Cambridge Viscosity Blog

Oil condition monitoring for online lubrication oil monitoring on gas screw compressors

Feb 17, 2021 11:55:02 AM / by Patrick Riley posted in viscosity control, viscosity management, compressor viscosity, in-line viscometers, ViscoPro 2100


2021-02-17-gas_screw_compressorsManaging lubricant viscosity is essential to maintaining the health of a compressor in a process plant, because a single compressor failure can cost $10,000 a day or more in lost revenue. Considering it’s another $10,000 to rebuild a compressor, or more than $100,000 to replace a compressor, maintaining the health and performance of compressors is important.

Many factors affect lube oil viscosity:

  • Oxidation occurs when churning lube oil foams, exposing more oil to surface air and causing oxidation, which lowers viscosity and threatens useful lubricant life.
  • Dilution results when lubricant oil is diluted with gas, such as methane, dropping viscosity.
  • Bubbles form as foaming oil churns against the screws or vanes of the compressor, instantly dropping the viscosity of the oil.
  • Contamination occurs when hydrocarbon vapors in the process mix with the lube oil

The situation can be further aggravated by significant changes in temperature  – such as during start-up – that affect the viscosity of the underlying lube oil. A range of compressor failures can result. Rotary and thrust bearings can fail, which in turn causes wear on the rotor assembly. Replacing bearings is less costly than a total rebuild or replacement, but either way, the plant faces downtime.

While refineries commonly perform monthly lab checks, the unpredictability of viscosity changes means that these monthly checks are not enough to prevent bearing failure and subsequent plant downtime.


“Despite using separators, the lubricant can become diluted by gas carry-over or contamination. If left unchecked, this can cause problems, especially during subsequent start-ups.” 

- Lead Engineer, Gulf Coast Refinery


Preventing Bearing Failure and Downtime

Refineries are finding that that monitoring lubricant temperature isn’t sufficient to protect compressor bearings, especially in applications where process starts and stops can occur. Despite using separators, the lubricant can become diluted by gas carry-over or contamination. If left unchecked, this can cause problems, especially during subsequent start-ups. 

Refineries can protect their large hydrogen screw compressors to improve refinery uptime by adding in-line lube oil viscometers to all their new and existing units. In-line, in situ viscosity monitoring provides plant operations with real-time data on the lubricant viscosity.

The VISCOpro 2100, along with a 301 in-line viscometer sensor, provides real-time continuous monitoring of the compressor bearing lubrication fluid throughout equipment operations.  This saves lab and technician time, and reduces the chance of damaging the equipment.


  • Save $10,000+ a day by avoiding unplanned shutdowns caused by compressor failure
  • Identify contamination, oxidation, dilution, and bubbles
  • Monitor viscosity across wide temperature swings
  • Measure under pressures of 1,000 psi and temperatures up to 190 °C


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Our Top 10 Favorite Questions Relating to Coatings

Feb 10, 2021 12:41:06 PM / by Patrick Riley


top 10 favorite question

What is viscosity?

Viscosity is an important characteristic of a liquid which helps predict its flow behavior.  It quantifies a liquid’s internal friction, determining its resistance to flow.  The higher the viscosity, the slower the flow.


Why is it important for coatings?

Coating companies use viscosity as a means to measure and control the percent solids in coatings, establishing their coat weight thickness.  Standard practice has been to maintain a constant cup viscosity target, day and night, summer and winter.  Viscosity is directly related to temperature, so to measure one without taking into account the effects of the other is inadequate.  For example, 70 secs @ 70°F, vs. 70 secs @ 100°F are dramatically different and produce significantly different coat weights.  The first example yields very light coat weights, the second, very heavy coat weights.  A temperature spread this large would probably yield out of spec product.



How is viscosity measured?

In the past, the cup method was a popular method of viscosity measurement in the coating industry.  Using this method, an operator dips a cup into the can coating material, and then uses a stopwatch to measure the time it takes for the fluid to flow through a hole in the bottom of the cup.  The longer it takes, the higher the viscosity.  It is a simple approach. However, in a situation with many operators, there are many different variations on the basic method of measurement, and therefore there are many different measurements.


Results obtained with the cup method are inaccurate and are not repeatable even if the same person makes measurements all the time.  Cups are just not accurate or reliable for today’s coatings, and that is why most professionals in the coating industry are installing process viscometers.


How do I know if I need a viscometer?


If you don’t have any problems with your coating process, and if you are completely satisfied with your finished quality and costs, then you don’t need a viscometer.  If, however, you would like to improve your process, improve your quality and save money, then a viscometer can help dramatically.


What should I look for in a viscometer?

Process viscometers can be excellent additions to the coating process. However, not all viscometers are created equal. Traditional process viscometers have been used in many coating applications, and although they are better than cups, there are still significant problems with accuracy, reliability, and repeatability.


The main problem with traditional process viscometers is the wet/dry interface.  Process viscometers are usually mounted in a coating tank with a constantly changing coating level.  Every time the level goes low, the coating dries, promoting a buildup on the traditional rotating spindle or a piston rod.  This is especially true for today’s water-based coatings which do not go back into solution after they have dried.  As the coating builds up on the viscometer, the drag on the viscometer is higher and the viscosity number goes up artificially.  The unit makes an adjustment to thin out the coating when it shouldn’t, resulting in bad product and lost production.


What’s different about viscometers from Cambridge Viscosity?

Viscometers from CVI provide a unique solution to the problem.  Based on a patented piston sensor design, Cambridge viscometers are accurate, reliable, and require little or no maintenance for most can applications.  For example, the ViscoPro 2100 accurately measures viscosity and temperature and calculates TCV (temperature compensated viscosity), the calculated value of viscosity at another temperature.  TCV is an important tool that accurately indicates if percent solids have changed, allowing plant personnel to eliminate the effects of process temperature variations on viscosity readings.


What does the systems consist of, and how is it installed?

The CVI viscometer system consists of a sensor, piston, cable, and electronics. The sensor is rugged and simple in design, and the electronics are easy to use. Also included are 4-20mA outputs for both temperature and viscosity which can be connected to a monitoring and control system.


Installation is simple and inexpensive.  Simply add a “tee” fitting into the existing coating line going to the applicator.  Install the sensor and run the cable back to the electronics.  The electronics come in an explosion-proof rated NEMA4 enclosure for protection or DIN-rail-mounted housing, which can be mounted hundreds of feet away if necessary.  Install the valves for your water addition and wire the solenoid back to the electronics.  It’s that simple.


What about maintenance?

Cambridge Viscosity viscometers are designed to be maintenance free.  A simple field calibration is recommended for most applications.


How do I know it will work?

CVI systems are currently operating well in coating applications across many industries, including optical lenses, medical applications, automobile headlights, telescopes and cameras, and many others.  Additionally, Cambridge Viscosity systems are guaranteed to perform to your satisfaction, or the system can be returned within 30 days for a full refund.


To ensure your success, CVI personnel will provided continued consultation after installation and make certain that it is installed correctly, and that its operation is understood by line personnel.


How do I order a system from CVI?

Cambridge Viscosity application engineers are available to discuss your specific needs.  First, you can build your viscometer by clicking the Build your own viscometer button below.

Build Your Own Viscometer

A member of our customer support team will contact you to discuss and clarify any areas as necessary, and a quotation will be generated.




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Your lab viscosity measurements are different from your in-line process measurements. What gives??

Feb 3, 2021 12:39:04 PM / by Patrick Riley posted in viscosity measuring solution, viscosity control, viscosity management, in-line viscometers, ViscoPro 2100, viscometer


How do you handle uncertainty in your measurements?There is always some level of uncertainty in comparing on-line viscosity measurements with laboratory measurements. When it comes to viscosity analysis, a major reason for that uncertainty – and inconsistent measurements – is because the fluids are, in fact, under different conditions.

Viscosity is the resistance experienced by one layer of a liquid in moving over another layer. The level of viscosity of a liquid is largely dependent on the size, shape, and chemical makeup of their molecules. However, several characteristics can also affect in-line and in-fluid measurements. In-line instrument and lab instruments obtain different results because the fluid being measured can be impacted by shear, flow conditions, exposure to air, changes in temperature, changes in measurement conditions, and sample timing. These characteristics actually change the fluid, so what is being analyzed in the lab is actually different from the fluid in the process.


Table: Comparison of characteristics that affect in-line and in-lab fluid measurements
Characteristic In-Line In Lab
Shear Uncontrolled Shear from pumps and pipe bends Controlled shear
Flow conditions Varying Fluid is static in a vessel
Closed/Open System Processes are frequently closed systems after the addition of the basic ingredients, water/solvents, surfactants, etc. Fluid is exposed to air which changes its composition through off-gassing or other interactions
Temperature Frequently process temperatures are elevated, and often fluctuating. Measurement is made at a different temperature than the process is running, and it is usually constant.
Measurement Measurement conditions are often consistent (experiencing the same levels of fluctuations in the process, measurement to measurement) Measurement conditions may vary from lab technician, especially with cups and capillary tubes. Calibration may not be recent
Timing of Sample

In a flowing line it is often difficult to be sure that sample passing over the sensor is exactly the same as sample drawn from a sample port. Any difference may cause the in-line measurement to differ from the sample taken to the lab

Sample can be tested and retested


Calibrating a Cambridge Viscometer

To ensure viscometer readings are accurate, it is necessary to calibrate the instrument in the factory, and periodically over the course of a viscometer’s lifecycle. Viscometer calibration is done using calibration fluids to ensure instrument accurate and alignment with industry standards. The calibration fluids Cambridge uses have known characteristics that are documented and tied to traceable standards. All Cambridge instruments are factory-calibrated with these traceable standards, and the calibration is certified. We note the particular fluids used, their traceability and the results of the calibration. In all cases the factory calibration sheets supplied with each instrument shows the instrument maintains its specified accuracy (1% of the full scale value for the VISCOpro 2100, for instance).


Calibration fluids can be used to evaluate process measurements. Specifically, by removing the process instrument from the line and testing it with calibration fluid, it can be compared to the result from a lab instrument using the same fluid. In such a test, both instruments should yield the same result.


Unfortunately, process fluids are typically not calibration fluids and are affected by the characteristics of the process itself.


In order to maintain consistency with historical data, we are sometimes asked if the in-line value could be calibrated to match the lab values adjusting for all of the process and temperature differences. By using the ASTM temperature compensation techniques incorporated in many of our viscometers, the effects of temperature fluctuations and differences can be mitigated.


The Relationship Between Viscosity and Temperature

The viscosity of most fluids decreases as its temperature increases and vice versa. This occurs because as the liquid is heated, the force of attraction between the molecules, the cohesive forces, is reduced. This principle is very important to understanding differences between laboratory viscosity measurements and process viscosity measurements when they are performed at different temperature. We use temperature compensated viscosity (TCV) to compensate for the varying temperatures of lab and process fluids. TCV is a highly accurate estimate of the viscosity of a fluid at a reference temperature that is different from the actual process temperature. The mathematical relationship is based on the ASTM standard D341 and is accurate for liquid hydrocarbons and most other fluids. TCV is used to relate process measurements to laboratory standard values and to mitigate the effects of process temperature fluctuations for tighter viscosity control.

A lubricant’s viscosity-temperature relationship is characterized by its viscosity index. VI is a measure of how much lubricating oil viscosity changes with temperature. The viscosity of lubricating oil with a high VI number will be less affected by changes in temperature while the viscosity of lube oil with a low VI number will be greatly affected by changes in temperature. The viscosity index is calculated by measuring the viscosity of the oil at two different temperatures (40°C and 100°C). Many labs utilize CVI’s VISCOlab 3000 with its integrated temperature controller for this calculation, but many refineries will use two VISCOpro 2100 systems installed in the production line with a heat exchanger in between the instruments to calculate the VI in real time.


If you have questions about the consistency of your lab and process measurements, reach out to our application specialists to discuss your challenges.

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CVI’s Viscometers are up to the Challenge of Supporting the Manufacture of Essential Safety Eyewear

Jan 26, 2021 12:35:09 PM / by Patrick Riley posted in viscosity control, eyewear viscosity, Coating, process viscometer


CVI helps ensure a high-quality coating on Honeywell safety gogglesSafety eyewear has never been more important than right now. In an industry that was already growing at a rate of 4% CAGR, with a projection to reach $3B by 2025, the COVID pandemic created a massive surge in demand for safety eyewear in 2020.

Honeywell Industrial Safety Group’s Smithfield, Rhode Island facility manufactures personal protective equipment (PPE) that includes high-performance safety glasses and goggles. One of the key elements that ensures a high-quality product is the coating on the lenses.

Honeywell safety eyewear – including the Uvex Genesis®, Uvex Protégé®, Uvex Seismic®, and Uvex Astrospec® brands – is available with anti-fog and anti-scratch coating. When coating is applied, viscosity is one of the properties that affect coating thickness on the lens. If coating thickness is too thick, clarity could be compromised. If too thin, the anti-fog and anti-scratch properties could be negatively impacted.

The biggest challenge in maintaining coating viscosity is how to deal with solvent loss from evaporation. Environmental controls are in placed to minimized solvent loss, but due to volatility, solvent loss is inevitable. To monitor coating viscosity, Honeywell uses Cambridge Viscosity’s ViscoPro controller and viscometers in their coating lines. The ViscoPro controller will determine and automatically add the proper amount of make-up solvent to maintain the ideal coating viscosity.

Cambridge Viscosity’s ViscoPro controller and viscometers were installed at Honeywell’s Smithfield site back in 2006. Despite being well over a decade old, the system is still running exactly as intended. However, the past few months have really put these viscometers to the test.

Since March 2020, Honeywell increased its capacity to manufacture safety goggles, such as the Uvex Stealth. The main drive for the expansion is to meet critical PPE demands for laboratories and hospitals due to COVID-19. Cambridge Viscosity’s ViscoPro controller and viscometers operating 24 hours every day without a single issue is essential to Honeywell’s success in meeting this demand.

Honeywell’s accomplishments during the past several months have been nothing short of impressive. In addition to ramping up their manufacturing processes for safety eyewear, Honeywell also – in the span of three months – created an entirely new production line that manufactures hundreds of thousands of N95 masks every day. While Cambridge Viscosity has no part of the N95 product line, we are proud of the work our customers are doing to help front-line workers during a pandemic.

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Lessons Learned: Viscosity Control for Converters

Jan 20, 2021 10:08:35 AM / by Patrick Riley posted in viscosity control, coating viscosity, viscosity management, in-line viscometers, process viscometer


Almost two months ago, while those of us in the United States were enjoying our Thanksgiving holiday, our associates in Italy were holding a webinar on viscosity measurement in pressroom converters. This event inspired a series of material discussing the coating application, including last week’s blog highlighting factors that influence viscosity measurement in the pressroom converter application. 

This week, we’ll talk about our five biggest lessons that we’ve learned about the pressroom converter application.


Lesson 1: Simple Closed-Loop Control Works Really Well

Sometimes, the simplest route really is the best route. Look at the illustration below.

press converter lessons learned graphic

This illustration represents a typical closed-loop control system. Starting at the mixer tank, you can see degraded material is returned from the process, while new base material enters from the base stock tank and solvent is added from the solvent tank. The function of the mix tank is to blend the materials so the coating or ink that is going to the applicator is perfect. The ViscoPro 2100 monitors and controls material as it is on its way to the applicator, which is the point when the viscosity must meet specification. The in-line viscometer sends its signal to a PLC, which controls the solvent.


Lesson 2: The Best Place to Mount the Viscometer is In the Line

Mounting the viscometer in-line minimizes maintenance and reduces the need for frequent re-calibrations and excess spare parts. In-line mounting also allows the sensor’s environment to be controlled so that the requirement for press operators to maintain the viscosity sensor is minimized, which frees up the press operator time for other responsibilities and reduces the need to carry the expense of spare sensors and parts. Cambridge Viscosity’s viscometers offer a lot of flexibility when it comes to in-line mounting, as shown in the photos below. It gets viscosity sensing away from high activity and high clutter areas around the mix tank.

In-Line Viscosity Mounting FlexibilityIn-Line Viscosity Mounting Flexibility


Lesson 3: Keep Maintenance Requirements Low

The time it takes to clean and maintain a viscometer can really add up – especially when the technician has plenty of other responsibilities. It’s important to choose a low maintenance viscometer. Cambridge Viscosity’s viscometers use a unique oscillating piston technology that delivers a highly accurate, highly repeatable measurement, while also continuously cleaning the chamber. This means maintenance requirements are low, and the operators and focus on other parts of their job. 


Lesson 4: An inconsistent ambient temperature can impact a fluid’s viscosity during the process.

Luckily, with a Cambridge Viscosity viscometer, adjusting for the effects of temperature on viscosity is easily accomplished. Cambridge viscometers incorporate a temperature detector in the heart of the sensor so both temperature and viscosity are recorded for each and every measurement. Cambridge’s electronics integrates these to calculate temperature-compensated viscosity so that it can tell whether the concentration measured is on target or not, and then take appropriate action.

VISCOpro 2100 Interface

Lesson 5: A Simple Operator Interface Makes All the Difference

We’ve found that it’s important to keep the operator interface simple and intuitive. While our sensors provide vast amounts of sophisticated information that is necessary for the complexities of a converting process, our interface is simple and can even be managed using a mobile phone. 

If you’re interested in more information on Cambridge Viscosity’s pressroom converter application, download our white paper:

Download the Pressroom Converter White Paper

If you have questions, feel free to reach out to our application engineers.

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Optimize your converter press room time usage

Jan 14, 2021 3:13:22 PM / by Patrick Riley posted in viscosity measuring solution, coating viscosity, viscosity management, process viscometer


Today's blog discusses pressroom converters. (And we're offering a free white paper on the topic  see the link at the bottom of this post.)

Coating, laminating, and printing are classified as converting processes – raw materials such as solvents, resins, additives, hardeners, aluminum paste, and catalysts are added to a tank to be converted into coatings, paints, or inks. This is the beginning of the converting process, and where the challenge begins. Almost as soon as the materials are put in a coating tank, the they begin to degrade. Solvents evaporate, resins deform and compact, hardeners congeal, additives lose effectiveness, and catalysts become poisoned. All of these issues compromise quality and drive up operating costs.

The average pressroom only runs about 54% of the time. The remaining 46% is made up of activities like color matching, maintenance, customer trials, plates and ink, and preparation to operate.

converter press room time usage_sm

Viscometers and viscometer control systems can influence the amount of time required to make the process ready and for color matching – which take up about 28% of typical operations – in three main areas: film consistency, temperature, and color consistency. 

  • Film consistency—and ultimately product quality—is directly impacted by the method of viscosity control. When viscosity is controlled manually by operators, it's natural for the operator to apply a thicker coating to account for a margin of error. 
  • Temperature has a significant impact on the relationship between viscosity and the concentration of solids in inks and coatings. When the ambient temperature drops, the viscosity of the inks and coatings is also impacted, and the viscosity must be adjusted to maintain a constant percent of solids. 
  • Color consistency relies on maintaining a constant viscosity because thicker ink, which has more solids, delivers more color. Drying rates can also be impacted, as viscosity can impact solvent evaporation. As such, deviations in viscosity can have an impact on consistent print quality.

Improved coating consistency, quality, and cost savings can all be achieved in the make-ready and color matching processes with in-line coating viscosity control. For more information, download our white paper which highlights how in-line viscosity measurement helps to manage in-process coating quality. 

Download the Pressroom Converter White Paper


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Viscosity Measurement Provides the Key to Uniform Coating and Improved Quality for Wire Manufacturing

Jan 4, 2021 1:17:06 PM / by Patrick Riley posted in viscosity measuring solution, viscosity control, wire coating, coating viscosity, viscosity management, in-line viscometers, ViscoPro 2100


2020-12-15-wirecoating and viscosity v4 copy


Spring and wire products are a substantial market – estimated to reach $468B by the end of 2020. Wire is widely used in manufactured goods, including electronics, automobiles, motors, transformers, and a wide array of other products. The coating on the wire is possibly the single most important variable in wire quality, and viscosity plays an important role in ensuring quality.


Manufacturers have several options when it comes to viscosity monitoring. The syringe sampling method involves manually taking samples out of the process via syringe and carrying them to the lab. This method was time consuming, and the lack of temperature control means accuracy is practically impossible. There’s also the cup method, where viscosity is measured by allowing coating fluid to drain through a hole in a cup, with a technician timing the length of time it takes for the entire fluid to drain. The longer it takes, the more viscous the fluid. This method has a variety of issues, including a lack of temperature control, whether the cup has dried coating impacting the integrity of the hole, and being susceptible to human error.


A more robust solution is to choose an in-line viscometer that includes an on-board temperature control unit. The VISCOPro 2100, manufactured by Cambridge Viscosity, uses TCV as a control variable.


The Cambridge Viscosity VISCOPro 2100 can store up to 1,000 data points in memory, yielding readily available reference data to verify wire coating temperatures are on target. The viscometer is a model of simplicity; it has only one moving part, a highly polished stainless-steel piston that moves back and forth in the sensor tip, driven by electromagnetic force from coils in the sensor body. The movement of the piston is resisted by viscous drag of the fluid around the piston. The more viscous the fluid or coating, the slower the piston moves. Having a single electromagnetically driven piston is also essential for keeping the measurement chamber clean. This results in extraordinarily low maintenance costs and reliable measurement accuracy.  The simple design ensures that the instrument is accurate, reliable and requires little maintenance.


Cambridge VISCOpro 2100/SPL311 viscometers can be installed directly in wire coating lines. 4-20 mA signals for viscosity and temperature from each Cambridge unit can be sent to a controller which uses these inputs as the basis for maintaining the appropriate level of solvent in the coating, neutralizing the effect of evaporation and other operating conditions that can result in coating variation.


Fine Wire Coating Process

2020-12-15-wirecoating and viscosity v3

In the schematic above, a Cambridge Viscosity SPL311, VISCOpro 2100 viscometer is shown installed between the coating enamel tank and the applicator. This in-line approach ensures the coating has ideal characteristics as close to application as possible.

Read other related articles:
Controlling Viscosity for Uniform Fine Wire Coating


Process Viscometer Options

Not all viscometers use the same mechanism of operation. Cambridge Viscosity instruments employ an innovative sensor technology that uses an oscillating piston and electromagnetic sensors. Competing viscometer technologies include falling piston, falling sphere, glass-capillary, U-tube, and vibration designs.

 Look for the following characteristics for in-line wire coating viscosity measurement:


  • Menu-driven electronic controls – simplify setting coating viscosity parameters
  • Small size – easy to install
  • Self-cleaning sensor – using the in-line solvent in the coating fluid can clean the sensor while it is taking measurements, reducing unscheduled maintenance.
  • Built-in temperature detection – the sensor should show temperature as an analog reading
  • Integrated Temperature Compensated Viscosity – essential to adjust for the normal changes in process temperature in the course of 24/7 – 365 operations.
  • Multiple output signals – the sensor should display temperature and temperature-compensated viscosity readings.
  • Automatic viscosity control – the sensor should be pre-set but reconfigurable. The sensor should be able to ‘learn’ how much control is needed for each fluid setting.
  • Data logging – date and time-code should be automatically logged, creating an audit trail and simplifying performance and quality trend measurement.
  • Security and alerts – designed to prevent unauthorized changes and sound an alarm when setpoints are reached so operators can take action quickly.
  • Quick-change memory settings – for process lines that run more than one fluid, this feature simplifies changing settings.

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Ensuring Quality of Wire Coatings with Viscometry

Dec 16, 2020 9:28:49 AM / by Patrick Riley posted in viscosity control, viscosity management, Coating, in-line viscometers, ViscoPro 2100, process viscometer



2020-12-15-wirecoating and viscosity v5

Wire is a component of nearly every manufactured product, from cars and computers, to generators, audio equipment, and watches. There are 80 feet of wire in a Slinky and 80,000 miles of wire in the Golden Gate Bridge. There are thousands of applications for wire. The global cable and wire market spans manufacturers of magnet wire, speaker wire, cable wire, integrated circuits, power transformers, electric motors and solenoids, and wire used in automobiles and electronics.


Wires can be as fine as a human hair (60 to 120 micrometers), thick enough to wrap into a bracelet (.4600 of an inch), or shaped into squares and rectangles for use in transformers. Regardless of how it is used, however, almost all wire must be coated with enamel, plastic, varnish, or a related substance. Too much coating, or too little, and wire will fail to meet specifications for manufacture or proper use.


Fine wire or magnet wire is particularly challenging. The enamel coating must be precisely controlled to achieve proper dielectric insulation so that electric motors, transformers, and other electrical devices operate properly in appliances, cars, and computers, to name only a few applications. Precise control of wire coatings is a critical job to ensure quality control and to meet customer requirements.


Why coat wire?

Wire is used in a variety of applications to enable electric current to pass from one component to the next. Controlling conduction the ability of an electric charge to jump from one atom to another is the primary reason wire is coated with a variety of substances, from varnishes to plastic, polymers, resins, and other non-conductive substances. Many wires are double-coated; coated wire is available in a variety of ‘build’ classes, ranging from single build to quadruple build. Build refers to the thickness of the coating, or insulation, which in turn corresponds to the ‘breakdown voltage’ rating, or the point at which the coating no longer prevents electric current from arcing. Coated wire is classified and sold by diameter, as measured in American Wire Gauge (AWG) or Standard Wire Gauge (SWG), in temperature class and insulation class.  


Wire coating application

Applying the proper film thickness is the most important part of the coating operation. Uniform film thickness is a function of the concentration of coating solids in the fluid. Measuring the resistance to flow, viscosity correlates well with the molecular concentration. The wrong film thickness makes the end product unusable for the application for which it is targeted. Many coating problems are blending or evaporation-related, making off-line measurement impractical.  


Most wire is coated using a dip-coating process.  Wire is run through a coating bath and then through a metal wiping die, where excess coating is removed. Dies may be constructed with holes calibrated for different gauge wires, or they may have a set of grooves cut into the die in which the depth of the groove controls the amount of solution that coats the wire. Often, coatings are applied in several passes with visits to an oven in between coats to dry or cure the coating.


Most coatings have a number of process variables which must be monitored, e.g. temperature - both of the solution and ambient temperature; ambient humidity, and percentage of solids and solvents in the mixture.  Variations in ambient temperature, for example, can evaporate solvents in the coating, increasing solvent costs and affecting coating thickness and drying times.  Coating viscosity is a critical variable, one that can be challenging to measure and control.


Approaches to controlling wire coating viscosity

The most basic approach to managing wire coating viscosity is off-line testing. Coating is removed from the process and taken to a lab where viscosity is measured using a viscometer. A number of Cambridge Viscosity customers who used off-line testing have found the process inefficient, allowing potentially out-of-spec wire to pile up or require line shutdowns. Additionally, the measurement is inaccurate: ambient temperature changes between the vat and the lab inevitably affect viscosity readings.   Viscosity measurement is very temperature dependent, often the lab is in a controlled environment.


Another approach to testing coating viscosity, the cup method, measures coating viscosity by placing a fixed volume of coating fluid in a cup and allowing it to drain through a hole, with a technician timing how long it takes for the fluid to drain. A longer drain time means higher viscosity. Many companies have discovered this method has a number of issues:


  • It’s not a continuous measurement, and cannot be included in an automatic feedback control loop
  • The cup method is dependent on the physical condition of the cup, which can become encrusted with dried coating
  • It does not measure temperature, and thus the effects of temperature on viscosity are not measured
  • The method varies with each technician, making it difficult to achieve consistency.


A more accurate, consistent and process-friendly approach to measuring coating viscosity involves installing an in-line viscometer. A wide range of viscometers are available commercially. One drawback:  many lack temperature measurement and thus do not have the capability to perform temperature compensated viscosity (TCV) readings.  

Article: Controlling Viscosity in Wire Coating Applications


TCV is a mathematical representation of the viscosity a process fluid would possess if its temperature were at a user-selected reference point or set point. Without TCV-capable in-line viscometry it is necessary to set the solution vat control unit at percentages above and below the optimal set point. This requires constant monitoring and adjustment of the temperature of the coating solution, which can lead to over-shooting or under-shooting the ideal solution temperature.


TCV allows wire manufacturers to monitor viscosity without having to factor in temperature fluctuations. The VISCOpro 2100 automatically calculates temperature-compensated viscosity. As the viscometer adjusts for temperature changes automatically, manufacturers have one less variable to worry about in a highly variable process. By keeping this factor constant, the manufacturer can easily fine-tune their process such as changing the coating thickness or speed with which they pull the wire through the coating bath.


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Viscosity is an important parameter when it comes to determining the quality of marine fuels.

Dec 8, 2020 3:44:17 PM / by Patrick Riley posted in viscosity measuring solution, viscosity control, heavy fuel oil viscosity, viscosity management, in-line viscometers


Viscosity is an important parameter in marine fuel

In shipping vessels, “bunker” refers to the fuel and lube oils that are stored on the ship and used for machinery operation. When the fuel or oil is intended for transfer to another ship for use in its machinery, the operation to transport the oil is called “bunkering.”

There are several grades of bunker fuel, knowns as A, B, and C:

  • Bunker A – the most valuable, typically called marine diesel or marine gasoil
  • Bunker B - Low-viscosity vac resid range bunker fuel. Often mixed lighter materials to reduce viscosity to the point that it will flow without heating
  • Bunker C – The least valuable and most common bunker. Composed primarily of vac resid range material, with a high viscosity that requires heating in order to pump. Sold at several viscosity specifications, including 180 centistoke, 380 centistoke, or 460 centistoke, with 380 being the most common grade.

Currently, most of the global shipping fleet relies on diesel Bunker C fuel oil, and bunker quality can be an issue. To verify bunker quality, vessel operators have traditionally relied on the testing of a sample that can take many days to process. This method has pretty severe limitations. It’s impossible to know if the sample is representative of the entire supply. Bunker fuel is a non­homogeneous fluid, so how can a tiny sample accurately reflect an amount of liquid that is possibly a million times its size? Doubtful. Also, manually testing a sample can be prone to human error, and getting timely results when they’re needed is a challenge.

Viscosity is an important parameter when it comes to determining the quality of marine fuels. Each grade of bunker is quoted with a specific viscosity tested at 50° Celsius. No matter if a load of bunker is refinery-produced or blended at a shore facility, it is expected to be within a few (cSt) centistokes of its specification. However, in reality, bunker loads can vary considerably from specification and are seldom homogeneous. The causes of off-spec bunkers vary from human error and corruption to instability of blend inherent in the original product. In many cases the supplier is as much a victim of the system as the end-user.

Understanding why the viscosity of blends can vary from load to load is only one piece of the puzzle. Understanding what happens as a result of varying viscosity is another. Varying grades of bunkers form layers when stored in the same storage tank. As a result, in order to maintain a viscosity set point, fuel oil combustion control systems are required to react to drastic changes of bunker viscosity when an interface between varying bunkers meets the fuel oil pump suction. The graph illustrates a considerable change of viscosity between layers of IF0120 referred to in the graph as loads “A" and "B". The change in viscosity required a reduction of fuel temperature from 240° F to 200° F in order to maintain the viscosity set point of 30 cSt. Consider what would happen if the operator relied solely on a theoretical temperature set point derived from typical fuel combustion curves. Burner tips would foul more frequently and emissions would be adversely affected.


Changes in Fuel Oil Temperature Required to Maintain Viscosity Setpoint

Changes in Fuel Oil Temperature


Cambridge Viscosity, Inc. offers a solution real-time monitoring of marine bunkers. Our bunker-monitoring version of the VISCOpro 2100 uses an in-line sensor and microprocessor technology to provide real-time viscosity data during bunkering operations. The unique oscillating piston makes our viscometers extremely rugged and insensitive to the harsh marine conditions. With no mechanical linkages and self-cleaning capabilities, the ViscoPro 2100 has virtually no downtime. It can run for years without recalibration. Other features include:

  • Viscosity Range: 25-10,000 cP
  • Repeatability: 5% of reading
  • Temperature Sensor: Up to 375° C
  • Pressure Range:  1000 PSI (70 Bar), higher pressures available
  • Wetted Parts: Standard 316L/430 Stainless Steel, other materials available upon request


If you’re interested in learning more about the ViscoPro 2100, reach out to our application experts.

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Optimize coating applications, reduce raw material waste, and improve the coating process through tighter viscosity control

Dec 2, 2020 9:07:18 AM / by Patrick Riley posted in viscosity measuring solution, viscosity control, coating viscosity, viscosity management, Coating, ViscoPro 2100


2020-12-02-Optimize-coating-applicationsWhen it comes to coatings, product quality can live or die by viscosity. A too-viscous mixture can result in bubbling and an inconsistent, bumpy, “orange-peel” texture. A solution that is not viscous enough can result in a coating that is too thin, drippy, or saggy. Plus, depending on the application, a coating that is too thin may not provide the necessary top-coat protection. In either case, a coating that has an off-spec viscosity in either direction can result in product rejection or product failure.

As such, it’s extremely important to monitor viscosity in coating applications. Doing so will result in higher product quality, less downtime, and improved product yields. Even better, viscosity management will deliver significant savings by optimizing the use of raw materials and reducing maintenance requirement.


Viscosity Measurement in a Wide Range of Coating Applications

By offering a permanent record of the viscosity, temperature, and temperature-controlled viscosity of the coating solution, in-process viscosity monitoring benefits all types of coating operations, from flow processes in optical coatings, dip processes in wire coatings, spray processes in automotive paints, and roll/printing processes in can coatings.

Wire enamel (dip coating). Magnet wire for the manufacture of electric motors, transformers and similar devices is coated with an electrically insulating enamel by a dip process (the coating process is repeated until the required thickness is obtained). In this application, the percent solids in the coating solution is the crucial parameter; if the coating solution contains a high percent-solids content, solvent costs can be reduced. Accurate management of the viscosity is crucial in controlling uniform film weight.

Optical Coatings (flow coating and dip coating). Traditionally, the cup method has been used to determine ideal viscosity for optical coatings, but the method lacks precision. To compensate, the operators typically add too much solvent to manage high-solid composition. In-line measurement with a viscometer ensures precise control of the viscosity so the product has the right amount of coating. This delivers tremendous savings by reducing raw material overuse and by reducing the amount of downtime required to measure the viscosity of the coating solution.

Beverage Can Coating (roll/printing process). Beverage, paint, and other types of commercial can packaging are commonly printed and then coated with a thin layer of overvarnish to protect the decoration. The varnish thickness is pretty important. If too much varnish is used, the can will appear bubbly, and if too little varnish is used the decoration will be easily scratched. The throughput of a can coating line is very high (>2,000 cans/mm. per machine). In this application the viscosity of the overvarnish should be managed on an in-line basis because of the rapid throughput and the significant potential loss. Cambridge viscometers are used to produce 28 billion cans in the United States alone on more than 50 can lines.

Automotive Paint (spray process). The paint job on a new car or truck is a vitally important part of the finishing process in automotive manufacturing. Mistakes in new vehicle paint jobs cost automakers millions of dollars each year. As many as 15-20% of vehicles are not painted correctly the first time, and the predominant reason for this is incorrect paint thickness. Viscosity management is the key to improving vehicle paint processes. By ensuring the correct viscosity, manufacturers can get a steady stream of painting through the system to the sprayer, to paint the vehicles right the first time. Cambridge Viscosity viscometers measure paint viscosity, temperature, and temperature compensated viscosity, sharing data with a central computer that monitors parameters and updates the viscosity every few seconds. This reduces viscosity-related paint defects.

Paper Coatings (roll process). Viscometers installed in coating lines monitor and help control the viscosity of coatings for specialty papers such as pressure-sensitive labels, folders and postcards. In-line viscometers provide more reliable viscosity measurements with a smaller degree of variability than rotational viscometers and require essentially no maintenance, thus minimizing the downtime of the process.

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Cambridge Viscosity’s ViscoPro reliably manages the viscosity of coatings used in a range of industrial processes. The system eliminates the difficulties inherent in the use of other systems, such as the problem of subjective data that is inherent in the cup method. Virtually all users of the viscometer report that the system provides more accurate, more precise and more reliable data than previously used cup methods. Since the system has only one moving part and no seals, it can be operated for long periods of time with minimum maintenance. The unit provides online real time measurements and is able to automatically control the composition of the coating to provide maximum product quality. Read more about the ViscoPro here

Download the VISCOpro 2100 Product Data Sheet

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