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Member postings for Tim Taylor 2

Here is a list of all the postings Tim Taylor 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Model Turbines
17/02/2019 02:18:03

TG,

The most efficient use of the Coppus type single stage turbine was/is in applications where there exists a need for low pressure process steam - the 15psig exhaust in your example was likely used to feed a deaerator, process heater, low pressure steam header or similar application. The power produced by the turbine is derived from the isentropic enthalpy drop. Obviously it varies somewhat with inlet/exhaust conditions, but the rule of thumb is that using a properly sized turbine increases the needed flow for the low pressure application by only about 8% over what would be supplied via a pressure reducing valve.

They did make some versions with integral gear reducers (TFR/RLR), and also could be used with an external gear reducer to improve overall efficiency.

Tim

17/02/2019 00:40:19
Posted by duncan webster on 16/02/2019 20:17:16:

The 1200 rpm is nowhere near fast enough for a 12" diameter 2 stage Curtis. 12000 might be nearer the mark.

The passage through the blades should be parallel for an impulse turbine, one can't achieve this with blades pressed from thin sheet, and they should be close pitch

Edited By duncan webster on 16/02/2019 20:17:30

Actually Duncan, not to rain on your parade, but the 1200 rpm is very real.

Coppus manufactured radially split 2 row turbines in wheel diameters from 9" to 23", specifically designed for hp ranges from fractional to 1000bhp, at speeds anywhere from 600 to 6600 rpm. As well as most typical speeds in the 3600 rpm range, low speed direct drive applications were quite common, such as lube oil pumps, boiler draft fans and feed pumps. While the lower speed applications were not very thermally efficient, the exhaust steam was typically used to feed a deaerator/feed water heater instead of using a PRV, thereby recovering the residual waste heat. I know this for fact, as I worked with literally hundreds of them over the course of 40+ years (as well as turbines manufactured by Elliot, Worthington, ABB & others).

I am aware that a formed bucket is not an ideal design - if you read my earlier posts, you will note that I stated that in the real world they are broached out of a steel alloy. Using a formed bucket is a compromise, as broaching buckets in the very small size for my scale model is not realistic. That said, I can very accurately produce a nozzle block with multiple parallel convergent/divergent steam nozzles whose flow is parallel and feeds the wheel at the correct angle. As designed, the blades will be deliberately wider than the final dimension, with post assembly machining to final dimension providing a knife edge.

Tim

Edited By Tim Taylor 2 on 17/02/2019 01:30:05

Thread: How many threads please?
12/02/2019 16:04:58
Posted by John Rudd on 10/02/2019 20:08:11:

sealant needs to be able to withstand steam temperature.....laugh

Edited By John Rudd on 10/02/2019 20:08:59

This is an excellent point. I would suggest using one of the thread sealing compounds designed for steam use - they come in a paste compound that typically includes nickel and copper, and are non-hardening, making later removal easier.

Tim

Thread: What Did You Do Today 2019
10/02/2019 23:42:53

Finally got around to making the final design changes for home/limit switch housings for my mill...

Thread: Micrometer woes
10/02/2019 23:40:28
Posted by Michael Gilligan on 10/02/2019 17:09:24:

Nice job, Phil yes

MichaelG.

I agree!

I have a number of 50+ year old internal & external mics that originally belonged to my Dad - all have felt lined wood cases........

Tim

Thread: Testing for isolation
06/02/2019 00:23:44
Posted by Mike Poole on 04/02/2019 19:02:47:

I suppose in most domestic situations the prospective fault current is going to be fairly low unless you live next to the substation so shorting the supply might not produce too big a bang. In a factory you are going to get a much more impressive bang and rather than save your life you might end it. Isolating and testing should be done properly and with proper equipment. If the proper process is followed then you should avoid having the “accident” if there is such a thing.

Mike

Mike,

Distance from the substation is not a factor - I have seen downed 12.KV distribution lines lay on the ground and continue to arc for quite a while( and cutting a trench in the asphalt street in the process) until utility crews arrived to disconnect them

The fault current is based on the full load current of the power transformer and it's %Z (impedance). All transformers have impedance, and it's generally expressed as a voltage percentage. This is the percentage of normal rated primary voltage that must be applied to the transformer to cause full-load rated current to flow in the short-circuited secondary. For instance, if a 480V/120V transformer has an impedance of 5%, this means that 5% of 480V, or 24V, applied to its primary will cause rated load current flow in its secondary. If 5% of primary voltage will cause such current, then 100% of primary voltage will cause 20 times (100 divided by 5) full-load-rated secondary current to flow through a solid short circuit on its secondary terminals. Obviously, then, the lower the impedance of a transformer of a given kVA rating, the higher the amount of short-circuit current it can deliver.

Certainly the current rating of a transformer feeding a group of residences is less than would be found in an industrial environment, but it is still large enough to be a very significant hazard.

Tim

04/02/2019 15:11:15

Ah yes, the venerable Tesla coil!

I built a table top version as a project for my high school physics class and displayed it as part of our annual tech show. For the demo I would hold a fluorescent tube in my hand and draw a corona streamer from the coil to the tube, lighting the tube - not that impressive until I also held a tube in my other hand away from the coil and it would light as well, though not as brightly.

Tim

04/02/2019 00:36:07
Posted by Robert Atkinson 2 on 03/02/2019 21:12:55:

Flash-over can be deadly.
I know of one case when a technician was working on some "low voltage" (240V) instrumentation in a cabinet with a 44kV underground cable termination in it. The instrumentation was blowing a small sand-filled ceramic fuse. The technician ran out of fuses and replaced it with fuse wire. The fuse wire blew and the plasma created in the cabinet caused the 44kV feed to short out. The cabinet exploded and the technician was killed.

Arc flash can indeed be very dangerous, and it's not so much dependent on the voltage as it is the bolted fault current. There are several videos online of high voltage failures, which are pretty spectacular, but low voltage failures can be just as dangerous, often more so because they don't have the sophisticated protection circuits of the medium & high voltage systems.

I was part of an investigative team on an industrial arc flash incident on a 480V 3 phase system. An old circuit breaker failed to clear & then exploded. The energy released was approximately 13 megawatts in a period of about a third of a second, and completely destroyed the breaker panel. The resultant arc flash plasma exceeded 20,000 deg F ( a 480V arc flash can exceed 35,000 deg) and vaporized about 2 sq. feet of steel enclosure, sending droplets of molten metal as far as 30 feet. The pressure wave was calculated as approx. 35,000 psi and crushed the side of a steel motor control enclosure 4 feet away. Fortunately no one was in the MCC at the time or they would very likely have been killed.

Tim

 

Edited By Tim Taylor 2 on 04/02/2019 00:38:54

04/02/2019 00:14:53
Posted by peak4 on 02/02/2019 16:16:57:
.

Lots of interesting videos on the internet, have a look at the sparks flying at the end of this one, so it works for people as well as birds.

Bill

Edited By peak4 on 02/02/2019 16:20:24

This is how utility companies clean & physically inspect high voltage transmission lines - they also use aerial IR inspections to look for loose connections.

The sparks seen are caused by corona on the transmission lines - the wand & clamps provide a way to discharge the energy so the worker can move between the helo and the lines without acting as the conduit.

Tim

01/02/2019 23:29:56

Get a wiggy solenoid type tester - accurate, reliable, inexpensive, and will test anything up to 600vac.

Thread: Proxxon MF70 went bang
01/02/2019 01:10:29

Bill,

IMHO, as an EE with >40 years experience, at this point you need to get some quantitative measurements.

If you don't have a multimeter, see if you can borrow one.

First, power off, disconnect the motor and check it's resistance - according to the posted schematic it should be 90 ohms. If it deviates from that by more than 10-12%, you likely have a motor problem.

Note: The following measurements need to be done with the power on and the motor disconnected.

SAFETY FIRST! The voltages present can kill you, so if you're not comfortable doing this, get some help.

AC voltage at the input to the control board
DC voltage at the control board output (will vary depending on the speed control pot setting.

If there is no DC output, next step is to check the AC voltage at the input of the rectifier bridge - it will also vary depending on the pot setting. This will isolate the problem to either the rectifier section or triac section of the circuit.

Let me know what you find and I will tell you where to look next.

Hope this helps..........

Tim

31/01/2019 16:50:21

Bill,

The intermittent sounds you heard prior to failure could still be related to the controller.

To check the motor, disconnect the leads from the circuit board and check resistance with a multimeter. If it is open or shorted, you have a motor problem....check the brushes as Andy mentioned.

From the circuit diagram posted this is a 220V motor - you should be fine using your 18V battery.......stick a fuse in series.........

Tim

Thread: Testing Models
28/01/2019 17:01:32

TG,

Don't know if you've seen these, but links to a couple references I thought you might find of interest...

https://www.forgottenbooks.com/en/download/The_Steam_Turbine_1000777956.pdf

https://www.osti.gov/servlets/purl/1376860

Tim

Thread: Learning CAD with Alibre Atom3D
25/01/2019 17:30:09

Andrew,

That's not the way mine works. Sketches that are not selected show up as a thin red line - when selected they turn blue.

In the viewing & analysis menu tab there are buttons to control the visibility of both sketches and references - I think David suggested earlier that might be where the problem is........

Tim

Thread: Precision Level or Precision Frame Level
23/01/2019 17:14:23
Posted by Pete Rimmer on 23/01/2019 15:07:38:
Setting the bed straight - level or not - is fundamental to the alignment of the lathe. It's such a trivial exercise (if you have a sensitive level) that there really shouldn't be any argument against it.

J Bennett - I'd you happen to be in N Kent you could borrow one of mine, then you can check your lathe without the expense of a seldom used tool.

I agree. I have both a 15" master precision level and an AliSensor electronic level, but both are really overkill - a simple good quality machinist's level long enough to fit across the ways is plenty adequate.

Much also depends on where the lathe is mounted. The surface of the stand or bench should be stable, flat and reasonably level. I have a 10x22 lathe that I built the stand for, including adjustable vibration isolating feet. In setting it , I first leveled the stand, making sure that all 4 feet were evenly loaded to eliminate any soft-foot issues. I then set the lathe in position on the stand, let it sit overnight, then re-checked & adjusted the stand as needed. Finally, I aligned the lathe using SS shims and bolted it to the stand.

As an aside, the AliSensor level did come in real handy when I set up my mill.......

Thread: Learning CAD with Alibre Atom3D
21/01/2019 17:15:30
Posted by JasonB on 21/01/2019 16:27:08:

John first you need to created a drawing so from the opening Atom window select the far right "Create detailed manufacturing drawings of your design" and from that select paper size and then browse to find the part.

You can also select more options and tick the "use design dimensions" but I prefer to lave that blank and just add my own in a tidy way on the final drawing rather than worry too much while sketching.

Font size and style can be changed when in the drawing by clicking "dimension Styles" and picking "Text" from the list on the left of the window that opens. You can also set the units and decimal places from here too.

Once you have the drawing you can export that as DXF or DWG

Jason,

Either way works - yours is probably more formally correct.. Personally, since I save related part designs in project sub-directories, I find it easier for me just to open the part first, rather than having to go searching for it. I also tend to generate the drawings immediately after I finish and verify the design, so I already have the part open anyway.

I agree with you on dimensions - I prefer to add them on the 2D drawing as well.......

Tim

21/01/2019 16:13:22

John,

Yes it will export:

1. Open the part
2. click on the jewel in upper left corner, then new/new drawing to create a 2D drawing
3. select the drawing parameters and views to create the drawing - you can edit or add additional dimensions at this point......
4. click on the jewel and click on export to export to common CAD format (DXF or DWG)

 

 

Edited By Tim Taylor 2 on 21/01/2019 16:17:05

21/01/2019 15:32:22

Yes, just make the change, exit 2d sketch mode, then click on regenerate to last feature....any subsequent feature affected by the changed sketch will update automatically.

This is one of the capabilities of A3D that can be a huge time saver. 

A good example is the design of the turbine wheel I posted back on page 23. Getting into the nozzle flow calculations, I found it necessary to increase the blade area by 50%. This involved three changes:

1. edit the sketch for the extrude buss of the rotor OD
2. edit the sketch for the extrude cut for the reversing sector clearance
3. edit the circular pattern to reduce the number of blades in the row by one to provide necessary blade to blade clearance.

Three simple edits that only took a couple minutes....then hit generate to last feature to create updated design.

 

Edited By Tim Taylor 2 on 21/01/2019 15:58:40

Thread: Use of Colour on Drawings
21/01/2019 07:16:33

1. My preference

2. OK as well

3. No

The only thing I use color on 2D drawings for is revisions, and those are in red - makes it easier to quickly see what has changed.

I do like the small isometric.

Edited By Tim Taylor 2 on 21/01/2019 07:19:43

Thread: ME vertical boiler
20/01/2019 22:39:35

I'm jumping in a little late as well.......a couple things:

The combustion air on any boiler should be adjusted for proper fuel/air ratio - excess air improves combustion, but too much can dramatically increase the stack temperature and reduce thermal efficiency. On full scale boilers, on gas fire, we target for about 3% excess O2, which translates to about 15% excess air.

I'd probably also fit a simple superheater coil - easiest place to add it would be right at the stack....

Tim

Edited By Tim Taylor 2 on 20/01/2019 22:41:42

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