After my last post detailing the magnetic pickup tool I made, I thought it may be useful to detail how I recycled some plastic to use in my workshop. But why go to the effort of recycling plastic? Well, I wanted to have some plastic pieces among my steel stock in case I needed something quick and easy to use on the lathe - for small wheels, spacers, bushes, fasteners etc. Apart from making actual items using the plastic, the plastic is far quicker to turn down on the lathe than steel (up to a factor of 10 for rough cuts) so I can quickly prototype something which I may later make from steel.
After some obligatory reading online & watching YouTube videos for ideas, I collected a few dozen empty white plastic milk bottles and lids (with the number 2 in the recycling symbol, indicating HDPE High Density Polyethylene), removed the labels and washed them to remove any milk residue. They were cut into small pieces (~1cm square) by hand / scissors... this took at least an hour ... and at that point I wasn't sure how many bottles or caps it would take get a reasonable sized solid block of HDPE. For a black color, I used one old 4L engine oil bottle (degreased and cleaned).
For a first test, I used a couple of empty food cans (pictured above) as well as some exhaust pipe tacked to a steel plate (to get a longer block of plastic) and with the oven set to 200degC I started putting a small amount of plastic at a time in the cans to see how well the HDPE plastic melted. The pieces of the milk & oil bottles melted extremely slowly and after a few hours, a couple of dozen milk bottles filled most of one food can and exhaust pipe piece. The pieces of one engine oil bottle filled up an entire deodorant can.
The bottle caps/lids melted much quicker than the bottle pieces, and air bubbles slowly made their way up and out the plastic without any poking or manipulation of the mixture. Once melted, the plastic has a consistency thicker than toffee rather than a flowing liquid. The caps seem to be the way to go for a consistent solid block of plastic... but it took 35 bottle caps to 3/4 fill a really small 125g food can so I'd have to be collecting bottle caps for months to get a decently big piece of stock without cavities from the bubbles.
One thing to note is that you don't really smell anything when the plastic is melting, and it does not burn (at 200degC). Also, it does shrink a bit once it cools.
To clean up the solid castings, I turned them down slightly on the lathe and found it's really quite nice to work with, providing quite a smooth surface and you can take heavy and fast cuts in the material. I ended with quite a lot of air bubbles in the white plastic from the milk bottles, even after repeated compressing of the mixture during the melting process. This is still useful stock even with the random cavities I found. Here you can see two cavities next to the centre hole in one of the pieces :
Once the pieces are melted into a solid block, it is surprisingly strong and rigid too. Rods of various sizes of HDPE/Acetal/Delrin are commercially available to buy if I wanted to make a good quality item, but using the recycled HDPE is a perfect no-cost alternative for random items around the workshop and prototyping. No-cost, except for the small amount of electricity used for the oven that is.
After some obligatory reading online & watching YouTube videos for ideas, I collected a few dozen empty white plastic milk bottles and lids (with the number 2 in the recycling symbol, indicating HDPE High Density Polyethylene), removed the labels and washed them to remove any milk residue. They were cut into small pieces (~1cm square) by hand / scissors... this took at least an hour ... and at that point I wasn't sure how many bottles or caps it would take get a reasonable sized solid block of HDPE. For a black color, I used one old 4L engine oil bottle (degreased and cleaned).
For a first test, I used a couple of empty food cans (pictured above) as well as some exhaust pipe tacked to a steel plate (to get a longer block of plastic) and with the oven set to 200degC I started putting a small amount of plastic at a time in the cans to see how well the HDPE plastic melted. The pieces of the milk & oil bottles melted extremely slowly and after a few hours, a couple of dozen milk bottles filled most of one food can and exhaust pipe piece. The pieces of one engine oil bottle filled up an entire deodorant can.
The bottle caps/lids melted much quicker than the bottle pieces, and air bubbles slowly made their way up and out the plastic without any poking or manipulation of the mixture. Once melted, the plastic has a consistency thicker than toffee rather than a flowing liquid. The caps seem to be the way to go for a consistent solid block of plastic... but it took 35 bottle caps to 3/4 fill a really small 125g food can so I'd have to be collecting bottle caps for months to get a decently big piece of stock without cavities from the bubbles.
One thing to note is that you don't really smell anything when the plastic is melting, and it does not burn (at 200degC). Also, it does shrink a bit once it cools.
To clean up the solid castings, I turned them down slightly on the lathe and found it's really quite nice to work with, providing quite a smooth surface and you can take heavy and fast cuts in the material. I ended with quite a lot of air bubbles in the white plastic from the milk bottles, even after repeated compressing of the mixture during the melting process. This is still useful stock even with the random cavities I found. Here you can see two cavities next to the centre hole in one of the pieces :
Once the pieces are melted into a solid block, it is surprisingly strong and rigid too. Rods of various sizes of HDPE/Acetal/Delrin are commercially available to buy if I wanted to make a good quality item, but using the recycled HDPE is a perfect no-cost alternative for random items around the workshop and prototyping. No-cost, except for the small amount of electricity used for the oven that is.
Comments
Post a Comment