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Post by madrocketscientist on Dec 3, 2017 1:45:18 GMT -5
I started machining the shaft nuts today, I was going to make the nuts for both ends out of titanium but I was having trouble tapping the M6LH thread for the front nut. I decided to use some 2024 aluminium instead, nut I was still having trouble tapping the thread!! Looking carefully at the tap the edges were ground slightly wrong, once I sorted the edges there were no problems tapping both the aluminium and the titanium. (cheap chinese taps!!) I think I will stick with the aluminium for the front nut as it is lighter and doesnt see the heat that the rear nut gets. I started the threads in the lathe and put them in a ER32 collet in the vice to finish them off by hand. I was quite impressed with how titanium machines. Having read on the internet how horrible it is and how is really hard on tools. I ran a reasonably slow speed and kept the feed rates up, and its not much different from turning stainless. Tapping is about the same but with more of a tendency to grab onto the tap. Compared to machining some things really nasty like hardened steel, give my the titanium any day. I also tried single point turning some threads in the lathe but I was having trouble getting them the correct size for a tight fit with the nuts. After some Thinking, I should have used some good quality steel for the test cuts rather than whatever was lying around. I gave up at that point and will try again tomorrow. Shannon
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Post by madrocketscientist on Dec 18, 2017 3:35:38 GMT -5
Time for an update, Yili has let me know that the turbine wheels are finished being manufactures and are being tested before being shipped out. I asked and they do Xray the parts. I have purchased a few more pieces for building. I got a stack of oven elements from Trademe for reasonably cheap, Shipping them cost more than the purchase price. About 2/3rds of them are brand new. I could have gone to the local recycling and dug some out of the old ovens they have but it worked out easier to buy them this time. I have been getting some of the FADEC electronics and various parts like thermocouples, magnets and rpm sensors from Xicoy in Spain. Their shipping is really fast, often faster than inside New Zealand. I need to make a new set of half nuts for my lathe. After quite a few attempts at threading and having not much success, I took the apron off the lathe. Surprise surprise, the half nuts are mostly worn out! I ordered some die nuts of ebay but I don't have much confidence that I will be able to adjust them big enough for tight threads. I will try to find some bronze for the half nuts after Christmas. I also finished machining the flats on the turbine nuts. Kavan pump From Germany via ebay. Cheap scale that came in chinese, I notified the supplier and told him I will keep it as it still works fine, he was most apologetic that it wasn't in English. I am going to modify the sensor for thrust measurement à la Gerald Rutten, (Must take more pictures of the other stuff!) Shannon
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Post by racket on Dec 18, 2017 4:24:26 GMT -5
Hi Shannon
With regards sheathing for the vapourisers , theres guys in NZ that manufacture elements , I'm currently sourcing some 12.7 mm OD and 9.5 mm OD X 0.6mm wall thickness Incoloy 800 tubing from them as my supplier here in Oz has "gone offshore" with manufacturing
I was recommended to try
BJC Elements Ltd in Wellington, NZ – Aaron; Aaron.Mason@bjcelements.co.nz
Hislop & Barley Ltd in Auckland, NZ – Vish: vish@hibar.co.nz
Currently working with BJC
Cheers John
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Post by madrocketscientist on Dec 18, 2017 4:32:06 GMT -5
Thanks for the contacts John, That must be a first, a product available in New Zealand! I think the numbers work okay with the element tube I have, The larger size is 5.5mm ID with a 0.5mm wall. If I use 12 (or 13) tubes the surface and tube area seems to work out alright. I might run out of room to fit the length of fewer larger tubes inside the chamber. Shannon
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Post by racket on Dec 18, 2017 4:37:59 GMT -5
Hi Shannon
Yep , we need to juggle the number, length and OD to get the required flow and surface areas...............LOL the bigger tubing might come in handy when you want to make bigger engines ;-)
Cheers John
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Post by madrocketscientist on Dec 18, 2017 5:07:22 GMT -5
Yep those turbine ice sleds the guys are building look way too much fun
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Post by madrocketscientist on Dec 20, 2017 1:03:29 GMT -5
Today I cut some elements into short lengths and drilled out the magnesium oxide. Putting the cordless drill set to hammer drill made the oxide break up way faster. The new elements drilled out far easier than the used ones, the heat must fuse the oxide together. I cleaned up one end in the lathe, the other end can wait until the final length is decided. I received some silver solder rods in the post, they may be a bit on the thick side at 1/16", time will tell. Shannon.
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reedy
Veteran Member
Joined: January 2017
Posts: 111
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Post by reedy on Dec 30, 2017 5:02:52 GMT -5
Hi Shannon
I've been quiet all summer,mainly stuck to commenting on Jeff's heineken build,just want to comment on a safety concern,try to stick to the normal metals, aluminium alloy steel and stainless, the titanium nut on the turbine end is a bad idea as we were warned off it in the GTBA. It can break down with heat and on the hot side of the turbine it will get no cooling. I tended to use the same material as the shaft, a 12.9 cap head bolt or 316 stainless which you can buy in hexagonal section. Stay away from hollow shafts you will get balance problems no small production engine does it as far as I know. The best way of reducing weight is to stay as small and short as you can on the engine and push the revs and case pressure up as per production engines but this does require a professionally produced cast turbine wheel and a good designed combuster. On the bearing tube material wren power systems went to stainless for stability but aluminium alloy does work.
Chris.
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Post by madrocketscientist on Dec 30, 2017 5:11:12 GMT -5
Hi Chris,
The overall engine weight isn't too much of an issue, but I was trying to reduce the overhung weight of the turbine end to keep the critical shaft speed safety margin high enough. I can make the turbine nuts out of 12.9 bolts without a problem. I am still thinking of making the shaft tunnel out of stainless, but haven't finished the design for that yet.
Out of curiosity, you have any datasheets or further info on titanium breaking down when hot?
I have some Yili 84mm turbine wheels and NGV's on order, but not sure when they will be shipped.
Shannon
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reedy
Veteran Member
Joined: January 2017
Posts: 111
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Post by reedy on Dec 30, 2017 6:26:29 GMT -5
Hi Shannon I worked in the aerospace industry now retired our firm made the typhoon, the canards are made of titanium which was hot bonded and superplastic formed the tools were heated to orange colour about 650 to 700c wikipedia say's 900c for the titanium superplastic forming, I was not involved with the process but the tools took a lot of damage developing cracks and impressions where it crushed the titanium to hold it round the edges as it was blown to shape. Titanium is good but at 650 to 700c exhaust temp I would not use it. www.baesystems.com/en/feature/even-pilots-think-superplastic-is-fantastic#Chris
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Post by madrocketscientist on Dec 30, 2017 16:14:57 GMT -5
Hi Chris, I found this image on the internet. It doesn't have the temperatures on the axes but they can be guessed at. Titanium strength does roll off a lot faster than the other steels so the superplastic thing makes sense to me! Shannon.
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Post by racket on Dec 30, 2017 16:45:31 GMT -5
Yep , don't use titanium at the hot end
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Post by smithy1 on Jan 1, 2018 20:58:51 GMT -5
Yep , don't use titanium at the hot end Totally agree...Rolls-Royce use Titanium for the C30/C40/C47 compressor impeller...but I doubt very much that any manufacturer use titanium for the hot bits. Smithy.
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reedy
Veteran Member
Joined: January 2017
Posts: 111
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Post by reedy on Jan 5, 2018 6:14:07 GMT -5
Hi Shannon, I've never seen a spring putting pressure on the outer race of the front bearing, only the rear. I have seen plans where a wave washer is used on the front bearing to apply bearing preload. Are your plans correct? Nice work so far. Regards Jeff Yes I do intend to have the preload spring pushing the front bearing, There isn't really any difference in the force between using a spring or a wave washer, Although it is somewhat easier to fit a spring in between the shaft and housing. Wave washer tend to be a smaller inner diameter and often there isn't space. The AMT Olympus uses what looks like a pair of conical washers at the front but the shaft has to be turned down just behind the bearing to fit them in. With the spring I can also have the sliding bush in front of it to keep the bearing (hopefully) square to the housing. There are pro's and con's as to whether the preload pushes forward or back, what they are I can't remember off the top of my head . Part of my reasoning for having it forwards is that the front runs cooler and is less likely to overheat the oil in that area, hopefully making it less likely for things to get gummed up and stick. I was considering using O-rings for bearing damping, but apparently they can also get sticky, with the consequence that the preload goes away. I am sure you can imagine what happens next.... There was an interesting discussion I was reading about how the air pressure on the backside of the compressor wheel helps offset the combustion exhaust pressure against the turbine blades and balances out the fore and aft forces on the bearings somewhat. Shannon. Hi Shannon There was a lot of talk,problems early on in the GTBA with lube to front bearing and which way to preload ,it's not an easy problem to fix or calculate people ended up making setups then they could preload at either end and see which worked. If you do have front bearing failures make sure the compressor wheel is balanced at both ends before being balanced as a whole you can get whirling problems unseating the front bearing. The compressor wheel can create a low pressure area on the backside of the wheel,some of the fix's to the KJ66 where to drill a hole in the diffuser to pressurize the area behind the wheel and fit the oil supply needle to the front of the front bearing and have the front bearing area open Tried to post pictures of Kurt Schreckling design of his TK50 which is front preloaded with a spring the engine is designed for max fuel efficiency using 50mm o/d wheels and a large outer can of 98mm o/d to increase efficiency. All to reduce his wing loading of his models as he felt the power and fuel weight was too much of the KJ66 . Not sure of you combustor design tin can shape seems to dominate as it works and easiest to do and you can spot weld the flanged fuel sticks on the rear wall,with the angle you show it will need to be tig welded,for thin sheet spot welding is better with less distortion. do not use silver solder on the combustor only welding is good enough. with your first engine leave the front cover inlet parallel on the outside for re chucking and as i said try to design the bearing tube with sleeves front and back.make your wedges 1mm higher(see G Rutten build thread) than the outflow of the compressor as it seems to help and can give you the option of a higher tip wheel .make the inlet piece separate it makes it easier to get the clearance correct. Trying to be constructive as time spent designing can save a lot of scrap as a caveat I have never designed a engine from scratch, question and read up on anything I say . If the pictures do not come through will try to re post. Chris
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Post by madrocketscientist on Jan 5, 2018 16:51:49 GMT -5
Hi Chris,
Thanks for the extra info,
The weird locating of the evaporator sticks is due to the NGV that I am getting from Yili castings. They are in NZ so I should get them in the next few days! The NGV has a tapered flange on the front of it and since it is Inconel, I am loathe to cut it off. Having said that the whole design is still in its early stages and will get changes before I make the rest of it!
I have access to a Tig welder and I also intend to make a spot welder for welding the combustion chamber. I haven't Tig welded Inconel before but have done plenty of stainless and 4130.
Shannon
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