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mold active cooling

This topic contains 3 replies, has 2 voices, and was last updated by  Stan 3 weeks ago.

Butte Metz btmetz

mold active cooling

02/05/2020 at 02:00

I posted in the discord, but will repost observations here.


I am making grain elevator buckets from recycled HDPE.


I shred the plastic and extrude in a v2 extrusion machine with the compression screw upgrade.


Melted plastic at 205c exits the machine and into a air turbo cooker where it is kept hot until enough plastic is there to make one item.


That piece of plastic int he trade is called a “slug”  If a piece of plastic is going into a injection mold, that is called a “shot”


Plastic is removed from the heated pot with 2 silicone spatulas and transferred to the compression molder.


The compression mold is hollow and has water pumped thru it via a aquarium pump.


Excess heat is transferred to a blue Plastic HDPE barrel full of water.  That water is not actively cooled, rather it uses thermal mass and convection to release the excess heat which seems to work well.


Initially we had a lot of problems, with bubbles and shrinkage.


I had assumed that the plastic viscosity was too low.  But then Peter, our guest engineer from the Netherlands suggested that we lower the plastic temp, and found the sweet spot between 200-205c


Previously the plastic was looking similar to the texture on the Precious Plastic building blocks, wrinkled.


Now the texture is super smooth.


second video turn down the volume.


I apologize for the build quality.  It was hacked together last year from scrap bits and I had not yet bought a good MIG welder to handle the thin tube.


The molder is made from a used 6 ton hydraulic log ssplitter.


However problems arose as the log splitter is unable to easily hold the pressed plastic under pressure.  There is no check valve and the cylinder moves backward.  Also the cylinder is offset from the mold and it has damaged the alignment pins.


Next version will be back to the pneumatic bag jack, and using a oiless air compressor (sound issue)

Also I will be disassembling this extrusion machine and reassembling into a more proper design with a better method of holding the molten slug of plastic.  Likely similar to a pizza oven


We have however been on virus extreme lockdown since March 15 and unable to do anything as we are banned from leaving the house.




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In reply to: mold active cooling

02/05/2020 at 21:19

Those look really great. I really like your “engineered with what’s cost effective locally” approach to building your machines.
Would a motor (drill?) driven scissor jack work as a replacement for the log splitter?

Thanks for the update.

In reply to: mold active cooling

03/05/2020 at 02:07

the scissor jacks, I just do not see them as useful.


Have built several machines for compression molding and broke 3 brand new jacks already.


As power for a injection molder yes, fine, but for the compression mold, not even close.

In reply to: mold active cooling

03/05/2020 at 03:57

I believe you. For general purpose, large area compression you need lots of force. The thought was for the relatively small, pyramid shaped mold that a 2 ton jack  might work. 3 broken jacks say otherwise.

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