Monday, March 17, 2008


A high temperature extruder?

I made a quick lash up which shows that it is feasible to replace the PTFE heat barrier with a short stainless steel pipe and a heat sink. That will allow the extruder to operate easily over the full temperature range for thermoplastics and make it far more mechanically stable.

More details here:


That's pretty cool. (Sorry...)

How about shifting the heat sink to a bit lower down to give yourself a cold run of about 20 mm at the top?

S/S is a bugger to machine, from memory. How is it for cutting threads?

All this is doubly interesting because, as you may remember, I have suspended my granule extruder experiments cos I couldn't get the hopper end cool enough.
Yes this was just a test, I will extend the cold end to meet the pump when I have selected the final heatsink and its mounting arrangment.

It was tough cutting the threads, the main problem being how to hold the workpiece and stop it turning. I have ordered some finer taps and dies so that should make it easier. I could also make it over long, cut a slot in the end to stop it spinning and then cut that bit off.
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Would it be easier to make the entire heater barrel out of stainless steel instead of connecting the stainless steel to brass?

Also, you mentioned in an earlier post that Cerastil works great and is probably a bit cheaper than J-B Weld per gram, but the smallest quantity is 1Kg, which cost over £100. Would furnace cement work also? It costs 5$ / pint and is supposed to stand 1650 C, according to the description at:
Hi Enrique,
The brass part is left over from my previous experiments. In the final form I plan to use an aluminiuim nozzle on the end of the steel tube, with the heater wound around the nozzle.

Furnace cement may work, although if it did one would wonder why Cerastil exists and is able to be sold at a higher price. As well as handling high temperatures it claims to be a strong adhesive and good thermal conductor / electrical insulator.

The only way to be sure would be to try some furnace cement for a period of time. As I have 1Kg of Cerastil to get through there is not a lot of incentive for me to do that at the moment!

I found somewhere in the UK that sells it but it is out of stock at the moment. I will try again later as it is an order of magnitude cheaper, so should not be overlooked.
Keep it up, this is great to hear work in this area.

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