Sealing anything at cryogenic temperatures requires extremely tight tolerances. If tight tolerances are not considered, holes may open at the source of the seal, allowing cold leaks to occur as referenced in this past post. In today’s How To, we’re going to discuss how to butt weld VCR fittings utilizing orbital TIG welding. Orbital welding has given the lab an advantage in that all our welds are now rid of human error and the whole operation is computer operated. The system being used is Swagelok’s M200 orbital welding system. The procedure is as follows:
Begin by flipping on the machine and selecting the “Program” key from the main menu.
Next, once the program is entered with specific parameters the following operating screen will appear.
Since the tube is 0.25 in., the Arc Gap must be set as to allow the tungsten rod to make accurate contact with the tubing. To do this, the height of the arc gauge must be set to a specific height. In this case, the height is 0.777 inches.
Next, place the arc gauge into the weld head where the tungsten rod is located. From there, loosen the top two bolts so that the tungsten rod can move freely. After, allow the rod to fall into the divot on the arc gauge. This will properly set the rod for welding. Finally, re-tighten the bolts and remove the gauge.
Since, the rod is now properly calibrated, the weld pressure must be set. First, review to the welders display and notice the “Normal Purge” table. The values are listed for correct ID flows and pressures. To test that the system is correctly measuring these values, the following system must be set-up as to accomplish this.
The system consists of a “T” with inlets from the weld pressure gauge and low-flow outlet. The tube at the junction is directed from the ID Weld outlet and the other is from the low-flow outlet. The crimped tubing is there to allow adequate back pressure so pressure measurements may be taken. To conduct the test, vent argon gas from the low-flow outlet and refer to the pressure and ID weld pressure gauge. If they correspond approximately with the values needed for your weld then the system is ready.
Next, the weld fixture must be set with the correct parts being welded. In this case, a piece of quarter tubing and a corresponding VCR fitting. Place one side of the tubing into the collet as shown with the stopper butting up against it to center the tubing within the fixture.
Next, tighten down the tubing fitted into the fixture and place the next half into its respective collet. Tighten down the tubing and the fixture is set and your piece is ready for welding.
Notice that the VCR side of the tubing has a male fitting with a crimped end attached. This ensures that during welding back pressure is kept consistent.
Finally, insert the weld held into the fixture and tighten it down. From there, attach the low-gas piping to the open side of the fixture. Once everything is tightened down and ready to go your system will look like this.
Start the weld by hitting the “Start” button on the control panel. The system will conduct a gas purge before welding as well as a post-purging. This ensures that there is no oxygen in the system before and after welding.
If the weld goes correctly and all pieces were set correctly, then you should have a beautiful weld as shown below. Congrats!
In the Fall of 2016 ME seniors Ryan Pitzer, Jake Enslow, and Austin Rapp designed the CLEAN (Cougar Lean) workbench. The CLEAN workbench is designed to maximize organization and accessibility in the work-space. These benches can easily be attached together to create a larger work-space, which can be largely beneficial in any research lab. This is an improvement from the work-benches previously found in the HYPER lab; while they were functional as a work-space, they did not have the practical modular features that the CLEAN workbenches include.
Old work-benches in the HYPER Lab provided a functional work-space, but were bulky, heavy, and lacked the modularity to properly implement all of our tools. New CLEAN work-bench (right) used during initial N2 cooling tests in the HYPER lab!
1. After ensuring that the chop saw has the aluminum cutting blade properly installed, and the tubes are properly clamped in place, cut the Bosch tubes in accordance to the following cut list:
2. Lay the maple top upside-down on the work surface and use the cordless drill with the (43/64″) bit to cut holes for the Horizontal Quick Connect barrels. Drill in a pattern shown below:
The center of the holes are to be marked 22.5 mm in from the side edges of the block. This ensures that the T-bolt notch for the Quick Connect is within tolerance.
The illustration above shows how a Quick Connect piece can clamp Bosch tubing up against the maple top. Above the notch rests a screw which pulls the head of the T-bolt in closer towards the barrel as it is tightened down.
3. In order for the Quick Connect assembly to work, a (7/16″) wide hole must be drilled on the side of the maple top perpendicular to the previously cut holes. This allows for the T-bolt to slide into the side of the barrel component of the Quick Connect.
4. Drop the barrel component of the quick connect piece into the maple block with the threaded side up. Then insert the T-bolt into the side of the maple block, and into the barrel. The notch on the T-bolt must be visible inside of the barrel. Slide the T-Bolt in to the point where the rubber seal is flush with the maple block. Next, slide pieces D1 and D2 on either side of the maple block, while the T-bolts are threaded through the Bosch tube. Tighten using the 8 mm Allen wrench.
The method we use here to connect the Bosch tubes to the maple block leaves a clean, seamless finish on the surface of the workbench.
5. Collect parts B1, B2, C1, E1, and E2. Prep the drill press with the (43/64″) drill bit. On each of the listed pieces, use a Sharpie pen and draw a dot marked 22.5 mm away from the edge of the tube. Repeat this process once for each tube so that one face of each tube is marked twice, once on each end. Align the drill press so the the bit is centered over the Sharpie mark. Drill through the tube. If using a drill press with a DVR, then align the drill bit on the corner of each tube. Move the drill bit so that the DVR reads -22.5 mm in both the x and y direction.
Then insert Horizontal Quick Connects on both ends of parts E1 and E2 as shown below:
6. Slide pieces E1 and E2 onto the short ends of the maple block. Tighten the Quick Connectors to complete the upper portion of the workbench.
Apply the end caps.
7. Collect parts A1-A4, L-mounting brackets, T-Bolt fasteners, and mounting hardware that is included with the purchase of the maple block. On one end of each tube, install the mounting brackets using the T-Bolt fasteners as shown below. Ensure that the mounting brackets are flush with the edge of the Bosch tube.
8. Using the same tubes from step 7. Before using the tap, apply a few drop of Aluminum cutting fluid to the area where you will be threading. Use the M12 x 1.75 tap to thread the four legs on the ends opposite to the mounting brackets.
Once completed, bolt on the adjustable feet or casters. When using casters, fully secure the bolt. When using leveling feet, ensure that all 4 leveling feet are extruded to the desired height.
9. The next step is to assemble the lower frame of the workbench. The lower frame requires nothing more than additional Quick Connects to assemble. Use the remaining Quick Connect pieces to assemble the lower frame as follows:
10. The final step to the CLEAN workbench assembly is to mount the upper half of the workbench to the lower half. Set the the maple block upside-down on the work-space. Set lower frame assembly upside-down on top of the maple block so that the four legs sit on the corners of the maple block. Use the included mounting hardware and cordless drill to connect the two halves together.
Complete CLEAN Workbench with casters ready for use in the HYPER Lab!
Estimated build time for each work-bench is 4-5 hours.
In this past post, we discussed using cryo-cycling to identify and fix possible cold leaks before installing equipment in the cryostat. This prevents a lot of problems before they can happen, often saving days of cool-down and warm-up if a test has to be called off. What happens, however, when the leak opens up cold? Your experiment is happily running along at cryogenic temperatures and, all of a sudden, that last temperature cycle proves too much. A crack is allowed to widen through an epoxy joint until you have a little leak and the test has to be called off. When you warm up, the expansion of the epoxy seals the crack and the leak is gone! One option in this situation would be to disassemble the entire system, testing each possible leak location as previously discussed. If your system isn’t a simple one, this could be a serious time investment, and opens up a lot of opportunity for you to break something else, improperly re-install a component, or otherwise mess up something that was already working fine. It was for this reason we developed a system for cryo-cycling in place – using nothing more than a Styrofoam cup and some Silly Putty!
Cryo-cycling in place – Instructions based off ASTM E499/E499M – 11 Test Method A:
Take a Styrofoam cup and cut a hole in the bottom or side of the cup just big enough to snugly fit around the test specimen.
Wrap a thin ring of Silly Putty around the test specimen where the cup will seal against the specimen.
Slide the Styrofoam cup onto the test specimen, the Silly putty should extrude into the cup a little bit and form a good seal against the cup and the test specimen.
Apply more Silly Putty, wrapping it around the test specimen and the inside of the cup to completely seal the bottom of the cup.
Fill the cup with liquid nitrogen (LN2) to start cooling down the cup and test specimen. As it cools, the Silly Putty will quickly transition through it’s glass transition temperature, first turning rubbery and then becoming a hard plastic that will be a sturdy seal.
Sniff all fittings, welds, and solder joints with mass spectrometer by passing the sniffer probe over likely leak points. Start at the bottom of the assembly and work your way up, holding the probe on or not more than 1mm from the surface. Do not move the probe faster than 20mm/s.
Continue sniffing in an orderly procedure from bottom to top. Mark any leaks so they can be remedied. Be aware that helium will rise, so a leak above a previously found leak may not actually exist. It is also important to be aware of the airflow in the room, as helium can be blown around the experiment and produce small “leaks” that don’t actually exist.
If any leaks are identified, take corrective action and restart this procedure. You may have to let the Silly Putty warm up a while before it is soft enough to be removed.
When I tell people I work on hydrogen fuel, they immediately say something very wrong like, “Are you worried about a mushroom cloud over your lab?” — Mushroom clouds are from a nuclear bomb detonation, and I don’t plan on starting thermonuclear fusion anytime soon in my lab, and if I did, it might save the planet. The other statement I usually get is, “Wow, don’t want another Hindenberg!” Again, very wrong. Several detailed studies from NASA and others have shown that the Hindenburg disaster was not caused by hydrogen. The Hindenburg’s sister ship, the Graf Zeppelin flew more than a million miles for nearly a decade on hydrogen before being grounded after the Hindenberg disaster. Go in and read the studies for yourself. The Hindenberg cut several corners the Graf Zeppelin did not, and you can’t expect the hydrogen to blow-out a diesel fire. The final one I sometimes get is, “Oh, the Challenger Shuttle!” again very wrong, Challenger was caused by the failure of a solid-oxide rocket booster o-ring.
So really, if I’ve just debunked the three most common misconceptions about hydrogen ‘incidents’ in a single paragraph, how dangerous is hydrogen fuel?
“Tests were devised in which tanks containing liquid hydrogen under pressure were ruptured. In many cases, the hydrogen quickly escaped without ignition. The experimenters then provided a rocket squib (a small powder charge) to ignite the escaping hydrogen. The resulting fireball quickly dissipated because of the rapid flame speed of hydrogen and its low density. Containers of hydrogen and gasoline were placed side by side and ruptured. When the hydrogen can was ruptured and ignited, the flame quickly dissipated, but when the same thing was done with gasoline, the gasoline and flame stayed near the container and did much more damage. The gasoline fire was an order of magnitude more severe than the hydrogen fire. The experimenters tried to induce hydrogen to explode, with limited success. In 61 attempts, only two explosions occurred and in both, they had to mix oxygen with the hydrogen. Their largest explosion was produced by mixing a half liter of liquid oxygen with a similar volume of liquid hydrogen. Johnson and Rich were convinced that, with proper care, liquid hydrogen could be handled quite safely and was a practical fuel — a conclusion that was amply verified by the space program in the 1960s. At the time, however, Johnson and Rich filmed their fire and explosion experiments to convince doubters.” https://history.nasa.gov/SP-4404/ch8-6.htm
This confirmed Kelly’s findings that the hydrogen fire ball dissipated quickly, providing less damage to the structure in every case versus the JP-1 test. The lightning test was inconclusive due to the container being obliterated in each case. The end result: hydrogen is safer than aviation fuel for aerospace applications involving an incendiary round penetrating the fuel tank. if you want more info on hydrogen safety in aerospace applications, NASA has loads of documentation on the history on-line, you can also check out Daniel Brewer’s book “Hydrogen Aircraft Technology.”
Very similar to the aerospace studies, when a hydrogen storage tank ruptures and the leak ignites, a hydrogen flame burns out, and up and away from the structure, very quickly. One number that I remember from an introductory hydrogen technology class is that hydrogen diffuses away at 40 miles/hour. Hydrogen literally is so fast that it has escape velocity and will eventually dissipate into space and the upper atmosphere. This is one of the inherent safety features of hydrogen — it doesn’t stick around long outside of a container. So as long as you don’t capture hydrogen beneath a structure where it can accumulate in dangerous quantities, you’re fine. Sadly, this excludes most research labs and garages where hydrogen sensors and ventilation must be carefully considered. Thankfully hydrogen is relatively easy to sense due to it’s high chemical activity.
So how dangerous is hydrogen fuel? In many situations where a vehicle is located outdoors, hydrogen is safer than conventional liquid fuels or natural gas. This in no way implies that hydrogen is not dangerous — there are many situations where hydrogen, like any other fuel, can cause an accident. As one life-long hydrogen expert said to me once, “Hydrogen is no better, nor worse, than any other fuel. You just have to know the rules for working with hydrogen.” Hence our work and mission.
If you’re thinking about doing a hydrogen experiment at home, best to use caution. Hydrogen, indeed, has the highest flammability range and lowest required ignition energy of any fuel (4%-80% H2 by volume is flammable with air and a grain of sand caught in a jet has enough kinetic energy to ignite a flow). The H2tools.org website has a wealth of information, including accident history to help guide you. Even the pros get caught in tough spots from time to time. Read about our near-miss hydrogen leak event sometime to get a feel for how very un-expected situations in complex systems can lead to risky situations. Regardless, with careful engineering, hydrogen fueled cars have a bright and safe future.
One of the promising undergraduate students within the lab I worked in at Wisconsin was machining a part one day on a mill. He passed on the unsupervised lab-specific machine shop for risk of safety and was in the established student shop in the College — a fancy facade of a facility with a carefully organized tool closet and a windowed observation office where the head machinist, a disliked authoritarian of a person with decades of experience, could watch the shop. The student was very sharp, but left the chuck key in the mill head and turned it on. The key spun around, flew out, and took with it two of his fingers. As he’s holding his bloodied hand the head of the shop comes running out and begins yelling at him, “why did you do that!!” This would surely be a mark on his safety record. The student, in shock, ran away to the hallway outside where other students applied paper towels to his hand and helped him to the hospital.
The problem here was not a lack of authority and control, or severity of consequences, but a lack of community connection and continuous improvement in the shop practices. A chuck key with an ejector spring prevents people from leaving it in the chuck, but is more expensive. The buddy system with a mentor can help spot some of these mistakes, whatever they may be. While these improvements may seem obvious to some, common sense isn’t so common.
I’ve written previously about how Universities evolved tree-like hierarchies. Nearly all of the reward system and feedback loops are geared towards promoting researchers to become power-driven authority leaders in their fields, which reinforces the extant authoritarian-legalistic system structure. The problem with these structures is communication. There is a very low amount of duplex communication, i.e. real conversations,,, talk. There just isn’t time for an administrator to sit down and spend quality time actually working with someone in a lab to mentor them — let alone knowing the people in their division. This results in a natural disconnection and un-grounding of administration from the people actually doing the work. I recently asked one of my friends, who is an administrator: “When was the last time you actually got a training by sitting down and doing the activity with someone, or a group of administrators?” He couldn’t remember a workshop that wasn’t primarily the traditional one way data dump.
Couple the difficulties in communication with declining resources, increasing performance pressures, and a 2-5 year graduation timer on all your primary lab personnel, and you have a recipe for a safety nightmare.
This means that it’s all too common to hear safety bulletins from administrators along the lines of the following: “make a new resolution to make this year accident free,” or to add “safety to annual performance evaluations,” or to “please report even the minor accidents,” and emphasis that “failure to report an incident… does result in consequences.” This is the easiest thing for an administrator in a power structure to do. Aside from invasive intrusions into labs, what else can they do? But this leads to other problems.
I once knew an administrator who still conducted research in their lab. One day, a post-doc accidentally mixed two substances in the fume hood, leading to an explosion that destroyed the hood. The administrator, under pressure to reduce accidents in their unit, did not report the incident to others as they were the only required chain of reporting. Months later, a young faculty member in their unit had a similar incident that destroyed another fume hood. A year later, a similar accident sent 16 people to the hospital at a neighboring institution.
When framed like this, the lack of communication almost seems criminal. Clearly, the sad reality is that these authoritative declarations coupled with punishments, within our communication-deficient authoritarian-legalistic system structure, can lead to corruption and actually be detrimental to the broader cause they intend to help. This command and control approach boils down to what is known as the deterrence hypothesis: the introduction of a penalty that leaves everything else unchanged will reduce the occurrence of the behavior subject to the penalty. I’ve previously written about the problems of applying the deterrence hypothesis to grading of coursework. In this case, safety is connected to my performance evaluation — which is primarily used for raise allocations and promotion. So in short, if an accident happens, my status and pay within the institution will suffer. This is assuming that the permanent disabling damage from losing fingers or another accident is not deterrence enough — the approach assumes that faculty delegate all risks to students rather than doing the activity themselves.
In a famous study titled, “A fee is a price” researchers investigated the efficacy of the deterrence hypothesis at mitigating the undesirable behavior of picking a child up late from daycare. This is low — abusing the personal time of a lower-paid caretaker charged with the health and well being of your child. In many ways this parallels the minor accidents, cuts, and knuckle bangs we’re being asked to report. In order to couple these to performance evaluations, a non-arbitrary metric must be created to decide how big the penalty, or price, should be. Contrary to expectations, the researchers performing the study found that adding the penalty actually increased the negative behavior that it intended to deter. The researchers deduced that the penalty became a price — if I’m late, I’ll pay the $20 and everything is ok — regardless of whether the caretaker had other plans. Perhaps the most troubling finding from the study was once the penalty was systemized, the bad behavior continued regardless of whether the penalty was removed or not. Once you marginalize or put a fee on a person, it’s tough to treat them as a person with dignity again.
I’ve seen this play out many times with daycares, teams, and communities I’ve been involved. Reliably the diminishing of people and disruption of personal connection leads to the demise and under performance of the organization. When an authoritarian is presented with this evidence contrary to their belief, they reliably counter with, “oh I’ll make the penalty severe enough to deter the behavior.” What else can they do? This approach, in the absence of appropriate developmental scaffolding, leads to a depressed environment adverse to uncertainty. Everyone becomes afraid to report safety, afraid to discuss safety, afraid to try new things and push the limits (isn’t trying new things and pushing the limits called research?) — often simply because trying new things is no longer the norm. When something is not the norm, it becomes an uncertainty risk and threat.
I once was having a discussion with an administrator about a new makerspace on campus. This prompted the statement, “But we’ll never be able to control the safety!” To this I immediately responded: 3D printers are robotic hot glue guns with safety shrouds! Every campus in the US has a gym with a squat rack (people put hundreds of pounds on their back on a daily basis with poor form), climbing wall (someone could fall!), pool (but what if someone drowned!), and a hammer/discuss/shotput/javelin toss (yikes!).
Arbitrary targeting of risk/blame is another characteristic of authoritarian/legalistic organizations because they lack established heuristics, a.k.a. processes, to work through safety scaffolding of new activities. Shot put and the hammer toss are established activities that our culture has normed to, where the risk in developing the established safety protocol was encumbered centuries ago. Less of a need for an administrator to CYA. Moreover, a command and control approach isn’t what makes them safe — it’s connections and discussions with people. The disincentive for not using the squat rack correctly is chronic back pain, something I deal with on a daily basis. That risk didn’t stop me from squatting incorrectly! The problem was ineffective coaching/scaffolding. Telling the coaches to coach better won’t explicitly fix that. And we can’t always rely on starting a new facility fresh with appropriate safety from the beginning.
I once attended a safety seminar, led by a well respected researcher at another academic institution. The researcher described the brand new building they were having built, and all of the safety protocols they implemented to make it safe. Afterwords I asked the researcher their approach for improving safety within established student clubs. The response stunned me: “I’m not really sure. We have another building for that. We never allow students to work after hours unsupervised.”
They had nearly entirely avoided teaching intrinsic safety culture! The students were never allowed autonomy to make decisions! I told myself I’ll never bring in a student from that institution. This exemplifies what happens when we are granted huge resources without having to perform or evolve to a level that justifies them like in industry. It was almost Orwellian. Certainly not the future our society and university needs.
After having a string of safety incidents in their unit, an administrator and safety board required every club and lab to have a “designated safety officer” or a designated authority to control safety for the group. After a few months in this position, one lab’s “safety officer” lamented to me, “Sometimes I need to be the bad guy because people don’t take safety seriously. But it gets tiring. They dislike me for it, blame me when stuff goes wrong, and they still don’t take safety upon themselves.”
This is directly analogous to the problem of quality control faced in Lean Manufacturing. In Lean, the question comes up of whether something you’ve manufactured meets the design specification. Do you hire a quality control czar to stop production if product starts coming out not to spec or unsafe? Ever heard a story of someone who was frustrated with the quality cop coming over to tell them things were wrong yet providing no explanation what was wrong or how to fix it? Moreover, the only way to ensure 100% quality/safety is 100% inspection — not a sustainable or scale-able approach. The Lean approach is to design quality/safety control into the production process — if the part can’t be made wrong/unsafe, it’s much easier to achieve 100% safety/quality. Moreover, if everyone is responsible for checking safety/quality during the production process, you just made everyone in your group a safety officer and multiplied the odds of spotting a risk before it’s realized.
Another common characteristic of authoritarian-legalistic approaches to safety is the posting of negative signage/reminders. “No ___ allowed.” “Don’t do this!” etc. Here’s a great counter example from Seth Godin titled, “How to make a sign.” The problem is we become numb to these negative associations and quit paying attention. That’s why we have “Did you know?” documents in our lab that just describe the right process for doing something. We try to include a funny meme at the top to get people to positively associate and look at these. Here’s an example posted near a compressed gas bottle area:
So we’ve shown through multiple ways the safety shortcomings of traditional authoritarian-legalistic bureaucratic structures. How do we get beyond these to cultivate a sustaining community and culture of safety within such institutions?
Let’s talk about Scaffolding Layers of Safety
In short, the real solution to safety is performance based funds from a diverse array of sources, like in industry. This naturally dovetails with a diverse, sustaining and supporting lab community. If you’re operating efficiently and effectively, you can’t stand the loss of a well trained person, even for a few days. But that’s a chicken or the egg conundrum for us in universities. I’ve written previously about the challenges and tips for building sustaining lab communities. It’s not easy! In short, you have to scaffold multiple orthogonal value sets. The end result can be a life-saver!
In a recent post I provided a scaffold to grow agency in engineering education. The key premise being that values change, and we need a scaffold that relates to many different value sets. Safety is no different. This provides the “layered” approach to safety that is popular in software security and other forward thinking fields. Here are several levels and examples of what we do in the HYPER lab to help activate the appropriate values:
Authority: Typical to most research labs. A grad student, or preferably a team of 2 grad students and 2 undergrads are responsible for maintaining an experimental or fabrication facility. Their names and pictures are associated with the project both in person and virtually through the lab website. They also are given an instant communication channel that the lab can see specific to the experiment/facility.
Legalistic: Each experiment has a Safety Protocols and Procedures manual that is continually refined (send me a note if you want to see ours, I don’t want to display online in case of nefarious actions.) The safety manual includes a Failure Modes and Effects Analysis (FMEA) that predicts all of the likely safety issues and emergency protocols. We implement the buddy system for changes to experiments and manuals — you need to have someone else there to approve. We also are continuing to develop a common lab-rules, standards, and values banner (tree of values for the design space) that goes above the doors to spaces. We are working to develop standard trainings for the right and wrong ways to utilize plumbing fittings and seals common in our work. We emphasize use of engineering standards wherever applicable.
Performance: Once a student is proficient with the responsibilities, literature, trainings, and practices in an area, they develop a did-you-know? heuristic process document. This informs people of the necessary steps unique to the space for accomplishing a task. Students at this level are expected to begin bringing in their own resources and recruit their own students to working on their project. We are also implementing a traveling safety award for the lab and tracking days without incidents.
Community: All of the lab members (without me) go to lunch together once a week. In addition we work together as a lab for a 3 hour time-block once a week on lab community builds and needs, including safety. This is greatly enabled by allowing all of the students to contribute to our community website (this site) and our Slack message board. We offer tours of our lab as frequently as possible to gain critical feedback and advise from potential stakeholders or partner labs. I’ve written previously about Tradings Places and Ways.
Systemic: We’ve established the expectation of all lab members to contribute and cultivate our system and community by looking for and enhancing restoring feedback loops that improve our efficiency in each of these levels. We do this by building our people from the ground up — we seldom import talent into our culture. This is very similar to Toyota and other lean production environments. No surprise, our lab has the Lean Philosophy of 5-S posted throughout: Sort, Sweep, Systemize, Standardize, Sustain.
So far things seem to be working. We have equipment and builds that I’m sure my colleagues think are ludicrously difficult and safety risks. We’re the only lab in the country that focuses on cryogenic hydrogen — which has the highest thermal, fluid and chemical power gradients. It’s ironically not something to be taken lightly! But I also know that the students are developing in incredible ways and coming together as a community to make it happen, safely. One of the reasons I know this is they’re not afraid to talk about safety, and they are having fun with it!
So let’s talk about safety! Send me your comments and suggestions: jacob.leachman<at>wsu.edu
Indium foil is used here in the HYPER lab to create gaskets for seals within cryogenic hydrogen systems. Research with cryogenic fluid systems requires uniquely shaped seals that do not degrade at the extreme cold temperatures, and Indium is recommended by several leading experts. The required gasket profiles are cut out of large thin sheets of Indium, this process produces scrap material that is not sufficiently large to use again. Due to a relatively low melting point we’re able to melt the scrap Indium to form an ingot that can then be re-rolled into a new sheet to be used. The preferred thickness of this sheet is 0.05-0.025 inch (1.27-.635mm) and the tooling in the WSU heat treatment lab has the ability to produce this thickness. Here’s a guide to the HYPER lab’s process for producing new sheets of foil from an ingot of Indium.
Slice the ingot into two, similarly, ~1 cm thick, ~3 cm in od, sized pucks so that the material will fit in the cold rolling mill.
The rolling mill is in Dana 236. You need to get approval from either Dr. Field or Dr. Wo before using the mill. Turn on the cold rolling mill and position the pedal so that it is accessible from both sides of the machine.
Cut a piece of wax paper that is large enough to fit through the mill while folded around the metal sample.
Fold the wax paper in half and place the metal sample inside to prevent sticking to the rolling cylinders.
Begin by setting the mill to the width of the first puck to be rolled.
Start making passes through the mill reducing the thickness by .4mm (1/4 turn of the adjustment handle) per pass until the puck is roughly 5mm thick.
After every 3-4 passes the thickness of the Indium measured with the caliper.
After reaching 5mm thick the metal will have to be rotated 90 degrees to prevent curling and each pass was lowered to a .2mm size reduction, slowing the rolling process will reduce waves in the sample.
At roughly 2.5mm sticking between the metal sample and roller will begin to become an issue that must be watched for and thickness measurements were taken after each pass.
Continue making passes through the rolling mill until the Indium sheet reaches the required 1mm in thickness.
Safe the rolling mill by backing off the adjustment handle, turning the machine off, and locking the room when you leave.
Once the material has been rolled, store it in a ziplock baggy in the drawer labeled “Indium” in ETRL 221.
Now you too can make effective thermal interfaces for use at cryogenic temperatures. Thanks for reading!
The following article provides an easy-to-follow guide to the HYPER lab’s indium extrusion process. The hope is that this guide will serve as training for those working in the HYPER lab, as well as a good starting point for others who would wish to extrude indium for cryogenic applications.
Hot plate capable of at least 200 °C (the higher the better)
Flat copper plate
Puck cast mold sized for extrusion chamber
Metal bin with 2-3 inches water for quenching
3/8″ Hex key
Metal shaft with diameter smaller than puck diameter
Slip-joint adjustable pliers
Retractable blade knife
Large pipe wrench
2 wood or metal blocks of the same size
Gather indium scrap. Make sure scrap pieces are small enough to fit into puck mold.
Place copper plate onto hot plate. Place puck mold onto copper plate.
Heat the hot plate to around 250 °C (or higher for faster melt).
Put indium scrap into mold and wait for indium to melt. For faster melting, push indium down into the mold.
While waiting for indium to melt, extruder can be assembled. The assembly consists of three parts: die, die holder, and extrusion chamber. Begin by placing the die into the die holder.
Screw the extrusion chamber into the die holder.
Bolt the assembly onto the end block of the hydraulic extruder.
Once indium has begun to melt, it will fill the mold cavity. At this point, add more indium scrap until the mold is full.
Using the adjustable pliers, grab the hot copper plate (with mold on top) and dip plate, mold, and indium into the water to quickly cool the assembly. You may now turn off the hot plate.
Once water has stopped boiling and making sure all parts of the assembly have been cooled, take the assembly back out of the water.
Placing the mold with indium stuck inside it onto two wood or metal blocks, use a hammer and shaft to knock the indium out of the mold.
Cut off impurities using the retractable blade knife.
Place indium puck into extruding chamber of extruder. Place the metal spacer behind it.
Turn on the hydraulic extruder by opening the compressed air valve and set it to ‘EXTEND.’ Then get ready on the output end of the extruder with the empty spool. It is best to have two people for this task: one controlling the extruder, one spooling.
Wait until the plunger reaches the indium and indium wire begins to emanate from the output end of the extruder. Be prepared, since wire will come out at high speed.
As wire emanates from the output end, wrap it around the spool while keeping a small amount of tension on the extruding indium.
When you hear the hydraulics begin working harder than they were initially, set the extruder to ‘RETRACT.’ When you hear this sound, the plunger is trying to extrude the metal spacer.
Break the end of the indium wire away from the extrusion outlet. You should now have a nice spool of indium wire.
Disassemble the extrusion assembly in order to remove the metal plunger. At this point a large pipe wrench will likely be necessary to unscrew the extrusion chamber from the end block. The remaining indium can be left in the extrusion die until the next extrusion.
Due to the very cold nature of our work, we find ourselves needing to design (and redesign) vacuum chambers on a regular basis. In order to do useful research, this usually means trying to pass electrical signals through a high vacuum seal, which as you may expect, takes time and money. However, we’ve come up with a few tricks to reduce our time and dollar expenditures.
First, we reduce the cost of our vacuum feedthrough components. An example of a prebuilt solution is $551 for 7 connection pins, but we can build a 26 pin passthrough for around $120. To reduce the cost of the hermetic connecter itself, we use a very common military hermetic specification, the MIL-DTL-26482 Series I MS3113 (Male) with matching a female connector MS3116F16-26S. The cheapest we’ve found this so far is through Detoronics. We will also order a KF blank through Ideal Vacuum Products or McMaster-Carr. By soldering the connector together, we save a significant amount of money.
Secondly, and most importantly, when we set up a vacuum feedthrough, we never solder connections directly to the hermetic connector. By putting a second, non-hermetic connector between sensors and the passthrough, we can avoid having to replace the expensive vacuum feedthrough, and instead just replace the inexpensive standard plug. For this second connector, the HYPER lab uses another inexpensive common connector, the 25 pin D-sub.
Instructions and pinout as follows:
Needed: 2 female 25 pin D-sub connectors, 1 MS3113M16-26S, 1 MS3116F16-26S, 1 KF blank (we usually use KF40, KF25 if a more compact application is required.)
25 pin D-sub to MS3113/MS3116F16-26S to 25 pin D-sub
Attach MIL-DTL-26482 Series I to KF flange, as shown in the post above.
Starting at Pin 25, follow pinout to connect D-sub to Hermetic
Pin 25 – Pin c
Pin 24 – Pin b
Pin 23 – Pin a
Pin 22 – Pin Z
Pin 21 – Pin Y
Pin 20 – Pin X
Pin 19 – Pin W
Pin 18 – Pin V
Pin 17 – Pin U
Pin 16 – Pin T
Pin 15 – Pin S
Pin 14 – Pin R
Pin 13 – Pin P
Pin 12 – Pin N
Pin 11 – Pin M
Pin 10 – Pin L
Pin 9 – Pin K
Pin 8 – Pin J
Pin 7 – Pin H
Pin 6 – Pin G
Pin 5 – Pin F
Pin 4 – Pin E
Pin 3 – Pin D
Pin 2 – Pin C
Pin 1 – Pin B
Note: Pin A on the hermetic connector should be free.
3. Starting again at Pin 25, connect the D-Sub to the other side of the hermetic using the same pinout.