Extruder Design Rationale

Are you familiar with any practical synthesis of bioplastics?

- No, plastic has pretty much come to me in a box or on a rail car in pellets or flakes

Let's start with a basic extruder for sheet - such as greenhouse glazing in 2 foot wide sheets. That would be a good prototype.

So how do we go about building an extruder? Main issue is controls and feedback?

- Controls for a simple one die one screw extruder do not have to be complicated I've been inside the boxes for these things (no real changes since the 70's) (just off the top of my head) 1. DC drive with Big Expensive DC motor 2. Gear Box < -- Pick Your Mechanical Advantage 3. Tachometer for DC drive and operator feedback 4. Manual adjustment of RPM's 5. A Couple of pressure transducers with possibly safety contact for MCR to prevent overpressure 6. Heater bands/Cartridge Heaters off the shelf heat controllers / thermocouples 5. Small PLC logic controller 10 or so discreet outputs and inputs.

How do we get a design of an extruder screw? Or do we just buy them?

- The screw is determined by much by the material being used and obviously the amount of material and back pressure and sheer you need for the end application. Some guidelines available. - I'm not entirely how you can go about this from scratch. Companies like Xaloy.com sell these parts perhaps we could get them to do some leg work/pick their brain with a quote request.

Is it 5 axis CNC milling that fabricates these screws? Are these heat-treated and ground at the end?

- Heat treated, alloys, ground, plated, coated, "very pretty" - The 5 axis CNC may not be good for screws but it may be used for the later addition of a "melt pump" to the extruder if further refinement of the process is required - The die may be in the realm of the CNC machine as well (creation of custom dies for local jobs)

I assume that a heart of an extruder is the screw, the chamber for the screw, and die for the exit. I assume that Prototype I would be getting these off-shelf, and filling in all feedback/heating details ourselves.

- Yes. I agree this is where all the refinement has been done already. Reinventing the wheel would waste a lot of time likely result in failure (IMO). There also safety concerns of high pressure in barrel. Off the shelf barrels have had safety factor work done. - The tolerance between barrel and screw is important.

Can you help first by writing up a systems engineering breakdown diagram for an extruder, including all desired heaters, controllers, details?

-I'll try ... point me toward what you think is a good example of what you want on another project, if u don't mind, and I'll try to get started. -I can leave the barrel and die alone and start thinking about the other stuff

-desired thickness spec ?

Now, do you also have experience with induction heating?

-Nope, but did some research looks like it helps variation quite a bit, along with cost savings, interesting to me. I can tinker on such stuff in my apartment. Don't think it's being used in the field a lot. Heater bands are primitive and are notorious for hot spots and air gaps.

Marcin

-ps The extruder is only about 2/3rds of what you need to make sheets. A sheet machine with process temp nip rollers with cooler / off load table will be needed. Slitting of the rough edges and handling off cut is actually a pain in the butt.

http://www.welex.com/products.html#sheetlines

-sorry try to be short so much info to give