Porosity in Paper, if you can measure it accurately and reliably you can control it!
There are several Online Porosity Measurement Systems on the market capable of measuring porosity in paper. Accurate on-line measurement and control of porosity or air-permeability is used in the pulp & paper industry.
Analogue porosity systems have been sold over the past 30-40 years. Some were not able to withstand the rigours and stringent requirements imposed by the paper industry and have been discarded. Others failed to maintain operator confidence due to calibration and reliability issues leaving mill managers wary of claims that ‘All problems have now been resolved znd several major supplier of scanning systems (QCS) to the paper industry have been selloing on line porosity system since early 1990s. Generally, these systems infer porosity measurements based on a series of assumptions and mathematical models.
Most Systems using an analytical platform for on-line measurement of porosity of most continuous sheet processes. It is a precision device that measures either air permeability or air resistance. In addition, these systems provides intelligence at the measurement sensor to ensure measurement reliability and accuracy required for closed loop control of refining, filler, stock flow ratios, etc
These Systems measures Porosity (Air Permeance or Air Resistance) of the continuous web of paper, glass fiber matt or any other continuous sheet or felt, using a measurement method similar to standard laboratories techniques.
The measurement system monitors the time required for a known volume of air, under a known differential pressure, to pass through a given area of the moving web. The elapsed time is converted into porosity or air permeance units used by the customer. Optionally, it measures the volume of air passed through the web using the unique TimeSlice platform supporting full web slice integration of scanning systems. The measurement sensor incorporates intelligent signal processing and its automatic calibration maintenance and self cleaning cycle will operate reliable in the manufacturing environment. The software platform provides data acquisition, analysis, presentation and reporting for real-time on-line usage for the operating staff and long term storage and grade data retrieval for management reporting and historical quality analysis.
The ability to measure sheet porosity on-line has been around for quite a few years, but many such on-line porosity systems have been discarded due to doubts about measurement accuracy and the need to reject a large proportion of the readings. Very few systems have therefore been used for closed loop control. The development of improved sheet sensor contacting technology in this category has greatly reduced the number of readings that need to be ignored and allowed closed loop control to become a reality and can now be clearly demonstrated.
Demand for these systems has continued as the high return on investment in it grows. Payback is typically measured in weeks rather than months or years. Every installation result in an increase in average porosity and a decrease in porosity spread.
Immediate benefits of a freer sheet include improved runnability, reduced draw between sections and fewer sheet breaks. Porosity related losses at grade change are generally eliminated isung these porosity measurement and control systems.
Keywords: porosity, multiperm, microperm, honeywell, air-permeability, Air Resistance, measurement, sensor, control, online, on-line, online porosity measurement, microperm, measurex, paper, pulp and paper, gurley, measurement and control