Advice on fixing blades.
|Mike Brett||24/09/2020 16:23:52|
|126 forum posts|
I am in the process of building a compressed air turbine. The main rotor is a 22 mm thick by 65 mm round piece of aluminium. Into this I have milled 1/16 inch slots around the perimeter into which I want to attach the blades made of brass.
At the present I can only think of two ways of fixing these, one is lock tight and the other is JB weld. As I have never used JB weld before my question is which would be strongest.
|Ian P||24/09/2020 16:58:37|
2420 forum posts
Not really enough detail in your post so the following is guesswork.
Are the slots on the outer surface of the hub or are they radial in the face?
Which ever they are I would not like to rely on any adhesive to keep them in place at high speed, keep out of the way!!!!
|Mike Brett||24/09/2020 17:06:01|
|126 forum posts|
They are on the outer surface. Welding does not seem possible with such a large piece of aluminium and small pieces of brass. It might be possible to insert a steel pin into each blade but I would still need to use adhesive of some description.
|Oven Man||24/09/2020 17:35:42|
70 forum posts
How about miniature Tee slots - just like real turbine blade fixings?
|Brian Wood||24/09/2020 17:58:38|
|2270 forum posts|
Aero engine practice for blade anchorage is with fir tree roots which would be much too fancy for this turbine.
The steam turbine alternative is with a round anchorage formed on the end of a short stalk, an easier alternative in this case. The blades should have a little radial freedom, ie not held rigidly, and kept in place with plates either side of the root to prevent them 'walking out' of the turbine disc.
|Tony Pratt 1||24/09/2020 17:58:59|
|1233 forum posts|
As Peter said some type of T slot.
|Jeff Dayman||24/09/2020 18:18:10|
|1895 forum posts|
Mike, if you were able to mil slots around the disc, could you mill the blades themselves from the disc, and then either form them curved with a pair of dies fitted to a mole wrench / vise grip pliers or leave them straight as cut? This construction would eliminate blade to disc joints and any issues with dissimilar materials. Just food for thought.
If you make he blades separate and glue them in, even with pins, I would suggest a sturdy blast shield to stand behind during testing. Unintended high velocity spontaneous disassembly is likely. Compressed air turbines can rotate at spectacularly high rpm. I worked with dental drill air turbines in industry for a while. I know of which I speak.
18885 forum posts
Could you cut a groove into each face of teh hub once the blades have been bonded in and then make a metal ring to set into the groove, this would give a solid means of retention should the adhesive fail.
Of the two I would go with JB Weld ( original), I know someone that retains the tops of their soft jaws with it
|Mike Brett||24/09/2020 18:57:59|
|126 forum posts|
So many good ideas. As I have already done some of the machining I think the tee slot idea would be the best way to go.If I drill a series of holes around the base of each slot then use brass angle reduced on one side so this pushes into the hole and leaves the long side of the angle sticking out as a fin. With GB weld this should hold it firmly.
The outer casing is substantial so if anything should come adrift it should still be safe.
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