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Problems with extrusion of PP beams – Help needed

This topic contains 15 replies, has 6 voices, and was last updated by  Brad Sheffield 3 weeks ago.

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JMot jmot

Problems with extrusion of PP beams – Help needed

16/10/2019 at 18:43

Hello PP community,

I am trying to extrude plastic beams for construction, in Maputo, Mozambique. Particularly, I am interested in developing a solution for roof structures, as plastic would have certain advantages compared to conventional solutions, e.g. not rotting or getting eaten by insects. I have setup a small workshop with a shredder and an extruder and we have run some tests but are facing some problems.

We are seeking to produce beams like in this video: https://www.youtube.com/watch?v=zNGuuSKE1pY

However, we haven’t been able to produce beams longer than 1,5-2 meters. The machine lacks capacity to fill up the mold before the plastic cools down and solidifies. Sometimes it clogs the mold and we have to make new molds.

Do you have any suggestions to how we can produce 3 meter beams, using our small scale machine? Or would i simply have to buy a machine with larger capacity?

Thank you in advance, Johan

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dedicated
17/10/2019 at 11:49
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Do you use the compression screw (as in the video) or the wood drill?
Which kind of motor do you use (power, rpm) ?

starter
17/10/2019 at 19:04
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You need to heat the beam molds or you will never get there even with a compression screw. That is quite a long length for the pp Extruder. It is possible it will not produce enough pressure to fill that length with such a small Extruder. Best of luck!

starter
23/10/2019 at 21:08
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hello,
it is a 2,2 Kw motor, single phase and around 1400 rpm. we are using a compression screw.

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starter
23/10/2019 at 21:10
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we are trying to produce beams for construction of simple roof structures.

Attachments:
starter
23/10/2019 at 21:13
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but i essentially have to acquire a machine with greater capacity in order to extrude beams at greater length?

thanks for the feedback.

starter
24/10/2019 at 01:14
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WOW Johan!  You are actually doing quite well with the beams you are creating with this machine!  Again if you search the forums for NiTi wire to heat the tube you should be able to produce longer beams.

https://davehakkens.nl/community/forums/topic/new-extruding-beam-technique/

Keep in mind that a larger machine just means a new set of problems and challenges!  More than likely more electrical requirements, more space and more costly failures.
Also grinding the plastic smaller will help the melting.
Your specifications do not necessarily tell the whole story…
“2,2 Kw motor, single phase and around 1400 rpm. we are using a compression screw.”  We also need to know the gear ratio of the gearbox, voltage of the motor, length of the working area of the barrel and screw, diameter of the screw and barrel, what does your connection from the motor to extruder screw look like in pictures, materials used (PP or HDPE or mixture), square size of the beams (25mm x 25mm)?
Are you grinding scrap at the same time as extruding plastic?  Just do one at a time to get maximum power.

I hope this helps and look forward to your response.

starter
24/10/2019 at 16:36
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i’m not aware of all the detailed specs of the motor. i will look into that and send more photos later.

we are not shredding and extruding at the same time.

we have used pp and hdpe – we haven’t tried mixing different plastics yet. we had better results using hdpe. we were able to extrude longer beams using hdpe and pp breaks more easily.

warrior
24/10/2019 at 18:32
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Great work, as a back-up if the long extrusion proves difficult, Maybe try some heat welded lap joints to create a longer beam. I would probably include a bolt just for extra security.

helper
25/10/2019 at 20:17
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Hey @jmot

Fantastic work! Really nice to see the beams used in this application. Can I ask a few questions?

How long have you had these beams in the roof? Any signs of warping from the load/sun heat?

starter
26/10/2019 at 16:39
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thank you for the positive feedback.

regarding the length – we haven’t been able to produce beams longer than two meters, so the prototype showed above is quite small. around 1,5m, i believe. it is a toilet. regardless, the beams are probably not strong enough to cover larger spans by themselves. however, we are trying to solve this by triangulating the structure and join several beams. i will upload images, once we are further in the process.

26/10/2019 at 17:03
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great work, yeah. I would pay quite some attention to the bolts or joinery – how it behaves over time. I can imagine that wind and heat could turn this roof into a deadly flying weapon 🙂

starter
26/10/2019 at 22:13
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If you are using plastics that have been recovered from sitting outside in the environment, then PP degrades very quickly in UV sunlight.  (In as little as 6 days.) That would explain the brittleness of the PP.
https://www.servicethread.com/blog/the-uv-resistance-of-polypropylene-and-polyester-explained

HDPE has much better natural resistance to UV Sunlight.
https://www.globalplasticsheeting.com/hdpe-vs-lldpe-vs-ldpe

starter
27/10/2019 at 09:53
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i don’t think brittleness is the issue – i think it is lack of pressure in the mold and speed/capacity of the machine are the main problems.

regarding safety. we joined the plastic beams with the wall with steel rods cast into the wall with concrete. should be safe.

27/10/2019 at 12:14
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@jmot, yeah, I just wanted to point this out also for other readers. I see very often projects being kinda stuck at the ‘make it work’ stage and so hardly make it to the next level, ‘make it good’ and then ‘make it fast’. Crucial details of successful projects are quite rare. I am happy to hear about the rods now, well done 🙂

starter
28/10/2019 at 05:10
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@jmot So i think your “brittleness” might be better described as the plastic not melting together very well in a cold mold.  (ie cold steel tube)  I would refer to this topic for more information.
https://davehakkens.nl/community/forums/topic/new-extruding-beam-technique/

Screw speed related to the gearbox ration will be important to outputting as much material as fast as possible.  Again that information should be located on the metal data plates affixed to the motor and gearbox.  I would just post a pic of the dataplate for all to see.

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