Comments on RepRap: Blog: Quenching baths for CAPA

The alternative, of course, is to draw the tempere...

2006-03-21T03:13:49.740Z

The alternative, of course, is to draw the tempered fillament down through a tapered die, like drawing wire. If that die is kept cold, it will skin the fillament over, and then you just have to take care not to draw it so fast that you overrun the extruder.

****You extrude the profile at a fixed volumetric ...

2006-03-21T02:53:47.273Z

****You extrude the profile at a fixed volumetric rate, and draw it out of the bath at a fixed linear rate, and the extrusion inevitably ends up with a steady cross section.****

Probably I ought to see if I can extrude at something considerably less than 120 Celsius. I don't have much in the way of speed control with the electric drill, however.

When I get that car window motor and a reasonable control board I should be able to get a lot closer to a controlled situation like you describe.

***His writeup is here. (Last post truncated the u...

2006-03-21T02:50:39.340Z

***His writeup is here. (Last post truncated the url)***

Cool! Thanks!

****You extrude the profile at a fixed volumetric ...

2006-03-21T02:49:55.413Z

****You extrude the profile at a fixed volumetric rate, and draw it out of the bath at a fixed linear rate, and the extrusion inevitably ends up with a steady cross section.****

I agree totally. You're absolutely right. While the commercial approach is quite reasonable, the filament that I am extruding, however, as a result of the thermal as opposed to mechanical approach to polymer heating is considerably hotter than what a commercial extruder puts out. It has no tensile strength to speak of. :-(

I don't have the degree of control over the extrusion rate to do that so I wind up with a bunch of extremely crooked squiggles in the quenching bath. If I try to tug on them to straighten out the extrusion it breaks at the extrusion tip just above where the quenching bath is.

While the commercial approach is quite reasonable, the filament that I am extruding, however, as a result of the thermal as opposed to mechanical approach to polymer heating is considerably hotter than what a commercial extruder puts out. It has no tensile strength to speak of so I have to explore different handling methods. :-(

If you really need exact temperature, Manfred made...

2006-03-21T02:24:02.393Z

If you really need exact temperature, Manfred made a photographic processor for processes requiring a quarter of a degree accuracy using very cheap parts (a heater, a temperature sensor, a microprocessor to connect the two and an aquarium pump to even everything out).

His writeup is here. (Last post truncated the url)

I think you're going down the wrong road, if you'r...

2006-03-21T01:39:29.930Z

I think you're going down the wrong road, if you're trying to achieve a bath temperature that the fillament can achieve thermal equilibrium with, and still be workable.

In commercial extrusion work, the bath is always maintained substantially below the working temperature of the extruded material. You extrude the profile at a fixed volumetric rate, and draw it out of the bath at a fixed linear rate, and the extrusion inevitably ends up with a steady cross section.

Minor temperature variations may alter the exact point in the tank where the fillament achieves it's final diameter, (Which occurs, of course, at the moment it becomes *too cold* to be worked any further.) but so long as the process parameters are anywhere near right, you'll get your product.