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Galvanic corrosion

Discussion in 'off topic' started by matt j, Mar 21, 2020.

  1. dweezil

    dweezil pfm Member

    Can't quite see clearly but if the outer is the Al bit heat the whole thing in an oven.

    I usually set it to 150C and the parts separate easily. The Al expands more than the ferrous shaft, thus loosening.

    On reassembly use a Moly assembly paste of some sort for Al / Fe combinations; i use Loctite LB 8012.

    If the stuff attached to the shaft won't take any heat you're back to making a puller and heating as much as you dare i guess.

    Can you get a puller on then turn the oven up to heat the assembly?
  2. Vinny

    Vinny pfm Member

    Its not clear to see, but an orthodox puller may not fit. If not, it is a simple and cheap job to make one so long as there is something that can be used to brace against.

    Drill and tap the end of the hub with as large and coarse a thread as possible, as deep as the end of the shaft. You then need a piece of studding or a bolt, threaded full length, at least a couple of inches longer than the depth of the thread in the hub.
    You then need a short length of pipe that drops over the hub, at least an inch longer than the length of the hub. Then a hefty cross piece with a clearance hole for the bolt. Run a nut up under the head of the bolt (or two lock nuts on studding) and then ideally a couple of penny washers with a cheap thrust bearing between them, put the pipe over the hub, thread the bolt through the hole in the cross piece and screw it into the thread you've just cut in the end of the hub.
    One spanner on the nut, one on the bolt head, pull the hub off (after heating ideally).
  3. matt j

    matt j pfm Member

    Well they're obviously already inside an oven so the heat from that should separate them if that is the case, which isn't. Can't fire up the oven as the fan comes on automatically and detects when it has been disconnected so just faults out if you try and disconnect the fan motor from spinning. I've had the blow torch on it with zero effect.

    Reassembly doesn't matter as the replacement part isn't an Al hub.

    We've already tried numerous combinations of pullers but none of us have managed to successfully get one off that way, even the ovens with both s/s motor shafts and fan hubs take some almighty force to pull off with the puller, not helped on this oven by the fact the element surrounds the circumference of the fan so access isn't great
  4. stevec67

    stevec67 pfm Member

    Can you drill and tap the hub and get a slide hammer in?
  5. matt j

    matt j pfm Member

    Possibly, but there'd not be much thread as the hub only sits proud of the end of the shaft by about 10mm.

    During bouts of frustration I've wondered about fetching the battery grinder from the van, but it's such an enclosed space that if a disc shatters I'll end up looking like something from a horror movie.
  6. Vinny

    Vinny pfm Member

    Heating the hub should be helpful. I strongly suspect that you haven't spent long enough heating it with a torch - it would take quite a while working the torch round the hub to get it hot enough right through.
    Colin Barron likes this.
  7. matt j

    matt j pfm Member

    I'll give it more heat next time then and see how that goes.

    It's one of those jobs that if it were on the bench with a vice and endless tools available it would be no trouble at all, it's the location that kills all the easy options, that and working with what is available to me from the back of the van.
  8. Vinny

    Vinny pfm Member

    If you were doing one or more a week, every week, the answer would undoubtedly be a bespoke splitter, ideally hydraulic. It would literally take a few tens of seconds, a couple of minutes at most, coming in from two positions. You'd just have the faff of getting the cutter design right to begin with, but once done....
  9. cubastreet

    cubastreet Espresso Fiend

    Have you tried an impact wrench on a hub puller? That's a powerful combo.
  10. matt j

    matt j pfm Member

    The problem is getting a puller on it in the first place, I don't have a manly enough impact driver to do it either. It's the sort of job you don't do often enough to spend serious money on tools to complete, it's just one of many very awkward semi regular jobs I get.

    One thing is for sure, I'd like 5 minutes in a room with the cretin that designed it.
    Vinny likes this.
  11. Vinny

    Vinny pfm Member


    Truth be told there is the mother of all splitters out there, sat in someone's workshop somewhere, built for some particular job, now surplus. Finding it though...………..
    That said, I wouldn't want one that relied on a thread at that sort of size. A total nightmare to use, even on a bench.
  12. stevec67

    stevec67 pfm Member

    Mother of all splitters. When I was a lad and buggering about with cars there was a local mechanic who was "Mr Puller" . Any special tools that were pullers, presses or splitters, he had. He used to collect them, as local garages got rid, yard sales, all that. "Jag XJS lower suspension swivels? Yeah, I think this will fit. It's a hub puller fro m a grey Fergy, I've made a bracket to fit the XJ6, it's a bastard without but this works ". He'd lend them out for beer money.
  13. matt j

    matt j pfm Member

    One of the other oven manufacturers that we pull fan wheels from on a regular basis do indeed make their own hydraulic puller, but access is better on them and a regular hub puller and a blow torch gets them off as they aren't mixed metals (@stevec67 may know of Rational combi ovens)

    But it's not cheap and we still don't do them often enough to warrant buying one

  14. stevec67

    stevec67 pfm Member

    I do know Rational, many years ago I looked at buying one for a manufacturer. They're very good quality, and not at all cheap. Oven fans are a pain, I sympathise. Our site engineers have it easy at sites where we have ovens, something like a Double D oven is dead easy, all the working parts are in the roof void, you just drag the assembly out and strip it down in the workshop.
  15. Colin Barron

    Colin Barron pfm Member

    Screwed rods, piece of scrap angle channel or rolled steel angle a few nuts and washers to make a puller. Apply plenty of heat on the aluminium and it will come off.
    An easier way would be take it to a local small garage who will have a hydraulic press.
  16. matt j

    matt j pfm Member

    Yes Rationals aren't cheap, I service/repair a lot of them but thankfully their motors are fairly robust so removal of the fan and motor isn't a regular occurrence.
  17. matt j

    matt j pfm Member

    Yes I'll just cart half a ton of oven off to the local garage and ask them to do it, that's entirely feasible.
  18. Colin Barron

    Colin Barron pfm Member

    I did think the motor and pulley was removed from the machine. The garage will also have oxy/acetylene gear for more localised heat. They do more difficult jobs than this removing hub bearings.
  19. matt j

    matt j pfm Member

    No I explained in my post the motor is one side of the oven cabinet and the shaft goes through with the fan on the other, those pictures are after I've removed both.
  20. a.palfreyman

    a.palfreyman pfm Member

    What thickness is the aluminium portion i.e. the wall of the boss? Could you drill it mid-wall to within 1-2mm of both the inner and outer wall in two diametrically opposite places and then drive a taper punch (such as a centre punch: https://docs.rs-online.com/2425/0900766b815840c5.pdf) into each hole, alternating hits left and right to split it? This will avoid damaging the shaft.

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