I don't know how you can tell what the material is made of from the photos. You have better eyes than me!
Hi Walt. My conclusion was not based on determining the exact material by sight. My conclusion was based on the shape/form of the material which proves it’s function. Again we can see in the photo three insulating elements;
1 – Round shaped insulating separator
2 – Insulating Washer under the bolt heads (on 2 of the 5 bolts in the photo, I would presume the other insulating washsers fell off either during operation or between disassembly and photo, and the 6th bolt hiding somewhere else).
3 – Insulated bolt-holes covering at least one of the two halves of the spacer/spool. (insulating sleeve can be longer such as extending past the joint interface, but it is not required)
Now look how these parts are arranged in slide 1 of my powerpoint. You can see they provide effective electrical isolation. Now remove any one of the three and electrical isolation is lost:
1 – Remove round insulating separator and the spacer halves contact each other... insulation is lost.
2 – Removing insulating washer under the bolt head allows the right half of the spacer to electrically contact with the bolt. Insulation is lost because that same bolt was already in contact with the left spacer.
3 – Removing the cylindrical insulating sleeve from a bolt-hole on the right side allows the right half of the spacer to come in electrical contact with the the bolt. Insulation is lost because the that same bolt was already in contact with the left half of the spacer. (Actually if you have perfect centering of the bolt within the hole to assure no contact between bolt and bolthole, insulating sleeve would not be required, but assuring such clearance would require an oversized bolthole which increases stress on the insulating washer which is already mechanically challenged. )
You can see that these three elements are required to accomplish electrical isolation of a bolted joint. Exactly these three are what is required for electrical insulation. Any more would be superfluous. Any less would not accomplish the task.
Now let us try to imagine that these are used for vibration isolation:
1 - Why do I need a flexible washer under the bolthead? If we wanted to alter axial vibration we can do so using the separating piece. More importantly, regardless of the intent of the flexible washer, it inhibits us from clamping the bolts tightly, which is required to prevent the halves of the spacer from slipping relatively to each other. It is not a design choice we would take if we could accomplish the same thing other ways, like using the separting piece. It is a design choice that is forced upon us for electrical insulation because the bolt must be completely insulated from one half.
2 – Why should we have flexible materials in boltholes of only one half of the spacer? It is asymmetrical.. no logical reason for vibration isolation (very logical for electrical isoltion).
3 – Is this mysterious vibration isolating device for axial or torsional purposes?.... the bolthole insulation can serve no axial thrust isolation purposes. The other two serve not much purpose for torsional isolation.
Hopefully the logic is clear. Now let’s go to experience:
Every electrically-insulated bolted connection I have ever seen has exactly these three elements (no more, no less). Off the top of my head, that includes upper bearing support ring bolting to upper flange on our circulating water pump motors, upper bearing suport ring bolting to upper flange on our condensate pump motors, lower bracket to stator flange on our essential cooling water motors, oil cooler pipe insulated flange for coolant pump motor, and generator stepup transformer mounting flange for low voltage bushing enclosure (doghouse). Construction details for the Circulating Water Pump motor are shown in the attachments to this thread:http://maintenanceforums.com/e...161080002#2161080002
(which coincidentally describes failure of insulating materials used in a mechanical joint).
In contrast, I have never seen a mechanical isolation device built anything like this (including all three elements). The few isolation couplings I have seen were all forum links, but none of them looked anything like this. One torsional coupling I remember seeing had removable elastomeric elements enclosed between jaws. Another I vaguely recall had flexible sleeve around pin similar to bolthole insulation, but I’m sure those pins were not used for axial clamping as these bolts are. I have seen nothing resembling all three elements discussed above. As always I could be wrong (we don't know what we don't know), but now you know the basis of my opinion and it remains strong.
The geometry configuration can indeed be used for vibration isolation or torsional stiffness control.
If you can post an example of vibration isolating or dampening coupling that includes all three elements discussed above, I will find a way to send you a beer ;-)