| 1. |
- Voltaire, Joakim, et al.
(author)
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Acoustic characterisation of film splitting in a HSWO printing nip
- 2007
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 22:4, s. 424-431
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Journal article (peer-reviewed)abstract
- An acoustic technique for investigation of ink film splitting was further developed and applied to monitor printing of light weight coated (LWC) papers on a heat-set web offset (HSWO) press. The acoustic average power from the nip exit was found to decrease with decreasing ink amount and ink tack and increasing fountain solution amount. When printing on the lower side, the average power increased with surface pore area of the LWC papers, presumably connected to tack build during the extended contact time with the blanket. The method is non-destructive, statistical, and readily automatable, with applications both as on-line sensor and research tool for probing dynamic interactions during ink transfer.
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| 2. |
- Voltaire, Joakim, et al.
(author)
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Acoustic emission and tack of heat-set inks during setting on MWCpapers and fountain solution emulsification
- 2007
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 22:4, s. 432-440
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Journal article (peer-reviewed)abstract
- To investigate the relationship between ink film splitting noise and ink tack, two tack-measuring devices were monitored by a microphone. The first of these was the Deltack(R) (Prufbau), to study tack build on paper, and the second was the Hydroscope(R) (Testprint), measuring ink tack change with fountain solution level. Three medium weight coated (MWC) papers and two heat-set inks of differing tack and emulsion capacity were analysed. It was concluded that acoustic average power is a consequence of cavitation and flow mechanisms, and not necessarily linked linearly to tack. The Hydroscope measurements usually gave decreasing tack, average power and average frequency with increasing fountain solution concentration; however fountain solution droplets can also act as an extra sound source. A relation between average frequency and droplet size was postulated. The results demonstrate the sensitivity of the acoustic method and support its implementation for further studies in the field.
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| 3. |
- Voltaire, Joakim, et al.
(author)
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Acoustic investigation of cavitation noise from offset ink film splitting
- 2006
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 21:3, s. 314-322
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Journal article (peer-reviewed)abstract
- The acoustic signal from the nip during film splitting between inked rollers and on ink transfer to paper was investigated on laboratory scale, using two sheet-fed offset inks (based on mineral oil and vegetable oil) and two coated fine papers (glossy and matte). Film splitting emits a broad noise-like acoustic spectrum in the range 5-50 kHz, from which the two simplest measures of average power and average frequency were derived. Using these two measures, four characteristic regimes of film splitting on the rollers could be distinguished as a function of ink load. Moreover, for intermediate amounts, average power was found to be accurately predicted by a simplistic model of sound produced by cavity expansion due to the under-pressure in the nip exit, thus providing a physical interpretation of the nip noise emission. For printing, the average power was higher for the glossy paper than the matte, presumably due to a more efficient sealing of the nip, or onset of ink setting. The vegetable oil-based ink gave higher power than its mineral oil counterpart. These results were found to be consistent with longer-time measurements of tack evolution from the Ink Surface Interaction Tester. This correlation and the verified theory thus provide support to practical applications of acoustic emission as an on-press monitoring tool.
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| 4. |
- Voltaire, Joakim
(author)
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Ink film splitting acoustics and tack on paper in offset printing
- 2004
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Licentiate thesis (other academic/artistic)abstract
- This licentiate thesis comprises two complementary studiesdealing with the sheet-fed offset printing of paper. The firststudy addresses the further development of a practical methodto acoustically monitor and analyse the film splitting ofoffset inks. This method was tested on laboratory printingequipment, specifically monitoring the continuous ink splittingin the nip of an IGT ink distribution unit and the short-timeink splitting in the inked print disc-paper nip of the printingunit of an ISIT instrument. The study verified that the inksplitting component of the acoustic signal contributes to thehigher frequency range (10-20 kHz) of the audible spectrum, andcan thus be separated from the lower frequency machine noise.Furthermore, the film splitting component is sensitive tochanges in the ink and printing conditions, thus enabling itsuse in probing the fundamental mechanisms occurring during inktransfer and also suggesting its applicability fornon-intrusive monitoring of industrial printing presses. Anincrease in film thickness during ink distribution correspondsto an increased acoustic power, with the exception of very lowink amounts, which give reduced acoustic emission due to alubricating effect. The effect of the presence of fountainsolution was simulated by adding emulsion-forming, butnon-evaporative, ethylene glycol. This produces an increase inacoustic power at low amounts, due to resistance to glycol dropdeformation, followed by a decrease at higher amounts owing toexcess glycol lining the rolls. During test printing on paper,increasing ink amounts also display an increased acousticresponse. The second study further developed a theoretical model toexplain and predict the evolution of ink tack in terms of inksetting directly after offset printing on coated paper. Asmeasured by the ISIT, the tack of the printed ink rises duringshorter time periods, attains a maximum, and then falls atlonger times. The proposed model described how the ink tack,characterised by the impulse during disc pull-off, dependsdynamically on the viscoelastic properties of the ink, thecontact with paper and disc, and the flow geometry. The inksetting was modelled as a diffusion-limited transport of theoil vehicle through the ink film and into the pores of thecoated paper. The coupling of the tack and setting models,compared to the ISIT experimental measurements, then provided adiffusion coeffcient for ink setting during the tack riseperiod. This coeffcient decreases with time, and increasinglyrapidly with decreasing ink amounts due to theconcentration-dependent diffusion. For an accurate descriptionthe elasticity and adhesion effects also have to be considered,at least for explaining the tack fall period.
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| 5. |
- Voltaire, Joakim, 1973-
(author)
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Ink Film Splitting Acoustics in Offset Printing
- 2006
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Doctoral thesis (other academic/artistic)abstract
- This thesis claims a relationship between the film splitting sound emission from the printing press nip and the dynamic interaction occurring there between ink, fountain solution and substrate in offset lithography. The film splitting sound derives from the cavitation formed by the pressure drop in the second half of the print nip flow passage. As the ink film is strained, the cavities expand and eventually implode into breaking filaments at the nip exit, while emitting a partly audible, broadband, high frequency, noisy sound. A free-field microphone, A/D-converter and laptop computer were used to record pressure signals in the frequency range of 10 Hz to 50 kHz emitted by a variety of printing instruments and presses for a range of offset ink and paper types. After signal acquisition and filtering two signal averages of power and frequency were estimated. This average power increased with increasing loads of sheet-fed offset ink on an ink distributor, in accordance with a mass-conservation model developed. The behaviour of average frequency and power over different ink load ranges indicated transitions between different flow regimes. A glossy fine-coated paper gave higher average power than a corresponding matte paper during printing with such inks on a laboratory device, possibly due to an air sealing effect. The sound from tack measurements with the Deltack instrument during setting of heat-set offset inks printed on MWC papers showed a relation between the measured tack rise and average power, reflecting changes in splitting mechanism during the course of setting. With the Hydroscope instrument the interaction between these heat-set inks and fountain solution was studied, with the measured tack and sound emission displaying a clear, but non-linear, correlation. A heat-set offset pilot trial showed that the acoustic response from the printing nip sensitively and systematically detected changes in (LWC) paper type, optical density, ink-fount balance, and press stability. Pilot trials of cold-set offset inks on newsprint by sheet-fed presses indicated a strong correlation between evolution in average power, optical density and fountain solution consumption during the first thousand sheets normally needed for stabilisation. Acoustic measurements of ink film splitting have, aside from the laboratory studies performed by one Japanese group, previously received little attention, with the current study showing that a great deal of information useful to the printer can be accessed from this sound emission. Although the detailed mechanisms for ink film splitting have to be further studied and supported by mathematical simulation, the sensitivity of the acoustic method recommends its implementation for monitoring and control of offset printing.
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| 6. |
- Voltaire, Joakim, et al.
(author)
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New technique for monitoring ink-water balance on an offset press
- 2007
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In: Appita journal. - 1038-6807. ; 60:2, s. 120-128
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Journal article (peer-reviewed)abstract
- An acoustic technique, with microphone placed near the print nip exit on a. sheet-fed offset press during trial printing of newsprint, was used to provide information relating to splitting of the ink-fountain solution film. The average acoustic power increased with tack of the ink used and with target optical density. Further, average power decreased during each run, reasonably strongly correlated to increase in fountain solution consumption. This indicates that average power is primarily sensitive to instantaneous tack of the ink-fountain solution film, and can be used to monitor tack and indirectly infer ink-water balance in the nip. Laboratory experiments were also performed using the Hydroscope instrument to simultaneously measure tack and average acoustic power of the splitting of inked rollers during fountain solution titration and evaporation. While these two measured parameters were not directly correlated over all conditions of emulsification, both decreased in tandem over intermediate amounts of fountain solution.
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| 7. |
- Voltaire, Joakim, et al.
(author)
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Use of an on-press acoustic sensor to monitor coldset offset printing of newspaper
- 2006
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 21:3, s. 323-327
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Journal article (peer-reviewed)abstract
- A newly developed acoustic emission on-line monitoring technique (Voltaire J. et al. 2004) provides insight into the dynamic interactions occurring between paper, ink-fount emulsion, and rubber blanket in offset printing. The technique uses a microphone placed in the vicinity of the exit of the paper-blanket nip. Through digital signal processing of the measured sound pressure it is possible to distinguish between machinery sound and that caused by the tacky ink splitting. In this study, printing of coldset inks on newsprint was carried out on a two-unit sheet-fed offset press. In line with earlier results, an increase in print density was found to correspond to increased sound pressure at the nip exit for higher frequencies (above 15 kHz). Depending on the status of the press at start-up, i.e. ink and fount condition and temperature, an increase or decrease towards a more stable value of the sound pressure was detected during the early running of the press, and in both cases this correlated well with the evolution in print density to its target value. This and related results can prove useful for monitoring, and adjusting by feedback, the initial press equilibration before the print-ready stage. Moreover, the acoustic emission can directly reveal destabilised conditions at longer running times that by other means would not be detected until later.
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| 8. |
- Zavalis, Tommy, et al.
(author)
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Mechanistic Model with Empirical Pitting Onset Approach for Detailed and Efficient Virtual Analysis of Atmospheric Bimetallic Corrosion
- 2023
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In: Materials. - : MDPI. - 1996-1944. ; 16:3
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Journal article (peer-reviewed)abstract
- A mechanistic model of atmospheric bimetallic corrosion with a simplified empirical approach to the onset of localized corrosion attacks is presented. The model was built for a typical bimetallic sample containing aluminum alloy 1050 and stainless steel 316L sheets. A strategy was developed that allowed the model to be calibrated against the measured galvanic current, geometrical corrosion attack properties, and corrosion products. The pitting-onset simplification sets all pits to be formed at a position near the nobler metal and treated all pits as being of the same shape and size. The position was based on the location of the highest pitting events and the pit attributes on an average of the deepest pits. For 5 h exposure at controlled RH (85%, 91%, and 97%) and salt load (86 μg NaCl/cm2), the model was shown to be promising: both for analysis of local bimetallic corrosion chemistry, such as pH and corrosion products, and for efficient assessment of pitting damage by computing a single largest pit depth. Parametric studies indicated that the pitting-onset approximation deviated the most at the beginning of exposure and when RH was below 91%. © 2023 by the authors.
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