Sunday, September 29, 2013

Tech Talk - Iran and a slight cough toward CNN

There has been considerable comment this week over the telephone call between President Obama and the President Rouhani of Iran. Certainly the election of a new President in Iran gives the opportunity for a fresh start, particularly given the belligerent attitudes of his predecessor. However the cynical side of me does wonder if there is more driving this than simply the change of personalities.

There are two points that need to be considered, as a possible new relationship between the two countries might slowly coalesce out of the mists of diplomatic effort. Firstly the major driver seen in moving Iran toward a more positive position is said to be the increasing bite that sanctions, and particularly oil sanctions, are having on their economy. As sanctions have tightened, so Iranian oil production has fallen, with reports suggesting that oil exports have fallen from 2.2 mbd to May’s value of 0.7 mbd. The reduction in income that this has had on the Iranian economy is significant, with the currency officially devalued to half, though the effect has been more of an 80% fall from peak, as inflation has reached 42%.

Easing sanctions to allow more oil flow would significantly improve the situation, although there is concern, expressed for example at CNN, that the increase in oil flow would weaken the positions of the Kingdom of Saudi Arabia and Iraq. They suggest that the advent of Iranian oil (presuming that they can bring 1.5 mbd to the market relatively quickly) is foreseen as having a potential impact on the United States in that it may, at least transiently, produce a glut in the market. That would drive down prices, until such time as KSA could drop production and bring the supply and demand back into balance, raising prices back to around $100.

In a peaceful world such a scenario might have some viability, but consider what is really happening in the world of global supply. Instead of the KSA moving toward a supply of 12.5 mbd (which was only a capacity number in the first place) they have backed this down to 12 mbd and have talked recently as lowering that number further as they hire more and more rigs to help sustain existing production at just under 10 mbd. Iraq, which was promising to rapidly increase production toward a target of 11 mbd, is instead considered by the IEA likely to reach no more than 6 mbd by 2020. Further with the ongoing increase in violence in the country being able to sustain current production at around 3 mbd and increase it beyond 3.5 mbd as the Majnoon field comes on line. However Shell’s target for the field is already below initial estimates for this year, and it is discussing lowering the 2017 target from 1.8 mbd to 1.0 mbd. There has recently been an outbreak of violence in Kurdistan, which might portend that even in this relatively stable part of the country oil production and security is becoming a greater target.

These events suggest that future increases in production from around the region are not as assured as one might hope. At the same time, while there are those who continue to expect the United States to become oil-independent in the next few years, the reality is somewhat different, and further increases in production much above current figures become more difficult to justify. If Russia, similarly, is unlikely to increase production – which it is not – then the questions that should be asked are rather where is the world going to get the additional 1 mbd that it requires every year to balance increasing demand against supply.

Over the course of this year Saudi Arabia has had to increase production from 9.1 to 9.96 mbd to keep supply in balance, and prices stable. At the same time production from Libya, which has run at around 1.6 mbd had fallen to 150 kbd at the beginning of this month. Hopes that this could be increased back up to 700 kbd rely on tribal militias that control strategic parts of the country, and their long term co-operation is dubious, while the fields and pipelines in the east remain shut down. It seems reasonable to anticipate that there will be at least a million barrels a day of Libyan production held off the market for some time.

If one goes around the world one sees that Brazilian promises of production increase are behind schedule, as are promises of production increases from countries such as Veneuela. And suddenly one is left with not much in the way of places left to balance off the current declines in supply and increases in demand.

At this point that 1.5 mbd of potential supply from Iran starts to look a little more promising as an answer. It might allow KSA to ease back on production levels that might be starting to impose a little strain on their infrastructure. It would help to provide balance if production increases around the world fail to show on time. One should recognize that negotiations to bring Iran back into the fold are going to take at least a year or two before it is realistic to anticipate full return to supply, but even the easing of sanctions a little might cause the flow to China, India and Asia to increase to meet the burgeoning demands that they have, and oil is still to some degree fungible.

But in that regard, Iran has also just recently reached 100% output from the first of the nuclear power stations at Bushehr and is about to start construction of the second unit. Nuclear fuel will be provided by Russia, and spent fuel returned to Russia. It is a 1,000-megawatt unit, and since the unit was built under supervision by the International Atomic Energy Agency it is not subject to sanctions.

Figure 1. Bushehr Nuclear Plant

If the protocols that worked to make this happen can be expanded, then it is possible that, though negotiation, the tension in the region can be eased. This could well have benefits all around, most particularly for ensuring that, for at least a sadly few more years, there will be enough oil on the market to meet demand at a reasonable price.

Figure 2. Location of the Bushehr Plant

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Friday, September 27, 2013

Waterjetting 13d - Pocket milling considerations

If I were to hand you a cake and suggest you take some, you would likely take a knife, and make two cuts to define a wedge of the cake, which you could then easily remove with your fingers, and easily eat.

Figure 1. Conventional cutting of a piece of cake.

However if one takes the approach used in many machine shops, and in many of the processes that are used to excavate soil and rock, then the process and product are a lot different. For, instead of just making two cuts that make it easy to remove and handle the product, instead the operator takes the knife and chops up the piece of cake into small particles.

Figure 2. Milling pockets into a piece of cake, with a pile of crumbs.

Now while it is true that this might produce nice clean pockets in the cake, it does leave the extracted cake in small pieces that cost a lot more energy to produce, are a lot more difficult to collect and handle, and are relatively worthless without being reprocessed back into a more useful form.

In some cases, where the cuts are made to the edge of the piece, it is not that difficult to adapt waterjet technology to emulate the knife in the above example. Cuts can be made along the edges of the pocket in such a way that they intersect within the piece to define a block of material that can be removed.

Figure 3. Piece of metal trimmed from a block in a form that allows it to be used for something else.

The savings can be considerable and are not restricted to small pieces such as this. Consider if you wish to create a tube, 2.5-inches long in Hastelloy. One could mill out the central volume to give the required shape:

Figure 4. Tube made from a block of Hastelloy

Or one could merely cut around the desired shape in the block, using a high-pressure abrasive waterjet, which would produce the central block as a single piece that could then be used as feed stock for another part.

Figure 5. Removed block of material from the piece shown in Figure 4. (For this initial demonstration the quality of the side cut was not considered important, it can be significantly improved for both internal and external surfaces, as discussed below).

Life becomes a little more complicated when the pocket must be generated without through cutting the part, and where the depths of the individual cuts must be precise, at the same time as the wall quality must my produced to final surface specifications.

There are a number of techniques that can be used in this case, depending on the material being cut, and on the depth that the pocket must be cut to. As mentioned in a previous piece, when higher quality surfaces are required then the cut must be made only with particles that have not cut, bounced and recut the work piece. Rather they must leave the cutting zone after the first cut, without further damage.

When the abrasive cutting conditions are controlled accurately, then the precision control in the depth of cut can be high, so that, for example, channels can be precisely cut into engine parts as needed.

Figure 6. Milled channels into a surface (note that the channels were deepened with three passes of the cutting head). (Courtesy Ormond)

In the above case the channels were narrow enough to be removed by the full width of the cutting jet, however, when larger pockets must be cut then this precision must be maintained over the full depth.

A problem that can then arise comes from the shape of the cut as it gets deeper. If the nozzle is not advanced into the cut (and this is not normally possible given the relative widths of the two) then there will normally be a slight taper into the cut as it deepens. With relatively thin work structure this taper will often be slight enough that it does not fall outside the tolerance required for the cut. Quality control can be achieved, therefore, with a series of rapidly moving nozzle, shallow individual cut passes. Omertz, for example, showed that a much better control of cut depth and wall quality can be achieved by twelve passes at a higher rate than a single pass over the surface with the same residence time on the part. However the optimal condition will depend on the tolerance on asperities in the floor, and the total depth of cut to be achieved, as well as the material being cut. In deeper parts the sides of the wall can narrow to interfere with the jet structure and create ripples that take the deeper wall surfaces beyond this acceptable limit.

Figure 7. Schematic of the jet structure as it moves away from the nozzle.

One solution to this is to return to the technology that we demonstrated with John Shepherd’s Wobbler namely to move the nozzle in such a way that the jet oscillates over the surface, not only making multiple passes along the floor of the desired cut at a high enough speed to achieve good depth control, but also by slightly widening the cut there is less chance of undesirable bounces from particles on the edge of the jet from causing out-of-tolerance rippling in the lower parts of the cut.

Figure 8. Exaggerated movement schematic to show how oscillating the head widens the cut, allowing the jet better access to the bottom of the cut without sidewall interference.

This particular aspect of nozzle motion has also been studied in Australia and Italy. The Australian results, for example, (Patel, Chen and Siores, 6th Pacific Rim Conference, Brisbane, 2000) looked at oscillation both along the cut and transverse to it. They found that surface quality was improved three-fold on the walls of the cut, and that, depending on oscillation angle and frequency, the smooth zone cut depth could be extended further into the work piece. The optimal angle of oscillation was found to be three degrees.

Figure 9. The effect of nozzle oscillation frequency on the depth of smooth cutting in the walls of the piece. (Patel, Chen and Siores, 6th Pacific Rim Conference, Brisbane, 2000)

How one breaks out the floor of the pocket, after defining the walls remains a work in progress.

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Wednesday, September 25, 2013

Tech Talk - The Rise and Fall and . . . . of Brazil

Brazil seems to be appearing in the news a little more regularly these days. Whether it is because the President objects to NSA activities or because Unilever is buying 3 million gallons of algae-produced oil from Solazyme, to be produced at a new plant in Brazil that will generate 30 million gallons a year, the emphasis has switched from a focus on their growing oil and ethanol economy, perhaps because it has stopped growing.

Back when The Oil Drum first started (where the last post has now gone up) one of the earliest posts noted that Petrobras was seeing a 14% increase in production, as they reached 1.82 mbd, back in May 2005. This was at the time that discoveries were being made offshore in what is now known as the Pre-salt deposits.

Figure 1. Nature of the offshore deposits that are being developed from under the Salt Layer. (Seeking Alpha )

Part of the problem with the development of these deposits comes from where they are and what they are. Rock salt is one of those materials that will flow under pressure. (One of the more interesting examples of this is in the Polish salt mine at Wielicza where old mining tools were found encased in salt in a region of the mine that was thought to have never been worked.) This poses some problems with drilling – although these are now relatively well understood. The other problem is that the reservoir rocks under the salt are recognized to be very weak, which makes it more difficult to drill long lateral holes, and keep them open. (The genesis of the basin has been described by Schlumberger).
Note: this post has been updated to include the new discovery in the SEAL-11 area.

Exploration first found the Espirito Santo, Campos and Santos basins and this was followed, in 2006, by the Tupi province which held the promise, at the time of discovery, of producing 8 billion barrels of light oil and natural gas.

Figure 2. The initial Tupi discoveries offshore Brazil (Offshore Technology )

Because of the location offshore the oil and natural gas would be recovered using a Floating Production Storage and Offloading unit (FPSO) and the first of these to be dedicated to the site was contracted in 2009, the first crude being produced in May, 2009. An earlier FPSO, the Cidade de Sao Vincente, was already in use as a test platform for the field. At the same time further development showed that three offshore fields (Tupi, Iara and Guara) held the potential to supply up to 40 Tcf of natural gas. Guara was discovered in 2008, and was initially anticipated to have 1-2 billion boe potentially available. Iara was also discovered in 2008, and holds a potential 3-4 billion barrels of light oil and natural gas. By the end of 2010 the collective potential for the three fields was estimated at 10.8 billion boe.

Figure 3. The development blocks around Tupi (Rigzone )

A second FPSO was ordered in June of 2010 with a capacity of 120 kbd of oil, and 5 mcf of natural gas. Initial production from the first FPSO, the Cidade de Angra dos Reis, began in October 2010 with a target of 100,000 bd, and an additional eight FPSO’s were ordered in November of that year, increasing capacity by up to 150 kbd each, although collectively they are anticipated to reach maximum production in 2017 at 900 kbd.

At the end of 2010 the Tupi development had been renamed as the Lula field, in honor of the retiring President, and two more FPSO’s were chartered to increase production by another 150 kbd each, from the fields of the region. By May the first well connected to the FPSO Cidade do Angra dos Reis was producing over 28 kbd as the first of six wells connected to the platform.

As the development of the platforms to commercial production became closer Petrobras also commissioned the construction of 2 more FPSO’s, noting that these would be able to inject some 200 kbd of water back into the formations, in order to assist with production and the maintenance of pressure.

By June of this year the first production was received on the Cidade de Paraty a third FPSO, although only at 13 kbd, rather than the target 25 kbd as the vessel and support structure was still in process. The platform will ultimately receive oil and gas from 7 production wells (for a total capacity of 120 kbd) while feeding water back through 6 injection wells.

The potential is thus evident for Brazil to become a significant producer to meet not only their domestic demand, but also to start exporting oil and natural gas, given the potential for these offshore fields. But, to date, this promise has yet to be fulfilled. Ron Patterson has been plotting production and I have taken this plot from his site.

Figure 4. Production of crude and condensate from Brazil (Ron Patterson )

As I noted last time, the EIA had been projecting that Brazil would be producing up to 2.8 mbd by the start of this year, rising to 3.0 mbd at the end of the year. The OPEC MOMR suggests that they will only make 2.67 mbd by the end of this year, but at the above chart shows, that would still be a considerable improvement, and reverse the drop.

The gain is anticipated to come from the FPSO Pappa Terra, which is the renamed Nisa, and which will be moored at the Pappa Terra field. This is in the Campos Basin, and is a heavy crude (API 14 – 17 degrees) with the potential to yield 380 million barrels.

Figure 5. Location of the Pappa Terra Field (Offshore Technology )

The vessel left China at the end of last year, and was completed in Brazil before sailing to the field in June.

Figure 6. The Pappa Terra FPSO (Shipbuilding Tribune )

On the other hand Brazilian production of ethanol had gone up by 6%.

UPDATE: Just after I had finished writing this Reuters carried a story which they had pieced together from other reports, and which indicates that Petrobras and an Indian partner have found a new large field of light crude about 1,000 miles north of the developments in the Lula area. The new discoveries have the advantage of not being covered with the salt layer, and so will be easier to develop. Currently production is anticipated for 2018.

Figure 7. Location of the new field off the coast of Brazil. (Energy-pedia)

There are a number of different development wells being drilled in the region, and they have found sufficient success to allow their results to be congregated into a field with a potential reservoir of 3 billion barrels of light oil. of which perhaps 1 billion will be produced.

Figure 8. The drilling blocks in the Sergipe Basin. (Petrobras)

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Sunday, September 22, 2013

Tech Talk delay

Due to travel, this week's post will be a couple of days late. Sorry!

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Wednesday, September 18, 2013

Waterjetting 13c - On Milling and bas reliefs

In the last two posts I have been discussing how, either with the use of masks, or with an orbiting nozzle tool, it is possible to mill the material from a confined space within a surface, thereby creating a pocket.

There are a number of advantages to the latter technique, albeit it does require a special tool, rather than using masks that can be made from material already available at a shop.

Figure 1. Using a steel plate to provide a mask, while cutting a square pocket in glass (Courtesy of Dr. Cutler)

Figure 2. Detail of the corner of the pocket (Dr. Cutler)

With the oscillating tool, which can go deeper into the part to keep the distance from the nozzle to the work surface short, the corners can’t be as sharp as they are with the mask, since the outer radius of the focusing tube provides a limiting bound, once it moves into the cut. However, for shallower pockets where the nozzle can be further away, then the limiting corner radius sensibly becomes the orbiting radius of the nozzle.

Figure 3. A milled pocket in glass made using the Wobbler.

Note that the floor is relatively even in both cases, though in the masked case the view is taken only after the first pass over the glass. With the orbiting head it is possible to slightly tilt the head (it only requires a couple of degrees – depending on the other operational parameters) to ensure that the walls are being cut to as tight a tolerance to spec as desired (give or take a thou).

Dr. Hashish has noted, from some of the early work that he carried out, that it is possible to mill materials so that very thin skins (around 0.02 inches) can be left at the bottom of the pocket. As I will note in more detail next time, it is also possible to mill using abrasive waterjets in such a way as to leave intervening walls between adjacent pockets that are only that thick. If you have never had to do this in a conventional machine shop, you should know that as the wall of the pocket gets this thin, particularly at significant milling tool depth, the heat from the milling process, and the forces on the metal under the cutter are such that the wall will likely have some permanent deformation after the milling is over. Such is not the case where an abrasive waterjet system, of either variety, is used to cut the pocket.

Depths of cut uniformity can be held to a thousandth of an inch, though this requires some careful selection of both the abrasive size, and feed rate as a function of the other operational parameters of the system. As I mentioned last time, and Dr. Hashish demonstrated, as increasing precision is required in creating the floor of the pocket, so the abrasive being used must become finer and more precisely sieved to keep the wear pattern consistent.

. Figure 4. The effect of change in abrasive size on the smoothness of the pocket floor (Hashish M.: An investigation of milling with abrasive-waterjets, Trans. ASME, Journal of Engineering for Industry, Vol. 111, No. 2, 1989, pp. 158–166.)

There is an interesting niche market waiting to be developed in sculpting, I believe, based on putting some of these factors together. It was Professor Borkowski of the Unconventional HydroJetting Technology Center at Koszalin University of Technology* who first demonstrated that, by controlling the jet feed rate over the target, that the depth of cut into the material (and thus the depth to the floor of the pocket) could be controlled.

If now a photograph is scanned, so that the color of individual pixels along the photograph can be identified, then this color can be translated into a required depth By then setting the speed of the nozzle over that point on the target surface to give the required depth, then the jet will profile, from the color changes along the scanned path, the depth of cut on the milling path over the target. The details of the process are specified in the paper cited above, and the result has been the transfer of a 2-D image from a photograph to a 3-D bas relief cut into metal or other material surface. The depth control was well achievable using the rotational frequency of a stepping motor to drive the motion of the nozzle.

Figure 5. Outline of the process turning pictures into bas-relief (Dr. Borkowski).

The initial pictures that were obtained with the very first experiments were somewhat simple, though more than adequate to validate the concept. Where a smoother surface was required secondary passes could be made either in a parallel or orthogonal direction.

Figure 6. Early ball shape cut into metal to demonstrate speed control effect (Dr. Borkowski)

The next trial was with a ladies photograph:

Figure 7. Early trial of the technique to validate the effectiveness of the computer control (Dr. Borkowski)

More recently, as the process has been refined, much more detailed profiles have been demonstrated, as was seen, for example at the 2010 BHRA meeting in Graz.

Figure 8. Lizard bas-relief as shown at the 2010 waterjet meeting.

The concept of changing depth of cut, and thus being able to transfer photographs from the screen or paper onto metals or rock was an interesting academic challenge, that MS&T chose to address in a slightly different way.

Consider that the depth can be achieved by changing the speed of the nozzle on a single pass, so that the depth is controlled, or one can control the depth when only plain waterjets are used, by rapidly switching the jet on or off, as it makes sequential passes over the projected picture area.

The first image on steel led the subject in the first photo to mutter something along the lines of putting them on tombstones to remember those who had passed, so the next tests used photographs of my Grandfather and Dr. Clark, who founded the RMERC.

Figure 9. Images of my Grandfather and Dr. Clark transferred to basalt. (Dr. Zhao)

The technology advanced to the point that it was used to generate the plaque presented to me on my retirement from active academia.

Figure 10. My retirement plaque

Which seems to be a good point to close until next time.

*This University was kind enough to give me an honorary diploma.

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Sunday, September 15, 2013

Tech Talk - changes in South American exports

One of the large concerns that came up repeatedly over the years of discussions, both of the articles and of Drumbeat at The Oil Drum (TOD) was the subject of growth in domestic demand from some of the larger suppliers of oil and natural gas. This growth would be to the cost of the export market, and will, therefore, over time, reduce the amount available to importing nations. This becomes an even more painful reality to the rest of the world when the projections about future performance turn out to have been overly ambitious. Consider the countries of Latin America, where, back in 2010, the EIA drew the following baseline:

Figure 1. The largest producers of liquid fuels in South America in 2010 (EIA )

The EIA anticipated that Brazilian production would reach 2.8 mbd in 2012, and 3.0 mbd this year. However, as the latest MOMR from OPEC notes, Brazil will likely produce only 2.61 mbd this year, with the potential to rise to 2.67 mbd by the end of the year. However the rise in domestic consumption, and the failure to achieve the production goals expected has had an impact on the exports to the United States.

Figure 2. The changing volumes of US imports from Brazil (EIA )

The EIA reported that Venezuela produced some 2.47 million barrels a day in 2011, of which the USA imported roughly 1 mbd. That volume has, however, been declining for some time. (Note that in the plot below the Virgin Island imports should perhaps be included, because the crude that runs through the refineries on the islands originates in Venezuela, but they are not in this plot). At the same time a significant proportion (250 kbd in 2010) is now being shipped from Venezuela to China.

Figure 3. The changing picture of US imports from Venezuela over the years (EIA )

The situation in Argentina similarly shows that as with the other countries internal consumption is rising, while in this case overall production is falling and there is a consequent impact on exports.

Figure 4. The oil balance in Argentina (EIA )

China has been getting around 20% of Argentinian exports, while, in 2011, the USA got 40%, but the volumes of US imports have now turned negative.

Figure 5. The changing picture of oil imports to the USA from Argentina (EIA )

Of the five countries that were tabulated at the top of the post, Colombia is the exception. Production is still rising significantly, however it should be noted that, back in 2010 when the USA received some 422 kbd of crude and refined products from the country, China was financing a pipeline to carry 600 kbd to the Colombian Pacific Coast.

Figure 6. The increase in oil production with little increase in domestic production in Colombia (EIA )

The oil for the pipeline is anticipated to come from both Venezuela and Colombia, and the preliminary agreement for its construction was signed in May, 2012. Venezuelan agreement is still lacking to the deal and Venezuela, which was supposed by now to be sending natural gas to Colombia (after having received supplies for years) has still not made the switch. Volumes of exports to the USA from Colombia have fluctuated recently, while India and China have been acquiring oil wells and their production, which then ships to Asia.

Figure 7. The changing picture of oil exports to the USA from Colombia (EIA).

And that leaves Ecuador., which for those who might have forgotten, is also a member of OPEC. (It rejoined in 2007 ) It produces around 500 kbd, and with internal consumption running at around 200 kbd, exports the rest.

Figure 8. The changing picture of oil exports to the USA from Ecuador (EIA )

The recent news that the President of Ecuador is opening the rain forest to oil development, after trying to find funds for preservation of the forest without it and failing. Ecuador has an increasing debt with China (about $20 billion) and this is forcing it to use oil exports as a way of servicing that debt. One $2 billion loan, for example, carries a return agreement for some 130 million barrels of oil over six-years (60 kbd). Part of the loan from China will be spent on refineries in country.

The point to note in all five cases is that the imports to the United States have been declining. Given the increase in US domestic production that is not wholly surprising, nor is there yet any immediate cause for concern. But it is what is happening to whatever excess that these countries produce, over that consumed domestically and in the US that is significant. Because, increasingly it is going to China, and to Asia in general.

The concern that this raises is that, should US production not continue to rise at the rates that the more cornucopian of the main stream commentators suggest, then there will come a time when the US will have to go back to its suppliers from the last decade to ask for more. And at that time the odds are going to be high that either the countries won’t be able to meet the demand because their own domestic consumption has consumed the surplus, or that the surplus has been sold to China.

Given that China is making investments at the moment in the South American oil infrastructure, from wells to pipelines, means that it will control this production, and that removes a significant source of supply, at a time when it will be needed.

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Thursday, September 12, 2013

Waterjetting 13b - Milling without a Mask

As abrasive waterjets have developed they have been used to both cut through materials, and, in more recent work, have been used to mill pockets within the internal part of the piece.

Figure 1. Milled Pocket in Glass

In the early parts of pocket milling simple linear cuts were made adjacent to one another across the space where the pocket needed to be created. However, with the need to slow the head down and reverse direction, the edges of the pocket were being cut deeper than the inside floor, and this could cause some problems with part life and utility.

The first step to overcome this problem was to provide a mask, cut to the size of the pocket to be cut, but made out of a harder material, such as steel. By placing the mask over the piece, and setting the machine so that the cuts were made at constant speed over the pocket, a flat floor could be cut. All the slowing and reversing of the head takes place over the mask, so that it is destroyed fairly quickly. But if it survives one milling, then for some parts this provides a process that cannot be achieved in other ways.

Consider, for example, the sheet of glass cut in figure 1. The corners of the pockets are relatively sharp and of consistent radius all the way down the wall, which is relatively straight. A conventional mechanical milling tool transmits high levels of force between the part being milled and tool holder. Therefore, to prevent vibrations, the tool diameter must be no less than a quarter of the tool length. This means that the radius of the pocket wall cannot be less than one-eighth of the pocket depth. That restriction does not exist with an abrasive waterjet milled pocket, where the radius can be much tighter.

This is a critical issue in the milling of parts, where the milling is to get weight out of the component. In many parts that are made for the aircraft industry the part can be designed so that much of the internal volume is not needed for strength, and can be removed to lower the weight. But with conventional tools there are limits to how much can come from a single pocket, not with the AWJ system.

As the above figure shows, and masking and other techniques allow, the radius of the corner can fall below a tenth of an inch even when milling pockets more than eight-inches deep.

There remain, however, a number of problems with the use of the masking technique. It takes time to make and install the mask, and it costs an additional expense that makes the process less competitive. One of the problems that arise with the use of masking comes with rebound of the abrasive from the mask. Dr. Hashish has illustrated this problem with a diagram.

Figure 2. Abrasive rebound from a worn mask (Dr. Hashish)

If the mask is not shaped properly, or if it has been used before and is worn, then it may have a chamfered edge. When the abrasive waterjet stream strikes the curved surface it can be reflected back onto the work piece, giving an unwanted erosion shadow along the edge of the pocket.

Another problem can arise if the speed of the nozzle, and the distance that the nozzle moves between passes is not controlled to ensure a smooth and even cut over the pocket surface. As mentioned in an earlier post, the roughness of the cut increases if the abrasive particles are allowed to bounce and make a second cut within the piece. To ensure quality, as a result, the nozzle should be moved, relatively quickly, over the workpiece.

Yet the inertia of the cutting head, and the drive assembly in the table motion controller make this difficult to do at relatively high speed. John Shepherd at PIW Corp came up with an answer to this problem, that coincidentally did away with masking.

Figure 3. The Wobbler showing the nozzle motion.

The concept behind the device is that, by slightly oribiting the motion of the focusing tube around an axis, the jet will sweep out a circular path on the workpiece. Because it is only the end of the focusing tube that is moving the forces involved are small, and easily provided through a small motor on the device. The relative speed with which the nozzle moves over the surface is now much higher, while the speed of the main arm remains relatively low. The device was studied at MS& T and the parameters that controlled the depth and quality of cut were found by Dr. Shijin Zhang as part of his doctoral research.

As with the control of single passes of a non-oscillating nozzle, the distance between adjacent passes is critical to the satisfactory performance. If the distance is too great then ridges will be generated in the floor that are almost impossibly to remove using abrasive waterjets alone. Dr. Hashish, in an early paper on milling, for example, showed that if the upper layers of a pocket are aggressively milled with higher pressures and larger grit sizes, that this floor roughness cannot be later removed by using finer grit sizes. This is because the finer grit, while removing some surface asperities will still erode the surface relatively evenly, so that the roughness pattern shown in figure 4, cannot be later removed entirely.

Figure 4. Rough floor to the pocket where the distance between adjacent passes is too great. (Dr. Zhang)

On the other hand it is not always necessary to have a high quality surface for the pocket. For example MS&T have made a number of plaques where metal plates, cut and lettered with the AWJ are then inset into pockets in polished samples of marble or granite. Since these are not strength-bearing, and the plates are glued in place, the pocket floor does not have to be of that high a quality.

Figure 5. Milled pocket in the shape of the United States, Note the edge sharpness and the narrow cutting radii.

On the other hand, where a smooth surface is required then this can be equally well achieved through programming the path of the overall head movement, so that the nozzle sweeps the floor evenly. The glass plate in Figure 1 was also milled with the Wobbler.

Figure 6. Pocket cut into metal without a mask, using the Wobbler. Note the smooth floor.

I will come back to this topic next time.

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Wednesday, September 11, 2013

Of Gas attacks, World War 1 and my Grandfather

With all the discussion of the use of chemical weapons in Syria, it is perhaps worth remembering that their first use against a Western Army at any scale took place at the Second Battle of Ypres almost one hundred years ago. My grandfather was there, serving in the Northumberland Fusiliers, and this is an account of that battle.

In August 1914, at the beginning of the First World War,, the German armies marched through Belgium, hoping by avoiding the French fortifications at Verdun, to swing around and capture Paris. En route they ran into the British Expeditionary Force, (BEF) and initially drove this, and the French armies back into France. A counter-attack in September pushed the German Army back to a line, running from the North Sea to Switzerland, that was the sensible length of the battle fields until the closing months of the war in 1918. The Belgians has opened the sluices to flood the ground west of Ypres.

Figure 1. Troop movements leading up to the establishment of the trench line.

By this time a large proportion of the BEF, which included most of the experienced troops in the British Army, had suffered considerable casualties, and as 1915 began they began to be replaced by troops from Britain. At the same time there was massive enlistment in the British Forces, averaging 125,000 men a month.

Such was the case with my grandfather, who joined the 7th Battalion of the Northumberland Fusiliers on October 19, 1914. The battalion was send to Le Havre, on the 16th April, 2015. From there they were marched forward, and held in GHQ reserve as part of the 50th (Northumberland) Division around Steenvoorde and Cassel, some 20 miles west of Ypres. At that time the British Army held the line running south from Ypres, with French and Belgian troops mustered from their North to the sea.

Figure 2. Location of the British Armies at the end of 1914.

By this time troops had dug trenches, with simple barbed wire entanglements, but these early dugouts were shallow. Because the water level was about 2 feet below the surface, the trenches could not be dug any deeper than that, and often were only about three feet wide. Full height was thus achieved by building up sandbag walls to a height of about four feet. In front of these trenches the wire entanglements were placed stretching continuously and over a width of perhaps 6 yards.

On the 14th April a captured prisoner (August Jager) revealed that the Germans were planning an attack for the following day, and that they planned to use gas. The French general requested that his men be withdrawn but was over-ruled (and after the battle dismissed). Jager, some 17 years later, was arrested in Germany and sentenced to 10 years for treason. Nothing else was done. There is some evidence that gas was used for the first time the following day. However the gas was fired from shells and was not widely effective.

German records revealed that Chloracetone, Benzylbromide and Benzyliodide were used in shells before the Battle of Ypres. Some 3 000 shells loaded with dianisidine which irritates the mucous membranes had been tried, with no effect, at Neuve Chappelle. This was changed to Xylyl-bromide and the shells marked with a T. (This led to Allied confusion and interpretation of these as tear gas shells, in fact the effect is mainly on the eyes but in stronger doses it can cause edema of the lungs,) While these had some effect, the shells were initially lined with lead and this reduced their effect. They had only little effect on troops before the main battle.

Figure 3 Gas shell bursting

The 22nd of April began as a beautiful spring day , at around 5 pm, 5,700 cylinders of chlorine, located along the German lines and about 3.7 miles long were opened in the space of 3 minutes. Each container held 44 lb. of liquid which vaporized as it escaped. (A total of 120 tons of chlorine).. The gas then spread over land which, at that time was still being farmed, and formed a cloud which rose to a height of 10 - 30 yards and moved over the ground at a speed of around 1 mph. After ten minutes, to allow the cloud to reach the trenches 40 yards away, the German guns opened up in a barrage. By 7 p.m. the French guns had stopped. The Germans advanced until they met the Canadian reserves , who had been called up, and had advanced just beyond Mouse Trap Farm.

In the ten minutes that the gas took to pass over the lines, 5,000 French had been killed, 15,000 gassed, and 6,000 were captured together with 51 guns and 70 machine guns. There were virtually no survivors left in place, but those left retreated to form a new line.

Figure 4. German First Gas attack.

South of the French the line was held by Canadian Divisions, but a series of large gaps rapidly grew between these troops and the remaining French. This gap was some 2 miles long. By 9 p.m. the gap had grown to 4.5 miles except for only three places, at the Polcappelle road held by the French Tirailleurs, and the 3rd Canadian Brigade, by 2.5 companies at St. Julien and by four companies around Mouse Trap Farm. This line was some four miles from the backs of the 27th and 28th divisions on the other side of the salient. But at 7:30 pm German troops stopped advancing and began to dig trenches and a new gas line.

Figure 5. Position of troops at 5 pm on 22 April 1915.

To provide new troops the 50th (Northumbrian) Division, which was 20 miles away at Steenvoorde, was ordered forward. Arriving in France on the 16th April it consisted of the 149th (Northumberland), 150th (York and Durham) and 151st (Durham Light Infantry) Brigades. It was the first full Territorial Division to reach the front, some being sent forward by bus.

At midnight the Canadian 45th Division counterattacked the German line with success but without adjacent support, it had to be withdrawn. (The 2 battalions were reduced to 10 officers and 400 men). Messages between forces were being sent around by foot and by mounted riders who got as near as they could on horseback before finishing on foot. Many runners did not make it, and communications were poor. It should be remembered that most of the troops, supplies, wounded etc. travelled over the same road network , and that troops had neither gas masks nor steel helmets.

Figure 6. Troops lie in a field near a farm.

By daybreak ten battalions had been moved into the gap between the French and the Canadians but had little cover, and some lay in the open, while rudimentary trenches were dug. Facing them were some 42 battalions of German troops, heavily armed with artillery, machine guns and already occupying the ridges that crossed the area. The German guns outnumbered the allied by more than 5 to 1. .

The following day also began with perfect weather, with little enemy activity as the allies tried to decide how to defend against the gas. The idea that they used was to hold wetted cloth (handkerchiefs or what was available) over their mouths, damped if possible with a solution of bicarbonate of soda. If it was too wet the men could not breath through it and took it off. This did not become evident until the next gas attack.

Figure 7. Early gas masks>

The British tried unsuccessfully to counter attack, using the 13th Brigade, but it suffered very heavy casualties. All the reserves had been committed and the 150th Brigade was brought forward in buses while the 149th Brigade were ordered to march to Brandhoeke. Three of the Colonels that had been commanding battalions were killed, together with 56 other officers and 2100 men. The 150th Brigade was therefore ordered up to provide support for the remaining troops. The flat land and troops could be seen advancing for a long way.

On the 24th April the Germans to turn the flank by attacking the Belgian army to the north. They also launched a second gas attack, at the Canadian troops. Again the gas was launched from cylinders, along a thousand yard front. Some 24 battalions of Germans attacked the defending eight battalions, which had had little protection from the gas, and a mile-wide gap developed. Canadian forces then created a second defensive line behind the gap.

The strong German attack, however continued and by 3 p.m. the Canadians were forced to fall back through St. Julien, and were reinforced by 150th Brigade, counterattacking and halting the German advance.

Rain had started during the night and it came down heavily before ending in the early morning. Communication remained very poor. But reserves were now coming forward, and a British attack was planned, initially for 3 am, but due to blocked roads and only two gaps in the British wire it was delayed until after dawn. “Without adequate artillery preparation and support, on ground unknown and unreconnoitred, they were sent to turn an enemy well provided with machine guns out of a position which had ready-made cover in houses and a wood, and splendid artillery observation from higher ground behind it.”

Figure 8. Situation after the 25th April Battle, showing troop movements

The 149th Brigade was to attack Kitchener’s Wood and St. Julien from the left, but as they moved forward they came under rifle and machine gun fire. They advanced within a hundred yards of St. Julien before they were stopped in place. The men were pinned down, and eventually retreated. The Brigade lost 73 officers and 2,346 other ranks.

The German lines were well defended, and the British troops carried banners to show where they were, supposedly to help British artillery , but it also helped the Germans.

Figure 9. British troops approaching German trenches, note the wire and the flags.

The 4th and 7th battalions of the Northumberland Fusiliers (including my grandfather) were to reinforce the right flank and extended it to the right. The attack was called off at 9:15 am. (My Grandfather was in the band, and for two more months those individuals served as stretcher-bearers and to recover the wounded, but in May they were moved back into the ranks as regular troops.)

During the day the Germans launched several heavy attacks further down the line and troops were called up as available to create a viable defensive position, although it was necessary to retreat on several points. German attacks continued all night By this time the 8th DLI had lost 19 officers and 574 men and was reorganized as a company of 6 officers and 140 men. The 149th were ordered to the south of Wieltje to act as a reserve. The Lahore Division had marched up at noon, and had been in huts 5 miles south west of Ypres.

General Smith-Dorrien ordered that the Lahore Division should attack towards Mauser Ridge, They Lahore Division marched out at 5:30 am and lined up at 11 am. Moving forward to attack at 1:20 pm. They continued forward until they were within a hundred yards of the German lines, where they were halted. At this point gas was released from the German lines and although the troops held position in time they were withdrawn back to the British front lines, The Division had lost 95 officers and 1,724 men including 3 Lt. Cols.

The Northumbrian Brigade “fared even worse.” Only the 4th 6th and 7th battalions were available. Brig. Riddell did not receive orders to participate in the attack until 10 minutes before it was due to start at 1:20 p.m. Neither he nor his men were aware of the British wire than ran obliquely in front of the GHQ line before them.

“Notwithstanding the lack of protection on the left, the Northumberland Brigade, the first Territorials to go into battle as a brigade - pushed through the 10th Brigade line with the greatest dash, but like Gen. Hull’s men on the previous day, it was met by machine gun fire from the houses. Without artillery support it could only advance a short distance beyond the British front trenches. About 3:40 Brig. General Riddell was killed and when soon after, the leading lines reached some old trenches it was obvious that no further progress could be made..”

The brigade had lost 42 officers and 1,912 ranks, over two thirds of its strength. “ My grandfather survived, though he was wounded, and was in hospital on the 5th May. He was back on the front lines when he was shot by a sniper in June, 2015, and was then invalided out to the UK where, after almost two years of treatment he came home. He was also gassed several times(German artillery were firing 40% gas shells at the time) and for all the time I knew him suffered with his breathing in the winter.

Subsequently the German Army used gas around the salient, leading to a British withdrawal to a more defensible line. This was completed by the 3rd May and sensibly ended the Second Battle of Ypres. There were two subsequent gas attacks that month, but in the one on the 11th May the wind shifted, and two of the German battalions were caught in the gas clouds. By the time of the second, on the 24th May there were sufficient gas masks and material that the Allies were able to withstand the attack. British losses over the month were 2,150 officers and 57,125 men. German losses were 860 officers and 34,073 other ranks.

Figure 10. Battle Lines for the gas attack on the 24th May.

Figure 11. My Grandfather Private Archibald Summers.

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