Extrusion screw types

Hi,
we have many requests to make the screw, from PP and our local network. After mastering the more basic types, I wondering what all the other types are. Please check here for some samples.

Can someone explain this in short to us ?
I understood some types are suited for mixing different plastics/colors, and others are for specific plastic types.

Would be nice to have a short explanation from the more experienced guys here !

thanks a lot,
guenter

Hi, I’ve been injection molding plastic since pretty much birth, and from all the machines I have used and still am, not ever the screw morphology was a problem.
I have processed almost all materials, from the basic PP, PE, PVC, ABS, Nylon, to more complex ones like TPU, PC, POM, etc… I you get to read different materials spec sheets, you’ll come across different types of screws, and maybe for a very specific high volume long term production they make a difference but for a day to day workshop, you just get the screw that comes with the machine, and that’s it, for life…
An screw is composed of 3 stages, loading the material, melting the material, and compressing the material, the ratios of each vary according to the material and the usage, but as I told you, it’s very rare. In fact, at least here in Argentina, if a screw breaks, you can repair it, or go to a supplier and say “I need a 35mm diameter screw, 125mm long” and that’s it, no one will ask you the intended use, the ratio of compression, etc.
A few years ago when a friend told me ppl where building extruders from auger bits, I tought “this people trying to do things beyond their comprehension” but they work, and they work surprinsingly well, so…
Further more, extrusion now a days is done with dual screw machines, and that’s a totally different bag of cats.
I think with this kind of machine, going from an auger bit, to a custom sized screw, is as far as good you can go…
If someone ever tries to make a dual screw extruder in a DIY fashion, I’ll be all over it.
I’m rumbling now, I’ll just stop here…

i finally found a good overview here.

hey @fmcatalan 

Do you think this type of screw would also work? It looks a little like the custom bit dave got made on ali baba for making beams.  I thought it might be a good compromise between auger and custom thread.

anyway see what you think,

https://www.amazon.co.uk/Irwin-10502061-600mm-Speed-Hammer/dp/B005KH7DPI

Will  🙂

That’s pretty motivating, so in short better quality with a dual extrusion. I buy that 🙂

Thanks a million ! If we ever got one dual screw done I will post it here of course 🙂
g

Dual screws use less heat an thus obtaining plastic with much less degradation…
When you process plastic with heat (injection, blowing, extrusion, etc) a part is lost, I will not get into polymer physics but you get the idea. Some materials lose more (PVC, ABS) some very little (PP, PE) but how does the petrochemical get to us those pellets for use if some is lost? Minimizing heat during process, ergo, dual screw extruders. Imagine that you are recycling plastic that has already been processed at least twice and they work just fine… So how important it really is? I guess not much, it’s just a matter of doing it because we can and it’s fun XD

@fmcatalan : thanks so much ! that cleared the sky. nonetheless I will do one or two screws with some extra cuts, in hope they archive better mixing of different plastic colors 🙂 Just to see the difference.

about the dual extrusion screw, I am actually also tempted to build one, no idea what really the benefit is but i guess it’s about mixing different colors ando/or materials and approaching slightly better outcome (no idea, really). it doesn’t look too hard to make it 😉 (actually it’s pretty difficult)

so, thanks again! greats from Moia-Catalonia 😉
g