Hello Robin,

I had completely forgotten about that approach; couplings like that were incorporated into spin dryer motor drives years ago and I recall thinking then how clever the idea was.

You are quite right about the action, the working medium is thixatropic, rather akin to stiff starch paste as you say and it will flow like mud until agitated.

And I am sure it could be resurrected into a machine drive clutch of some sort, with or without magnetic 'switching'

Regards

Brian

" couplings like that were incorporated into spin dryer motor drives years ago "

Yes, but didn't they use steel shot like the bigger industrial types? Can't remember the name but Sir John will.

Regards Ian

" I took one to pieces as you do to see what it contained. "

So did me mate, – – – – His wife was really pleased and his life was interesting till she got a new twin tub.

Regards Ian.

I've used dry magnetic powder clutches in the past. They are little more than steel filings held in a small gap between the input and output shafts. A control current in the solenoid coil induces a field across the gap and causes the particles to adhere to each other and to the faces, causing drag. The nice thing about this concept is that the developed torque is proportional to the control current and independent of speed, so they are ideal for wire tensioners and small dynos.

Here's the model from Simplatrol/Lenze that I used on a large wire tensioner, probably the 250mm size. I don't recall how we drove the clutch but the tension feedback was by strain gauge load cell so there must have been a control amplifier somewhere. For simple systems, you can drive the coil directly with a variable power supply. Between the solenoid dissipation and the frictional heat generated, this required the (dotted) finned heatsink to keep the temperatures down but then it would work all day with almost no moving parts. With 80-100Nm of torque available, we were able to mount the wire drum directly on the clutch to keep things simple.

Quite a few vehicles have been fitted with magneto-rheological dampers. The fluid in these possibly behaves as you discuss and its viscosity can be modulated by varying a magnetic field. I've no experience of MR dampers but they must be neater and faster then the electromechanical alternatives with their valves and solenoids

Murray

Brians description of the spin dryer drive is basically correct. a pulley fixed to the pancake or "Doughnut" coupling was driven by the motor and the centrifugal force compacted the shot (about 1/32" dia) onto the disc vanes and the drive picked up. Think it was only used with a vertical spin dryer (Pancake/doughnut spun horizontally) but the bigger ones I was involved with were mounted on the shaft of a 25HP motor and spun vertically.

Regards Ian.

Edited By Circlip on 21/09/2014 19:28:49