The Niagara Branch of the Pulp and Paper Technical Association of Canada (PAPTAC) has enjoyed a renaissance. The organization put on its second annual meeting in April after many virtually idle years….
The Niagara Branch of the Pulp and Paper Technical Association of Canada (PAPTAC) has enjoyed a renaissance. The organization put on its second annual meeting in April after many virtually idle years. Branch chairman Ed Slachta, Donohue, estimated that 80 people attended the technical conference, which included 10 technical presentations and 15 commercial exhibits. More than fifty people attended the problem solving short course, which was co-sponsored by PAPTAC’s Professional Development Committee.
“The branch was inactive for several years, so we feel that the participation and support we are getting for our efforts is great,” said Slachta.
The performance of the area’s health and safety record was the first item of the technical conference program.
The average age of the workforce in the region, according to the Pulp and Paper Health and Safety Association (PPHSA) is between 40 and 45 years. With the ageing of the work force the PPHSA often sees reoccurrence or aggravation of an injury that happened years earlier. Ergonomic injuries, where the worker does not work well in his environment, kept employees off the job the most, causing the most lost time claims. Strains, sprains and back injuries top the list. For this reason the PPHSA has recently increased its focus on ergonomic intervention.
Many of these injuries have been seen in older workers. Older workers are also more prone to accidents, according to Thom Foster, a consultant and trainer with PPHSA. He said that senior workers are intimidated by new technology and make mistakes that can lead to an injury. The PPHSA is addressing this problem.
The association, funded by the Worker Safety and Insurance Board, designs programs to help get workers working safely. It provides health and safety related services to support workplaces to become more self reliant in health and safety. Foster reported that the association has a membership of about 160 firms, each of whom pay membership fees, and 26 000 employees. Along with increasing worker self-reliance the association seeks to increase the recognition of its work and to increase its membership.
The Niagara branch of PPHSA, said Foster, has a focus on reducing the potential for and/or severity of workplace injury or occupational illness. As well, the branch strives to achieve the lowest total accident frequency among the five local branches of the PPHSA in the province of Ontario. The branch, said Foster, had recently slipped from first place in its safety effort to third, with increased medical aid injuries, from 64 in 1998 to 82 in 1999 and an increase in incident frequency from 6.66 to 7.93. The Niagara Branch has crept up above the Ontario average in lost time accidents forcing the need for better accident tracking and the need to target problem areas. Foster noted however that fine paper manufacturers had a decrease in lost time injuries and that these firms generally have good return to work programs.
When does paper rip?
The technical program began after Foster’s presentation, two sessions running concurrently.
Robert Pelton, director of McMaster University’s Centre for Pulp and Paper Research, studied the performance of splicing and other pressure sensitive adhesive tapes on paper. He asked, “When you peel the tape off paper, when does it rip?” This, he said, has packaging applications.
When you peel the tape off paper you get two types of results: Interfacial failure, where the adhesive comes off with the tape as with Post It notes, or paper failure, where the paper rips when the tape is lifted off, as with Scotch tape.
When the paper breaks, the fibre bond comes apart or the fibre breaks and paper fails. Some factors influencing this phenomenon include peel rate, roughness, porosity and sizing.
Peel rate: If you pull very slowly you get a low peel force, which should give interfacial and not paper failure.
Roughness and porosity: increase paper failure.
Sizing: decreases paper failure.
Paper failure can also be sensitive to peeling direction.
The strain on paper
Paper failure, ripping, was a topic of another presentation. Jean Pierre Gay, NLK Consultants, gave some insight and made some observations about the integrity of paper and how it is affected by paper machine design. He said in a later discussion that many of the points he brought up came not only from his own research but that of others.
Increasing paper machine speed, the goal of all paper makers, increases the strain on paper. For a 20% increase, strain increases by about 40%, within certain limits, said Gay. To compensate dryness could be increased by 8% and strain will decrease by 40%.
So how do you get 8% dryness? Gay said that anyone who talks about speeding up a paper machine talks about putting in a shoe press.
A steam box will change the moisture profile. A steam box will give you weaker paper in the press section but more stability in the dryer section. Nevertheless, Gay said that the paper machine operation gains overall with a steam box.
Peeling, gravity, air currents and wrinkling were identified as some of the strains on a piece of paper.
More runnability concerns were raised in a presentation given by George Weiss, technical consultant. His presentation looked at press runnability problems experienced by an Abitibi-Price (now Abitibi-Consolidated) mill in the first 36 weeks of 1990, and the search to find its cause and a solution. The paper also made recommendations for a monitoring system where the quality of the paper production, the consumption of rolls on a FIFO (first in/ first out) basis, plus the performance of the printing presses are all recorded meticulously over a long period of time.
The collected data included: the number of rolls consumed by the pressroom on a weekly basis; paper breaks recorded on a weekly basis; the quality data for the manufacture of the production designated to this customer.
NUI formation was found to have the highest correlation with roll breaks in both studies of bivariate linear relationship and multivariate and polynomial linear relationship.
Various analyses of NUI against all other parameters show NUI has the highest influence of pressroom runnability.
The researchers graphed actual vs. predicted breaks based on NUI formation. For this mill an NUI value in excess of 9.3 caused press performance problems and was designated as a threshold value for alarm at that mill.
The cause of the problem at the mill in question was a paper machine run with a new top and bottom fabric.
Weiss said that the need for close cooperation between the mill and the pressroom couldn’t be over-emphasized. Pressrooms need to keep good visual feedback records. The regular strength parameters used in this mill proved to be misleading. The results of this case study show that the proper or improper distribution of fibres has more influence on the press room performance than the strength of the individual fibres.
Another industry veteran, Ross MacDonald, formerly of Donohue Inc., discussed Improving newsprint runnability. His presentation discussed his former company’s approach to assess runnability data. Techniques applied to the data include control charting, segmentation and multivariate analysis.
Paper breaks are used to measure performance. For break frequency the number of breaks per roll is used, as breaks occur randomly from roll to roll. There is variation due to roll density and roll parameter, but the researchers felt that this was small.
There are two methods in common use, according to the research — rolls per break (RPB) and Breaks per 100 rolls (B/100R). The researchers found that “after thousands of statistical analyses, the assumption of normality for B/100R is very reasonable, given an appropriate sample size).” Breaks per 100 rolls is a better measurement for statistical analysis, according to MacDonald.
Control chart analysis was applied to data collected for one press over a 10-day period. The analysis showed a significant process shift after 5:30 a.m. from about 60 minutes between breaks to about
105 minutes. One advantage of roll specific data, according to the research, is the opportunity to re-order data by time of manufacture.
For control charting only data where at least 200 rolls have been run off and at least one break has occurred is used.
Performance of pressroom units is segmented by difficulty of lead. Lead is defined as the path from the unwind stand through one or more press units to a folder. Color (i.e. black/spot, color, and Tower or four-color back-to-back) and distance (i.e. number of pages) used as the units. Roll width and winder position and day of the week are also considered.
Air in paper stock incresases viscosity,
and makes it harder for water to drain.
— EMILE DELAZZER MEUNIER
In the air
Emile DeLazzer Meunier, BASF Canada, gave a presentation on Successful air content control benefits to the papermaker. He spoke about entrained air in the paper machine circuit: how it gets there; how it stays there; what it does to the paper machine itself and; how to deal with it.
Meunier said that entrained air could be introduced into the paper machine circuit by high-speed paper machines, increased turbulent flows, narrowing of white water circuit, intensive agitation, leaking pumps and cascades. Coated broke and ground calcium carbonate (GCC) or precipitated calcium carbonate (PCC) in coated furnish can also be the culprit.
What is the effect of all this air in the system and what impact does it have on the paper machine? Air in paper stock, said Meunier, increases viscosity, and makes it harder for water to drain. It compromises machine speed due to fan pump capacity. It causes problems for inter-fibre bonding. Retention and drainage are compromised. A lot of foam develops with entrained air in paper stock “which can translate to deposition problems… or holes in the sheet.” Formation, smoothness and porosity are also affected.
Meunier showed various mill cases and the various effects of entrained air in the papermaking process. He concluded that:
Almost every paper machine has a certain level of air in its system.
Air has a negative impact on paper machine runnability
Deaeration of PM stock is a major prerequisite for efficient production of quality paper.
Chemical deaeration is an effective way to reduce entrained air in PM stock.
Branching out
The Niagara Branch has two more events scheduled for this year, including a golf tournament in July and an industrial site tour in November. The third of the new generation of annual conferences will be held in Niagara in April 2001.
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