My two cents:
No nylon bolts. Use metal. As was previously noted, nylon will creep.
There are two potential problem areas here: unintentional magnetic paths and eddy current losses either in the bolts or by shorting of laminations. Each has potential implications for transformer distortion.
The most important thing to do is DO NOT short transformer laminations with the hardware. This will allow eddy currents to flow in the bolts and you _will_ get measurable distortion. Therefore do use some insulating washers at both ends, fiber or nylon or similar, and always maintain an air gap between the bolts and the laminations.
The bolt holes in transformer laminations are specifically placed where flux density is lowest, and since the transformer laminations are far more permeable than air, or the insulators, and you have maintained a nice air gap between the bolts and the laminations, there is not a good magnetic path through the bolts and the flux density (and the rate change of flux) in the bolts will be negligible. This is especially true with output transformers, since the flux densities in them are typically kept significantly lower than in power transformers, to avoid operating in the saturation region (for low distortion).
For those reasons, it is probably not necessary to use non-magnetic bolts here. I would be surprised if you could measure any significant flux density in the bolts except possibly under conditions of extreme overdrive, though I've never tried to make the measurement.
If you are still worried about a magnetic path through the bolts though, use something non-magnetic, like 300 series (18-8) SS or brass.
And if you are worried about eddy currents in the bolts, then select a material with a high bulk resistivity.
Oh, and something else never to do: NEVER polish the transformer laminations. You can create unintentional inter-laminar shorts that way.
Cheers,
No nylon bolts. Use metal. As was previously noted, nylon will creep.
There are two potential problem areas here: unintentional magnetic paths and eddy current losses either in the bolts or by shorting of laminations. Each has potential implications for transformer distortion.
The most important thing to do is DO NOT short transformer laminations with the hardware. This will allow eddy currents to flow in the bolts and you _will_ get measurable distortion. Therefore do use some insulating washers at both ends, fiber or nylon or similar, and always maintain an air gap between the bolts and the laminations.
The bolt holes in transformer laminations are specifically placed where flux density is lowest, and since the transformer laminations are far more permeable than air, or the insulators, and you have maintained a nice air gap between the bolts and the laminations, there is not a good magnetic path through the bolts and the flux density (and the rate change of flux) in the bolts will be negligible. This is especially true with output transformers, since the flux densities in them are typically kept significantly lower than in power transformers, to avoid operating in the saturation region (for low distortion).
For those reasons, it is probably not necessary to use non-magnetic bolts here. I would be surprised if you could measure any significant flux density in the bolts except possibly under conditions of extreme overdrive, though I've never tried to make the measurement.
If you are still worried about a magnetic path through the bolts though, use something non-magnetic, like 300 series (18-8) SS or brass.
And if you are worried about eddy currents in the bolts, then select a material with a high bulk resistivity.
Oh, and something else never to do: NEVER polish the transformer laminations. You can create unintentional inter-laminar shorts that way.
Cheers,
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