zshupe
29th October 2015, 09:30 PM
Hey all,
I am training to be a process engineer, and today I was shooting a new tool that uses Toray 1401X PBT. One of our sales guys stops by and freaks out at how fast I was injecting it. He told me, per our customer, that PBT should not be shot faster than 60mm per second (seriously? go sell some parts and stay out of processing :mad:).
Now I haven't been processing for more than a week, but how can you limit the LINEAR VELOCITY instead of the VOLUMETRIC FLOW RATE? Am I right in saying that unless your nozzle tip and barrel area are the same, the linear velocity tells you very little about the effects of shear. A 1" barrel is going to shoot a lot less material than a 10" barrel at the same linear velocity.
Does anybody know of a shear limit on PBT? And wouldn't they give me that figure in mm^3/s (or maybe s^-1)? Tell me if I'm wrong, but since the viscosity is reduced the faster you inject, wouldn't the shear rate be lower at faster speeds as well? When I shoot it slower, it puts the process very high on the Rheology curve. My understanding is you want the process to lie towards the low end (the more linear section) to make a stable process. At the slower speed, my injection time goes from .75 seconds (determined by scientific molding) to almost 2 seconds!
Feel free to lecture me on any of these topics! I got put on the processing fast track when our last engineer quit, so I'm trying to soak up as much as I can!
Thanks,
-Zach
I am training to be a process engineer, and today I was shooting a new tool that uses Toray 1401X PBT. One of our sales guys stops by and freaks out at how fast I was injecting it. He told me, per our customer, that PBT should not be shot faster than 60mm per second (seriously? go sell some parts and stay out of processing :mad:).
Now I haven't been processing for more than a week, but how can you limit the LINEAR VELOCITY instead of the VOLUMETRIC FLOW RATE? Am I right in saying that unless your nozzle tip and barrel area are the same, the linear velocity tells you very little about the effects of shear. A 1" barrel is going to shoot a lot less material than a 10" barrel at the same linear velocity.
Does anybody know of a shear limit on PBT? And wouldn't they give me that figure in mm^3/s (or maybe s^-1)? Tell me if I'm wrong, but since the viscosity is reduced the faster you inject, wouldn't the shear rate be lower at faster speeds as well? When I shoot it slower, it puts the process very high on the Rheology curve. My understanding is you want the process to lie towards the low end (the more linear section) to make a stable process. At the slower speed, my injection time goes from .75 seconds (determined by scientific molding) to almost 2 seconds!
Feel free to lecture me on any of these topics! I got put on the processing fast track when our last engineer quit, so I'm trying to soak up as much as I can!
Thanks,
-Zach