RWF compressor coupling

[duke717]

Hey Guys,

Went to replace the drive coupling on a Frick RWF compressor. It has the BPU style. Simple job I thought. The coupling hubs would not come off the compressor shaft or the motor shaft. Ended up having to cut off the hubs.
When they were finally off, it looked like the hubs had been spot welded to the shaft. (not by anyone actually welding on it).
Has anyone seen this before, or have any ideas what would cause this?

The YDCT starter was replaced with a soft start after this problem occurred, due to contactor damage.

Thanks

[Josip]

Hi, duke

Hey Guys,

Went to replace the drive coupling on a Frick RWF compressor. It has the BPU style. Simple job I thought. The coupling hubs would not come off the compressor shaft or the motor shaft. Ended up having to cut off the hubs.
When they were finally off, it looked like the hubs had been spot welded to the shaft. (not by anyone actually welding on it).
Has anyone seen this before, or have any ideas what would cause this?

The YDCT starter was replaced with a soft start after this problem occurred, due to contactor damage.

Thanks

just two questions

1. sorry, I don't know .... what is BPU style?

2. when, the last time, that coupling have been removed for check ... approximately?


Best regards, Josip

[duke717]

Josip,

Hee is what the coupling looks like. The pic I have is too large to put on here.

I replaced the shaft seal on this compressor within the past year. I had this coupling off then with no problems.

thanks

[Josip]

Hi, duke 717

Josip,

Hee is what the coupling looks like. The pic I have is too large to put on here.

I replaced the shaft seal on this compressor within the past year. I had this coupling off then with no problems.

thanks

Yes, I know this type of coupling it shouldn't be a problem to remove the hubs. The same type of coupling we have on Sabroe and some other compressors .....

I remember, few decades ago, suggestion given by Stal specialist to remove coupling hub from compressor for check and cleaning every year, otherwise there can happen something they called "cold welding". I do not remember about explanation, but something like crystal lattice (metal formation of atoms) can come (dive, ingress, intrude ... sorry, don't know a proper word in English) from one part of metal(hub) into another part of metal(shaft) making connections similar to spot welding.

We know, even if we have a "highly" polished surfaces they are very rough (looks like mountains) when observing them over magnified glass or kind of microscope . Thus our hubs and shafts are not in contact with full surface, better to say, only in some spots which became highly loaded with force which must be transferred from electric motor to compressor...

I believe, all this is consequence of micro vibrations due to micro gaps between hub and shaft (due to years of wear gap became a little too big/loose)... and at the end we have what you find out ... like a forged connection but cold one

Something similar happened to me many years ago, fortunately no need to cut hub ... a very big puller and heating torch were enough .. Of course I can be wrong ....


Best regards, Josip

[duke717]

Josip,

I have never heard of anything like this. This is very interesting. Is there anything that can be done to stop this from occurring again?

Here are a couple of pics that show the damage to the shaft and coupling.

Thanks for your help.

[Josip]

Hi, duke717

Josip,

I have never heard of anything like this. This is very interesting. Is there anything that can be done to stop this from occurring again?

Here are a couple of pics that show the damage to the shaft and coupling.

Thanks for your help.

there is also known term material fatigue due to too much micro vibration caused maybe with misalignment, but I'm not an expert and cannot tell more about that .... see the link ...

http://en.wikipedia.org/wiki/Fatigue_%28material%29

http://materials.open.ac.uk/mem/mem_mftext.htm

hope some other RE member can tell us more about in a plain words

... don't know how to stop this from occurring again, except to remove coupling hub for check and cleaning and recheck alignment every year ... by the book

Hope this help a little....

Best regards, Josip

[SeanB]

Use loctite on the replacement - there is a white one that prevents chattering, yet is removable easily. I can't remember the number, but it is the only white one in the range. It prevents metal to metal contact as well as corrosion, both of which cause problems. Best is regular removal, and reapplication every time.