Stirlingengineforum.com

Hi ,I hope you do not mind me leaking over from an other forum.
I normally hang out on the G.R.F. page but have been looking at alternative ways to produce a reciprocating action for a project I am working on.
Are you familiar with what is called a "Shaker Table"?
It is a method of gravity separation using a back and forth motion along a horizontal plane.
There are actually two different schools of thought about table motion. One school holds that the table needs to be pushed foreword, towards the concentrate end of the table , with a smooth slightly accelerating movement and then suddenly and very rapidly pulled back in the opposite direction. This is motion that cam drives provide. It is akin to the old magicians trick of pulling the tablecloth out from under the china.
The other school of thought believes that the deck needs to be pushed very rapidly forward and suddenly halted in a small jerk as the deck is pulled backwards at a slightly slower velocity. This motion is akin to what you do when you toss a load of gravel off the end of a shovel. There really isn’t a noticeable ‘bump’ or ‘impact’ in this system but merely a rapid change of deck direction.
Neither of these two types of motion are in a any way uniform as would be the case if you were using a simple eccentric or crankshaft to drive the table.
So I have been looking at alternatives.
pneumatic did look interesting as the safety concerns of using electricity and large amounts of water never sat well with me.
Then I was thinking what would old Isambard Brunel do,Could a steam piston work.well pressurized vessels and lots of water can not be considered any safer than electricity .
But a Sterling Engine is low pressure,is perfect for isolated places where they have kerosene but little else .
We are not talking about a lot of power,in fact as there would be no conversion of energy from on plane to an other and only need travel back and forth form 1" to 5" ,it should be quite efficient.
The problem being you can not just order a Stirling engine piston from Maplins.
Is there any one who builds such things to order and if so how controllable would such a power system be?
Any ideas or suggestions?
Regards
Justin

Is this for gold recovery?

Well technically it is to separate uniform particles based on density.
Not having any gold laden ore as you have in the states my interest is in running electronic material,there is a notable amount of Au and P.G.M.'s in the concentrate.
I tend to build all my own equipment as it is cheaper than importing it and once I have built some thing I have a better understanding of the system dynamics.
If I can incorporate an improvement or a number of other peoples bright ideas so much the better.

why don't you just use a motor?

yes the normal way is to use a crank and shaft with a cam arrangement.
The draw back with this is that when you want to change the nature of the interaction of cam and table you have to make a came with the profile that you hope will elicit the right reciprocal motion.
That is fine if you are processing a standard type of material.
You experiment until you get close enough for your needs and then push tun's of material all just about identical through it.
My problem is that I get sent lot's from one or two kilos up to about 40.
each one needs to be assessed and slowly tested as to work out the optimal processing method.
Looking at the system I believe a drive that would let you fine tune each stroke effectively would be a boon.
My search has extended through basic mechanics and pneumatics but as I said I would like to try and find an alternative to using electric power as a lot of the people I associate with operate in quite bad conditions in any case so any improvement in safety is to be encouraged.
And though I have not had any access to Mr Stirling's work I have had daily interaction with the legacy of Isambard Brunel and his atmospheric railway.
I quite like the idea,The force needed to operate a small 900mmx600mm table would be quite small, and how cool would it be to have a practical use for such a simple but powerful device.
From my research in pneumatics I think you should be able to control the timing and torque curve by controlling the passage of internal pressure.
But as it is a somewhat specialist subject I was hoping some one who had actual experience of running such units might have an opinion.It seems to me to be by far the simplest solution if you can get the tuning right.
It is the simplest motor I know of.
Victorian technology and gold recovery two of my favorite things.

justincase, What part of the world do you hang out in? There is gold in most countries, just not always easy to get at. As for a simple Stirling Engine big enough to power a shaker table, it might not be too practicle as it would be much larger than a small Honda, or Brigs & Stratton, or similar motor that you could buy for just a few hundred dollars.
Ian S C

yes the normal way is to use a crank and shaft with a cam arrangement.

No. The normal way is to attach an engine/motor to the table and mount an off center axis weight. When the motor turns, the whole table shakes.

Thank you for taking the time to answer.
I had seen similarity's in frequency and reciprocal motion that the two devices share.
But if you are of the opinion that it has too low a power density to be of use I will have to take your opinion as text book.
I thought it would be a nice idea and of great help to other workers who work with out mains electricity.
Having a table that would run of any thing from a camp fire to a propane burner would have been very handy.
Very similar to pneumatic but with out a compressor and a single cylinder with out linage seemed to be the simplistic solution.
I live in the old Roman Town Of Isca or Exeter as it is called to day in the South West of England.
There are trace deposits of interesting values but nothing that could be mined.
I have found small bits of gold coming from old tin mines and in streams on Dart Moor and Exmoor,but only one or two flakes after days of hunting.
So I stick to urban mining.
Thanks for you help.
Regards
Justin.

Aviator168 wrote:

yes the normal way is to use a crank and shaft with a cam arrangement.

No. The normal way is to attach an engine/motor to the table and mount an off center axis weight. When the motor turns, the whole table shakes.

That would just make a shaker deck,It would not have the kinetic transfer of energy that is required to make use of table friction.
I am trying to improve on the programmability of each stroke so that when I combine that data with velocimetry I can better understand the effect on each type of material.

That is odd.I have been stopped for editing my post's.
This is the simplest method that tends to be productive.
https://www.youtube.com/watch?v=rLZ4dYErsko
Note that the deck only moves about 1" if that.
I use Linear bearing so the friction is very much reduced and with the right counter spring half the job of return is self regulating.

justinhcase, you'll have to take a trip up to Wales, some say there is a bit of a gold rush.
Ian S C

Ian S C wrote:justinhcase, you'll have to take a trip up to Wales, some say there is a bit of a gold rush.
Ian S C

Welsh Gold is worth about twice the value of gold from else where if you can prove the provenance.
Unfortunately the Romans did a very good job of Hydraulic mining , They managed to get at most of the easaly accessed value.
What is left is not rich enough to make a going concern out of.
If you see any jewellery that is described as "Touched Welsh Gold" stay away form it the lightly hood of even the small amount that is meant to have been added is not actually welsh at all and the seller is just trying to make unfair profit for a standard alloy.