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    Discussion in 'The main mechanical design forum' started by tesseract, Jun 30, 2013.

    1. tesseract

      tesseract New Member

      Jun 2013
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      Hi I am in the process of designing/building a small extruding device it will take plastic pellets and melt them and extrude them into a filament and I have a few mechanical design questions I am hoping you can help me with. I am new to this forum so please bear with me.

      In my system I have a tube going from point A to point B in this tube is an auger that for the most part completely fills the ID of this tube. At point A is the nozzle, the nozzle had a small concave section to begin channeling the molten plastic into the nozzle. just in front of the nozzle is the heating element that melts the plastic pellets prior to extrusion. The auger is cut flat at the tip end and rest right up to the nozzle at point A and extends past point B and point C on to Point D where it attaches to the motor. From point B to point C it is not surrounded by any type of tube it is the entry point for the plastic pellets.

      tube ID = 3/4"
      auger OD = ~ 3/4" :it just fits inside of tube very small gap surrounding it maybe 1/32"-1/16"
      Point A to Point B = ~ 5"
      Point B to Point C = ~ 6"
      Point C to Point D = ~ 2"

      Conditions: Mechanics are put into place to prevent auger from moving away from nozzle tip yet allowing for free rotation inside of tube.

      Goals to achieve fast extrusion of material that is uniform in nature.

      To achieve these goals I have a few questions
      1. Does it matter if the auger extends completely to the Point A or can it be shortened to say point A1 and leave an open area between the end of the auger and the nozzle that would be simply enclosed by the tube?
      My thoughts: Having the auger go completely to Point A maintains as much as possible the flow of material into the nozzle eliminating much of the outward force directed toward the inside of the tube between point A and point A1. Here, the forces will spread equally toward the nozzle opening AND the inside of the tube. Is this difference negligible?

      2. Would increasing the distance between point A and point B by 3" and decreasing the distance between point B and point C by the same amount add any benefit to the flow of material?
      My thoughts: Between points A and B it is a more of closed system where direction is primarily driven by the auger with a minimal chance to move in other directions. If this area is increased, is this a benefit to increasing extrusion speed and uniformity? Beyond point B pellet material can move in and out of the auger area freely, reducing the driving force into the nozzle area.

      3. Would simply reducing the overall length of the system by shortening the distance between points A and B and points B and C as well as the auger length be of any benefit other than a shorter overall length or would it have an effect on the the uniformity and speed at which we could extrude material?

      I mention uniformity because coloring can be added to material to change its overall color and it should all be the same color the coloring is controlled by the addition of a colored pellet at approximately 1 per 50 of the colorless pellets. My concern is that in a shorter system the color will not be mixed well enough to become uniform.

      Thank you for your assistance and please feel free to ask me any question I will do my best to answer them.
    3. DrZ

      DrZ New Member

      Jul 2013
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      polymetr extruder designs

      I work on 15 inch diameter single screw extruders and also twin screw extruders. Scaling down their desighns to the size you require may be the most helpful answer. I will say that the single screw extruders use a seperate mixer wereas the twin screw extruders mix and extrude at the same time. We have several miniature extruders that would be helpful to your project. The barrel ID is one inch and the screw length is approximately 12 inches. The secret is in the flights of the screw. It starts out with feeding flights, then kneeding flights, transition flights and then extrusion flights. The transition flits is the area the polymer is melted.
    4. Michael Ross

      Michael Ross Well-Known Member

      Mar 2012
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      I can't understand why you would want to build your own extruder. If there is any profit in the extruding itself, then you will make much more profit by buying the good pre-existing equipment that has been around for decades, than by trying to reinvent the extruder. I feel pretty much the same about research - you can buy existing small extruders for lab work.

      If you intend to become an extruder manufacturer, then you have so very much to learn and this forum, at its best will barely scratch the surface. The first step is to actually use existing equipment of the scale you need, and see how the dirty work of running and repairing them goes, changing over from one material to another, know about the various screw profiles used for the various materials, all the conventions for attaching to molds, etc. there are so, so many ways you can go wrong if you do this yourself.

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