Your experience is respected. Welcome to Jet City!

Thanks! Welcome to Jet City.

@@AgentJayZ love your channel, you've taught me so much and all free of charge from the comfort of my soft desk chair. The next time I fly I'll remember and appreciate everything that goes into it! Keep up the great content!

I see that he puts a line under numbers so they can't be inverted :)

Yeah, tried to put the timing close enough so that it cannot be easily spotted. You eagle eye :P

Indeed.

I'd prefer that to the smudges you're finding...

i was scanning before i made a similar comment. this would be my vote; same alloy but a heat treatment process resulted in a crystalline lattice structure boundary layer.

@@LogicallyCompromised Nevertheless, the disc and its shaft are supplied as a single unit: as you will see in my other comments, I've checked on this and, when you look closely at the complete turbine rotor, that becomes fairly obvious. However, I think it highly unlikely that the disc/shaft unit is a one-piece forging, which would be extremely difficult to manufacture and horrendously expensive. My very tentative conclusion is that the bi-metallic feature is part of the joining process ..... and it still puzzles me.

@@grahamj9101 The turbine rotor disk has a Timken 16-25-6 alloy rim TIG welded to an AMS 4340 steel hub to provide higher strength at the flowpath.

The problem with stainless steel is the steel. Iron has a comparatively low melting point, and although you can change that by alloying it with other materials, you're better off to go with different material altogether. The other problem with steel of any kind is creep. All that said, they do totally make turbine blades out of stainless steel. Go figure. =P lol

Austenitic steel is also just one step away from molten steel. ;) Hot metal goop in your turbine blades is not ideal. lol

good stuff good stuff! the real mechanics do sheet metal ;) this is actually a really good channel i just found it myself.

It's a craft and JayZ has mastered it. No one better to learn from than a master.

hell yea

Early 1950's so would that have been Elvis, or before?

You're smacking a pin into a hole 96 times, be organized and focused. ez

This process step is taken directly from GE Gas Turbine rebuild manual in the electrical generation Thermal Power Division.

It's also described and illustrated with photographs in the GE J47 overhaul manual.

Aluminum, Copper.

Better practice is to follow the manufacturer's instructions to the letter.

You're right!

Damn rights! As always, there's a money back guarantee. Thank you; come again!

@@AgentJayZ make your own jetsuit.

Austenite

This video is part of a playlist.

From my experiences, the pins are all very close tolerance in terms of weight and shape. It is easier to make the pins all the same versus the blades.

I don't know if it's easier or not. What do I know? Pins are all the same, blades aren't. How do I know this? measured 'em!

I would think since the pin is so light relative to the blade that the unevenness in weight is so minute it really doesn't matter at all. For example let's say the blades have a 1% weight tolerance. In a 200gr blade that would be 2 grams between the heaviest and lightest blade. That is a significant weight difference. But let's assume the pins are less carefully made and have a weight tolerance of 5%. Still if the pins average weight is 2 grams that would be 0.1 gr between heaviest and lightest pin. (keep in mind that would be the most extreme difference possible) 0.1 gr is the resolution used to weigh the blades themselves. So the average variation in weight of the pins, is less that what you would care to measure anyway and thus can be considered zero. So for all intents and purposes, pins are all the same (as jay said)

They're ceramic coated. The blades will see high temps so I doubt it matters as any residue will be quickly burned off.

well you should. we use tested tapes and markers and you shouldn't touch it without clean gloves either.

Should is a bad word, but it can sometimes be useful. Example, you should listen to the dinosaur, because he is right.

No mistakes were made in this video. The haters should watch it. Trying to rethink a process specified by the manufacturer is why they don't work on jet engines, or anything for that matter.

@@AgentJayZ - Dunning Kruger comes to mind.

Being able to read, understand, and follow procedures is the most important thing that was emphasized in both jet training school, and in my evaluation for service as "agent"...

I am lucky to be able to take my time to do this job.

Check out the first episode of this series of videos.

I was wondering about that disk too. Is the steel stronger than the nickel alloy? Is the steel cheaper? Was this somehow easier to manufacture?

​@@zapfanzapfan I'm still fascinated and horrified, but now I'm also getting suspicious and curious. The junction or interface between the two materials is not uniformly circular, which it should be, if the disc had been formed with an insert into an outer ring. In any case, having thought about this further, I doubt that, back in the 1940s, there would have been any manufacturing technology anywhere near good enough to produce the required high integrity joint, even for a low life disc. I'm now wondering whether the magnetic material is a 'laminated' reinforcement onto the the rear face of the disc. Even so, I'm still horrified by both the irregularity of the boundary between the two materials and the surface finish of the magnetic material. Could it be some form of metal spray or weld deposition, possibly for repair and salvage reasons? Any disc that I've ever been involved with would have been rejected immediately with that standard of surface finish. In most cases, a scratch that could be detected by a fingernail would be cause for rejection. In terms of the relative strengths of the two materials, I can't answer that authoritatively, not knowing what the materials are and their specifications. However, I would have expected one of the early nickel-based alloys of the day to have a relatively higher strength at operating temperature than the available steel alloys. In terms of cost, any potential cost saving from using two materials would, I believe, have been totally nullified by the process and manufacturing costs of joining them. I'm hoping that AgentJayZ can shed some more light on this.

I'm very curious how that is manufactured as well. Your mention of the 'free ring radius', (we call it the 'self supporting' radius or diameter, SSR) made me take a slightly deeper look. I'm guessing from JayZ's magnet test the hub section is a 400 series stainless, a ferritic stainless steel that's slightly magnetic and the outer ring is probably IN718, a pretty common disc material. The SSR for annealed 410SS at 8000 RPM would be almost 9 inches. As 410 can be heat treated to much higher strength levels and 718 is even stronger I'd say the joint is well within the SSR for either material. Also, the stress across the disc joint won't be very large. In spinning discs it the hoop stress that's the big one. Radial stresses are generally less important for the disc than for the blade roots. That being the case I'm still fascinated how it was manufactured. Is it welded, friction, TIG or EB? Is the hub cast in place? I don't believe it's just an interference fit as that would always show cracks at the seam. Thanks for your videos AgentJayZ. They're almost always fascinating.

@@yabojabo8578 Starting with your last comments first, you are thinking in terms of manufacturing processes that hadn't even been thought of in the mid/late 1940s, apart from the 'conventional' welding processes of the day. Henry Wiggin at Hereford, here in the UK, were certainly well advanced with the development of their range of Inco alloys in the late 1940s, before Special Metals took on the range. However, my recollection is that IN718 is more recent than that and, In any case, would the UK government have allowed the technology transfer (they might, considering they allowed GE to have a Whittle engine in 1942)? As a designer (now long retired), I wouldn't have dreamt of trying even a modern EBW process in joining the inner and outer portions of a bi-metallic disc of that size: in any case, the thickness of the disc would probably preclude it. There was also limited understanding of the optimum grain flow requirements in a disc forging back in the 1940s and more than a few engines 'threw' turbine discs as a result. Even as late as the 1970s, R-R lost a few RB211 fan discs, not to mention a couple of HP turbine discs, because of forging problems. You may well be right about the free ring radius/SSR issue, but the fundamental problem remains that any joint in the body of the disc would disrupt the integrity of the disc. There would be no continuity of the forged grain structure and any fusion process would result in a localised 'as cast' structure, with a heat affected zone. I am more and more uncomfortable with the idea of a bi-metallic disc formed from inner and outer rings and I am increasingly suspicious of the irregularity of the 'junction' between the two materials, which suggests to me that it represents material added to the face of the disc. OK, I could be wrong, but .....

@@grahamj9101I agree with everything your saying. I'm a turbine design engineer as well and I would never feel comfortable with a bi-metallic or 2 piece disc like that. That's why I'm fascinated by it. I'm pretty sure the disc JayZ is working with is not original. I'd assume the turbine discs and blades are all upgraded materials from the 1947 originals. The original blades were probably steel alloys with very little life even at relatively low firing temperatures. But that's all beside the point. Could it be that the disc is actually a single part/alloy and there is some processing difference of the center hub vs. outer hub that results in the different magnetism? I've had cold worked austenitic stainless parts that were slightly magnetic as a result of the cold work while machined parts from the same billet weren't. Perhaps the inner hub is as forged and the outer hub was forged with stock on and was then machined to size. That would explain the irregular transition from one section to the other. Very curious.

I once heard from a psychologist that chewing ice, represents sexual tension/frustration. But those people always make weird stuff up.

I'm wondering this myself, but I think it might be weight and/or heat resistance or even thermal expansion.

If you actually look at the equations for gas turbine engines, you'd see that as you increase stagnation temperature in the turbine, the thermodynamic efficiency of the engine also increases. But obviously this temperature is limited by the materials you use. So engineers had to find clever ways of alloying materials or cooling the blades to allow higher temperatures.

Please see my comments on this topic.

Exactly what I was thinking.

It's made of Timken 16-25-6 alloy.

The manual refers to the discontinuity as the transition zone.