Paper (Part 2) – how is it made?

January 28, 2013

in Paper

In this post we’re going to look at the process of how paper is made.  There used to be a time when anyone involved with buying print could arrange a paper mill visit, nowadays these mill visits are about as rare as the proverbial rocking horse dung.  Many of the UK-based paper mills have closed, due to the reduction in global demand and today there are more pubs in the UK called the Paper Mill than actual working mills.  We all have contact with paper whether as part of our day-to-day lives and possibly as part of our job, this gives a brief overview of how it gets from wood pulp to the final product.

Unless the paper is made by hand, where it is made in sheet form, all large scale papermaking is on a continuous format and uses a fourdrinier process.  The Fourdrinier machine was invented in the early 1800s and is accredited to Henry Fourdriner, a London-based stationer, although it was actually invented by a Frenchman called Louise-Nicholas Robert.  Robert was unable to have the machine financed in France due to the disruption of the French Revolution, so using his brother-in-law as an intermediary he brought the patent to England and used Henry and Sealey Fourdrinier to finance it’s design and manufacture.  The first Fourdrinier papermaking machine was built and commissioned in Frogmore, Hertfordshire in 1803.  So that’s the history of the machine, now lets see how it works.

The Fourdrinier machine is made of four sections – Forming Section or Wet End, Wet Press Section, Dryer Section and Calendar Section.

 © Egmason 2010

Because woodpulp fibre has a strong tendency to clump, it needs to start off with a very high percentage of water content, allowing the pulp to have an even distribution, the slurry (or furnish) held in the Headbox contains around 99% water.  The furnish travels down the Slice onto the revolving Wire at the Breast Roller point of contact.  As the furnish travels along the wire, so water is removed and the wood fibres are aligned in a uniform direction.  It is this process that allows perfect distribution of the pulp fibre across the sheet as well as giving the paper strength and stability from aligning the fibres.  Suction rollers hold the furnish to the mesh and help remove the water content.  By the time the paper or web has reached the Wet Press Section the consistency has gone from 0.5% pulp content to 25%.

The Wet Press Section carries the wet web between a series of rollers under high pressure to squeeze more water from the paper, much like a mangle.  The Felts support the web and also aid water removal by absorption.  As the web enters the third section the paper web consistency can be as high as 40%.

Steam heated rollers in the Dryer Section cause further water removal through evaporation as well the further use of Felts bringing the water content down to as low as 6%, where it will remain at indoor atmospheric conditions.  It is in the Dryer Section that the web will be treated with Sizing to change the characteristics of the paper and via a coating unit, the surface will be covered with calcium carbonate or china clay for coated papers such as gloss, silks and velvet types.

The final Calendar Section allows the web to pass between Calendar Rollers that smooth out the surface of the paper.  If the paper has a coating then the degree of calendering will change the characteristics of the coating.  For example, gloss artpapers have a higher degree of calendering than a velvet sheet, as the coating is practically ironed smooth and glossy.  A silk coating would be calendered somewhere between a velvet and a gloss.

Now one thing that is not shown in the diagram and is the first thing that strikes anyone that visits a paper mill for the first time is the absolute vastness of Fourdrinier machines.  Each roller in the Dryer Section can have a diameter of several metres, the width of the a reel of paper can be 10 metres long and weigh several tonnes.  From Top Box to Dry End could cover the distance of a football field…the machines are so large that operatives have to use three wheel scooters to move from one end to the other.  The images below will hopefully give a better understanding of the scale and the video allows you to easily identify the four sections of the Fourdrinier machine.

 In Paper (Part 3) we’ll discuss how paper mills have changed over the years to ensure minimum environmental impact.

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