Need suggestions for Max Compression

[BretMan]

I'm on a project to build a prototype, about 20"H x 10"W x 10"D.
It needs to compress powders into tablets about the size of an asprin tablet, which takes a minimum of 1/2 ton of compression pressure to accomplish.

I need some ideas on mechanisms that don't include hydraulics, but which will give the necessary compression at the compression point. It needs to be run via an electric motor.

I'm thinking of mechanisms along the lines of a worm gear or threaded means connected to the motor which will move a lever on a fulcrum back and forth which is connected to compression area. Any pulleys or gears in between to multiply the forces is fine, as long as it all fits within the dimensions mentioned.

Does anyone have any suggestions? Is there a known maximum mechanical pressure making mechanism already established so I don't need to re-invent given knowledge.

Many thanks beforehand!

 

[MikeHalloran]

Asprin tablets are made by devices called tableting presses, that are in production now, and do exactly what you want. I'm pretty sure that most of them are electromechanical. I think they also run in semi-closed environments to limit incoming contaminants and outgoing dust, so there are incentives to limit their physical size. I'd bet you could find one intended for pilot production that would meet your needs just fine.



Mike Halloran
Pembroke Pines, FL, USA

 

[BretMan]

Thanks Mike. There should definitely be some known configurations to absorb from one of those machines. I have searched and found manually operated ones with a handle lever, but the "throw" of the lever exceeds the dimensions I'm constrained to. The next level I found were the full production types that are way beyond what I need. You're suggesting something in between, that's the right size. I'll search for one but if you happen to know the link or some specific info. on it, I'd greatly appreciate it if you could forward that to me.

Bret

 

[MikeHalloran]

I used to get a fish wrapper devoted to the pharmaceutical manufacturing trade; it was full of ads for stuff like that. It's been a while, and I've forgotten the mag's name. It's probably changed publishers, its name and its format by now anyway.



Mike Halloran
Pembroke Pines, FL, USA

 

[eromlignod]

How about a slider crank and flywheel? You can get a tremendous force at BDC due to the toggling action.

Don
Kansas City

 

[BretMan]

Mike: "fish wrapper" lol. That's just what junk mail is! But hey, back in the day, wrappers were the only way many people in isolated places got news. Treasures in junk I guess. But that gave me a search idea. Thanks!

Don: Thank you. That's an interesting configuration. What would you say to a dual set up of that, but add opposing rollers somehow?

Bret

 

[eromlignod]

Do you mean smash the pill from both ends? You could gear two flywheels to do this, or even run the opposing sliders 180 deg. apart on the crankshaft, but I'm not sure what that would accomplish.

Don
Kansas City

 

[BretMan]

No, I'm going from a powder to a tablet. Not a tablet to a powder.

 

[unclesyd]

Here is a common type of tableting press available on the surplus market that is all mechanical. We had two of these that made pellets by compressing Cobalt Bicarbonate for use as a process catalyst. These Stokes machines ran for over twenty years with very little maintenance other than changing out the punches.

http://www.unionmachinery.com/Product.asp?pid=2734

The BB2 was some early Aspirin tableting machines.

 

[BretMan]

Thanks unclesyd. I asked them for schematics on that one. All the ones listed there are much bigger and faster than what I need, but you did provide an idea as to a mechanism and it looks like they're close to Don's Flywheel suggestion.

My machine can't have those size pulleys but then for the mass production purposes they're for, that's what's required. If I can press 4 tablets per minute I'd be very happy - even just 2. So a high torque albeit slow motor, would be needed. I need to multiply the force from the torque of the motor to the point of compression somehow.

 

[eromlignod]

The key to this type of press is to take advantage of the stored energy of the flywheel. The motor should keep the flywheel turning all the time with a belt. You connect the wheel to the crankshaft with a single-revolution clutch. When you want to make a pill, you trip the clutch and "kachunk!" you get one cycle.

If a slow stroke is critical, just use a large gear for the flywheel and drive it with a low rpm gearmotor and pinion. Alternately, it could be a chain & sprocket.

Be careful in your calculations. You will find that the force at BDC is theoretically infinite (!), which can make it tempting to undersize the mechanism. You need to carefully graph what your maximum available force is throughout your compression stroke and add a healthy safety factor.

Don
Kansas City

 

[BretMan]

Thank you Don. That sounds simple enough in that what you're suggesting can be done with off-the-shelf parts. Would you have a supplier recommendation?

If the BDC is theoretically infinite, then that means the flywheel can be small enough to fit w/i my dimensions. That's great news! Now I need to figure out the motor specs. Its physical size, so all this fits into the space, has to be under 5" but can be about 10" long and high torque and should be located on the bottom of the unit to keep a safe low center of gravity. If you have any other suggestions please let me know - and that supplier too.

I'm headed now to the electric motor forum to see what they may suggest.

 

[eromlignod]

Well, be careful, like I said. The force is theoretically infinite, but the stroke is also theoretically zero at that point too! The critical thing to consider is what angle your crank is at when compression starts and what the compression force is for all points between there and BDC. I'm not familiar with how a powder compresses...you might need to experiment a little with an arbor press.

Remember that the point of maximum compression force won't be the same as the point of maximum crank torque, since you get an increase in mechanical advantage as you approach the toggle point at BDC. You'll have to do a little trig. and statics.

There will be some angle where you see your maximum torque. You will also get some help from the gear or chain drive. If your ratio is, say, 5:1, then you can divide this maximum torque by 5 to get an approximation of what the motor will see. Also, the shorter the crank-stroke and the larger the bull gear the better.

Most of what you need you can probably get at McMaster-Carr and/or Grainger.

Don
Kansas City