Value Is Performance To Cost

The value of viscosity measurement is well known.  Yet, most lab extrusion lines don't measure viscosity.  Why?  Because there just hasn't been an extrusion system that gives you simple, reliable, accurate, price worthy  on line measurements of viscosity.   Now, there is.  Randcastle introduces a simple low cost method of measuring viscosity while on-line.   We adapted the principles of a coaxial cylinder viscometer to a tiny extruder screw.  You pull off a tiny side stream into the rheometer and measure the viscosity.
 
 

HOW Easy Is IT To Use?

Well, typically, you start the rheometer at the same temperatures as your last barrel zone (or transfer tube depending on where it's installed.  The picture below shows it in the transfer tube.)  You select a rheometer speed and then wait for the extruder to stabilize.  The viscosity readout will tell you when the extruder is stable.   If that's the only viscosity you want to know, your done.  If you want to characterize the material at that set of extrusion conditions, you select other shear rates and then plot.  In a recent study of conductive carbon black loadings, it took about an hour per material including purging.  We could see clear differences in loadings of only 0.9%!  No, you don't need a Ph.D. to operate the unit.  The same technician who runs the extruder will generate the data.

  ACCURATE MEASUREMENT OF VISCOSITY

We are consistently asked if the viscosity we get is the same as from other techniques like capillary rheometers and melt indexes.  We have trials that correlate with rigid and flexible PVC and styrenes that say it is.  Technical information is available.  Just ask us.  There are on going studies on other materials.  If you have material you would like to investigate, call us.
 

Application Ideas

Investigations into the properties of new materials has many obvious advantages.   Did that last change you made to the material formula affect the viscosity and by how much?   You need to make a film for physical testing from a feed stock with different components.  You mixed them up in a drum but now you're concerned about component separation in the hopper.   A check of the viscosity while you run can reassure you that your film is representative of all the feed components--or warn you that it's not.  You're about to pelletize a mix for later use in injection molding when you notice that the viscosity is way off what you would expect.  You investigate and find that the sample wasn't dried fully.  It was dried just long enough to degrade your material in the presence of a little moisture.  Out in production, they're having trouble recycling the regrind.  You investigate and find that the viscosity is becoming newtonian at the process temperatures they're using.  You find that changes in temperature don't help but that increasing the screw speed on the extruder lowers the residence time enough to keep the viscosity in a normal range.  Your supplier always says the viscosity is the same and gives you a melt index number to prove it.  You find, before you put the next lot of material into production, that the MI (a single data point of viscosity) doesn't tell the whole story.  Your characterization of his material shows a distinct difference from the norms that you've established.   Purchasing found a new vendor for color concentrate and intends on saving 10% on color costs.  The color is guaranteed to be the same.  That's good.  You find out the new color makes a 15% change in viscosity before it goes into production.  That's better.
 
 

The Information Age

Twenty five years ago or so, a lot of extruders didn't come equipped with pressure gages or melt temperature indication.  Those were the good old days when you had to guess a lot because you didn't know what the pressure was and the head blew off.  Those were heady days of shipping degraded materials because you didn't know the melt temperature.  How many mistakes are you making because you don't know the viscosity?