Quartz glass melting.

Precise monitoring of viscosity during the melting process is crucial for quality assurance in quartz glass production. In this project, a Sensor Technology TorqSense torque transducer (SGR541) was used to enable real-time conclusions to be drawn about material homogeneity, purity and the progress of material bonding.

In modern glass technology, precise control of melting conditions is of fundamental importance: the viscosity of a melt in particular has a decisive influence on its further processing, quality and homogeneity. In the laboratory, viscosities are often determined using rotational viscometers: a spindle is rotated at a constant speed in the sample, the required torque is measured and the viscous resistance – i.e. the viscosity – is determined.

In their customer's project, this concerns the melting of quartz glass. Viscosity is not only a measure of fluidity but also allows conclusions to be drawn about the internal state of the melt – for example, cavities (air bubbles) or incomplete material bonding. Focusing on precision glass components to improve the manufacturing process for quartz glass in terms of quality and process reliability. The challenge was that the glass is first melted at high temperatures and then has to reach a defined viscosity zone for further processing. Only in this range can it be guaranteed that the melt is homogeneous (no air bubbles), the connection or fusion of different material batches has taken place completely, the transition to the shaping or quenching/pre-forming process starts reliably.

The objective was to reliably monitor the viscosity of the quartz glass melt in order to detect deviations in the melting process at an early stage and to establish process-reliable feedback for control and quality assurance.

The viscosity of molten glass plays a key role in processing, as it determines the flowability and thus the moulding behaviour, bubble removal, degassing and homogenisation. In the case of quartz glass, the conditions are particularly demanding with: high temperatures and viscosities having a strong influence on the viscosity curve.

The TorqSense SGR541 was chosen because of its great robustness against extreme process conditions (temperatures, thermal shocks, possible vibrations) in the melting range of quartz glass with separate sensor unit and electronics. Calibration was performed using reference samples or model melts in order to map the torque ↔ viscosity relationship in detail in the specific process setup.

The sensor was integrated into the process—typically between the motor/agitator (or melt mixing system) and the impeller (or melt stirrer)—and connected to the process control system in real time. Since torque transducers can be sensitive to lateral forces, double bearings should be used to avoid transverse forces.

The relevant target values for viscosity were defined together with the customer: e.g., a range from x to y Pa·s at temperature T, at which the melt is considered homogeneous and no bubbles are mobile.

Reference curves were created using laboratory or pilot melts with known compositions and viscosity values. This allowed the sensor output to be mapped to absolute or relative viscosity (see Basics: “Torque ↔ Viscosity” at constant speed conditions). The sensor continuously provided torque data from which the viscosity was derived. Trend analysis enabled early detection of deviations – for example, if the viscosity did not fall within the target range, which could indicate trapped bubbles or incomplete mixing of the material batches.

As soon as the measured viscosity deviated from the target curve, measures were taken immediately: adjustment of the temperature, extension of the stirring time, addition of degassing (refining), or even return of the batch for reprocessing.

The introduction of monitoring using SGR541 had the following positive effects: The melt could be continuously monitored for homogeneity and freedom from bubbles. Deviations were detected early and corrected. The data obtained (torque/viscosity curves) provided valuable insights into the behaviour of the quartz glass melt, enabling future process optimizations.

This method is also used successfully in other applications—e.g., plaster mixtures, coal slurries, and liquids containing magnetic particles—where conventional viscometers fail and viscosity monitoring is required. In industries such as cosmetics and pharmaceuticals—e.g., in the manufacture of shampoos or medical solutions—it is also important to monitor viscosity during mixing. This allows you to determine when the process is complete and the desired consistency has been achieved.

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@Sevcon #PAuto #viscosity TorqueSense #Transport

Ultra-accurate viscosity measurement.

A pre-pilot mixing plant is using wireless TorqSense transducers for ultra-accurate viscosity measurement of high-value compounds.

The plant is used to prepare small batches of compounds from shampoo and detergent to cosmetics, therapeutic and medical preparations. Some of the ingredients in the compounds are very expensive, so product developers are loath to make large batches early in the formulation process. 

Instead, they start with 850 millilitre samples for the early stages of each project, then once the recipe is well-proven, move on to pilot-scale work where the samples are measured in thousands of litres. The final stage is, of course, full-scale production where volumes may be truly enormous.  

The TorqSense transducers were supplied by Sensor Technology,  whose Mark Ingham explains the design of the pre-pilot plant: “It can take three hours or more to make a single sample, each produced with precision accuracy – and development programmes need a great many samples. Clearly this cannot be done manually. Automating the basic mixing process is in principle straightforward; for this the plant has four workstations based on paddle mixers, each of which is monitored by a TorqSense.”

TorqSense constantly assesses the level of torque in a driven shaft. Often, this is used to measure the power being provided by the drive motor. However, in this case it is the opposite – TorqSense is used to calculate the drag being exerted on the paddle and shaft by the liquid being mixed.

“The mixing process changes the viscosity of the liquid, which is what causes the drag,” says Mark. “In the first instance the TorqSenses are looking for the viscosity to stabilise to a steady value that won’t change any further no matter how much more mixing is done. 

“Then they measure that very accurately. The viscosity is what gives the final commercial product its sense of quality: a low viscosity and the product feels watery, cheap and ineffective; overly high viscosity and it is unpleasant and greasy. 

“There is an optimum point where the product feels luxurious and high quality, which is what needs to be identified for each formulation. In the past this was done manually, so was completely subjective and unquantifiable: TorqSense has changed this to a precise and scientific procedure.”     

TorqSense is a wireless sensor, which is not physically connected to the mixer shaft by slip rings. Instead, it monitors the torque via radio waves.

A shaft deforms very slightly when it rotates, the amount of deformation being proportional to the torque. TorqSense measures the deformation so that it can calculate torque. To do this two tiny piezoelectric combs are glued to the surface of the shaft at right angles to one another; shaft deformation will expand one comb and compress the other. The radio frequency signal emitted by the TorqSense is reflected back by the combs, with its frequency changed in proportion to the combs' deformation.

"The procedure to set up the TorqSense is very simple," says Mark. "Solutions using other technologies would probably take several hours to set up. With a regime of up to 30 tests per day, TorqSense is the only real solution for this plant.”

Other TorqSense attributes that have been made full use of are its enormous overload capacity, which enables it to cope with robust and demanding test cycles, and its digital output. The output is fed straight into a computer program that compares viscosity measurements with the ingredient ratios and calculates changes to the recipes for optimised results.

Mark sums up: “This plant is in effect a totally automated laboratory that can develop perfect formulations in a closed loop calculation. It has changed pre-pilot tests from time-consuming trial and error procedures to precision materials science.”

@sensortech #PAuto 

Process viscosity analyser.

ViscoSure from PAC, combines the proven oscillating piston technology with tight temperature control, to provide viscosity analysis with unmatched precision. With internal temperature control without using the traditional external oil bath, the ViscoSure requires little to no maintenance bringing maximum instrument uptime and low cost of ownership.

The fast and reliable measurements allow for precise and continuous adjustment of the process, while maintaining a high correlation with ASTM D7483 and ASTM D445 test methods.ViscoSure

Performance, reliability, and precision are critical for viscosity measurements in bottom of the tower applications. ViscoSure is the only viscosity analyzer designed specifically for these complex applications:

• Asphalt: (135°C): With its fast cycle time, it replicates lab results in real time, avoiding the process of sending material to the slop tank to be adjusted and retested.
• Heavy Fuel Oil (50°C): ViscoSure helps refiners reduce overblending of costly diesel.
• Lubrication Oil (40°C/100°C): ViscoSure makes it possible to fine-tune the process performance to improve output, reducing the bottleneck that can occur on the dewaxing unit of a lubricant line.

The patented sample conditioning system (SCS) optimizes the instrument’s performance and protects the analyzer from process disruptions which reduces downtime.

“The ViscoSure is a game changer, when it hits the market, particularly in the black products. such as asphalt, it will make an impression” says Alex Lau, chairman of ASTM’s Coordinating Subcommittee on Quality Assurance and Statistics.

#PAC #PAuto 

Revised method for kinematic viscosity!

The ISL Houillon Viscometers, the VH1 and VH2, from PAC, comply with the recently released revised version of ASTM D7279-14 Standard, “Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids by Automated Houillon Viscometer”.

The new revision of the standard extends the scope from lubricating oils to include distillates (e.g., base oils, formulated oils, fuels, and biodiesel) and also adds a new precision at 40°C and 100°C, established through an interlaboratory study.

Our customers can now run their distillate oil samples on the VH1 and VH2 while complying with ASTM D7279. Requiring less than 1 ml of sample, the Houillon approach is applicable to both transparent and opaque samples, while needing less manpower to run. Since the kinematic viscosity results are produced within 60 seconds, the ASTM D7279 method has proven to be ideal for rapid testing of in-service engine oil conditions.

In addition to small sample size and fast analysis, the ISL Houillon Viscometers are easy to operate, flexible due to the capability to accommodate one or two solvents for cleaning, and robust in construction. Finally, the single-bath design, including 4 Houillon tubes, combined together with advanced automatic features, enable the simultaneous run of up to 16 tests.

Flanged process viscosity sensor!

PAC recently released its latest 393 flanged process viscosity sensor. The 393 sensor’s new design is configurable to the end user’s needs; it has numerous industry standard process connection options, including ANSI, DIN, and RTJ flanges. With these new connections, it is easy to install CVI’s patented sensor technology in petrochemical  plants and refineries, including hazardous areas. CVI’s technology is based on the oscillating piston method, which has only one moving part with no mechanical linkages. The sensor electromagnetically drives a piston through a fluid in a controlled measurement chamber at a constant force. Proprietary circuitry analyzes the pistons two-way travel time to measure the absolute viscosity. The sensor is constructed of all 316L stainless steel and the piston is constantly mixing the sample and scrubbing the measurement chamber clean.

Next generation Fork Viscosity Meter!

Direct insertion Micro Motion® Fork Viscosity Meter is designed for demanding applications where accurate, fast-response viscosity and density monitoring is required

Micro Motion® Fork Viscosity Meter, the next generation of the market-leading Micro Motion 7827 and 7829 direct insertion viscosity and density meters has been announced by Emerson. Incorporating the same rugged and reliable tuning fork design as its predecessors, the Fork Viscosity Meter is built to tackle demanding process applications such as oil fired heater combustion control, HFO blending/production and pump protection.

In applications where accurate, fast-response viscosity and density monitoring is required, this instrument is the ideal choice. The meter helps solve problems customers face on a daily basis, such as reducing oil fired heater combustion emissions, minimising cutter-stock usage in HFO blending and reducing contamination risks on multi-product pipelines.

The Fork Viscosity Meter incorporates a hazardous area approved head-mounted transmitter that has the flexibility to connect to control systems via a wide range of digital and analogue protocols. Because it supports 4-20mA, HART, WirelessHART, FOUNDATION fieldbus and RS485 Modbus, system integration and start-up/commissioning costs are significantly reduced.

An additional benefit of the Fork Viscosity Meter is the capability of accepting and processing external signals from other field instrumentation such as temperature, pressure and mass/volumetric flow devices. The input of these external measurements enables the Fork Viscosity Meter to calculate and output enhanced process measurements while minimising installation and cabling costs.

The Fork Viscosity Meter also incorporates a new diagnostic capability called Known Density Verification that checks the meter for measurement alarm conditions, sensor integrity and the presence of coating, erosion or corrosion. This new technology expands the availability of diagnostics information in critical viscosity and density measurement applications which can result in significant maintenance costs and cycle time reductions.