The Siren Board

Posted: **Mon Feb 09, 2015 5:31 am**

federalfan wrote:
theroofable wrote:Take it to a motor shop that does balancing. They will let you know what condition it is in, and if it can be salvaged or not.
I assume the rotor can be rebalanced in its current condition but my concern is whether it's safe to use at all. I don't know if it's possible to safely repair cracks in these cast aluminum rotors using standard welding techniques, since the rotor is subjected to very high stress when rotating at about 3400-rpm. We also don't know much about the composition of the alloy. This would determine what kind of welding material to use. There are some new alloy brazing rod materials that will repair aluminum without having to heat the base metal to the melting point. This might work to repair small cracks or broken edges.
I've been thinking about how to make a new rotor using aluminum plate material, starting with a large aluminum disk about 1/4" thick which would be the base of the rotor. The center of this disk would have a piece of aluminum rod about 3"-dia. welded vertically to the base plate. A hole would be drilled in the rod to the size of the motor shaft. It could also be broached with a keyway slot. The base plate would be surrounded by a rolled plate of thinner aluminum having the circumference of the base. This would form a vertical wall around the base and become the ports of the rotor when the openings are cut in the outer wall. The rest of the fabrication would involve cutting and welding the upright sections which define the partitions between each port and finally the top ring which ties the port partions and outer wall together. I think it would be an interesting project for a welding school class.

A motor shop would let you know. Much safer than building your own, which would still have to be balanced anyway. Also as holler said, you should be fine... I don't even see any of the cracks you are talking about. I see some scratches.

Posted: **Mon Feb 09, 2015 8:04 am**

theroofable wrote:A motor shop would let you know. Much safer than building your own, which would still have to be balanced anyway. Also as holler said, you should be fine... I don't even see any of the cracks you are talking about. I see some scratches.

As I mentioned in my original post, the picture I attached is not my rotor. I included it as an example of a rotor which seems to be identical to mine. I'll try to take some pictures of the defects on my rotor. Sorry for the confusion.

Posted: **Tue Feb 10, 2015 1:44 am**

federalfan wrote:As I mentioned in my original post, the picture I attached is not my rotor. I included it as an example of a rotor which seems to be identical to mine. I'll try to take some pictures of the defects on my rotor. Sorry for the confusion.

I took some pictures of the damaged areas on my Federal AV37X (Model-5) 12-port rotor, made in the late 1930s. The first two are a wide shot and a close up of the blade which has the chipped edge with the crack behind the chip. This is the area which has the most damage on the rotor. The third picture shows another blade from an edge view. The blade is bent inward about 1/4" but doesn't appear to have any cracks. Finally I included a shot of the bottom of the rotor showing the balance holes which were drilled by Federal. Is this the way they balanced later versions of the Model-5 rotor?
I don't see any other damage to the rotor on the inner vanes or the top and bottom. My main concern is the fairly large crack near the chipped edge. I think it has the potential for spreading under stress. Maybe I should stop drill the ends of the crack to prevent it from growing. I'm also thinking about trying to repair the crack with the new kind of aluminum alloy brazing rods which don't require heating the base metal close to the melting point.
In any case, if I used this rotor, it would only be for short runs. I wouldn't put the siren back into regular service without replacing the rotor. That's why I inquired about whether I have a good chance of finding another rotor from a 'real' Model-5. Did Federal use this rotor design throughout the production of the Model-5 series?

Thanks

Posted: **Tue Feb 10, 2015 3:00 am**

Ok yeah thats pretty bad. Don't run that, I have no idea about repairing that, probably unlikely but not my area of expertise.

The other option would be to have that area cut out, and rebalanced by a motor shop. It will probably be somewhat expensive.

Posted: **Tue Feb 10, 2015 4:02 am**

theroofable wrote:Ok yeah thats pretty bad. Don't run that, I have no idea about repairing that, probably unlikely but not my area of expertise.
The other option would be to have that area cut out, and rebalanced by a motor shop. It will probably be somewhat expensive.

The thing that has me wondering is the fact that there is no visible damage of any kind to the stator. Not even a small nick. How did the rotor get chipped, cracked or bent in several places without doing anything to the stator? My guess is someone put a large tool, like a crowbar, in the rotor openings to keep the rotor/motor from turning for some reason. That kind of abuse would most likely have damaged the aluminum rotor before something happened to the cast iron stator. Another possibility is a foreign object got into the rotor but I would expect the stator to have been damaged too. Regardless of the cause, if no one realized the seriousness of the damage, the siren could have been operated for years with the rotor in its current condition. The siren was used for the noon whistle, six days a week, in addition to the occasional fire calls. In that case the fire department was very lucky.

Posted: **Tue Feb 10, 2015 9:03 am**

Looks like it sucked in something while it was running. Like a bird or part of a birds nest.

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