Bad grinding wheel?

[Sonic EscapeParticipant @sonicescape38234]

I bought a stack of unmarked large grinding wheels. I know that “the maximum safe RPM for an unknown grinding wheel is 0”. But they all sound fine when I hit them with a screwdriver handle. Except two.

This two, one black and one brown, don’t ring at all!

Are they bad? After a brief research I found out that the black one could be either black silicone carbide wheel or a Bakelite bonding wheel. The Bakelite wheels are supposed to be more elastic and maybe this is why they don’t ring?

Here you can see how a normal wheel rings comparing with this two:

 

[roy entwistleParticipant @royentwistle24699]

I don’t think that i’d risk it

Roy

[Sonic EscapeParticipant @sonicescape38234]

Yes, agreed. I didn’t realized how heavy this wheels are. There is a lot of energy stored in them when spinning fast. Breaking one at 1500rpm or more would be a spectacular event.

[David JuppParticipant @davidjupp51506]

I can see what could well be cracks in both wheels, just from a quick glance at the photo.

[bernard towersParticipant @bernardtowers37738]

Is it worth the risk?

[Michael GilliganParticipant @michaelgilligan61133]

If you really can’t bear to throw them away, either break them in half, or stick them down to a board, and then use them by hand. … Don’t put them on a grinder!

MichaelG.

[Sonic EscapeParticipant @sonicescape38234]

I have no problem to throw them away. I have enough wheels. I just want to be sure that the wheel is bad. I’m pretty sure the black one is using Bakelite as bonding material. Bakelite phenolic resins are also used for acoustical insulation. So maybe it is normal to not ring. But I can’t find more info.

[Sonic Escape]

On Sonic Escape Said:

I have no problem to throw them away. I have enough wheels. I just want to be sure that the wheel is bad. I’m pretty sure the black one is using Bakelite as bonding material. Bakelite phenolic resins are also used for acoustical insulation. So maybe it is normal to not ring. But I can’t find more info.

But if there are no internal problems the “knock” would resonate around the ring and, hence, produce the tone.  No tone would mean the vibration doesn’t resonate, but gets damped down by something (a crack).  I would think that all rings would produce ringing tones, just different in frequency.

[old martParticipant @oldmart]

When I was working, our grinding department used to break up old and faulty wheels into many different bits, drill them and glue in an arbor with epoxy and true them up for internal wheels. they were washed first under a hot tap and dried. Some grades they wanted to use for specific jobs were not available ready made.

Suspect wheels would run safely at 120 rpm in a water bath to sharpen wood working tools.

[Mark RandParticipant @markrand96270]

I’m with David Jupp. There appear to be a pair of cracks on the first picture starting at 12 ‘o’ clock on the inside and spreading out left and right from there and a single crack on the second picture starting at just before 3 ‘o’ clock. They look like vitrified wheels and may well be silicon carbide. The second one could be a general purpose aluminium oxide as well (I have one with a similar appearance, was using it today on the surface grinder). Wheel colours aren’t really a very good guide to their composition.

If you do decide to mount them and run them. Stay away (in the axial direction, but nowhere near the radial direction) from them until they’ve run for several minutes. But I would break them and would expect to see them split where the cracks appear to be.

This opinion applies *100 if there is any similar sign of the cracks on the other side or the periphery of the wheels…

[peak4Participant @peak4]

This is a UK Health and Safety Executive document which you may find useful
https://www.hse.gov.uk/pubns/priced/hsg17.pdf

Bill

[Author]

Posts