposium on Jet Cutting Technology, Hanover, FRG, June, 1980, pp. 229 – 236.)

Now you may note that I said something about mistakes – it turns out that we had made an identical mistake a few years earlier and had added a second 10-ft length of narrow diameter tubing to the nozzle, and suddenly a system that had cut adequately with 10-ft of tubing did not work with 20-ft. The reason was that the pressure loss in the tubing was too great at the longer length, and the pressure fell below that required to cut into the rock. (But at the shorter length we were drilling the hard sandstone at 12-ft/minute).

It is a very simple mistake, and many folks have made it over the years. The system has to be designed from one end to the other to ensure that all the parts are properly sized for the systems that are to be used. (And I will refer to other cases such as that above as we go through this series.)

It is not just the diameter of the feed lines that is important. In 1972 it took, on average, 150 man-hours and about $2,000 for the U.S. Navy to clean a single ship boiler using chemicals and mechanical scrubbing and cleaning. An enterprising company showed the Navy that it was possible to use waterjet lances to clean the tubes. In the demonstration they cleaned a boiler in 10 hours, and it cost around $700. This being Government work, the Navy then arranged a competition to find the most effective contractor. Based on the performance of the system that had been used in the first demonstration they asked 5 companies to compete in cleaning boilers. The operating equipment was designated as having to operate at 20 gpm, at a pressure of 10,000 psi. The results were not even close, even with systems nominally the same.

Relative cleaning efficiency in areal percentage cleaned, of five competing systems in cleaning heat exchanger tubes in Navy boilers

Figure 3. Relative cleaning efficiency in areal percentage cleaned, of five competing systems in cleaning heat exchanger tubes in Navy boilers. (Tursi, T.P. Jr., & Deleece, R.J. Jr, (1975) Development of Very High Pressure Waterjet for Cleaning Naval Boiler Tubes, Naval Ship Engineering Center, Philadelphia Division, Philadelphia, PA., 1975, pp. 18.)

One of the differences between the competing systems, you won’t be surprised to hear, was that some had smaller feed hoses than others.

There are many different reasons that the various systems performed as they did. One of the aims of this series is to ensure that, should you be asked to engage in such a competition, you will know enough to follow the path of company A, rather than company E.

As systems have become more sophisticated the different factors that control the performance of the jets have increased in number. As a simple example, when abrasive particles are mixed with high-pressure water in streams of abrasive-laden waterjets at pressures that can run up to 90,000 psi in pressure, for high precision cutting of material, the factors controlling performance now include not only the delivery system for the water, but also that for the abrasive, the type of abrasive and the configuration of the nozzle through which that final cutting jet is created.

Again, when we were asked to compare the performance of these different systems we set up nominally identical test conditions under which to determine which nozzle system would perform better. If I were honest I would tell you that before the tests began I expected that the variation in performance of the systems would vary by perhaps 10% between the best and the worst. We were quite surprised by the result.

Comparative performance between 12 nominally similar abrasive waterjet cutting nozzles

Figure 4. Comparative performance between 12 nominally similar abrasive waterjet cutting nozzles in cutting through steel at a standard speed, pump pressure, and abrasive concentration.

I use these last two figures to show that all the details of a high-pressure waterjet system are important, when it comes to optimizing performance. One of the reasons to write this series is to ensure that folk that use these systems in the future do not make the mistakes that we made, as we learned how to tune the systems from getting poor performance to the commercially viable rates that are achieved today.

Unfortunately much of the early research and tests that are the basis for this knowledge were performed before the Internet existed. As a result I will have to use references to books and papers (as above) rather than using the electronic references that are the more common habit now.

This concludes the basic introduction to the series, which will now focus on more specific subjects.

Waterjet Technology: More than Cutting Metals

By Dr. David A. Summers, Curators’ Professor at Missouri University of Science & Technology

KMT Waterjet Systems Weekly Waterjet Blog

KMT Waterjet Systems Weekly Waterjet Blog

Wandering the aisles at the IMTS and Fabtech trade shows that bring the latest tools to the attention of the manufacturing industry, there is always a group of folk standing watching the cutting demonstrations. The waterjet cutting booths in particular have always seemed to attract more of a crowd over the course of the day, and the relative quiet where you can still talk as you stand by the waterjet table is, perhaps, one of the benefits that waterjet technology has brought as it grows increasingly popular. It similarly does not hurt when the demonstration involves cutting those show trinkets which can, after a quick rinse, be given as a souvenir and reminder of the tool capabilities.

Waterjet Cutting Foam

Figure 1. Small foam give-away of a female Missouri Miner

The introduction of high-pressure waterjet jets into the industry was not quite that high tech, since it had been discovered quite early in the technical history that waterjets at a pressure of around 5,000psi/350 bar were quite effective in removing the burrs left when parts are machined conventionally. (Robert Burns has since written that the test of jet effectiveness is that it can be used when a 0.5 mm lead in a mechanical pencil will move the burr, rather than breaking the lead). (http://www.processcleaning.com/articles/water-jet-deburring-for-complex-metal-parts). The water jet stream had the advantage, over mechanical probes, that they could also bounce around corners in the parts, thereby reaching regions more difficult to clear. The de-burring step can be eliminated in many processes today by integrating a high-speed waterjetting in with the cutting tool in conventional machining. However tool design and integration has proceeded much further in the larger-scale mining and excavation industry than in metal cutting, where it remains still as more of a demonstration in a University laboratory than a tool that has become established in the market-place, even though it has been shown to make it possible to machine even difficult materials).

Waterjet assisting PCD cutter

Figure 2. Schematic showing the location of a high-pressure waterjet acting as a waterjet assist to a mechanical tool in machining rock and metal.

Yet the de-burring example shows one of the advantages that high-pressure water jet cutting has demonstrated in growing applications over the years. The highly focused force of the jet, when properly placed on the target cuts without significant damage along either edge of the cut surfaces left afterwards. The early examples of this (and one of the first commercial successes) was in the cutting of cardboard, where the jet will cut across the sheet without crimping the edges, which keeps the strength of the box edge that would otherwise be lost.

Waterjet cutting edge cardboard

Figure 3. Waterjet cut across cardboard showing the lack of a crimp

Waterjet System cutting Cardboard

Figure 4: First Commercial sold “water only’ waterjet system sold by Ingersoll Rand in 1971 (now KMT Waterjet Systems).

In a similar way, when abrasive is added to the waterjet stream so that it can cut through metals, glass and other ceramic materials (such as those used in computer chips and similar applications), the cut surfaces that are left are unchanged by the cutting process. The heat-affected-zone that is induced with thermal and mechanical tool cutting is removed, and the local stresses induced in thicker material as it is cut or milled are much reduced, so that there is less distortion around the cutting path, and in any narrow ribs of material left either in the part, or the material separating pieces in the initial sheet. This, again, is more critical in thicker parts, where an abrasive jet can be used to outline the final shape of a milled pocket, for example, before the mechanical tool removes the central material, so that, in this way, a very narrow rib around the pocket can be left undistorted by the stresses imposed by the mechanical tool.

And the lack of a de-burring step remains since, in contrast with more mechanical cutting processes, two parts can be located and fixed together in their final alignment, before cutting fastener holes between them. The fasteners (whether rivets, or bolts) can then be inserted and made tight without the need to take the pieces apart to remove the residual burrs that would otherwise develop on both pieces of metal.

There are, in short, a variety of different ways in which the opportunities for business that a high-pressure waterjet cutting table brings can be developed. Some of these opportunities come from learning what is already being done in other aspects of waterjet technology, and some are unique to this application. Some of these ideas are well known, and others less so. But to try and cover them in a single article is difficult, which is why I will be writing this KMT Waterjet Technology Blog posted on www.kmt-waterjet.com. It is meant to give, at about five hundred to a thousand words a week, a more detailed explanation and background to why some things work, and others don’t, as well as thoughts on where the waterjet industry can grow. I look forward to the KMT Waterjet Weekly Waterjet Blog Series.

Waterjet Weekly Blog-A New KMT Waterjet Series

KMT Waterjet Systems Weekly Waterjet Blog

KMT Waterjet Systems Weekly Waterjet Blog

I have been a Curators’ Professor at the University of Missouri Science and Technology since 1980. For most of my career I have led a team developing the uses of high pressure waterjets, and these have ranged from the removal of skin cancer, and precise material cutting at the millimeter level, up to the carving of statues (including a Stonehenge) some 5 meters high. Waterjet technology has been developed to cut open, disarm, and remove the explosive from munitions, and mines.

In October of 1965 I started work on a doctoral dissertation that would look at whether streams of high-pressure water could be used to mine minerals, rather than using the mechanical tools that my ancestors had been using for many generations to mine coal. Until the time of my great-grandfather the main tool had been a hand-swung pick, but he had made the transition to become a compressed-air-powered, coal-cutter operator, and worked with my grandfather on running that machine until the first World War, when his son joined the Northumberland Fusiliers and went off to Belgium.

When I started my work, after my mining engineer father had approved, I found that there was little information on hydraulic mining available in the technical literature. The Internet did not exist, and the few books and articles that I could obtain came through the Brotherton Library at Leeds University, where Inter-Library Loans would find a source, and even, on occasion, a translation, but in weeks not days.

Those conditions no longer hold true, and yet, while a computer now makes it easier to get instant access to all the world’s knowledge, filtering through that vast stack to find that needed bit of information still takes time. And there are other factors that have come into play, so that much of the knowledge that has been gained may soon be lost, forgotten or spread into so many distant places as to be effectively gone. And so I am going to put together a new series of posts about this technology. Since this is the first it is more of an explanation of the background, and as the posts continue so the structure and location may change, trying to better serve those who follow me in what has been the truly fascinating development of a new very broad-based industry.

Over the past decades high-pressure waterjets have found a wide variety of different uses around the world. From the small pumps that can be bought at the local hardware store and allow you to clean houses, furniture and cars through the thousands of horsepower used in pumps for the excavation and mining/petroleum industry a quiet revolution has occurred in many industries, beyond the sight of the general public. I was fortunate enough to be a part of the relatively small group of scientists/engineers/technicians who helped bring these changes about. Around the world there were perhaps 50 or so of us, and much of our interaction took place at conferences, where we learned more from each other in bars and restaurants than we did from the formal papers that we all gave. Some changes were fairly dramatic, the use of cleaning jets on oil platforms comes to mind, and were instantly adopted, others were a longer struggle, and yet these tools have yet to find more than 90% of their ultimate market, which will likely be in fields that most of us have not even thought of yet. And the tools that have already been developed are used in many more industries than the general public understands.

I retired a couple of years ago, and followed many of that original group in moving on to other interests. Before I left, however, I had written a book, and taught a class to senior undergraduates dealing with manufacturing use, as well as the earlier mining applications. The class is not taught now, and interest in the topic has also shrunk at the other major universities, as faculty have changed, and other topics bring the “research rain” that is needed to sustain the graduate classes of today.

This does not mean that waterjetting is less valuable, but instead is recognizes that the first flush of development is over, and that the really low-hanging fruit of application has been picked by folks such as myself. The range of applications remains immense, but the rewards are not now as easily obvious, and the research results now are not so dramatic.

The current plan is to begin the series with posts that come from my lecture set. But instead of being of the usual length they will be broken down into a set of sub-topics, so that there may be three or four posts that will cover the material of a single class. This will make each post of around a thousand words, and then the four sub-topics will be combined into a “class” version which will be posted as a pdf, and this will be down-loadable, and could be printed and put into what will, over time, become a somewhat updated version of that earlier book, but in a different format.

Since none of the anticipated readership is yet aware that this is happening, I expect that it will take some time for comments and questions to develop, but as these do they will be added into the mix.

Once the original posts have become established I hope to be joined by some of the folk that are still working in the field – as I said earlier it is one that is still continuing to grow at a fairly steady pace (one of the companies that makes equipment was on the national news recently because it could not get enough trained folk to help it meet demand). New ideas will turn up, and I look forward to giving my opinions. Sadly these may appear a bit negative at first, but there were many things we tried that looked good, but did not pan out. And those were usually not, therefore, the things that we wrote papers about. But knowing something won’t work, and more particularly why not, is also useful.

The early posts will also deal more with the history and general background, since these are likely to have a more general interest, and the more technical parts of the discussion will come later, though I will try and keep that at a relatively simple level for explanation.

I got my last patent this week, it dealt with drilling oilwells – the one before that dealt with treating skin cancer. I have worked on intercontinental ballistic missiles, at nuclear facilities, on land-mine clearance and in blocked caves. So perhaps I could claim to be a surgeon, rocket scientist, nuclear scientist, fire-fighting expert, and hazardous material specialist – and that neglects all the work on manufacturing and the evolution of tools that can cut through an inch of material within an accuracy of a thousandth of in inch.

All because of the power that comes when you push a pint of water through a tiny hole. Who’d a thunkit!!