|
Post by Roger on Apr 24, 2019 7:51:11 GMT
Hi Roger, Apologies for my poor syntax - it is only the bolts that are stainless, not boiler bushes or regulator flanges or smokebox flanges/bushes. Cheers, Julian Thats how I read it in the first place Julian. I've been wracking my brains (whatever is left of them) trying to think why Roger suddenly started talking about silver soldering stainless steel! Yes, David has followed Alec's practice and used thick wall gunmetal bushes fo various things including the cylinder mountings on top of the barrel, with the stud holes all safely in the thickness of the bush wall. I've gone one further and used blind PB bushes where David specified blind tapped holes in the shell for various other fittings. The fixings that started off this discussion are for the cylinder bottom end covers, which, because the cylinders are mounted on top of the boiler and partially submerged in it, are in the steam space of the boiler. The load they take is minimal, really only to provide a seal. The boiler pressure is acting to push the cover on to the cylinder, and even when the regulator is open and steam in the cylinder, the net pressure will still be of the order of 10 psi or so pushing the cover on. David didn't specify a material for the screws, but as he did suggest sealing them over with Comsol on final assembly, I suppose he intended ordinary steel to be used. I settled the matter (or so I thought) this sfternoon, by buying some 3mm stainless csk Allen screws when I was at my local fixings suppliers, but then after I had got home, realised that to replace 4BA screws, I should have got 4mm----. Grr. Still, the 3mm must come in for something around the loco. Ah, so that's what they are for, something in the steam space seemed likely to be Silver Soldered too.
|
|
|
Post by ettingtonliam on Apr 24, 2019 8:48:52 GMT
In the first post I did describe the screws as being for fixing an end cap on to a flanged fitting in the steam space.
|
|
|
Post by Roger on Apr 24, 2019 9:40:59 GMT
In the first post I did describe the screws as being for fixing an end cap on to a flanged fitting in the steam space. I think you could interpret that in a number of ways, it's not that clear in my opinion. It could be something to do with a regulator, it could be a permanent inaccessible feature that's also Silver Soldered. It might be highly stressed and critical to the boiler integrity. It might be removable, involve a seal, almost anything. Without drawings or pictures, readers are left to imagine what they will. Reading through other replies, it would appear that I'm not alone in not being sure exactly what was being asked. My interpretation was clearly not what was intended, that's all.
|
|
|
Post by ettingtonliam on Apr 24, 2019 9:51:47 GMT
OK, I think its clear now. It was only intended initially as a general query so I didn't, perhaps wrongly, give as mass of detail regarding the purpose. Given the detail you now have, can you see any objection to the use of stainless screws in this particular case?
Stainless csk allen screws securing a gunmetal end cover to a gunmetal cylinder casting in a low stress situation, (steam pressure in the boiler is pushing the cover onto the cylinder, the reverse of the normal situation where steam in the cylinder is acting to push the cover off the cylinder) immersed in steam at 60 psi, 160 deg C. The whole fitting is removable from the boiler if necessary, by dismantling the valve gear and motion, and undoing a ring of nuts. Copper boiler.
|
|
|
Post by Roger on Apr 24, 2019 10:01:07 GMT
OK, I think its clear now. It was only intended initially as a general query so I didn't, perhaps wrongly, give as mass of detail regarding the purpose. Given the detail you now have, can you see any objection to the use of stainless screws in this particular case? Stainless csk allen screws securing a gunmetal end cover to a gunmetal cylinder casting in a low stress situation, (steam pressure in the boiler is pushing the cover onto the cylinder, the reverse of the normal situation where steam in the cylinder is acting to push the cover off the cylinder) immersed in steam at 60 psi, 160 deg C. The whole fitting is removable from the boiler if necessary, by dismantling the valve gear and motion, and undoing a ring of nuts. Copper boiler. From Julian's experience it sounds like you could use specific types of Stainless Steel without any issues. Since you can access it anyway and it's not highly stressed or critical then it sounds fine. Obviously you don't want them to be corroded and snap off if you ever have to take it apart, so choosing a suitable Stainless grade makes sense.
|
|
|
Post by 92220 on Apr 24, 2019 12:34:59 GMT
If you use 316 stainless screws you should have no issues as these are for use in salt water craft. 316 stainless is the same as the old EN58 and this is what we used to use at the company I worked for, as a trainee draughtsman, that made straight line windscreen wipers for ships, including all RN ships.
Bob.
|
|
|
Post by atgordon on Apr 24, 2019 19:36:00 GMT
If you use 316 stainless screws you should have no issues as these are for use in salt water craft. 316 stainless is the same as the old EN58 and this is what we used to use at the company I worked for, as a trainee draughtsman, that made straight line windscreen wipers for ships, including all RN ships. Bob. You are right, stainless steel, particularly the 300 series - which is marine grade - will work fine ... in an oxygen rich environment. All 300 grades will corrode in still water conditions where there is low dissolved oxygen (perhaps inside a boiler...?). There is a lot of stuff out there on low oxygen corrosion of SS. The boating company that I make parts for will not use stainless in tanks or other areas where the fastener will be immersed in a liquid, and not in free air .. they use bronze in such situations. The following article gives more info (and points out that 316 or 316L is susceptible, but at a slower rate). Given the fact that most folks will empty boilers between use, this probably isn't an issue, but I'd rather avoid the problem of having to remove broken machine screws if at all possible! I'll use PB for my boiler fasteners.
|
|
|
Post by 92220 on Apr 25, 2019 9:44:08 GMT
Thanks for pointing that out. Obviously my experience with EN58 use on the wipers, didn't include low or zero oxygen levels, ever, so I had no idea that was a problem.
Bob.
|
|