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Injection Moulder- Help Needed for Mould Capacity!

  • This topic has 13 replies, 5 voices, and was last updated 2 years ago by Anonymous.
Replastic replasticuk

Injection Moulder- Help Needed for Mould Capacity!

01/04/2019 at 20:42

Hi All,


We are looking for some help in understanding whether we can create a medium sized planter from a mould using the injection moulder.

The idea:

We are wanting to do workshops with schools, where students will be able to make planters from littered plastics, which they can then attach to walls around their schools to improve air quality and biodiversity.

Why the injection moulder?

Although we could create a similar planter with the compressor, we would like to try and explore the possibilities of using either the precious plastics injection moulder, or an adapted version of it. The main reason for this is because we need a process that will deliver our planters quicker than when using the compressor, which will allow the public to be taking a more active role in producing the planters.

Size & Dimensions:
I’ve attached a PDF documents of the basic mould design – this is just a basic drawing to give an idea, not the final design for the mould.

The thickness of the planter is 1cm, the top is 15cm x 15cm, the bottom is 10cm x 10cm, and the height is 10cm.

This creates a volume of 572cm3 that will be needed to be filled with plastic (Ideally HDPE)

Would this be achievable with the current Precious Plastic Injection Moulder?
If not then…

1) What is a volume of similar planter mould that would be achievable with the injection moulder?


2) What modifications to the current machine design would be required to achieve making a planter like this.

Has anyone tried using the extruder to create products of similar size?

– Katie

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02/04/2019 at 11:01

hey Katie,
I’ve done some number crunching. It’s quite some volume and I don’t see other than abusing an 20T press (couple of hundred euros) but with hydraulics (manual=slow or pump=fast). The hardware itself is around 1000 Euro, labor another 1000; ballpark figure, +/- 700

Here’s the closest I’ve got : https://www.youtube.com/watch?v=E1dTwm8Lmpc&ab_channel=colinfurze

This would enable to detach the force module from the injection and so you can simple plug it to the next whilst it’s cooling down.

I hope I am wrong but to me it’s time anyways to get out of that lever based stuff and get a little more volume out of PP.

maybe @andyn still has some other ideas …


03/04/2019 at 00:25

@replasticuk , That is a large plastic volume. Since they are going on a wall, maybe change the design to a sconce planter for less volume?

I think the precious plastic injector does not scale up easily. If you are willing to experiment, the rack and gear (arbor press) actuated machine may scale up to the size you need. There is an example in the bazar https://bazar.preciousplastic.com/en/listings/727598-arbor-injection-press-catalonia . The nice thing about this approach is the stroke length can be long without impacting the force it takes to actuate. It also has higher leverage so you can go with a larger diameter. Those two size increases may get you to what you need for your design. I would size for at least 50% margin, maybe 5 cm diameter and 45 cm stroke as an example. I think one advantage of your design is that you don’t have any narrow passages so the injection pressure required may not be that high and you can use a larger diameter piston. If the machine ends up being too tall, that design can work in a horizontal configuration. It may be worth contacting the seller (not me) and ask about possible scaling.
I think even with the injection machine, the cycle time will not be super fast. The plastic still needs to be loaded, heated, compacted before it is ready. The mold will take some time to cool as well.

The other option is a version of the press machine that uses heated molds instead of an oven. @andyn showed a wonderful example in the video in this thread http://onearmy.world/community/forums/topic/v4-beyondplastic-process-heatable-mould/ . You could possibly have several molds being heated and then pressed in sequence.

You are pushing the injection limits here, please post what you end up selecting as the approach.

03/04/2019 at 22:16

Hey Katie,
looking at prices, limitations, problems etc (thanks Stan)… The best I can offer is to wait for finalized experiments with a modded standard 20T hydraulic press. According to my calculations, it should be possible to get that volume (you need 20% more than needed due to shrinkage) in a 7-9 cm barrel. It can be done with a manual 50 cm hydraulic center, it just needs time to fiddle this out. The price will be around 1000 Euro for such thing. What worries me more is to keep the mold heated enough. Injecting that way will last quit long (the handle on the hydraulic needs dozens of strokes…). Anyway, regardless this can be done for your case, I wanted to do such machine since quite a while, you just gave me the last push 🙂 I will ping you via email in 2 weeks.

03/04/2019 at 23:10

I think heating the molds with a cartridge heater and the standard PID controller should be a low cost solution. The heaters and the thermocouples are very cheap so you could dedicate them to each mold.

03/04/2019 at 23:37

yeah, what about this here or this ? I’d love to know this stuff is kinda flexible in a way you could wrap any mold with a heating wire. in some cases it would be already cool to make a small oven with this, near the size of the molds one is using. I saw folks doing furnaces with this but no idea what to look for on ebay, … prices vary from low to insane.

04/04/2019 at 02:47

Those oven heating elements are big and high power for just a mold, though you could sit the mold on a hot plate I guess.

If you search cartridge heater or cartridge mold heater on ebay, there are many to choose from. I used the 9.5mm x 80mm 300w version. Either drill a hole or cut an external groove to clamp them on. They should very easily heat an aluminum mold. Ebay prices are between 2 and 5 USD depending on where and how many. If you buy them from engineering supply they will be quite a bit more.

04/04/2019 at 10:06

perfect, so those could be plugged into the mold plates, funtastic, thanks so much Stan,

04/04/2019 at 16:12

@pporg and @s2019

I’ve changed the wall thickness to 8mm and the bottom to 8cmx8cm, that has managed to get it down to 378.119mm3

04/04/2019 at 17:47

or to increase the size of the planter, just reduce the overall thickness of the product; shouldn’t that work easily?
edit : woops just read last post this thread after posting 😮

04/04/2019 at 18:08

@replasticuk, that won’t change much, any chance to get a 3d file ? (send it to my email), I am lazy and quite busy but i accept the challenge 🙂

07/04/2019 at 14:35

Sent to you yesterday 🙂

If anyone else wants it please just ask!!

16/04/2019 at 04:47

At the risk of sounding very naive..can you add an injection site on the other side and inject the mold sideways?

16/04/2019 at 19:50

@replastikuk, I ‘ve done some number crunching and simulation; I think i will pass on this one. The efforts needed to build a machines don’t really outweighs the benefits in short-term for us.  I think it’s possible to hire someone near you who can this done with some pro equipment; I know for sure he’s gonna busy for 2-4 days …

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