One of my clients is using several bench-mounted grinders which, when the stop button is pressed, only run down to a stop (which takes at least a couple of minutes). Should the wheels be fitted with brakes to bring them to a halt more quickly?

I am concerned about inadvertent contact by a passer-by with a still rapidly rotating wheel after it has been turned off.

LB

Frank

I haven't got the details to hand, I'm afraid. My concern is that there is quite a large segment of the wheel which is not covered by the fixed guard and, when the clear perspex guard is pushed out of the way, there is quite a lot of the wheel exposed (probably 20 - 30º).

LB

Many thanks, Frank

LB

Hi, Paul

Could you expand on that, please?

LB

Probably best by example.
I was at one time a Service Engineer with a grinding machine manufacturer, UK based company.
We put machines into automotive mainly.
I was involved in an investigation into issues we had with grinding wheel balance.
We used dynamic balancers on the wheels, and, we check balanced at every start.
We were finding that we had to do a full re-balance after every wheel start.
This was unusual.
Our designers, the wheel makers and the balancing equipment makers all became involved as it was primarily a load of machines I had put into one customer.
So I was suspected!
However, it came down to a clients spec of stopping the wheels in less than 10 sec.
Once this was looked into it was found that the forces on the wheel were outside those allowable.
Also, the wheels were actually rotating in the flanges, thus moving the heavy point at every stop, rather than every start!
The wheels were driven by some "clever" drives, so the decel ramps were re-programmed this alleviated the issue.
These wheels were clamped by flanges with a ring of bolts.
Right hand threaded.
I was at another time involved in an investigation where a wheel had come off a spindle.
We checked everything out mechanically and could find no issues.
So the machine was rebuilt.
No balancer fitted.
No changes by us.
No changes reported by client.
Machine was run up OK & returned to use OK.
Machine was stopped OK.
Machine was started and wheel was loose, but did not come off the spindle.
Further checks etc.
Nothing found however, every time the wheel stopped it came loose.
We then found out that a customer person had reprogrammed the drive.
Decel ramp increased.
The wheel was undoing itself due to the decel.
Single Left Hand Threaded nut.
We did not immediately link the wheel spinning in the flanges with the decel, because everything was always tight.
The clamping forces were re-caclulated and confirmed, the clamping bolts were tightened to the correct torque.
The wheels were correctly mounted.
The clamping forces were even measured and found to be correct with the wheel slipping issue.
However in both cases the "inertial" forces were above those the design could take.
This led to a re-thing and a re-design as well as re-programming, hardware and software re-configuration to prevent this on these and future machines.

If you were to retrofit braking then I would very strongly consider WHY you feel this so essential.
You could easily cause more danger than you eliminate.

By the way, why do you want to brake the wheels?
They pose little danger in comparison to a spinning chip forming tool.
What machines are you looking to brake, remembering the cost of a d.c. injection brake could probably be well in excess of the machine itself, as could a programmable soft start / variable speed drive to give you programmable accel & decel ramps.
If you put a braked motor on then you would probably find that the braking forces are quite high. Possibly higher than the wheels can tolerate.

Does this help?

Yes frankc they did, they were totally guarded production machines.

They were sufficiently guarded to contain a wheel burst, and we were know to try it on times when we got the programming wrong!

1000kg of grinding wheel is a mess to clean up let me tell you.
None ever got out though!

Yes! - the Abrasive Wheels Regs were made in 1970 because in Summers v Frost (from failing memory) the Judge held the employer was in breach of the absolute requirement of the Factories Act to fence dangerous parts of machinery. I seem to recall the judge in that case recognised that fully guarding the wheel "disabl(ed) its requirements" but said that was what the Act, as written, required.

Long run down times have always been a feature of these machines. That's the case even in schools, though I suspect they're now normally located in prep rooms, that wasn't always the case.

Thing is, I registered under a traceable ID!
I can be found from my log in, so I can't really tell lies or provide nonsense in my posts.
They are my opinion, however, even though I am NOT CMIOSH, I DO have a LOT of experience in Engineering.
I am also a member of another Professional Institute so, I still can't hide.
So, if I provide a post, and, IF you notice I only comment on certain areas, I feel that under my professional membership requirements I am competent to comment.