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"zero waste" key tag & buckle! Insert mould.


  • This topic has 27 replies, 10 voices, and was last updated 2 years ago by Stan.
riceandcarry riceandcarry

"zero waste" key tag & buckle! Insert mould.

20/05/2017 at 09:30

Hi all,
Here is our latest product made with the injection mold and the off cuts from our bag production here in Sri Lanka. Key tags made from Polypropylene. Mold by @leebaz.
We can only recommend the injection mold if you have access to somebody passionate with a cnc machine. It’s the best way to make nice looking products and if you feed the off cuts or you just cut PP sacks, you won’t even need a shredder.
Cheers from Sri Lanka,
Rice & Carry

Just added pics of the new buckle mould that came in. Finally buckles not from virgin plastic! Same as the key tag it’s an insert mould. It could make two buckles at atime but we did not file a channel to the second chamber yet. Few more pics are instagram @riceandcarry

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21/05/2017 at 16:20


16/06/2017 at 20:10

Great idea. I love the impression – very clear and legible. I wish mine came out so well…

20/06/2017 at 13:07

Thank @becka, did you post your attempt somewhere?

02/07/2017 at 10:11

Hi all, we’ve learned quite a bit through making the moulds for @riceandcarry – happy to help out with any questions you might have if you’re finding it frustrating. Happy to design and make moulds for you too of course 🙂

03/07/2017 at 17:42

hi @leebaz,

Am I right to assume that the rectangular part of the mould (with rounded corners) is an insert you can replace with some other insert for a different product?

04/07/2017 at 04:31

Hi @jegor-m

yeah, exactly. I wrote a little blog about it here: http://colombodesignstudio.com/insert-mould-zero-waste-recycling/
The limitation then becomes the size of the insert, obviously.

In this case we based it on a few factors, such as the size of a key ring and also a fin key I’ve got in mind, but also the size that my cnc can handle.


04/07/2017 at 12:56


This is a great design, mate. Do you preheat the mould before plastic injection?

04/07/2017 at 13:02

@jegor-m there doesn’t seem to be the need, but @riceandcarry are really the moulding experts! The mould does get pretty warm though.

By splitting the mould across the pipe thread it means you can easily clean out the material at the mould entrance. We call those the ‘spinning tops’

04/07/2017 at 13:16


It is just from my injection moulding experience, if the mould is too ‘cold’ for the hot plastic, there is a layer of plastic, that solidifies very fast when it comes in touch with a relatively cold mold and some surface features (like letters if they are smaller) can be left unfilled.
The way around it is to pre-heat the mould, so that it gives good parts straight away.

04/07/2017 at 13:18

@jegor-m yeah – I thought we would need to too… but it doesn’t seem to be the case. However, there was an early blockage coming out of the injection pipe, but now we use a plumbing tap to seal it while the mould is emptied… seems to work pretty well.

One of the early lessons was getting enough venting! That seemed to make a big difference. We send @riceandcarry the mould prepped for venting, but they add it with a file until it’s enough… a bit of trial and error.

04/07/2017 at 13:22

@jegor-m no need to preheat. What is crucial is good size vents and a big enough entrance. You don’t push plastic down into the mould, it’s more like you are pushing plastic through hardening plastic (if that makes any sense). So for example you have red plastic furthest down in the pipe and white flakes on top, your product will get red near the entrance to the mould and not at the bottom. So when the entrance to the mould is to small it blocks too easy. Luckily they are aluminium so pretty easy to modify. We use PP which seems to be easy to inject. I tried HDPE one time and that was more difficult in terms of fluidity.
Good luck.

04/07/2017 at 13:35

@jegor-m as @leebaz mentioned it makes a big difference to use a plumbing tap to close of the pipe while you empty the mould. We tried to attach the last heating clamp as low as we could but the last bit of polymer that is exposed to air will never be ideal to inject. The plumbing tap will have a bit of hardened plastic attached to it that sort of fills the first bit of the pipe. So when you take of the tap you will have straight away ‘ideally’ heated polymer from 2cms up the pipe. Can make a big difference.

11/07/2017 at 12:03

@riceandcarry – do you have pictures of that process/plumbing tap?

14/07/2017 at 22:01

Hello! No, I have not posted my attempt. I re-melted it, actually 🙂 I’m still working with compression and striving for bubble free blanks. Once I get that worked out, I’ll go back to dealing with how to get my impression in the piece.

30/07/2017 at 05:15

Hi @soeren,
Here the pic of the plumbing tap. That bit of plastic pushes into the heating pipe so when you start working you don’t have the solidified bit of polymer at the end because it’s exposed to air or a not heated mould.
It just ended up coming off like this so if you get a tap like this no need to do anything really, just wait until it fills up like this and when you finished heating and you take it of it looks like this. We reattach it after every injection.
Good luck.

07/08/2017 at 12:43

this is awesome! looks super clean, great detail on the debossing.

did you do any volumetric analysis of the object to figure out how much plastic to inject? or are you playing it by ear for now?

any issues with draft angles etc. to be able to remove the piece from the mould?

it’d be great to see photos of the piece out of the mould, before and after trimming!

keep up the great work.

30/08/2017 at 12:26

@anujkd Thanks.
No volumetric analysis necessary as long as the items are this small. How much to inject will be memorized by your arm real quick. We also put some lines on the plunger which helps to press long enough.

14/02/2018 at 12:41

@riceandcarry I just drew up a mold based on your mold design that I am planning to try out with our injector. Does this design look like it would work to you? We were thinking of trying epoxy for the mold insert.

16/02/2018 at 12:56

Hi @marcusinnovate, it looks pretty good to me. Just make sure the completed mould is thick enough so you can get proper thread made into it.

is the one who designs and makes our moulds. @leebaz what do you think? Guidance pins?

19/02/2018 at 12:22

@marcusinnovate looks good. Dont forget you need venting to let the air out of the mould cavities and make way for the plastic.

01/02/2020 at 14:28

Hi @riceandcarry,

sorry to wake this up after so long, but it is the only place I find info on this hack, to use the plumbing tap with lever..
may I ask why not use just a simple male blind end cap and a female-female 1 1/4″ adapter, if I understand that you remove/replace the tap each time you inject? Cut down each to maybe a couple of mm of thread, the blind end cap should occupy even less space internally than the tap..? It does not have to resist pressure, just avoid molten drip, no?

Even better, if using a female end cap straight off directly on the pipe, would totally block off right at the end of the pipe: if then using a 1 1/4″ tapped thread in the mould one would get the maximum available plastic input with no bottleneck from anything in between that would otherwise add more pressure to be required?
Or, why not use the tap as a tap? This would avoid needing to remove anything each time one adds/removes a mould.. Is it because there is teflon inside the tap and this may decompose (depending on type of teflon) above 200+˚C?

Andy (built one injector, now building another and have mods in mind!!)

02/02/2020 at 06:37

Hi @andymid,
By now we have move away from the tap, except with the mold the have a thread.
We now use a piece of threaded pip at the end of the machine that ends in a small hole. Conical shaped. The we press the newer mold we have without a thread onto that and inject. It is much quicker to inject like that as no threading is needed. We also use a clamp for the mold now instead of nuts and bolts to keep the mold closed. That is also much quicker to release the product. Maybe you can send a pic of your hack? I am not sure I can follow your description as I am not familiar with some englisch terms.
The tap never worked as a tap, would have been my dream scenario also :). It does not get hot enough and the plastic blocks the mechanism straight away.
Cheers from Sri Lanka,

02/02/2020 at 11:39

Hi Henry,

So I haven’t yet made the new injector with what I mention above, but here are a couple of images from google to get the idea: female-female adapter gets cut short to maybe 1 – 1 1/2cm long (thick red line), is screwed on to tube until thin dotted line, then the male end cap, also cut shorter (to reduce dead space at end) is screwed in to stop molten drip…
However, the second image is just a female end cap, which would do exactly the same, with no cutting and also even less dead space…

This is all with the idea that having as large as possible hole for plastic to enter the mould is advantageous, based on my experience with a first injector that we soldered a F-F reducing adapter 1 1/4″ – 1/2″ (a few cms of dead space) and also have perforated male end cap screwed in there (hole is about 8-10mm) – this small hole (compared with having a huge 26mm hole), I think causes back pressure not related to the mould but to the passing of the molten plastic thru the small hole, so is what  am thinking of getting rid of – moulds would have to have a threaded 34mm hole instead of a soldered 17mm perforated end cap, and would require a way of restraining the insertion of the pipe into said 34mm hole so that do not enter so much into the mould that impides plastic entry, but was thinking of just soldering a blob of solder onto the pipe at the correct height (also the reason for using cut down adapter/end cap)…

02/02/2020 at 12:03

about the newer way:
Cool! I have seen mention of the quick coupling via pressure/jack/clamping, and am also investigating this, but hadn’t yet seen how to close that conical hole to stop molten drip… although I’m ruminating something that may or may not work, but not sure of the hole sizes yet…: if we make a screw thread on both the inside and outside of the pipe – a male end cap (cut down as short as possible to reduce dead space inside) with the conical hole, on the inside of the pipe,… there are 2 types, one with hex head, the other with reduced square head (see photo) – the idea is that the spanner head part is smaller than the outside diameter of the pipe – then you can also screw on the outside of the pipe a female end cap, that would cover the interior end cap when needed and stop drip… 😉

What size conical hole is being used? What size is the interior hole where the plastic passes? Is it considered that a small hole can cause back-pressure from the plastic before even entering the mould (as I am thinking)? If so, then always a bigger hole would be better, if not then what is the min hole size before this does occur?
These questions I do not yet have the answers, so maybe I am a bit wrong thinking there is back pressure caused by hole size (I also just remembered that any reduction in the passing of a fluid causes an increase in its speed, which at the same time causes a reduction in its temperature… if I remember my physics classes correctly!! (Although might be thinking more of how air speeds up going thru a gap, causing lower air pressure and apparent temp🤔) Another reason to have as big a hole as possible)

PD maybe this should be in a new thread…? Sorry, this is my first time posting here!



02/02/2020 at 17:42

I just press a block of wood against the nozzle during heating and compaction to contain the plastic. Works well.

03/02/2020 at 12:26

🤦‍♂️ of course! If one is using a clamp system, just clamp the wood! even faster!!
Thanks, that’s a worthy hack!! 👏👏👏

03/02/2020 at 19:13

Actually, on my desktop unit, I just use a pair of shallow wedges to press either the molds or the block of wood against the nozzle, no clamp.
http://onearmy.world/community/forums/topic/portable-desktop-injection-machine/ (see Jan 31 post).

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