Air bubbles in plastic tiles

HI Forum,
We have a small manufacturing company here in Sri Lanka and we trun old rice sacks into new bags. We have loads of off cuts se we are looking into how to melt and reuse this material to produce with as little waste as possible.
We can make OK tiles with our compression machine and a friend with a cnc to turn the tiles intonew products but we keep getting air bubbles inside the plastic tiles.
Does anyone have experienced this? I tried diffrent temperatues, time in the oven up to 2 hours but the bubbles never disappear completely.
Maybe someone has an idea.
Cheers

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What type of plastic is it? Anyway a few suggestions on the top of my head; Apply more pressure, let it cool down under pressure or heat is shorter but hotter.

 

Hi @davidpaag, I haven’t tried lately as we got our injetcion machine to work but I guess your are right as the mould i used for the oven was super accurate but had no vents. When I move the “lid” up and down it creates sucktion even, so it must be hard for gases to get out.
We’ll get back to the compression soon and post here how it goes.
Thanks a lot for the input to all @davehakkens, @mattia-io, @xxxolivierxxx

Is there any way for the bubbles to escape?
It could be gasses from chemicals, or water, in which case it needs to get out somehow.

Another idea would be to apply vibration during the melting phase, many resin and plaster moulders use big vibrators to make the molten plastic sink to the bottom of the mould and push the air to the top

My suggestion would be to apply pressure slowly, a lot but slow. If you press fast plastic might overflow before it actually fills all the bubbles…

I had major problems with bubbles too 😡