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The 8.9% Risk To Tensile Strength: A Case In Roll Grinding

Posted by Robert Rourke on May 13, 2015 2:44:19 PM

Screen_Shot_2015-05-13_at_2.40.59_PMFor some time, the newspaper industry has had issues with four-color printing, and the culprit is poor roll grinding.

Publishers need paper that runs on a color printing press, requiring the utmost quality from paper manufacturers. When this became standard, the newspaper and paper manufacturing industries changed for good.

Large newspaper publishers have three main concerns with the paper they purchase: its cost, whether the ink will print clearly and whether or not the sheet will break during the printing process.

But, like many paper manufacturers, one of the most prominent and modern paper mills in North America learned the importance of precision grinding through a long process of trials and errors. 

The Specifics Of This Roll Grinding Case Study

This paper manufacturer owns a machine designed to produce 650 tons of paper per day at a speed of 4,000 feet per minute. These days, however, running your paper machine at its originally designed speed is a recipe for unemployment. The fact of the matter is that those design speeds simply do not meet the modern expectations of the paper industry.

Instead, this paper mill produces over 800 tons of paper per day at a speed budget of between 4,250 to 4,300 feet per minute. 

The Paper Manufacturer’s Search For Roll Grinding Services 

Using an in-house grinder at the time, the aforementioned mill searched for roll grinding services and eventually chose an OEM to grind its rolls. Upon completion of the OEM’s services, documentation indicated that the manufacturer’s rolls were in spec. 

When paper production began again, the mill started to experience high vibration and excessive caliper variation. Due to feedlines and barring – induced into the rolls from imperfections in its shape and roundness – the subject paper manufacturer simply couldn’t run its machine and produce a quality, acceptable product. 

As it turned out, the issues with the rolls’ shape and roundness were a product of manipulated data – an imprecise presentation that masked the true roll measures and falsely indicated that the mill’s rolls were in spec. 

Finding A Precision Roll Grinding Company And Testing The Difference

After experiencing these problems, the paper mill brought its rolls to PRG and employed FP Innovations – a leading research institute – to test the paper. The world-renowned consultant and research group found significant problems with the rolls that the paper mill had ground.

Its testing showed that the work done in house, or by the OEM roll grinding company, reduced the overall tensile strength by 8.9%, due to the aforementioned irregularities.

Sheet elasticity was also weakened by 11.9%. With less stretch, publishers have reduced runnability and suffer more breaks on the printing press. 

Last, they found that barring in the paper mill’s rolls, which transferred to the sheet, decreased Total Energy Absorption (TEA) by 18.8%.

It was clear: The paper mill had received anything but precision grinding

Read the full case study to learn how the paper mill’s quality improved after precision grinding.

 

View The Case Study

Topics: Paper Industry, Roll Grinding, Process Improvements

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