[erase42]

im not really sure how to formulate this question, but ill just open it up and perhaps my answer will just drop out. In the old style meat grinder we have all seen, the auger has a progressively tightening pitch toward the cutter plate where the meat is forced through. what though is actually causing the pressure that builds up behind that plate. i can see how the auger would force the meat that direction, compressing it due to the decreasing space between auger "blades". But what prevents the whole screw from "loading up" and just rotating the whole mass in the cylinder. Is it simply the friction with the walls of the cylinder? If the auger was incased in a sleeve that rotated with it would the concept still work? anyone care to throw in your 2 cents worth, at least it might help me figure out what im trying to ask.

Ed

[HuFlungDung]

Ed,
IMO, yes the stock must be held by friction with the wall. The inside of a meat grinder chamber has a certain amount of ribbing that assists in increasing the friction. The only reason that pressure increases is because the incoming stock is being 'overfed' at a higher rate than the screw is outputting at the plate.

I once worked on a grape press that was just like a giant version of a meat grinder. This press had been adapted for use in seperating honey and wax in a honey operation. The designers of this press had added a lobed gear, which engaged the main screw, something like a worm and gear assembly. This lobed wheel was near the input end of the screw and its axis was crosswise to the screw axis. The purpose of the lobed wheel was to 'shut off' the flow of material that wanted to bypass over the top of the screw. This also caused a positive flow of material to build up in front of the lobed wheel, and the effect carried all the way forward to the front of the main screw extruder plates. The pressure buildup caused honey to flow out through holes along the main cylinder of the press. The wax went through the extruder plates at the output end of the screw. In this application, I guess there was no way to get enough friction from the stock to keep it flowing through the screw, so I guess this was their solution.

[erase42]

im having a problem understanding your description, but i think its the hour.
what im wanting to do is force some chips and small chunks of eps foam thru a cone shaped heated nozzle to bind them together to help me control the waste at my shop. i had another idea of a reciprocating piston style pump that would pretty much pound the stuff thru, but if i could get away with an auger id prefer it.

[Geof]

Look for information about injection molding machines, I think augers are used to feed the plastic pellets in; heated augers actually that melt and blend the pellets together. You seem to be planning on making the same type of system.

[JerryFlyGuy]

Look for information about injection molding machines, I think augers are used to feed the plastic pellets in; heated augers actually that melt and blend the pellets together. You seem to be planning on making the same type of system.

True Geof, infact there are systems out there in the plastic field where the force of the screw does the heating of the plastic [due to increase in pressure] and thats all there is to taking the pellets and making them extrudable. I do lots of work in a cable/wire plant and thats how there extruders work, I was amazed to learn there is no heating ellements in the entire extruder, its all due to increasing pressure of the screw [its usually about 10ft long] They can put a full cover on a 2" cable running at 13m/min thru the machine.. its pretty impressive when you see it all in action..

Jerry

[merl]

Yes you guys are quite right in your answers.
erase42, if your still uncertain about Hu Flung's explination he is simply conferming your suspitions about how an auger works.
If I may further add to what JerryFlyGuy and Geof have said.
Typicly an auger that is used to transfer material from point A to point B has constant pitch fliteing for the entire length. If you decrease the pitch,say from one turn in 12" to three turns in 12" you are forceing the same amount of material into a smaller space. Of corse anytime you compress somthing you create heat, get that somthing hot enough and it will "flow"
I wonder, will the stuff you want to get rid of will re-melt? This will determin at what PSI it will flow.
Anything will flow if it is compressed high enough (you know how diamonds are made ) how big a press do you need ?
If you have enough waste to justify it you might Google for a used extrusion press or the like. It might not form a new conglomerit from your waste but, you might make a good solid "cake" out of it.
At one shop I was at we seperated the swarf from the grinder coolent with the "cake" method and it worked very well.

merl

[erase42]

Actually what Hu said makes perfect sense to me now. And yes the foam scraps I will melt redily. Im thinking that I might need to build my own custom unit since the volume will me quite large. The grinder unit I am building has a 50 inch wide throat so I can eliminate most of the bigger chunks without taking time to break or cut it down into more managable size peices. The original size of my billets is 50 x 42 x 96 and I may cut 4 or 5 a day sometimes. You can imagine the volume of scrap. Anyway the grinder will go a long way towards reducing the space it takes up. But ideally if instead of airborn fluff as a byproduct I could extrude it into something i could toss or convey into my trailer without the mess. Im figuring to handle that volume that ill have to use a screw more similar to a

[erase42]

oops. not sure how that happens. Anyway a screw similar to a digging auger but with a progressivly tight pitch, or maybe progrssivly shallow whichever is easier for me to make. Perhaps start with a commercially made 6 or 8 inch post hole auger and modify it to my needs. Anyone think that would handle the volume.

[HuFlungDung]

I'm not sure if grinding foam up makes less or more volume What kind of foam?

I've never made a variable pitch auger flite, and I think it would be an intriguing project to machine one. I would probably lay it out as a flat map and use 4th axis wrap to machine the flute.

So far as modifying an existing fixed pitch auger, I don't know how you would do it. It is a practical impossibility to change the pitch of a heavy flighting such as you would need for a high pressure application.

Perhaps another method to increase the pressure would be to turn a taper on the the outside of the constant pitch auger and make a matching tapered chamber, with internal ribbing. I suppose you would not want to make the taper too severe, or the material may simply stall in the flow. Smoothness of the fliting and ribbing would be quite important for the auger to keep itself and the chamber wiped clean. Take your best guess and try a couple of different ones, I guess.

[merl]

erase42, HuFlung,
Consider that the casing walls on a butter packing press are 1/4 thick, 316 SST. The auger is made from cast SST and polished. You're not going to make somthing that works out of the auger from a post hole digger.
Befor you build somthing from sratch go to a place on line like Surplus Record and try to find somthing that meets your needs.
Consider also it takes tons of pressure to cause the flow effect, I don't know what it is that your working with so I don't know how many tons but, I'm sure it's several. You will probably have better luck using a heated nozzel and there are a number of ways to do this.
As to making your own auger, Hu you are correct, if you force the stuff into a taperd barrel you will compress it further. You will also increase the exit velocity of the waste matl. unless you slow the pitch down as well.
It is easy enough to turn or mill your auger flites as either a constant or variable pitch from a solid bar. Any FANUC 6 or better controle should handle it.
Hu, if you were going to do it on a 4th axis you would simply program to turn so many degrees for so many inches of X travle that would represent the first part of the pitch then the same again for the next part and so on...
The greater number of steps you take to go from your begining pitch to your ending pitch will give you a smoother transition.
Look at your post hole digger or ice auger and, imagine it as the configuration of your pitch. You would load your waste at the top end and run it in reverse to force it to what was the digging end to compress it. As a pitch modle the post hole digger is probably pretty close but, I would guess from the size of the grinder your building it would need to be a larger diameter and MUCH more roebust.
If you insist on building your own waste compactor, have you thought about starting with a log spliter insted of a post hole digger, then you would only have to build the compactor bin insted of the entire machine (fun as it sounds)

merl

[Geof]

Have you looked into buying a chip compactor? They are not cheap but you would have something up and running quickly and some are designed for plastic waste.