We’re at the tail end of our paper making process series. We know some of you like to ask the big questions like “How” and “Why” so that’s what prompted this in depth series. In case you missed the last one, you can check it out here. Today you’ll learn about the final drying stages of how your paper is made!
One of the last processes is drying. There are many configurations of dryers but for the most part, they are a series of rolls and either two or a single fabric referred to now as felts. These carry the paper on a winding course around a series of drive roll, guide rolls and another type of roll referred to as dryer rolls or dryer cans, which are large diameter rolls heated internally with steam. These dryer cans heat the paper as it passes around the roll and dry it. Upon exiting the dryer section the paper is now dry and strong enough to wind its way through the rest of its course without the support of fabrics.
At this point, various different types of paper machines take many different combinations and configurations. These include winders, re-winders, calendar stacks, breaker stacks, size presses etc. For simplicity sake, as we selected a modern SC machine earlier as an example we will use that as our model. Once the paper exits the dryers it is wound onto a reel. These reels continue to turn and wrap the paper until a specific diameter of paper has been wound. Once that is achieved the paper machine breaks the sheet and the reel is removed. A new reel is put in place by an overhead crane and the paper sheet is fed onto it and the wrapping continues. Any waste paper from the removal of the full reel and the placement of a new empty reel goes into a re-pulper where it is agitated and diluted back into a slurry which can be pumped back to the mix tank at the head of the machine for re-use. The reels of paper are then taken via the overhead crane to the calendar stack. A calendar stack is a vertical group of rolls which operate in very close tolerances. The paper reel is threaded into the calendars and it passes between these rolls and is subjected to pressure and heat. This pressure and heat in combination with various additives from the wet end of the machine such as clay (up to 30% of the paper sheet in some cases) smooths and polished the sheet resulting in a very high quality glossy sheet. It should be noted that throughout the machine there are a whole assortment of online scanners that detect abnormalities in the paper from holes, to darkening, and all sorts of optical properties. The paper is constantly monitored by online sensors as well as manual testing by lab technicians so machine operators can make any corrective measures necessary via the computer based control system in the paper machine control room to ensure quality.
Once the paper exits the calendars it heads to the winder. The winders purpose is to split the large length roll of paper into smaller length rolls as determined by customer needs. These smaller rolls are wound to specific diameters as well per customer requirements. Once the rolls are completed they move to an automated wrap line to be packaged and labeled. Even in the wrap line, modern technology plays an important part. Many mills use computer controlled robotic arms in the wrap line. Finally, once they have been labeled with dimensions, weight, grade, customer name, order number, etc. they are conveyed to the warehouse where they await loading onto trucks or rail cars to be sent to customers press rooms.
While we don’t normally think about it, lots of work goes into each piece of paper we use. There are many different types of paper, and from a marketing standpoint, we have different uses for all of them. It’s important to know which paper goes with which type of job. PMD Group knows paper and we know what works best for all your different jobs- if you want to know what different options we have, just ask your marketing rep!