Tuesday, March 21, 2006
Quenching baths for CAPA
It appears that the bath temperature where CAPA remains pliable yet has enough tensile strength to hold together is somewhere in the range of 58-60 degrees Celsius. Get any higher than that and the filament comes apart. Get any lower and it is unworkable.
It would appear that a thermostat/heater system with a pretty narrow deadband is going to be required for the quenching bath. :-(
Comments:
<< Home
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.
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.
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)
His writeup is here. (Last post truncated the url)
****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. :-(
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. :-(
****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.
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.
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.
Post a Comment
<< Home
