5. Magnetic seal replacement procedure*

5.1.1. Rotating anode (RA) assembly removal

5.1.2. Magnetic seal removal

5.1.3. Bearing assembly removal & installation

5.1.4. Installation of magnetic seal


5.1.1. Rotating anode (RA) assembly removal

  1. Switch the x-ray generator off, close the chilled water supply to the Haskris water chiller, however, maintain the water circulation to the generator and wait for 1/2 hour.
  2. Shut the rotating anode (RA) off, if it is not already off, and shut down the vacuum pumps. Switch off the main powers at the gray breaker box on the wall and switch off the Haskris water chiller and wait for another 1/2 hour.
  3. Using the special tool (flat steel plate with a wedge) loosen the vacuum release valve underneath the front cover of the anode chamber and let in air slowly. Once the anode chamber is equilibrated with outside pressure, tighten back the vacuum release valve to the same tension (hand tight).
  4. vacuum release tool
    Figure 5.1.1.1 Special tool for vacuum release
  5. Place a plastic tray underneath the water connections to the RA assembly and to the anode housing and disconnect the two sets of water hoses. Remove quick-connects of the two sets of hoses and reconnect them in such a way that the flow will resume without interruption. However, this time the path of the flow should not contain the RA assembly.
  6. Remove the v-belt protection plate and the rotation sensor from the anode assembly. The v-belt protection plate is a perforated steel plate that is attached in front the anode rotation motor. The rotation sensor is a small device with a black cable and attached to the assembly with two Phillips screws.
  7. Using a #2 Phillips screw driver loosen, in cycles, the four Phillips screws found on the rotating anode assembly and remove all but one of them completely. The last screw should be removed ONLY after firmly holding the anode assembly by hand; otherwise, the surface of the anode assembly will get damaged.
  8. Take the RA assembly to a room with minimum dust, as the magnetic cassette assembly is very sensitive to dust and place it on a smooth spongy surface.
  9. To remove the magnetic seal the following materials are required:
    1. New magnetic seal
    2. Phillips screw driver (M40)
    3. "Compass"
    4. Minus screw drive
compass
Figure 5.1.1.2 Special tool "compass"

5.1.2. Magnetic seal removal

  1. Place the rotating anode assembly on a smooth thick sponge and using either a vacuum hose or a compressed air supply remove all the water in the water ports. There are three water ports: one for anode in/out, one for housing in/out and the third main target in-out. Consult Figure 5.1.2.1 for details.
  2. Figure 5.1.2.1 Rotating anode (RA) assembly with v-belt in place
    RA assembly full set
    Figure 5.1.2.2 RA assembly with v-belt, water cooling main port and water sealing shaft removed
  3. Remove the separator lock nut (See Figure 5.1.2.2) with the help of the "compass". This has a left hand threading.
  4. Disconnect the water cooling main port by removing the three screws (two long and one short Phillips screws (See Figure 5.1.2.2) and pull out the water-cooling port main body. Flipping the water-cooling main port assembly reveals the water seal (a rubber seal underneath a brass ring).
  5. It is a good idea at this point to replace the water seal by first removing the brass ring using the "compass" and then removing the water seal. These two can be seen in Figure 5.1.2.3.
  6. water port
    Figure 5.1.2.3 Water-cooling main port with brass ring and rubber water seal
  7. Take a fresh water seal and fill the grooved portion of the seal with silicone vacuum grease. Then place the steel washer on the side of the grease (and the groove).
  8. Flip the seal with the washer side facing toward the opening and gently place it on the opening. The water seal needs to be installed tight and flat and therefore requires the special tool "Plunger". Take the plunger and insert the thinner part in a press (or in the drilling machine at workshop) and tighten it to the press. Now slowly and uniformly lower the plunger while applying pressure on the water seal with wider part of the plunger in such a way that the seal gets inserted flat. Place the brass ring on top of the inserted water seal and hand tighten it using "compass".
  9. plunger
    Figure 5.1.2.4 Special tool "Plunger"
  10. Going back to the magnetic seal replacement, now remove the four counter-sunk Phillips screws seen on the water-sealing shaft. Thread in two long screws into the water-sealing shaft and gently pull it out. See Figure 5.1.2.5 for details.
  11. RA assembly
    Figure 5.1.2.5 Rotating anode assembly after removing water-cooling main port
  12. Now remove the pulley fixing ring (Figure 5.1.2.6) with the help of the "compass" and pull out the pulley (Figure 5.1.2.6).
  13. target and components
    Figure 5.1.2.6 Copper target, magnetic cassette seal and pulley
  14. Detach the target drum by gently pushing the top stem by hand while holding underneath the copper drum with another hand over a soft sponge. If it is hard to remove the target drum gently tap the copper drum with a rubber mallet and pull it out.
  15. Flip over the assembly and remove four cassette fixing Phillips screws (Figure 5.1.2.7) and pull out the magnetic seal. Once again, if the seal does not come out easily, tap it gently with a rubber mallet.
  16. Wipe out oil and dirt sticking to the flange. Also, thoroughly wipe out water drops that may remain on the circumferences of the magnetic cassette seal and in the o-ring groove.
  17. Now one can install the magnetic seal. However, this may be the time to replace the bearing assembly as well, if it has been more than 5000 h since the last change or you hear vibration while the RA is running. A new bearing assembly hardly makes audible sound. Please refer to section 5.1.3 for bearing assembly removal and installation.
RA flange
Figure 5.1.2.7 Magnetic cassette seal and RA flange

5.1.3. Bearing assembly removal & installation

  1. If you are only removing bearing assembly you have to consult section 5.1.2 and should at least perform steps 1 through 9 before you begin this section. However, if you have already performed steps 1 through 12 in section 5.1.2 you can continue.
  2. Flip the RA flange (RA assembly's main steel housing), if it is not already flipped correctly, such a way that the bearing assembly is facing you. Notice that the bearing assembly's two ends look different. The side facing you now has a flat surface (inner tube and outer bearing is flush with each other, see Figure 5.1.3.1), where as the side facing away from you and toward the magnetic seal has a recessed inner tube.
  3. bearing unit
    Figure 5.1.3.1 Bearging unit, bearing fixing ring and RA flange
  4. The side facing magnetic seal is called the vacuum side and the side facing you is called the water side (according to Rigaku engineer Steve Kirkorian). Using the compass remove the brass ring and slide out the bearing assembly.
  5. Wipe clean the interiors of the RA flange with lint-free wipe and remove all traces of water.
  6. Slip in a new bearing assembly ensuring that the face with recessed inner tube goes in first. This is very critical since the recessed portion of the bearing has to lock in with the inner tube of the magnetic seal to provide proper rotation of the magnetic seal.
5.1.4. Installation of magnetic seal
  1. Flip the RA flange such a way that bearing assembly faces away from you and clean the inside of the flange if you have not already done so as described in section 5.1.2.11.
  2. One should see two holes for cooling water in/out and a wedge on which the magnetic seal will seat with an o-ring. This o-ring is very critical and is NOT supplied with new magnetic seal. Notice that there are two o-rings in the magnetic seal itself. One on the steel face (#3) and another (#5) just above the rim for the water grooves. The third o-ring (#6) is what I have referred to above. Place this o-ring (S42) first and then place magnetic cassette seal.
  3. magnetic seal
    Figure 5.1.4.1 Magnetic cassette seal
  4. Tighten the seal with four Phillips screws cyclically ensuring the pressure is applied uniformly. Properly installed seal should sit tightly mating with the back of the bearing and flush with the brass surface.
  5. Insert the target drum, while making sure that the o-ring on the steel face is intact (#3).
  6. Flip the RA flange and slip in the pulley (#11) onto the stem of the target drum and insert it in such a way that the groove in the stem and the wedge inside the pulley match properly and fit snuggly.
  7. Slip in the pulley-fixing nut (#13) and tighten it with the compass. The pulley-fixing nut has threads inside.
  8. Grab a new water-sealing shaft (#15) and slip in a new S15 o-ring (#14) with little vacuum grease inside the shaft.
  9. Slip in the water-sealing shaft onto the stem and press it firmly and match the four counter sunk holes in the shaft to that on the pulley. Tighten all four Phillips screws, as before do this cyclically to ensure uniform pressure.
  10. Do not forget to apply the v-belt to the pulley at this stage, since we have come to a stage where the RA assembly can be mated with the water cooling port.
  11. From section 5.1.2 step 6 you would have installed a new water seal onto the water cooling port. Now install water cooling port onto the RA assembly. While doing this pay attention to the v-belt and do not allow either to slip out or get caught.
  12. Another essential point is that the pin on the target stem has to match correctly with the groove in the water cooling port. It can go only in two ways. However, only one of them is correct. To find out which one is correct, first insert a screw driver in to the main water port marked "IN" and make a mark on the stem of the screw driver flush with the surface of the cooling port. Now take the screw driver and insert it in to the port marked "OUT" and mark again. If the stem is installed correctly in the "OUT" port screw driver should have gone more and in the "IN" port less. If installed wrong, pull out the water port and rotate the stem 180° and repeat the procedure.
  13. Insert the three Phillips screws in the water cooling port and tighten them evenly there by attaching the port to the RA assembly.
  14. Insert o-ring KS-8(#21) outside the stem and before nut (#22). Using the compass tighten the nut. Notice it is a left hand threaded nut.
  15. This completes the installation of new magnetic seal, bearing assembly, new water shaft and water seal. The RA assembly can be attached to the generator and all water connections restored.