2.0 KiB
Remarks on the network
Plasticbay - Scotland (yeah)
Well I have mentioned a few times that there was a problem with the strategy of overshooting melting temperature by 50 or 60 deg C. It generates fumes and degrades the plastics seriously. I am very concerned by this advice and I am basically told to just get on with it. Here a little explanation of what is going on: You may know that plastic is a good thermal insulant, meaning its thermal conductivity is low. That means that if you heat up a mass from the outside, it will take a long time to be at the same temperature in the inside. The gradient between the core and the outside of what you want to melt is depending of the thermal conductivity. For the sake of simplicity, lets say the "instantaneous" thermal gradient needed to melt your example is 60 deg C. So to get the inside to melt, either (1) you heat up to the melting temperature or just above and wait that the heat transfers inside let say it takes 12h or (2) you rise the outside temperature 60 degrees above the melting temperature so "relatively" quickly the inside reaches the melting temperature.
(2) is what the Team is advising and I am firmly against it because while you do that, the outside of the mass (here sheet) is at 220-240 degs, the mass that is overheated generates a lot of fumes and looses its chemical properties and basically its capacity to bond. That's why many complain that the sheets have a random output. All the charts should be changed with a proper time-to-temperature-to-mass output. I find the current advice dangerous.
RENN
Hi there,
I am starting my sheetpress workplace and I just run our machine yesterday and the result was bad :( It didn't melt properly, some parts didnt melted at all. (It didnt burn) I want to know why it failed.
I followed the guide from preciousplastic official site. (see the pic) I melted HDPE in 220 degree for 1 hour (for 22MM thickness) I know the melting point of HDPE is 120 degree but I just followed the guide.
Do you guys think the temperature was wrong?