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Hydrogen Properties for Energy Research (HYPER) Lab How To

Orbital TIG Welding – How HYPER strives for the best welds!

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:

Procedure:

1.

Begin by flipping on the machine and selecting the “Program” key from the main menu.

  2.

Next, once the program is entered with specific parameters the following operating screen will appear.

3.

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.

4. 

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.

5.

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.

6.

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.

7.

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.

8.

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.

9.

If the weld goes correctly and all pieces were set correctly, then you should have a beautiful weld as shown below. Congrats!

 

CLEAN Workbench Assembly

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 feature.

 

MATERIALS:

  • 2   Bosch Tubes, 20′ long
  • 1   Maple wood workbench top 60″ x 24″, straight edge
  • 12 Bosch Horizontal Quick Connects
  • 12 Bosch Vertical Quick Connects
  • 8   Bosch T-Nut bolt fastening kit, L-19
  • 4   Tube end covers, 45 mm profile
  • 8   L-Mounting brackets
  • 4   Leveling feet, M12 x 44 OR 128 mm locking casters
  • Aluminum cutting oil

 

TOOLS:

  • Chop saw
  • Aluminum chop saw blade
  • Cordless drill
  • Drill bits: (43/64″), (7/16″)
  • 8mm Allen wrench
  • Drill Press, DVR preferred
  • Phillips Screwdriver
  • Adjustable wrench
  • Rubber Mallet
  • Clamps
  • M12 x 1.75 tap

 

PROCEDURE:

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

Cryo-cycling in place – Styrofoam cups and Silly Putty to the rescue!

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.

    Styrofoam cup photo
    A Styrofoam cup with hole cut in the bottom.
  • 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.

    Styrofoam cup fit around hotwire plug image.
    Styrofoam cup in place. Notice the Silly Putty sticking through at the seal.
  • Apply more Silly Putty, wrapping it around the test specimen and the inside of the cup to completely seal the bottom of the cup.

    Image of cup fitted around hotwire sensor with Silly Putty seal.
    Filling in the Silly Putty for a complete seal.
  • 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.

    Image of LN2 in the Styrofoam cup
    Sealed Styrofoam cup filled with LN2
  • 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.

 

Cold Rolling Indium Foil

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.

 

MATERIALS:

  • Indium scrap ingot
  • Wax paper
  • Digital caliper
  • Hydraulic cold rolling mill
  • Retractable blade knife
  • small container for indium scrap

 

STEPS:

  1. Using the retractable blade knife cut off any surface impurities from the indium ingot while collecting any material cut off for re-melting. Here’s a guide to safe use of a retractable blade knife.

    Ingot after removing surface impurities.
    Ingot after removing surface impurities.
  2. 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. ingot-mid-cutingot-cut-in-half
  3. 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.

    Available hydraulic cold rolling mill.
    Available hydraulic cold rolling mill.
  4. Cut a piece of wax paper that is large enough to fit through the mill while folded around the metal sample.

    Indium puck after one pass.
    Indium puck after one pass.
  5. Fold the wax paper in half and place the metal sample inside to prevent sticking to the rolling cylinders.
  6. Begin by setting the mill to the width of the first puck to be rolled.
  7. 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.

    Rolling mill adjustment handle.
    Rolling mill adjustment handle.
  8. After every 3-4 passes the thickness of the Indium measured with the caliper.
  9. 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. 1925-inch-measurment

    Indium sheet before first rotated pass.
    Indium sheet before first rotated pass.
  10. 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.
  11. Continue making passes through the rolling mill until the Indium sheet reaches the required 1mm in thickness.

    Finished Indium sheet
    Finished Indium sheet
  12. Safe the rolling mill by backing off the adjustment handle, turning the machine off, and locking the room when you leave.
  13. 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!

 

Extruding Indium Wire

We use indium wire for creating cryogenic seals in the HYPER lab. We buy most of our wire from Indium Wire Extrusion (IWE). Indium is expensive however, quoted by IWE at $180/oz. Rather than selling the wire back for half its original price, we like to recycle our indium by melting it down and re-extruding it into usable indium wire. Indium’s low melting point of 156.6 °C (313.9 °F) and softness (Mohs hardness 1.2) make this process cheap and easy. We have the capability of extruding 0.0625 inch (1.5875 mm) and 0.1 inch (2.54 mm) diameter indium wire with the equipment we have in the lab.

20160707_123729_HDR
A 13.6 oz. block of indium worth $2,450.

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.

 

20160708_103308_HDR
HYPER’s extruder setup.

 

MATERIALS:

  • Hydraulic extruder
  • Hot plate capable of at least 200 °C (the higher the better)
  • Flat copper plate
  • Puck cast mold sized for extrusion chamber
  • Indium scrap
  • Empty spool
  • Metal bin with 2-3 inches water for quenching
  • 3/8″ Hex key
  • Hammer
  • 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

 

STEPS:

  1. Gather indium scrap. Make sure scrap pieces are small enough to fit into puck mold.

    Indium scraps in a cup and in the puck mold. Notice the puck mold is placed on top of a copper plate.
    Indium scraps in a cup and in the puck mold. Notice the puck mold is placed on top of a copper plate.
  2. Place copper plate onto hot plate. Place puck mold onto copper plate.
  3. Heat the hot plate to around 250 °C (or higher for faster melt).
  4. Put indium scrap into mold and wait for indium to melt. For faster melting, push indium down into the mold.
  5. 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.

    20160706_152637_HDR
    From left to right: Extrusion chamber, die, die holder.
  6. Screw the extrusion chamber into the die holder.
  7. Bolt the assembly onto the end block of the hydraulic extruder.

    20160706_153825_HDR
    The completed assembly attached to the end block.
  8. Once indium has begun to melt, it will fill the mold cavity. At this point, add more indium scrap until the mold is full.

    20160706_161106_HDR
    Melted indium.
  9. 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.

    20160706_161142_HDR
    Quenching.
  10. Once water has stopped boiling and making sure all parts of the assembly have been cooled, take the assembly back out of the water.
  11. 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.

    Here’s one way to get the indium out…
  12. Cut off impurities using the retractable blade knife.
    20160706_161741_HDR20160706_161901_HDR (2)
  13. Place indium puck into extruding chamber of extruder. Place the metal spacer behind it.

    20160706_161935_HDR
    Indium puck inserted in the extrusion chamber (without metal spacer).
  14. 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.
    20160708_103330_HDR (2)
  15. 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.
    20160706_162201_HDR (2)20160706_162326_HDR (2)20160706_162357_HDR (2)
  16. As wire emanates from the output end, wrap it around the spool while keeping a small amount of tension on the extruding indium.
  17. 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.
  18. Break the end of the indium wire away from the extrusion outlet. You should now have a nice spool of indium wire.

    20160706_162415_HDR
    The final product.
  19. 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.

Surplus: What, Why, and How

Sometimes it’s necessary to remove the junk, and here’s how we do it:

  1. #1Log in to myFacilities with your WSU Network ID
  2. #2In the list, select the link for Work Request
  3. #3 Select “Request pick-up or drop-off of Surplus items”
  4. #4 Fill out the items to be surplused, and then choose “Landeen, Gayle” in the dropdown menu for approval authority.
  5. Submit the form, and you’re done!

Slide1

Saving money (and time!) with HYPER’s wiring system – Vacuum Feedthroughs

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.

Male side installed on a KF flange
MIL-DTL-26482 Series I MS3113 installed on a KF flange
IMG_1226
MS3116F16-26S with installed leads

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.

A 25 pin D sub connector installed inside CHEF
A 25 pin D sub connector installed inside CHEF

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

  1. Attach MIL-DTL-26482 Series I to KF flange, as shown in the post above.
  2. Starting at Pin 25, follow pinout to connect D-sub to Hermetic
    26 pin MIL-SPEC connector pinout
    26 pin MIL-SPEC connector pinout
    25 pin D Sub pinout
    25 pin D Sub pinout
    1. Pin 25 – Pin c
    2. Pin 24 – Pin b
    3. Pin 23 – Pin a
    4. Pin 22 – Pin Z
    5. Pin 21 – Pin Y
    6. Pin 20 – Pin X
    7. Pin 19 – Pin W
    8. Pin 18 – Pin V
    9. Pin 17 – Pin U
    10. Pin 16 – Pin T
    11. Pin 15 – Pin S
    12. Pin 14 – Pin R
    13. Pin 13 – Pin P
    14. Pin 12 – Pin N
    15. Pin 11 – Pin M
    16. Pin 10 – Pin L
    17. Pin 9 – Pin K
    18. Pin 8 – Pin J
    19. Pin 7 – Pin H
    20. Pin 6 – Pin G
    21. Pin 5 – Pin F
    22. Pin 4 – Pin E
    23. Pin 3 – Pin D
    24. Pin 2 – Pin C
    25. 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.

Your completed passthrough!
Your completed passthrough!

Finding Cryogenic Material Propeties

Many people don’t consider from day to day how we know properties of any given material for use in design. It seems to be common knowledge that water freezes at 0°C, and it’s easy enough to look up thermal conductivities or heat capacity of common metals, gasses, and building materials. What happens, however, when your operating conditions are hundreds of degrees below room temperature? You can’t assume the same, easily found values anymore – you have to find someone who has taken the measurements at those extreme temperatures. So where do you go? Here’s a list of some good options we’ve used in the past to find data.

  1. Engineering Equation Solver (EES)
    • The lab uses EES for much of the thermodynamic calculations we do, and one reason is that it has standard curves for thermodynamic properties of many materials across a wide range of operating conditions. Through available function calls, you can get accurate thermodynamic properties for the most common real and ideal fluids, even at cryogenic temperatures. EES also has a selection of commonly used incompressible substances. Whenever using a material for the first time, make sure you look at the substance properties and references to ensure you understand the valid operating conditions and assumptions the substance is using.
  2. NIST Cryogenic Materials Database
    • NIST has data for several common structural materials at cryogenic materials. Some of these are referenced as incompressible substances in EES, some are not. The specific properties given varies for the different substances.
  3. Researchmeasurments.com / Jack Ekin’s Experimental Techniques for Low-temperature Measurements: Cryostat Design, Materials Properties, and Superconductor Critical-Current Testing
    • This site provides supplemental information and updates for the book Experimental Techniques for Low-temperature Measurements: Cryostat Design, Materials Properties, and Superconductor Critical-Current Testing, published by Oxford University Press in 2006, 2007, and 2011. The book is a handy guide we often use for reference in building our cryogenic systems. The site has many figures and data tables from the book, including many on the varies properties of materials commonly used in cryogenic design. The book provides much further insight into design that is not available on the website, and the lab owns several copies for reference.

These are the sources we’ve used the most in the lab – please let us know if you have a favorite we haven’t listed!

Cryogenic Seals using Indium

Finding a way to seal small, mobile molecules such as hydrogen and helium at cryogenic temperatures can be quite difficult. Most common seals break down at such cold temperatures, and even a tiny leak path can be catastrophic when working with flammable gasses and temperatures that can freeze the oxygen right out of the air. Luckily, we have wonder element 49: Indium. High purity indium has a lower melting point, and hardness than lead, making it malleable enough to be an effective sealing material. In addition, at high purities, indium readily pressure welds to itself, and bonds to other metals, glass, and ceramics.

Lab member Casey Evans installing a cryogenic indium seal.
Lab member Casey Evans installing a cryogenic indium seal.

In the HYPER lab, we’re set up to extrude 0.0625 inch (1.5875 mm) and 0.1 inch (2.54 mm) diameter wire, and therefore use this wire size most often. For most seals we create, this is a usable size, and allows us to standardize seal design and indium extrusion. Although much of our wire is recycled and re-extruded, we will occasionally buy new indium wire from Indium Wire Extrusion, currently priced at $150 /oz.

A good indium vacuum seal is designed to fill a small gap around the sealed volume with pure indium through an even application of pressure, usually using a bolted flange. Making things easier for us, Indium Wire Extrusion has some helpful guidelines for proper indium seal design. Indium Wire Extrusion recommends three types of indium seals:

  1. A semicircular indium seal. This seal is created by using a ball end mill to machine out a rounded ring in one side of the sealing flange. The other side of the sealing flange should be polished smooth to provide a good sealing surface. Recommended geometry is to use a ball end mill the same diameter as the wire you’re using and machine to a depth equal to half the wire diameter.
  2. A rectangular groove seal with mating surface. This seal is created by machining a rectangular step groove into one side of the flange, and a smaller rectangular step protrusion on the other side of the flange. This geometry has the advantage of not only providing a secure effective seal, but also self aligning the flanges so the seal occurs in the same place every time. Recommended geometry is a groove the same width as the the wire being used to seal and a gap area equal to ~80% of the wire cross sectional area. The protruded step should be chamfered to allow the indium to easily flow into the gap to the sides of the protrusion.
  3. Similar to the first sealing method, you can use a single seal on the flange, but with a square step groove. This can be machined with a standard flat nosed end mill. Again, the gap area of the seal should be 80% or slightly less of the cross sectional area of the wire.

Some other general suggestions when creating / using indium seals:

  1. While HYPER lab hasn’t done this extensively in the past, it can be very helpful to include a jack screw in the flange design. Indium seals after compression and cryo-cycling can be very difficult to pull apart and a jack screw will ensure that you can get the flange back apart for the next run!
  2. When creating the indium o-ring, cut the ends at as shallow an angle as possible. Ensure these ends are overlapping, so that one end of the indium wire will crush on the other to seal the ring together. A straight 90° cut will leave a gap between the ends of the indium wire in the ring, which can allow a leak path through the seal.

Cleaning Helium Compressors

The helium compressor that drives a cryocooler has to effectively reject the heat it’s removing from the helium stream to prevent itself from overheating, and keep the cryocooler cooling efficiently. In most cases, this means running a heat exchanger with a cooled water loop to keep everything cool. This can be very effective when you’re running high purity, clean water through the heat exchanger, but dirty, rusty, or impure water can reduce performance and foul the heat exchanger tubes. In the lab, we use a cooling loop independent from the building water paired with a water filter to help keep water as clean as possible in the loop. Unfortunately, our water pump in the loop had a cast iron casing and impeller, which began to rust and dirty the water. During the process of cleaning out the water and rebuilding the system, we’ve learned a few things about our cryocoolers and keeping them clean.

Sumitomo (SHI) Cryogenics:

The heat exchanger built into the SHI HE-4 cryocooler is a 1/2″ flattened copper tube, and pretty robust. It’s unlikely for anything to get stuck in the tube, although fouling on the surface is possible. Calling Sumitomo, they recommended reversing the water flow through the heat exchanger while the compressor is off to ensure the heat exchanger is free of obstruction. Running vinegar solution through the lines will help remove fouling.

Cryomech Compressors:

Similar to the Sunitomo cryocooler above, the Cryomech cryocoolers also use copper tube in their heat exchangers. The technical representative from Cryomech recommends reversing the flow on the heat exchanger and to flush the system with a standard strength Calcium, Lime, and Rust (CLR) Remover solution. In the event of sludge build up, a 50 wt. % solution of hydrogen peroxide (H2O2) is a viable option in extreme cases.

Washington State University