As many of you know, I have been fortunate enough to do my senior year in high school in the wonderful land of Germany. But of all the super cool and amazing things to do in Germany, so far the best one has been the Praktikum. The Praktikum is a student internship lasting one or two weeks at a place of the student’s choice. They are mandatory in the 9th class, but anyone can do them. This past week (Jan 28th to Feb 1st), I did a Praktikum at Rolls Royce Deutschland (RRD).
Here’s a bit about RRD. First, it’s not Rolls Royce Germany, it’s Rolls Royce Deutschland. That’s its name, so don’t translate it. Second, RRD works on jet engines. There are 2 centers in Germany: one in Oberursel and one in Dahlewitz near Berlin. I’m at Dahlewitz. Oberursel is the location of most part manufacturing within RRD and specializes in “Blisks,” which are a single component consisting of the blade and disk, while in Dahlewitz the engines are assembled and tested. Dahlewitz specializes in 2-shaft turbofan engines. Third, employees may work any time between 6 am and midnight, provided that they do NOT work more than 10 hours, which due to labor laws is illegal and would get RRD into a lot of trouble. Finally, the site is secured. I was not allowed to take any photographs. The pictures in the blog are from the Internet.
Because of the sheer amount of stuff I did at RRD, the rest of this blog post is split into what I did each day. Monday was the day to be trained in safety and basic operations, get all the safety equipment, and get introduced to the site of RRD. The first thing was a program called “Journey Through a Jet Engine.” This is provided by Rolls Royce, and is a thorough explanation of how turbofan jet engines work. Anyone can watch this, and it is in English. The link is below, and anyone even remotely interested in aircraft should look at it. And just a random fun fact from that: In temperatures of more than 600oC and in places where it can rub on other metals, titanium can burn. Following this was some boring safety stuff, most of which didn’t even apply to me since I don’t have a car and I wasn’t at RRD long enough to let me handle anything truly important. One of my guide’s colleagues also gave me a really interesting book published by Rolls Royce about jet engines, though I was not allowed to take it off site to read it. Then I acquired steel toed shoes and goggles for use on site before going on a tour of the test chambers.
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| Adam and Eve. Adam is closer to the camera |
Tuesday was more focused on beginning work, though first was another tour. This was to MTOC, or Materials and Operations Testing Center. In 3 words, what they do is “shake and break.” MTOC is in charge of characterizing all the attributes of the components of the engine (especially any blade) and to determine if the component is strong enough to easily survive the forces it experiences in flight. To do this, they use vibration testing on the components, vibrating them and recording their motion until they break. This serves the dual purpose of finding the failure point, which should be well above average conditions, and validating the computer models, which are used since titanium and nickel alloys aren’t cheap, and pixels are. MTOC also uses special ovens and lasers to heat the components to running temperature before pulling on them to determine at what force the component breaks, since the titanium fan blades need to survive forces equivalent to the weight of 13 African elephants while at speed. Finally, MTOC runs the Blade-Off and Bird Strike tests. Both of those are exactly what they sound like. In Blade-Off, a small explosive charge is used to break one of the blades off a fan, and the fan casing has to keep all of the debris within the engine and direct the debris in such a way that it would not make the engine completely unusable. Bird Strike involves MTOC shooting specially raised dead poultry at a fan to see how much damage it does. For all of the Bird Strikes tests the engine still needs to be usable, and for more of them the engine needs to only suffer a maximum decrease in performance of 20%. There are high speed videos of both, which links are below, but as a warning, the Bird Strike video is a bit messy.
The rest of the day was spent working. I wrote up the report to the LED test, which was used as the actual official report, and then also tested an inclinometer. This measures incline in the X and Y directions (of for you who like degrees of freedom, pitch and roll) up to 80 degrees, and will be used for people who use really long tools in really dark places, allowing them to know if they have put the tool in without any incline so it does not scratch part of the engine. At the end of the day I was writing up the report before I left so I didn’t miss my bus home.
Wednesday was sensor day. The entire day had something to do with sensors, including MI cables, pressure sensors, flow meters, accelerometers, thermocouples, strain gauges, and thermal paints. All of these are used on engines to determine the kind of loads the engine components are receiving. Strain gauges in particular were interesting because they measure the amount of bending and twisting a component receives since the expansion of the component also expands the strain gauge, changing its resistance. More on how they work is in a link below. Thermal paints were by far the coolest thing, though. They measure the maximum temperature a part receives by changing color as the temperature, and thus energy imparted into the paint, increases. There are about 15 different types of paint, all with different ranges and shift points. However, one limitation of them is that they are time dependent, meaning that in the test to determine temperature they run the engine with the paint for 10 minutes acceleration, 3 minutes exactly at speed, and 10 minutes deceleration. Any more or less would change how much energy the paint received. There is a second method, silver melt-off, which will measure where the temperature is more than 980oC, independent from time.
The first thing that happened Thursday is that I got to see the mobile data acquisition trailer, called MIDAS. It has been all across Europe, including elsewhere in Germany, France, Spain, and England. It has to be able to be ready for use with just a couple weeks warning because tests can pop up at any time. Currently, there are no tests in the near future, so they are renovating the trailer. Following MIDAS I was introduced to how thermocouples work. Thermocouples consist of 2 unlike metals that, when exposed to heat, generate a voltage, and how large the voltage is (after being corrected for any extension wires of a different metal) can be used to find the temperature difference from a point of known temperature. There are many, many different types that can be used for temperatures above 2100oC all the way to about -250oC. Currently, thermocouples need to be used in high temperature material tests at MTOC because the heat causes the strain gauges to expand, changing their resistance and displaying a load even when no load is present.
Friday (last day. :’( ) was much less exciting than the other days. Most of what I did was pick up packages, delivery the measurement tools for the thermocouples and strain gauges to MTOC, and read a fascinating book about jet engines. I still did get introduced to 2 new sensors, though. They are fishbone strain gauges and accelerometers.
Fishbone strain gauges are 2 strain gauges set at 45 degree angles. The angle allows them to compensate for temperature, force, and other unwanted measurements, so fishbone strain gauges are only used to measure torque on an engine component. The way they work is the same as regular strain gauges, though.
As most people know, accelerometers measure acceleration or vibration. But the output from an accelerometer isn’t the actual acceleration of the component. When an accelerometer is attached to a component, it is recommended that they are attached with a screw. However, at Rolls Royce this isn’t always possible because they can’t damage the component. Instead, they glue it to the component using either epoxy or HBM adhesive. They also place a piece of aluminum tape before applying adhesive since it is difficult at best to remove the glue. However, the glue isn’t as rigid as a screw, and so something called dampening occurs. Dampening is the absorption of some of the vibration by the adhesive. Lower dampening coefficients mean the more effective the energy transfer is, and the more accurate the accelerometer is. Following this, it was time for me to check out, and my internship came to an end. It is a memory I will take with me for a long time, though, and I am glad I had the opportunity to work at Rolls Royce. If any of you ever get a chance to do a short work session at any company, I strongly recommend taking that chance, as there is a lot of how companies work, what they do, and how what you are learning actually applies that you simply cannot get in school.
All links are below, and if you have any questions or comments, please leave a message on the discussion board or personal message me. I will gladly answer any questions you have.
Links:
Journey through a jet engine: http://www.rolls-royce.com/interactive_games/journey03/index.html Want more Rolls Royce games/activities? http://www.rolls-royce.com/about/education/resources/12_19_year_olds/index.jsp
Blade-Off: http://www.youtube.com/watch?v=Ek6adm4iV4Y
Bird Strike for those of you who do want to watch it: http://www.youtube.com/watch?v=y2OS2pwrZTI
Strain gauges: www.sensorland.com/HowPage002.html
Discuss this blog here: http://tinyurl.com/bloginspire12
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