Nelson Systems

Hydramotion Authorized Distributor

Blog – Through Thick and Thin

Hydramotion release polymer-melt viscometer

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The viscosity of polymer melts is a key parameter for quality and control during every stage of the polymer manufacturing process, including injection molding, compression molding and extrusion. Molecular chain length (or molecular weight) is the most important indicator when measuring polymers across every stage. Chain length tells the operators how well the product has polymerized, which is critical for the properties of the finished product, which might be granules, film, fibers or molds. The strength, hardness and density are all key parameters for product quality, and can be controlled by viscosity.

In the textile industry viscosity is a key parameter in understanding how well the polymer can be forced through the fine holes of the spinneret, to produce the fibers. This enables extrusion of filaments of one denier or less. Tensile strength is a particularly important property to control for fiber. As a general rule, tensile strength increases as polymer viscosity increases.

To achieve their desired behavior, polymers are often blended to alter their properties. Properties such as solubility, water-repellence and flexibility can be altered by substituting other organic groups for the methyl groups. For example, silicones with phenyl groups are more flexible polymers than those with methyl groups. They are also better lubricants and are superior solvents for organic compounds. Picking up changes in viscosity and molecular weight is critical in order to control the addition and blending of co-polymers.

Why is XL7-d16 good for Polymers?

The XL7-d16 spike has been developed to be the ultimate tool for managing polymer melt, right where its needed most. In the pipe. The d16 spike has been completely redesigned to operate at a lower shear-rate than the standard XL7 viscometer, which results in an optimum response to changing molecular weight within the polymer.

The spike design also has no bob. This means the viscometer can easily be extracted without damage if the polymer hardens in the pipe. The flange includes two jacking bolt threaded holes, so the sensor can be extracted with ease. For further simplicity of use, the d16 has been designed to retro-fit existing polymer melt equipment without the need to change pipework.

The sensor also has all the attributes found in every Hydramotion viscometer: high accuracy, no moving parts, negligible maintenance, and a robust construction to withstand harsh duty and high pressure. The all-welded solid sensor rod also has an open construction to ensure no trap areas or dead-zones for polymer melt.

Further information and specification can be found on our XL7-d16 product page. 

Applications

Any industry processing polymer melts. Typically the textile industry which turns PET into textile threads, “Lycra” has seen particularly successful results using d16.

The following melts are currently being measured:

  • PP
  • PE
  • PET
  • PBAT (polybutylene adipate terephthalate) – biodegradable polymer
  • Polycarbonate
  • Polyester
  • Polyamide (nylon 6,6)
  • “Lyocell” cellulose – natural fiber used in clothing
  • Lycra or “Spandex” (polyether-polyurea copolymer)
  • Silicone-based polymers

We have in-line viscometers for every stage of polymer processing and handling: material manufacture, melt pipe, or extruder. Please see our polymers industry page for more information. 

We would be glad to answer any questions you may have about polymer melt-pipe viscometer or any of our other products. 

Please use the Contact page or contact us at sales@nelsontech.com or call us at 530-446-6722

How Brexit can help your process control

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Dollar symbol isolated on a white background, vector illustration

You may have a personal opinion for or against the result of the recent Brexit vote in the UK (in case you’ve been off the planet, they voted to leave the European Union…).  But one bit of good news for any US business that needs premium viscometers is that the Brexit vote quickly resulted in a better exchange rate for the US Dollar against the British Pound.  That means you can currently buy Hydramotion viscometers at lower prices than we’ve had in years – and thus improve your process control with precision viscometry, whether you need  inline XL7 or ViscoJet viscometers for oils or food processing, a ReactaVisc for the lab, or Viscolites for ink samples on the production floor.

Currently the Pound (GBP) is about 9% lower against the Dollar (USD) than it was before the Brexit vote.  There’s no guarantee of where that exchange rate will be in a month, but we will work with our customers to pass along the most favorable prices we can.  If you’re thinking about purchasing and have been postponing or letting the decision slip, you may want to accelerate it and make your CFO happy!  Contact us to figure out the best approach for your specific situation.

Rotational vs. Torsional Vibration Viscometers – What’s the Big Deal??

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A common question is how the Hydramotion torsional vibration (resonant) viscometers are different from the older rotational devices.  On the surface the technologies may sound similar, but they’re completely different, and in many cases you’ll get different measurements with the same fluid and conditions.   That’s another question we also get a lot: why does my Brookfield lab viscometer give me viscosity readings that are so much higher than my Hydramotion inline XL7 (or ViscoJet)?  Here are some of the basic answers.

The Old Way: Rotating at Low Speed

Rotational viscometry dates back to the mid-20th century, along with dial telephones and gas-guzzling cars.  The most common commercial versions use a motor-driven spindle or bob immersed in the fluid in a sample cup of a specific size.  The torque required to turn the spindle in the fluid is a measure of the fluid’s viscosity.  The geometry of the spindle and cup and the spindle’s rotational speed must match the fluid’s properties, and the cup and spindle must be changed for different viscosity ranges.  Rotational viscometers typically operate at very low shear rates.

New and Improved! Vibrating at High Speed

While vibrational viscometry technology was also conceived many years ago, the resonant torsional vibration method wasn’t perfected until Hydramotion figured it out about 20 years ago.  Vibrational viscometers work by creating waves within the liquid, A resonanting sensor using Hydramotions technologyand there are many types of waves that can propagate in a liquid, but the specific type is critical.  Viscosity is a shear measurement that can only be truly assessed under shear conditions, so the Hydramotion technology uses shear waves.  Other types of vibrational waves are avoided since they can behave unpredictably in real-world process environments.

That may sound complex, but in operation these units are simplicity itself.  In the most common configuration, the solid stainless steel cylindrical sensor is submerged in the fluid and vibrated at its natural frequency around the long axis.  The dissipated energy from the fluid’s resistance is measured electronically and equated to viscosity.  All the action takes place near the sensor surface, which means these instruments aren’t affected by pipe or tank sizes, flow, or any of the things that limit other techniques.  This brings huge benefits: high accuracy, robustness and virtually no maintenance.

This is done at very high shear rates, which has some key advantages – especially for non-Newtonian fluids, where viscosity is a function of shear rate.  One great advantage is the high in-process repeatability, normally achieved only in Newtonian fluids.  Another is that true viscosity changes are measured – some low-shear devices (including rotational viscometers) can impart sufficient shear energy to alter the effective viscosity of the fluid.  We’ll get back to that in a future post.