A shear rheometer may or may not be the most expensive instrument in your lab, but it is a piece of sophisticated equipment with delicate components that need proper care. Regardless of the model, you need to know how to keep your investment working for years to come. Avoid these five pitfalls - a happy rheometer makes for a happy lab!
1. Do not turn on Peltier temperature control without first ensuring that the counter-cooling is circulating.
Peltier elements make for quick and consistent temperature control, but they require a means for removing excess heat so that they themselves do not deteriorate over time. Most modern rheometers have Peltier heating and cooling units that rely on water circulation to remove excess heat, which keeps the Peltier unit running. That water circulator next to your rheometer should not be ignored – even measurements conducted at 25°C should have water circulation actively running to reduce the thermal strain on the Peltiers. Monitor the circulation with a flow indicator to see if the circulation is flowing. For those with advanced air-cooled Peltier heating elements, this is much easier – just make sure the fans in the Peltier unit are not obstructed.
2. Clean the water circulator to prevent algae build up and sludge.
The longevity of the Peltier elements relies on effective water circulation to remove excess heat. Quick-flowing water in the circulator keeps the unit healthy, but sluggish water flow can result in dying Peltiers over time. Clean out the water circulator at least every three months to avoid these pitfalls. This vital cleaning typically involves draining the water bath and using paper towels to scrub the inside of the bath. A deep-clean may be needed if it has been a long time since the last cleaning; to do this, disconnect all water hoses, drain them, and then circulate fresh water (distilled or tap water, not deionized water). Precautions can be made against algae accumulation by adding a few drops of algaecide or using a water and ethylene glycol mix for the circulation fluid. The lucky few who have air-cooled Peltiers do not have to deal with this.
3. Do not clean the measuring system (plate, cone, cylinder) while it is connected to the motor.
This piece of advice is all about protecting the
instrument from you, and not the other way around. Rheometers with air-bearings housed in the motor are extremely sensitive to lateral forces, such as moving the measuring system left and right instead of allowing it to spin. The 30 seconds of time saved by wiping off a measuring system without disconnecting it are not worth the risk of damaging a $15,000 air bearing. Remove the measuring system to clean it, and then re-attach it. This should be an undisputed lab rule.
4. Use only moisture-free compressed air, and avoid running a rheometer with a cheap air compressor.
Labs obtaining their first modern rheometer are understandably eager to get their new investment up and running, but settling for a low grade air compressor has severe consequences in the long term. Do not connect a rheometer to a compressed air line that does not have moisture filters or dryers attached. An unknown amount of water and contaminants can be entering the air bearing – typically the most expensive component of a rheometer – and cause issues either right away or long-term. Portable air compressors may seem desirable for getting a rheometer up and running while waiting for the installation of a compressed air line, but they produce large amounts of water that even an attached dryer cannot remove all the moisture. Industrial-scale air compressors outfitted with appropriate filters and dryers are the most reliable option.
5. Always properly secure the rheometer’s air bearing prior to moving it across the lab or transporting it across the country.
When the air supply is disconnected from the rheometer, the air bearing becomes even more vulnerable to damage. Slight bumps can cause the delicate air bearings to slide, produce friction, and chip; the best-case result from this misfortune is having the low-end torque resolution drastically decreased (say goodbye to measuring low viscosity fluids). The worst-case scenario entails a $15,000 or more service bill from your rheometer manufacturer and an instrument completely out of order until that expensive bill can be paid. Do not assign the task of moving a rheometer across the lab to your muscular intern – this is an important task that needs special care. To stabilize an air bearing, consult the rheometer manufacturer for best practices that do not risk breaking the warranty of the instrument. A service visit for securing the rheometer may be worthwhile for your peace of mind if preparing it for freight shipment.
Contact us to learn more about the maintenance and use of shear rheometers.